Polyethylene fibers structure

Grubb DT, Prasad K. High-modulus polyethylene fiber structure as shown by X-ray diffraction. Macromolecules 1992 25 4575 582. 

J. R. Dees and J. E. Spmiell, Structure Development During Melt Spinning of Linear Polyethylene Fiber, J. Appl. Polym. Sci. 18, 1053 (1974). 

Extended-chain polyethylene fiber became available commercially in 1984 when DSM, a Dutch firm in the Netherlands, introduced Dyneema , and Mitsui Petrochemicals in Japan announced Tekmilon . Allied Signal of the United States entered the field in 1985 when it introduced Spectra fibers. These materials are characterized by very high strength and modulus, which are achieved by the use of ultrahigh molecular weight polyethylene spun by the gel spinning method into fibers having extended-chain structures and near perfect orientation. 

The ultra-high molecular weight polyethylene fiber is a highly crystalline fiber with very high stiffness and strength. All of this results from some innovative processing and control of structure of polyethylene. 

Commercially available polyethylene fiber has a degree of crystallinity between 70 and 80% and a density 0.97 gcm . There is a linear relationship between density and crystallinity for polyethylene. A 100% crystalline polyethylene will have a theoretical density, based upon an orthorhombic unit cell, of about lgcm . A totally amorphous polyethylene (0% crystallinity) will have a density of about 0.85gcm . Khosravi et al. (1995) used nitric acid attack on gel-spun polyethylene fibers to observe structural imperfections such as fold, molecular kinks and uncrystallized regions. Raman spectroscopy has been used to study the deformation behavior of polyethylene fiber. This technique gives peaks for the crystalline and amorphous states of polyethylene (see Chapter 9). 

High performance polymer fibers (HPPF) have excellent mechanical properties compared to traditional textile fibers such as nylon. The typical HPPFs are aramid and polyethylene fibers (6). Aramid is a generic name for a class of aromatic polyamide fibers, most of which are varieties of poly(p-pheny-lene terephthalamide). Kevlar is the trade name of the varieties of aramid polymers introduced conunercially by Dupont. The molecules in the fibers of these materials are oriented in the axial direction. Poly(p-phenylene terephthalamide) is a rigid molecule with the following structure ... 

Structural changes during the creep process of ultrahigh-strength polyethylene fiber (UHSPE) were investigated using X-ray and the solid-state NMR techniques. As the creep strain increases, the quantity of the amorphous phase area estimated by the NMR method increases until the final creep rupture. " ... 

Dees, J.R. Spruiell, J.E. (1974). Structure development during melt spinning of linear polyethylene fibers.. Appl.PolyntSci., Vol. 18, Issue, Issue 4, pp.1053-1078. 

Fu Y, Chen W, Pyda M, Londono D, Annis B, Boiler A, Habenschuss A, Cheng J, Wunderlich B (1996) Structure-property Analysis for Gel-spun Ultra-high Molecular-mass Polyethylene Fibers. J Macromol Sci, Phys B35 37-87. 

Polypropylene is a versatile polymer used in applications from films to fibers, with a worldwide demand of over 21 million Ib. It is similar to polyethylene in structure except for the substitution of one hydrogen group with a methyl group on every other carbon. On the surface, this change would appear trivial, but this one replacement changes the symmetry of the polymer chain. This allows for the preparation of different stereoisomers, namely, syndiotactic, isotactic, and atactic chains. These configurations are shown in the introduction. 

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