Preparation Of Particle Foam Stabilizer And Its Application In Waterborne Polyurethane Foam Coating

A large number of studies have shown that amphiphilic solid particles can be prepared by physical or chemical methods.Specifically,the surface of inorganic particles is adsorbed or grafted by hydrophobic molecules.The foam stabilization of amphiphilic solid particles is better than that of the surfactants,especially heat-resistant foam stabilization.However,the current research on particle foam stabilizers is mainly concentrated on water-based foam,and there are few reports on foam stabilization of that in waterborne polyurethane emulsions（WPU）.At the same time,studies have proved that solid particles can also act as fillers or functional additives for WPU foam coatings,effectively improving the mechanical strength of the coating,and greatly reducing production costs.In this paper,amphiphilic calcium carbonate（CaCO₃）and silicon dioxide（SiO₂）were prepared by modifiers.The amphiphilic CaCO₃ particles and SiO₂ particles have the characteristics of both solid particles and surfactants,which can not only enhance the mechanical strength,heat and water resistance of the foamed coating,but also enhance the foam stability by adsorption at the gas-liquid interface.It is beneficial for the economy and environment.The main research and conclusions are as follows:（1）CTAB/SiO₂ particles,SA/CaCO₃ particles and FC/SA/CaCO₃ particles were prepared by physical and chemical modification.The surfaces of SiO₂ and CaCO₃ particles were adsorbed or grafted by cetyl trimethyl ammonium bromide（CTAB）,stearic acid（SA）and perfluorooctanesulfonic acid potassium salt（FC）.The structure and performance of the products were characterized by fourier transform infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）,thermal gravimetric analysis（TGA）,and contact angle testing.The results showed that the modifiers were successfully adsorbed or grafted on the surface of the solid particles,and the interaction between the modifier and the solid particles will only increase the hydrophobicity of the solid particles,but will not change the appearance and crystal structure.The influence of the amount of SA,reaction time and pH of the aqueous solution on the preparation of SA/CaCO₃ particles were explored by activation degree test and sedimentation volume analysis.The results show that the activation degree of CaCO₃ increased with the increase of the amount of SA,the reaction time and the pH of the aqueous solution.However,the sedimentation volume of CaCO₃ decreased with the increase of these factors.The preparation process of CTAB/SiO₂ particles was optimized based on contact angle.The contact angle of the CTAB/SiO₂ particles can be controlled at about 90°.The performance of FC/SA/CaCO₃ particles was evaluated by a floating experiment.The results showed that the CaCO₃ particles modified by FC and SA have both hydrophobic and oleophobic properties and can be adsorbed on the gas-liquid interface directionally.（2）WPU foam and WPU foam coatings were prepared by mechanical foaming method blends of waterborne polyurethanes（WPU）and particles foam stabilizer,which were CTAB/SiO₂ particles,SA/CaCO₃ particles and FC/SA/CaCO₃ particles.The foam stabilization performance of CTAB/SiO₂ particles,SA/CaCO₃ particles and FC/SA/CaCO₃ particles were optimized based on half-life of WPU foam and average pore size of WPU foam coatings.The results show that FC/SA/CaCO₃ particles have the best foam stability performance,followed by SA/CaCO₃ particles,and they are better than CTAB/SiO₂ particles.The influence of many factors were explored on the stability of WPU foam,which were the grafting degree of SA,the adsorption amount of CTAB,the addition of SA/CaCO₃ particles and CTAB/SiO₂ particles,and the particle size.The results show that when the degree of SA grafting was 2.73%,the foam stability of SA/CaCO₃ particles was the best.When the adsorption amount of CTAB was 1.12%,the contact angle of CTAB/SiO₂ particles was closest to 90°,and its foam stabilization performance was the best.As the addition of SA/CaCO₃ particles and CTAB/SiO₂ particles gradually increased,the half-life of WPU foam gradually increased,and the average pore diameter of WPU coatings gradually decreased.It indicated that the average pore size of the WPU foam coatings will decrease with the increase of particle foam stabilizer addition.Solid particles with a diameter of 0.5 μm had better foam stability than solid particles with a diameter of 2μm,and the pore size of the WPU coatings made with the former was smaller.Through comparative experiments,it can be found that CTAB/SiO₂ particles have better foam stabilization performance than a mixture of CTAB and SiO₂.It indicated that the amphiphilic particles can improve the foam stabilization performance of the product,which is conducive to saving costs and improving production efficiency.The foam stabilizing mechanism of particle foam stabilizers in WPU foam was explored based on the directional adsorption of FC/SA/CaCO₃ particles.The results show that when the solid particles were adsorbed at the water-air interface,the life of WPU foam was longest.However,when the solid particles were adsorbed at the WPU-water interface,the stability of the WPU foam was worst.（3）The WPU foam coatings（SA/CaCO₃/WPU）were prepared with SA/CaCO₃ particles as foam stabilizer.The impact of SA/CaCO₃ particles on the mechanical strength,friction resistance,heat resistance,water resistance and moisture permeability of SA/CaCO₃/WPU foamed coatings were explored.The test results showed that SA/CaCO₃ particles have both the characteristics of surfactants and solid particles.Compared with WPU foam coating without SA/CaCO₃ particles,when the addition of SA/CaCO₃ particles was 10%,the tensile strength of SA/CaCO₃/WPU coating increased from 1.57MPa to 1.86MPa.It indicated that SA/CaCO₃ particles can improve the mechanical strength of the coating.The friction coefficient of SA/CaCO₃/WPU foam coatings was lower than WPU foam coatings.The results of the heat yield test and TGA analysis showed that the heat resistance of SA/CaCO₃/WPU coatings was better than that of blank WPU coatings.The water resistance test and moisture permeability test results showed that the SA/CaCO₃/WPU foam coating has better water resistance and moisture permeability than the blank WPU foam coatings.The ASE/WPU foam coatings were prepared with ammonium stearate emulsion（ASE）,which is commonly used in the market.The results of stabilization performance test showed that SA/CaCO₃ has better foam stability than that of ASE.The effect of drying temperature on the foam stability of ASE and SA/CaCO₃ particles was explored.The results showed that when the drying temperature increased from 80℃ to 160℃,the pore size of the ASE/WPU foam coating increased from 129μm to 232μm.In the same temperature range,the average pore diameter of the SA/CaCO₃/WPU coatings hardly changed,maintaining about 100 μm,which showed that SA/CaCO₃ has better heat resistance and foam stability than ASE.The results of product performance tests showed that the performance of SA/CaCO₃/WPU foam coatings were better than ASE/WPU foam coatings.