Study On Structure And Properties Of Waterborne Polyurethane Modified By Acrylate

Waterborne polyurethane not only has the characteristic of environmental protection,but also has unique physical and chemical properties,such as the advantages of the adjustability of hard and soft segments,good abrasion resistance,good weather resistance,and high adhesion,which had attracted extensive concerns.WPU,which combines high performance and low volatile organic compound(VOC)content,has been widely used in coating,wood coating,leather,textile and adhesive,etc.However,WPU also has its inherent disadvantages such as poor water resistance,poor mechanical properties,poor lightfastness and relatively high cost.Acrylates have significant advantages in water resistance,yellowing resistance and aging resistance,etc.But acrylates are sticky in high temperature and crisp in low temperature.In view of those,the application of the two with the method of organic combine can produce complementary advantages,which could take advantages of each other’s strengths.In this study,acrylic monomers were used to modify polyurethane,at the same time,a small amount of organic silicone was introduced to prepare a double-modified waterborne polyurethane-polyacrylate(WPUA)hybrid emulsions.Based on this,studied by designing particle structures,the WPUA with different internal structures of the emulsion particles and WPUA with crossed-linked structures were prepared via changing the way of adding acrylic monomers and introducing crosslinking agent,respectively.The structures and properties of the hybrid emulsions as well as dried films were systematically researched,and the relationship between the structure and property was elaborated.First of all,PU prepolymer was prepared by the reaction of isophorone diisocyanate,polytetramethylene ether glycol,dihydroxymethyl propionic acid and polydimethylsiloxane as main raw materials via gradual polymerization mechanism,and then three different internal structures of WPUA were prepared by changing the feeding manners of acrylate monomers,including core-shell structure,inversed core-shell structure and semi-interpenetrating polymer network structure,and stable WPUA hybrid emulsions were obtained.Transmission electron microscopy(TEM)photographs demonstrate that the three kinds of WPUA hybrid emulsion particles with different internal structures were successfully synthesized.The results show that WPUA with core-shell structure has the largest tensile,but has lower elongation at break;WPUA with semi-IPN structure has the best water resistance,lower contact angle,lower water absorption,but has lower thermal stability compared with the other two types of WPUA.The influence of the amount of DVB on the properties of the hybrid emulsions and their coating films was mainly discussed.Secondly,on the basis of acrylate-modified polyurethane,a serious of cross-linked WPUA hybrid emulsions with storage stability were synthesized by introducing crosslinking agent divinylbenzene(DVB).The modified coating films have good water resistance and mechanical property.The microscopic morphology of the emulsion particle is similar to the core-shell structure.The results show that the introduction of crosslinking agent plays an important role in particle size of the emulsion.With increasing the content of crosslinking agent,the emulsion particle size decreases and the size distribution becomes narrow;as the crosslinking agent increases,the tensile strength,water resistance and thermal stability of the sample coating films are all enhanced.