Preparation,Properties And Modification Of UV-Curable Waterborne Polyurethane Acrylate

In recent years,with the enhancement of people's awareness of environmental protection and the strict restrictions promulgated by the government of the Volatile Organic Compounds?VOCs?content in coatings,the coatings industry has developed towards the direction of green environmental protection,high performance,and high functionality.UV-Curable Waterborne Polyurethane Acrylate?UV-WPUA?coatings,combining the advantages of UV-Curable coatings and water-based coatings,have the advantages of low VOCs emissions,fast curing speed,low energy consumption,and can be used in wide application range.However,it also has the disadvantages of poor water resistance and high surface gloss.A series of WPUA emulsions were prepared using isophorone diisocyanate?IPDI?,polybutylene adipate glycol?PBAG?,2,2-dimethylolpropionic acid?DMPA?,hydroxyethyl acrylate?HEA?and pentaerythritol triacrylate?PETA?.The suitable process conditions for synthesizing WPUA prepolymer were discussed,and the effects of different experimental variables(R-value i.e.n _NCO/n _OH,DMPA content,and double bond density)on the properties of WPUA emulsions and films were studied.Simultaneously,WPUA was modified by Hydroxyl-Terminated Polydimethylsiloxane?HTPDMS?copolymerization to improve the hydrophobicity and water resistance of WPUA film.Besides,WPUA film with a self-matting surface was obtained by preparing WPUA emulsion with a large particle size.Firstly,by monitoring the NCO group content of prepolymer in the synthesis process,the suitable process conditions for synthesizing WPUA prepolymer were explored:the reaction of the first stage was the pre-polymerization reaction of IPDI and PBAG under 60?for 1 hour;the reaction of the second stage was a chain extension reaction with the addition of a hydrophilic chain extender DMPA under 80?for 3 hours;the reaction of the third stage was the end-capping reaction with the end-capping agent HEA or PETA under 70?for 6 hours.The infrared spectroscopy analysis results indicated the smooth synthesis of WPUA prepolymer.Secondly,the effects of R-value,DMPA content,and double bond density on the particle size,Zeta potential of the WPUA emulsion and the hardness,adhesion,tensile properties,water absorption,gelation content and thermal stability of WPUA film were studied.The results showed that:with the increase of the R-value,the particle size and the absolute value of the Zeta potential of the WPUA emulsion decreased,both the tensile strength and hardness of the film increased first and then decreased,the water absorption of the film decreased,the initial decomposition temperature first decreased and then increased.With the increase of DMPA content,the particle size decreased,the absolute value of the Zeta potential increased,the tensile strength and elongation at break of the film significantly increased,and the adhesion performance of the film improved,but water resistance and thermal performance declined.With the increase of the molar ratio of PETA/HEA,the particle size,tensile strength,tensile modulus,and the hardness of the WPUA film increased significantly,and water resistance and thermal performance enhanced.Then,a series of WPUA emulsions with different HTPDMS contents were prepared by introducing HTPDMS into the WPUA molecular chain.The results showed that:with the increase of HTPDMS content,the particle size of WPUA emulsion increases,while the absolute value of Zeta potential remains unchanged,the surface of WPUA film was modified from a hydrophilic surface to a hydrophobic surface,and when the HTPDMS content was 10 wt%,the water contact angle of WPUA film reached a maximum of 114°.With the increase of HTPDMS content,the water resistance and thermal performance of WPUA film became better,the water absorption gradually decreased,from 8.34%to 5.72%,and the initial decomposition temperature gradually increased from 262.7?to 277.6?,but the light transmittance and tensile strength decreased.Finally,the WPUA emulsion with large particle size and the self-matting WPUA film was prepared by adjusting the experimental formula and supplemented by moderately reducing the emulsification stirring rate.The research results showed that:As the particle size of the WPUA emulsion increased,the gloss of the surface of the film also decreased.When the particle size of the WPUA emulsion was around 1600 nm,the film has an excellent matting effect,and the gloss was below 10,and as the particle size further increased,the gloss did not decrease further.When the root-mean-square roughness?Rq?of the WPUA film surface was above 300 nm,the film has an excellent matting effect,but the surface roughness is not the only factor that determined the gloss,but also depended on the size of the overall convex or concave area.