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This series of papers explores the effect of structural characteristics of 2,2,6,6-tetramethylpiperidine-based hindered amine light stabilizers (HALS) on the longterm (40 months) thermal (110°C in air) and photo-stabilization (Microscal unit wavelength Ͼ300 nm) performance characteristics of high-density polyethylene formulations. Possible synergism with a triazine functional UV absorber is also explored. Under thermal degradation (measured by carbonyl index) the polymeric HALS performed best, mainly because of reduced volatilization. Additionally, ϾN-methyl HALS generally showed superior performance under thermal degradation. There was no synergism between an N-CH 3 polymeric HALS and the UV1164 triazine additive. However, the equivalent N-H polymeric HALS interacted in a complex manner with UV1164, giving synergism and antagonism, depending on HALS/UV1164 ratio. Strong synergism was evident with the monomeric HALS when the total stabilizer level was 0.2% w/w. Reduction in the overall stabilizer level to 0.05% w/w eliminated the synergism. The UV1164 alone led to rapid and intense yellowing; however, the rate and intensity of yellowing reduced dramatically upon combination with HALS, particularly when the UV1164 level was above 0.1% w/w. When the formulation was under UV attack, the molar mass and the type of N-substitution had no influence on stabilization performance because of the relatively low temperature of testing (leading to reduced volatilization), and the similarly effective UV-stabilization routes for N-methyl HALS and N-H HALS. Under UV attack, yellowing reached a maximum and then decreased to approximately the initial level, while HALS/UV1164 combinations generally showed weak antagonism.

Specimens of two engineering plastics i.e., poly(ether imide), PEI, and poly(2,6dimethyl-1,4-phenylene ether), PPE, were injection molded employing a 40t Van Dorn injection molding machine and industrial practices. The mold and melt temperatures and the injection speed were varied in a limited range which furnished acceptable samples. The density, birefringence, residual stress distributions, flexure and tensile properties, and crack development of the injection molded specimens were studied. Vacuum compression molded samples were also prepared to investigate the role played by the cooling rate in shaping microstructural distributions. The results revealed significant differences in the development of microstructure of the molded specimens of the two resins, which was related to rheology and molding conditions on one hand and to development of cracks and ultimate properties on the other hand.

The extensional flow behavior of a Nylon 6 based engineering plastic filled with short glass fibers was characterized using a Meissner-type uniaxial extensional rheometer. The fiber orientation distributions of the resin samples at various Hencky strains were also determined by X-ray microradiography and image analysis techniques. The uniaxial extensional stress growth function was found to be intimately related to the orientation distribution function of the fibers.

Parison formation and inflation behavior of three polyamide 6 resins during extrusion blow molding were investigated using cinematography, a transparent mold, a pinch‐off mold and a modified blow pin, which allowed the pressure inside the parison to be determined during inflation. The glass fiber filled polyamide exhibited negligible extrudate swell and significant drawdown, whereas polyolefin modified polyamide exhibited appreciable extrudate swell and relatively small drawdown effects. The inflation behavior of the polyolefin modified polyamide was similar to the behavior of conventional blow molding grade polyolefins, whereas the unmodified and glass filled polyamides exhibited different inflation characteristics. Their inflation behavior at different internal pressures was characterized by decreasing and increasing Hencky strain rates with inflation time at high and low internal blow pressures, respectively. The characterized parison formation and inflation behavior of the polyamides emphasize the importance of rigorous blow moldability experiments and the difficulties associated with linking various rheological material functions to the blow moldability of modified polyamides.