Study Of The Structure Of High-Performance Fiber And The Preparation Of Specialty Paper

PPTA (poly (p-phenylene terephthalamide)) short-cut fiber is a kind of high-tech fiber with high strength, high modulus and thermal resistance. The fiber is a new indispensable material in national economic development and defense construction. Studying the structure of PPTA fiber and the preparation of PPTA-Pulp and PPTA paper become a hot research subject both at home and abroad. The strutuce of PPTA short-cut fiber and the preparation of PPTA paper are discussed which is significant and practical to the application of PPTA short-cut fiber.PPTA short-cut fiber was treated by higher power ultrasonic treatment and the fiber's deep structure was exposed by exfoliated the outer layers. The ultrafine structure of the fiber was studied by means of Scanning Electron Microscopy (SEM). PPTA-Pulp of different beating degree was prepared by beating. The relationship between beating degree, water retention value, rate of fibrillation and fines content of PPTA-pulp was investigated. The appropriate process to produce PCB aramid base paper made of PPTA short-cut fiber and PPTA-Pulp was studied. And the hot pressing of base paper was preliminarily discussed.The results obtains are as follows:1. The structure of PPTA short-cut fiber was complicated. The fiber not only had skin-core structure and multiple fibrillar structure, but also had tie bundles vertical to the fiber axis and kink banding existed on the surface of PPTA short-cut fiber. There were large fibrils with a diameter of 600nm on the surface layer of PPTA short-cut fiber, which had high orientation along the direction of the fiber axis. There were microfibrils with cylindrical structure paralleled to the fiber axis in the inner region of PPTA short-cut fiber, whose diameter was 30nm. The tie bundles had different length, the longer was 3μm and the shorter was 100nm. The width of tie bundles was between 30nm and 100nm, while the distance was between 100nm and 500nm. The existence of kink banding changed the fiber axis of PPTA short-cut fiber, and the changed angle of the axial direction a and (3 were 40°,25°respectively.2. The relationships between beating degree of PPTA-pulp and water retention value, rate of fibrillation and fines content was linear. The numerical relationships among them were Wrv=1.0958×Bd+40.809, Rf=0.0367×Bd+1.4944, and Fc=0.6886×Bd+43.774 respectively。The properties of PPTA-pulp could be evaluated through the determination of beating degree.3. The optimum process for PPTA base paper was as follows:the beating degree of PPTA-Pulp was 25°SR, the content of PPTA-Pulp and the PPTA short-cut fiber length of 3mm and 6mm were 80%,4% and 16% respectively. the obtained base paper weight was 75g/m2, the density was 0.26 g/m3,the tensile index was 10.2N·m/g, the tear index was 23.8mN·m2/g, the elongation percentage was 2.57%.4. The structure of PPTA paper after hot pressing became compact, and the density and the strength increased greatly. The optimum condition of hot pressing was as follows:the pressing was 2MPa, the temperature was 140℃. The tensile index and tear index of the obtained paper were 43.8N·m/g and 30.9mN-m2/g respectively.