Frącz Wiesław, Janowski Grzegorz, Bąk Łukasz
Department of Materials Forming and Processing, Rzeszow University of Technology, 35-959 Rzeszow, Poland.
Polymers (Basel). 2021 Jun 14;13(12):1965. doi: 10.3390/polym13121965.
This study assessed the impact of alkali treatment of hemp and flax fibers on mechanical properties (determined by means of the uniaxial tensile test, impact tensile strength test and hardness test), processing properties (the course of the extrusion and injection process) and usable properties (shrinkage of molded pieces, degree of water absorption) of biocomposites on the base of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) biopolymer. For this purpose, 1 mm of length flax and hemp fibers was surface-modified by means of aqueous solution of NaOH (sodium hydroxide) with concentrations of 2%, 5% and 10%. The composites were made using the extrusion technology. The test specimens were produced by injection molding technology. In total, eight types of biocomposites with modified and non-modified fibers were produced, and each biocomposite contained the same filler content (15 wt.%). Their properties were compared in some cases with pure PHBV polymer. In the case of biocomposites filled with hemp fibers, it was noted that an increase of the alkalizing solution concentration improved most of the tested properties of the obtained biocomposites. On the other hand, in the case of flax fibers, there was a significant decrease in most of the mechanical properties tested for the composite containing fibers etched by 10% NaOH solution. The obtained results were verified by examining fibers and the destroyed specimens with a scanning electron microscope (SEM) and an optical microscope, which confirmed, especially, the significant geometry changes of the flax fibers etched by 10% NaOH solution. This procedure also resulted in a significant change of processing properties-a composite of this fiber type required about 20 °C lower temperature during the extrusion and injection molding process in order to obtain the right product. These results lead to the important conclusion that for each filler of the plant-origin and polymer matrix, the fiber alkalization method should be selected individually in order to improve the specific properties of biocomposites.
本研究评估了碱处理大麻纤维和亚麻纤维对以聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（PHBV）生物聚合物为基体的生物复合材料的机械性能（通过单轴拉伸试验、冲击拉伸强度试验和硬度试验测定）、加工性能（挤出和注塑过程）以及使用性能（成型件收缩率、吸水率）的影响。为此，将长度为1毫米的亚麻纤维和大麻纤维用浓度为2%、5%和10%的氢氧化钠（NaOH）水溶液进行表面改性。复合材料采用挤出工艺制备。测试样品通过注塑工艺生产。总共制备了八种含改性和未改性纤维的生物复合材料，每种生物复合材料的填料含量相同（15重量%）。在某些情况下，将它们的性能与纯PHBV聚合物进行比较。对于填充大麻纤维的生物复合材料，发现碱化溶液浓度的增加改善了所得生物复合材料的大部分测试性能。另一方面，对于亚麻纤维，含10% NaOH溶液蚀刻纤维的复合材料的大部分测试机械性能显著下降。通过使用扫描电子显微镜（SEM）和光学显微镜检查纤维和破坏的样品对所得结果进行了验证，这尤其证实了10% NaOH溶液蚀刻的亚麻纤维的显著几何形状变化。该过程还导致加工性能发生显著变化——这种纤维类型的复合材料在挤出和注塑过程中需要约低20°C的温度才能获得合格产品。这些结果得出一个重要结论，即对于每种植物来源的填料和聚合物基体，应单独选择纤维碱化方法以改善生物复合材料的特定性能。
