Study On The Preparation And Properties Of Textile-ramie Fiber Reinforced In-situ Anionic Polyamide-6 Composites

Anionic polyamide-6(APA6),as a kind of excellent engineering plastics,is widely used in the machinery,chemical industry,metallurgy and other fields because of its higher molecular weight,crystallinity and excellent mechanical properties.However,due to the poor dimensional stability,low thermal deformation temperature,the strength and stiffness are not high enough of APA6 products,so the modification of APA6 has become a hot research topic in recent years.The glass fiber,carbon fiber and aramid fiber used for the modification of APA6 is the most common and effective method.However,with the enhancement of people’s awareness of environmental protection,to replace these synthetic fibers by the eco-friendly natural fibers as the reinforcement of polymer resin has attracted more and more attention.In this paper,by the means of vacuum assisted resin transfer molding(VARTM),textile-ramie fiber(RF)reinforced in-situ anionic polyamide-6 composites were prepared successfully with the heat treated ramie fiber and caprolactam as monomer.The effects of different surface modification methods of the ramie fiber on the polymerization system were mainly discussed,and found a set of effective heat treatment procedures.And the effects of the heat-treatment on the functional groups,the crystallization,the mechanical properties and the fracture morphology of the ramie fiber were studied.Meanwhile,the mechanical properties,thermal stability,as well as interfacial properties of the RF/APA6 composites were also investigated.At the same time,the effects of the different heat-treatment temperature of the ramie fiber and its content on the properties of RF/APA6 composites were investigated.The results showed that the crystallinity,the tensile strength andthe number of hydroxyl groups on the surface of the ramie fiber decreased after the heat-treatment.When the heat treatment temperature was lower than 260℃ the effect of the polar functional groups remained on the surface of the ramie fiber was not small in the process of in-situ anionic polymerization,thus the preparation of the RF/APA6 composites failed.The hydroxyl groups covering on the ramie fiber surface decreased significantly,the crystallinity,the tensile strength and modulus decreased after the 280℃ heat-treatment,but no obvious changes in the morphology of the ramie fiber.The mechanical properties of RF/APA6 composites was the best,the interfacial adhesion between the resin and the ramie fiber was excellent.Compared with the neat APA6,with the increasing of RF mass fraction in the composite,the tensile,flexural strength and modulus were found to be improved by the mechanical test.The degree of crystallinity of the composites slightly reduced as seen from the differential scanning calorimetry(DSC)measurements and a small amount of they-PA6 crystalline form appeared because of the inclusion of ramie fiber,which can be also confirmed by the X-ray diffraction analysis(XRD).Thermo-gravimetric analysis(TGA)showed that thermal stability of RF/APA6 composites was notably improved compared to the neat APA6.