| Using selectively permeable membrane as the principal protective material, this thesis extensively studied and established the membrane processing, mass transport model, and protection mechanisms. Following conclusions has been obtained:1. The membrane structure was analyzed through WAXD, DSC, SEM, FESEM, and Porosimeter testing. The results showed the porosity and pore diameter of the membrane increases with the stretching ratio and heat setting temperature, and with the increase of the transverse stretching velocity, the porosity increases and pore diameter decreases. Stretching and heat setting will decrease the crystallinity, and after heat setting, the structure of the PTFE membrane is stabilized with its breaking extension decreased.2. Two types of selectively permeable PTFE/PU membrane were made by PU coating and co-stretching approach.. SEM analysis results showed that micropores may exist on the PU layer of the PU coated membrane due to the solvent volatilization, but the PU layer of the co-stretched PTFE/PU membrane was solid without micropores.3. The gas permeation mechanism was analyzed by the self-made gas permeation meter. The test showed that the gas molecules permeate the membrane through Knudsen diffusion and viscous flow, and the gas permeation coefficient is proportional to the 3.68 power of the pore diameter, and proportional to the -0.5 power of the gas molecular weight. This result reveals that the PTFE membrane has the ability to prohibit the permeation of partial toxic gas with large molecular size, and the membrane can used as the basic component for the building of chemical protective material. Under the guidance of the mass transport model, PTFE membranes with smaller pore diameters were made in order to lower the gas permeation coefficient. PTFE/PTFE asymmetrical membranes were made by base belt welding, laminating and biaxial stretching successively, and this asymmetrical membrane has much lower porosity and pore size due to the crossing and overlaying of the fibrils. Under the same process parameters, the average pore diameters of the PTFE/PTFE asymmetrical membrane are decreased from 0.560 to 0.369 nm, which considerably lowered the gas permeation coefficient and greatly improved the protection against the poisonous gas with large molecular size. Gas permeates through the membrane by dissolution-diffusion mechanism, and permeation through the PU layer is critical and dominant of the whole permeation process of the PTFE/PU membrane.4. The water vapor transmission (WVT) property was tested in accordance to the GB/T 12704-91 standard, and the results indicated:(1) With the same porosity, pore size and thickness of the PTFE membrane, the dominating factors which influence the WVT are the ambient temperature and humidity.(2) For the membranes made by co-stretching method, water molecules are dissolved into the PUlayer first, and then diffuse to the under PTFE layer by dissolution-diffusion mechanism, and then by molecular diffusion to the surface of the water absorbable material. The dissolution-diffusion process in the PU layer is critical to the whole water vapor transmission rate. The PU layer thickness and ambient temperature and humidity all contribute to the WVT. (3) For the membranes made by PU coating method, the WVT is much higher than the membranes made by co-stretching method because of the pores in the former membranes.5. The PU coated selectively permeable membrane laminated fabrics were tested for its anti-virus, WVT, waterproof, antistatic, antibacterial properties. Results showed the anti-virus property is more than 99%, WVT is more than 10000 g/m2.24h, which resolved the contradiction between virus protection and water vapor permeation. Besides, this laminated fabric also has good protective abilities against blood and body fluids penetration, and good properties of waterproof, bacteriostatic, antistatic, flame retardant properties, which can be used as medical protective material, and played critically important role in the success against SARS last year.6. This thesis put...
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