Melt reaction in blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and epoxidized natural rubber

摘要

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with hydroxyvalerate content of 12 mol % is a natural aliphatic polyester. At temperatures above its melting point, thermal decomposition occurs leading to shorter chains with carboxyl end groups. In blends with epoxidized natural rubber (ENR), 50% epoxidation level, these carboxyl chain ends may trigger reactions between the constituents since the epoxidized groups provide reactive sites. Glass transition temperature studies reveal immiscibility of the polymers over the entire composition range. Hence, any reaction between the constituents is restricted to the interfacial region between the components. We report here on studies on melt reactions between the components at elevated temperatures. DSC traces display an exothermic peak when the blends are annealed at temperatures ranging from 220 up to 234 degreesC. The kinetics of the reaction are discussed in terms of a serial reaction scheme. It turns out that the reaction rate increases with annealing temperature (T-a) and with descending PHBV content in the blends when PHBV is the minor component. Morphological studies by optical microscopy reveal that PHBV is still capable of crystallizing at 50 degreesC after melt reaction at 234 degreesC. Either ring-banded or fibrillar spherulites can be seen in blends with PHBV in excess. We note, however, that the rate of crystallization is dramatically reduced after melt reaction at T-a = 234 degreesC. (C) 2004 Elsevier Ltd. All rights reserved.