Vidhya Nagarajan

Overcoming the Fundamental Challenges in Improving the Impact Strength and Crystallinity of PLA Biocomposites: Influence of Nucleating Agent and Mold Temperature

Poly(lactic acid) (PLA), one of the widely studied renewable resource based biopolymers, has yet to gain a strong commercial standpoint because of certain property limitations. This work is a successful attempt in achieving PLA biocomposites that showed concurrent improvements in impact strength and heat deflection temperature (HDT). Biocomposites were fabricated from a super toughened ternary blend of PLA, poly(ether-b-amide) elastomeric copolymer and ethylene-methyl acrylate-glycidyl methacrylate and miscanthus fibers. The effects of varying the processing parameters and addition of various nucleating agents were investigated. Crystallinity was controlled by optimizing the mold temperature and cycle time of the injection process. With the addition of 1 wt % aromatic sulfonate derivative (Lak-301) as a nucleating agent at a mold temperature of 110 °C, PLA biocomposites exhibited dramatic reduction in crystallization half time to 1.3 min with crystallinity content of 42%. Mechanical and thermal properties assessment for these biocomposites revealed a 4-fold increase in impact strength compared to neat PLA. The HDT of PLA biocomposites increased to 85 °C from 55 °C compared to neat PLA. Crystallization behavior was studied in detail using differential scanning calorimetry and was supported with observations from wide-angle X-ray diffraction profiles and polarized optical microscopy. The presence of a nucleating agent did not alter the crystal structure of PLA; however, a significant difference in spherulite size, crystallization rate and content was observed. Fracture surface morphology and distribution of nucleating agent in the PLA biocomposites were investigated through scanning electron microscopy.

1 – Commercial potential and competitiveness of natural fiber composites

Todays social conscience, driven by environmental consciousness, is challenging and demanding the industry and designers to develop ingenious and revolutionary materials that will reduce the greenhouse gas footprints left on the earth. Several years of cumulative research has been conducted on the usage of natural fibers for various applications, one main area being composite materials. Natural fiber composites (NFCs) are also alternatively referred to as biocomposites. For any potential application of NFCs to be commercially successful, it is important to realize the full advantage of material properties and have a general understanding of challenges involved in adopting them, including processabilty on a commercial scale and sustainable scalability. The first part of this chapter provides an overview of natural fiber classification, advantages, and challenges with a special focus on supply chain management. Factors that offer NFCs a competitive edge over traditional composites are elaborated, followed by a discussion on the current market scenario, growth prospects, and future developments.