The differences between thermoplastic composites and thermoset composites are briefly described

Thermosetting and thermoplastic composites are distinguished in terms of composition according to the resin matrix used.

Thermosetting resin is composed of reactive low molecular weight prepolymers or high molecular weight polymers with active groups. In the forming process, under the action of curing agent or heat, cross-linking and polycondensation are carried out to form an insoluble and insoluble cross-linking type structure, and a chemical reaction occurs. Mainly epoxy resin, polyimide resin (PI), bismaleic polyimide resin (BMI), phenolic resin and unsaturated polyester and so on.

Thermoplastic resin is composed of linear high molecular weight polymer, dissolved and melted under certain conditions, only physical changes, the use of the matrix polyethylene (PE), polyamide (PA), polyphenylene sulfide (PPS), polyether imide (PEI), polyether ketone ketone (PEKK) and polyether ether ketone (PEEK) and so on.

The raw materials used in recent years are thermosetting carbon fiber prepreg cloth, thermoplastic carbon fiber products have seen but have not done the product, but the data see more, feel the same reinforced fiber, but also with thermosetting resin and thermoplastic resin impregnation, carefully look at the appearance is still different, thermosetting resin impregnation of the raw material appearance is usually dark, such as black or dark blue, there is shine, While the appearance of thermoplastic resin impregnation usually appears light, such as light gray or light blue, but dark, thermoset composites have a smooth surface and uniform color, while thermoplastic composites have a textured surface and uneven color.

In terms of feel, the cured thermoset material is harder and more brittle, while the thermoplastic material is more elastic.

Performance aspect

Thermosetting resin has good technability (thickness, overhang), high elastic modulus and good solvent resistance, but low fracture toughness. Taking epoxy resin matrix composite material, which is the most widely used, as an example, epoxy resin has strong bonding force and can bond the reinforced fiber firmly into one body. The curing process forms a three-dimensional network structure with high cross-linking density, so the curing shrinkage rate is low. With high strength, modulus and elongation at break, the molding process is relatively mature, the shortcomings are poor weather resistance, poor impact resistance.

Thermoplastic resin has high fracture toughness, but the process is poor, resulting in the thermoplastic composite molding process is more difficult, and the toughness and fatigue resistance of thermoplastic composite based on this kind of resin is much better than that of thermosetting composite. The higher the toughness, the stronger the ability to resist crack generation and propagation, and the higher the damage tolerance limit.

Application aspect

Thermosetting composites

Thermosetting composites, represented by epoxy resin matrix composites, have early research and application, excellent mechanical properties, and can be used as the main bearing structural parts, but the material manufacturing cost is high, and the prepreg/autoclast technology used in the manufacturing process is also very expensive. In addition, in today's increasing emphasis on environmental protection, the environmental friendliness of thermosetting composites is poor and the waste is difficult to recycle and treat, which also restricts the expansion of its application.

However, the research and development of thermosetting resins has never stopped, focusing on the toughening modification of thermosetting resins, improving impact resistance and recyclability. In a tweet a few days ago, [Carbon Fiber Institute] reported that Japanese DIC company developed a heat resistant above 200 ° C and recyclable epoxy resin curing agent basic technology, this basic technology was introduced into epoxy resin, epoxy resin glass transition temperature increased to 240 ° C, The application scenario of the thermosetting composite of the epoxy resin in this temperature range is greatly expanded, and the heat resistance and mechanical property recovery rate of more than 90% can still be maintained after 5 times of recycling, and it is possible to replace the thermoplastic composite in this temperature range.

Thermoplastic composites.CFRTP

Thermoplastic composites started late, but in recent years, the development speed has greatly exceeded the thermoset composite materials, and has become the main direction of composite materials research and application, because thermoplastic composite materials not only have excellent mechanical properties, but also its production cycle is not as long as thermoset composite materials, and it can also be recycled.

Although there are so many advantages, but the domestic thermoplastic composite industrialization path is not smooth, there are several difficulties to overcome, one is the raw material, low viscosity, high flow thermoplastic Resin matrix (Resin) development and modification technology lack, single variety, high price, This has also pushed up the raw material cost of high-performance thermoplastic composite materials represented by PEEK, the second is the molding process, including automatic placement in situ curing process, encapsulation molding process and various connection processes, and the third is to strengthen downstream applications, especially to increase the proportion of application in the main bearing structure.

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