Polyethylene, crystalline Fiber production

Table 17.4 shows the well-known fiber polymers, and a few which seem unsuitable as fiber material, namely polystyrene and poly(vinyl chloride). The latter finds limited fiber application, but a special syndiotactic grade with some crystallinity is then used. Polypropylene has a fairly low melting point but is nevertheless a large fiber product, because the material is cheap and versatile. Polyethylene is even lower melting and is used only as a superstrong fiber at ambient temperature. 

Unlike nylon, which in the as-spun state contains a high amount of crystalline component, polyethylene terephthalate fibers are essentially amorphous as spun. In order to secure a usable textile yarn or staple fiber, this product must be drawn under conditions that will result in an increase in both molecular orientation and crystallinity. This is done by drawing at a temperature well above the glass transition point, 7, which is about 80 C. Conditions of rale and temperature must be... 

The solid state stability of indinavir sulfate has been evaluated under a variety of storage conditions and containers. For materials stored in open dishes or in double polyethylene liners within fiber containers, changes in crystallinity i.e., conversion of the crystalline etlranolate to amorphous material or to a hydrate crystal form) have been detected using XRPD or KF methods [7]. Changes in chemical purity i.e., formation of degradation products) have been detected using GC and HPLC methods... 

Greater success was achieved by DuPont who copolymerized, the sodium salt of 5-sulfoisophthalic acid into PET to render the polymer dyeable with cationic (basic) dyes. Basic dyeable PET was successfully launched as Dacron 64 in the form of a low-pill staple product [64]. The presence of the sulfonate groups in the polymer chain also acts as an ionic dipolar cross-link and increases the melt viscosity of the polymer quite markedly. Thus, it is possible to melt-spin polymer with IV 0.56 under normal conditions, giving a low-pill fiber variant. The fiber also has a greater affinity for disperse dyes due to the disruption of the PET structure. Continuing this theme, there are deep dye variant PET fibers, often used in PET carpet yarns, which are copolymers of PET with chain-disrupting copolymer units like polyethylene adipate. They have less crystallinity and a lower Tg. therefore, they may be dyed at the boil without the use of pressure equipment or carrier at the cost of some loss of fiber physical properties. 

Industrial films of such chemical composition as polyethylene, polypropylene and polyester are manufactured for a wide range of applications. Accordingly, the morphology of these materials is studied to determine structure-property relations, to understand how to improve properties and also to control the quality of commercial products. Although model studies provide considerable detail relating to the structure, both before and after deformation of such films, model materials are generally thinner than commercial films, and thus the real product must also be evaluated. The types of preparation methods and instrumental techniques utilized closely parallel those described for polymer fibers. These techniques include (1) birefringence, (2) crystallinity... 

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