Preparation Of Silica/Polyurethane Hybrid Rigid Foam And Study On Its Mechanism Of Enhancement And Thermal Insulation

Water is the most environmentally polyurethane?PU?foaming agent.but water-foamed PU rigid foam has the disadvantages of low compressive strength,high thermal conductivity,poor heating aging resistance?thermal conductivity increases significantly with increasing temperature?.The introduction of inorganic particles to prepare organic-inorganic hybrid PU rigid foam is an effective method to overcome the above drawbacks.In this paper,organic-inorganic hybrid water-foamed PU rigid foams were prepared by sol-gel method and in-situ method.This two methods were discussed in the water foaming system through the combination of experimental test and mathematical simulation to study the mechanism that affects the compressive strength and thermal conductivity of PU rigid foam.Firstly,a self-made interface agent was used to control the particle size of silica sol,and a polyether-based silica sol with polyether polyol as dispersion medium was obtained.Silica?SiO₂?enhanced PU rigid foam was prepared by using silica sol.The mechanism of the interface agent to stabilize the silica sol was studied by particle size test and infrared characterization.The foaming reaction characteristics test,electron microscopy observation of the cell structure and the compressive strength test of PU rigid foam were used to investigate the effect of sol-gel-generated SiO₂ on PU cell structure,and the results of mathematical simulation were used to investigate the the strengthening mechanism of rigid foam.Through the thermal conductivity test,the effects of SiO₂ and temperature on the thermal conductivity of PU rigid foam were studied,and the results of two mathematical models were combined to simulate the results,as well as the closed porosity test,water absorption test and dimensional stability test at high and low temperatures.The mechanism of SiO₂ affecting the thermal aging properties of PU rigid foams was discussed.The results show that the interface agent inhibits the condensation of silica sol by hydrogen bonding.The sol-gel-formed SiO₂does not enhance the PU matrix,but improves the foam compression strength by controlling the cell structure.When SiO₂ is 8 wt%,the compressive strength is increased by about 50%.At higher temperatures,convective mass transfer between closed-cell foams significantly reduces the thermal aging properties of water-foamed PU foams?the thermal conductivity increases significantly with increasing temperature?.SiO₂ improves the thermal aging properties of the foam and reduces the thermal conductivity by suppressing the transmission of CO₂ in the PU matrix and increasing the closed cell content.When SiO₂ is 8wt%,the closed cell content is the highest,the thermal conductivity is the lowest,and the heat aging performance is the best.On this basis,a foam stabilizer which can be cross-linked and condensed?CFS?was prepared.The foam stabilizer was used in combination with a commercially available foam stabilizer to prepare SiO₂/PU hybrid PU foam with smaller particle size and denser packing by in-situ formation.It was studied that whether smaller particle size and tighter stacking of silica were more conducive to foam compressive strength,heat aging performance and flame retardant performance,and the corresponding mechanism was discussed.The results show that the mechanism of in-situ generated SiO₂ particles affecting foam compressive strength and heat aging performance is the same as that of sol-gel method,but smaller particle size and tighter stacking can improve foam compressive strength,heat aging performance and flame retardant properties more effectively.Compared with the unmodified foam,when SiO₂ is 3wt%,the compressive strength is increased by about 50%,the thermal conductivity is the lowest,and the heat aging performance is the best.When the amount of SiO₂ added is 6wt%,the flame retardancy of the foam is remarkably improved.