Study on the Application of Kenaf Core as a Composite Reinforcement: Injection Molding of Kenaf Core/Poly(l-lactide) Compounds

ABSTRACT

Injection molding was performed using poly(l-lactide) (PLLA) as a matrix and by varying the reinforcements, i.e., dry-distilled kenaf core (D-core) or untreated kenaf bast fibers, and the physical properties for these composites were subsequently compared. The dry-distillation was able to reduce the moisture content of D-core by a maximum of 4.2% as compared with untreated control core. As a result, the hydrophobicity was increased, which contributed to favorable Charpy impact strength and tensile properties of the D-core/PLLA composite relative to the kenaf bast fiber/PLLA composite. Moreover, the puffing phenomenon, which arises when heating with a microwave oven due to the vaporization of water dispersed within the interfacial regions and associated softening of the PLLA matrix by the heated vapor, was completely suppressed for the D-core/PLLA composite, whereas a large puffing ratio was observed for the kenaf bast fiber/PLLA composite. Reducing the moisture content also effectively suppressed the occurrence of transesterification reactions, leading to a decrease in the molecular weight of PLLA. However, the apparent nucleation effect of the D-core remains slightly inferior to that for the hydrophilic bast fibers due to its stronger affinity for PLLA molecules.

摘要

在本研究中，使用聚（L-丙交酯）（PLLA）作为基质，并改变增强成分（即干燥的槿麻核，D核）或未经处理的槿麻纤维来进行注塑，然后比较这些复合材料的物理性质。与未经处理的对照核相比，干馏能够将D核的水分含量最多降低4.2%。结果，疏水性增加，从而使D核/PLLA复合物的夏氏冲击强度和拉伸性能高于槿麻纤维/PLLA复合物。此外，膨化现象（在微波炉中加热时产生的水蒸气分散在界面区域内，导致PLLA基质软化的现象）在D核/PLLA复合物中完全被抑制，而在槿麻纤维/PLLA复合物中观察到相当明显的膨化比。降低水分含量还有效抑制了酯交换反应的发生，从而导致PLLA的分子量降低。然而，由于D核对PLLA分子的亲和力更强，D核的表观成核效应仍略逊于亲水性韧皮纤维。

KEYWORDS:

• composite
• dry-distillation
• injection molding
• kenaf core
• PLLA
• surface affinity of reinforcement

关键词:

• 复合材料
• 干馏
• 注塑
• 槿麻核
• 增强的表面亲和力

Acknowledgments

The authors would like to thank Prof. Hitomi Ohara for the measurements of molecular weight of PLLA.