study of the thermal conductivity of leather having

i

Study of the Thermal Conductivity of Leather Having Various Compactness and Geographical Origin

By

Gopal Krishna Saha

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

Department of Mechanical Engineering

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY 2014

ii

Certificate of Approval

The thesis titled Study of the Thermal Conductivity of Leather Having Various Compactness

and Geographical Origin submitted by Gopal Krishna Saha, Roll No-040310049p, and

Session:April’2003 to the Department of Mechanical Engineering of Bangladesh University

of Engineering and Technology has been accepted as satisfactory for partial fulfillment of the

requirements for the Degree Master of Science in Mechanical Engineering in 17th December,

2014.

BOARD OF EXAMINERS

1. -------------------------- Dr. Maglub Al Nur Chairman Professor (Supervisor) Department of Mechanical Engineering BUET, Dhaka -1000 2. ---------------------------- Dr. Md. Zahurul Haq Member Professor (Ex-officio) Department of Mechanical Engineering BUET, Dhaka - 1000 3. --------------------------- Dr. M.A.Rashid Sarker Member Professor Department of Mechanical Engineering BUET, Dhaka - 1000 4. --------------------------- Dr. Parimal Bala Member Professor (External) Jagannath University Dhaka - 1100

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Candidate’s Declaration

It is, here by, declared that this thesis or any part has not been submitted elsewhere for the

award of any degree or diploma.

------------------------- Gopal Krishna Saha

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Table of Contents

List of Tables vii

List of Figures x

Nomenclature xi

Acknowledgements xii

Abstract xiii

CHAPTER 1 INTRODUCTION 1

1.0 Motivation 1

1.1 Objectives 2

1.2 Possible outcome 2

1.3 Scope of the thesis 2

CHAPTER 2 LITERATURE REVIEW 3

CHAPTER 3 LEATHER-IT’S CLASSIFICATION AND TECHNOLOGY 4

3.0 Definition of leather 4

3.1 Classification of leather 4

3.2 Processing of leather 5

3.2.1 Curing 5

3.2.2 Tanning 6

3.2.2.1 Pretanning 8

3.2.2.2 Soaking 8

3.2.2.3 Fleshing 8

3.2.2.4 Unhairing + liming 8

3.2.2.5 Deliming and bating 9

3.2.2.6 Pickling 9

3.2.3 Main Tanning and wet-blue 9

3.2.3.1 Chrome tanning 9

3.2.3.2 Sammying 9

3.2.3.3 Sorting 10

3.2.3.4 Splitting 10

3.2.3.5 Shaving 10

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3.2.4 Wet-finishing and crust 11

3.2.4.1 Neutralization 11

3.2.4.2 Re-tanning 11

3.2.4.3 Drum dyeing 11

3.2.4.4 Fatliquoring 12

3.2.4.5 Sammying and setting 12

3.2.4.6 Drying 12

3.2.5 Finishing Operation of leather 13

3.2.5.1 Conditioning 13

3.2.5.2 Stacking 13

3.2.5.3 Buffing 14

3.2.5.4 Trimming 14

3.2.5.5 Finishing and plating 14

3.3 Properties of leather (Mechanical or Physical) 15

3.3.1 Thermal conductivity 15

3.3.2 Tensile strength and percentage of elongation at break 16

3.3.3 Tearing strength 16

3.3.4 Bursting strength 16

3.3.5 Water vapor permeability 17

3.3.6 Softness 17

CHAPTER 4 EXPERIMENTAL SET-UP AND DATA COLLECTION 18

4.0 Design and manufacturing of Fitch type thermal conductivity

apparatus (Suitable for leather) 18

4.1 Collection of hides and skins 21

4.2 Preparation of sample 21

4.3 Thickness, Softness and Contact area measurement 23

4.4 Thermal conductivity measurement 37

4.5 Experimental Data 40

CHAPTER 5 RESULT AND DISCUSSION 61

5.0 Introductory remarks 61

5.1 Variation of thickness 61

5.2 Variation of softness 62

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5.3 Variation of thermal conductivity 64

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS 66

6.0 Conclusions 66

6.1 Recommendations 67

References 67

vii

List of Tables

---------------------------------------------------------------------------------------------------------------- Table No Title Page No ---------------------------------------------------------------------------------------------------------------- 4.1a Thickness, softness and heat exchange surface area of butt at origin

Chittagong 24

4.1b Thickness, softness and heat exchange surface area of belly portionat origin

Chittagong 25

4.1c Thickness, softness and heat exchange surface area of shank portion at

origin Chattagng 26

4.1d Thickness, softness and heat exchange surface area of shoulder portion at

origin Chittagong 27

4.2a Thickness, softness and heat exchange surface area of butt portion at origin

Rajsahai 28

4.2b Thickness, softness and heat exchange surface area of belly portion at origin

Rajsahai 29

4.2c Thickness, softness and heat exchange surface area of shankportion at origin

Rajsahai 30


origin Rajsahai 31

4.3a Thickness, softness and heat exchange surface area of butt portion at origin

Dhaka 32

4.3b Thickness, softness and heat exchange surface area of belly portion at origin

Dhaka 33

4.3c Thickness, softness and heat exchange surface area of shank portion at origin

Dhaka 34


origin Dhaka 35

4.4 Comparative statement of thickness and softness with respect to sample location

and geographical origin 36

4.5a Data of galvanometer defection with respect to time intervals

(Belly, Origin- Chittagong) 41

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4.5b Data of galvanometer defection with respect to time intervals

(Butt, Origin- Chittagong) 42

4.5c Data of galvanometer defection with respect to time intervals

(Shank, Origin- Chittagong) 43

4.5d Data of galvanometer defection with respect to time intervals

(Shoulder, Origin-Chittagong) 44

4.6a Data of galvanometer defection with respect to time intervals

(Belly, Origin- Rajsahai) 45


(Butt, Origin- Rajsahai) 46


(Shank, Origin- Rajsahai) 47


(Shoulder, Origin- Rajsahai) 48

4.7a Data of Galvanometer defection with respect to time intervals

(Belly, Origin- Dhaka) 49


(Butt, Origin- Dhaka) 50


(Shank, Origin- Dhaka) 51


(Shoulder, Origin- Dhaka) 52

4.8 Logogrammatic data of galvanometer defection with respect to origin, location

and time intervals 53

4.9a Linear regrassion for data table-4.9 (Belly and butt,Origin-Chittagong) 54

4.9b Linear regrassion for data table-4.9 (Shank and shoulder, Origin-Chittagong) 55

4.10a Linear regrassion for data table-4.9 (Belly and butt,Origin-Rajshahi) 56

4.10b Linear regrassion for data table-4.9 (Shank and shoulder,Origin-Rajshahi) 57

4.11a Linear regrassion for data table-4.9 (Belly and butt,Origin-Dhaka) 58

4.11b Linear regrassion for data table-4.9 (Shank and shoulder,Origin-Dhaka) 59

4.12 Calculation of thermal conductivity of leather with respect to sample

location and geographical origin 60

5.1 Thickness of leather at different location of different region 61

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5.2 Variation of softness at different location of same leather with respecct to

Geographical origin 63

5.3 Thermal conductivity at different location of same leather

with respect to geographical origin 65

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List of figures ---------------------------------------------------------------------------------------------------------------- Fig. No Title Page No ---------------------------------------------------------------------------------------------------------------- Fig. 3.1 General flow diagram for the leather tanning and finishing process 7

Fig.4.1 Tharmal conductivity apperatus 19

Fig.4.1a Measuring instrument base module 20

Fig.4.2 Different region of hides and skin 22

Fig.4.3 (a,b) Time vs Logarithm of galvanometer deflection(Origin-Chittagong) 54

Fig.4.4 (c,d) Time vs Logarithm of galvanometer deflection(Origin-Chittagong) 55

Fig.4.5 (a,b) Time vs Logarithm of galvanometer deflection(Origin-Rajshahi) 56

Fig. 4.6 (c,d) Time vs Logarithm of galvanometer deflection(Origin- Rajshahi) 57

Fig. 4.7 (a,b)Time vs Logarithm of galvanometer deflection(Origin- Dhaka) 58

Fig. 4.8 (c,d) Time vs Logarithm of galvanometer deflection(Origin- Dhaka) 59

Fig. 5.1 Variation of thickness at different location and origin of leather 62

Fig. 5.2 Variation of softness at different location and origin of leather 63

Fig. 5.3 Variation of thermal conductivity graph with respect to geographical origin 65

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Nomenclature Symbols

BOD Biological oxygen demand

COD Chemical oxygen demand

SS Solid state

N Nitrogen

Cr Chromium

k Thermal conductivity for tested material

Q1 Heat transferred from the heat source through the sample to

the heat sink

Q2 Heat stored in the heat sink

l Specimen thickness

TH Heater temperature

T Heat sink temperature

M Heat sink weight

c Heat sinks specific heat

s Heat exchange surface area (Heat sink surface area)

i Galvanometer deflection

β Factor of proportionality

t Time

xii

Acknowledgement

The author likes to express his heartfelt and profound gratitude to the thesis supervisor

Dr. Maglub Al Nur, Professor, Department of Mechanical Engineering, BUET, Dhaka for

his invaluable and continuous guidance, suggestions throughout the entire work.

The author will never forget the strong support of Md.Shaheen Ahamed, Chairman,

Bangladesh Tanners Association, Dhaka, Bangladesh, towards the achievement of his degree.

The author extremely grateful for continuous cooperation of the technicians of Mechanical

and Welding workshop.

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Abstract Thermal conductivity is considered as one of the most impotant parameters to characterze the

thermal response of leather.The comfort of leather shoes largly depends on inshoe climate

which is mainly responsible on the thermal conductivity of leather. In the present

investigation a modified Fitch type thermal conductivity apperatus has been designed and

manufactured.The thermal conductivities of leather having different geographical variation

such as Rajshahi,Dhaka and Chattagong district of Bangladesh have been investigated.

The variation of thermal conductivities of different parts such as butt,belly,shank and

shoulder of a leather have also been investigated.The softness of the leather has also been

measured with the variation of geographical origin and location of each leather.The thermal

conductivities of leather originated from Rajshahi,Dhaka and Chattagong district of

Bangladesh have been found to be 0.149 Watt/mº K, 0.101 Watt/mº K and 0.102 Watt/mº K

respectively.The thermal conductivity of belly and shank portion of leather from Dhaka were

0.095 Watt/mº K and 0.096, Watt/mº K and that of Chittagong district 0.098 Watt/mº K and

0.098 Watt/mº K.Thermal conductivity of butt portion of leather originated from Rajshahi,

Dhaka and Chattagong district of Bangladesh have been found to be 0.160 Watt/mº K,0.112

Watt/mº K and 0.110 Watt/mº K.The softness of leather oroginated from Rajshahi district is

found to be 4.30,and that of Chittagong and Dhaka district are 3.52 and 4.15 respectively.The

present investigation indicates that leather originated from Rajshahi district is more suitable

for making shoes for warm countries due to their relatively greater thermal conductivities and

that of Dhaka and Chittagong may be suitable for cold countries due to their lower thermal

conductivity values.

CHAPTER 01

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INTRODUCTION

1.0 Motivation

Leather is one of nature's more appealing gifts to mankind. It has great aesthetic

appeal. It appeals to our eyes, it smells good and it feels good to the touch. Leather

goods such as shoes, gloves, jacket, trousers etc maintain the body temperature and

guard against the larger heat changes. Thus the thermal insulating property of leather

is one of the most important properties to have knowledge for better and effective

applications of leather. The thermal insulating power is expressed as thermal

resistance that is directly proportional to thickness and inversely proportional to the

thermal conductivity of the sample [1]. So the precise measurement of thermal

conductivity of leather is considered an important area of investigation for better

understanding of the thermal insulating behavior of leather. Different methods have

been proposed to measure the thermal conductivity of leathers [1][2].

Leather is considered as porous material and water molecules are present in it. The

thermal conductivity of a porous and water containing material have large

dependency on their porosity and water content. Interestingly, the fiber compactness,

hence the porosity of leather is not the same for leather produced from a specific

cattle or goats. It also has the variation over living conditions and areas. Thus, the

thermal conductivity of the different parts of leather and their comparison may

provide important information for future application of it. Again, the variation of

thermal conductivity over the variation of origin of cattle or goats in Bangladesh may

provide information suitable for the section of leather to produce suitable leather

goods.

These type studies have not been done in Bangladesh so far. Thus, in the present

project the thermal conductivity of leather produced from different parts of

Bangladesh as well as of different parts of the same leather is studied.

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1.1 Objectives

The objectives of the study are as follows-

i) Design and manufacture of a modified Fitch type thermal conductivity

apparatus suitable for the measurement of thermal conductivity of leather

samples.

ii) Measurement of thermal conductivity of different parts of the same leather

[belly, butt, shank, shoulder], and their comparison.

iii) Measurement of thermal conductivity of leather according to their

geographical origin.

iv) Investigations on the variation of thermal conductivity of leather with the

variation of compactness of the fiber.

1.2 Possible Outcome

Comfort of leather product largely depends on their thermal properties. This study

may be suitable for correct selection of leather for appropriate leather goods

production, especially in which thermal properties are more important. Since

Bangladesh is a major exporter of footwear and leather goods, this study eventually

may add the value to export of leather products.

1.3 Scope of Thesis

This thesis paper covers to determination the variation of softness in different region

with respect to geographical origin of the same leather as well as quantitative

determination of thermal conductivity. The other measured parameters are the contact

heat exchange area, thickness and temperature difference between the two sides of a

leather specimen. It also covers the knowledge to designing and manufacturing

technique of all parts of the Fitch type conductivity instrument.

The variation of comfort property at different location of the same leather and over

the variation of origin of cattle or goats in Bangladesh may provide information

suitable for the selection of leather to produce suitable leather goods. In this

dissertation, the available literature is reviewed in Chapter 2. A brief description of

classification and manufacturing technology of leather is given in Chapter 3 which

also discusses different comfort properties of leather. The experimental set-up and

data collection procedure is given in Chapter 4. In Chapter 5, result and discussion of

the study are explained in detail. Conclusion and recommendations are given in

Chapter 6.

3

CHAPTER 2

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LITERATURE REVIEW

The end use of leather in various environments largely depends on their response in

different thermal events. Thermal variation can change the physical as well as comfort

properties like softness, feel etc of leather. Thermal conductivity is considered one of

the most important parameters to characterize the thermal response of leather. Thus,

the studies on the variation of thermal conductivity of leather in different

physiochemical environment and designing suitable apparatus for measuring thermal

conductivity and development of methods are considered important areas of

investigations.

Marcinkowska [2004] studied the thermal conductivity of leather by Cenco-Fitch

method. In his study he modified the method to improve the accuracy of the heat

conductivity measurement. To do this, a computer measuring system was developed

and some important modifications related to measuring, data recording and result

analysis were proposed.

Mohammad et al. [2011] investigated in-shoe temperature and relative humidity on

comfort to identify the most appropriate upper materials of shoe. They studied the

thermal conductivity, water vapor permeability and water absorption properties of

range of upper, lining and interlining materials of shoes. Their investigations indicate

that the in-shoe climate is mainly dependent on the thermal conductivity, water vapor

permeability and water vapor absorption properties of the upper materials of the shoe.

Their research helped a lot to select a range of possible materials for practical testing.

Kazanavicius [2008] studied leather softness using different methods to develop a

reliable and commonly acceptable leather softness evaluation method. His

investigation indicated that the most appropriate method for defining leather softness

can be the values of conditional elasticity in percentage under certain load. Due to

peculiarities of leather structure no clear correlation between the uni-axial and bi-axial

tension results were obtained.

4

CHAPTER 03

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LEATHER-IT’S CLASSIFICATION AND TECHNOLOGY 3.0 Definition of leather

Leather is a durable and flexible material created by the tanning of animal raw hide

and skin, often cattle hide. It can be produced through manufacturing processes

ranging from cottage industry to heavy industry. Raw hides and skin consists of some

layers such as epidermis,dermis and hypodermis. To convert raw hides and skins to

leather, epidermis layer is first removed through pre-tanning operations like

liming,bating etc and the remaining called derma,is tanned.Before tanning certain

amount of hypodermis layer also removed during fleshing of pre-tanning

operations.Rest of the amount is removed after tanning by shaving and splitting

operations. Leather is therefore, made from dermas only which have mainly two

layers, corium mainor and major.

3.1 Classification of leather

a. By tanning process

i) Vegetable-tanned leather

ii) Chrome-tanned leather

iii) Aldehyde-tanned leather

iv) Formaldehyde-tanned leather

v) Brine-tanned leather

vi) Chamois leather [Aldehyde and brine-tanned]

vii) Rose-tanned leather

viii) Synthetic leather

b. By solid form

i) Full-grain leather

ii) Top-grain leather

iii) Corrected-grain leather

iv) Split leather

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c. Less-common leather

i) Buckskin or brine leather

ii) Patent leather

iii) Fish leather

d. Others

i) Nubuck leather

ii) Suede leather

iii) Belting leather

iv) Napa leather

v) Reconstitute leather

vi) Bonded leather

vii) By cast leather

3.2 Processing of leather

3.2.1 Curing

Curing means temporary preservation of hides and skins. It is not possible always to

send the hides and skins to the tanneries immediately just after flaying. Flaying is a

method of removing hide or skin from an animal carcass. The source of collection

hides and skins and the tanneries are not generally located in the same area. The time

gap between the flaying operation and the start of tannery operations vary from one to

two months. If hides and skins are not cured just after flaying they get completely

putrefied within 2/3 days. That is why, collected hides and skins require immediate

curing to stop the deterioration. Some methods of curing are discussed below-

a. Air drying

Moisture content of hides and skins are reduced to 10% to 14% by drying it. These

hides and skins are known in different names such as flints, crumbled hides, papras

etc. During this process, it should be remembered that drying under strong sun light

forms an impermeable layer on the flesh sides which prevents further drying. That is

why, hides and skins are always dried under mild sun. The ordinary drying creates

problems in tannery operations and produce inferior types of leather. Rate of drying is

a very important factor. If the hide is dried very slowly or too rapidly then the inner

layer putrefies.

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b. Salting

i) Brined - treating the hide with a saturated solution of salt

ii) Wet salted - rubbing the flesh side with salt

iii) Dry salted - air drying after doing b. i) or b.ii)

c. Pickling (Salt and Alum)

i) Brined - Soaking the hide in an alum/salt solution

ii) Wet pickling - rubbing the flesh side with salt and alum (2:1 ratio)

NB: Cold storage acts as a further preservative.

3.2.2 Tanning

Leather tanning is a general term for the numerous processing steps involved in

converting animal hides or skins into finish leather. The two most widely used

methods of production of leather are known to be vegetable and chrome tanning.

Chrome tanning accounts for approximately 90 percent of tanning production.

Figure 2.1 presents a general flow diagram for leather tanning and finishing

processes. Trimming, soaking, fleshing, and unhairing the first set of steps of the

process, are referred to as the beam house operations. Bating, pickling, wringing, and

splitting are referred to as tan-yard processes. Finishing processes include

conditioning, staking, dry milling, buffing, spray finishing, and plating.

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Process Waste RAW HIDES PRETANNING

MAIN TANNING

WET-BLUE WET-FINISHING

CRUST FINISHING OPERATIONS

LEATHER

-Soaking -Fleshing -unhairing+liming -Bating -Pickling

Fleshings

-Chrome tanning -Sammying -Sorting -Splitting -Shaving

-Neutralizations -Retaining -Drum dyeing -Fatliquaring -Sammying and setting -Drying

Solvents, Formaldehyde

Liquid residues

Solid residues -Conditioning -Staking -Buffing -Trimming -Finishing

BOD,COD,Chrome, dyes, fat.

BOD,COD,SS,Salts.Organic N.

H2S,NH3

BOD,COD,SS Salts chrome.

Trimmings

Shaving, trimming.

Fig. 3.1 General flow diagram for the leather tanning and finishing processes

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3.2.2.1 Pre-tanning

Pre-tanning is the processing of hides and skins in which hides and skins are

preserved through different methods such as sun drying, dry salting, using brine

solution, freezing, spraying of disinfectant etc. This preservation is done to avoid

spoilage of hides and skins by micro organism naturally present in skin.

3.2.2.2 Soaking In the process known as soaking, the hides are soaked in clean water to remove the

salt left over from curing and increase the moisture so that the hide or skin can be

further treated.

3.2.2.3 Fleshing

Fleshing is the removing from the skin all meat and fat, as well as the more obvious

and loose parts of the membrane. Some tanners remove most of the membrane during

fleshing, by using a sharper tool and spending more time on this step. However, the

preference is to scrape off mostly flesh, fat, and blood with a tool and then remove the

membrane in a later step. Blood stains are removed by scraping over them repeatedly

and hard. The skin becomes more or less clean after rinsing before proceeding with

the next step.

3.2.2.4 Unhairing + liming

After soaking the hides and skins, they are taken for liming treatment with milk of

lime that may involve the addition of sharpening agents like sodium sulfide, cyanides,

amines etc. The main objectives of this operation are to remove the hairs, nails, other

keratinous substances and the interfibrillary soluble proteins from hides and skins. To

bring the collagen in the hide to a proper condition for satisfactory tannage it is

swelled up and the fibers are split up. Unhairing is one of the most important

objectives of liming. Unhairing agents are used in this process. The majority of hair is

then removed mechanically, initially with a machine and then by hand using a dull

knife, a process known as scudding.

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3.2.2.5 De liming and bating

The pH of the collagen is brought down to a lower level so that enzymes may act on it,

in a process known as de-liming. Depending on the end use of the leather, hides may

be treated with enzymes to soften them, a process called bating.

3.2.2.6 Pickling

After completing the bating operation, the hides and skins are treated with a mixture

of common salt and sulfuric acid, in case a mineral tanning is to be done. This is done

to bring down the pH of collagen to a very low level so as to facilitate the penetration

of mineral tanning agent into the substance. This process is known as pickling. The

common salt penetrates the hide twice as fast as the acid and checks the ill effect of

sudden drop of pH.

3.2.3 Main tanning and wet-bleu

As stated earlier, most widely used tanning processes are:

i) Chrome tanning

ii) Vegetable tanning

Tanning processes of these two types are briefly described in the following sections.

3.2.3.1 Chrome tanning

Several steps are required in this process to produce a tanable hide. These steps are

removing the hair, the introduction of alkali agents such as sodium hydroxide,

restoring neutral pH, softening the skin with enzymes, and lowering pH of the hide

with salt and sulfuric acid. The pH value goes down from the neutral value of 7 when

the chromium is introduced to ensure that the chromium complexes are small enough

to fit in between the fibers and residues of the collagen. The desired level of

penetration of chrome into the substance is achieved; the pH of the material is raised

again to facilitate the process. This step is known as basification. In the raw state

chrome tanned skins are blue and therefore it is known as wet blue. Chrome tanning is

faster than vegetable tanning and produces stretchable leather which is excellent for

use in footwear and leather garments.

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3.2.3.2 Sammying

After tanning, leathers are dried by hanging up or subsequently sammying to reduce

the moisture content before further mechanical action. In the process, approximately

50% to 60% water is taken out for further finishing operations. The excess water from

wet blue is squeezed out by pressing the hide between pressurized rollers. This

operation is carried to stretch out the leather and work over the grain surface of wet

leather to remove excess water. It eliminates wrinkles, granulations and gives the

leather a good pattern form and work out stresses so that the leather lies flat.

3.2.3.3 Sorting

All leather pieces in a lot are not alike. Some pieces may have agar in defects; some

may have perfect grain but with slight looseness and few may be sound and silky

without any defects. Grain defects may be slight or of severe type. The finishing

technique of these different natured leathers are bound to be different .So the leathers

are carefully sorted according to the degree of grain defect and are passed on to do the

next step.

3.2.3.4 Splitting

The function of the splitting operation is to cut through longitudinal section of

leathers at a set thickness. If the leather is sufficiently thick, splitting can yield a grain

split and a flesh split that may both be processed into finished leather. Although

splitting can be performed before tanning, after tanning, or after drying, it is usually

performed after tanning.

3.2.3.5 Shaving

Quality of finish leather depends on a great extent on the degree of uniformity in

shaving. If the thickness of the leather is not uniform through out the area, the

mechanical effects like glazing, stacking, ironing, pressing etc.This process is

generally carried out on wet stock. Shaving of leather has two important objectives,

firstly, to level out the substance (thickness) of the leather and secondly, to bring the

substance to a precise figure. Hides and skins all have areas where the substance is

naturally heavier - the spine, the butt and the neck, and areas where it is noticeably

thinner than that in the bellies. The act of shaving the skin reduces the variation that

occurs, although in many cases, the substance will still be less in the belly edges. The

11

shaving machines can shave to a surprising degree of accuracy for betterment of next

operations.

3.2.4 Wet-finishing and crust

This is the second Stage of leather manufacture from raw materials to finished

product. It takes an important role on quality product for leather manufacturing. Most

of the important operations or activities during the stage are discuss here.

3.2.4.1 Neutralization

Oxidation of Cr(III) into Cr(VI) normally occurs in presence of strong oxidation agent

in acid environment but it can also take place in presence of mild oxidation agents at

high pH. In leather processing, neutralization is a stage when such conditions are

created. Comparing the neutralization of wet blue for upholstery crust, clothing and

water resistant shoe-upper leather carry out conventionally (with sodium formate and

sodium bicarbonate) with neutralization when a reducing auxiliary agent is used, no

relation can be establish between the chromate reduction potential of the float and the

Cr(VI) content of the leather produced. No relation can be established between the pH

and the Cr (VI) content of the leather produced either. Partial replacement of

conventional neutralization agents by a reducing auxiliary has been found to reduce

chromate formation.

3.2.4.2 Re-tanning

The purpose of re-tanning is to produce a further stabilization of the collagen network.

This involves further processing of the stabilized collagen network and may comprise

a further tannage when special characteristics such as perspiration resistance are

required. Conditioning, softening, dyeing or bleaching may also be carried out.

3.2.4.3 Drum dyeing

Almost all leather is dyed. With few exceptions such as vegetable tanned leathers with

the natural look, leather is artificially colored and this visual aspect is an essential part

of its aesthetic properties. Dying of leather is an application of soluble organic dye

stuffs in aqueous floats to wet leather. This leads to fixation of the dye molecules not

only on the surface of the tanned fiber network but inside as well. The type of

coloration of leather is completely different from the finish operations which is

performed on crust leather manufacture where insoluble dyestuffs and pigments are

12

applied together with binder substances on the surface of the leather. The application

of water soluble dye stuffs to leather results in colored leather which can be used to

produce aniline leather without pigment finishing, providing the grain quality is

appropriate. Dye stuffs are generally synthesized organic chemical molecules of an

aromatic or sometimes heterocyclic nature.

3.2.4.4 Fatliquoring

Fat liquoring is a process of coating the surfaces of fibers and fibrils of the leather

with a thin layer of oil. Unless leather is fat liquored it becomes hard on drying as the

fibers can not slide over one another. Almost all light leathers need a greater softness

and flexibility. This is attained in the fat liquoring process by introducing oil into the

leather, so that the individual fibers are uniformly coated. Small quantity of oil

distributed throughout the leather materially affects the subsequent finishing operations and the character of the leather. Proper lubrication or fat liquoring greatly

affects the physical properties of break, stretch, stitch tear, tensile strength, and

comfort of leather. Over lubrication will result in excessive softness. Improper

penetration results in hard bony leather that may crack in use.

3.2.4.5 Sammying and setting

Sammying and setting out is one of the important operations on hides and known as

double face tanning process. This operation removes the creases and excess water on

hides by sammying and setting at the same time. It also reduced the energy consumed

during in a stage of drying hides. Sammying operation also removes the chemicals,

dyestuffs and fats from hides and skin. During this operation tightening hides with

loosen fibers and reduction of deformation of hides takes place. The sammying and

setting out processes are provide directly to make quality leather.

3.2.4.6 Drying

The re-tanning, dyeing and fat liquoring chemicals are allowed to penetrate and

distribute within the collagen fiber structure before the pH is lowered and the

astringency causes them to fix to the tanned material. The final binding of chemicals

is encouraged by the drying process. Batches of leather are commonly toggle dried on

frames in heated tunnels for four to six hours or are vacuum dried individually for two

to ten minutes. Drying is usually followed by buffing, conditioning and staking or

13

milling. The resultant curst material is resistant to microbial attack and contains all the

leathering properties desired of leather and is ready for finishing.

3.2.5 Finishing operation of leather

The most important operation in a tannery is the finishing operation where the leather

can be manipulated for a variety of looks and textures. At the tannery the leather

undergoes a series of wet operations for coloring and oiling. After the hide dries and it

is in the naked state, it can be mechanically conditioned for different look or feel.

Some of these same techniques can be used at work bench. Beyond dying and oiling

the leather, physical conditioning methods are also applied to give plain old leather a

new and different look.

3.2.5.1 Conditioning

The natural fibers of leather breaks down with the passage of time. Acidic leathers

are particularly vulnerable to red rot, which causes powdering of the surface. Damage

from red rot is aggravated by high temperatures and relative humidity and is

irreversible. Long periods of low relative humidity (below 40%) can cause leather to

become desiccated and irreversibly changing the fibrous structure. Chemical damage

can also occur from exposure to environmental factors, including ultraviolet light,

ozone, acid from sulphurous and nitrous pollutants in the air. Oxidation and chemical

damage occur faster at higher temperatures. Various treatments are available such as

conditioners, impregnate the structure of the leather artifact with active chemicals are

sticky and attract stains. Saddle soap is used for cleaning, conditioning and softening

of leather. Leather shoes are widely conditioned with shoe polish.

3.2.5.2 Stacking

Stacking is a method of massaging a hide to make the leather more pliable. During the

process, a skin is held against a bar, the hide is grabbed with rubber rollers and blunt

blades are used to pull and flex the skin. This stretching makes the leather softer and

more pliable. Modern tanneries use large machines with many thumb-size pins that

oscillate and pound the leather as it travels along a conveyor. This same technique can

be applied by rolling, stretching, or massaging a stiff piece of leather at the bench.

14

3.2.5.3 Buffing

Buffing is a light sanding operation to either side of the hide. Buffing the underside

improves the nap and produces a velvety texture known as suede, while buffing the

grainy surface will smooth out some natural imperfections such as scratches, scars,

etc. Full grain leather has nothing removed except the hair, and possesses the original

grain of the animal. This is the strongest portion of the hide. Buffing the grain with an

emery wheel will produce an altered grain known as snuffed top grain, hand buff,

nubuck leather, or corrected top grain. This is typically the same as full top grain

leather, but the hide is lightly sanded to remove only the top of the hair follicles.

Tanneries use machines to buff approximately 1/64 in or 1oz in thickness from the

grain. This should leave a portion of the grain on the entire hide and results in a

cleaner surface.

3.2.5.4 Trimming

Final look of leather largely depends on trimming. If best quality leather looks

unattractive it means that is not trimmed properly. It is true that during trimming the

loss of leather should be revising. The trimming knife should be sharp like a shaving

razor. The knife should be absolutely vertical during trimming otherwise the inclined

cut portion of the trimmed leather will reduce the asthetic value of the finished

leather.

3.2.5.5 Finishing and plating

The quality of a finished leather depends on degree of uniformity in saving. If the

thickness of leeather is not uniform throughout the area after saving operation, the

mechanical effects like glazing,stacking,ironing,pressing etc, will be ununiform on the

leather surface area.No finisher can finish such leather of uneven thickness to a class

one product.

The final conditioning processes is embossing the hide with heat and pressure to

create a chosen grain in the surface of the hide. Sometimes leathers are embossed to

make them appear to be another leather, such as embossing an alligator or ostrich

pattern into cowhide. It requires hundreds of tons of pressure to emboss a full hide

may.

15

3.3 Properties of leather (Mechanical or Physical)

Leather is a wonderful material with many uses. Unique properties and characteristics

make it the ideal choice for many different applications.Some of the most useful

properties of leather are as follow. It has a high tensile strength and is resistant to

tearing. This helps leather items last for a long time while retaining their look and

feel. It is a good heat barrier and provides excellent heat insulation. Leather contains a

large amount of air that is a poor conductor of heat. This makes leather a very

comfortable item for the human skin. It is able to hold large quantities of water vapor

such as human perspiration and then dissipate it later. This makes leather a

comfortable item to wear or sit on. Leather is resistant to abrasion in both wet and dry

environments. This makes leather an excellent protector of human skin. It is resistant

to heat and fire. It is also resistant to fungal growth such as mildew. It consists of

many fibers that are breathable. This breathability makes it very comfortable to wear

in any climate. Leather can be dyed in many different colors that makes it attractive in

the production of leather clothing. Leather clothing becomes a literal second skin. It

warms our body temperature. It is not itchy and does not scratch. It is non-irritating to

the skin. Leather is a fantastic material with excellent physical properties that enables

it to be used in many diverse applications from furniture to clothing.

3.3.1 Thermal conductivity

Heat always tends to move from higher temperature to lower temperature to make an

equilibrium condition. Heat transfer through the materials is mainly dependent on its

thermal conductivity.Heat can pass more quickly through material of higher thermal

conductivity than lower.

Part of the function of a shoe and leather garments are to assist the foot and body in

maintaining comfort temperature and to guard against large heat changes. That is

why, thermal conductivity is an important characteristic of leather for manufacturing

of footwear and leather garments.In the cold weather the outside temperature is very

low and in-shoe temperature is comparatively higher.At that condition the heat tends

to move from inside to outside and fell discomfort.On the other hand in the hot

weather there is not much difference between the inside and outside temperature,in

that case the heat transfer is less.

The insulating property of leather used for making shoes and leather products which

also depends on the porosity or the amount of air spaces present. A good insulating

16

material has a low thermal conductivity value but conductivity value increases with an

increase in moisture content.

3.3.2 Tensile strength and percentage of elongation at break

Tensile strength indicates the overall strength of the leather which is ascertained by

small leather customers by pulling the leather with his two hands. Tensile strength is

determined practically for all types of light leathers like shoe upper, lining, upholstery

and for industrial leathers.

Tensile strength in kg./sq. cm is given as Breaking load (kg)/ Cross section (sq.cm).

Breaking load mainly depends upon the number of collagen fibers acting in the

direction of applied load and so is more or less constant for a piece of leather

specimen because the number of fibers in that piece is always constant. The tensile

strength of leather in different direction is different because the number of fibers and

their wovenness are different in different directions of the hide by nature. The percent

elongation at break can be defined as the extension in cm. at the breaking point of a

100 cm long leather specimen during tensile strength determination.

3.3.3 Tearing strength

This property is generally carried out on shoe uppers as well as on leathers to be used

for leather goods making to know the fiber strength of the leather. Tensile strength

and stitch tearing strength thus say about the strength of the leather whereas tearing

strength gives an idea about the strength of its fibers. During tensile strength and

stitch tearing strength test, large numbers of fibers are ruptured all at a time whereas

in tearing strength determination few fibers are ruptured at a time. The tearing

strength of leather can be defined as the load in kg. required for tearing the leather

sample one centimeter thickness.

Thus, Tearing strength kg/cm = Tearing load/ Leather thickness.

3.3.4 Bursting strength

Bursting strength of leather is measured by the force required to force a spherical

ended plunger through a piece of leather. The bursting load and extension will be

generally proportional to the diameter of the plunger. This is suitable for

development, control and service evaluation of the leather. There is good correlation

between bursting strength and tensile strength. Determination of the bursting strength

17

of leather uses different methods. It may be used to test a large variety of leathers and

leather products. It is particularly applicable to light and medium weight leathers,

such as shoe uppers and garments. This test method does not apply to wet blue.

3.3.5 Water vapor permeability

Water vapor permeability is one of the important properties of leather that makes it so

desirable for use in making of shoes and leather garments because of the perspiration

formed inside the shoes and garments. The water vapor permeability of tanned leather

is generally high but is gradually braught down by adding fats, oils and waxes into

the tanned leather during finishing. The foot and body may be comfortable under a

particular set of temperature and humidity conditions which the wearer of the shoes

and garments may encounter. The rate of penetration of water vapor through the

leather is mainly governed by the vapor pressure difference between the two sides of

the leather. It would be desirable to maintain water vapor transmission at a high level

while simultaneously liquid water transmission is maintained at a low level.

3.3.6 Softness

One of the most important characteristics during exploitation of leather products is

leather softness. Deformability of leather during measurement will be within the

limits of elastic and compactness deformations. This investigation is done by finding

the relative elasticity during bi-axial tension with leather softness. This characteristic

depends on the tanning process of hides and skins such as chemical and mechanical

treatments during different kinds of operation and geographical origin. Softness also

varies with respect to its thickness and fiber compactness at different zones of the

same leather.

.

18

CHAPTER 4

------------------------------------------------------------------------------------------------------

EXPERIMENTAL SET-UP AND DATA COLLECTION

4.0 Design and manufacture of Fitch type thermal conductivity apparatus

The Fitch method to determine the thermal conductivity was developed by Fitch in

1935 (Mohsenin, 1980),the Fitch apparatus uses a plane source of heat. It is applicable

to poor conductors of heat that can be formed into a slab. The apparatus is designed

and manufactured to determine the thermal conductivity of leather and other

insulating materials such as rubber, textile, and cork used in footwear manufacturing.

The base unit is composed of the body guides and cover plate that houses the vessel

and cylindrical heater with flange. The steel vessel is heat insulated on the sides and a

temperature sensor is installed in the base of the vessel. It is known as the heat source.

The heater cover with gasket is secured with fixing bolt to the vessel flange. There is

an inlet pipe and an outlet pipe that connect the cover to feed and discharge oil/water

to/from the vessel. The temperature sensor is installed at the heater foot. There is a

step motor linked with a lead screw in the drive sleeve which is centrally built in the

movable housing of the heat sink. A wheel is also fastened with the lead screw to

control the drive sleeve manually.The heat sink is a copper slab fitted with the

temperature sensor and thermal insulation is known as the heat receiver.

The movable housing along with the heat sink is fastened into the guides connecting

to the body base and cover plate. The thermocouple wire are connected to the binding

post on the source and the receiver. The other end of thermocouple wire are

connected the galvanometer terminals. The source vessel is filled with oil and

cylindrical immersion heater is placed in it to maintain the oil at a constant

temperature, controled by a temperature controller.

The receiver is kept at approximately room temperature, A suitable series resistance is

fitted with the galvanometer to bring the deflection onto the scale. When the

galvanometer deflection is steady the test sample is placed on the heat sink. By using

the positioner the sink with a sample placed on it is lifted until the source protrudes

from the body cover and rests under gravity on a specimen. A mass of 5 kg. vessel

with it’s collar was used to ensure close contact between the surface of the apparatus

and the specimen [4]. The galvanometer deflection is then taken at regular intervals of

1, 2, or 3, minutes depending on the heat rate of heat conduction. The whole setup is

shown in figure 4.1 and 4.1a.

19

Fig.

4.1

The

rmal

con

duct

ivity

app

arat

us

20

Figure 4.1a Measuring instrument base modules

21

4.1 Collection of hides and skins

Physical properties of leathers vary from piece to piece, geographical origin and

different locations of same piece; it is not possible to comment about the average

properties of leathers only by testing one or two pieces from that. Thermal

conductivity, as well, depends on geographical origin and compactness of their fiber.

To investigate the properties, the sample pieces have been collected from Chittagong,

Rajshahi, and Dhaka.

4.2 Preparation of sample

The properties of leather vary from piece to piece, fiber structure, ages and also

geographical origin. That is why, it is not possible to comment about the average

properties of leather. By nature, the outer coverings of live animals possess high

degree of different physical properties and those very rapidly go down after the death

of the animals. To preserve physical properties as far as possible tanning and finishing

operations are done on leather. The dermis which is made up of interwoven fiber

bundles is not uniform throughout its area and cross-section. The substance, the

compactness, the feel etc. are therefore different in different regions of the hides and

skins. It is the same in case of finished leather also. So sampling location (Figure 4.2)

should be carefully selected so that the sample becomes the representative of the full

piece of the leather.

22

Figure 4.2 Different regions of hides and skin

23

4.3 Thickness, Softness and Contact area measurement

Thickness

Most of the leather are soft and depressable with wooly flesh side, that makes it

difficult to measure their thickness. It is true that certain amount of pressure always

necessary to measure the thickness especially due to wooliness on the flesh side. On

the other hand, if the pressure is different during measurement of thickness of the

same specimen different values are obtained due to different compression of the

leather. Moreover, thickness of the leather varies with area of the leather through

which the measuring pressure is applied. A thickness gauge with a dead load of 370

gm, is used to measure the thickness of the leather which is shown in tables 4.1a to

4.3d and 4.4 are shown in details.

Softness

Suitable parameter for leather softness evaluation can be elasticity and fiber

compactness, because it defines deformability of leather within the limits of elastic

deformations. The pneumatic device ST 300D is recommended by the Society of

Leather Technologists and Chemists, EU and Lithuanian standards [11,13] to

measure the depth of punch in millimeters of a fixed sample when it is under clamp of

the pin of a certain size and mass. Softness varies with respect to its thickness and

fiber compactness at different zones of the sample.The softness of selected samples

are measured by the recommended instrument and are shown in table 4.1a to 4.3d and

4.4.

Contact Area

The test specimens are generally regular in size and therefore their surface areas are

determined by using the formula πr² where r is the radius of circular test specimen.

Thickness, softness and contact area of circular test specimen are shown in tables 4.1a

to 4.3d,4.4 with respect to its location and geographical origin.

24

Table 4.1a Geographical origin: Chittagong, Bangladesh

Chrome tanned leather. Sampling position : Butt Standard weights used for thickness 370gm and softness 530gm

Load plunger diameter 7mm [softness instrument] Thickness, softness and heat exchange surface area of Sample

Sample no. Thickness

[mm]

Average thickness.

[mm]

Thickness

[mm]

Area

[cm2]

Softness

[mm]

Average softness [mm]

Softness

[mm] 01. 1.60

1.60 1.61 1.61 1.61

1.61

1.60

19.63

4.07 4.14 4.41 4.35 4.15

4.22

4.20

02.

1.60 1.60 1.55 1.55 1.55

1.57

4.31 4.25 4.06 4.13 4.23

4.19

03.

1.60 1.61 1.60 1.61 1.61

1.61

4.31 4.43 4.17 4.32 4.33

4.31

04. 1.60 1.62 1.62 1.61 1.60

1.61

4.38 4.32 4.10 4.25 4.30

4.27

05. 1.60 1.63 1.65 1.62 1.60

1.62

4.02 4.05 4.00 4.04 4.03

4.03

25

Table 4.1b Geographical origin: Chittagong, Bangladesh

Chrome tanned leather Sampling position: Belly

Thickness, softness and heat exchange surface area of sample

Sample no.

Thickness

[mm]

Average thickness

[mm]

Thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.50

1.55 1.50 1.50 1.52

1.51

1.51

19.63

3.38 3.16 3.25 3.20 3.23

3.24

3.33

02.

1.60 1.55 1.61 1.57 1.56

1.58

3.44 3.69 3.34 3.50 3.45

3.48

03.

1.50 1.50 1.50 1.50 1.50

1.50

3.35 3.22 3.18 3.23 3.17

3.23

04. 1.55 1.55 1.50 1.50 1.50

1.52

3.24 3.32 3.42 3.38 3.30

3.33

05. 1.50 1.55 1.50 1.50 1.55

1.52

3.252 3.430 3.513 3.350 3.300

3.37

26

Table 4.1c Geographical origin: Chittagong, Bangladesh

Chrome tanned leather Sampling position: Shank


Sample no.

Thickness

[mm]

Average thickness

[mm]

Thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.55

1.52 1.55 1.55 1.55

1.54

1.53

19.63

4.05 3.90 3.91 3.90 3.95

3.94

3.37

02.

1.55 1.50 1.50 1.55 1.55

1.53

3.11 3.36 3.06 3.26 3.30

3.22

03.

1.55 1.55 1.50 1.50 1.50

1.52

3.23 3.29 3.37 3.30 3.25

3.29

04. 1.55 1.55 1.50 1.50 1.55

1.53

3.18 3.12 3.38 3.18 3.12

3.19

05. 1.55 1.55 1.55 1.55 1.55

1.55

3.18 3.12 3.38 3.18 3.12

3.19

27

Table 4.1d Geographical origin: Chittagong, Bangladesh

Chrome tanned leather Sampling position: Shoulder

Thickness, softness and heat exchange surface area of sample materials

Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.61 1.60 1.60 1.60

1.60

1.60

19.63

3.06 3.13 3.06 3.06 3.06

3.06

3.17

02.

1.55 1.55 1.55 1.55 1.60

1.56

3.20 3.40 3.20 3.30 3.20

3.26

03.

1.60 1.55 1.60 1.61 1.60

1.59

3.07 3.06 3.26 3.08 3.06

3.11

04. 1.50 1.55 1.55 1.52 1.52

1.53

3.37 3.56 3.20 3.40 3.25

3.36

05. 1.61 1.61 1.60 1.60 1.62

1.61

3.06 3.13 3.06 3.06 3.06

3.08

28

Table 4.2a Geographical origin: Rajshahi, Bangladesh

Chrome tanned leather Sampling position: Butt


Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.55

1.55 1.56 1.56 1.55

1.55

1.56

19.63

4.24 4.33 4.32 4.24 4.32

4.29

4.16

02.

1.60 1.55 1.55 1.60 1.55

1.57

4.06 4.19 4.06 4.18 4.06

4.11

03.

1.50 1.60 1.56 1.50 1.60

1.55

4.20 4.30 4.07 4.25 4.20

4.20

04. 1.60 1.60 1.60 1.60 1.60

1.60

4.07 3.42 4.06 4.07 4.00

3.92

05. 1.55 1.55 1.56 1.56 1.55

1.55

4.24 4.33 4.32 4.24 4.32

4.29

29

Table 4.2b Geographical origin: Rajshahi, Bangladesh



Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.50 1.60 1.50 1.60

1.56

1.57

19.63

4.49 5.31 5.00 5.20 5.00

5.00

4.45

02.

1.55 1.60 1.62 1.60 1.55

1.58

4.29 4.13 5.12 4.50 4.15

4.44

03.

1.55 1.60 1.57 1.60 1.55

1.57

4.60 4.52 4.15 4.52 4.50

4.46

04. 1.60 1.60 1.62 1.61 1.60

1.61

4.31 4.06 4.10 4.20 4.15

4.16

05. 1.50 1.55 1.53 1.55 1.50

1.53

4.23 4.10 4.36 4.20 4.10

4.20

30

Table 4.2c Geographical origin: Rajshahi , Bangladesh


Thickness, softness and heat exchange surface area of Sample

Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.55 1.60 1.55 1.60

1.58

1.59

19.63

5.00 5.25 5.02 5.00 5.25

5.10

4.43

02.

1.55 1.45 1.62 1.55 1.50

1.53

4.45 4.50 4.45 4.50 4.45

4.47

03.

1.60 1.65 1.60 1.60 1.60

1.61

4.41 4.43 4.35 4.41 4.35

4.39

04. 1.65 1.60 1.60 1.65 1.60

1.62

2.97 3.29 3.29 3.00 2.97

3.10

05. 1.60 1.55 1.60 1.55 1.60

1.58

5.00 5.25 5.02 5.00 5.25

5.10

31

Table 4.2d Geographical origin: Rajshahi, Bangladesh



Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.60 1.60 1.60 1.60

1.60

1.62

19.63

4.06 4.24 4.30 4.30 4.22

4.22

4.14

02.

1.62 1.62 1.62 1.62 1.62

1.62

3.43 4.05 4.05 4.05 4.00

3.92

03.

1.60 1.65 1.60 1.60 1.65

1.62

4.42 3.99 4.43 4.42 4.42

4.34

04. 1.60 1.65 1.60 1.60 1.65

1.62

4.10 4.45 4.29 4.30 4.35

4.30

05. 1.65 1.60 1.65 1.60 1.65

1.63

4.05 4.00 3.43 4.05 4.05

3.92

32

Table 4.3a Geographical origin: Dhaka, Bangladesh

Chrome tanned leather Sampling position: Butt


Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softnes

[mm] 01. 1.60

1.50 1.60 1.50 1.60

1.56

1.57

19.63

4.24 4.33 4.32 4.24 4.32

4.29

4.16

02.

1.60 1.65 1.60 1.60 1.60

1.58

4.06 4.19 4.06 4.18 4.06

4.11

03.

1.50 1.60 1.56 1.50 1.60

1.57

4.20 4.30 4.07 4.25 4.20

4.20

04. 1.60 1.65 1.65 1.60 1.65

1.61

4.07 3.42 4.06 4.07 4.00

3.92

05. 1.55 1.55 1.56 1.56 1.55

1.53

4.24 4.33 4.32 4.24 4.32

4.29

33

Table 4.3b Geographical origin: Dhaka, Bangladesh



Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.60 1.60 1.60 1.60

1.60

1.59

19.63

4.19 4.11 4.00 4.20 4.10

4.12

4.15

02.

1.55 1.60 1.62 1.60 1.55

1.61

4.21 4.13 4.12 4.10 4.11

4.13

03.

1.50 1.55 1.50 1.50 1.50

1.55

4.10 4.12 4.15 4.12 4.20

4.14

04. 1.65 1.60 1.65 1.65 1.60

1.63

4.31 4.06 4.10 4.20 4.15

4.16

05. 1.60 1.55 1.60 1.55 1.60

1.55

4.23 4.10 4.36 4.20 4.10

4.20

34

Table 4.3c Geographical origin: Dhaka , Bangladesh



Sample no.

Thickness

[mm]

Average thickness

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.55 1.60 1.55 1.60

1.58

1.57

19.63

4.00 4.25 4.02 4.00 4.25

4.10

4.03

02.

1.55 1.45 1.52 1.45 1.50

1.50

4.45 4.50 4.45 4.50 4.45

4.47

03.

1.55 1.60 1.57 1.60 1.55

1.51

4.41 4.43 4.350 4.41 4.35

4.40

04. 1.60 1.60 1.62 1.61 1.60

1.67

2.97 3.29 3.29 3.00 2.97

3.10

05. 1.50 1.55 1.53 1.55 1.50

1.58

4.00 4.25 4.02 4.00 4.25

4.10

35

Table 4.3d Geographical origin: Dhaka, Bangladesh



Sample no.

Thickness

[mm]

Average thickness.

[mm]

Average thickness

[mm]

Area

[cm2]

Softness

[mm]


Softness

[mm] 01. 1.60

1.55 1.60 1.55 1.55

1.57

1.55

19.63

4.06 4.24 4.30 4.30 4.22

4.22

4.26

02.

1.55 1.50 1.55 1.50 1.55

1.53

4.43 4.05 4.05 4.05 4.00

4.12

03.

1.50 1.55 1.50 1.50 1.55

1.52

4.42 4.99 4.43 4.42 4.42

4.54

04. 1.60 1.55 1.60 1.60 1.55

1.58

4.10 4.45 4.29 4.30 4.35

4.30

05. 1.55 1.60 1.55 1.60 1.55

1.57

4.05 4.00 4.43 4.05 4.05

4.12

36

Table 4.4 Comparative statement of thickness and softness with respect to sample location and

geographical origin in Bangladesh

Geographical origin

Sample Location Thickness

[mm]

Thickness of Leather

[mm]

Softness Average softness [mm]

Chittagong.

Belly Butt Shank Shoulder

1.51 1.60 1.53 1.60

1.56

3.33 4.20 3.37 3.17

3.52

Rajshahi


1.57 1.56 1.59 1.62

1.59

4.45 4.16 4.43 4.14

4.30

Dhaka


1.59 1.57 1.57 1.55

1.57

4.15 4.16 4.03 4.26

4.15

37

4.4 Thermal conductivity measurement Heat transfer in transient state is employed to determine the thermal conductivity for

leather and other footwear materials. The measurement is based on the thermal

balance of heat sink and the rate of temperature difference between the heat source

and the heat sink. The sample of leather is placed between two plates of different

temperatures. The upper plate (heat source) is kept at constant temperature, while the

temperature of lower plate (heat sink) is variable. The temperature difference between

heat source and heat sink gradually decreases until thermal equilibrium is achieved.

The temperature difference that varies in time is measured through galvanometer

deflection directly. In addition, it is assumed that the heat transfer through the sample

is directly proportional to the heat transfer area and temperature difference on both

sides of the sample and is inversely proportional to its thickness. Thus, if no heat loss

occurs, the heat transfer rate through the sample corresponds to the heat received by

the heat sink in unit time.

Assumptions and the thermal conductivity measurements are valid if the apparatus

and test procedure meet the following requirements-

- The temperature of top surface of the sample is constant during measurement

and equal to that of the heat source, while the temperature of the bottom side

of the sample varies in time and is equal to that of heat sink.

- The temperature of heat sink varies in time only and does not depend on its

thickness and radius.

- The temperature difference between the heat source and heat sink is indicated

immediately without delay and the measuring signal is proportional to it.

- Heat transfer through the sample is stored in the heat sink without loss.

- There is no heat transfer on the sides and heat storage in the sample.

- The thermal properties of tested materials and heat sink remain unchanged

during measurement (specific heat, thermal conductivity, water content).

Deviations from above assumption would lead to less reliable results. According to

the method for evaluation of leather thermal conductivity by using the apparatus, the

temperature difference between the heat source and heat sink is measured with a

galvanometer at regular time intervals, e.g., every 1, 2 or 3 minutes. For each sample,

10 readings are taken. According to the standard, the relationship between the

38

logarithms of galvanometer readings vs. time should be linear and the slope can be

determined. The linear equation provides only approximate description of the heat

transfer in the apparatus.

The differential thermal balance for the slab (heat sink) can be written as follows-

dtdQ

dtdQ 21 = (1)

T)sT(kdt

dQH

1 −=l

(2)

dtdTMc

dtdQ 2 = (3)

dtdTMcT)sT(k

H =−l

(4)

dtdT.

TT1

Mcks

H −=

l (5)

Here, Q1- heat transfer from the heat source through the sample to the heat sink, Q2-

heat stored in the heat sink, t-time, l -specimen thickness, k-thermal conductivity of

the material,TH-heater temperature,T-heat sink temperature,M- heat sink weight,c-

heat sink specific heat, s-heat exchange surface area or heat sink surface area. The

gauge reading i is proportional to the temperature difference of the heaterTH and heat

sink T.

T)T( i H −= β (6)

dtdT

dtdi β−= (7)

Here, β is the factor of proportionality. Substituting equations 6 and 7 into equation 5,

results.

39

dtMcks

idi

l−= (8)

The value of t is obtained after integrating equation 8,

10 ciln ksMct +−=

l ( 9)

Where, c1 is the constant of integration. If the initial conditions are i = i0 at time t = 0

then equation (9) gives

01 iln ksMcc l

= (10)

and equation (9) can be rewritten as,

)iln -i (lnksMct 0

l−= (11)

When logarithms to base 10 are used then, equation (11) becomes,

)i log-i log(ksMc303.2t 0

l−= (12)

From equation (12) it follows that the graph of log i plotted against t should be a

straight line and the slope m is,

ksMc-2.303

log.itm l

=−= (13)

msMc303.2k l

−= (14)

The weight,surface area and specific heat of the used copper sink slab are respectively

M = 207.15gm s = 19.63 cm2 and c = .096cal/cm 0C. The slope m, is determined

from the graphs and submitted equation (14) to calculate the thermal conductivity.

Calculated data of thermal conductivity “ k” shown in table 4.12.

40

4.5 Experimental Data

The above mentioned relationships are used to gather data from various sample of

leather obtained from the three region mentioned previously.Four samples each of 130

mm diameters are taken out from each of the three zones of a particular leather from

one region. Each sample is then tested following the above mentioned procedure.The

data gathered for such sets are shown in the table 4.5a to 4.7d.

Table 4.8 shows the aggregate log i values for different zones of different regions.

The data thus obtained are plotted on time versuss log.i values for each sample and

linear regressions done to estimate the intercept and slope of the line.

R-squared values along with standard deviation and standared error for each are

shown in table 4.9a to 4.11b.

41

Table 4.5a Data of galvanometer deflection with respect to time intervals

Sample location : Belly Geographical origin : Chittagong

Time[t] [Minutes] Observation Galvanometer deflection [i] Average deflection [i] log.i

0

1 2 3 4

4.00 4.00 4.00 4.00

4.00

.6

1

1 2 3 4

3.50 3.00 3.50 3.40

3.35

.53

2

1 2 3 4

3.25 2.75 3.00 3.20

3.05

.49

3

1 2 3 4

3.00 2.25 2.75 3.00

2.75

.44

4

1 2 3 4

2.75 2.15 2.25 2.75

2.48

.39

5

1 2 3 4

2.50 2.00 2.15 2.50

2.29

.36

6

1 2 3 4

2.25 1.85 2.00 2.30

2.21

.34

7

1 2 3 4

2.15 1.70 1.85 2.10

1.95

.29

8

1 2 3 4

2.00 1.55 1.70 2.00

1.81

.26

9

1 2 3 4

1.95 1.45 1.55 1.85

1.70

.23

10

1 2 3 4

1.90 1.40 1.50 1.85

1.70

.23

42

Table-4.5b Data of galvanometer deflection with respect to time intervals

Sample location : Butt Geographical origin : Chittagong


0

1 2 3 4

3.50 3.50

3.50 4.00

3.63

.56

1

1 2 3 4

3.15 3.20 3.20 3.65

3.30

.52

2

1 2 3 4

3.00 3.10 3.10 3.20

3.10

.49

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25

2.10

2.21

.35

5

1 2 3 4

2.15 2.10 2.15 2.10

2.12

.33

6

1 2 3 4

2.00 1.95 2.00 2.00

1.99

.30

7

1 2 3 4

1.95 1.80 1.95 1.90

1.90

.28

8

1 2 3 4

1.80 1.75 1.80 1.70

1.76

.25

9

1 2 3 4

1.75 1.70 1.75 1.75

1.74

.24

10

1 2 3 4

1.75 1.70 1.75 1.75

1.74

.24

43

Table-4.5c Data of galvanometer deflection with respect to time intervals

Sample location : Shank Geographical origin : Chittagong


0

1 2 3 4

3.50 3.50 3.50 3.50

3.50

.54

1

1 2 3 4

3.15 3.20 3.20 3.15

3.18

.50

2

1 2 3 4

3.00 3.10 3.10 3.10

3.08

.49

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.15 2.10 2.15 2.10

2.13

.33

6

1 2 3 4

2.00 1.95 2.00 2.00

1.99

.30

7

1 2 3 4

1.95 1.80 1.95 1.90

1.90

.28

8

1 2 3 4

1.80 1.75 1.80 1.70

1.76

.25

9

1 2 3 4

1.75 1.70 1.75 1.75

1.74

.24

10

1 2 3 4

1.75 1.70 1.75 1.75

1.74

.24

44

Table 4.5d

Data of galvanometer deflection with respect to time intervals Sample location : Shoulder

Geographical origin : Chittagong


0

1 2 3 4

3.50 3.50 3.50 3.50

3.50

.54

1

1 2 3 4

3.25 3.20 3.25 3.25

3.24

.51

2

1 2 3 4

3.00 3.10 3.10 3.10

3.08

.50

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.10 2.10 2.10 2.10

2.10

.32

6

1 2 3 4

2.00 1.95 2.00 2.00

1.99

.30

7

1 2 3 4

1.90 1.80 1.90 1.90

1.89

.28

8

1 2 3 4

1.70 1.75 1.80 1.70

1.74

.24

9

1 2 3 4

1.60 1.70 1.70 1.60

1.65

.22

10

1 2 3 4

1.60 1.70 1.70 1.60

1.65

.22

45

Table 4.6a

Data of galvanometer deflection with respect to time intervals Sample location : Belly

Geographical origin : Rajshahi


0

1 2 3 4

4.00 3.50 3.50 4.00

3.75

.57

1

1 2 3 4

3.60 3.20 3.20 3.65

3.41

.53

2

1 2 3 4

3.00 3.00 3.00 3.20

3.05

.48

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.10 2.10 2.10 2.15

2.11

.32

5

1 2 3 4

1.70 1.70 1.70 1.80

1.73

.24

6

1 2 3 4

1.60 1.65 1.60 1.70

1.64

.22

7

1 2 3 4

1.50 1.50 1.50 1.60

1.53

.19

8

1 2 3 4

1.40 1.40 1.40 1.45

1.41

.15

9

1 2 3 4

1.35 1.30 1.35 1.35

1.34

.13

10

1 2 3 4

1.35 1.30 1.35 1.35

1.34

.13

46

Table 4.6b

Data of galvanometer deflection with respect to time intervals Sample location : Butt



0

1 2 3 4

4.00 3.50 3.50 4.00

3.75

.57

1

1 2 3 4

3.60 3.20 3.20 3.65

3.41

.53

2

1 2 3 4

3.00 3.00 3.00 3.20

3.05

.48

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.10 2.10 2.10 2.15

2.11

.32

5

1 2 3 4

1.70 1.70 1.70 1.80

1.73

.24

6

1 2 3 4

1.60 1.65 1.60 1.70

1.64

.22

7

1 2 3 4

1.50 1.50 1.50 1.60

1.53

.19

8

1 2 3 4

1.40 1.40 1.40 1.45

1.41

.15

9

1 2 3 4

1.35 1.30 1.35 1.35

1.34

.13

10

1 2 3 4

1.35 1.30 1.35 1.35

1.34

.13

47

Table 4.6c

Data of galvanometer deflection with respect to time intervals Sample location : Shank



0

1 2 3 4

4.00 3.50 3.50 4.00

3.75

.57

1

1 2 3 4

3.70 3.20 3.20 3.75

3.46

.54

2

1 2 3 4

3.00 3.00 3.00 3.20

3.05

.48

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.10 2.10 2.10 2.15

2.11

.32

5

1 2 3 4

1.70 1.70 1.70 1.80

1.73

.24

6

1 2 3 4

1.60 1.65 1.60 1.70

1.64

.22

7

1 2 3 4

1.50 1.50 1.50 1.60

1.53

.19

8

1 2 3 4

1.40 1.40 1.40 1.45

1.41

.15

9

1 2 3 4

1.30 1.25 1.25 1.25

1.26

.10

10

1 2 3 4

1.30 1.25 1.25 1.25

1.26

.10

48

Table 4.6d




0

1 2 3 4

3.50 3.50 3.50 3.50

3.50

.54

1

1 2 3 4

3.20 3.20 3.20 3.20

3.20

.51

2

1 2 3 4

2.70 2.70 2.70 2.70

2.70

.43

3

1 2 3 4

2.40 2.45 2.45 2.40

2.43

.39

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.10 2.10 2.10 2.10

2.10

.32

6

1 2 3 4

2.00 1.95 2.00 2.00

1.99

.30

7

1 2 3 4

1.90 1.80 1.90 1.90

1.88

.27

8

1 2 3 4

1.70 1.75 1.80 1.70

1.74

.24

9

1 2 3 4

1.65 1.70 1.75 1.60

1.68

.23

10

1 2 3 4

1.65 1.70 1.75 1.60

1.68

.23

49

Table 4.7a

Data of galvanometer deflection with respect to time intervals Sample location : Belly

Geographical origin : Dhaka


0

1 2 3 4

4.00 3.50 3.75 4.50

3.81

.58

1

1 2 3 4

3.70 3.20 3.45 3.45

3.5

.54

2

1 2 3 4

3.25 2.75 3.00 3.00

3.03

.48

3

1 2 3 4

3.00 2.25 2.75 3.10

2.8

.45

4

1 2 3 4

2.70 2.10 2.25 2.50

2.41

.38

5

1 2 3 4

2.30 1.80 2.10 2.10

2.13

.33

6

1 2 3 4

2.00 1.50 1.80 1.80

1.83

.26

7

1 2 3 4

1.80 1.30 1.55 1.50

1.61

.21

8

1 2 3 4

1.60 1.10 1.30 1.30

1.4

.15

9

1 2 3 4

1.50 1.00 1.20 1.10

1.3

.11

10

1 2 3 4

1.50 1.00 1.20 1.10

1.3

.11

50

Table 4.7b

Data of galvanometer deflection with respect to time intervals Sample location : Butt



0

1 2 3 4

3.50 3.50 3.50 4.00

3.63

.60

1

1 2 3 4

3.25 3.25 3.20 3.75

3.36

.53

2

1 2 3 4

3.00 3.10 3.10 3.20

3.10

.49

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.15 2.10 2.15 2.10

2.13

.33

6

1 2 3 4

2.00 1.95 2.00 2.00

1.99

.30

7

1 2 3 4

1.95 1.80 1.95 1.90

1.90

.28

8

1 2 3 4

1.80 1.75 1.80 1.70

1.76

.25

9

1 2 3 4

1.75 1.70 1.75 1.60

1.70

.23

10

1 2 3 4

1.75 1.70 1.75 1.60

1.70

.23

51

Table 4.7c

Data of galvanometer deflection with respect to time intervals Sample location : Shank



0

1 2 3 4

3.50 3.50 3.50 3.50

3.50

.54

1

1 2 3 4

3.15 3.20 3.20 3.15

3.18

.50

2

1 2 3 4

2.80 2.90 2.90 2.80

2.85

.46

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.15 2.10 2.15 2.10

2.13

.33

6

1 2 3 4

2.00 1.95 2.00 2.00

2.00

.30

7

1 2 3 4

1.95 1.80 1.95 1.90

1.90

.28

8

1 2 3 4

1.80 1.75 1.80 1.70

1.76

.25

9

1 2 3 4

1.70 1.60 1.70 1.60

1.65

.22

10

1 2 3 4

1.70 1.60 1.70 1.60

1.65

.22

52

Table 4.7d




0

1 2 3 4

3.50 3.50 3.50 3.50

3.50

.54

1

1 2 3 4

3.25 3.20 3.25 3.25

3.24

.51

2

1 2 3 4

3.00 3.10 3.10 3.10

3.08

.49

3

1 2 3 4

2.50 2.45 2.65 2.60

2.55

.41

4

1 2 3 4

2.25 2.25 2.25 2.15

2.23

.35

5

1 2 3 4

2.10 2.10 2.10 2.10

2.10

.32

6

1 2 3 4

2.00 1.95 2.00 2.00

2.00

.30

7

1 2 3 4

1.90 1.80 1.90 1.90

1.9

.28

8

1 2 3 4

1.70 1.75 1.80 1.70

1.74

.24

9

1 2 3 4

1.60 1.70 1.70 1.60

1.65

.22

10

1 2 3 4

1.60 1.70 1.70 1.60

1.65

.22

53

Table 4.8 Logogrammatic data of galvanometer deflection

with respect to origin, sample location and time intervals

Geographical origin

Time [Minutes]

Sample location [log.i] Average log.i Belly Butt Shank

Shoulder

Chittagong

0 1 2 3 4 5 6 7 8 9

.60

.53

.48

.44

.39

.36

.34

.29

.26

.23

.56 .52 .49 .41 .35 .33 .30 .28 .25 .24

.54

.50

.49

.41

.35

.33

.30

.28

.25

.24

.54 .51 .49 .41 .35 .32 .30 .28 .24 .22

.56

.53

.49

.42

.37

.34

.31

.29

.26

.24

Rajshahi

0 1 2 3 4 5 6 7 8 9

.57

.53

.48

.41

.32

.24

.22

.19

.15

.13

.60

.51

.47

.41

.35

.31

.24

.16

.08

.05

.57

.54

.48

.41

.32

.24

.22 .19 .15 .10

.58

.54

.48

.45

.38

.33

.26

.21

.15

.11

.58

.53

.48

.42

.35

.28

.23

.18

.13

.10

Dhaka

0 1 2 3 4 5 6 7 8 9

.54

.51

.43

.39

.35

.32

.30

.27

.24

.23

.60 .53 .49 .41 .35 .33 .30 .28 .25 .23

.54 .50 .46 .41 .35 .33 .30 .28 .25 .22

.54

.51

.49

.41

.35

.32

.30

.28

.24

.22

.56

.51

.47

.40

.35

.33

.30

.28

.24

.22

54

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65

0

2

4

6

8

10Ti

me[

t] in

Min

utes

Logarithm of galvanometer deflection[log.i]

(a) Belly

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60

0

2

4

6

8

10

Tim

e[t]

in M

inut

es


(b) Butt

Fig.4.3[a,b] Time vs Logarithm of galvanometer deflection [Origin-Chittagong]

Table 4.9a

Linear regression for data table 4.8[Origin-Chittagong]

t = c1+m*log.i (a) Belly (b) Butt

Parameter value Error Parameter value Error C1 14.32 0.46 m -25.03 1.11 --------------------------------------------------------R2 0.98 SD 0.40 N 10

C1 13.11 0.72 m -23.65 1.80 -------------------------------------------------------- R2 0.96 SD 0.58 N 9

55

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

0

2

4

6

8

10Ti

me[

t] in

Min

utes


(c)Shank

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

0

2

4

6

8

10

Tim

e[t]

in M

inut

es


(d) Shoulder

Fig. 4.4[c,d] Time vs Logarithm galvanometer deflection [Origin-Chittagong]

Table 4.9b

Linear regression for data table 4.8

t = c1+m*log.i

(c) Shank (d) Shoulder Parameter value Error Parameter value Error C1 13.57 0.68 m -25.00 1.71 ----------------------------------------------------- R2 0.97 SD 0.52 N 9

C1 13.83 0.63 m -25.55 1.64 --------------------------------------------------------- R2 0.97 SD 0.57 N 10

56

0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10Ti

me[

t] in

Min

utes


(a) Belly

0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

Tim

e[t]i

n M

inut

es


(b) Butt

Fig. 4.5[a,b] Time vs Logarithm galvanometer deflection [Origin-Rajshahi]

Table 4.10a

Linear regression for data table 4.8 [Origin-Rajshahi]

t = c1+m*log.i (a) Belly (b) Butt

Parameter value Error Parameter value Error C1 10.32 0.43 m -17.97 1.20 ------------------------------------------------------- R2 0.97 SD 0.60 N 10

C1 9.69 0.17 m -16.34 0.47 --------------------------------------------------------- R2 0.99 SD 0.26 N 9

57

0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10Ti

me[

t] in

Min

utes


(c) Shank

0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

Tim

e[t]

in M

inut

es]


(d) Shoulder

Fig. 4.6 [c,d] Time vs Logarithm galvanometer deflection [Origin-Rajshahi]

Table 4.10b

Linear regression for data table 4.8 [Origin-Rajshahi]

t = c1+m*log.i (c) Shank (d) Shoulder

Parameter value Error Parameter value Error C1 10.14 0.36 m -17.56 1.00 --------------------------------------------------------R2 0.97 SD 0.51 N 10

C1 10.90 0.15 m -18.33 0.39 --------------------------------------------------------- R2 0.10 SD 0.19 N 10

58

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

0

2

4

6

8

10

Tim

e[t]

in M

inut

es

Logarathm of galvanometer deflection[log.i]

(a) Belly

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65

0

2

4

6

8

10

Tim

e[t]

in M

inut

es


(b) Butt

Fig. 4.7[a,b] Time vs Logarithm galvanometer deflection [Origin-Dhaka]

Table 4.11a

Linear regression for data table 4.8 [Origin-Dhaka]

t = c1+m*log.i (a)Belly (b) Butt

Parameter value Error Parameter value Error C1 14.29 0.72 m -27.40 1.94 -------------------------------------------------------- R2 0.96 SD 0.63 N 10

C1 13.28 0.77 m -23.36 1.96 --------------------------------------------------------- R2 0.95 SD 0.74 N 10

59

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

0

2

4

6

8

10

Tim

e[t]

in M

inut

es


(c) Shank

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

0

2

4

6

8

10

Tim

e[t]

in M

inut

es


(d) Shoulder

Fig. 4.8 [c,d] Time vs Logarithm galvanometer deflection [Origin-Dhaka]

Table 4.11b

Linear regression for data table 4.8 [Origin-Dhaka]

t = c1+m*log.i

(c) Shank (d) Shoulder Parameter value Error Parameter value Error C1 14.31 0.54 m -27.06 1.44 --------------------------------------------------------R2 0.98 SD 0.48 N 10

C1 13.88 0.63 m -25.63 1.65 ------------------------------------------------------- R2 0.97 SD 0.57 N 10

61

CHAPTER 5 ------------------------------------------------------------------------------------------------------- RESULTS AND DISCUSSION

5.0 Introductory remarks

Raw leather, leather goods and footwear is one of the main export items in our

country. Huge foreign currency is earned from this sector. It is important to know the

different properties of leather for quality production. Thermal conductivity is one of

them but there is no instrument in our country to measure these properties of leather.

For this investigation a Fitch type thermal conductivity instrument was designed and

manufactured. The samples used in the experiments were collected from a variety of

sources. The chemical composition of tanning agents might not have been the same

for all samples and also they might not have been properly conditioned. Thus there

might have been some inaccuracies in results. However the results give important

insights into the quality of leather manufactured in Bangladesh.

5.1 Variation of thickness

The thickness of leather varies at different area of the same specimen. It is very

difficult to measure the thickness because they are soft, depressible and wooly in flesh

side and also varies naturally on sex, age, and living origin due to their fiber

construction. A load of 370gm was used to measure the thickness. Fig. 5.1 shows

average thickness of different parts of leather according to its geographical origin.This

parameter is used in equation number (14) to determine the thermal conductivity.

Table-5.1 shows the collected data.

Table 5.1 Thickness of leather at different location of different region

Geographical origin

Sample location Thickness [mm]

Thickness of leather[mm]

Chittagong


1.51 1.60 1.53 1.60

1.56

Rajshahi


1.57 1.56 1.59 1.62

1.59

Dhaka


1.59 1.57 1.57 1.55

1.57

62

1.441.461.48

1.51.521.54

1.561.58

1.61.621.64


Location of leather

Thi

ckne

ss[m

m]

ChittagongRajshahiDhaka

Figure 5.1 Variation of thickness at different location and origin of leather

5.2 Variations of softness

Softness is another important characteristic of leather. This characteristic depends on

chemical and mechanical treatment of hides and skins to produce leather as well as

natural climatic conditions where the animals live. Naturally the growth rate of fiber,

degree of wave angle, compactness of fiber structure and its arrangement of an area

varies on the origin of leather. In tanning process such as liming, de-liming, bating,

neutralization, fat-liquoring can play an important role to increase or decrease the

softness of the leather during the process. On the other hand, revolution of tanning

drum, dry milling and stacking operation can also change the softness of leather.In

this study the softness is measured by a softness meter using constant load at different

location of leather.

The variations of softness are shown in figure 5.2. Collected data are shown in table

5.2.

63

Table 5.2

Variation of softness at different location of same leather with respect to geographical origin

Geographical origin Sample location Softness Softness of leather

Chittagong.


3.33 4.20 3.37 3.17

3.52

Rajshahi


4.45 4.16 4.43 4.14

4.30

Dhaka


4.15 4.16 4.03 4.26

4.15

Figure 5.2 Variation of softness at different location and origin of leather

64

5.3 Variation of thermal conductivity

The thermal conductivity of porous and water containing material have large

dependency on their porosity and water content. Leather is considered as porous

material and water molecules are present in it. The fiber compactness, hence the

porosity of leather is not the same for leather produced from a specific cattle or goats.

It also has the variation over living conditions and areas. Thus the thermal

conductivity of the different parts of leather and their comparison may provide

important information for future application of it.

The variation of thermal conductivity of different locations and geographical origins

in Bangladesh is shown in table 5.3 and fig. 5.3.

Heat can pass from one place to another only when there is a temperature difference.

Heat always moves from higher temperature to lower temperature to make an

equilibrium condition. Heat transfer through the materials is mainly dependent on its

thermal conductivity.Heat can pass more quickly through material of higher thermal

conductivity than lower. In cold climate,the heat loss from inside shoes will be

quicker if the thermal conductivity of the shoe material is high.To make shoes

comfortable for cold weather, shoe materials of comparatively lower thermal

conductivity are generally choosen.These materials protect the heat loss from inside

the shoe in cold weather. On the other hand, in hot weather, there is not much

difference between the inside and outside temperatures and consequently the heat

transfer is less.

Thus,leather from Dhaka and Chittagong regions are more suitable for use in cold

countries.More specifically belly and shank portion having lower thermal

conductivities are better for making shoes than butt and shoulder.In case of shoes for

warm countries, porous, i-e.,leather with a higher conductivity is more suitable.

65

Table 5.3

Thermal conductivity at different location of same leather with respect to geographical origin

Fig. 5.3 Variation of thermal conductivity graph with respect to geographical origin

Origin

Location

Chattagong

[k=Watt/m° K]

Rajshahi

[k=Watt/m° K]

Dhaka

[ k=Watt/m° K ] Belly 0.098 0.147 0.095 Butt 0.110 0.160 0.112

Shank 0.098 0.147 0.096 Shoulder 0.102 0.141 0.102 Average 0.102 0.149 0.101

66

CHAPTER 6 ----------------------------------------------------------------------------------------- CONCLUSION AND RECOMMENDATIONS 6.0 Conclusions In the present investigation a modified Fitch type thermal conductivity apparatous

suitable for the measurment of thermal conductivity of leather samples has been

designed and manufactured.Thermal conductivity of leather originated from

Rajshahi,Dhaka and Chittagong district of Bangladesh have been

investigated.Thermal conductivity of butt,belly,shank and shoulder portion of each

leather have also been investigated. Variation of softness with geographical origin of

sample and location of each sample have also been studied.Variation in thickness of

butt,belly,shank and shoulder portion of each leather have also been investigated.

Thermal conductivity of leather originated from Rajshahi district of Bangladesh has

been found to be 0.149 Watt/mº K and that of from Chittagong and Dhaka district of

Bangladesh observed to be 0.102 Watt/mº K and 0.101 Watt/mº K respectively. The

highest thermal conductivity occurs in the leather originated from Rajshahi district

which may be related to it’s greater value of softness with compared to others.

Relatively, lower values of thermal conductivities in belly and shank portion has been

observed as compared to butt and shoulder portion. In the present investigation, the

comfort of shoes can be related to the heat flow inside the shoes and outside climate

which can be finally co-related to the thermal conductivity of the leather used in

manufacturing of shoes.

It is obsevved that leather from Dhaka and Chittagong regions are more suitable for

use in cold countries due to their lower thermal conductivities.More specifically, belly

and shank portion having lower thermal conductivites are better for manufacturing

shoes than butt and shoulder.In case of shoes for warm countries like

Bangladesh,leather with higher thermal conductivity is more suitable.It appeared in

the present investigation that leather of Rajshahi origin is more suitable for making

more comfortable shoes compared to that from Chittagong and Dhaka origin for

Bangladesh and having similar climate as Bangladesh.

67

6.1 Recommendations

- Relation between softness and thermal conductivity shows a complex relation.

More investigations are required to explore this behavior. Proper understanding

between the relation of softness and thermal conductivity will be helpful to

correlate the comfort of leather goods with their thermal conductivity.

- More geographical origins can be included to study the properties of leather.

REFERENCES

1. Marcinkowska, E., Estimation of the Thermal Conductivity of Leather, JALCA, vol-99, 2004.

2. Fitch,A.L.,A New Thermal Conductivity Apparatus, American Physics Teacher, 3,135-136, 1935.

3. Wong, H.Y.; Heat Transfer for Engineers, Handbook of Essential Formulae and Data on, Longman, New York 1977.

4. ASTM D2214-00; Standard Test Method for Estimating the Thermal Conductivity of Leather with Cenco-Fitch Apparatus.

5. Taylor, J.R, An Introduction to Error Analysis. The Study of Uncertainties in Physical Measurements, 2ed. University Science Books, California 1997.

6. Marcinkowska, E. and Waldemar, Z., “Hy-Tester”-An Instrument for Testing Comfort Properties of Leather and Leatherlike Materials, JALCA,vl-95,2000.

7. BASF-Pocket Book for Leather Technologists.

8. Dutta S.S- An Introduction to the Principles of Leather Manufacture.4th.Edition.

9. Dutta S.S- An Introduction to the Principles of Physical Testing of Leather.

10. Mohammad, An Investigation to Identify Upper Materials for Optimum

In shoe Climate, DUJASE vol-2(1)45-51, 2011(July)

11. Kazanavicius, Evaluation of Leather Softness, ISSN 1392-1320 M S vol- 14,

no 2. 2008.

12. WILFORD, A.(1998) Warming to thermal insulation. SATRA Bulletin,

November,p.2

13. LST EN ISO 17235:2003 Leather-Physical and Mechanical Tests-Determination

of Softness (ISO 17235:2002).

study of the thermal conductivity of leather having

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