Study On The Preparation And Characterization Of Polyoxymethylene Fiber

Polyoxymethylene (POM) is a linear polymer with high strength and high crystallization. It is a synthetic fiber with the best combination properties including high strength, high modulus, outstanding dimensional stability, excellent alkali resistance and chemical corrosion resistance, which provides POM fiber a promising future of all-round application.There are several major methods to prepare polyoxymethylene fiber. As far as we know, melt spinning, which can reduce costs and greatly improve efficiency, is a best method to realize POM fiber industrial preparation. However, high crystallinity, fast crystallize rate and the closeness of the melting point to the decomposition cause POM fiber structure non-uniform and affect fiber mechanical and thermal properties, which are the difficult points to steady production and improve the fiber properties. Therefore, it is very important to study POM melt spinning process and drawing process.In this study, thermal property, rheological behavior and thermal decomposition kinetics of POM were studied; the melt spinning process and drawing process of POM fiber were investigated. Finally, crystallization behavior, orientation structure, mechanical property, alkali and acid resistance of the fiber were analyzed.The physical properties of POM utilized in this study are as followed:melting point=162.03℃; melt index=9g/10min. It was found that the thermal decomposition of POM obeyed the first order law, decomposition activation energy E =367.87kJ/mol, thermal decomposition rate was less than 0.02%/min as temperature below 230℃. It was also found that POM is a non-Newtonian fluid, as temperature increasing from 190℃to 230℃, the non-Newtonian index of POM raised from 0.53 to 0.61, indicating polymer chains became more flexible. At the same sharing rate, the apparent viscosity of the system would decrease as the temperature increased. The viscous flow activation energy changed between 11.36-24.90kJ/mol at the shearing rate around 90-2500s-1.POM fiber was prepared by two step processes, melt spinning by twin-screw extruder and drawing in a water bath. Water medium had fast heat transfer rate and large heat capacity while water molecules served as plasticizer to reduce internal stress and make relative slip of molecule chains easily, which would certainly beneficial to steady production and improve the performance of POM fiber. The results show that the maximum draw ratio and crystallinity increased while the temperature of water bath increased; fiber orientation, breaking strength, initial modulus increased and elongation at break decreased while draw ratio increased. The mechanical properties of POM fiber attained were as followed: the maximum breaking strength 7.44cN/dtex; the maximum initial modulus 54.04cN/dtex and the minimum elongation at break 15.00%.