Kenaf Bast- Unsaturated Polyester Composite: The Effect of Different Alkaline Treatment Condition on Tensile properties

A.R Rozyantya, M.Y Nur Firdausb & L. Musac

Center Of Excellence Geopolymer & Green Technology (CEGeoGTech) School of Material Engineering, University Malaysia Perlis, Malaysia

arozyanty@unimap.edu.my, bfirzad@yahoo.com and cluqman@unimap.edu.my

Keywords: Kenaf bast, unsaturated polyester, lignocellulosic, composite

Abstract

The biocomposites were prepared by using kenaf bast fiber mat as reinforcing materials at different

percentage. The kenaf bast fiber was treated with alkaline at different sodium hydroxide (NaOH)

percentage. Composites which were made from treated alkaline kenaf treated bast fiber showed

better mechanical properties (tensile) than those of the unmodified. Scanning electron microscope

analysis showed the evidence of the enhancement of the compatibility between kenaf bast fiber and

the matrix. The percentage of kenaf fiber in composites also plays a crucial role in determining the

composite properties.

Introduction

Recently, there is a drastic growing attention in utilization of lignocellulosic materials as reinforcing

component in thermoplastics as well as thermosets. The advantages of lignocellulosic fibres over

tradisional reinforcing materials such as lower cost per unit volume, lower density, less abrasive

acceptable specific strength and stiffness, greater deformability and less irritation to skin and

respiratory [1]. Lignocellulosic fibres such as oil palm empty fruit bunch (EFB), rice husk, kenaf,

flax, hanequeen, pineapple leaf and many others have been used as reinforcing material or filler in

composites by researchers [2]. This natural fibers has the potential to substitute fiberglass and other

synthetic fibers that are currently used [3].

Extensive studies have been done by the researcher on lignocellulosic fibers and results

showed an effective reinforcement of lignecellulosic fibers in thermoset and thermoplastic

composites [4]. However to produce a polymer composite with acceptable mechanical and physical

properties, the main obstacle to be resolved is the compatibility between the lignocellulosic material

and the polymer matrix. The weak bonding at the interfaces between the natural fibers and the

polymer matrix is surely a critical cause of the reduction of the properties and performances of the

composites. Chemical modification or treatment of the natural fibers, including kenaf, is generally

carried out using reagents, which contain functional groups that are capable of bonding with the

hydroxyl group from the natural fibers. Several types of chemical modifications have been reported

in previous literatures, which include alkaline treatment, silane treatment, isocyanate treatment, and

acetylation [5]. From various studies in biocomposites, the treatment of natural filler with chemical

modification increases the strength as well the modulus of the composites [6]. In view of above

advantages, attempst have been made to biocomposite filled with kenaf bast fibers in mat form

treated with different alkaline treatment condition.

Experimental

Materials

The kenaf fiber is already supply in non-woven kenaf bast fiber mat by Dr Rahmatullah Holding

Sdn. Bhd.,Bukit Mertajam, Penang, Malaysia. Sodium hydroxide (NaOH) was supply from

HmbG® Chemicals, with 40.00 g/mol molar mass and 1.829 g/cm3 density. While, unsaturated

Key Engineering Materials Vols. 594-595 (2014) pp 644-647Online available since 2013/Dec/05 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/KEM.594-595.644

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polyester and Methyl Ethyl Ketone Peroxide (MEKP) grade Reverson P9509 was supplied by

Echemo Trading Sdn. Bhd., Penang, Malaysia.

Composite Preparation

The kenaf bast reinforced unsaturated polyester resin composite is prepared using combination of

hand lay-up technique and compression moulding technique. First, kenaf bast fibre mat were cut

into mould size (15.5cm X 13.5cm) and placed into the mould. The unsaturated polyester resin was

mix with 2% of Methyl Ethyl Ketone Peroxide (MEKP). Then, the unsaturated polyester resin was

impregnated into kenaf fiber mat. After that, composite was compressed to achieve desired

thickness and cured about 30 - 45 minutes. Finally, mould was taken out and removed the

composite from the mould.

Alkaline treatment of kenaf bast fiber

The kenaf fiber mats which had cut into mould size (15.5cm×13.5cm) were placed in a container

containing 6% sodium hydroxide (NaOH) solution. The kenaf mats were treated at different soaking

time for 3, 6 and 9 hour at room temperature. After that, the treated fibers mats were washed

thoroughly with distilled water for seven times. Then, the treated kenaf fibers mat was dried in the

oven at 80°C for 24 hours.

Mechanical testing

The composite produced were cut into flexural testing size. Flexural tests were conducted according

to ASTM D638 method using Universal Testing machine model 5569. The samples, with

dimension of (10cm×1.5cm×0.3cm) were tested at cross-head speed of 5.0 mm/min.

Scanning Electron Microscopic Study

Samples were studied with a Scanning Electron Microscope (JEOL JSM-6460LA). The sample

were mounted on an aluminium stub using double-sided tape and then coated with gold to avoid

electrostatic charging during examination.

Results and Discussion

1000

1500

2000

2500

3000

3500

Untreated

Kenaf/UPE

Treated 3H

Kenaf/UPE

Treated 6H

Kenaf/UPE

Treated 9H

Kenaf/UPE

Ten

sile

Mo

du

lus

(MP

a)

1 Layer

Kenaf Fiber

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

Untreated

Kenaf/UPE

Treated 3H

Kenaf/UPE

Treated 6H

Kenaf/UPE

Treated 9H

Kenaf/UPE

Ten

sile

Str

eng

th (

MP

a)

1 Layer Kenaf

Fiber

Fig. 1 : Effect of alkaline treatment with

different soaking time and kenaf bast fiber

content on tensile strength

Fig. 2 : Effect of alkaline treatment with

different soaking time and kenaf bast fiber

content on tensile modulus

Key Engineering Materials Vols. 594-595 645

Fig. 1 shows that the kenaf bast-unsaturated composites using 2 layer of kenaf bast fiber mat have

the higher tensile strength compared to 1 layer of kenaf bast fiber mat for all alkalized treated and

untreated kenaf fiber composites. Fiber in mat form of 2 layers will lead to better fiber dispersion,

where stress can be transferred more effectively. As the treatment soaking time increase, the tensile

strength improve significantly. This indicates that through treatment of kenaf fiber surface with

NaOH, the distribution of stress transfer from the matrix to the fiber is improved. This may be

attributed to the increased compatibility between kenaf fibers and the polyester resin at the

interfacial region. The increase of interface compatibility between kenaf fiber and matrix is due to

the removal of foreign particle and decrease in lignin level in kenaf fibers compared to untreated

[7].

Fig. 2 shows the different fiber content (1 layer and 2 layer kenaf fiber mat) of tensile

modulus increase with increasing fiber content. The increasing of fiber content contributes to the

overall stiffness of the composite. As for alkaline treatment with different soaking time, it is

obvious that all treated fiber composite showed higher modulus values compared to the untreated

fiber composites. This is due the alkalization treatment of fibers helps in improving the surface

interaction between the resin and fiber due to increasing of the surface roughness resulting in

superior mechanical properties. Modification of natural fiber with alkaline treatment has disrupted

the hydrogen bonding in the networking structure, thus increasing surface roughness which

improved the surface interaction between fiber and matrix [8].

Fig. 3 shows the SEM micrograph of tensile fracture surface of untreated kenaf bast-

unsaturated polyester composite. While, fig. 4 shows the SEM micrograph of tensile fracture

surface of treated kenaf bast-unsaturated polyester composite (9 hour treatment). It is obvious that

the treated kenaf bast-unsaturated polyester composite fibers are tightly embedded in the matrix

with fiber breakage during failure. This indicates good wetting and compatibility between fiber and

matrix. Tearing or breakage of the fiber occurs as a consequence as possibly other adhesion

mechanisms induced by the greatest roughness of the fiber [9]. In this case, the interaction between

the kenaf fiber and UPE matrix result in a greatest roughness surface allowing the polymer to

adhere to the fiber through mechanical interlocking.

Fig. 3: SEM micrograph of 2 layer

untreated kenaf bast fiber taken embedded

in unsaturated polyester matrix,

magnification (500x)

Fig. 4: SEM micrograph of 2 layer for 9

hours alkaline treated kenaf bast fiber taken

embedded in unsaturated polyester matrix,

magnification (500x)

646 Advanced Materials Engineering and Technology II

Conclusion

The effects of the incorporation of kenaf bast fiber in the unsaturated polyester composite

were investigated. Overall, it was obvious that the incorporation of kenaf bast fiber in the form of

mat had improved the tensile properties of the composites. Alkaline treatment of kenaf bast fiber

had produced composites with significant improvement in tensile properties compared to untreated

kenaf bast fiber. This was attributed to the improvement in compatibility in the interfacial between

kenaf bast fiber and polymer matrix.

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Key Engineering Materials Vols. 594-595 647

Advanced Materials Engineering and Technology II 10.4028/www.scientific.net/KEM.594-595 Kenaf Bast-Unsaturated Polyester Composite: The Effect of Different Alkaline Treatment Condition

on Tensile Properties 10.4028/www.scientific.net/KEM.594-595.644