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 mechani cal spectroscopy, transmitted optical microscopy and transmission electron microscopy techniques. The PK samples studied are found to have a crystalli nity of about 38%. The fracture mechanisms observed in the PK samples are f ound to be sensitive to strain rate, notch, and stress state. Upon double-n otch four-point-bend fracture, the PK fails in a brittle fashion under impa ct condition and fails in a ductile manner when the testing rate is low. Cr azing is the dominant fracture mechanism under the low-rate test conditions , even in the region close to the surface (plane stress region) of the samp le. The dominant fracture mechanisms under uniaxial tension are found to be shear yielding and voiding due to debonding of the less-compliant sub-micr ometer particles in the PK matrix. No sign of crazing is observed in uniaxi al tensile specimens. (C) 2000 Kluwer Academic Publishers.