Changes in the Amorphous Phase of Polyethylene upon High Extension

Abstract

The structure of noncrystalline regions of HDPE oriented filaments prepared by two different techniques with various degrees of orientation X has been studied by density measurements, small-angle X-ray scattering and DTA. It is shown that at A > 10 the noncrystalline regions of the oriented structure prepared from a crystallized material have 80 nrn voids (pores) in addition to an amorphous phase. The volume fraction of pores grows with increasing A. If a sample is prepared by crystallization from apre-orientedmelt, it does not contain discontinuities, and its noncrystalline regions consist of the amorphous material alone. In this case the density of the amorphous phasedoes not depend on the degree of sample orientation and has a constant magnitude typical of highly oriented PE samples.

Effects of simulated functional loading conditions on dentin, composite, and laminate structures

“…The increase in flexural modulus for composite in this study was not unanticipated, because such an increase has been reported in the polymer literature 46–48. The increase in modulus in the amorphous regions of polyethylene has been attributed to realignment of the polymer chains along the extension axis at low extension rates 46.…”

“…A slight increase in tensile strength has been reported to occur with uniaxial extension of polyethylene46 and in natural and synthetic rubbers 50. The increase in strength, as with modulus, has been attributed to chain realignment along the extension axis at low extension rates in the amorphous regions of polyethylene46 and crystallization in natural and synthetic rubbers 50. Not surprisingly, just as with the dentin fatigue studies, the results of this study are not supported by previous composite fatigue studies, which report a decreased fatigue life with increasing loading cycles and indirectly, decreased strength 19, 20.…”

“…The increase in composite flexural strength following cyclic loading can also be related to previous polymer literature. A slight increase in tensile strength has been reported to occur with uniaxial extension of polyethylene46 and in natural and synthetic rubbers 50. The increase in strength, as with modulus, has been attributed to chain realignment along the extension axis at low extension rates in the amorphous regions of polyethylene46 and crystallization in natural and synthetic rubbers 50.…”

“…The increase in flexural modulus for composite in this study was not unanticipated, because such an increase has been reported in the polymer literature. [46][47][48] The increase in modulus in the amorphous regions of polyethylene has been attributed to realignment of the polymer chains along the extension axis at low extension rates. 46 Loadinginduced crystallization or localized order is also possible in some polymer systems, 49 and crystallites can function as cross-links, 47 thus restricting molecular motion, at least while present, as they may be temporary.…”

“…[46][47][48] The increase in modulus in the amorphous regions of polyethylene has been attributed to realignment of the polymer chains along the extension axis at low extension rates. 46 Loadinginduced crystallization or localized order is also possible in some polymer systems, 49 and crystallites can function as cross-links, 47 thus restricting molecular motion, at least while present, as they may be temporary. 50 Within the dental literature, another study which utilized parameters similar to this study to test resin composite cement 38 also reported an increase in flexural modulus after 13k loading cycles and attributed this increase to reorganization within the resin matrix.…”