DEFORMATION OF RUBBER-TOUGHENED POLYCARBONATE - MICROSCALE AND NANOSCALE ANALYSIS OF THE DAMAGE ZONE

Deformation of polycarbonate (PC) impact-modified with a core-shell ru bber (MBS) was examined at the microscale and nanoscale. The stress-wh itened zone (SWZ) that formed ahead of a semicircular notch was sectio ned and examined in an optical microscope and transmission electron mi croscope. At the microscale, the texture of the SWZ consisted of fine shear lines that formed when cavitation of the rubber particles reliev ed triaxiality and enabled the PC matrix in the SWZ to deform in shear . Examination of thin sections from the SWZ in the transmission electr on microscope revealed nanoscale deformation of the rubber particles. When the particle concentration was low (2%), only random cavitation o f rubber particles was observed. At higher particle concentrations (5 and 10%), cooperative cavitation produced linear arrays of cavitated p articles. The matrix ligaments between cavitated particles were strong enough that they did not fracture; higher strains were accommodated b y particle cavitation and matrix extension in the regions separating t he arrays. The cavitated arrays were also observed in the damage zone that accompanied the fracture surface of specimens impacted at -20 deg rees C. Cooperative cavitation may have implications for the impact st rength of blends with higher concentrations of rubber particles. The p ossibility that particle-particle interactions facilitate cavitation a nd promote matrix shear deformation is especially relevant to low-temp erature impact strength. (C) 1995 John Wiley and Sons, Inc.