A method is developed for determining the environmental stress cracking resistance (ESCR) of blow molded poly(ethylene terephthalate) (PET) containers. By this method, the internal chamber of a container is presurized in 68.9 kPa (10 psi) increments while the outside of the base is being exposed to an environmental stress cracking (ESC) agent. The base of the container is examined after each 68.9 kPa of pressurization if crazing has occurred. The process is continued until a threshold value of craze initiation pressure (CIP) can be determined. Low CIP for the type of containers tested generally corresponds to a high rate of field failures. The method does not only gage the susceptibility of different types of one‐piece PET containers to ESC but also provides helpful information to improve the container designs.

The prediction of stiffness in short fiber reinforced thermoplastics is studied as a function of fiber length using injection molded blends of PS and PPO. The theoretical models for predicting composite stiffness are reviewed. The results are first compared with the theoretical models advanced for uniaxially aligned composites. These models predict higher than experimental values. However, agreement between the predictions and experimental values improves when the effect of fiber orientation distribution in the injection molded samples is taken into account and as the ductility (or the PPO content) of the matrix increases. Cox's model when used with the "laminate analogy" gives the closest prediction to the experimental stiffness. Reinforcement efficiency factor for stiffness is a strong function of retained fiber lengths. The dependence of composite stiffness on the matrix ductility and the effects of compatibility on the mechanical properties of PS-PPO blend system are also discussed.

Substrate compositions having a polymeric matrix, a reinforcing compo nent, and a conductive filler were developed for bipolar electrodes to be used in zinc- bromine battery systems. Among the various possible composite combinations, those based on carbon black as a conductive filler were given special attention. They combine the inherent properties of polymers—such as toughness, flexibility, low density, etc—with a high conductivity (σ = 0.2 to 1 ohm-1-cm-1). One of the problems recognized with the use of bipolar electrodes containing high surface area carbon blacks in zinc-bromide bat teries is the warpage of the electrodes. Under service conditions, warpage causes an uneven flow distribution of the electrolyte on the electrode surface and results in loss of cell capacity at low cycle life. The warpage was found to occur because of physical expan sion of electrodes resulting from bromine absorption by the high surface area carbon black. Composite substrate compositions with excellent dimensional stability that have eliminated electrode warpage as the primary battery failure mechanism were prepared by using two novel thermoplastic-composite fabrication techniques.