Li Li, Zhang Shujing, Xue Meiling, Sun Xiaoli, Ren Zhongjie, Li Huihui, Huang Qigu, Yan Shouke
State Key Laboratory of Chemical Resource Engineering , Beijing University of Chemical Technology , Beijing 100029 , China.
School of Chemistry and Chemical Engineering , Heze University , Heze 274015 , China.
Langmuir. 2019 Aug 27;35(34):11167-11174. doi: 10.1021/acs.langmuir.9b01814. Epub 2019 Aug 15.
The band spherulites grown in neat poly(3-hydroxybutyrate) (PHB) and its blends with poly(propylene carbonate) (PPC) were observed by polarized optical microscopy. For the spherulites in neat PHB, it is evident that the band spacing increases first and then decreases with melting time. As the melting time is within 7 min, the band spacing increases continuously, which should be attributed to increasing mobility of polymer chains or decreasing viscosity of the melt. When the melting time is prolonged, evident thermal degradation of PHB occurs and results in a great deal of noncrystalline fractions, which is similar with addition of miscible amorphous polymers in the melt, and the band spacing decreases accordingly. The thermal degradation of PHB cannot, however, be detected by a thermogravimetric analyzer because of less volatile productions. An evident decrease of molecular weight can be measured by gel permeation chromatography, indicating occurrence of serious degradation. The decrease of crystallization and melting temperature revealed by differential scanning calorimetry (DSC) also prove the thermal degradation. For spherulites in PHB/PPC blends, however, the variation of band spacing differs from that in neat PHB. The band spacing increases continuously when melting time is within 15 min. The crystallization and melting behaviors are not influenced greatly by prolonging melting time in PHB/PPC blends. The variations of for PHB/PPC are slighter than those of the neat PHB and PPC upon heating at 190 °C. Combined with the corresponding DSC results, it is conjectured that blending may prohibit the degradation of PHB to some extent. An intermolecular interaction can be detected between PHB and PPC via Fouriertransform infrared spectra and should help to avoid degradation of PHB to a certain degree. The present results may help widen the applications of PHB and shed some light on understanding the formation mechanism of the band for aliphatic polyester polymers.
通过偏光显微镜观察了在纯聚（3-羟基丁酸酯）（PHB）及其与聚（碳酸亚丙酯）（PPC）的共混物中生长的带状球晶。对于纯PHB中的球晶，很明显带间距随着熔融时间先增加后减小。当熔融时间在7分钟以内时，带间距持续增加，这应归因于聚合物链的流动性增加或熔体粘度降低。当熔融时间延长时，PHB发生明显的热降解并产生大量非晶部分，这与在熔体中添加可混溶的无定形聚合物相似，并且带间距相应减小。然而，由于挥发性产物较少，PHB的热降解无法通过热重分析仪检测到。通过凝胶渗透色谱法可以测量到分子量明显降低，表明发生了严重降解。差示扫描量热法（DSC）显示的结晶和熔融温度降低也证明了热降解。然而，对于PHB/PPC共混物中的球晶，带间距的变化与纯PHB中的不同。当熔融时间在15分钟以内时，带间距持续增加。在PHB/PPC共混物中延长熔融时间对结晶和熔融行为影响不大。在190℃加热时，PHB/PPC的变化比纯PHB和PPC的变化更轻微。结合相应的DSC结果，可以推测共混可能在一定程度上抑制PHB的降解。通过傅里叶变换红外光谱可以检测到PHB和PPC之间的分子间相互作用，并且应该在一定程度上有助于避免PHB的降解。目前的结果可能有助于拓宽PHB的应用范围，并为理解脂肪族聚酯聚合物带的形成机制提供一些启示。
