Preferred helmet material

Text/Polymer Meite

The helmet made of PC/ABS alloy has greatly improved its strength and toughness, it can maintain good performance in a variety of high and low temperature environments, and some performance is even better than pure PC or ABS. Significantly improved characteristics make PC+ABS most popular helmet material.

Fig. 1. Alloy PC/ABS

One, PC/ABS alloy

The structure and characteristics of PC and ABS have been described in detail in a previous article. Today we will focus on characteristics of PC/ABS alloy. PC/ABS alloy, which uses PC and ABS as main raw material, combines good physical properties of two materials, has good low temperature formability and impact resistance, high heat distortion temperature and light fastness. Compared with PC, alloy system reduces overall melt viscosity, improves processing performance, and greatly improves stress cracking resistance of product; Compared with ABS, it improves heat resistance and weather resistance, and cost is between PC and ABS. has both good properties and can be better used in helmets, automobiles, electronic appliances and other industries.

2. Factors affecting modification of PC/ABS alloy blend

In order to achieve excellent mixing effect, five principles must be considered when mixing PC/ABS alloys: matching polarity, same surface tension and diffusivity, same viscosity, and similar solubility parameters. The distribution ratio of various components in PC/ABS alloy, choice of compatibilizer and process conditions have a great influence on its comprehensive performance,

Table 2-1 Factors affecting PC/ABS alloy variation

Among them, influence of compatibilizer on whole system is very significant. The compatibilizer can reduce surface tension between polymers and particle size of dispersed phase, increase thickness of interfacial layer, and improve stability. mixed phase structure, thereby improving mechanical properties of alloy.

Fig. 2. SEM photographs of PC/ABS alloy and PC/ABS/MBS alloy

[1]Wu Qianqian, Cheng Fengmei, Luo Yi, Zheng Yaxuan, Li Haidong. Elastomer MBS Toughened PC/ABS Alloy[J].Elastomer, 2019, 29(06):7-11.

By observing Figure 2 (1), we can see that there is an obvious interface between two phases of PC and ABS, and cross section of alloy is uneven. The capacity is limited, as can be seen from Figure 2. (2) After adding MBS to system, two-phase interface becomes blurred and distribution becomes more uniform, and a certain interface transition layer is formed between two-phase interfaces, indicating that addition of MBS can improve compatibility. made of PC/ABS alloy.

3. Common PC/ABS Helmet Grades and Casting Problems

3.1 PC/ABS grades for conventional helmets

There are many grades of PC/ABS alloys and their properties also vary slightly. When choosing a brand, manufacturers are guided by characteristics of their products in order to optimize brand.

Table 3-1 is a common grade of PC/ABS alloy

3.2 Causes of molding defects in PC/ABS helmets

In general, materials from which helmets are made are complex, but most of them are cast directly from raw materials, and if defects occur, they must be eliminated purposefully.

1. When forming a PC/ABS alloy material, raw material is not completely dried. If an easily hydrolysable heterochain compound is not sufficiently dried, it hydrolyzes readily upon melting, and small molecules gasify to form bubbles, forming voids in polymer. These voids are central fulcrums that are most likely to collapse after material is subjected to stress. .

2. During processing, such as melt injection, part close to mold is cooled first, and then middle part is cooled. Therefore, due to different temperatures caused by cooling rate, states of molecules are different. , and misoriented or oriented molecules are different. Cooling in mold for a long time will cause internal structure unevenness and internal stresses, which will cause cracks, cracks and other defects inside polymer.

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