The composition and structure of plastic raw materials

Some plastics themselves are pure resins, such as polyethylene can produce belt hooks, PE hooks, polystyrene can produce some shoe hooks, slippers hooks, etc., which are called single-component plastics. In addition to synthetic resins, some plastics also contain other auxiliary materials, such as plasticizers, stabilizers, colorants, various fillers, etc., which are called multi-component plastics.

(1) Synthetic resin

Synthetic resin refers to the high molecular compound synthesized by chemical, physical and other methods by first producing low molecular compounds (monomers) with certain synthesis conditions using coal, calcium carbide, petroleum, natural gas and some agricultural and sideline products as the main raw materials. The properties of these compounds are similar to those of natural resins (such as rosin, amber, shellac, etc.), but their properties are superior to those of natural resins. For example: synthetic resin dentures.

The content of synthetic resin accounts for 40% to 100% of the total components of the plastic, which plays a role in bonding. It determines the main properties of the plastic, such as mechanical strength, hardness, aging resistance, elasticity, chemical stability, photoelectricity. sex, etc.

(2) Plastic additives

Plastic additives The purpose of adding additives to plastics is to improve processing performance, improve efficiency and reduce costs. The proportion of additives in plastic materials is small, but it has a great influence on the quality of plastic products. Different types of plastics require different types and amounts of additives due to different molding processing methods and use conditions. The main additives are as follows:

  1. Plasticizer

Plasticizers can increase the flexibility, extensibility and plasticity of plastics, reduce the flow temperature and hardness of plastics, and are beneficial to the molding of plastic products. Commonly used are phthalates, sebacates, chlorinated paraffins and camphor. Our most common is camphor.

  2. stabilizer 

We all know that in the process of processing, storage and use of plastic products, under the action of light, heat and oxygen, the aging phenomenon of fading, embrittlement and cracking will occur. In order to delay and prevent the occurrence of aging, stabilizers must be added. Those mainly used to prevent thermal aging are called thermal stabilizers; those mainly used to prevent oxidative aging are called antioxidants; those mainly used to prevent photoaging are called light stabilizers, and they are collectively referred to as stabilizers. The best plastic stabilizer today is methyl tin heat stabilizer (181 for short), which is very effective for calendering, extrusion, injection molding and blow molding of rigid polyethylene (PVC). And because of its high safety, it is especially used in food packaging and high-definition rigid polyethylene products. At the same time, it is also widely used in plastic doors and windows, water pipes, and decorative materials to replace other highly toxic plastics. Heat stabilizers. It is widely used in America, Europe, Japan. In recent years, 181 methyl tin heat stabilizer has been widely used in my country.

3. flame retardant

The additives that can improve the flame resistance of plastics are called flame retardants. Most plastics containing flame retardants are self-extinguishing, or the burning rate is slowed down. Commonly used flame retardants are antimony oxide and compounds of aluminum and boron, halides and phosphates, tetrachlorophthalic anhydride, tetrachlorophthalic anhydride, etc.

4. Antistatic agent

Antistatic agents play a role in eliminating or reducing static electricity generated on the surface of plastic products. Most of antistatic agents are electrolytes, which have limited compatibility with synthetic resins, so that they can migrate to the surface of plastics to absorb moisture and eliminate static electricity.

5. foaming agent

Plastic blowing agent is a low-molecular organic compound that can be vaporized at a certain temperature, such as dichlorodifluoromethane; or an organic compound that decomposes gas when heated. These gases remain in the plastic matrix to form a foam with many fine foam structures. Commonly used are azo compounds, nitroso compounds, etc.

6. Colorant 

Colorants are used to color plastics. Mainly beautify and modify. About 80% of plastic products are colored into final products.

7. lubricant

Lubricants are substances added to improve the mold release properties of plastics during thermoforming and to improve the surface finish of products. Commonly used lubricants are: stearic acid and its salts, paraffin wax, synthetic wax, etc.

  8. Reinforcing materials and fillers

In many plastics, reinforcing materials and fillers occupy a considerable proportion, especially reinforced plastics and calcium plastic materials. The main purpose is: In order to improve the strength and rigidity of plastic products, various fiber materials or inorganic substances are generally added. The most commonly used reinforcement materials are: glass fiber, asbestos, quartz, carbon black, silicate, calcium carbonate, metal oxides, etc.