The effect of recycling on the properties of injection molded polycarbonate was investigated. One unreinforced and two glass‐reinforced grades were studied. Fiber degradation was distinguished from molecular scission by spiral flow measurements and molecular weight analysis. During the first cycles the average fiber length was significantly reduced, but at later stages it approached an equilibrium. The number of scission per original polymer molecule increased linearly with the number of recycles for all systems studied, but the degradation reaction did not follow random scission kinetics. The glass reinforced grades exhibited degradation rates which were at least twice as high as that of an unreinforced polymer. This discrepancy was most probably the result of a more extensive viscous heating in the glass‐reinforced systems. The decrease in molecular weight as well as in fiber length greatly affected the impact strength of the material. The effect of processing temperature on polymer degradation during recycling was evaluated. The fraction of virgin material that has to be added to the regrind to maintain a certain property level was determined. On a 90 percent property level, an icrease in melt temperature by 1°C corresponded to an increase of 1 percent in the required amount of virgin material. Aging tests indicated that there was no significant difference in degradation rate between recycled and virgin material, although the former certainly exhibited lower absolute values of the measured property (impact strength).
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Kent B. Abbås (1980) studied this question.