Study Of EVA Foamed Materials By Thermal Expansion Microcapsules Synthesized In Different Water And Oil Phase Systems

The structure of thermal expansion microcapsules is similar to a macroscopic spherical closed tank,the shell is composed of a pol ymer with good air tightness,and the wrapped core material is gen erally low-boiling hydrocarbons.At the outside temperature rises,th e gasification of the internal core material promotes expansion of th e polymer shell when the shell reaches the glass transition temperat ure,produce thermal expansion effect.Due to it is unique core-shel l structure,after expanding the microcapsules can maintain a stable form within a certain temperature range.Based onthis feature,therm al expansion microcapsules have broad application prospects in the fields of microfoam products,fabric printing and microfluidics.How ever,thermal expansion microcapsules have technical problems such as wide expansion temperature window and uneven expansion in actual production,The intuitive performance is that the particle size of the microcapsules is different,and the microcapsules do not expand simultaneously during processing,the result is that there is a wide distribution of bubbles in the materials,this greatly affects the appli cation of foam products.Currently most of the research is still focu sed on the influence of the basic formulas such as the liquid chara cteristics and shell composition on the thermal expansion performan ce of microcapsules,physical factors such as particle size and shell thickness have little research on their thermal expansion properties,and basic data are lacking.Therefore,realize the control of expansi on temperature and expansion ratio of thermal expansion microcapsu les by adjusting the water phase and oil phase system of thermal e xpansion microcapsules,it is of great significance to broaden the a pplication of environmentally friendly and lightweight products.In this paper the suspension polymerization system was constru cted to prepare thermally expandable microcapsules by selects AN,MA,HPA as polymerized monomers,and the core material is Hexa ne,the saturated sodium chloride solution is the aqueous phase,ma gnesium hydroxide as dispersant.The effects of the water phase sys tem and the oil phase system on the particle size,shell thickness a nd thermal expansion performance of the thermal expansion microca psules were systematically studied;The relationship between the particle size of the microcapsule,the thickness of the shell layer and t he thermal expansion performance was established.and further expl ore the effect of microcapsules with different particle size and shell thickness on the comprehensive properties of foamed EVA composit e,the effect mechanism of different types of microcapsule foaming agents on the cell quality and thermal insulation performance of the prepared microfoaming materials was clarified.Get the following co nclusions:(1)As the amount of dispersant added increases,the average p article size of the thermally expandable microcapsules tend to decre ase;properly increasing the volume ratio of water-oil phase can ef fectively reduce the chance of collision and agglomeration of oil-ph ase droplets,there by achieving control of the average particle size of microcapsules,the average particle size of microcapsules decreas es from 10.8 μm to 3.5 μm,when the volume ratio of water-oil ph ase increases from 3/1 to 9/1.(2)The smaller the average particle size of the thermally expa ndable microcapsules,the higher the expansion temperature.the corr esponding expansion temperature increased from 124 ℃ to 138 ℃when the average particle size of microcapsules decreased from10.8μm to 3.5 μm;and the excellent thermal expansion performance,st able foam temperature range of 30 ℃,expansion ratio of more than 2 times,when the average particle size of the microcapsules is maintained at 7.6-4.9 μm.the thermal expansion performance becom es worse,when continue to reduce the particle size of the microcap sules.(3)The thickness of the thermal expansion microcapsule shell l ayer can be adjusted by changing the amount of core material adde d,The shell thickness decreased from 436 nm to 196 nm when the amount of core material added increased from 21.30 wt% of the oil phase to 52.00 wt%.(4)The expansion temperature of the thermal expansion microc apsules present increase first and then decrease as the amount of co re material added increases.The expansion temperature increased fro m 122 ℃ to 149 ℃,when the amount of core material added incr eased from 11.92 wt% to 54.90 wt%.The thermal expansion perfor mance increases first and then decreases with the increase of the a mount of core material added,the microcapsules have an expansio n ratio of 4 times,and the stable bubble temperature range is abov e 20 ℃,when the amount of core material added is 35.13-52.00 w t%,and the thickness of the shell layer is between 290-196 nm.(5)As the particle size of the microcapsules decreases,the cell morphology of the foamed EVA composite material is significantly improved,and the thermal conductivity of the material graduallydecreases,when thermal expansion microcapsules are used as the foaming agent.The regularity of the cells is increased,the cell size distribution is more concentrated,and the thermal conductivity of the foamed EVA composite material is reduced from 0.0724 W/m·K to0.0607 W/m·k,when the average particle size of the microcapsules is reduced from 10.8 μm to 3.5 μm.(6)As the thickness of the shell of the microcapsules foaming agent decreases,the cell morphology of the foamed EVA composite material has a positive effect within a certain range;simultaneously,the coefficient of thermal conductivity increases first and then stabil izes.The cell morphology of the foamed EVA composite was excell ent,and the thermal conductivity decreased from 0.0709 W/m·K to0.0552 W/m·K,when the shell thickness of the microcapsules blowi ng agent was reduced from 436 nm to 221 nm.