| Abstract: | The maximum degree of molecular orientation and deformation obtained by ultradrawing of high-density polyethylene in air is limited by formation of internal voids (both longitudinal separation of fibrils and perpendicular cracking), and thus values of Young's moduli which are achievable by ultradrawing techniques are also limited to values much below the theoretical limit for fully extended chains. Temperature has a significant effect on the critical draw ratios at which intensive void formation begins, and also on the draw ratio at which failure occurs during the ultradrawing. The temperature effect is observed only for high-density polyethylene having a wide molecular-weight distribution, and which can be drawn at higher temperatures (30–40°C below its melting point), e.g., Dow Chemical polyethylene LP51.1. As a result of ultradrawing at higher temperatures, transparent, ultrahigh modulus samples having draw ratios of order of 40 have been obtained. The higher drawing temperatures significantly reduce fibril separation, and perpendicular cracking is shifted toward higher draw ratios. Hence, with LP51.1 the highest Young's moduli (65–70 GPa) have been exhibited by the samples which were ultradrawn at 100–105°C. |
