TOPIC 14 NATURAL POLYMERS- SILK, COTTON AND WOOL

Synopsis

Natural polymers are used widely every day. This topic will discuss the main types of natural polymers, namely, cotton, wool and silk. It will explain the properties, the processing, and the uses of these natural polymers.

Learning Outcomes

1. State the type of natural polymers2. State the properties of natural polymers3. Explain the processing of natural polymers4. Explain the uses of natural polymers

Overview

Figure 14.1 Overview of content

Content 14.1 Polymer

The term ‘polymer’ originated from Greek words, ‘poly’ means ‘many’ and ‘mer’ means ‘parts’. Polymers are long chain molecules formed by joining together many identical repeating sub-units called monomers. Polymers can be divided into two types:

natural polymers synthetic polymers

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Natural polymers are polymers obtained from living things such as plants and animals. Some examples of natural polymers are shown in Figure 14.2.

,Figure 14.2 Types of natural polymers

Surf the Internet (1 hour)

Access the internet to gather information to compare natural polymers and synthetic polymers.

14.2 Silk

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Silk is a natural protein fiber obtained from cocoons made by the larvae of silkworm reared in captivity. Silk is actually made of proteins secreted in the fluid state by silkworm caterpillar. These silkworms feed on selected food plants, namely mulberry leaves, and spin cocoons as a protective shell to perpetuate life.

Figure 14.3 Silkworm feeding on mulberry leaves(Source: http://images.google.com)

Properties of silk are:

has natural shine has smooth and soft texture resistant to mineral acids has good moisture regain poor resistance to sunlight exposure moderate elasticity and wrinkle resistance strongest of all the natural fibers but loses 20% of its strength when wet

Figure 14.4 A silk fabric(Source: http://images.google.com)

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Figure 14.4 shows some of the uses of silk

Figure 14.4 Uses of silk

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The flowchart below explains the processing of silk:

Cocoons that have been spun by the silkworm are hand-picked and placed in oven

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The heat of the oven is enough to kill the silkworm but not damage the silk in the cocoon

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The cocoons are soaked in water

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Multiple threads from the soaked cocoons are unraveled to form a single thread

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Silk thread is further combined to form thicker strands and dyed to create desired colours

Figure 14.5 Process of manufacturing silk

14.3 Cotton

Cotton is a soft fiber that grows around the seeds of cotton plant, a shrub native to tropical and subtropical regions around the world, including Africa, India and America. Cotton is a thirsty crop, so it must be cultivated in areas with less rainfall. The fiber is most often spun into yarn or thread and used to make soft breathable textile, which is the most widely used natural fiber cloth in clothing today.

Figure 14.5 Cotton plant (Source: http://images.google.com)

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Below are the properties of cotton:

Strong Durable Prints well Comfortable Good absorbent of moisture Low resiliency (easily wrinkled) High resistance for alkali and organic solvent

Figure 14.6 Cotton (Source: http://images.google.com)

How cotton is processed?

Cotton fiber, once it has been processed to remove seeds (ginning), consists of nearly pure cellulose, a natural polymer.

Each cotton fiber is made up to twenty to thirty layers of cellulose coiled in a neat series of natural springs.

When the cotton ball is opened, the fibres dry into flat, twisted, ribbon-like shapes and shapes and become kinked together and interlocked.

This interlocked form is ideal for spinning into fine yarn.

Cotton production is very efficient, only ten percent or less of the weight is lost in subsequent processing to convert the raw cotton bolls (seed coat) into pure fiber.

The cellulose is arranged in a way that gives cotton fibers a high degree of strength, durability, and absorbency.

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Figure 14.7 A worker carrying Figure 14.8 Cotton buds and swabs harvested cotton

(Source: http://images.google.com)

Cotton is used in the making of:

Towel Socks Bed sheets T-shirts Coffee filters Jeans Cotton buds and swabs

Surf the Internet (2 hours)

Access the internet to gather information on types of cotton.

14.4 Wool

Wool is a fiber derived from the specialised skin cells, called follicles, of animals in the Caprinae family, principally sheep, but the hair of certain species of other mammals such as goats, llamas and rabbits may also be called wool. Wool has several qualities that distinguish it from hair or fur: it is curly, it has a different texture or handle, elastic and grows in staples (clusters).

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Figure 14.9 Wool from sheep (Source: http://images.google.com)

Below are the properties of wool:

Warm materials

Tightly crimped fibers

The outer cells of the fiber repel water while the inner cells absorb moisture

High elasticity-wool possesses much greater ability to return to its natural length after being stretched than any artificial fiber.

Highly absorbent-capable of retaining up to 25 percent of its weight in moisture.

ideal for dyes-wool takes on richer, deeper, purer colors than vegetable fiber

The processing of wool is listed below:

After shearing, wool contains a high level of grease which contains valuable lanolin, as well as dirt, dead skin, sweat residue, and vegetable matter.

Before the wool can be used for commercial purposes it must be scoured, or cleaned.

Scouring may be as simple as a bath in warm water, or a complicated industrial process using detergent and alkali.

After that, the wool is separated into five main categories: Fleece, broken, pieces, bellies and locks.

The quality of fleece is determined by a technique known as wool classing

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Reference ( 3 hours)

The processing of wool involves: spinning, carding, weaving, combing, dyeing, knitting and combing. Explain each process and the purpose of these processes in manufacturing wool. You may refer to http:www. austech.unimelb.edu.au/tin/267.html

Figure 14.10 Wool Figure 14.11 Scarf made from wool (Source: http://images.google.com)

Wool is objectively measured for micron, yield, staple length, staple strength and sometimes color and comfort factor.

Wool is widely used in making of:

Clothes such as sweaters

Traditionally used to cover cloth diapers

absorb odours and noise in heavy machinery and stereo speakers

Blankets, horse rugs, saddle cloths, carpeting, felt, wool insulation and upholstery

Some modern cloth diapers use felted wool fabric for covers, and there are several modern commercial knitting patterns for wool diaper covers

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Thinking (2 hours)

Based on your study, construct a graphic organiser to compare and contrast the properties and the uses of silk, cotton and wool.

References

http://en.wikipedia.org/wiki/silk (silk)

www.fabrics.net/silk.asp(silk)

http://en.wikipedia.org/wiki/cotton (cotton)

www.fabrics.net/wool.asp(wool)

http://en.wikipedia.org/wiki/wool (wool)

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