Study On Preparation And Performance Of Nylon Membrane

In this dissertation,skinless polyhexamethylene adipamide(Nylon66)membranes were prepared by immersion-precipitation process,which have the unique structure of net-shape.The mechanisms of membrane formation and absorption of nucleic acid were studied.The main experiments and results were summarized as follows:Nylon66 membranes were prepared by three Nylon66 materials with different molecular weight.It was found the morphology of Nylon66 membranes was greatly influenced by the molecular weight of polymer.The pore sizes and the crystallization particle inside the structure increase along with the increase of the molecular weight of polymers.When the molecular weight was less than 30,000,the prepared membrane was fragile.The membrane prepared in the following experiments used the 2th Nylon66,for the particle can reduce the adsorption of nucleic acid.By adding different alcohol as additives in the casting solution,the phase diagrams for polymer solution of Nylon66/formic acid/Water/Additive system were determined by cloud-point method.The additives were methanol,ethanol,n-propanol or n-butanol respectively.It was found that both solid-liquid and liquid-liquid demixing existed during phase-inversion process.Solid-liquid demixing is ahead of the liquid-liquid demixing,and crystallization result in the solidification of membrane in the membrane formation process for the studied system.The capability of additive leading to the action of crystallization was decrease along with the sequence of methanol,ethanol,n-propanol and n-butanol.Membrane prepared by adding methanol as additive possesses better morphology and performance.In the further experiments, the effect of content of additive on the prepared membrane was studied using methanol as additive.With the increasing of the content of methanol in the dopes,the mean pore size of the prepared membrane were decreased.The pore sizes were between 0.293μm to 3.288μm.Temperature and composition of the coagulation bath can influence the membrane obviously.Adding solvent in coagulation bath would lower the diffuse of solvent and non-solvent between casting solution and bath.The influence of the amount of formic acid in coagulation bath was studied.When formic acid is free in the coagulation bath,the membrane prepared had crystallite on he surface because of rapid reaction,and the membrane was fragile when the coagulation bath had high content of formic acid.Moreover,it was found that higher coagulation bath temperature tends to increase the porosity,water flux and pore size of the prepared membrane.The adsorption mechanism of Nylon66 membrane to nucleic acid was researched. The adsorption appeared to follow a typical Langmuir model.The free enthalpy of the adsorption reaction of nucleic acid onto the membrane surface was -40.95kJ·mol^-1, and the activation energy was 16.94kJ·mol^-1,the results shown that the adsorption of nucleic acid was physical adsorption.The action may attribute to Vander waals interaction,hydrophobic bonding and hydrogen bonding.The adsorption reacted by itself as the Gibbs free energy was less than zero.By studying the effects of different pore size on the amount of adsorbed nucleic acid,it was found the amount had no distinction when the pore size within the range of 0.2-0.4μm.But when the pore was larger than 0.4μm,the adsorption amount tended to decrease with the increasing of the pore size.The largest adsorption amount was 84.2μg/cm².