Toughening Glassy Poly(lactide) with Block Copolymer Micelles

Abstract

Poly­(lactide) (PLA), a compostable bioderived polyester, can be produced at a cost and scale that makes it an attractive replacement for nondegradable petroleum-derived thermoplastics. However, pristine PLA is brittle and unsuitable for use in applications where high impact strength and ductility are required. In this work we demonstrate that poly­(l-lactide) (PLLA) in the glassy state can be toughened significantly via addition of an amphiphilic diblock polymer. Notably, a PLLA blend containing only 5 wt% poly­(ethylene oxide)-b-poly­(butylene oxide) (PEO–PBO) exhibited tensile toughness and notched Izod impact strength over an order of magnitude higher than neat amorphous PLLA without a significant reduction in transparency or elastic modulus. For a series of PLLA blends containing PEO–PBO of fixed composition (∼70% volume fraction PBO), the toughness was inversely related to the molar mass of the added modifier with the highest toughness observed for the blend containing the smallest diblock (∼7 kg/mol). Interestingly, at fixed composition and molar mass poly­(l-lactide)-b-poly­(butylene oxide) (PLLA–PBO) exhibited a substantial but reduced toughening efficiency compared to PEO–PBO. We attribute this difference to a change in the solubility parameter of the amphiphilc block. Using TEM, we show that the greatest toughening is observed when the diblock modifier forms small cylindrical micelles that are well dispersed in the PLLA matrix. This morphology is facilitated by a negative Flory–Huggins interaction parameter (χ) between PEO and PLLA. These insights suggest a new and versatile strategy for the facile and efficient toughening of brittle thermoplastics.

Toughening modification of PLLA with PCL in the presence of PCL‐b‐PLLA diblock copolymers as compatibilizer

“…Tensile toughness of these blends was significantly enhanced through reactive processing, but the application of these blends was limited in the fields with high biomedical safety requirements, because of possible toxicities derived from the residual triisocyanate incorporated. Furthermore, the presence of copolymers could provide another route to enhance the toughness and compatibility of immiscibility blend systems, whose chemical nature was identical to the main components of blends . Thus, the different molecular structures of PCL‐co‐PLLA copolymer were extensively synthesized and widely acted as compatibilizer in reducing interfacial tension and improving interfacial adhesion of PCL and PLLA blends …”

Fabrication of PLLA with High Ductility and Transparence by Blending with Tiny Amount of PVDF and Compatibilizers

“…The brittleness does hinder its applications ranging from packaging materials to medical implants . To improve the elongation at break and impact strength, various modifier polymers (e.g., rubber or other polymers with excellent flexibility) have been widely employed to blend with PLLA . The binary blend, however, always undergoes phase separation because of weak interfacial interaction and poor miscibility between PLLA and other polymers.…”

The plastics revolution: how chemists are pushing polymers to new limits

“…This route typically has downsides, such as rendering some plastics less transparent. But CSP researchers have got around that problem by adding just 5% by weight of a low-cost, petroleum-derived polymer that contains some sections that are hydrophobic -water-insoluble -and others that are hydrophilic, or water-soluble 3 . These additives cluster together to create spherical structures, which render PLA substantially tougher without reducing its transparency.…”