Enhanced thermal, mechanical and migration properties of extruded PHBV/graphene hybrids for packaging

Aiming to improve the properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), hybrid materials were prepared. PHBV was mixed with poly(ethylene-co-vinyl acetate) (EVA) by extrusion at different compositions, in the presence of a plasticizer and a graphene derivative. A reduced graphene oxide-zinc oxide composite (rGO-ZnO) was added as a nucleating agent. X-ray diffractometry (XRD) showed that rGO-ZnO, added at 0.5 and 1.0 mass%, was well-dispersed within the polymer matrix. XRD and differential scanning calorimetry results indicated that the crystallinity of the PHBV phase was reduced in the hybrids. However, an increase in crystallinity was observed for the PHBV/EVA hybrids at 50:50 and 25:75 compositions, when the rGO-ZnO content was increased to 1.0%. This increase in crystallinity was associated to the formation of smaller spherulites. Tensile tests showed improved mechanical properties for the hybrids in relation to PHBV and the neat blends. For the hybrids, while a reduction in Young’s modulus was observed, elongation at break values varied from 307.5% to 822.6%. 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.为优化聚(3-羟基丁酸酯-co-3-羟基戊酸酯) (poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV)的综合性能，本研究制备了其杂化复合材料。将PHBV与聚(乙烯-co-乙酸乙烯酯) (poly(ethylene-co-vinyl acetate), EVA)按不同配比通过挤出成型工艺进行共混，同时添加增塑剂与石墨烯衍生物。另将还原氧化石墨烯-氧化锌复合物 (reduced graphene oxide-zinc oxide composite, rGO-ZnO)作为成核剂引入体系。X射线衍射 (X-ray diffractometry, XRD)测试结果表明，添加量为0.5%和1.0%质量分数的rGO-ZnO可在聚合物基体中实现均匀分散。X射线衍射与差示扫描量热法 (differential scanning calorimetry, DSC)分析结果显示，杂化材料中PHBV相的结晶度整体有所降低。但当PHBV/EVA配比为50:50与25:75时，随着rGO-ZnO添加量提升至1.0%，该类杂化材料的PHBV相结晶度反而出现提升。该结晶度提升与更小尺寸球晶的形成密切相关。拉伸测试结果表明，相较于纯PHBV及未添加rGO-ZnO的共混物，本研究制备的杂化材料力学性能得到显著改善。对于此类杂化材料，尽管杨氏模量出现一定程度下降，但其断裂伸长率可达307.5%至822.6%。最终整体迁移性测试结果显示，PHBV/EVA配比为50:50的杂化材料，其迁移量低于欧盟脂肪类食品包装相关法规要求的限值。