Research And Development Of Long Fiber Reinforced Polyamide 6 Composites

Long fiber reinforced thermoplastics (LFT) technologies have been achieved a rapid and constant development in recent years, and resulted in a significant method of preparing high-performance engineering materials. The main reason that LFT composites show more excellent properties than traditional short fiber reinforced thermoplastics (SFT) is that LFT technique could retain the fiber length in the greatest degree thus resulting in a higher reinforcing efficiency. LFT composites possess excellent mechanical properties, and have been widely used in industry area especially the automotive industry due to their characteristics of high manufacture efficiency and recyclability. In this paper, we prepared two types of LFT composites on a melt impregnation apparatus using long glass fiber (LGF) and long carbon fiber (LCF) as the reinforcement elements and polyamide 6 as the matrix, meanwhile various measurements were implemented to study the performance of the objective LFT composites. The main works include two parts as follows:1. Long glass fiber reinforced polyamide 6 composites were initially prepared to explore the LFT technique. The relationship between the content of LGF and the mechanical properties, heat distortion temperature (HDT) was discussed. The comparison of mechanical performance and fiber residue length between LGF/PA6 and SGF/PA6 composites was conducted. The results indicate that the enhancement of mechanical properties especially impact strength of LGF/PA6 composites exceeds that of SGF/PA6 composites, and it is interesting to note that the fiber residue length of the former one is almost as six times as that of the latter one. The primary factor that influences the properties gap of these two composites is the fiber residue length of them. The scanning electron microscopy (SEM) results indicated that the LGF was well impregnated in polyamide 6 matrix.2. LCF reinforced PA6/nickel powder composite that fully takes advantage of the conductivity of carbon fiber and the permeability of nickel powder was designed and fabricated on the basis of LFT technique for electromagnetic shielding and high mechanical property. The mechanical measurement indicates that the mechanical performance increased with the content of LCF, while that the addition of nickel powder did not have a great influence on mechanical properties. The conductivity measurement demonstrated that the composites presented excellent volume conductivity and the percolation network was formed under a low content of LCF. The dielectric test results indicated that the LCF/N1/PA6 composites exhibited a high lever of dielectric loss which suggested that much electromagnetic waves energy could be attenuated in the way of absorption loss. The investigation of electromagnetic shielding property and shielding mechanism that performed through a vector network analyzer, indicated that the composites obtained an outstanding shielding effectiveness and the primary shielding mechanism was absorption of electromagnetic waves. Moreover, thermal stability of LCF/Ni/PA6 composites was investigated by thermogravimetric analysis (TGA), and the resulting thermogramsdemonstrated the incorporation of LCF and nickel powders showed a positive improvement on thermal stability. The SEM observation on the microstructure of the resulting composites illustrated that good interfacial adhesion was formed between LCF and the matrix.