Research On Modification Of Waterborne Polyurethane With Silica Sol/Soy Protein

Waterborne polyurethane were easily modified and controllable in the structures of segment chain and cross-linked in molecule, because of rich raw material sources for preparation, and these formed films own high strength, high adhesive strength, tear resistance, abrasion resistance, oil resistance, low temperature resistance, good deflection, which are widely used in coatings, leather coating agents, adhesives, textile printing and dyeing agent, ink and other fields. However,the presence of the hydrophilic group in the molecule and the limitation of the preparation process, namely, the low molecular weight, linear structure and the low crosslinking degree of the resulting polymers result in long film forming time, poor water and solvent resistance, poor thermal stability, bad elasticity and other shortcomings, which narrow their application in more areas.Soybean protein have low obtaining cost, simple processing, easy industrialization, good corrosion resistance, structured packing repairability, biodegradable, hydrophilic and biocompatible.The structure of soy protein molecular is loose and disordered, and plenty of polar groups (such as:-OH,-COOH,-NH2,> NH,-SH, etc.) are in the surface of the polypeptide chains, which are easily in combination with the active groups of the aqueous polyurethane, constituting the physical and chemical crosslinking points and increasing the strength and elasticity of films. The subject chose soy protein to modify waterborne polyurethane. A series of good stability IPDI-based polyurethane were synthesized, with isophorone diisocyanate (IPDI) of the less yellowing, poly tetrahydrofuran (PTMG) of the molecular chain soft, dimethylol propionic acid (DMPA) as main raw materials by using the non-solvent method. Effect of the controllable change of the soft and hard segments and preparation process on emulsion type, particle size distribution, stability, film formation time and the mechanical properties of waterborne polyurethane were studied. Soy protein/waterborne polyurethane composite films were obtained by blending and modifying the waterborne polyurethane with soy protein. The study found out that hydrogen bonds among C=O group, C-O-C group, and N-H group form in soy protein and waterborne polyurethane molecule chain in the film-forming process. The mechanical properties, surface hydrophilicity and UV radiation resistence of the modified film have been improved. Furthermore, nano silica sol were added into the slurry of soy protein/waterborne polyurethane:the multi-level action occurred between nano silicon dioxide particles generated in situ from silica sol and reactive groups of waterbome polyurethane and soy protein, which played a role of fixing and reinforcing the film in curing process. The film not only showed excellent interface performance and inertia to the human body and the ecological environment but also improved significantly in the tensile strength, the elasticity and surface properties, thermal stability and solvent resistance.