STEADY SHEAR AND DYNAMIC PROPERTIES OF BIODEGRADABLE POLYESTERS

The rheological properties of three biodegradable partially crystallin e alipathic polyesters-poly epsilon caprolactone (PCL), polylactic aci d (PLA), and polyhydroxybutyrate-co-hydroxyvalerate (PHBV)-were invest igated, Low shear viscosity (eta), first normal stress difference (N-1 ), and dynamic properties (G' and G ''), were measured for each polyme r using rotational instruments. High sheer viscosity data was obtained using a capillary rheometer. Gel permeation chromatography indicates that both PLA and PHBV undergo degradation during processing. Thermal degradation rate constants for PLA and PHBV were determined from the t ime-sweep data. Data indicates that material functions are proportiona l to the molecular weight for PCL and PLA samples, and directly relate d to the HV content in the PHBV samples, The relaxation spectra were c alculated from the G' and G '' data using the regularization method an d the applicability of the nonlinear Wagner equation was checked on th ese materials. Results are discussed in terms of variations in the mol ecular characteristics on rheological properties and their possible in fluence on the processability.