Natural Fiber-Reinforced Polylactic Acid, Polylactic Acid Blends and Their Composites for Advanced Applications

Polylactic acid (PLA) is a thermoplastic polymer produced from lactic acid that has been chiefly utilized in biodegradable material and as a composite matrix material. PLA is a prominent biomaterial that is widely used to replace traditional petrochemical-based polymers in various applications owing environmental concerns. Green composites have gained greater attention as ecological consciousness has grown since they have the potential to be more appealing than conventional petroleum-based composites, which are toxic and nonbiodegradable. PLA-based composites with natural fiber have been extensively utilized in a variety of applications, from packaging to medicine, due to their biodegradable, recyclable, high mechanical strength, low toxicity, good barrier properties, friendly processing, and excellent characteristics. A summary of natural fibers, green composites, and PLA, along with their respective properties, classification, functionality, and different processing methods, are discussed to discover the natural fiber-reinforced PLA composite material development for a wide range of applications. This work also emphasizes the research and properties of PLA-based green composites, PLA blend composites, and PLA hybrid composites over the past few years. PLA’s potential as a strong material in engineering applications areas is addressed. This review also covers issues, challenges, opportunities, and perspectives in developing and characterizing PLA-based green composites.

Treatise on Sustainable Infrastructure Construction: Green Composites, Cross Laminated/Mass Timber, Wood Truss Connectors, Nondestructive Technologies, Health Assessment and Monitoring: Utility Poles and Geofoam

The understanding of the engineering performance of green laminated composites is necessary to the design of load bearing components in building and infrastructure construction, and packaging applications. These components are made of outer thin laminae called skins or faces and a thick inner layer called core. The use of bonding is unavoidable in the assembling of these composite products. Like all materials, the bonding materials have finite mechanical properties, e.g. stiffness, but when used in the literature, they are assumed perfectly rigid. That is an unrealistic assumption. Our analytical solutions change this assumption by using the real properties of bonding. In general, the analytical formulations are based on the equilibrium equations of forces, the compatibility of interlaminar stresses and deformation, and the geometrical conditions of the panels. Once solutions are obtained, the next step is to evaluate them. The numerical evaluations proved that perfect rigid bonding in laminated composites greatly underestimates the true performance. At low values of adhesive stiffness, the serviceability is multiple orders of magnitude of that at high values. The logical question is thus: what constitutes perfect bonding? The answer to this question lies in the core-to-adhesive stiffness. The lower the ration is the higher the error in using the rigid-bond theories. It is worth noting that green-composites in this chapter refer to components made of traditional materials such as wood, in addition to newly developed bio-based and bio-degradable and bio-based composites, made of renewable resources. In addition, bonding and adhesive are used interchangeably.

The Use of Mussel Shell as a Bio-Additive for Poly(Lactic Acid) Based Green Composites

Mussel shell is one of the most hazardous aquaculture wastes and its powder was used as an additive for bio-degradable poly (lactic acid) in this current study. Bio-composites were fabricated via conventional melt mixing technique followed by an injection moulding process. The effects of mussel shell powder inclusion on mechanical, melt-flow, water uptake and morphological performance of poly (lactic acid)-based green composites were reported.

Improving the Mechanical Ductility and Toughness of Injection-molded Polylactide Pieces by the Dual Incorporation of Liquor Waste Derived Spent Coffee Grounds and Oligomers of Lactic Acid

This work puts the Circular Bioeconomy’s concept into action, originally valorizing residues from the beverage liquor coffee industry into reinforcing fillers for green composites of polylactide (PLA). The as-received spent coffee grains derived from liquor waste were first milled to obtain the so-called spent coffee grounds (SCGs), which were then incorporated at 20 wt.% into PLA by extrusion. With the aim of improving the compatibility between the biopolyester and the lignocellulosic particles, two oligomers of lactic acid (OLAs), namely OLA2 and OLA2mal, being the latter functionalized with maleic anhydride (MAH), were both added during the extrusion process at 10 wt.%. The resultant compounded pellets were finally shaped into pieces by injection molding for characterization. Results showed that, as opposite to most claims published in the literature of PLA composites based on lignocellulosic fillers derived from soluble coffee wastes, the incorporation of liquor waste derived SCGs increased the ductility of the pieces by nearly 280% due to their high coffee oil content. The incorporation of OLA2 and OLA2mal contributed to improve the impact strength of the pieces by approximately 6% and 12.6%, respectively. The higher performance of OLA2mal was ascribed to a reduction of crystallinity in the green composite due to the chemical interaction by the MAH groups. However, the incorporation of SCGs into PLA slighlty reduced the thermal stability and yielded a dark-to-brown color, whereas it also delayed the disintegration rate of the pieces in controlled compost soil. Therefore, the results attained herein open up novel opportunities for the development of green composites of PLA with higher ductility and toughness through the valorization of liquor coffee wastes.