Effects of Methylenediphenyl 4,4'-Diisocyanate and Maleic Anhydride as Coupling Agents on the Properties of Polylactic Acid/Polybutylene Succinate/Wood Flour Biocomposites by Reactive Extrusion

Enhancing interfacial interaction and crystallization in polylactic acid-based biocomposites via synergistic effect of wood fiber and self-assembly nucleating agent

Incorporation of natural fibers into polylactic acid (PLA) provides a feasible pathway to improve the performance of PLA with a low environmental impact. However, the insufficient interfacial adhesion between fiber and matrix limits the reinforcement efficiency of fiber and final mechanical properties of the biocomposites. Herein we reported an efficient method to simultaneously enhance interfacial interaction, crystallization and mechanical performance of PLA-based biocomposites via combination of wood fiber (WF) and a self-assembly nucleating agent (TMC-300). The interactions between WF and TMC-300 and its influence on PLA, including interfacial crystal morphology, crystallization behavior, and mechanical performance were studied. The results showed that TMC-300 could self-assemble into dendritic-like structure on WF surface driven by hydrogen bonding, inducing the epitaxial crystallization of PLA. This unique interfacial crystallization integrated PLA matrix with WF, resulting in better interfacial adhesion. Under the optimal TMC-300 content (0.5 wt%), the flexural strength and notched impact strength of PLA composites increased by 10 % and 69 % compared with neat PLA, respectively. Additionally, TMC-300 and WF synergistically functioned as effective nucleating agents, which significantly accelerated the crystallization rate and improved the crystallinity of PLA. This work provides a new insight into the enhancement of interfacial bonding in natural fiber/PLA biocomposites.

Strategies and techniques for improving heat resistance and mechanical performances of poly(lactic acid) (PLA) biodegradable materials

Poly(lactic acid) (PLA) has attracted much attention as a substitute for petroleum-based plastics, but its low heat resistance limits its application range in packaging fields and disposable products. This paper summarizes the structural factors affecting the heat resistance of PLA and systematically summarizes methods to improve its heat resistance. PLA is a semi-crystalline polymer, and crystallinity, crystal size, and other factors are important factors affecting heat resistance. This paper systematically analyzes the means to control the crystallization behavior of PLA, and summarizes the effects of nucleating agents, cross-linking, grafting, and annealing processes on the crystallization behavior and heat resistance of PLA. The effects of PLA molecular chain cross-linking and grafting on the motility of PLA molecular chains and the heat resistance of PLA materials are further discussed from the perspective of PLA molecular chain segment movement. The research work on combining PLA with reinforcements such as high heat-resistant polymer materials, fiber, and nanoparticles to improve the mechanical properties and heat resistance of PLA by introducing rigid groups or structures is described in detail. Improving the heat resistance of PLA material is an important strategy to promote the application of biodegradable materials, and has broad research value and application prospects.

Effects of Coupling Agent and Thermoplastic on the Interfacial Bond Strength and the Mechanical Properties of Oriented Wood Strand-Thermoplastic Composites

Wood-plastic composites (WPC) with good mechanical and physical properties are desirable products for manufacturers and customers, and interfacial bond strength is one of the most critical factors affecting WPC performance. To verify that a higher interfacial bond strength between wood and thermoplastics improves WPC performance, wood veneer-thermoplastic composites (VPC) and oriented strand-thermoplastic composites (OSPC) were fabricated using hot pressing. The effects of the coupling agent (KH550 or MDI) and the thermoplastic (LDPE, HDPE, PP, or PVC) on the interfacial bond strength of VPC, and the mechanical and physical properties of OSPC, were investigated. The results showed that coupling agents KH550 and MDI improved the interfacial bond strength between wood and thermoplastics under dry conditions. MDI was better than KH550 at improving the interfacial bond strength and the mechanical properties of OSPC. Better interfacial bonding between plastic and wood improved the OSPC performance. The OSPC fabricated using PVC film as the thermoplastic and MDI as the coupling agent displayed the highest mechanical properties, with a modulus of rupture of 91.9 MPa, a modulus of elasticity of 10.9 GPa, and a thickness swelling of 2.4%. PVC and MDI are recommended to fabricate WPCs with desirable performance for general applications.