Significant accelerated crystallization of long chain branched poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with high nucleation temperature under fast cooling rate

The long chain branched poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (LCB-PHBV) with rapid crystallization rate and high nucleation temperature was fabricated by only adding small amounts of dicumyl peroxide (DCP). NMR and FTIR spectra confirmed that long chain branched structures of LCB-PHBV were formed in the melting reaction process. The results from non-isothermal crystallization indicated that crystallization rate and crystallinity of LCB-PHBV presented an obvious increase while half crystallization time decreased obviously. Interestingly, during melting crystallization, the crystallization rate of LCB-PHBV increased with the increase of cooling rate and curves of crystallization peaks shifted obviously to higher temperatures. Based on polarized optical microscopy observation, it was found that the nucleation abilities of LCB-PHBV under a higher temperature had been improved, whereas the diffusion of molecular chains inhibited the radial growth of spherulites. However, such contribution of nucleation promoting effect on crystallization of polymers was larger than dispersion inhibition effect of segments, resulting in an inducement and acceleration on crystallization process of LCB-PHBV.