Thermo plastics: plastic that melts when heated, flows to molds that cool down, take shape, and then melts when heated. You can use heat and cooling to make a reversible change (liquid/solid), which is called a physical change. Common thermoplastics its continuous use temperature under 100 ℃, polyethylene, PVC, polypropylene, polystyrene and common plastic known as the big four. Thermoplastic plastics are divided into hydrocarbon, vinyl class containing polar genes, engineering class, cellulose class and other types. Soft when heated and hard when cooled, it can soften and harden repeatedly and maintain a certain shape. It is soluble in certain solvents and has the property of melting and dissolving. Thermoplastic has excellent electrical insulation, especially polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), polypropylene (PP) have very low dielectric constant and dielectric loss, suitable for high frequency and high voltage insulation materials. Thermoplastics are easy to form and process, but they have low heat resistance and are easy to creep. The creep degree varies with load, ambient temperature, solvent and humidity. In order to overcome these weaknesses of thermoplastics and meet the needs of application in space technology, new energy development and other fields, various countries are developing fusible heat-resistant resins, such as PEEK, PES, PASU and PPS. The composites with them as the matrix resin have higher mechanical properties and chemical corrosion resistance, can be hot formed and welded, and the interlayer shear strength is better than epoxy resin. For example, the fatigue resistance of composites made of polyether ether ketone as matrix resin and carbon fiber exceeds that of epoxy/carbon fiber. Its good resistance to impact, good creep resistance at room temperature, good workability, can be used in 240 ~ 270 ℃, is a kind of ideal high temperature resistant insulation materials. With polyether sulfone made of resin as matrix and carbon fiber composite materials in the 200 ℃ has high strength and hardness, at 100 ℃ can keep good impact resistance; Non-toxic, non-combustible, least smoke, good radiation resistance, it is expected to be used as a key part of the spacecraft, but also can be molded into radar radome.
Formaldehyde crosslinked plastics include phenolic plastics, amino plastics (such as urea-formaldehyde - melamine - formaldehyde, etc.).
Other crosslinked plastics include unsaturated polyester, epoxy resin, phthalic diallyl ester resin, etc.
(2) thermosetting plastics
Thermosetting plastics refer to plastics that can be cured or have insoluble (melted) properties under heat or other conditions, such as phenolic plastics, epoxy plastics, etc. Thermosetting plastics can be divided into formaldehyde crosslinked and other crosslinked two types. The resin molecules are crosslinked by linear structure to form a network structure. More heat will break down. Typical thermosetting plastics include phenolic, epoxy, amino, unsaturated polyester, furan, polysilane and other materials, as well as newer polypropylene phthalate plastics. They have the advantage of high heat resistance, not easy to deform when heated. The disadvantage is that the mechanical strength is generally not high, but can be added to the filler, laminated materials or molded materials to improve its mechanical strength.
Thermosetting plastics made with phenolic resin as the main raw material, such as phenolic molding plastics (commonly known as bakelite), have the characteristics of durability, size stability and resistance to other chemical substances except strong alkali. Various fillers and additives can be added according to different USES and requirements. If high insulation properties are required, mica or glass fiber can be used as filler; Asbestos or other heat-resistant fillers may be used for heat resistant varieties; If the variety that asks aseismatic, can use all sorts of appropriate fiber or rubber are filler and agent of a few toughening to make high toughness material. In addition, phenolic resins modified by aniline, epoxy, polyvinyl chloride, polyamide and polyvinyl alcohol acetal can be used to meet the requirements of different USES. Phenolic resin can also be used to make phenolic laminate, which is characterized by high mechanical strength, good electrical performance, corrosion resistance, easy to process, widely used in low-voltage electrical equipment.
Amino plastics are urea formaldehyde, melamine formaldehyde, urea melamine formaldehyde and so on. They have a hard texture, scratch resistance, colorless, translucent and other advantages, adding color material can be made into colorful products, commonly known as dianyu. Due to its resistance to oil, not influenced by weak base and organic solvent (but not acid), can be long-term use under 70 ℃, short-term resistant to 110 ~ 120 ℃, can be used for electrical products. Melamine formaldehyde plastic is higher than urea-formaldehyde plastic hardness, has better water resistance, heat resistance, arc resistance, can be used as arc insulation material.
There are many kinds of thermosetting plastics with epoxy resin as the main raw material, among which about 90% are bisphenol A epoxy resin as the base material. It has excellent adhesion, electrical insulation, heat resistance and chemical stability, small shrinkage and water absorption rate, good mechanical strength and other characteristics.
Both unsaturated polyester and epoxy resins can be made into FRP with excellent mechanical strength. Such as unsaturated polyester fiberglass, its mechanical properties are good, small density (only steel 1/5 to 1/4, aluminum 1/2), easy to process into various electrical parts. The electrical and mechanical properties of plastics made of dipropylene phthalate resin are superior to those of phenolic and amino thermosetting plastics. It has small hygroscopicity, stable product size, good molding performance, acid and alkali resistance and boiling water and some organic solvents. Molding plastics are suitable for manufacturing parts with complex structure, high insulation and temperature resistance. Can generally be in 60 ~ 180 ℃ temperature range use for a long time, heat resistant level can reach class F to H, is higher than phenolic amino plastics and heat resistance.
Silicone plastics with polysiloxane structure are widely used in electronics and electrical technology. Silicone laminated plastics are mostly reinforced with glass cloth. Silicone molding plastic is mainly glass fiber and asbestos as the filler, used to manufacture high temperature resistance, high frequency or submersible motor, electrical appliances, electronic equipment parts and so on. This kind of plastic is characterized by a small dielectric constant and tg delta value, small frequency effect, used in the electrical and electronic industry corona resistance and arc, even if the discharge caused by decomposition, the product is silicon dioxide rather than conductive carbon black. This kind of material has outstanding heat resistance, can be used in 250 ℃. The main disadvantages of polysiloxane are low mechanical strength, small adhesion and poor oil resistance. Many modified silicone polymers, such as polyester modified silicone plastics, have been developed and applied in electrical technology. Some plastics are both thermoplastic and thermosetting. Polyvinyl chloride (PVC), for example, generally for thermoplastic, Japan has developed a new type of liquid PVC is thermosetting molding temperature is 60 ~ 140 ℃; Lundex, an American plastic, has both the characteristics of thermoplastic processing and the physical properties of thermosetting plastics.
Hydrocarbon plastics. Belongs to the non-polar plastic, has the crystallization and the non-crystallization divides, the crystallization hydrocarbon plastic includes the polyethylene, the polypropylene and so on, the non-crystallization hydrocarbon plastic includes the polyphenyl b and so on.
(2) vinyl plastics containing polar genes. In addition to fluorine plastic, most of the amorphous transparent body, including PVC, teflon, polyvinyl acetate, etc. Most vinyl monomers can be polymerized by free - base catalysts.
(3) thermoplastic engineering plastics. It mainly includes polyformaldehyde, polyamide, polycarbonate, ABS, polyphenyl ether, polyethylene terephthalate, polysulfone, polyether sulfone, polyimide, polyphenyl sulfide, etc. Teflon. Modified polypropylene is also included in this scope.
(4) thermoplastic cellulose plastic. It mainly includes cellulose acetate, cellulose acetate butyrate, cellol, cellophane and so on.