RADIATION CROSS-LINKING OF A BACTERIAL MEDIUM-CHAIN-LENGTH POLY(HYDROXYALKANOATE) ELASTOMER FROM TALLOW

Pseudomonas resinovorans produces a medium-chain-length poly(hydroxyal kanoate) (MCL-PHA) copolymer when grown on tallow (PHA-tal). This poly mer had a repeat unit composition ranging from C4 to C14 with some mon o-unsaturation in the C12 and C14 alkyl side chains. Thermal analysis indicated that the polymer;was semi-crystalline with a melting tempera ture (T-m) of 43.5 +/- 0.2 degrees C and a glass transition temperatur e (T-g) of -43.4 +/- 2.0 degrees C. The presence of unsaturated side c hains allowed crosslinking by gamma-irradiation. Irradiated polymer fi lms had decreased solubility in organic solvents that indicated an inc rease in the crosslink density within the film matrix. The addition of linseed oil to the gamma-irradiated film matrix enhanced polymer reco very while minimizing chain scission. Linseed oil also caused a decrea se in the enthalpy of fusion (Delta H-m) of the films (by an average o f 60%) as well as enhanced mineralization. The effects of crosslinking on the mechanical properties and biodegradability of the polymer were determined. Radiation had no effect on the storage modulus (E') of th e polymer. However, radiation doses of 25 and 50 kGy did increase the Young modulus of the polymer by 129 and 114%, and the tensile strength of the polymer by 76 and 35%, respectively. Finally, the formation of a higher crosslink density within the polymer matrix decreased the bi odegradability of the PHA films. (C) 1998 Elsevier Science B.V. All ri ghts reserved.