Fibers of long-fiber-reinforced thermoplastic (LFT) pellets are longer than those of short-fiber-reinforced thermoplastic (SFT) pellets produced by extrusion. To overcome the fiber length limitations of the SFT pellets, LFT pellets were prepared by a pultrusion process using continuous fibers, which afforded longer fibers. Currently, long glass-fiber-reinforced polypropylene (LGF-PP) materials, which are one of the growing markets of the plastics industry, are typically used, particularly for applications in the automotive industry where lightweight performance and cost savings are required. The LFT pellets are primarily converted into the final product by injection molding. During the injection molding process, the LFT pellets are broken and the fiber length decreases as a consequence. In this study, glass and carbon-fiber-reinforced polypropylene of various pellet lengths (3-16 mm) were prepared by impregnating pultrusion process to evaluate the effect of mechanical properties according to fiber length. The length of the residual fibers recorded after injection molding were observed to decrease in proportion to the pellet length. Even with LFTs having the same material composition, the mechanical properties was different after injection molding according to the residual fiber length. In this injection molded LFT, the flexural modulus was higher as the residual fiber length was shorter. The impact strength was larger in samples without adhesive resin and the observed differences were larger for longer fiber lengths. From these results, the mechanical properties of LFT can be improved by understanding the properties of long fibers.

中文翻译：

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纤维长度对注塑长纤维增强热塑性塑料力学性能的影响

长纤维增强热塑性（LFT）颗粒的纤维比通过挤出生产的短纤维增强热塑性（SFT）颗粒的纤维更长。为了克服SFT粒料的纤维长度限制，通过拉挤法使用连续纤维制备LFT粒料，所述连续纤维提供更长的纤维。当前，通常使用长玻璃纤维增​​强聚丙烯（LGF-PP）材料，该材料是塑料工业的增长市场之一，特别是在要求轻量化和节省成本的汽车工业中。LFT颗粒主要通过注塑成型转化为最终产品。在注塑过程中，LFT粒料破裂，因此纤维长度减少。在这个研究中，通过浸渍拉挤成型工艺制备各种颗粒长度（3-16 mm）的玻璃纤维和碳纤维增强聚丙烯，以根据纤维长度评估机械性能的影响。观察到注塑后记录的残余纤维的长度与粒料长度成比例地减少。即使具有相同材料组成的LFT，注射成型后的机械性能也会根据残余纤维长度而有所不同。在该注射成型的LFT中，残余纤维长度越短，弯曲模量越高。在没有粘合剂树脂的样品中，冲击强度较大，并且对于较长的纤维长度，观察到的差异较大。从这些结果，可以通过了解长纤维的性质来改善LFT的机械性质。