The surface melting and crystallization behavior of two biodegradable polyesters, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx)) (HHx=12 mol%) and poly(3-hydroxybutyrate) (PHB), were investigated by using attenuated total reflection (ATR) and transmission infrared (IR) spectroscopy coupled with the generalized two-dimensional (2D) correlation analysis. IR bands in the C=O stretching vibration region were analyzed to explore the changes in crystallinity at the surface and those in the bulk of the polymer film samples during the melting and crystallization processes. Due to the intrinsic sub-micrometer sampling depth of the ATR technique, spectral information attributed to the chemical moieties situated at the surface region of the film samples can be observed. The present study revealed that the surface melting of P(HB-co-HHx) takes place through an intermediate state. The distribution of crystalline phase detected by the ATR technique and that detected by the transmission technique suggested that the polymer crystals tend to grow at the surface in a manner different from that in the bulk. It is very likely that the population of polymer crystals at the surface is higher than that in the bulk for both P(HB-co-HHx) and PHB. The time-dependent IR spectral variations for P(HB-co-HHx) and those for PHB indicated that P(HB-co-HHx) crystallizes much slower than PHB. This observation suggested that the HHx units incorporated in P(HB-co-HHx) markedly reduce not only the degree of crystallinity but also the crystallization rate of PHB homopolymer.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry