Srihanam Prasong, Srisuwan Yaowalak, Phromsopha Theeraphol, Manphae Apirada, Baimark Yodthong
Biodegradable Polymers Research Unit, Department of Chemistry and Centre of Excellence for Innovation in Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand.
Scientific Instrument Academic Service Unit, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand.
Polymers (Basel). 2023 Oct 1;15(19):3966. doi: 10.3390/polym15193966.
Flexible poly(L-lactide)--poly(ethylene glycol)--poly(L-lactide) block copolymer (PLLA-PEG-PLLA) bioplastic has been blended with low-cost thermoplastic starch (TPS) to prepare fully biodegradable bioplastics. However, the mechanical properties of PLLA-PEG-PLLA matrix decrease after the addition of TPS. In this work, citric acid (CA) was used as a compatibilizer to improve the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. TPS was first modified with CA (1.5 %wt, 3 %wt, and 4.5%wt) before melt blending with PLLA-PEG-PLLA. The PLLA-PEG-PLLA/modified TPS ratio was constant at 60/40 by weight. CA modification of TPS suppressed the crystallinity and enhanced the thermal stability of the PLLA-PEG-PLLA matrix, as determined through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The compatibility between the dispersed TPS and PLLA-PEG-PLLA phases was improved through modification of TPS with CA, as revealed by the smaller size of the co-continuous TPS phase from scanning electron microscopy (SEM) analysis. Increasing the hydrophilicity of the blends containing modified TPS confirmed the improvement in phase compatibility of the components. From the tensile test, the ultimate tensile strength, elongation at break, and Young's modulus of the blends increased with the CA content. In conclusion, CA showed a promising behavior in improving the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. These PLLA-PEG-PLLA/modified TPS blends have potential to be used as flexible bioplastic products.
柔性聚（L-丙交酯）-聚（乙二醇）-聚（L-丙交酯）嵌段共聚物（PLLA-PEG-PLLA）生物塑料已与低成本热塑性淀粉（TPS）共混，以制备完全可生物降解的生物塑料。然而，添加TPS后，PLLA-PEG-PLLA基体的机械性能下降。在本工作中，柠檬酸（CA）用作增容剂，以改善PLLA-PEG-PLLA/TPS共混物的相相容性和机械性能。TPS首先用CA（1.5%重量、3%重量和4.5%重量）进行改性，然后与PLLA-PEG-PLLA熔融共混。PLLA-PEG-PLLA/改性TPS的重量比恒定为60/40。分别通过差示扫描量热法（DSC）和热重分析（TGA）测定，TPS的CA改性抑制了PLLA-PEG-PLLA基体的结晶度并提高了其热稳定性。扫描电子显微镜（SEM）分析显示，通过TPS的CA改性，分散的TPS相和PLLA-PEG-PLLA相之间的相容性得到改善，这表现为双连续TPS相的尺寸更小。含有改性TPS的共混物亲水性增加，证实了各组分相相容性的改善。拉伸试验表明，共混物的极限拉伸强度、断裂伸长率和杨氏模量随CA含量的增加而提高。总之，CA在改善PLLA-PEG-PLLA/TPS共混物的相相容性和机械性能方面表现出良好的效果。这些PLLA-PEG-PLLA/改性TPS共混物有潜力用作柔性生物塑料制品。
