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SynopsisAn extensive experimental study of structure development during the melt spinning of polypropylene and in as-spun polypropylene filaments is reported. Five polymers representing different molecular weights and polymerization methods were studied. WAXS, SAXS, and birefringence measurements were used to characterize the structure of the filaments. Spinning through air gives rise to monoclinic crystalline structures and spinning into cold water, the paracrystalline smectic form. Both crystalline and amorphous orientation factors were found to correlate with spinline stress for the different polymers studied, Mechanical properties of as-spun fibers such as modulus, yield strength, tensile strength, and elongation to break also correlate with spinline stress.

The importance and characteristics of viscoelastic fluid behavior are briefly reviewed, as are theoretical predictions of the relationships between the stresses developed in such a fluid and its deformation rate and history. It is seen that most of the equations available for the prediction of these stresses(variously termed “constitutive equations” or “rheological equations of state”) either do not predict the properties of real materials correctly or, alternately, are of such overriding complexity that they cannot be applied to the solution of any but the simplest real problems. A new constitutive equation in which all the significant parameters may be evaluated from only two sets of experiments is developed. Comparison with available experimental results, while not entirely conclusive, indicates that the equation may predict correctly the behavior of nonpolar solutions and polymeric melts and that it may work well on polar systems in the range of high deformation rates, i.e., the region of primary industrial interest. Several problems of interest to the plastics industry are worked to illustrate the use of this constitutive equation.

The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide‐6, polystyrene/polyamide‐6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.

A basic study of the kinematics, dynamics, and heat transfer occuring during tubular film extrusion of polyethylene is outlined. Three rheologically characterized polyethylenes, a lowdensity polyethylene (LDPE), a linear-low-density polyethylene (L-LDPE), and a high-density polyethylene (HDPE) were used in this study. The kinematics and stability of the tubular film process were investigated over a wide range of blow-up ratios, drawdown ratios, and frost-line heights. Local deformation rates along the bubble have been determined. Regions of stability and instability are described. Tensions and inflation pressures have been measured and expressed in terms of local elongational viscosities. Temperature profiles along the bubble were determined and interpreted in terms of local heat transfer coefficients. Positions of crystallization and temperature profiles have been noted and used to estimate rates of crystallization. The characteristics of the LDPE, LLDPE, and HDPE are contrasted.