december 5, 2012 eq: how can synthetic fibers be used to solve crimes? warm-up: the following slide...

DECEMBER 5, 2012

EQ: How can synthetic fibers be used to solve crimes?

WARM-UP:

The following slide will have 9 pictures (A-I). Identify the animal hair shown and answer the questions. You may use the pgs in Ch 10 (blue)/11 (orange) of your book.

Can you identify the animal hairs shown?

A B C D

E F

G

IHThink About It …

(1) In which samples are we viewing the cuticle? How do they compare?

(2) In which samples are we viewing the medulla? How do they compare?

(3) What characteristics can be used to identify hair samples?

Types of Animal Hairs - Key

A B C D

E F

G

IH

Cat Horse Pig Human

Deer Dog RatRabbit Human

1. All 2. All but two (B & I)3. Medulla absent or present, shape of medulla, cuticle, diameter

of medulla, etc.

- Root Characteristics: Removal

Pulled Forcibly removed Shed

Burned Cut Razored Split

- Tip Characteristics

Fiber Evidence

A fiber is the smallest unit of a textile material that has a length many times greater than its diameter.

Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation.

The discovery of cross transfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the chances that these two individuals had physical contact.

Many different natural fibers that come from plants and animals are used in the production of fabric. (Wool, mohair, cotton, cashmere, mink, etc.)

http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm

Cotton fibers are the plant fibers most commonly used in textile materials. Cotton fibers have a ribbon-like shape with twists at irregular intervals.

The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.

Natural Fibers

What are some common natural fibers that come from animals?

Images: http://www.trashforteaching.org/phpstore/product_images/YarnWS.JPG http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence

http://www.jivepuppi.com/images/fiber_evidence.jpg

More than half of all fibers used in the production of textile materials are synthetic or man-made.

Nylon, rayon, spandex, and polyester are all examples of synthetic fibers.

Cross-section of a man-made fiber

Synthetic (Manufactured) Fibers

Fibers under a microscope

5 Characteristics used to identify Fibers:

1. Color (comparison microscope)2. Diameter (comparison microscope)3. Lengthwise striations4. Pitting of fibers surface5. Cross-sectional shape

More than half of which fibers

are used to make fabrics?

Analytical Techniques used in Fiber Examination:

Visible-light micro spectrophotometer-compare colors of fivers through spectral patterns

Chromatography-Separating colors in dyes that come from the fibers for comparison

Chemical composition-Test for chemical make-up of fibers to see if they are in the same class

Birefringence-Double refraction (two bends), when substance is melted & crystallizedInfrared Light-Use of a microscope and infrared spectrophotometer for infrared analysis

3 Challenges in Identifying Fiber Evidence:

1. No analytical technique to trace a fiber to a single garment with certainty

2. No databases for fibers origin

3. Mass distribution of fibers and changing fashions

Collection & Preservation of Fiber Evidence:

1. Clothing packaged in paper bags

2. Carpet, rugs, & bedding folded carefully

3. Articles shouldn’t be placed on same surface

4. Loose fibers removed and placed on paper, folded and labeled

Which fiber analysis technique involves separating

dyes to see patterns of color?

HAIR & FIBERS DRAWINGS:Draw the following fibers and include the following:1. Specimen name (Dog, cat, etc.)2. Magnification (100x, 400x, etc.)3. Contain a Medulla4. Is medulla continuous, fragmented, or

interrupted?HAIR:HumanDogDeerRabbitCatMouse

Draw the following NATURAL & SYNTHETIC fibers as seen under a microscope and include the following:1. Specimen2. Magnification3. One characteristic4. Uses (at least two)

CottonWoolMohair

RayonPolyesterSpandex

Can you identify the types of fibers shown?

Think About It …

(1) Which samples are natural fibers?

(2) Which samples are synthetic fibers?

(3) What characteristics can be used to identify fiber samples?

A B C

D E F

Answer Keys

http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/images/humansmall.jpg

Types of Fibers - KeyAcrylic Yarn Cotton Yarn Nylon Rope

Polyester Yarn Rayon Rope Wool Yarn

A B C

D E F