Crystallization of polyolefins induced by liquid crystalline polymers

✍ Scribed by Simona Percec

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 293 KB
• Volume: 8
• Category: Article
• ISSN: 1042-7147
• DOI: 10.1002/(sici)1099-1581(199711)8:11<707::aid-pat705>3.0.co;2-x

✦ Synopsis

The objective of this study was to determine the influence of very low levels (less than 2%) of liquid crystal polymer (LCP) molecules on the properties of polyolefin matrices. The higher level of crystallinity obtained from nuclear magnetic resonance and Raman measurements suggests the possibility of nucleation and oriented crystallization of polyolefins upon the LCP phase during the orientation process. Wide-angle X-ray powder diffraction data from unoriented and uniaxially oriented films of high-density polyethylene (HDPE) containing LCP analyzed by the Rietveld method reveal that the dimensions of the orthorhombic unit cell are not affected but the crystallite size and the orientation parameters are changed. Furthermore, changes in transport properties of these materials are observed. In particular, the chemical resistance to hydrocarbons of uniaxially oriented HDPE containing LCP molecules improves significantly in comparison with untreated samples. In additon to orientation, all data suggest that lowering solvent permeability on drawing may be related to changes occurring in crystalline and amorphous regions of HDPE. Chemical resistance enhancement also is confirmed for biaxially oriented films of HDPE, linear low-density polyethylene and polypropylene containing low levels of LCPs. In all cases, molecular orientation does not appear as the single cause of reduced permeability to hydrocarbons.