Improvement in Phase Compatibility and Mechanical Properties of Poly(L-lactide)- b-poly(ethylene glycol)- b-poly(L-lactide)/thermoplastic Starch Blends with Citric Acid

Prasong Srihanam; Yaowalak Srisuwan; Theeraphol Phromsopha; Apirada Manphae; Yodthong Baimark

doi:10.3390/polym15193966

Improvement in Phase Compatibility and Mechanical Properties of Poly(L-lactide)- b-poly(ethylene glycol)- b-poly(L-lactide)/thermoplastic Starch Blends with Citric Acid

Polymers (Basel). 2023 Oct 1;15(19):3966. doi: 10.3390/polym15193966.

Authors

Prasong Srihanam¹, Yaowalak Srisuwan¹, Theeraphol Phromsopha¹, Apirada Manphae², Yodthong Baimark¹

Affiliations

¹ Biodegradable Polymers Research Unit, Department of Chemistry and Centre of Excellence for Innovation in Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand.
² Scientific Instrument Academic Service Unit, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand.

Abstract

Flexible poly(L-lactide)-b-poly(ethylene glycol)-b-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.

Keywords: block copolymer; citric acid; poly(ethylene glycol); poly(lactic acid); thermoplastic starch.

Grants and funding

This research project was financially supported by Mahasarakham University. YB is also grateful to the partial support provided by the Centre of Excellence for Innovation in Chemistry (PERCH-CIC), Office of the Higher Education Commission, Ministry of Education, Thailand.