Effect Of Foaming Agent System On The Structure And Properties Of Starch-based Foaming Materials

Starch-based foaming material is a green,degradable loose filler material,which is of significance to replace the traditional petroleum-based foaming material to reduce environmental pollution.However,starch-based foam materials have defects such as low material expansion rate and poor mechanical properties,which limits their general application.Foaming agents play an important role in starch processing.During the starch expansion process,the gas generated by thermal decomposition will affect the formation and growth of the internal bubble core.Based on the"two-step method"extrusion foaming technology independently developed by the research group,this work firstly discussed the mechanism of water molecules in the foaming process,and used starch granules as raw materials to prepare starch-based foaming materials.Establish a blowing agent system with water as the blowing agent On this basis,sodium bicarbonate and water were added to the mixture as a composite blowing agent system;and sodium bicarbonate modified with glyceryl monostearate was used to improve its thermal decomposition interval,and different composite blowing agents were established Systems to improve the structure and performance of foam materials.The specific research is as follows:1. The influence of different moisture and temperature on starch-based foaming materials were investigated,and a single foaming agent system for starch extrusion was established.The results show that when the water content of the starch granules increases from 12%to 18%,the glass transition temperature of the starch granules gradually decreases from 170°C to 120°C,and the granules are easier to plasticize;the number of material cells gradually changes The pore size becomes larger,and the structure changes from a closed cell structure to an open cell structure;when the moisture content is 14%-16%,The expansion rate of material is from 3.6Increased to 5.5,density decreased from 38.3kg/m~3 to 30.2kg/m~3;resilience and recovery rate increased from 105.2%,69.3%to 113.1%,73.7%;As the foaming temperature increases,starch plasticizing effect,the water utilization and evaporation rate is improved,foaming gas is sufficient,the cell pore diameter of the material becomes larger,and the open structure of the combined fracture becomes more;when the foaming temperature is 190°C-205°C,The expansion rate of material is increased from 4.2 to 5.3,the density is reduced from 60.1kg/m~3to 30.1kg/m~3;the resilience and recovery rate are increased from 111.2%and 69.8%to120.2%,77.7%;2. The composite foaming agent system with water and sodium bicarbonate was established,the effect of bicarbonate content on the microstructure and mechanical properties of starch-based foaming materials was discussed.The thermal decomposition range of sodium bicarbonate is 70°C-160°C,which is lower than the processing temperature of the conveyor section of the extruder:130°C-150°C;the content of sodium bicarbonate is increased from 0‰to 6‰,the number of cells in the material increases and the distribution become more uniform;the expansion rate increases from 5.2 to 6.6,and the density decreases from 34.2kg/m~3o 28.1kg/m~3;The recovery rate increased from 113%,73.7%to 118.5%,80.1%;when the content of sodium bicarbonate was further increased to 9‰,the starch was thermally degraded during extrusion,the melt strength of the extrudate is reduced,the material cells are merged,and the pore size is uneven;the expansion rate is reduced by 2.3,the density is increased by 22.1kg/m~3;the resilience and recovery rate are reduced by 5.2,respectively%,6.4%;3. The sodium bicarbonate was modified by glyceryl monostearate to improve thermal decomposition interval,and the effect of the degree of agreement between the thermal decomposition temperature of the modified sodium bicarbonate and foaming temperature on the starch-based foaming material was discussed.The thermal decomposition interval of sodium bicarbonate increased from 70°C-160°C to 125°C-190°C with the increase of the amount of glyceryl monostearate;when the thermal decomposition interval of sodium bicarbonate changed from When 70°C-160°C is increased to 110°C-180°C,the number of cells of the material increases and the distribution is uniform,which is a complete open cell structure;the expansion rate is increased from 6.6 to 7.6,and the density is increased from28.3kg/m~3 decreased to 23.2kg/m~3;resilience and recovery rate increased from 117.5 and 74.1to 127.9 and 82.2.The reason is the closer the thermal decomposition temperature range of sodium bicarbonate is to the foaming temperature,the more synchronized the thermal decomposition of sodium bicarbonate and the generation of bubble nuclei,the generated gas can be maximized for the growth of bubble nuclei.