Study On The Stability And Influencing Factors Of Siloxane Hybrid Waterborne Polyurethane

Volatile organic compounds(VOCs)produced by solvent coatings is one of the main sources of PM2.5.Therefore,the development of waterborne coatings is significant for improving air quality and solving air pollution in China.Modification of waterborne polyurethane by various organosilanes and siloxanes to improve the performance of paint film is a hot research field of waterborne coatings.However,there are few studies on the structure and colloidal stability of this kind of organic-inorganic hybrid waterborne dispersion.In this dissertation,hybrid waterborne polyurethane(WPU)was prepared by using amino functionalized silane coupling agent(APTES)and silsesquioxane(POSS)as the blocking monomers.The stability of WPU dispersion modified by different organosilicon was characterized by multiple light scattering technology combined with other testing methods.The state,structural evolution,interaction and influencing factors of the dispersed particles were systematically studied,and hybrid WPU with excellent comprehensive performances including stability was finally obtained.The main contents are as follows:(1)Using polyesterpolyols,isophorone diisocyanate and dimethylolbu-t anoic acid as monomers,APTES and POSS as capping or co-capping agents,a series of WPU with different end-capping structures,R values,hydrophilic monomer contents,silane and/or POSS contents were synthe-sized by prepolymer method.(2)The backscattering or transmitted light intensity was taken as the variable in the different positions of the dispersion,and the stability of WPU was traced as the function of time.Through this way,the degradation process and related mechanism of WPU as one special kind of dispersion was revealed.The results show that the stability of WPU is obviously affected by its composition content.When the hydrophilic monomer content was low or the R value was too high,sedimentation would occur.The stability of the system would be increased by either increasing the hydrophilic monomer content or decreasing the R value,and degradation would also changed into being dominated by particle flocculation.With the increase of APTES or POSS content,the stability of WPU becomes worse,and the degradation process is also changing from the local flocculation to the gelling of the particles on the whole volume.(3)Optical micro-rheometer was used to characterize the curve of root mean square displacement versus the decorrelation time of the dispersed particles in WPU.In the absence of external shear,a series of rheological parameters were calculated including viscosity,storage modulus and loss modulus.Further,the same technique was used to study the corresponding changes in rheology of during the degradation of WPU synthesized above.It is found that different WPU exhibits two different kind of rheological feasures of Newton fluid or non Newton fluid,and the viscoelastic dispersion is generally stable.With the increase of R value,the unperturbed heat movement of particles was accelerated.With the increase of hydrophilic monomer content,the viscous flow characteristics gradually appeared.With the increase of APTES or POSS content,the dispersion changed from viscous to elastic characteristics.(4)Different WPU films were formed at room temperature and mechanical tensile tests and water absorption tests were carried out.The results show that the increase on the content of hydrophilic monomer,the siloxane and POSS would all enhance the toughness,but the water absorption would also increase to some extent.The storage stability is consistent with the properties of the film.The best storage stability with acceptable comprehensive film performance was achieved under the conditions of 6%hydrophilic monomer,6%APTES and 4%POSS.