| Basalt fiber reinforced thermoplastic composites possess several excellent properties, such as, high strength, high modulus, thermostable performance, recyclable, environmental adaptability and other characteristics. They were widely used in the automotive industry, aerospace and shipbuilding to achieve energy saving, environmental protection purposes. Research basalt fiber reinforced thermoplastic composite material has a certain practical significance.Long basalt fiber reinforced nylon 6 composites(LBF/PA6) were prepared by melting-impregnation method in this paper, and the optimal process parameters for preparing the composites were determined by studying the influences of different impregnation mold, tension force, mold temperatures on the efficiency of impregnation. The mechanical properties, non-isothermal crystallization, melting behavior, crystal structure, crystal morphology and interface morphology of the composites were investigated. Two interface modification methods were adopted to overcome the weak interfacial bonding of the composites. Hydrochloric acid and silane coupling agents to improve the effectiveness of the composite interface were also discussed.The results of the study on preparation process parameters of LBF/PA6 composites show, that the fibers impregnation in the composites was best by a group of roll system impregnation mold. Tension force has great influence on the effect of the composites impregnation, and the fibers were impregnated best when the tension force was 19 N. Mold temperature is also an important affecting factor for the impregnation, and the optimum temperature is 255℃.The mechanical properties of PA6 were significantly improved by the incorporation of long basalt fibers. The tensile, flexural and impact strength of the composites were improved 179.69%, 178.42% and 306.36% when the long basalt fiber loading comes to 40wt%. The results of dynamic mechanical analysis(DMA) show, that the storage modulus and glass transition temperature of the composites were also increased with the increase of fiber loading. The contribution of basalt fiber on storage modulus at high temperatures was significantly higher than that of low temperatures, and the incorporation of basalt fiber can significantly compensate for the wastage of modulus. This indicates that the increase of deflection temperature under load for composites.The long basalt fiber plays dual rules in the crystallization process of composites. Firstly, long basalt fiber work as nucleating agent accelerated crystallization speed leading to higher T0 and Tp, and on the other hand, large number of fibers restricted the mobility of PA6 chains result in the lower T0 and Tp. Melting curves of LBF/PA6 composites after non-isothermal crystallization and wide-angle X-ray diffraction(WAXD) analysis results revealed that two different crystal polymorphs α and γ crystals were formed in composites, whereas neat PA6 only the α structure appeared. A trans-crystallization layer around basalt fibers could be observed by a polarizing optical microscopy(POM) and their distribution is not uniform. Theoretical calculation of the critical fiber length suggested that poor interfacial bond strength existed between the fiber and the matrix; meanwhile, this phenomenon was revealed by scanning electron microscopy(SEM) images.The interface of composites can be effectively improved after fibers were treated by hydrochloric acid and coupling agents. The tensile strength and IZOD impact strength of the composites were improved 8.94% and 23.02% when the concentration of hydrochloric acid was 10%, and the processing time came to 1h. The mechanical properties of the composite were greatly improved because of the chemical bond formed by addition of silane coupling agents. The best interface obtained by using KH550 while the tensile strength and IZOD impact strength of the composites were improved 17.46% and 30.52%. |
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