The effect of molecular weight on the rheological and tensile properties of poly(epsilon-caprolactone)

Molecular weight fractions of poly(epsilon-caprolactone) (PCL) were obtained by catalytic degradation and characterised by rheological measurements. Pseudoplastic behaviour was found the higher molecular weight fractions, the degree of which lessened as the thermal motion of the polymer chains increased. The exponential factor of the viscosity/molecular weight relationship indicated that the fractions were above the critical molecular weight for viscous flow determined as 15-16 000. Activation energies for viscous flow showed an inverse relationship with molecular weight, the significance of which has been discussed. Melt quenching resulted in lower melt viscosities due to a reduction in melting point by formation of additional amorphous regions. Tensile measurements indicated that PCL was a brittle material with a molecular weight of > 16 900 being required for free film formation. Elongation and tensile strength values increased with molecular weight although remaining low, indicating both the low molecular weight range investigated and the high degree of PCL crystallinity. PCL showed that it had rheological and tensile properties that with modification would make it a potential candidate in the novel technique of powder coating of pharmaceutical compacts.