Abstract
Abstract Poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) (PLLA-PEG-PLLA) is found to be more flexible than PLLA due to the flexibility of PEG middle blocks. Melt flow and mechanical properties of PLLA-PEG-PLLA were improved through post melt blending with a chain extender (CE). In this work, in situ chain-extended PLLA-PEG-PLLAs were synthesized by ring-opening polymerization in the presence of Joncryl® CE. The influence of CE content (1.0, 2.0, and 4.0 phr) on the gel content, melt flow index (MFI), thermal properties, and mechanical properties of the obtained in situ chain-extended PLLA-PEG-PLLAs was investigated. The gel content of in situ chain-extended PLLA-PEG-PLLA increased while the MFI and degree of crystallinity significantly decreased with increasing CE content. The in situ chain-extended PLLA-PEG-PLLA with 1.0 phr CE showed the best tensile properties. The extensibility of in situ chain-extended PLLA-PEG-PLLA films decreased when the CE contents were higher than 1.0 phr. These in situ chain-extended PLLA-PEG-PLLA films can be used as highly flexible bioplastics.
Highlights
Nowadays, biodegradable bioplastics are being extensively investigated as replacements of nonbiodegradableBlock copolymerization of PLLA with flexible polymers such as polyethylene glycol (PEG) forms PLLA-bPEG-b-PLLA triblock copolymers (PLLA-PEG-PLLA) with improved ductility and PLLA crystallization due to the high flexibility of the PEG blocks [9,10,11]
The in situ chain-extended PLLA-PEG-PLLAs were synthesized by ring-opening polymerization in the presence of chain extender (CE)
The in situ chainextended PLLA-PEG-PLLA with 4.0 phr CE had the highest gel content (70.4%), which was largely caused
Summary
Biodegradable bioplastics are being extensively investigated as replacements of nonbiodegradableBlock copolymerization of PLLA with flexible polymers such as polyethylene glycol (PEG) forms PLLA-bPEG-b-PLLA triblock copolymers (PLLA-PEG-PLLA) with improved ductility and PLLA crystallization due to the high flexibility of the PEG blocks [9,10,11]. High molecular weight PLLA-PEGPLLA has a melt strength that is too low for conventional processing. It has been reported that the chain extension of this PLLA-PEG-PLLA with chain extender (CE) improves its melt strength by the formation of branched structures [11]. CE has been extensively used for maintaining or increasing the molecular weight of PLLA [11,12,13], improving the melt strength of PLLA [14,15], and enhancing the phase compatibility of the PLLA-based blends [16,17]. Joncryl® is an important epoxy-based CE for PLLA. The epoxy groups of Joncryl® react with both the –OH and –COOH end groups of PLLA-forming branching structures [16,18]
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