Radiation-induced crosslinking: II. Effect on the crystalline and amorphous densities of polyethylene

Abstract

Small-angle x-ray scattering (SAXS) was used to determine the structural changes in polyethylene induced by radiation. The changes in densities of the crystalline and amorphous phases, pc and Pa, were calculated after direct determination of the 9 9 2 ...... mean square denszty fluctuatzon < 7? >. pa increases with increasing radiation dose for both linear and branched polyethylene. This accounts for the serious discrepancy between crystallinities determined from wide-angle x-ray scattering and density measurements. This study confirms our previous proposal that crosslinks occur primarily in the noncrystalline phase, most likely at the defects in the lateral grain boundary regions.

Surface Modification of Polyhydroxyalkanoates toward Enhancing Cell Compatibility and Antibacterial Activity

“…PHB and PHBV produced similar carbonyl radical anion and various carbon radicals via abstracting primary, para, and tertiary hydrogen when subjected to γ‐radiation at 77 K. Chain crosslinking would therefore happen between these radicals to increase the molecular weight. The scission of the polyester chain occurred adjacent to the ester moiety, resulting in a decreasing molecular weight …”

“…The scission of the polyester chain occurred adjacent to the ester moiety, resulting in a decreasing molecular weight. [54,55] Both reactions take place primarily in the amorphous region, while some may occur in the boundary between the crystalline and amorphous regions. [56] The scission reaction via γradiation could significantly reduce the onset degradation temperature and the temperature of the maximum weightloss rate of PHBV.…”

“…[54,55] Both reactions take place primarily in the amorphous region, while some may occur in the boundary between the crystalline and amorphous regions. [56] The scission reaction via γradiation could significantly reduce the onset degradation temperature and the temperature of the maximum weightloss rate of PHBV. The first and second melting temperatures of the irradiated PHBV were 5.7 and 6.1 °C (10 MRad dose) or 11.7 and 9.8°C (25 MRad dose), respectively, lower than those of the control PHBV due to the decreasing size of PHBV crystals after irradiation.…”

Radiation Crosslinking of Poly(ethylene‐co‐octene) with Electron Beam Radiation

“…These defects can serve as sites for subsequent crosslinking. Chen et al measured the density by SAXS and concluded that the density of the amorphous phase increases with dose whereas that of the crystalline phase remains essentially constant 15…”

“…The net effect on the network formation results from the two competitive and simultaneous mechanisms of crosslinking and bond scission 17. The introduction of metallocene copolymers of polyethylene of very low density brings new questions because not only the crystallinity is lower and less well organised (micelles and sometimes lamellae are present) but also the interfacial domains between crystalline and amorphous phases may play an important role 15…”