Outstanding mechanical and thermal properties of PHBV/EVA hybrids by nucleant and plasticizer action of ionic-liquid and graphene derivative

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ethylene-co-vinyl acetate) (EVA) hybrid materials were prepared by extrusion at different compositions. The ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and reduced graphene oxide-zinc oxide composite (rGO-ZnO) were used as plasticizer and reinforcement agent, respectively. Differential scanning calorimetry (DSC) analyses showed the increase in crystallinity of the PHBV phase associated with the reduction in melt temperature for the PHBV/EVA hybrids at 50:50 composition. XRD data corroborated these results, indicating a higher crystallinity for the hybrids with rGO-ZnO added at 1.0% content. DSC also showed the better compatibilizing effect at higher content of the composite. It seems evident that the composite had its dispersion favored by the ionic liquid and improved the crystallization behavior with smaller crystallites. As well, tensile tests showed the notable effect of thermal properties on the elongation at break ( = 389.8 %) for the hybrid with the highest composite content. By contrast, for the hybrids with EVA at 75% composition, the reduction in crystallinity for both EVA and PHBV phases was determinant for better deformations. Finally, overall migration tests revealed that the hybrids with PHBV/EVA at 50:50 composition presented migration levels lower than those required by the European legislation for fat food packaging.

聚(3-羟基丁酸酯-co-3-羟基戊酸酯)（Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV）与聚(乙烯-co-乙酸乙烯酯)（Poly(ethylene-co-vinyl acetate), EVA）的共混复合材料通过挤出法制备，调控不同组分比例。实验分别采用离子液体1-丁基-3-甲基咪唑六氟磷酸盐（1-butyl-3-methylimidazolium hexafluorophosphate）作为增塑剂，还原氧化石墨烯-氧化锌（reduced graphene oxide-zinc oxide, rGO-ZnO）复合填料作为增强剂。差示扫描量热法（Differential scanning calorimetry, DSC）分析结果表明：当PHBV/EVA组分为50:50时，共混物的PHBV相结晶度提升，同时其熔融温度降低。X射线衍射（X-ray diffraction, XRD）数据佐证了上述结论，即添加1.0%含量rGO-ZnO的共混物结晶度更高。DSC测试还发现，复合填料含量越高，其增容效果越佳。显然，离子液体可促进rGO-ZnO在基体中的分散，细化晶粒并优化结晶行为。此外，拉伸测试结果显示，复合填料含量最高的共混物，其热性能对断裂伸长率（ε=389.8%）具有显著影响。与之相对，当EVA组分占比75%的共混物中，PHBV与EVA两相的结晶度均出现降低，这是其形变性能提升的关键诱因。最后，整体迁移性测试结果表明：PHBV/EVA组分为50:50的共混材料，其迁移量低于欧盟脂肪类食品包装法规的限定要求。