Reprocessing of thermoplastics. II. Polycarbonate

Abstract

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).

Effect of reprocessing and accelerated ageing on thermal and mechanical polycarbonate properties

“…This decrease of impact strength as the material is reprocessed is in agreement with the observed by other authors. Eguiazabal and Nazabal (1989) observed a continuous decrease in the impact properties of PC with the number of processing cycles, in clear agreement with the observations by Abbas (1980) using a Charpy impact test. An even faster loss of impact strength was observed from the third cycle onwards.…”

“…The decrease of the molecular weight with the number of reprocessing cycles has been already reported by Abbas (1980) and Eguiazabal and Nazabal (1989), However, they only evaluated the injection process and a lower number of reprocessing cycles.…”

“…Similarly, Chrysostomou and Hashemi (1996) reported that tensile, impact and dynamic properties, as well as the glass transition temperature, varied negligibly with the number of the injection molding cycles. Abbas (1980) and Bernardo et al (1996b) showed that molecular weight of dehumidified PC decreased as the number of recycling operations increased, greatly affecting some of its mechanical properties. In these studies, the presence of fiber reinforcement was shown to enhance the molecular degradation with reprocessing.…”

“…Reprocessing of polycarbonate has been studied for more than 20 years but continues to attract attention nowadays. The degradation reactions of PC and their effect on its mechanical properties have been studied by different authors and several papers have been published concerning hydrolytic degradation (Long and Sokol, 1974), the effect of processing temperature on polymer degradation during recycling (Abbas, 1980) and the effect of recycling with emphasis on molecular weight and impact strength (Abbas, 1981). The degradation and recycling of an extrusion grade polycarbonate sample and the effect of the humidity have also been studied (La Mantia and Correnti, 2003).…”

Polyethersulfone (PES) and Its Processing

“…Properties of plastics deteriorate mainly as a result of significant changes in polymer structure. In general, the reaction involves main chain scission, and this leads to a decrease in average molecular weight and viscosity of the melt polymer [30][31][32].…”