Correlation between degree of crystallinity, morphology, glass temperature, mechanical properties and biodegradation of poly (3-hydroxyalkanoate) PHAs and their blends

Abstract

Bacterial thermoplastic polyesters poly (3-hydroxyalkanoate) PHAs are produced by the fermentation of renewable materials, such as sugars or molasses. The pure homopolymer, PHB, and pure copolymer (3-HBP-CO-HV) (88:12) are brittle materials. PHB or PHB/V are mixed with other biodegradable materials to improve their mechanical properties. The aim is to develop biodegradable polymers of PHB-base with improved mechanical properties, such as fracture stress (27-18 MPa), strain (400-660%), impact strength and long-term stability, and to compare them with PE, PP and PET. When nucleating agents are added, smaller spherulites are formed, thus improving the mechanical properties. The mechanical properties of PHB and its blends are related to processing conditions, morphology, crystallinity and glass transition. The blends are ductile polymers with plastic deformation (necking). They are biodegraded in aerobic tests, under compost conditions in soil and water, and many pores are to be found on the surface. The blends are degraded more easily in the aerobic test, i.e. in the river water and compost, than in the soil. © 2002 Elsevier Science Ltd. All rights reserved.