The effect of an increase in chain length on the mechanical properties of polyethylene glycols

The mechanical properties of different molecular weights of polyethylene glycol (PEG) have been determined by formation of compacted tablets and beams, which were subjected to diametral compression and 3-point bending, respectively. From diametral compression, the tensile strength for the different grades of PEG was determined. Flat beams made from powder by compaction were used to determine Young's modulus of elasticity. Beams into which a notch had been introduced after formation allowed the fracture mechanical parameters of critical stress intensity factor, K-1C, and fracture toughness, R, to be determined. Evaluation of these parameters as a function of compact porosity allowed extrapolation to values at zero porosity, providing an estimate of the material properties. The increase in chain length of the PEG was found to have a non-linear effect on tensile strength and Young's modulus. The ductility of the polymer increased proportionally to the increase in chain length, reflected by the linear relationship between K-1C and the molecular weight. Young's modulus and critical stress intensity factor allowed the estimation of the strain energy release rate, Gic, which is the driving force in crack propagation. Consequently, the tensile strength at zero porosity was found to be predictable from the values of G(1C) and the molecular weight of the different grades of PEG. (C) 1998 Elsevier Science B.V. All rights reserved.