Photografting Of Modified Nano-ZnO Photoinitiators And Photopolymerization Of Acrylate Emulsions

Photopolymerization is a highly efficient and environmentally friendly technology.It is prospective and widely used in the UV-curing process of homogeneous single-phase resins and multi-phase dispersion systems.Generally,the organic photoinitiators will cause residues of unreacted molecules and photolyzed fragments,which diffused,transferred or migrated to the surface of the UV-cured coatings of waterborne polyurethane acrylates.The photopolymerization of "turbid" systems,such as emulsions,needs to deal with heterogeneous distribution of radiation,which leads to lower monomer conversions.In our study,in order to apply the photoinitiation properties of ZnO nanoparticles(NPs)after their modification,VOCs as well as the oxygen inhibition were avoided,and waterborne polyurethane acrylates were photografted by the photolyzed free radicals containing ZnO to improve the comprehensive performance of UV-cured coatings at the same time.To obtain a higher monomer conversion and good emulsion properties,we investigated the process conditions using DAAM modifying acrylate emulsions' photopolymerization.A novel inorganic photoinitiator(ZnO-TDI-1173 NPs)was synthesized by surface modification of ZnO NPs with toluene diisocyanate(TDI)and 2-hydroxyl-2-methyl-1-phenyl-1-acetone(Darocur 1173),which were employed as a "bridge" and modifier,respectively.Then,ZnO-TDI-1173 NPs/waterborne polyurethane acrylate resins formed an inorganic/organic composite.ZnO-TDI-1173 NPs and composites were characterized through infrared spectroscopy,scanning electron microscope and XRD,etc.Results of material measurements showed the success of Darocur 1173 grafting onto ZnO NPs and a decrease of agglomeration.The real-time infrared method displayed the highest photoinitiation efficiency(35%)of modified ZnO NPs when Darocur 1173 served as the modifier and water as the solvent.The analysis of photocurable composite showed that its photo-curing process was a zero-order reaction through the real-time ultraviolet monitoring;the addition of ZnO-TDI-1173 NPs at 0.4 wt.% not only acted as inorganic nanofillers but also as photoinitiators chemically bonding to the macromolecular chains via photolysis,which thus increased the hardness,water resistance,thermal stability,and tensile properties as well.In addition,the photoinitiation and photografting mechanisms of ZnO-TDI-1173 NPs are also proposed,and antibacterial studies confirmed that surface modification did not affect the antibacterial properties of ZnO NPs.Under ultraviolet light irradiaton,the DAAM modifying acrylate emulsions' photopolymerization was conducted.The main factors,such as the emulsifier type,dosage,ratio,as well as the amount of photoinitiator and content of DAAM,were determined for impacts on the monomer conversions and performances.Due to the hydrophilic and stable properties of DAAM,the amphoteric emulsifier CO-436 and the nonionic emulsifier OP-10 were combinated as a mixed emulsifiers.With the condition that the amount of them was 20.0 wt.%,the performance of DAAM modifying acrylate emulsion photopolymerization was better,and the monomer conversion even reached 83.27% while the monomer content was 30%.