Design And Preparation Of Multifunctional Polyurethane Acrylate And Its UV-Curing Properties

As an emerging green industrial technology in twenty-first century,ultraviolet?UV?curing technology is attracting more attention and application because of its characteristics of energy saving,environmental protection and high efficiency.Polyurethane acrylate?PUA?resin has great adjustability to its resin formulation and properties,so its molecular structure can be designed to prepare materials with desired properties.However,ordinary UV-curable acrylic resin has low UV-curing activity,resulting in the thickness of its curing products is not enough and the curing time is longer.So,the development of UV-curing resin were mostly limited to thin layer curing system,such as coating,paint and so on.These problems restricted the wide application of UV-cured PUA resin in the matrix of composite materials.Therefore,improving the UV-curing activity of PUA resin,improving the strength,modulus and heat resistance of UV-cured products are of great significance for its application in the field of composite resin matrix.In this paper,we optimized the reaction conditions and synthesized a series of multifunctional PUA by two steps,where the mechanism was the stepwise polymerization and the method was bulk polymerization.The PUA resins were obtained by the combination of the crosslinking monomer and photoinitiator.After curing by UV lamp,the UV-cured casting and the UV-cured composite?GFRP?samples were obtained.The effect of the functional degree of PUA on the UV-curing properties of the material was investigated.The results were as follows:?1?A series of high functionality polyurethane acrylate?PUA-6,PUA-9,PUA-12?were synthesized by using phthalic anhydride polyester polyol?PAPP?as the core and isophorone diisocyanate?IPDI?,pentaerythritol triarylate?PET3A?as the branch.The FTIR results showed that the synthesis was successful.The UV-curing properties results showed that,with the increase of the functionality from 6 to 12,the curing time of wet film?100?m?decreased from 21s to 18s,which indicate the UV-curing activity of the resin gets larger.The UV-curing activity of the PUA resins is higher than the commercial resin 4431.With the increase of the double bond functionality,the bending properties,tensile properties of the UV-cured PUA resin castings became better,while the impact strength decreased.The mechanical properties are as follows:bending strength is at the range of 85⁹5 MPa,bending modulus is 4.0⁴.8 GPa,tensile strength is 31⁴1 MPa,tensile modulus is 4.0⁴.4 GPa,impact toughness is 4.1⁵.8 kJ·m^-2.The comprehensive mechanical properties are excellent.With the increase of the double bond functionality,the T_g of UV-cured PUA product increased from 135 to147?,and the T_{5 wt%}were all above 258?,which all showed good heat resistance and thermal stability.?2?A series of low functionality polyurethane acrylate?PUA-2,PUA-3,PUA-4?were synthesized by using PAPP as the core and IPDI,HEMA as the branch.The FTIR results showed that the synthesis was successful.The UV-curing properties were characterized,and the results showed that,with the increase of the double bond functionality,the UV-curing activity of PUA resin increased slightly.The UV-curing time of the PUA resin wet film?100?m?in this system were between 21²4 s,showing a high UV-curing activity.With the increase of the double bond functionality,the tensile properties of UV-cured PUA resin castings increased,and bending properties were relatively stable,and impact properties decreased.The mechanical properties of UV-cured PUA resin castings are as follows:bending strength is 137¹40 MPa,bending modulus is 4.3⁴.5 GPa,tensile strength is 72⁸5 MPa,tensile modulus is 3.6⁴.0 GPa,impact toughness is 18.6²4.0 kJ·m^-2.The comprehensive mechanical properties are excellent.The SEM results showed that with the increase of the double bond functionality,the impact fracture surfaces of UV-cured PUA resins were changed from rough to smooth,showing a transition from ductile fracture to brittle fracture.This indicated a reduce of the toughness of the UV-cured PUA resins.With the increase of the double bond functionality,the T_g of UV-cured PUA product increased from 87 to105?,and the T_{5 wt%}were all above 258?,which all showed good heat resistance and thermal stability.This system PUA resins have low viscosity at room temperature?465 mPa·s,10??,and its process performance were good.?3?The UV-cured glass fiber/PUA composites were prepared by hand lay-up.The test results showed that the hardness of the UV-cured composites were all above 30HBa.The mechanical properties of UV-cured composites were as follows:bending strength is 720⁷60 MPa,bending modulus is 25²9 GPa,tensile strength is 470⁵02 MPa,tensile modulus is 22²6 GPa.The comprehensive mechanical properties are excellent.In addition,the UV-cured GFRP had smooth appearance and had no obvious defects.The SEM results showed that,the PUA resin and the glass fiber had excellent infiltration,and the interfaces bonding were reliable.