Most plastics are light in weight, chemically stable and will not rust;
Good impact resistance;
Good transparency and wear resistance;
Good insulation and low thermal conductivity;
Generally, it has good formability and coloring, and the processing cost is low;
Most plastics have poor heat resistance, high thermal expansion rate and easy combustion;
Poor dimensional stability and easy deformation;
Most plastics have poor low temperature resistance, become brittle at low temperature and are easy to age;
Some plastics are soluble in solvents.
Plastics can be divided into thermosetting and thermoplastic, the former can not be used in plastic, and the latter can be produced repeatedly. The physical elongation of thermoplastics is relatively large, generally 50%~500%. Under different elongation, the force does not change completely linearly.
The different characteristics of plastics determine their industrial use. With the development of technology, the research on plastic modification has never stopped. It is hoped that in the near future, this modified plastic can be widely used, even replacing steel and other materials without polluting the environment.
molecular structure
There are basically two types: the first is linear structure, and the polymer compound with this structure is called linear polymer compound; The second is the bulk structure, and the polymer compound with this structure is called bulk polymer compound. Some polymers have branched chains, which are called branched polymers and belong to linear structure. Although some polymers are cross-linked between molecules, the degree of cross-linking is low, which is called network structure and belongs to bulk structure.
Two different structures show two opposite properties. Linear structure, melting by heating, less hardness and brittleness. The body structure is hard and brittle. There are two kinds of polymers in plastics, one is thermoplastic made of linear polymer, and the other is thermosetting plastic made of bulk polymer.
The plastic we usually use is not a single component, but is composed of many materials. Polymer (or synthetic resin) is the main component of plastic. In addition, in order to improve the properties of plastics, various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, colorants, antistatic agents, etc. , must be added to polymer compounds to become a plastic with good performance.
Plastic additives, also known as plastic additives, are some compounds that must be added to improve the processability of polymers (synthetic resins) or the properties of resins themselves. For example, adding plasticizer to reduce the molding temperature of PVC resin and make the product soft; Another example is to add foaming agent to prepare lightweight, vibration-resistant, heat-insulating and sound-insulating foam plastics; The thermal decomposition temperature of some plastics is very close to the molding processing temperature, so it can't be molded without heating stabilizers. Therefore, plastic additives play a particularly important role in plastic molding.
synthetic resin
Synthetic resin is the most important component in plastics, and its content in plastics is generally 40% ~ 100%. Because of its large content and the nature of resin often determines the nature of plastic, people often regard resin as synonymous with plastic. For example, PVC resin and PVC plastic, phenolic resin and phenolic plastic are confused. In fact, resin and plastic are two different concepts. Resin is an unprocessed primitive polymer compound, which is not only used to make plastics, but also used as raw materials for coatings, adhesives and synthetic fibers. Except a few plastics contain 100% resin, most plastics need to add other substances besides the main component resin.
infilling
Fillers, also called fillers, can improve the strength and heat resistance of plastics and reduce costs. For example, adding wood flour to phenolic resin can greatly reduce the cost, make phenolic plastic one of the cheapest plastics, and significantly improve the mechanical strength. Fillers can be divided into two categories: organic fillers, such as wood flour, rags, paper and various fabric fibers; Inorganic fillers, such as glass fiber, diatomite, asbestos and carbon black. The content of fillers in plastics is generally controlled below 40%.
plasticiser
Plasticizer, or plasticizer, can increase the plasticity and softness of plastics, reduce brittleness and make plastics easy to process and shape. Plasticizer (plasticizer) is generally a high-boiling organic compound which is miscible with resin, non-toxic and tasteless, and stable to light and heat. Phthalate esters are the most commonly used. For example, in the production of PVC plastics, if more plasticizer is added, and if no plasticizer is added or less plasticizer is added (dosage
stabilizing agent
Stabilizers mainly refer to agents that keep polymer plastics, rubber and synthetic fibers stable and prevent them from decomposition and aging. In order to prevent synthetic resin from being damaged by light and thermal decomposition during processing and use, and to prolong its service life, stabilizers should be added to plastics. Commonly used are stearate and epoxy resin. The dosage of stabilizer is generally 0.3 ~ 0.5% of plastic.
dyestuff
Colorants can make plastics have various bright and beautiful colors. Organic dyes and inorganic pigments are usually used as colorants. The natural color of synthetic resin is mostly white, translucent or colorless and transparent. In industrial production, colorants are usually used to increase the color of plastic products.
lubricant
The function of lubricant is to prevent the plastic from sticking to the metal mold during molding, and at the same time, it can make the plastic surface smooth and beautiful. Commonly used lubricants include stearic acid and its calcium and magnesium salts.
Oxidation inhibitor
Prevent plastics from yellowing and cracking due to thermal oxidation during heating molding or high temperature use.
In addition to the above additives, there are flame retardants, foaming agents, antistatic agents, conductive agents, magnetic conductive agents, compatibilizers and so on. It can also be added to plastics. So as to meet different use requirements.
antistatic (agent)
Plastics are excellent insulators and easy to carry static electricity. Antistatic agents can give plastics light to medium conductivity, thus preventing the accumulation of static charges on products.