Free radical crosslinking of unsaturated bacterial polyesters obtained from soybean oily acids

Summary Poly(-3-hydroxy alkanoate) containing unsaturated side chains, PHA-soybean, were produced by feeding Pseudomonas oleovorans with soybean oily acids obtained from soybean oil. Unsaturation of PHA-soybean were found to be 10 mol-% of unsaturated side chains. Main saturated part of the biopolymer was Poly(3-hydroxy octanoate) with minor hexanoate and decanoate units. PHA films were crosslinked via free radical mechanism by means of thermally or under UV irradiation in the presence of benzoyl peroxide, benzophenon, and /or ethylene glycol dimethacrylate (EGDM). Crosslinking yield of the PHA films were found to be from 81 to 93 wt.-% from the sol-gel analysis. Swelling properties of the crosslinked PHA films in chloroform and toluene were also studied. Mc values of crosslinked PHAs were also calculated using Flory-Rehner equation. The crosslinked biopolyester obtained by thermally at 60 °C with benzoyl peroxide indicated the highest crosslinking density. Glass transition temperatures (Tg) of crosslinked biopolyester samples were changed from −33 to −45 °C while that of PHA-soybean was −60 °C. Received: 16 June 2000/Revised version: 22 January 2001/Accepted: 20 May 2001