| The hydrophilic of waterborne polyurethane affected the mechanical properties and hydrophobicity of water borne polyurethane film, and it affected the water repellency and hydrostatic pressure of coated fabrics, which could affect its application in the field of coating. For this reason, people tried to modify waterborne polyurethane in order to improve its water repellency and hydrostatic pressure, thereby increase the application degree of waterborne polyurethane in coating areas. Jiang Hongquan who used castor oil to modify polyurethane in order to increase the degree of crosslinking of film by castor oil crosslinking and double bond oxidative self-crosslinking for good mechanical properties of waterborne polyurethane; at the same time through the introduction of a hydrophobic group of castor oil, the hydrophobic properties of the water polyurethane film was improved. However, the hydrophobicity of the film surface still did not reach the requirements for ideal hydrophobic of coated fabric. Hua Jijun who used silicone to modify polyurethane, the study results had shown that the polysiloxane segments could migrate and enrich easily to the surface of modified polyurethane film during its forming process, which reduced greatly the surface energy of the film, and improved greatly the film’s water resistance. In this paper, on the basis of the above-mentioned previous studies, waterborne polyurethane was modified by castor oil and polysiloxane in order to improve hydrophobicity and mechanical properties of waterborne polyurethane film. The research contents and results were as followings. Part 1 Preparation and application of castor oil modified waterborne polyurethaneIn order to enhance hydrostatic pressure of the fabric coated with waterborne polyurethane, a castor oil(CO) modified waterborne polyurethane emulsion was prepared with isophorone diisocyanate and polyether 210 as raw material, CO as a modifier, 2,2-dimethylol propionic acid(DMPA) as hydrophilic linear chain extender, and applied in coating for polyester fabric. The effects of dosages of CO and DMPA on the properties of modified waterborne polyurethane emulsion and its film were studied, the conditions of coating process of the modified-waterborne polyurethane were optimized and the application performance of the coated fabric was tested. The results showed that: with the increase of the dosages of CO, the particle size of modified emulsion became larger, and its distribution became wider, the stability of the emulsion deteriorated, and appearance of the emulsion became milky white from transparent; the water contact angle of the film increased, and water absorption of the film decreased, tensile strength of the film increased first and decreased then, and its elongation at break decreased. With the increase of the dosages of DMPA, the particle size of modified emulsion became smaller, and its distribution became narrower, stability of the modified emulsion became good, appearance of the modified emulsion became transparent from milky white; water contact angle of the film of modified emulsion decreased, water absorption of the film increased, the tensile strength of the film increased, and its elongation at break reduced. When dosage of CO was 7%, and dosage of DMPA was 4%, the stability of modified emulsion was good, the contact angle of film was 97.5° and water absorption of the film was 15.3%, tensile strength of the film was 27.5Mpa, its elongation at break was 407%. the optimal conditions of coating process of modified waterborne polyurethane were as follow: the dosage of coating agent was 10 g / m2, baking temperature was 160℃,baking time was 90 s. The contact angle of the coated fabric was 114.2 °, hydrostatic pressure of the coated fabric was 1.34 Kpa, the tear strength of coated fabric was 168.1N. The results showed that modification of waterborne polyurethane with defined amount CO could help to improve the hydrostatic pressure of the coated fabric. Part2: Preparation and application of castor oil and double-end hydroxy polysiloxane modified waterborne polyurethaneIn order to enhance further the hydrostatic pressure of waterborne polyurethane coated fabric,a castor oil and double-end hydroxy polysiloxane modified waterborne polyurethane were prepared with isophorone diisocyanate and polyether 210 as raw materials, castor oil(CO) and double-end hydroxy polysiloxane(DH-Si) together as modifier, 2,2-dimethylol propionic acid(DMPA) as hydrophilic linear chain extender. The influences of the dosages of DH-Si and the relative molecular mass of DH-Si on properties of polyurethane emulsion, its film and coated fabrics were researched, the structure and thermal stability of the modified-waterborne polyurethane were tested, the conditions of coating process of the modified-waterborne polyurethane were optimized and the application performance of the coated fabric were tested. The results showed that: with the increase of the dosages of DH-Si, the particle size of waterborne polyurethane emulsion increased, its distribution became wider, the appearance of the modified emulsion became milky white from transparent, the stability of the modified emulsion deteriorated; water contact angle of the film increased, water absorption of the film decreased, tensile strength of the film increased first and decreased then, and its elongation at break increased; water contact angle of the coated fabric increased, hydrostatic pressure and tear strength of the coated fabric increased first and decreased then. With the increase of the relative molecular mass of DH-Si, the particle size of modified emulsion increased, its distribution became wider, the stability of modified emulsion deteriorated; water contact angle of the film increased, water absorption of the film decreased, tensile strength of the film increased, and its elongation at break decreased; water contact angle of the coated fabric increased, hydrostatic pressure of the coated fabric increased. When the dosage of DH-Si was 8%, the relative molecular mass of DH-Si was 1695, water contact angle of the film was 116.3°, water absorption of the film was 13.75%, tensile strength of the film was 28.9Mpa, elongation at break of the film was 870%, the thermal stability of the modified waterborne polyurethane became better. The optimal condition of coating process were as follows: the dosage of coating agent was 10 g / m2, baking temperature was 160℃, baking time was 90 s, water contact angle of the coated fabrics was 138.03 °, hydrostatic pressure of the coated fabrics was 1.64 Kpa, tear strength of the coated fabrics was 176.5N, Studies had shown that the modification of waterborne polyurethane with defined amount and appropriate relative molecular mass of the DH-Si could help to improve water resistance and mechanical properties of the waterborne polyurethane film and help improve hydrostatic pressure of the coating fabric.Studies had shown that the modification of waterborne polyurethane with defined amount castor oil and define amount and appropriate relative molecular mass of double-end hydroxy polysiloxane could enhance water resistance and mechanical properties of the modified film, coating with modified waterborne polyurethane emulsion for fabric can better improve water contact angle and hydrostatic pressure of coated fabric. |
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