Poly – formaldehyde (POM), is one of the five engineering plastics, molecular structure and crystallization make its physical and mechanical properties is very excellent, is a kind of thermoplastic resin with excellent comprehensive properties.
POM is divided into homopolymer and copolymer. Homopolymer POM is directly polymerized by high purity gas formaldehyde, which does not contain ethyl in the molecular chain. It has good extension strength and fatigue strength, but has poor thermal stability and is not easy to process. At present, only DuPont and Asolectron supply homopolymer POM in the world
Copolymer POM is obtained from trimethylformaldehyde and copolymerization. Because the ethoxy group in the molecular chain can effectively stop the chain decomposition, copolymerized POM has good thermal and chemical stability, and is easy to process. At present, the market share of copolymerized POM is more than 80%.
Polyformaldehyde is a highly crystalline polymer with excellent mechanical properties, electrical properties, wear resistance, dimensional stability, chemical corrosion resistance, fatigue resistance, self-lubrication, etc., known as “competition steel”, is an ideal material to replace metals (such as copper, aluminum, zinc and other non-ferrous metals and alloy products).
The fatigue resistance and repeated impact performance of POM is better than that of nylon 66, ABS and other general engineering plastics. The repeated impact resistance of POM makes it have unique advantages in application. And compared with ABS, POM made of keyboard because of better wear resistance, less prone to “oil” phenomenon.
In addition, POM has low water absorption, wear resistance, organic solvent resistance, chemical corrosion resistance, and good electrical properties. The excellent comprehensive performance makes POM widely used in many fields such as electronics and electricity, automobile, machinery manufacturing, chemical industry, building materials and so on.
However, POM also has some shortcomings, such as low impact toughness, notch sensitivity, poor heat resistance, easy decomposition, friction coefficient and so on. These shortcomings greatly limit the expansion of the application scope of POM in various fields. Therefore, the modification of POM has become a hotspot of current POM research.
Although polyformaldehyde is engineering plastics with good comprehensive properties, in order to further improve its heat resistance, rigidity, dimensional stability, fatigue resistance, creep resistance and mechanical properties, polyformaldehyde is often composite enhanced to meet the use of a variety of special purposes. The fillers used in the composite reinforcement of polyformaldehyde are mainly glass fiber, carbon fiber, glass beads, talcum powder or potassium titanate whiskers.
It is mainly used to replace copper, zinc and other metals to make bearings, high strength gears, structural parts, etc.
Due to the high crystallinity (generally up to 70% ~ 85%) of POM, the crystalline grains are large and the notch impact strength is low, and the fracture is often brittle. There are two ways to improve the impact toughness of POM: one is to toughen the elastomer; The second is the toughening of rigid particles
Toughened modified POM is widely used in car door buckles, safety belt buckles, transmission gears and other products
POM itself has good wear-resisting and self-lubricating properties. However, it is still difficult to meet the requirements of high load, high speed, high temperature and other working conditions, and the wear resistance of POM needs to be further improved. There are two ways to improve the wear resistance of POM: one is chemical modification. By means of grafting and block, a lubricity segment is introduced into the POM molecular chain. The other is physical blending modification, the most common is PTFE, molybdenum dioxide modification.
The photodegradation of POM results in the formation of hydroxyl and carbonyl groups on its molecular chains, and with the increase of carbonyl concentration, POM’s ability to absorb ultraviolet light is enhanced, leading to more chain breaks. Current studies have shown that nano-sized zinc oxide and carbon black can effectively slow down the photodegradation process of POM.
POM has a limiting oxygen index of only 15%, making it an extremely flammable plastic. As an engineering plastic, POM is widely used in automotive, electronic and electrical, building materials and other fields, which require high flame retardancy of materials. However, POM has poor compatibility with other materials, and it is difficult to prepare flame retardant POM with excellent performance by directly adding flame retardant, so there is no flame retardant POM product with excellent performance up to now.