Structural Reminiscence in the Products Derived from Polyethylene Nascent Powders pp. 317-342
Authors: (Alexander Tshmel and Pavel Pakhomov)
Abstract: The polyethylene reactor powders (RP) are very promising material for manufacturing the high-strength, high-modulus fibers using the submelt technology, but their industrialy application is restrained by the strong changeability of the RP-derived products in dependence on variations in catalytic systems and synthesis conditions. The mechanism of this dependence remains unclear, and, correspondingly, the actual knowledge of the role of initial structure and its transformation during the RP processing remains insufficient to construct an industry-significant schedule for submelt polymer manufacturing. The correlation between the properties of initial and final products means the presence of a mechanism of structural memory inherent in RPs. This memory is quite resistant in the case of the submelt treatment of RP, but it can be more or less efficiently suppressed either by melt recrystallizing or when using the gel-technology. The melt crystallized RP are not suitable for manufacturing high-strength fibers. The gelling, in contrast, destroys substantially the RP supermolecular structure with forming a tenuous, stable network made of long chain molecules; this allows one to prepare fibers and films with excellent mechanical properties. In the latter case, the problem of selection of optimal RP characteristics is converted to the problem of obtaining the gel network whose characteristics would be mostly appropriate for making the high-performance fibers. It is the problem that is considered in this chapter. The consideration is based on previously published results of instrumental studies carried out using a set of experimental methods, such as the electron microscopy, low-frequency Raman spectroscopy, infrared spectroscopy, and differential scanning calorimetry.