Preparation And Properties Of UV-curable Waterborne Polyurethane Acrylate With Low Moisture Absorption

Nowadays,Waterborne polyurethane acrylate（WPUA）has already widely applied in the field of wooden furniture,leather and paper coating.However,due to numerous hydrophilic groups in matrix resin making the cured film of WPUA performs certain hygroscopicity,which significantly decreases lifetime of the materials.Therefore,in view of the deficiencies of WPUA film with poor water resistance in general,based on the basic molecular structure and composition of UV-Curable WPUA,the following research work was done to improve the water resistance of WPUA by increasing the cross-link density of WPUA and introducing low surface energy hydrophobic chain segments for molecular design.Firstly,a series of WPUA emulsions with different experimental ratios were synthesized by anionic self-emulsification method.The experimental variables including R value(n_-NCO/n_-OH),TMP content were varied so as to investigate the effect of the crosslinking density of the system on the appearance,particle size,zeta potential of WPUA emulsions as well as the mechanical properties,pencil hardness,adhesion,water absorption,contact angle of water and thermal stability of UVWPUA cured films.The results of characterization and analysis of WPUA emulsions and cured films showed that when the R value increased,the appearance of WPUA emulsions changed from translucent to milky white,the particle size decreased from 287 nm to 95 nm and the dispersion stability also decreased,the surface hydrophobicity and water-resistance of WPUA cured films improved.When the R value was2.0,water absorption rate reached the minimum of 4.65%.The tensile strength and hardness increased,but the elongation at break and the initial decomposition temperature declined.As the TMP content increased,the appearance of WPUA emulsion transformed from slightly white bluish to milky white,the particle size increased to 165 nm and the dispersion stability decreased.The surface hydrophobicity and water resistance of the WPUA cured film became better,water absorption rate reached the minimum of 4.96%when the contents of TMP was0.5%.The tensile strength and hardness increased,while the elongation at break and the initial decomposition temperature was declined.Secondly,hydroxy-terminated polydimethylsiloxane（HTPDMS）was used as a hydrophobic modification component of WPUA molecules to introduce the silicones in the main chain by block copolymerization,and a series of WPUA emulsions with different HTPDMS contents were synthesized.The results showed that with the increase of HTPDMS content,the surface hydrophobicity and water resistance of the WPUA cured film became better,and the water absorption reached 2.86%when the content of HTPDMS was 10%,and the water contact angle was 132°.The appearance of WPUA emulsion transformed from translucent bluish to milky white,the particle size increased significantly and the dispersion stability also decreased,but the tensile strength,elongation at break,hardness and adhesion properties decreased,and the initial decomposition temperature was declined significantly after the content of HTPDMS exceeded 5%.Thirdly,a series of WPUA emulsions with different APTES contents were synthesized by using 3-aminopropyltriethoxysilane（APTES）to hydrophobically modify the ends of WPU molecular chains.The results showed that the introduction of APTES effectively improved the surface hydrophobicity and water-resistance of the cured films,and the water absorption reached a minimum of 3.53%when the APTES content was 3%,at which the water contact angle was 104.8°.With the increase of APTES content,the particle size of WPUA emulsion decreased and dispersion stability maintained at a good level,while the tensile strength and elongation at break of the WPUA cured film both increased first and then decreased,the initial decomposition temperature decreased significantly.Finally,a series of WPUA emulsions with different AEAPTMS contents were synthesized by using（3-（2-aminoethyl）-aminopropyl）trimethoxysilane（AEAPTMS）on the interrupted WPUA molecular chain embedded with small molecule organosiloxanes as side groups for hydrophobic modification.The results showed that the water-resistance of the modified cured films was improved significantly.When the AEAPTMS content was 4%,the water absorption was declined to the minimum of 2.74%while the contact angle of water had the maximum of 115°.With the AEAPTMS content increased,the particle size of WPUA emulsion increased,the dispersion stability decreased,and the tensile properties of WPUA cured films was increased significantly to 23.9 MPa,while elongation at break decreased,the initial decomposition temperature increased to 274.8°C.