Novel Surface Modification Methods For High Performance Fibers And Its Interfacial Design And Adhesion Study With Rubber Matrix

Due to the excellent mechanical performance, chemical stability and special functionality, high performance fibers are regarded to be ideal reinforcement materials for high performance composites, and increasingly popular in the application of space and aviation, military and national defense, industry and medical treatments. Ultra-high molecular weight polyethylene fibers and aramid fibers are representative among the organic high performance fibers, owing to the excellent properties and processibility, as well as relatively mature industrialization. However, the inherently inert surface and high crystallinity confined the application of these two fibers in composites. Although high performance fibers are also best choice for framework materials of rubber composite, the application of high performance fibers in rubber industry is not common. Bio-inspired dopamine deposition and UV-induced graft polymerization were utilized in this study to modify above mentioned two fibers on account of simple procedures, eco-friendly raw materials, high efficiency, low cost and feasible equipments. Further interfacial design and adhesion properties of high performance fibers/rubber composites were studied. The application of ultra-high molecular weight polyethylene and aramid fibers in rubber composites was explored.(1) The bio-inspired surface modification of ultra-high molecular weight polyethylene (UHMWPE) fibers by dopamine was conducted. Thereafter, y-(2,3-epoxypropoxy)propytrimethoxysilane (KH560), bis[y-(triethoxysilyl)propyl]tetrasulfide (Si69) and ethylene glycol diglycidyl ether (EGDE) were applied for secondary functionalization, introducing epoxy and sulfide groups to the surface of UHMWPE fibers. The influence of grafting procedure, temperature and concentration of monomers on grafting yield were studied. Improved grafting degree was achieved with increase of temperature and concentration of monomers. The "one-step" process exhibited higher efficiency rather than the "two-step" method, and the mechanism behind was revealed. According to the results of single-fiber pull-out test and peeling test, the adhesion properties of UHMWPE fibers or fabrics were effectively improved. Resorcinol-formaldehyde-latex (RFL) dipping further enhanced the improvement, and exhibited excellent adhesion properties with satisfying aging and fatigue resistance.(2) Surface modification of meta-aramid (MPIA) fibers and para-aramid (PPTA) fibers by the bio-inspired poly(dopamine) (PDA) deposition and secondary functionalization was demonstrated in Chapter 4. Epoxy groups were introduced to the surface of MPIA fibers by using KH560 and EGDE as functionalization monomers, improving the adhesion of MPIA with rubber matrix by 62.5% and 53.8%, respectively. RFL dipping was followed after EGDE functionalization, and the improvement was increased to 132.2%. y-(methacryloxy)propyltrimethoxysilane (KH570) and butadiene-vinylpyridine (VP) latex were used to functional ize the PDA deposited PPTA fibers, introducing carbon double bonds. As a result, the adhesion properties were increased by 44.2% and 198.6%, respectively. What’s more, excellent heat and aging resistant adhesion properties were obtained. The adhesion properties after secondary functionalization with VP latex were comparable to that of industrial two-bath dipping treatment. Therefore, we can come to the conclusion that the bio-inspired secondary fucntionalization with VP latex is a feasible way to prepare eco-friendly bio-inspired dipping system.(3) In Chapter 5, y-(methacryloxy)propyltrimethoxysilane (KH570) and glycidyl methacrylate (GMA) were grafted to the surface of aramid fibers by UV-induced polymerization. Better adhesion properties with aging resistant were obtained for the aramid fiber treated by UV-induced graft polymerization, compared with that treated by industrial two-bath dipping method. However, the UV-induced surface modification would result in decrease of fiber strength due to the UV irradiation induced degradation of aramid fibers.(4) Tentative application of high performance fibers in rubber conveyor belts were explored in Chapter 6. Low rolling resistance (LRR) and low gravity of belts were two methods for preparation of energy saving conveyor belts. Aramid pulp--Sulfron(?) was applied to prepare LRR bottom cover of belts, resulting in the decrease of tan delta, heat build up and compression set. The test report of Hannover University, Germany illustrated that the belt with LRR bottom cover was 10-15% lower in indentation rolling resistance, indicating lower energy consumption. Aramid fabrics were supplied for preparation of three kinds of high performance conveyor belts with high strength, heat resistance and flame retardance. The mechanical properties of domestic aramid fibers are comparable to imported ones, however, more efforts should be made to improve the surface activity and adhesion properties, so as to enhance the industrial application of domestic aramid fibers. UHMWPE fibers with high surface activity and adhesion property can be also obtained with help of plasma treatment and dipping treatment, therefore, further application as reinforcement materials in rubber industry is promising.