Cellulose As A Polymer Essay
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Cellulose is a polysaccharide found in the cell walls of plants. It consists of long chains of beta-D-glucose molecules linked by 1-4 glycosidic bonds which were formed by condensation polymerisation. These glycosidic linkages encourage the polymer chains to adopt a linear structure. The celluose molecule consists of a number of these polymer chains joined together by hydrogen bonds
Cotton is an excellent source of cellulose . Each cotton fibre is just a single cell. The cell wall is made of cellulose, containing approximately 9000 glucose molecules. The polymer chains themselves held by the hydrogen bonds chains are aligned in bundles, called microfibrils orientated along the fibre. Cotton is highly crystalline. This means that most of the glucose chains of the cellulose are closely packed in a regular way, making it a tough and fibrous polymer. So it follows that cotton fibres are stiff and have a high tensile strength which means that the are not likely to break when stretched. Cellulose itself has a large number of hydroxyl groups on the polymer chains and so cotton is a able to absorb a large amount of water without feeling wet.
A number of different cellulose-based artificial fibres were manufactured in the early twentieth century. The idea behind this was to make full use of and add to the properties of cellulose fibres such as cotton. The processes involved usually aimed to increase the crystallinity of the fibre. These were manufactured by making derivatives.
Viscose rayon is can be manufactured using either the xanthate process or the cuprammonium process. The xanthate process involves treating the cellulose with sodium hydroxide(aq) and carbon disulphide(aq) to make a soluble viscose product, sodium cellulose xanthate. This is then forced through either plates with fine holes to be reprecipitated in a bath of sulphuric acid to give fine filaments, or, the sodium cellulose xanthate is forced through a narrow slit to eventually produce a fine film, marketed as cellophane. The alternative, cuprammonium process, is less economical because of the recycling of the copper and ammonia involved. This process involves dissolving the cellulose in a solution of copper(II)hydroxide in ammonia(l) and then the ensuing washing and drying to give the fibres. The advantages of the cuprammonium process despite its cost were that the rayon fibres produced were so fine that they could be marketed as a very good artificial silk.
Celluloid, the main constituent of cinema and x-ray films is manufactured by treating cellulose with dilute nitric acid and then mixing the product with camphor, a ketone, which acts a plasticiser and so stabilises the celluloid nitrate. Plasticisers make the plastic more flexible by reducing the glass transition temperature, so the plastic can survive lower temperatures without becoming brittle. Celluloid can be used not only for films but also for anything that needs a mock ivory or tortoiseshell appearance such as spectacle frames, the only problem is that it is very flammable. If the camphor is left out of the manufacture the result is cellulose nitrate which can be made into a huge number of products as the properties differ depending on the...
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