Research On The Coagulation Of Waterbrne Polyurethane Film In The Acid Bath

Waterborne polyurethane (WPU) was a new type of polymer developed in the 1950s, which had characteristics of a wide range of adjustable hardness, wear resistance, water resistance, chemical resistance, good adhesion, and film formation at lower temperature, and so on. The main chain of WPU was carbamate (-NH-COO-) chain, the biggest advantage of WPU was that its solvent was water, which had a series characteristics of non-toxic, non-pollution, non-combustible, energy saving and security, meanwhile, WPU also had the same characteristics to Solvent-based polyurethane,such as easy operation, modified and film formation at low temperature. With the environmental pressures increasing, water-based polyurethane instead of solvent-based polyurethane had become an indisputable trend facts. Although the performance of WPU was good, some areas of its application was still in the experimental research and development stage, and there was a certain gap between WPU and solvent-based polyurethane.In this paper, the WPU was prepared by acetone method. Fourier transform infrared scanner (FTIR) was uesed to representation of WPU, and the results showed that the product had the expected chemical structure. By thermal gravimetric analysis (TGA), thermal stability of polymers was characterized, gel permeation chromatography (GPC) was used to analyze molecular weight, and the film's solid content, modulus (kg/cm2), elongation (%) and tensile strength (kg/cm2) were tested. The results showed that the prepared waterborne polyurethane (WPU) had good thermal stability and molecular weight distribution, phase separation in the hardness degree and the mechanical strength of membrane reached the demands of synthetic leather water-based polyurethane.Adding a certain proportion of thickener, flow agent, wooden powder additives into WPU, in acetic acid bath, film was prepared after demulsification. Comparing the mechanical strength of this film to that made with natural drying method; and comparing scanning electron microscope (SEM) to that membrane perpared by solvent PU wet method, results showed that:thickener and flow agent were helpful to obtain uniformity and flat membrane in acid bath; Comparing mechanical performance of acid bath demulsification method to natural drying method, it was found that: membrane prepared by acid bath demulsification method was thin enough to get transparent film, its mechanical performance had little difference from natural drying method; If the film prepared by acid bath method was thicker or added wood powder, Film attained was not transparent, its mechanical performance had much difference from natural drying method.SEM characterization showed there were lots of porous structure in the surface and cross section of WPU demulsification acid bath method, among them its porous structure without adding wood powder was more abundant than that adding wood powder; but no matter what kind, compared to solvent-based PU wet method, microporous structure difference was more obvious.