Band 2, Heft 3

Kinematic and rheological considerations have been used to design and analyze the processing steps for obtaining biaxial chain orientation in poly(p-phenylene terephthalamide) (PPTA) films. A semi-quantitative approach to the mandrel design allows one to predict the type and degree of molecular orientation obtained. For the case of PPTA dissolved in H2SO4, the basic steps are extrusion of the liquid crystalline solution through an annular die followed by expansion and elongational flow over a mandrel. The mandrels used include conical, hyperbolic and ogival shapes. Molecular orientation as well as mechanical properties were found to be dependent on mandrel shape and presence. Wide angle x-ray diffraction (WAXS) techniques using White-Spruiell orientation factors and pole figures were used to characterize the films. Mechanical properties as well as the above techniques indicate a high degree of biaxial orientation can be obtained with a bias in certain film directions depending on the mandrel used. Tensile strength and Young's modulus values were found to be on the order of 30 000 psi and one million psi respectively. They also can be equally distributed in the film plane depending on mandrel shape. White-Spruiell orientation factors were as high as 0.49 and 0.5 for f1B and f2B $f_{1}^{B}\text{ }and\text{ }f_{2}^{B}$respectively. Scanning electron microscopy was used to observe the film superstructure as a function or processing conditions. All films exhibited a skin-core structure. Uniaxially drawn films are fibillar while the biaxial films appear to be more homogeneous.

A method of determining uniquely the best fitting temperature shift parameters of viscosimetric data over the full range of shear rates, based on the Carreau formula, has been presented in Part I. The method is in accordance with the temperature-time superposition principle of viscoelasticity and works fully numerically, thus providing an objective approximation criterion with optimal compensation of scatter and dispensing with any visual control at all, and includes, if necessary, the Rabinowitsch and Bagley corrections. Evaluations of this kind have been carried out for a multitude of old and new measurements of current types of thermoplastics (PE, PP, PS, PA, PC, PMMA, etc.), for which capillaries as well as rotational systems had been employed. In this way, a comprehensive viscosity data bank is built up containing a 5 or 6-parameter set for each material as a compact information about its flow behaviour and serving as a valuable means for numerical process analyses. At the same time, the usual shift formulas (Arrhenius, WLF, etc.) are compared in respect of their applicability and the typical parameter ranges are marked out. Some attention is given to the physical meaning of the material parameters. Part II deals with the validity of the temperature shift principle in general, the incorporation of correction procedures and the evaluation of the pressure dependence of the viscosity.

Conducting thermal analysis of fibers in the swollen state possesses certain characteristics and advantages. The thermograms including both TMA and DSC of 12 acrylic fiber samples of different composition and mode of formation are given in this part of the paper. The lowering of the transition temperature as a depression of the melting points according to the theory of Flory is tested. The DSC thermograms of a commercial acrylic fiber sample are separated into its constituent peaks and the bond energy of the four regions is calculated. Finally the relation of the magnitudes of the different peak of a PAC Abbreviation of polyacrylonitrile copolymer. ) fiber sample is sought and the effects of annealing and hot stretching of acrylic fibers on its texture are demonstrated.

We describe an experimental and theoretical study of the mechanisms of flow of rubber compounds in a screw extruder. Two compounds, a typical synthetic rubber (butadiene-styrene copolymer-cis-1, 4 polybutadiene) based passenger tire tread (PTT) and a natural rubber based truck tire tread (TTT), were investigated in a 1 12 ${}^{1}/{}_{2}$inch NRM cold feed screw extruder using a screw with a constant channel depth and constant channel pitch along the whole screw length. The rubber was cured in place and the screw removed. The screw exhibited starvation behavior except near the die. The length of the rubber strip in the screw is proportional to the pressure developed at the die. Marker studies showed transverse circulating flows beginning in the region immediately downstream from the hopper. These observations indicate that cold feed extruders exhibit a metering region flow, albeit sometimes starved, from entry port to die. Under these conditions the extruder is independent of the pressure developed in the screw channel. A simple non-Newtonian isothermal mathematical model for the metering zone is described. The rubber compound is considered as a pseudoplastic material with a yield value. A comparison of theory and experiment shows that a one dimensional isothermal model quite accurately predicts the flow rate pressure development of the rubber compound in our screw (with a shallow prismatic channel) when starvation is considered. The yield value of the rubber compound influences screw characteristic curves only for very high values of the dimensionless pressure gradient.

Theoretical analysis of the tubular film extrusion using computer simulation presented has been used to preduct bubble shapes, velocity profiles and stretching stresses. From the theoretical analysis, maximum stretching stresses, which are closely related to film physical properties, were predicted under various process conditions. This theoretical analysis was applied to high molecular weight HDPE tubular film process. It was found that high strength HDPE film can be produced by maintaining high stretching stress, which is obtained on the conditions of high out-put rate, high take-up speed and low temperature by reducing the heat generated by viscous dissipation. Further, the processability of HDPE film produced using bubble stabilizing equipment was discussed.

A polyurethane reaction under different mixing rates and reaction rates are studied in an adiabatic batch reactor. Results are explained by using a slab model and dimensional analysis. Four characteristic times are used to describe the interactions of mixing, diffusion and chemical reaction, which may serve as conceptual guidelines in determining the proper reaction rate and mixing power for a specific reaction system.