Studying The Synergy Mechanism Of Blowing Agent Blend During Foaming Process

The compounding of the blowing agent is a new method to improve the expansion ratio and product quality,but the synergy mechanism of blowing agents is not yet clear.In this paper,the batch foaming and extrusion foaming experiments were carried out to study the dissolution and diffusion of the blowing agent blend,and the online rheological and foaming properties of the polymer/blowing agent blend.In view of the blowing agent blend system,the model of cell growth and the corrugation formation mechanism of foaming sheet were revised,and the synergy mechanism of the blowing agent blend was discussed.The specific research and results are as follows:1.Dissolution and diffusion properties of PP/CO2,PP/CO2/ethanol and PP/CO2/water were studied by gravimetric analysis.The results showed that the solubilty of the blowing agent blend in PP was higher than that of the sum of each.It indicates that the plasticizing effect of the co-blowing agent is beneficial to increase the solubility of the blowing agent blend in PP.The diffusion coefficient of the blowing agent blend increased with solubility,which revealed significant synergy between two blowing agents.2.The online rheological properties and critical degassing pressure of the PP/blowing agent blend were studied using a self-designed online rheological slit die equipped with an ultrasonic device.The function of the viscosity of polymer/blowing agent and degassing critical pressure with foaming agent content and ratio were deduced.The results showed that the degassing critical pressure of CO2/ethanol blowing agent blend in PP was approximately the sum of the degassing critical pressures of each.For certain content of blowing agent blend,its degassing critical pressure dropped with the increase of ethanol.3.The effect of blowing agent blend on bubble growth was studied by extrsion foaming experiment and theoretical calculation of bubble growth.The results showed that the addition of ethanol was beneficial to decrease the bubble growth rate,reduce the escape of blowing agent and increase the expansion ratio.Product with high expansion ratio can be obtained in a wider foaming temperature range with the addition of ethanol.Compared to pure CO2,CO2/ethanol blowing agent blend broadened the foaming temperature range by 20°C.4.Revised the extrusion foaming corrugation model,and extended it to blowing agent blend system.The accuracy of the theoretical model was verified experimentally,and on this basis,the influece of the ratio of the blowing agent blend to the corrugation of PP foamed sheet was calculated.The results showed that the addition of ethanol can reduce the corrugation of PP foamed sheet and improve the surface quality of the product significantly.At 165?,compared with pure CO2,CO2/ethanol blowing agent blend containing 25%ethanol can reduce the corrugation of the product by 39%.