Study Of Synthesis And Modification Of Blocked Water-borne Polyurethane

The WBPU is short for water-borne polyurethane, which is dispersed in the water medium. It is non-toxic, non-polluting and beneficial for environment. The blocked water-borne polyurethane is synthesized through blocking the isocyanate groups which may improve its storage stability at normal temperature, however at the high temperature the blocked isocyanate groups can be released and react with fabrics, coatings and dyes. As a result it gives certain performances to the fabrics. Applying the WBPU rationally is not only useful for fabric finishing, but also does good to the environment.In this paper, toluene diisocyanate(TDI), polyether polyols(F-6), and sodium bisulfite were used for reaction. By pre-polymerizing, blocking and emulsifying the blocked water-borne polyurethane was obtained finally. Meanwhile it could be modified with organic silicon. The influences of condition on the performance of water-borne polyurethane were discussed, such as the condition of pre-treatment of raw materials, pre-polymerizing and blocking process factors, etc. The best synthesis technology was obtained:the temperature rising rate was2℃/min, the dehydration temperature was120℃, the dehydration time was120minutes; the R value was2.0, the pre-polymerizing temperature was65℃, time was180minutes, the ratio of n(NaHSO3)/n(-NCO) was2.0:1, the ratio of n(Na2SO3)/n(NaHSO3) was0.2, the mass concentration of sodium bisulfite was15%, the dosage of isopropanol was30%(relative to the whole mass of pre-polymer), the blocking temperature was about0～5℃, the blocking time was30minutes, the emulsifying time was60minutes. At the same time blocked water-borne polyurethane was modified by organic silicon coupling agent KH-550, the modifying temperature was45℃, time was60minutes and KH-550dosage was5%.The blocked water-borne polyurethane using as cross-linker was applied in pigment printing, which could raise the dry rubbing fastness of cotton fabric grade from grade3-4to grade4-5and wet rubbing fastness of dyed cotton fabric from grade3to grade4. The modified blocked water-borne polyurethane was applied for anti-wrinkle and the pilling resistance, which could not only raise the wrinkle recovery angle of cotton fiber from79.4°to152.0°and that of CVC fiber from220.2°to279.7°, but also improve the pilling resistance grade of cotton knitted fabric from grade2～3to grade4. Meanwhile the product with chain extending course and without chain extending course were compared. The result shows that the performance of product without chain extending course was as well as the other.Moreover, the FTIR analysis revealed that the products were organic siloxane modified blocked water-borne polyurethane. According to the SEM test, the products were reacted to fabrics with film on the surface. To sum up, this water-borne polyurethane product was a new excellent finishing agent without formaldehyde and had an extensive applying prospect.