1. Compatibility of additives with polymers
If the compatibility is not good, the additives will be easily precipitated. The precipitation of solid additives, commonly known as "blooming"; the precipitation of liquid additives, called "exudation" or "sweating." After the precipitation of the auxiliary agent, the effect of the auxiliary agent is lost, and the appearance of the plastic product is affected. However, it should also be noted that for certain auxiliaries, it is not required to have good compatibility with the polymer. For example, the compatibility of the lubricant should not be too large, otherwise it will act as a plasticizer to soften the polymer.
The compatibility of the auxiliaries with the polymers depends primarily on their structural similarity. For example, a more polar plasticizer is more compatible in polar polyvinyl chloride than a weaker one. As another example, the introduction of longer chain alkyl groups in antioxidants and light stabilizers improves their compatibility with polyolefins.
For inorganic fillers and inorganic pigments, they are insoluble in the polymer, but are dispersed heterogeneously in the polymer. For this type of auxiliaries, their dispersibility is required, and the fineness is as small as possible.
2. Interaction between additives and polymers in terms of stability
Auxiliaries must be stably present in plastic products for a long time. Therefore, attention should be paid to the interaction between the additive and the polymer in terms of stability. Some polymers (such as polyvinyl chloride) decomposition products are acid-base, which can decompose some additives; some additives can accelerate the degradation of polymers.
3. Auxiliary durability
The loss of additives is mainly through three routes: volatilization, extraction and migration. The magnitude of the volatility depends on the structure of the auxiliaries. For example, since the molecular weight of butyl phthalate is less than that of dioctyl phthalate, the former is much more volatile than the latter. The extraction of the auxiliaries is directly related to their solubility in different media, and the appropriate auxiliaries should be selected according to the environment in which the products are used. Mobility refers to the transfer of an adjuvant from an article to an adjacent article, the likelihood of which is related to the solubility of the adjuvant in the different polymers.
4. Adaptability of additives to processing conditions
Processing conditions The requirements for additives are mainly heat resistance, that is, the additives are not decomposed, less volatile and sublimated at the processing temperature. At the same time, it is necessary to pay attention to the corrosive effects of additives on processing equipment and molds. Different polymers have different processing conditions; the same polymer may have different auxiliaries depending on the method of processing. In short, the selected additives should have applicability to the processing conditions.
5. Relationship between product use and selected additives
The important basis for the selection of additives is the ultimate use of the product. Products with different uses have certain requirements on the appearance, odor, durability, pollution, electrical properties, thermal properties, weather resistance and toxicity of the additives used.
The toxicity of additives has long been a cause of concern. In particular, the health and safety issues of food and pharmaceutical packaging materials, medical devices, water pipes, and plastic products for toys have received increasing attention. The auxiliaries used in the above plastic products by various countries strictly stipulate the variety and dosage.
6. Synergistic action and phase interaction
A variety of auxiliaries in the same polymer, such as appropriate blending, often synergistically between the auxiliaries, one of the main purposes of the "synergy" polymer formulation research is to find synergy between the auxiliaries. Of course, simplifying the components and reducing the cost are also the purpose of formulation research. If the formula is not properly selected, it may cause a "phase reaction" between the additives, so it should be avoided as much as possible. Chemical changes and discoloration between different additives should also be avoided.
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