Renewable poly(lactic acid) (PLA) exhibits high strength and stiffness PLA is fully biodegradable and has received great interest However, the inherent brittleness of PLA largely impedes its wide applications In this article, the recent progress in PLA toughening using various routes including plasticization, copolymerization, and melt blending with flexible polymers, was reviewed in detail PLA toughening, particularly modification of impact toughness through melt blending, was emphasized in this review Reactive blending was shown to be especially effective in achieving high impact strength The relationship between composition, morphology, and mechanical properties were summarized Toughening mechanisms were also discussed © 2011 Wiley Periodicals, Inc J Polym Sci Part B: Polym Phys, 2011

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.22283

Research progress in toughening modification of poly(lactic acid)

Evolution of the bioplastics industry has changed directions dramatically since the early 1990s. The latest generation is moving toward durable bioplastics having high biobased content. The main objective is to replace “fossil carbon” with “renewable carbon”, a holistic strategy to mitigate climate change by minimizing the environmental impact of a product throughout its life cycle. Durable bioplastics is desired for multiuse long-term application in automotive, electronics and other industries. One necessary requirement for them is to be both tough and strong, yet the two attributes are often mutually exclusive. Does this mean a biobased and biodegradable polymer as polylactic acid (PLA) with its high strength but low toughness cannot be adopted for durable applications? Well, not exactly; this is where the concept of tailoring the properties of PLA to achieve stiffness–toughness balance along with acceptable heat resistance comes into play. In this perspective, we summarize the recent research progress ...

http://pubs.acs.org/doi/pdf/10.1021/acssuschemeng.6b00321

Perspective on Polylactic Acid (PLA) based Sustainable Materials for Durable Applications: Focus on Toughness and Heat Resistance

Super-tough poly(lactic acid) materials : Reactive blending with ethylene copolymer

Based on Takayanagi's two-phase model, a three-phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (E-c). In this model, fillers (sphere-, cylinder- or plate-shape) are randomly distributed in a matrix. If the particulate size is in the range of nanometers, the interfacial region will play an important role in the modulus of the composites. Important system parameters include the dispersed particle size (t), shape, thickness of the interfacial region (tau), particulate-to-matrix modulus ratio (E-d/E-m), and a parameter (k) describing a linear gradient change in modulus between the matrix and the surface of particle on the modulus of nanocomposites (E-c). The effects of these parameters are discussed using theoretical calculation and nylon 6/montmorillonite nanocomposite experiments. The former three factors exhibit dominant influence on E-c At a fixed volume fraction of the dispersed phase, smaller particles provide an increasing modulus for the resulting composite, as compared to the larger one because the interfacial region greatly affects E-c. Moreover, since the size of fillers is in the scale of micrometers, the influence of interfacial region is neglected and the deduced equation is reduced to Takayanagi's model. The curves predicted by the three-phase model are in good agreement with experimental results. The percolation concept and theory are also applied to analyze and interpret the experimental results.

Tensile modulus of polymer nanocomposites

Polyactide (PLA) was blended with an ethylene/n-butyl acrylate/glycidyl methacrylate (EBA-GMA) terpolymer and a zinc ionomer of ethylene/methacrylic acid (EMAA-Zn) copolymer. The phase morphology of the resulting ternary blends and its relationship with impact behaviors were studied systematically. Dynamic vulcanization of EBA-GMA in the presence of EMAA-Zn was investigated by torque rheology, and its cross-link level was evaluated by dynamic mechanical analysis. Reactive compatibilization between PLA and EBA-GMA was studied using Fourier transform infrared spectroscopy. The dispersed domains in the ternary blends displayed a “salami”-like phase structure, in which the EMAA-Zn phase evolved from occluded subinclusions into continuous phase with decrease in the EBA-GMA/EMAA-Zn ratio. An optimum range of particle sizes of the dispersed domains for high impact toughness was identified. Also, the micromechanical deformation process of these ternary blends was also investigated by observation of the impact-fra...

Interaction of Microstructure and Interfacial Adhesion on Impact Performance of Polylactide (PLA) Ternary Blends

The intrinsic brittle-ductile (craze-yield) behavior of polymers and blends are controlled by two chain parameters: entanglement density ve and characteristic ratio Cx. These chain parameters can be predicted from chemical structure. Therefore, the intrinsic brittle-ductile behavior of polymers and blends can be controlled by chemical structure using group additivity. The chemical composition and chain structure which can give the ultimate toughness in polymers and blends are discussed.

Souheng Wu

Papers

Control of intrinsic brittleness and toughness of polymers and blends by chemical structure: A review