Viscoelastic properties of linseed oil-based medium chain length poly(hydroxyalkanoate) films: effects of epoxidation and curing

Medium-chain-length poly(hydroxyalkanoate) (mcl-PHA) polymers derived from linseed oil (PHA-L) have a relatively small molar mass and contain a high c oncentration of unsaturated side-chains. As such, these polymers are amorph ous and take on the consistency of a viscous liquid at room temperature. In order to increase the application potential of this material, the side-cha in olefinic groups of PHA-L were converted to epoxy derivatives (PHA-LE) us ing m-chloroperoxybenzoic acid (m-CPBA). Epoxidation resulted in a 37% conv ersion of olefinic to epoxy groups. The epoxy groups enhanced the PHA-LE fi lm susceptibility to crosslinking upon exposure to air. PHA-LE films began to crosslink and stiffen in less than 25 days, whereas PHA-L films began to crosslink between days 50 and 75. The PHA-LE films showed an increase in t ensile strength (TS, from 4.8 to 20.7 MPa) and Young's modulus (YM, from 12 .9 to 510.6 MPa) between 25 and 100 days. In contrast, PHA-L had a TS of 25 .0 MPa and YM of 767.8 MPa after 100 days. Epoxidation helped induce crossl ink formation; however, aging for 100 days ultimately resulted in crosslink ed films from both PHA-L and PHA-LE with higher strength and durability tha n the original materials. (C) 2000 Elsevier Science B.V. All rights reserve d.