Band 5, Heft 2

A basic study of melt spinning of polypropylene is reported. This study is aimed at developing a new technology for the manufacture of fine denier polypropylene fibers for clothing end uses. It was found that the molecular weight of the polypropylene resin has-a key influence on structure development in the fiber spinline. By aiming at achieving a smectic structure of the as-spun fiber through a controlled degradation of polypropylene, we can spin fine denier good quality polypropylene fibers at temperatures below 280°C and speeds up to 2000 meters/minute.

Thermal gradients in the walls of polyester parisons play a major role in determining the morphology and superstructure in the walls of the stretch blow molded bottles. This is associated with both the variation in material characteristics with temperature and the greater stretch ratios on the inner surface of the bottle. The influence of thermal equilibration time following a constant preheating period on bottle appearance, void content, oxygen permeability and other bottle characteristics was studied.

A theoretical model of the dynamics, heat transfer and crystallization processes in tubular film extrusion is presented. It is presumed that the polymer melts flow behavior is dominated by the temperature dependence of its rheological properties, as opposed to the specific rheological model used to represent it. Specifically we presume the melt is a Newtonian fluid with a temperature dependent viscosity, characterized by an activation energy of viscous flow E. The shape of the bubble and radius and film thickness profiles are primarily influenced by E. Crystallization makes a second order correction. Detailed comparisons are made to experimental investigations for low density polyethylene, linear low density polyethylene and high density polyethylene and generally good agreement is found.

A numerical experiment has been carried out to assess the errors involved in using Han’s exit pressure method for the determination of the first normal stress difference with a slit die. The creeping flow equations for a viscoelastic fluid model have been solved using the finite element method. The calculated exit pressures are used in the determination of normal stresses and are compared to those obtained directly from the constitutive model. The results show that the exit pressure method gives reasonably accurate estimates of the first normal stress difference.