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Unformatted text preview: Hallie Benezra Advanced textiles Midterm 2/26/08 Question 1: Cotton fiber is perhaps the most recognizable is regards to its microstructure. Under a microscope, you can see the characteristic convolutions, the twisted structure of cotton. Overall the components of the microstructure include cellulose (80-90%), water (6-8%), waxes and fats (.5-1%), protein (.5 %), hemicelluloses and pectin (4-6%), and lastly ash (1-1.8%). Upon further examination, the microstructure of cotton consists of the cuticle, primary wall, secondary wall and the lumen. The cuticle is the first layer of the fiber and is the primary defense against pesticides. It is known as the skin of cotton and is very smooth due to the waxes, whose purpose is to restrict water from flowing in and out of the plant. The second layer in the primary wall is 200nm thick and made up of fibrils. The fibrils, which spiral at 70*, are responsible for the strength of the fiber. The secondary wall, then, forms the bulk of the fiber. It contains three different layers that include fibrils with an 80* spiral. The last component of the microstructure is the lumen. The lumen is a hollow canal that runs the length of the fiber during development. When the fiber is mature, the lumen collapses and disappears, causing the fiber to flatten and twist so that under a microscope one will see a “twisted ribbon”, or convolutions. This natural twist in cotton increasing its elasticity and makes it easy to spin into yarn. Compared to flax fiber, cotton has a lower DP. The DP, or degree of polymerization, estimates the length of a polymer by counting the number of structural units in the polymer. If the length of the molecular chain is longer, then the degree of polymerization is higher, along with a higher strength. The specific DP of cotton is 5,000, while the DP of flax can be as high as 18,000. Flax is known as the longest linear textile polymer, making its strength and extensibility much higher than cotton. In regards to the degree of spiral, cotton is superior to flax, with 70* verses 6* respectively. The degree of spiral is important because it affects many properties of the fiber such as orientation, crystaillinity, elongation, stiffness, wrinkling and tenacity. Question 2: Viscose, acetate and lyocell are all fibers obtained from wood pulp; however all have a unique manufacturing process and use different solvents. For example, viscose is wet spun, acetate is dry-spun and lyocell is solvent spun. In regards to viscose, the first step in processing is known as the sleeping and lyocell is solvent spun....
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- Spring '08