Abstract: Thermoplastic composite material (FRT) has outstanding characteristics of low density, high strength, fast processing, recyclability, etc. It is a new type of composite material with high performance, low cost, and environmental protection. It has partially replaced expensive engineering plastics and thermoset composite materials. (FRP) and lightweight metal materials (aluminum-magnesium alloy), have broad application prospects in aircraft, automobiles, trains, medical treatment, sports, etc. This article summarizes the types, structure and performance characteristics of thermoplastic composite materials (FRT), and introduces in detail the latest domestic and foreign processing technologies, applications and development trends, as well as obstacles and challenges facing in the future.

Composite materials are divided into two main types: thermosetting (polymer resin-based) composite materials (FRP) and thermoplastic (polymer resin-based) composite materials (FRT). Among them, FRT (such as GFRT and CFRT, Fiber Weight) %: 40-85wt%) has the outstanding characteristics of low density (1.1-1.6g/cm3), high strength, good impact resistance, good fatigue resistance, recyclability, fast processing and forming, and low cost. It belongs to high performance, low cost, Green and environmentally friendly new composite materials.

Multi-component, multi-phase, multi-scale by selecting the type of raw materials (fiber and resin matrix), the ratio, the processing method, the content of the fiber (GF, CF) and the fiber (monofilament and braid) layup method Macroscopic and (sub)microscopic composite processes (including physical processes and chemical processes) can prepare FRT, and design and manufacture composite material structures and properties according to requirements to achieve different physics, chemistry, mechanical mechanics and special functions, and finally make Various products have significant advantages such as large design freedom, dimensional stability, low warpage, fatigue resistance, and creep resistance. They partially replace expensive engineering plastics, non-environmentally friendly F RP and light metal materials (such as aluminum-magnesium alloys) . At present, FRT is widely used in electronics, electrical appliances, airplanes, automobiles, trains, energy, ships, medical equipment, sports equipment, construction, military industry and other industrial products. With the continuous improvement of requirements such as recycling, FRT has developed more rapidly, and relevant new materials, new technologies, and new equipment continue to emerge.

Basic types

According to the maximum fiber retention size in the product, FRP (GFRT and CFRT) can be divided into: (1) Non-continuous fiber reinforced thermoplastic composite materials (N-CFT), including chopped fiber reinforced engineering plastics (SFT, maximum fiber retention size) 0.2-0.6mm); (2) Long fiber reinforced thermoplastic composite materials (LFT-G, LFT-D, maximum fiber retention size 5-20mm); (3) Continuous Fiber Reinforced Thermoplastics , CFT, Maximum fiber retention size>20mm; including: glass fiber felt reinforced thermoplastic composite material (GMT). The traditional molding process—injection and molding, can realize the manufacture of N-CFT non-structural parts or semi-structural parts (such as automotive engineering plastic parts). Although compared with CFT, the mechanical properties are quite different, it can satisfy the general civil industry. Product cost-effective use requirements, so the market capacity is huge, the development speed is fast, and the manufacturing technology and application are relatively mature. Foreign companies such as R TP in the United States, Ticona in the United States, Kawasaki in Japan, and Sabic Industries (Sabic) have realized the industrial production of LFT carbon fiber composite materials, and they are used in automobiles that require high strength and light weight. Non-structural parts are used to replace parts of aluminum alloy materials, and they also have special functions such as electrical conductivity, heat conduction, wear resistance, and electromagnetic shielding. This has also become a new field for domestic and foreign modified plastics companies to develop and apply first. In 2012, Beijing Nashengtong Company (NST) adopted independent innovation and patented technology to realize the industrial production of LFT carbon fiber composite materials (granules) in China, and applied them in wind turbine blades, LED display module brackets, electric vehicle hubs and other products. CFT (mainly including GFRT and CFRT) is a new lightweight material with higher performance. It is also one of the composite materials with the fastest development of new technology in recent years. It can be divided into four types: 1) Continuous monofilament fiber unidirectional Aligned CFT (also known as unidirectional continuous fiber reinforced thermoplastic composite prepreg tape). The continuous monofilament glass fiber reinforced thermoplastic impregnated PP tape developed by Owens Corning (OCV) in the United States can be used to prepare thermoplastic composite pipelines and thermoplastic sheets or profiles with controllable molding thickness. It has outstanding mechanical properties and processing. Formability; 2) Glass fiber mat reinforced thermoplastic composite material (GMT). Dong Weiguo of Tianjin University of Technology invented a lighter needle punched glass fiber felt reinforced PP thermoplastic composite material (S-GMT), which is reinforced by using chopped needle punched felts with different long fiber sizes (15-25mm) as a fiber-wound skeleton structure Function; 3) Continuous fiber woven fabric reinforced thermoplastic composite material (2D-CFT), including various advanced impregnation technology and composite preparation methods such as front impregnation and post impregnation, original polymerization impregnation, mixed fiber yarn impregnation, etc. Phase interface bonding strength and mechanical properties; 4) Multi-angle, multi-phase composite structure of continuous fiber woven cloth reinforced thermoplastic composite material (3D-CFT), including braid (belt, cloth, felt) structure, sandwich solid structure and sandwich The structure design of new CFT composite materials such as sandwich foam structure, Z-type multilayer column structure, and thermoplastic resin matrix (Resin) "in-situ" and "off-site" reinforcement and toughening, structure/function integrated design and full automation The development of intelligent manufacturing technology has improved the comprehensive performance of high-performance continuous carbon fiber reinforced thermoplastic composite materials (CFRT).

New processing technology

1) Injection dipping technology (In situ T-RTM)

According to the characteristics of different CFTs (GFRT and CFRT), the molding stages such as melting, prepreg, and forming have specific technical requirements for equipment and processing techniques. The thermoplastic resin matrix (Resin) has high viscosity and it is difficult to infiltrate the fibers. Therefore, the preparation of thermoplastic prepregs is the key technology and difficulty in the preparation technology of CFT and related products. In 2013, the injection molding machine manufacturer Engel successfully developed the in situ thermoplastic reaction injection molding (In situ T-RTM) technology, using injection molding technology to polymerize monomers in situ with The continuous fiber hot-melt impregnation process is completed synchronously, and the automatic, controllable, high-efficiency melt impregnation process and the composite forming process are integrated, thereby reducing the process flow and improving the product performance. The principle is to inject the monomer ε-caprolactam (or CBT, alkylene oxide) with low viscosity coefficient into the continuous fiber (GF, CF) at high speed and low pressure, and then polymerize the monomer in situ in the mold to form PA-6 , And then injection into the mold to become a product or part, the forming time is 60-120 seconds. Because of the RTM process technology principle similar to the thermosetting polymer resin (FRP) molding process, it is also called the RTM process technology (ie T-RTM) for thermoplastic polymer resin (Resin) molding. Compared with thermosetting HP-RTM, the advantages are: (1) low raw material and manufacturing costs; (2) superior impact resistance of parts; (3) products are easy to recycle and reuse, and have weldability; (4) resin Resin has a low viscosity like water, making it easier to impregnate continuous fibers (belt, cloth, felt) and improve efficiency. As early as the K 2010 exhibition in Germany, Engel and Krauss Maffei were shown on-site in two forming units of complex structural parts for the first time respectively, which once again proved the feasibility of this technology.

2) Gap Impregnation Technology (GIT)

In March 2014, the reaction injection pressurized gap immersion technology (Gap impregna tion technology, GIT) invented by Professor C.Hopmann of Germany won the German National Plastics Industry Award. This process technology has good versatility, suitable for thermosetting/thermoplastic resin matrix (Resin) composite system, fast molding time (2-5 minutes), low molding temperature (120-150℃), and high mold pressure (>25bar) , At the same time, the operation is relatively simple, the controllability is good, the stability is good, the equipment investment cost is low, the parts are easy to realize mass automated production, the production efficiency is high, and it is more suitable for the manufacture of smooth curved surfaces. It is also a non-complex 3D structure of the automobile structure. part.

GIT technology can also be applied to the thermosetting resin HP-RTM process. The higher molding pressure and molding temperature can be adjusted in the vacuum mold cavity, and it can be used to prepare large auto parts through two injection RTM processes, so it is also called high pressure Injection R TM-HP-RTM process technology.

3) Continuous running double belt roller isostatic pressing technology (DBP)

Fully automatic tape laying is a new technology and new equipment for faster automatic production of CFT composite prepreg tape. Continuous running dual-belt roller isostatic pressing technology (DBP) can realize high-speed processing and shaping of thermoplastic prepreg tapes and semi-finished sheets. The DBP constant temperature press can heat-melt and compound two or more single-layer woven fabrics (cloth) and two or more thermoplastic resin matrix films (0.01-2mm), and apply uniform isostatic pressure. , While heating, plasticizing and cooling, the tensile and torsion resistance at each point can be kept basically the same. The temperature in the entrance, high temperature heating and cooling zone is controlled by heating and cooling plates to control the temperature change, which can meet the production of different CFT thermoplastic sheets. DBP technical advantages: 1) High temperature, high pressure and high speed operation-integrated; 2) According to the specific temperature changes required by CFT, the temperature changes are automatically and accurately controlled in real time for each individual area of the upper and bottom respectively; 3) Plus While maintaining the isostatic pressure, the nip is heated and cooled separately to eliminate internal stress.

3) Continuous running double belt roller isostatic pressing technology (DBP)

Fully automatic tape laying is a new technology and new equipment for faster automatic production of CFT composite prepreg tape. Continuous running dual-belt roller isostatic pressing technology (DBP) can realize high-speed processing and shaping of thermoplastic prepreg tapes and semi-finished sheets. The DBP constant temperature press can heat-melt and compound two or more single-layer woven fabrics (cloth) and two or more thermoplastic resin matrix films (0.01-2mm), and apply uniform isostatic pressure. , While heating, plasticizing and cooling, the tensile and torsion resistance at each point can be kept basically the same. The temperature in the entrance, high temperature heating and cooling zone is controlled by heating and cooling plates to control the temperature change, which can meet the production of different CFT thermoplastic sheets. DBP technical advantages: 1) High temperature, high pressure and high speed operation-integrated; 2) According to the specific temperature changes required by CFT, the temperature changes are automatically and accurately controlled in real time for each individual area of the upper and bottom respectively; 3) Plus While maintaining the isostatic pressure, the nip is heated and cooled separately to eliminate internal stress.

4) Deep processing technology of thermoplastic prepreg (sheet)

Common molding methods of CFT thermoplastic prepregs (sheets): injection molding, simple process, continuous batch production; water-assisted injection molding, which has a shorter cycle than gas-assisted injection molding; hot press molding, used for parts under high pressure and high temperature The preparation method of low strain rate can form high-density and compact CFT; vacuum heating molding requires the use of CFT thermoplastic prepreg sheet to pass the vacuum heating mold, heat preservation and pressure, and then release the mold after cooling. The single-layer film forming process under the generated pressure, the heating temperature is controllable, and it can be cooled to room temperature while maintaining the specified temperature to achieve a better effect of eliminating internal stress; cold film compression molding (CDF) is based on heating compression A new technology developed by molding technology can improve CFT mass production capacity and product quality. CFT thermoplastic prepreg is fixed in a recessed inner mold and placed in an infrared heating chamber, and polymer backing material is fixed on the surface of the prepreg. Heat to the required forming temperature, pressurize and pass inert gas or form under vacuum, and then take it out of the mold after the temperature drops. In the market, cold diaphragm compression molding technology has been used to make helicopter CFRT shells, as well as GFRT thermoplastic prepreg tape (filament) winding molding and hot extruding sheet technology to manufacture conveying pipes and building boards.

5) Fully automatic laying technology of fiber prepreg tape (silk)

Automatic fiber placement technology is one of the key manufacturing technologies for the automatic molding of aircraft composite material components. It can be divided into: automatic fiber prepreg tape (silk) placement technology and automatic fiber tape placement technology. The former is suitable for flat or low-curvature curved surfaces, or quasi-planar composite material components; the latter combines the advantages of automatic fiber winding and automatic fiber prepreg tape (silk) laying technology, which can realize complex Laying and manufacturing of curved CFT thermoplastic fiber prepreg tape (silk). CFT automatic fiber prepreg tape (silk) laying technology can be used for processing raw materials usually continuous glass fiber or carbon fiber single

To strengthen the thermoplastic composite prepreg tape (wire). In the automatic fiber prepreg tape (filament) laying process, using carbon fiber reinforced thermoplastic resin-based prepreg or prepreg tape as the processing object, combined with in-situ curing technology to produce aircraft composite components, is an important development in the aircraft industry The trend is reported to have been applied to Airbus A380 and A350. In addition to the advantages of thermoplastic resin (Resin) with good weldability, high impact resistance, recyclability, and chemical corrosion resistance, the new in-situ curing technology has the advantages of being unsuitable compared with the commonly used autoclave technology. According to literature reports, the interlayer strength of the fiber prepreg tape (silk) processed by the in-situ curing molding technology is 89-97% of that of the high-pressure curing molding process. CFT thermoplastic prepreg fiber prepreg tape (filament) laying technology is an important direction for the development of component manufacturing in the future.

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