| Polyvinyl chloride(PVC)sealant is a thick paste composed of PVC resin,plasticizers,solvents and tackifiers.It is sprayed or extruded on the body welds,solder joints and structural parts through coating equipment,play a role in sealing,shock absorption,anti-corrosion and sound insulation.However,in the sizing process,the uncured sealant exposed to the humid and hot environment will absorb moisture in the air,and bubbles will appear during the heating and curing stage,accompanied by the occurrence of flow,and the adhesion of the sealant to the substrate will also be reduce.Therefore,the preparation of PVC sealants with good moisture absorption resistance has very important practical significance.The purpose of this subject is to study and prepare a new type of PVC sealant for vehicles that has moisture absorption resistance,excellent sag and slip resistance,and good adhesion to the substrate.In this thesis,the author adopted a silane coupling agent system,a hydrophobic agent system and an acid anhydride-epoxy system,respectively,and carried out the hygroscopic foaming,sagging and slipping,adhesion,viscosity,pressure flow,and fuming of the prepared sealant.The fourier infrared(FTIR),thermogravimetry(TG),differential scanning calorimetry(DSC),tensile and lap shear tests,researched and analyzed the moisture absorption resistance,sag and slippage of sealants prepared by different systems performance and adhesion performance,etc.The results are as follows:(1)In the commercial PVC sealant(LOT)containing polyamide(PA)and isocyanate(Iso)tackifiers,the PVC sealant(KH-Sealant)was prepared using different silane coupling agents as additives.Improved its moisture absorption resistance,sagging and slipping performance,and adhesion performance.The study found that 1%KH-1170-Sealant has better moisture absorption resistance,sag and slip resistance,and adhesion increased by 10.69%.The performance of the sealant(0%PA-2%KH-Sealant)prepared by replacing the polyamide(PA)tackifier in LOT with a silane coupling agent was studied.The study found that 0%PA-2%KH-187-Sealant,0%PA-2%KH-189-Sealant and 0%PA-2%KH-1170-Sealant have better moisture resistance,0%PA-2%KH-1100-Sealant and 0%PA-2%KH-1872-Sealant has better anti-sagging and sliding properties.Compared with LOT,the adhesion of 0%PA-2%KH-189-Sealant is improved by 16.79%.In addition,the performance of the sealant(0%Iso-2%KH-Sealant)prepared by replacing the isocyanate(Iso)tackifier in LOT with a silane coupling agent was studied.The study found that 0%Iso-2%KH-1100-Sealant,0%Iso-2%KH-189-Sealant and0%Iso-2%KH-1170-Sealant have better moisture absorption resistance,sag and slip resistance.Compared with LOT,the adhesion of 0%Iso-2%KH-1170-Sealant is improved by 12.21%.The application performance test of the sealant with good moisture absorption resistance has been carried out.The viscosity test shows that the LOT viscosity is greater than 170000 m Pa·S,and0%PA-2%KH-187-Sealant,0%PA-2%KH-189-Sealant The viscosity range of 0%Iso-2%KH-189-Sealant is between(120000～150000)m Pa·S,which meets the requirements of sealant manufacturers.The pressure flow test shows that the pressure flow test time of LOT is more than 43 s,while the pressure flow time of 0%PA-2%KH-189-Sealant and 0%Iso-2%KH-189-Sealant is about 30 s,which is consistent with requirements of sealant manufacturers.TG test and analysis show that the initial decomposition temperature and maximum decomposition temperature of the prepared PVC sealant are not much different from LOT.DSC test and analysis show that the PVC sealant prepared by using silane coupling agent instead of tackifier has the same glass transition temperature(Tg)before and after curing and LOT.The tensile test shows that the overall tensile test result of 0%PA-2%KH-189-Sealant is close to that of LOT.The lap shear test shows that the shear strength of 0%PA-2%KH-189-Sealant is 7.08% higher than that of LOT.On the whole,0%PA-2%KH-189-Sealant has the best moisture absorption resistance,which meets the requirements of actual use.(2)On the basis of commercial PVC sealant,it is prepared by modified castor oil derivative(hydrophobic agent CA220),modified polyurea compound(hydrophobic agent CA227)and polysiloxane hydrophobic agent(hydrophobic agent SH-Q)The PVC sealant was used,and its moisture absorption resistance,sagging and sliding properties,and adhesion properties were studied.The study found that in the PVC sealant(LOT-SH-Q-Sealant)prepared by adding hydrophobic agent SH-Q to LOT,LOT-4%SH-Q-Sealant has better moisture absorption resistance,sag and slip resistance,adhesion increased by 24.43%.The application performance test of LOT-4%SH-Q-Sealant was carried out,and the viscosity test showed that the sealant had a higher viscosity.The pressure flow test shows that the pressure flow test time of the sealant is longer.TG test and analysis show that when the temperature of the uncured sealant is lower than 300 °C its thermal performance is close to that of LOT;when it is higher than 300 °C,the thermal performance is slightly reduced.When the temperature of the cured sealant is lower than 300 °C,its thermal performance is close to that of LOT,and when it is higher than 300 °C C,the thermal performance is greatly reduced.DSC test and analysis show that the Tg of the sealant is about 3 °C higher than LOT before curing,and about 10 °C lower than LOT after curing.The tensile test shows that the overall tensile test result of the sealant is about 50% of LOT,and the performance is not good.The lap shear test shows that the shear strength of the sealant is 42.14% of LOT,and the performance is not good,but cohesive failure occurs between it and the substrate.The contact angle test showed that the water contact angle of the sealant surface increased from 83.3 ° of LOT to 88.7 °,and the surface hydrophobicity was enhanced.(3)The PVC sealant was prepared by using acid anhydride-epoxy instead of calcium oxide in LOT.The study found that the PVC sealant prepared by methyltetrahydrophthalic anhydride and epoxy soybean oil(MTHPA/ESO sealant,MT-E-Sealant)and PVC sealant(Mc HHPA/ESO sealant,Mc-E-Sealant)prepared by methylhexahydrophthalic anhydride and epoxy soybean oil,its moisture resistance is not good.Although the sealant prepared by the acid anhydride-epoxy system has better anti-sagging and sliding properties,the adhesion performance is not ideal.In addition,for the PVC sealant prepared by adding silane coupling agent to compound MT-E-Sealant or Mc-E-Sealant(1%MT-3%E-KH-Sealant and 1%Mc-3%E-KH-Sealant),1%MT-3%E-3%KH-1170-Sealant has fewer bubbles but cracks;1%MT-3%E-1%KH-1872-Sealant has more bubbles,but The surface is relatively flat,and the overall moisture absorption performance is better.1%Mc-3%E-3%KH-1170-Sealant has better antisagging and sliding performance,and has improved adhesion,but the surface appears to be cracked,and the effect of moisture absorption is poor;Although 1%Mc-3%E-3%KH-187-Sealant has a large number of bubbles,the surface is relatively flat and the overall moisture absorption resistance is better.For hydrophobic agent SH-Q compounded with MT-E-Sealant or PVC sealant prepared by Mc-E-Sealant(MT-E-SH-Sealant and Mc-E-SH-Sealant),1%MT-3%E-2%SH-Sealant has better moisture absorption resistance,sag and slip resistance,and has improved adhesion.The application performance test of the sealant with better moisture absorption resistance has been carried out.The viscosity test shows that the viscosity of 1%Mc-3%E-3%KH-187-Sealant is between(120000～150000)m Pa·S.Pressure flow test shows that the pressure flow time of 1%Mc-3%E-3%KH-187-Sealant is about 21 s.TG test and analysis show that the thermal performance of uncured PVC sealant before 200 °C is close to that of LOT,and when it is higher than 200 °C,the thermal performance is significantly lower than that of LOT.After curing,the thermal performance of PVC sealant before 200 °C is close to that of LOT,and when it is higher than 200 °C,the thermal performance decreases more significantly than that of LOT.DSC test and analysis show that the Tg of the prepared PVC sealant before and after curing is higher than that of LOT by more than 2 °C.This is because the formation of the semi-interpenetrating network structure increases the movement resistance of the PVC molecular chain.The tensile test showed that the tensile strength and elongation at break of the prepared PVC sealant were lower than that of LOT.The lap shear test showed that the shear strength of the prepared PVC sealant was lower than that of LOT,and the overall mechanical properties were poor. |
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