Effect of ionic additives on deformation behavior of bisphenol A polycarbonate

The deformation behavior of bisphenol A polycarbonate containing only a sma ll amount of oligoionomeric additives in the range of a few parts per hundr ed parts of resin was examined. The impact strength of polycarbonate marked ly decreased as the content of additive increased, and brittle fracture of polycarbonate was observed in tensile tests when the concentration of addit ive was above 2.5 phr. The ductile-to-brittle transition that was determine d using a comparison of the critical shear yield stress and the critical cr aze stress appeared to exist in the range of 2.5-3.5 phr of additive. The m easured entanglement density was also found to decrease significantly with the addition of a few parts per hundred parts of resin of additives, and th e change of the dominant deformation mechanism from ductile to brittle fail ure was recognized as a result of the change of the entanglement density of polycarbonate. Therefore, it was concluded that the presence of a small am ount of ionomeric additives caused the loss of entanglement density that in duced transition of the deformation mechanism of polycarbonate from ductile to brittle failure and led to the corresponding deterioration of impact st rength. (C) 2001 John Wiley & Sons, Inc.