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Composition and classification of plastics

Composition and classification of plastics2017.01.18

The plastics that we usually use is not a pure substance, it is made of many materials, and polymer (or synthetic resin ) is the main component of plastic. Besides, it also need to add a variety of auxiliary materials to the polymer to improve the performance of plastic, such as fillers, stabilizers, colorants, plasticizers, lubricants, etc. Thus it can become a high performance plastic.

Synthetic resins is the main components of plastic, their content is 40%~100%. Due to the large content and its properties often determine plastic properties, so resin is often viewed as synonymous with plastic. Actually, resins and plastics are two different concepts. Resin is the original polymer, it is not only used to make plastics, but also paints, adhesives and synthetic materials. But a tiny part contains 100% resin, the vast majority of plastic need the main components resin and other substances.

Fillers can increase strength and heat resistance performance and reduce costs. Adding wooden powder to phenolic resin can greatly reduce costs, this makes bakelite became one of the most cheapest plastic, also it can significantly improve the mechanical strength. There are organic fillers and inorganic fillers, the former has wood powders, rag, paper and fabric fibers, etc; the latter are glass fibre, diatomaceous silica, asbestos, and so on.

Plasticizers can increase plasticity and flexibility of plastics, reduce the brittleness and make it easy for the processing. Plasticizers are high-boiling organic compounds that generally mixed-soluble with resin, nontoxic, odorless, light and thermal stability, the most commonly used are phthalic acid esters. For example, soft PVC can be obtained if add more plasticizer when producing PVC, if add less or not add plasticizer it can get rigid PVC.

In order to prevent synthetic resin has light and heat of decomposition and destruction during processing and use, and extend the service life, it needs to add stabilizer to plastic. Commonly used are stearate, epoxy resin and so on.

It can be divided into thermoplastic and thermosetting plastic according to the nature of plastic heating.


Thermoplastic molecular structure is linear structure, soften or melt when heated, it can be made into a certain shape, cooling and hardening. Heated to some extent it soften again, cooled and hardened. This process can be repeated several times.

Molecular structure of thermosetting plastics is the body structure, softens when heated. It can plastic into definite shape, but heated to a certain degree or after adding a small amount of stabilizer, then hardened stereotype, it does not become soft and change its shape when reheating. Heating won't make it soften after processing of thermoset plastic, therefore, it cannot be recycled. Bakelite, amino plastics and epoxy belongs to this type of plastic. Molding process of thermoset plastic is complex, so continuous production is difficult, but it has good heat resistance, not easy to deformation and relatively inexpensive. If you think this is helpful and have interest in plastics raw materials, you can follow OKCHEM Linkedin Page or visit our website directly!

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