Preparation Of PDMS Graft-Modified Waterborne Polyurethane Dispersion And Investigation Of Its Latex Film Morphology

With the improvement of every country laws and regulations and enhancement of people environmental awareness,traditional solvent-based polyurethanes are decreasing and replaced by waterborne polyurethane(WPU)gradually,a kind of green and environmentally friendly materials.However,WPU has a poor water resistence because of introducing hydrophilic chain extender or chain segment during the synthesis process.Polydimethylsiloxane(PDMS)is used widely for modified WPU due to it owned many advantages,such as low surface free energy,good water resistance and weather resistance,etc.PDMS modified waterborne polyurethane(SiPU)can provide WPU with good water resistance and smooth feel because PDMS could migrate and enrich on the latex films surface during the latex film formation process due to its low surface free energy.Usually,double hydroxy-terminated PDMS block modified WPU is the most widely used way.But the PDMS chain is located between WPU main chains,which seriously restrict the freedom of PDMS chain and PDMS couldn't migrate and enrich on the latex films surface effectively,so the best modified effects can not get.And single dihydroxy-terminated PDMS graft modified WPU is an alternative way that just one end of PDMS chain was connected to WPU main chains,which provided PDMS chain with more freedom for migration and enrichment and can get a better modified effects.As we all know,the structure of the material determines the performance and the performance is the reflection of the structure.At present,people pay more attention to the increased extent of PDMS modified waterborne polyurethane,only little to the morphology and structure of latex films.In this paper,organosilicone modified WPU were prepared by single dihydroxy-terminated PDMS.The characterizations were conducted by FTIR,particle size analysis and mechanical properties testing.And the morphology of latex film was investigated particularly.The main works and the results obtained are as follows:(1)Preparation and characterization of PDMS grafted-modified waterborne polyurethane dispersionOrganosilicone graft-modified WPU were synthesized with single dihydroxy-terminated PDMS,IPDI,PTMG,DMPA,DEG and EDA by pre-polymerized method.And organosilicone block-modified WPU were synthesized with hydroxy-terminated PDMS.The differences of graft and block were investigated.The results showed that the graft modification had a better promotion on mechanical properties and waterproof properties than block modification.The PDMS migrated and enriched to surface of latex films more obviously for graft modification.(2)Investigation of the latex films morphologyThe IPDI and DEG were replaced by TDI and BDO,and the organosilicone graft-modified waterborne polyurethane dispersions were synthesized.The dispersions were diluted with water and used for latex films.Then poured on the hydrophilic glass tanks under ambient conditions for a week.The result latex films were about 30 ?m in thickness and stored in desiccator.The cross-section of films were sliced by Cryo-Ultramicrotome(including complete films surface,inner and bottom).Then the morphology of cross-sections were observed with TEM.The surface morphology of latex films were observed with SEM.The results showed that PDMS aggregated into microspheres which distributed in the near surface and the inner of latex films,even on the surface contacting with air directly for graft modification.