Drawing ultra high-modulus polyethylene

During the last ten years there have been several notable advances in the development of ultra high modulus polyethylene and polypropylene. This has been achieved most simply by tensile drawing , but also by hydrostatic extrusion , ram extrusion and die drawing all of which are solid phase deformation processes. In polyethylene, an alternative approach has been the production of fine ultra high modulus fibres from dilute solution, either by crystallisation in an elongational flow field or by stretching fine fibres spun to form a gel from dilute or reasonably dilute solution, 13 ... 

The thermal expansion behaviour of ultra high modulus polyethylene is very anisotropic. Transverse to the draw direction the thermal expansion coefficient is positive and comparable to that for isotropic polymer. In the draw direction the coefficient is negative and very small ( v 10" / ). For low molecular weight polymers the value... 

The principal guidelines have now been established for the production of ultra high modulus polyethylene and polypropylene by tensile drawing to give fibres and tapes, and by hydrostatic extrusion and die drawing to give a variety of shapes including rod, sheet and tube. 

Recently, various techniques that produce highly oriented linear polyethylene with a ultra high modulus (hereafter, referred to as UHMPE) have been developed. In this section, we will examine the structure of the UHMPE that was prepared by highly drawing a dried gel [69]. Even if bulk polyethylene is uniaxially highly drawn by a normal method at a temperature between the Tg and Tm, the phase structure is essentially similar to the undrawn sample. That is, it involves three phases of the crystalline and two noncrystalline phases, although the mass fraction and detailed content of each phase are somewhat different. However, UHMPE samples may have a particular phase structure. 

G. Capaccio and I. M. Ward, Ultra-high Modulus Linear Polyethylene through Controlled Modulus Weight and Drawing, Polym. Eng. Sci., 15, 219-224 (1975). 

The effect of annealing on the properties of ultra-high modulus linear polyethylene has been studied. There was a good correlation between the modulus and lamellae thickness irrespective of annealing temperature. On drawing, annealing, and rapid quenching to room temperature there is an immediate fall in... 

Capaccio, G. and Ward, I.M. (1973) Properties of ultra-high modulus linear polyethylenes. Nature Phys. Sci., 243, 143 (1974) Preparation of Ultrahigh Modulus Linear Polyethylenes - Effect of Molecular-weight and Molecular-weight Distribution on Drawing Behavior and Mechanical-properties. Polymer, 15,223. 

T. Kanamoto, A. Tsuruta, K. Tanaka, M. Takeda, R.S. Porter, On ultra-high tensile modulus by drawing single crystal mats of high molecular weight polyethylene. Polym. J. 15(4), 327-329 (1983)... 

Figures VII.3 and VII.4 show the experimental values of the Young s modulus and the tensile strength, respectively, for thick films of undoped trans-polyacetylene as a function of draw ratio (all samples were derived from the same polymerization batch). Although there is some scatter in the data, the modulus and tenacity increase approximately linearly with the draw ratio, as is commonly observed for most polymers drawn to moderate draw ratios. The modulus and tensile strength of trans-polyacetylene films stretched up to 15 times are 50 GPa and 0.9 GPa, respectively. These values are essentially equivalent to those observed for ultra-high molecular weight polyethylene [83] drawn to the same draw ratio. Recently, Akagi et al.[78] reported remarkable mechanical properties for drawn polyacetylene films prepared by non-solvent polymerization (100 GPa and 0.9 GPa for the modulus and tensile strength, respectively). The origin of difference in the modulus (in the two studies) is unknown.

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