Study of the crosslinking reaction (natural and UV induced) in polyunsaturated PHA from linseed oil

Linseed oil was used as the carbon source for the production of polyunsaturated polyhydroxyalkanoates in cultures of Pseudomonas aeruginosa 42A2. The polymer obtained, PHA-linseed (PHA-L) contents 36.5% of unsaturated side chains. 16% of the monomers were polyunsaturated, with two or three unsaturations (Cl 2:2 Delta(6.9), C 14:2 Delta(5.8) and C14:3 Delta(5.8.11)), whereas the saturated part was mainly poly(3-hydroxyoctanoate) and poly(3-hydroxydecanoate). Up to 13 different monomers, ranging from C6 to C14, were identified. We found that the stability of the PHA-linseed side chain olefinic groups was affected by time-dependent autoxidation, which induced a crosslinking reaction with the other polymer chains at room temperature. To accelerate this process, the polymer was UV-treated (lambda = 300 nm) and changes were monitored at different reaction times (0, 3, 6, 15 and 24 h). Among other techniques, curing reaction and polymer composition were also followed by FTIR, GC/MS and NMR. Thermal properties of the PHA-L and the UV-irradiated polyhydroxyalkanoates were studied, showing an increase in the glass transition temperature from -51 to -32 degrees C due to the crosslinking reaction. The accelerated curing of irradiated PHA-L films was compared to the natural curing of the films at room conditions. (C) 2008 Elsevier B.V. All rights reserved.