Thermal and mechanical properties of highly flexible poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) bioplastics: Effects of poly(ethylene glycol) block length and chain extender

Abstract

The brittleness of poly(L-lactide) (PLLA) bioplastic is the main disadvantage for practical applications. Herein, we report the synthesis of high-molecular-weight PLLA- b-poly(ethylene glycol)- b-PLLA (PLLA-PEG-PLLA) block copolymers by ring-opening polymerization of LLA. The highly flexible PLLA-PEG-PLLAs were prepared by reactive melt blending with an epoxy-based chain extender formed as long-chain branched structures. The effects of PEG block length and content of chain extender were investigated. The results showed that the chain extension reaction reduced crystallinities of the PLLA-PEG-PLLAs. All the chain-extended PLLA-PEG-PLLA films had no phase separation. The lower crystallinities of PLLA-PEG-PLLA films obtained with higher contents of chain extender enhanced the film drawability. The longer PEG block length resulted in higher strain at break and lower stress at the break of PLLA-PEG-PLLA films. These chain-extended PLLA-PEG-PLLAs have potential for use as highly flexible bioplastics.

Improvement in Thermal Stability of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic by Blending with Native Cassava Starch

“…PLLA and PLLA-PEG-PLLA were synthesized through ring-opening polymerization of L-lactide monomer (96% L-enantiomer content) at 165 °C in bulk under a nitrogen atmosphere, as described in our previous works [ 11 , 12 , 14 ]. Stannous octoate (95%, Sigma, St. Louis, MO, USA) was used as a catalyst.…”

“…However, the low flexibility of PLLA, due to its high glass-transition temperature (T g , around 60 °C), limits its use in many applications [ 7 , 8 , 9 ]. High-molecular-weight PLLA- b -poly(ethylene glycol)- b -PLLA triblock copolymers (PLLA-PEG-PLLA) have exhibited more flexibility than PLLA because of the high flexibility of PEG middle blocks [ 10 , 11 , 12 ].…”

“…Unfortunately, these pure PLLA-PEG-PLLAs had high melt flow ability (low melt strength), which is not appropriate for many processing applications, such as injection molding, blow film molding and extrusion molding [ 11 , 12 ]. The melt flow properties of PLLA-PEG-PLLA can be controlled by reaction with a chain extender to form long-chain branching structures.…”

“…The melt flow properties of PLLA-PEG-PLLA can be controlled by reaction with a chain extender to form long-chain branching structures. However, our previous works reported that the thermal stability of PLLA-PEG-PLLA decreased after the chain extension reaction [ 11 , 12 , 13 ]. The branching structures of the chain-extended PLLA and PLLA-PEG-PLLA suppressed its thermal stability by preventing molecular interactions.…”

On briefing the surface modifications of polylactic acid: A scope for betterment of biomedical structures

“…[48][49][50] Despite all, the degradation, molecular weight, and molecular weight distribution of PLA can be controlled through its crystallinity, which usually lend it a longer in vivo lifetime. [51][52][53][54] Being hydrophobic,…”