Development of LDPE/EVA foaming materials for modern plastics processing Li Xuefeng Peng Shaoxian Yu Huaxing (Department of Chemical Engineering, Hubei Institute of Technology, Wuhan, 430068) Wu Hua (Shanghai No. 6 Plastics Plant, 20020(1)08% with low permanent deformation (25%), gelled The rate of 7553% cell size is uniform and the performance is good.
Low density polyethylene (LDPE) foam plastics have excellent physical, chemical and mechanical properties. It is strong, resistant to flexion, abrasion resistance, excellent electrical insulation, thermal insulation and chemical resistance, and is widely used in packaging, chemical, construction and other fields. One of the directions for the further expansion of LDPE is to develop a closed-cell foam product that is soft, flexible, and has uniform cells and fine densities. This article uses ethylene vinyl acetate copolymer (EVA) modified LDPE, and then mold foaming, mainly discussed the impact of components, process conditions on the performance of the foam. Yongchun Light Industry Machinery Plant; QLB-350X350X2 flat vulcanizing machine, Wuxi First Rubber Machinery Equipment Factory; XL-100A tensile testing machine, Guangzhou Experimental Instrument Factory; XS-B1 laboratory optical microscope, Jiangnan Optical Instrument Factory; LX-A Shaw A type hardness tester, Shanghai Liuzhong Measuring Instrument Experimental Factory.
4 Performance Test 1.4.1 Performance Test (See Table 1) Table 1 Performance Test Instrument and Method Used Performance Sample Size Instrument Test Method Apparent Density Standard Sample Vernier Caliper Analysis Balance 66 Tear Strength 50mm Long, Wide Cut Tear 20mm Impact Resilience Long and thick 16mm steel ball Diameter of steel ball from the surface of the sample 476mm Compression set length 20mm, Plate vulcanizer GB6669-86 Compression sample 25%, Keep 1h Shore A hardness Sample preparation Standard Shore A hardness tester GB2411 2 Gel Rate test 1 Experimental part 1 Raw material 075 (IC7A), Beijing Yanshan Petrochemical Company; EVA, Mitsui Petrochemical Company; Azodicarbonamide (AC), Dicumyl peroxide (DCP), Stearic acid (SA) Zinc oxide (ZnO) is a commercially available industrial product.
1.2 Sample preparation Add 100 parts (mass part, the same below) of LDPE to the double-roll mill (roller temperature is 110°C), add appropriate proportion of EVA and EPDM after melting and mix evenly (5min), then add DCP in order. (1.5 parts), and mix well (10 min) to make flakes. The appropriate amount of material is added to the preheated mold, placed on a plate vulcanizing machine, pressurized to 8 MPa at 170° C., maintained pressure for 15 minutes, and pressure relief foamed.
1.3 Instruments and Equipment Accurately weigh the filter paper on the analytical scale. Cut the sample into small strips of 5mm in width and 1mm in width, wrap it in filter paper, and have a master's degree in weighing materials. 5 papers have been published. Now mainly engaged in polymer modification and molding processing research.
The modern plastics processing application m2 is placed in a three-necked flask with xylene as a solvent and boiled under reflux for 20 h continuously, placed in a vacuum oven, baked at 80° C. for 6 h, weighed m3 after removal, and calculated the gelation rate according to the following formula.
1.4.3 Microscopic analysis The specimens were cut into thin slices, soaked in blue ink for 8 min, taken out and allowed to dry. Microscopic structures of the cells were observed on a glass slide and photographs were taken.
2 Results and Discussion 21 Effect of Process Conditions on the Properties of Foamed Materials Table 2 shows the influence of the molding temperature on the properties of foamed materials. From Table 2, it can be seen that when the molding temperature is 160° C., the apparent density of the obtained foamed material is 0.570 g/cm 3 , and the foaming amount of the blending system is very small. This is because the AC foaming agent decomposes at this temperature condition. The amount is too small. As the mold temperature rises, the apparent density of the foamed material decreases with increasing temperature, and the AC decomposition progresses gradually. The difference between the Shore A hardness and the impact resilience above 170° C. is not significant, which is related to its foaming multiple, but the mold temperature is The 170C foam material exhibits a lower compression set due to the higher number and small size of cells at lower temperatures and the larger cell size at higher mold temperatures. The difference in the two cell sizes is clearly seen. This is associated with lower melt viscosity at higher temperatures, which favors gas diffusion, expansion, and the formation of large cells. Smaller cells can better maintain the structural dimensions of the foam, resulting in low compression set.
Because the gas can diffuse and dissolve in the polymer melt.
At the same time, it was found that the impact of molding pressure on the properties of the foaming material is much smaller than the molding temperature and time. When the pressure is between 4 and 10 MPa, there is almost no change in the properties of the foaming material. This is because high pressure favors the formation of supersaturated melts, while low pressure favors gas diffusion in the melt. If the pressure is too low, because the gas generated by AC decomposition is too large in the melt and the solubility is small, it will cause a large amount of gas to escape. Therefore, the molding temperature is 170°C, the pressure is 8MPa, and the pressure is kept for 15 minutes. Research.
Table 3 Effect of Molding Time on the Properties of Foaming Material Molding Time/min Shore A Hardness Impact Resilience, % Compression Set, % Table 2 Effect of Molding Temperature on the Properties of Foamed Materials Table 3 shows the properties of foaming materials for molding time influences. It can be seen that the foaming time of the foaming material with a molding time of 10 min is small, and as the time goes by, the density of the foaming material decreases, and the foaming ratio gradually increases. There is still a large amount of AC without decomposition during 10 minutes of molding, and after 15 minutes, the density of the foamed material changes little, AC decomposition is complete, and the longer the molding time, the more complete the AC decomposition. The EVA resin and NR, BR, EPDM elastomer modified LDPE foam materials are also selected by the effect of the 2EVA modifier on the properties of the foam material. These resins and elastomers are not as sensitive to LDPE changes in viscosity during the processing temperature range. In a wider temperature range, it can be adapted to the preferred viscosity state of foaming to form a stable cell structure. Experiments have shown that the cell structure of the NR modified LDPE foamed material is better, but the material color is darker. The LDPE/BR system is unstable in foaming, and can easily form uneven pore structure and connected large bubbles, which deteriorates the quality of the foam body. The foamed material of EVA and EPDM modified LDPE has uniform, fine and flat appearance and is a good modifier for LDPE foaming materials. The effect of EVA and EPDM content on the density and tear strength of modified LDPE, LDPE/EVA exhibited a higher foaming ratio and higher tear strength; at the same time, LDPE/EVA has a stronger intermolecular force. This foaming material is suitable for bonding in applications. With the gradual increase of the content of EVA, the apparent density of the foamed material gradually increases. This is because EVA increases the viscosity of the melt and limits the expansion of the gas to some extent. At the same time, it can form small and uniform cells. , excellent elasticity, small permanent deformation of the foam material.
The content/parts by mass of the modified LDPE in the modified LDPE can be seen that the impact resilience of the foamed material gradually increases with the increase of the EVA content, reaches the maximum when the EVA is 30 parts, and then gradually decreases. The compression set shows a similar pattern of change, with a minimum at 30 parts of EVA. The LDPE/EVA mass ratio of 100/30 foamed material has better overall performance. From the change trend of the gelation rate, it can be seen that the foam has a higher gelation rate when the EVA content is 30 parts. In the blending modification system, both LDPE and EVA cross-linking reactions occur. As the content of EVA increases, the degree of cross-linking gradually increases to a maximum value. Excess EVA consumes a large amount of cross-linking agents, which in turn cross-links the system. Declined. The main factors influencing the performance of foamed materials are the cell structure, including the open or closed cells of the cell, the size and degree of compaction. 51. The moderate temperature, viscosity and strength of the melt can evenly wrap the gas generated by AC decomposition. At the nucleation sites, the cell size is uniform and dense. From the micrographs, the cell size gradually decreased with the increase of the EVA content. When the EVA content was 30 parts, the cell structure was more uniform and dense than the other ones, showing a regular polygonal shape. The walls are also uniform compared to other components, exhibit moderate melt viscosity and strength, and at this time also exhibit large impact resilience and small compression set. Effects of Elastomers on Tear Strength of Modified LDPE Foaming Materials 1994-2014 China Academic Journal 60 photos of LDPE/B/A foamed materials with different EVA content (100X magnification) 3 Conclusion The test results show that the foaming temperature is suitable for this system. For 170°C, the molding time is 15 minutes and the pressure has no significant effect.
Adding EVA to LDPE can increase melt viscosity, reduce cell size, increase tear strength and have a good appearance.
(100/30) Foaming material has a high gelling rate, uniform cell size, and dense cell walls.
The (100/30) foam material exhibits high impact resilience (38.08%), low compression set (5%), and good overall performance.
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