Adding EVA to PC/PE alloy can reduce the interfacial tension between PC and PE phases and decrease the size of dispersed phases. As the EVA content increases, the particle size of the dispersed phase decreases. When the EVA content is 1%, the particle size of the dispersed phase tends to be constant. Continuing to increase the EVA content to 3%, the particle size of the dispersed phase remains unchanged. The compatibilization effect of EVA on PC/PE is also manifested in increasing the impact strength of the alloy. When the EVA content exceeds 5%, the trend of increasing impact strength is not significant.
The biggest feature of EVA is that it can improve the weld seam strength of PC/PE alloy. The strength of the weld seam is a serious problem in plastic processing, especially injection molding. The weld seam is usually the weakest mechanical performance area in molded products, especially in blends. The weld strength of PC/PE alloy is lower than that of pure PC, and adding EVA can make the dispersed particles of PE smaller and more evenly dispersed. Adding 1% EVA can increase the weld strength of PC/PE alloy by three times. The weld seam strength of EVA expanded PC/PE alloy increases with the increase of injection molding temperature. This is because as the temperature increases, the viscosity of the blend decreases, which is beneficial for the dispersion of EVA. The EVA expanded PC/PE alloy was injection molded into single gate tensile specimens without fusion joints and two gate tensile specimens with joints. The tensile strength ratio, elastic modulus ratio, and elongation ratio of the two specimens with different EVA contents were measured at different injection temperatures. The results are shown in Figure 5-11. As shown in Figure 5-11, when the EVA content is about 0.5%, the tensile strength ratio, tensile modulus ratio, and elongation ratio of the welded and non welded samples of the alloy all reach their maximum values. Single layer co extrusion cast film production line www.handern.com
In the EVA enhanced HDPE/PC system, EVA can improve the processing flowability of the alloy system, but significantly reduces the mechanical properties of the alloy. This is because EVA introduces short branches composed of polar acetic acid groups in the ethylene chain, disrupting the crystalline structure of polyethylene, reducing crystallinity, increasing the distance between macromolecular chains, making EVA more flexible and elastic than polyethylene, and increasing the overall fluidity of the system. At the same time, for HDPE/PC blends without EVA, as the PC content increases, the flowability of the blend system first increases and then decreases. When adding around 15 units of PC, the system has the best fluidity. The impact strength increases with the increase of EVA dosage. Because EVA can increase the interfacial force between HDPE/PC phases, reduce interfacial tension, and better transfer stress between the two phases when the material is subjected to external forces, the ability of the interface to resist crack propagation is increased, resulting in higher impact strength of the system compared to the unmodified system. But when the amount of EVA exceeds 15 parts by mass, the effect is not ideal.
Ionomer compatibilizer is a new type of compatibilizer for PC/PE alloys. It is a product of random copolymers of ethylene and methacrylic acid neutralized to varying degrees by zinc or sodium ions. This compatibilizer has been commercialized, such as DOW’s Sur lyn8940 (acrylic acid content 15%, sodium salt neutralization degree 30%) and Du Pont’s Surlyn 8660 (acrylic acid content 5%~20%, sodium salt neutralization degree 70%). Surlyrn 8940 increases the elastic modulus, yield strength, and elongation at break of PC/HDPE (80/20) alloy, and the maximum performance is achieved when its addition amount is 1%.
The combination of ionomer and polyhydroxybisphenol A ether in a 1:1 ratio has a better compatibilization effect on PC/HDPE alloy. The compatibilization effect of ionomers on PC/PE alloys is related to the acrylic acid content and sodium ion neutralization degree in the ionomers. The suitable acrylic acid content is 12%~15%, and the sodium ion neutralization degree is 50%.
