Morphology and fracture behavior in aliphatic polyketones

Morphological features and fracture mechanisms in aliphatic polyketone (PK) samples, prepared via compression molding and injection molding processes, were investigated using differential scanning calorimetry, dynamic mechanical spectroscopy, transmitted optical microscopy and transmission electron microscopy techniques. The PK samples studied are found to have a crystallinity of about 38%. The fracture mechanisms observed in the PK samples are found to be sensitive to strain rate, notch, and stress state. Upon double-notch four-point-bend fracture, the PK fails in a brittle fashion under impact condition and fails in a ductile manner when the testing rate is low. Crazing is the dominant fracture mechanism under the low-rate test conditions, even in the region close to the surface (plane stress region) of the sample. The dominant fracture mechanisms under uniaxial tension are found to be shear yielding and voiding due to debonding of the less-compliant sub-micrometer particles in the PK matrix. No sign of crazing is observed in uniaxial tensile specimens. (C) 2000 Kluwer Academic Publishers.