Study On Preparation And Properties Of Waterborne Polyurethane Heat Reflective Coatings With Phase Transformation And Temperature Reduction

In view of the high temperature disease of asphalt pavement caused by high temperature in summer and the problem of"urban heat island effect",the heat reflective materials which could reduce the temperature of pavement were widely concerned.Nano fillers with high refractive index were commonly used in heat reflecting materials to reduce the thermal radiation of the reflecting part.The addition of nano particles could also improve the wear resistance of the coating.Howere,excessive addition of nano particles would affect the wear resistance of the coating.At present,the thermal reflective coating had some problems,such as insufficient cooling performance and poor wear resistance.Aiming at the above problems,this paper designed a kind of waterborne polyurethane(WPU)resin with phase change function,combined with high refractive index filler to prepare a kind of heat reflecting material,so as to improve the refrigeration performance,saved the use of reflective filler,and improved the wear resistance of the coating by using the good viscoelasticity and resistance deformation ability of polyurethane.When the material was applied to the surface of asphalt concrete specimens,the pavement temperature could be reduced by more than 10?and the wear resistance was good.First of all,polyacrylic acid-1,4-butanediol glycol(PBA)with resin phase change function and polypropyl glycol(PPG)which gave resin hydrophobicity were selected as the main reaction monomers.By controlling the ratio of NCO/OH(R)and the amount of crosslinking agent,WPU emulsion was prepared by phase inversion method and formed in teflon film forming board and its performance was tested.The results showed that when the R value was 1.1,the stability of WPU emulsion was poor.The crosslinking density of materials had a great influence on the properties of materials.The crosslinking density was inversely proportional to the enthalpy of change,and was directly proportional to the hardness.The higher the crosslinking density,the better the thermal stability.Then,waterborne polyurethane heat reflective coatings(WPURC)were prepared by self-made WPU emulsion and titanium dioxide(Ti O₂)with high refractive index.The water,alkali resistance and adhesion properties of three kinds of materials such as WPURC7,WPURC9 and WPURC10 were tested.A WPURC was selected to study the effect of anti-settling agent,thickening agent,wetting agent and film builder on the performance of WPURC.The results showed that WPURC10 had better performance in water resistance,alkali resistance and adhesion.It was found that the coating can be stored stably for more than one year when the dosage of anti-settlement agent was 2%,and the viscosity of the material could be improved obviously by adding 0.75%thickener,so that the material could better cover the asphalt pavement in the curing process.When 2.5%wetting agent and 5%film-forming agent were used,the film-forming performance was the best,which could significantly reduce the occurrence of pores and cracks,and reduce the three-dimensional defects of WPURC,anti-skid particles and asphalt pavement the interface tension of the operator.Next,AC-13 asphalt concrete specimens were formed,and self-made cooling performance test box was used to study the cooling performance,bonding performance,wear resistance,skid resistance and weather resistance of WPURC coating in asphalt concrete.When the internal temperature of blank asphalt concrete specimen was 60?,the internal temperature of WPURC specimen was 50?,and the maximum cooling value could reach 12?.WPURC was paved on outdoor asphalt pavement,and its surface temperature was measured by infrared thermal imager.When the air temperature was35?,the temperature of asphalt pavement could reach 52?,which indicates that WPURC had good cooling effect in asphalt pavement.The bonding strength between WPURC and asphalt pavement was 0.6MPa.The bonding strength of WPURC modified by 1.5%silicone could reach 0.74mpa.The wear test showed that the self-made WPURC coating had excellent wear resistance compared with the common reflective cooling coating on the market.By testing the pendulum value(BPN)of wear specimens at different stages,the results showed that the anti-sliding performance of coatings paved with 1-2mm and 2-3mm were decreased,but they were all higher than the required 45.The mechanical properties,cooling properties and structural changes of WPU,WPURC,oil-based polyurethane heat reflective material(PURC)and epoxy heat reflective material(EPRC)were tested by UV irradiation.The UV aging resistance of WPU and WPURC was analyzed.The results showed that the mechanical properties of WPU and WPURC decreased significantly in the initial stage,but not in the later stage.The UV aging resistance of WPURC was better than that of PURC and EPRC.The results showed that the structure of WPU changed obviously during the aging process,the C=O group increased significantly,and the C-N bond did not show a downward trend,indicating that the bond breaking mainly occurred in the C-O position of carbamate,and there were a lot of carbamoyl groups in the structure.Finally,DMA was used to test the thermal and dynamic mechanical properties of WPU,WMMA and WEP.By comparing the cooling values of WPURC,WMMARC and WEPRC,the contribution rate of cooling was proposed to evaluate the contribution rate of phase transition and reflection function to cooling.The results showed that WPU had obvious endothermic melting peak,WEP and WMMA had no phase transition function,the storage modulus of WPU and WEP were significantly higher than the loss modulus,and the storage modulus of WPU was higher than WEP,which indicates that WPU had better anti fatigue performance.Through the fitting analysis of WPURC and WEPRC cooling values,the proportion of cooling values of phase transformation and reflection(phase transformation contribution rate and reflection contribution rate)was calculated,and the cooperative cooling mechanism of phase transformation function and reflection were studied.It was found that phase transformation cooling plays a leading role at low temperature.When the temperature reacheed 55.42?,the two functions had the same contribution rate.When the temperature rises to 80?,the phase transformation endothermic gradually increased.The contribution rate of phase transition decreased to40%at saturation.