Study On The Process And Property Of Polyurethane Meltblown Nonwovens

It is a severe shortcoming for traditional nonwovens that they have rather low elasticity and elastic recovery. This dissertation is done forresolving this problem.It is a good solution to make elastic nonwovens using elastic fibers. Some developed counties such as U.S. and Japan have made relative research in this field and accumulated some experience. However, it is in the beginning in China. The study of polyurethane meltblown nonwovens is seldom reported. This dissertation is helpful for developing the elastic nonwovens.Two kinds of polyurethane chips, G83 and B87, are used in the research. German HAAKE rheometer, DSC analyzer and X-ray diffractive instrument are used to analyze physical indexes. Polyurethane melt is pseudoplastic fluid presenting shear-thinning property. B87 shows higher apparent viscosity than G83 at the same temperature. The non-Newtonian index n of polyurethane melt is large at a high temperature, approaching Newtonian fluid. And the non-Newtonian index n increases with the rise of temperature. It presents that rise of temperature can enhance the flowing property, and reduce the elasticity of melt, which is of great avail for meltblowing production. The activation energy of viscose flow En decreases significantly with the increasing of shearing rate. Polyurethane is sensitive to the temperature, so the temperature control must beemphasized. X-ray diffractive method is used to measure the degree of crystallization. The result shows that the degree of crystallization of meltblowing nonwovens is higher than that of filament. The increasing of the degree of crystallization can enhance the strength of nonwovens.The production of meltblown nonwovens is carried out on the machine developed by our staff. The process is controlled by changing four parameters: die temperature, air pressure, die-to-collector distance (DCD) and the number of layer. The influence is analyzed on fiber fineness, tenacity, elongation, elastic recovery, pore size, warmth retention property and filtration property of nonwovens by changing these parameters. Die temperature is the final temperature of melt. Die temperature should be raised properly to reduce the elasticity of the melt on the premise of preventing the degradation of polyurethane. Thus the meltblowing is stable. In the case of DCD is more than 10 cm, the fiber fineness is influenced by the second drawing of air and interaction of fibers in the air. The largest pore size and mean pore size of meltblown polyurethane nonwovens increase with rising of the die temperature, decrease with rising of the air pressure and increase with DCD. The nonwovens have a good elasticity. The largest elongation is beyond 500% for both kinds of nonwovens. The elastic recovery is beyond 90% in the condition of 50% drawing. The elastic recovery decreases slightly with increasing the drawing ratio. In general, the polyurethane meltblown nonwovens show good properties. It can be used to produce elastic lining and elastic warmth retention materials.The application of neural network for the meltblown polyurethane nonwovens is studied in the end of the paper. Back-propagation network is used to predict the elastic recovery under four parameters, die temperature, air pressure, DCD and the number of layer. The prediction result is quite precise. The mean error is 2.99%. It is prompt and convenient to use BP in prediction. So neural network may take theplace of experience to guide the production of the meltblown polyurethane nonwovens.