Study on Liquid Crystalline Properties and Fiber Forming Technology of Poly (p-Phenylene Terephthalamide) Solution
|Keywords||Poly- p-phenylene diamine terephthalamide Liquid crystal solution Dynamic Rheological Dry spray - wet spinning Heat treatment|
Poly-p-phenylene terephthalamide phenylenediamine (Poly (p-phenylene terephthalamide), PPTA) fiber is a high-performance aramid fibers in the aerospace, defense, composites and other aspects important applications. In this paper, polarized light microscope hot stage process and its solution dissolving PPTA LCD phenomenon; through differential scanning calorimetry PPTA molecular mass fraction and other factors on the melting temperature of the liquid crystal solution and phase transition temperature influence; using tablet rotational rheometer Research PPTA-H 2 SO 4 crystal solution of the dynamic rheological properties, analyzed and discussed the solution temperature, PPTA molecular weight and its distribution, mass fraction of complex viscosity, loss tangent, storage modulus, loss modulus and other parameters. Through mathematical fitting of the experimental results obtained PPTA-H 2 SO 4 index of non-Newtonian liquid crystal solution, zero shear viscosity, relaxation time, viscous flow activation energy and other parameters, and the establishment of a zero shear viscosity and weight average molecular weight between the empirical formula. Through the above experimental results for the subsequent spinning process provides a theoretical basis. Twin-screw fast dissolving PPTA-H 2 SO 4 LCD solution spinning. During spinning by varying the solids content of the spinning solution, the spinning pressure, nozzle diameter, the nozzle stretch ratio, the winding speed, the ratio of coagulation bath temperature and other factors which influence the performance of the fiber; by X-ray diffraction, stress relaxation, TG-depth study of experimental methods such as crystal fibers, orientation and other structural factors on the performance impact. Try different temperature and residence time and different strains of changing conditions on the mechanical properties of the fibers, preliminary exploration to obtain high modulus PPTA fiber heat treatment process. During the dissolution of the PPTA is dissolved after the first swelling, dissolution after a certain time, PPTA solution phenomenon will appear on the LCD, the liquid crystal in shear phenomenon is more pronounced. Compare PPTA Import and homemade liquid crystal solution prepared under a polarizing microscope pictures taken no significant difference. Take the first temperature and then cooling the process of raising the temperature differential scanning calorimetry analysis of the phase transition temperature is more accurate; endothermic peak when the temperature increased with PPTA mass fraction and molecular weight moves to a higher temperature rise; when the mass fraction of not PPTA solution of 19.5% of the melting peak and phase transition peak completely overlap in the melting process is accompanied by phase transformation; the contrary, the phase transition temperature higher than the melting. PPTA-H 2 SO 4 -shaped liquid crystal solution is a typical shear thinning fluid shear frequency increases with the solution of complex viscosity decreases rapidly, and the loss modulus loss tangent tanδ increased gradually and tends to increase slowly, the storage modulus curve does not change substantially; complex viscosity, storage modulus, loss modulus, loss tangent with the mass fraction of the polymer solution and the increase in molecular weight curve on the move, with the increase in temperature down. PPTA-H 2 SO 4 LCD solution to meet the power law flow curve equation obtained by fitting the non-Newtonian index n is very small, serious deviation from Newtonian fluid; n values ??with the solution the PPTA mass fraction increases, the temperature decreases, PPTA decreased with increasing molecular weight, but several aspects of the knife change impacts are not large. PPTA-H 2 SO 4 LCD solution to meet the Cross-Williamson equation, obtained by fitting the zero shear viscosity and relaxation time with the mass fraction of the solution increases, the temperature decreases , PPTA molecular weight increased with; PPTA-H 2 SO 4 crystal solution is highly viscous flow activation energy ΔE η , as the solution the PPTA mass fraction and molecular weight increases slightly increased. WLF equation using the time-temperature equivalence principle under the flow curve maximum scanning frequency 100rad · s -1 sup> widened to nearly 1000rad · s -1 sup>. Different temperatures logη 0 ~ logM w graph, you can get zero shear viscosity η 0 and the weight average molecular weight M w < / sub> relationship. vGP figure the minimum molecular weight greater the phase angle is smaller, plateau modulus G N 0 sup> = 1.92E5. Molecular weight distribution does not change the shape of the graph vGP, homemade polymer is slightly narrower than the imported polymer. As the draw ratio increased, decreased ejection velocity, the spinning temperature and the solids content increases the dope and polymer inherent viscosity increase, the fiber breaking strength and initial modulus were significantly increased, the fiber elongation at break decreased. Stretching ratio of discharge velocity and orientation of the fiber is not obvious; simultaneously with the ejection speed increases little change in crystallinity of the fiber, with the draw ratio increases, the crystallinity of the fiber increases, the stress relaxation rate. An ideal spinning process parameters: slurry temperature: 80 ℃; slurry concentration: 19%; spinneret diameter: 0.07mm; ejection speed: 25 ~ 40m/min; stretching ratio: 6 to 7; coagulation bath concentration: 8 ~ 10% H 2 SO 4 ; coagulation bath temperature: 5 ℃; dope can not place a long time. As the heat treatment temperature fiber, the fiber breaking strength and elongation at break decreased, and the initial modulus increased CV values ??of elongation at break increases. As the residence time increases, the heat treatment after the fiber breaking strength and initial modulus, first increased and then decreased, while the elongation at break decreases, increasing the CV value; as the temperature increases, the residence time of the fiber, the shorter the heat treatment, breaking strength and initial modulus maximum easier. The increase in tension as the heat treatment, the fiber breaking strength and initial modulus of the first increased and then decreased, continues to decrease the elongation at break, elongation at break value of CV rising; as the temperature rises, the heat treatment of the fiber Good tension reduction. Thus, the tension fiber fracture treatment helps to improve the strength and initial modulus. Initial modulus fibers and modulus after heat treatment is approximate linear relationship. With the initial modulus of the fiber increases, the modulus of the fiber after the heat treatment increases. After heat treatment, the fiber orientation changes slightly, the increase in crystallinity is more obvious; heat treatment temperature and tension changes on the fiber orientation and crystallinity obvious effect; residence time increases as the heat treatment, continues to have a small degree of crystallinity the increase step; increase in tension as the heat treatment, the fibers first decreased and then increased stress relaxation. The main innovation of this thesis points: (1) via differential scanning calorimetry analysis of two temperature method PPTA molten liquid crystal solution and phase transitions. (2) systematic analysis of the PPTA-H 2 SO 4 crystal solution of the dynamic rheology, and its influencing factors. (3) establish a zero shear viscosity and weight average molecular weight between the empirical formula. (4) using a twin-screw fast dissolving PPTA-H 2 SO 4 crystal solution is spun to prepare a high strength, high modulus of the PPTA fibers. (5) Direct treatment of PPTA spun fiber, preparation of high model PPTA fibers.