Graft copolymerization of maleic anhydride (MA) onto poly(3-hydroxybutyrate) (PHB) was carried out by use of benzoyl peroxide as initiator. The effects of various polymerization conditions on graft degree were investigated, including solvents, monomer and initiator concentrations, reaction temperature, and time. The monomer and initiator concentrations played an important role in graft copolymerization, and graft degree could be controlled in the range from 0.2 to 0.85% by changing the reaction conditions. The crystallization behavior and the thermal stability of PHB and maleated PHB were studied by DSC, WAXD, optical microscopy, and TGA. The results showed that, after grafting MA, the crystallization behavior of PHB was obviously changed. The cold crystallization temperature from the glass state increased, the crystallization temperature from the melted state decreased, and the growth rate of spherulite decreased. With the increase in graft degree, the banding texture of spherulites became more distinct and orderly. Moreover, the thermal stability of maleated PHB was obviously improved, compared with that of pure PHB. Its thermal decomposition temperature was enhanced by about 20°C. In addition, the introduction of the MA group promoted the biodegradability of PHB.

In order to modify poly [(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV), the crosslinking of this copolymer was carried out at 160 °C using dicumyl peroxide (DCP) as the initiator. The torque of the PHBV melt showed an abrupt upturn when DCP was added. Appropriate values for the gel fraction and crosslink density were obtained when the DCP content was up to 1 wt% of the PHBV. According to the NMR spectroscopic data, the location of the free radical reaction was determined to be at the tertiary carbons in the PHBV chains. The melting point, crystallization temperature and crystallinity of PHBV decreased significantly with increasing DCP content. The effect of crosslinking on the melt viscosity of PHBV was confirmed as being positive. Moreover, the mechanical properties of PHBV were improved by curing with DCP. When 1 wt% DCP was used, the ultimate elongation of PHBV increased from 4 to 11 %. A preliminary biodegradation study confirmed the total biodegradability of crosslinked PHBV. Copyright © 2004 Society of Chemical Industry