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PLA

 

Poly(D,L-Lactide)

PLA is a leading candidate for consumer and biomedical applications, and the ability to tailor its mechanical, physical, microstructural, chemical and degradation properties for specific applications makes the market capacity of PLA products unlimited and that has catalyzed an extensive and growing amount of research aimed at utilizing these materials in innovative ways and applications. The intention of this work is to give an overview on the state of the art of research activities on PLA’s physical and mechanical properties, detailing a wide range of options for properties improvement such as chemical composition manipulation (D/L ratio), processing, additives, and plasticizers, and polymeric component blending. This review has also covered the major concerns about PLA physical and mechanical property variation during processing, recycling, biodegradation, and aging, as well as discussed the thermal instability impact on these properties. The last part of this review has provided an overview of PLA’s physical and mechanical properties’ role and function in widespread application. Our vision for PLA’s future comes in agreement with the logical belief that there is no one material able to satisfy all design parameters in all applications. So, it can be anticipated that future development will keep including blends of PLA, copolymers, and impact-modified products, which will also further expand the applications where this unique polymer can be used. Besides that, we do expect for the nearby future to increase research interest in the following four areas: a) PLA blends stability: recently, several PLA blends based synthetic or natural components have been reported and found very efficient in PLA properties improvement [235,330–343]. However, very limited attention has been given to studying blends stability under different aging conditions (e.g. in different environments, during storage, during reprocessing), this part is highly essential and should be further focused on the impartial evaluation of these new compositions advantage, in terms of durability and applicability, in comparison to classical reported compositions (PLA: PGA, PLA: PCL, etc.). b) PLA-based nanocomposites: the linkage of a 100% bio-originated material and nanomaterials opened new windows for becoming independent from petrochemical-based polymers and many of PLA’s weaknesses have been resolved [172,173]. This new generation of PLA-based nanocomposites was found to exhibit significant improvements, at very low filler contents (0.5–5% w/w), with the help of nanotechnology and providing safe PLA nanocomposites. The research and development of bio-nano composite materials for packaging applications (especially for direct food contact packaging materials) are expected to grow in the next years, due to the possibility of improving both packaging performances and process technology of biopolymers. In this area, we have also found that less attention has been given to inorganic nano-particles while various have been recognized as possible additives to enhance the polymer performance, their potential in combination with PLA should be further studied. c) Composites of fiber mixtures: such mixtures combine the positive properties of different fibers. Learning from nature what the function of fiber in a plant is we can design the composite properties by adding seed fibers with high elongations for improved impact or stem fiber for improved stiffness. The role of the reinforcing fiber should be more focused on future research activities of PLA composites. Playing with the different fiber characteristics a design of composite properties is possible. The results have shown so far that the investigated composites with their various characteristics can be used for different technical applications, each suiting specific requirements. d) Computational modeling of PLA behavior for different applications: the magnitude of experimentally observed nonlinear behaviors of PLA’s properties increases the importance of computational modeling to both understand how a device-based lactic acid will behave in a given environment, and to optimize the device for a given application. Several carefully developed constitutive models are now under development for predicting the material response in different load environments (i.e. simulating PLLA stent fixed inside the artery). These models, if applied properly, can provide great insight into the response of various materials and designs. Due to the high interest in this area from both academia and industry, we can only expect computational modeling to become even more powerful in the coming years.