The development of the composite material industry is changing with each passing day. Because of its advantages of good toughness, fast curing, environmental protection and no volatility, polyurethane resins have been gradually replaced by applications that have been dominated by unsaturated resins and epoxy resins for a long time.
Development of polyurethane composites
.In 1937, German Otto Bayer invented polyurethane
.In the 1960s, Bayer and Swiss CIBA developed RIM (Reactive Injection Molding Process)
.In the 1970s, American GE Company launched RIM automatic line; glass fiber began to be used for RIM reinforcement
.In the 1980s, S-RIM (Structure Reaction Injection Molding Process) appeared; my country introduced RIM technology
.For more than 20 years since the 1980s, the FRSP polyurethane composite technology is mainly RIM
.To date, fiber-reinforced polyurethane composite materials have developed long fiber injection (LFI), pultrusion, winding, resin transfer molding and other processes. They mainly use non-foamed polyurethane composite materials to produce window frames, telephone poles, bathtubs, and large automotive components. product.
Technological development makes the applicability of polyurethane composites wider
1. R-RIM (Reactive Injection Molding)
The standard RIM is not enhanced, and the enhanced RIM is classified into R-RIM and S-RIM according to the enhanced material.
R-RIM (Reinforced Reaction Injection Moulding): reinforced with powdered materials such as ground glass fiber.
S-RIM (Structural Reaction Injection Moulding): reinforced with glass fiber fabric, chopped mat/continuous mat, and preformed material.
VFI (Variable Fiber Injection): In order to overcome the shortcomings of SRIM pre-release felt and glass fiber (the increase of glass fiber amount, the decrease of resin fluidity, and small bubbles), Germany and Italy developed VFI. Directly disperse the chopped glass fiber roving into the mixing chamber, and then inject it into the mold together with polyurethane to cure and shape it. Compared with S-RIM process, VFI high-density products have better performance.
2. LFI (Long Fiber Injection Molding)
LFI (Long fiber Injection) is mainly used to produce interior components with lower mechanical properties but more complex designs, such as instrument panels, interior trim panels, and underbody panels.
In this process, the cutting machine cuts 25-50 mm long chopped yarn from the plied yarn and enters the temperature control mold. At the same time, a mixture containing isocyanate, polyol and catalyst is also fed into the mold. LFI can efficiently produce lightweight, high-strength polyurethane components.
LFI is an interesting alternative to S-RIM molding methods. LFI is basically a single operation, and S-RIM requires multiple processes: preparing glass fiber mat, laying the mat into the mold, and then injecting polyurethane. Since the fiber and resin are input simultaneously in the LFI process, the molding time is shorter. LFI achieves a higher glass fiber addition than S-RIM, and is also suitable for more polyurethane formulations, which can produce lighter products with better performance.
The automotive industry first adopted polyurethane composite materials manufactured by the LFI process for structural and semi-structural panels, such as roof components. According to reports, the LFI polyurethane roof of a sports car is 20% lighter than a steel roof, and its stiffness is more than double that of an aluminum roof or other fiberglass roofs.
In the agricultural and commercial vehicle industries, LFI polyurethane composite materials are used in tractor covers, heavy truck plates, bulldozer outer body panels, bus luggage racks, etc.
3. FCS (Fiber Injection Molding)
The FCS (Fiber Composite Injection) technology of polyurethane composites is a novel solution. It can be applied to the market of large-scale fiber composite products. Typical applications are body parts for general-purpose vehicles (such as buses, tractors, etc.) and windshields, cabs, etc. for trucks. There are also many potential applications in the construction and infrastructure industries.
The hand lay-up method is still very common in the production of composite materials. The obvious advantage of the hand lay-up method is that the equipment cost is the lowest, and products with very complicated shapes can be manufactured. The disadvantages are high labor cost, long cycle time, and unstable product quality. In addition, the styrene emitted during production is unhealthy. To reduce this risk, additional operating costs are required. While the fiber composite spraying technology can meet the production requirements of the product, it can avoid the disadvantageous factors in the hand lay-up process to a certain extent, and can obtain products of superior quality.
The 4-component mixing head used in the FCS process offers the possibility of choosing multiple materials. For example, choosing different polyols (up to 3 kinds) can be compatible with dense layer and foam layer in the same product. The foam layer can reduce product weight and improve acoustic performance. Another variation is to use two different polyols and two isocyanates. In other words, the system can be made into two completely different polyurethane systems. For example, the outer layer of the product is a UV-resistant skin layer made of aliphatic polyurethane, while the inner layer is a general polyurethane.
Baypreg method
This is a manufacturing process of sandwich panels. The core material such as paper honeycomb is buried between two layers of glass fiber mat, spray impregnated with two-component polyurethane, and then compression molded and heat cured in a closed mold. This kind of board is lighter than other sandwich products, so it is very attractive for automobiles and other uses. Typical uses include underbody panels, luggage compartment bottom panels, spare tire covers, sunroof panels, etc.
Baypreg can be reinforced with various fiber materials such as glass fiber, carbon fiber or natural fiber. It is suitable for various compression molding processes and is compatible with various types of core materials. No solvent is used in the entire process.
Multitec method
This is the newer open-mold injection technology. The chopped glass fiber and the fast-curing polyurethane mixture are sprayed into the mold at room temperature and cured in the open mold.
Manufacturing a small number of parts can be sprayed manually, while mass production can be automatically sprayed by the robot. Typical products of this process are spa equipment, fish tanks, shower trays, recreational vehicle parts, tractor shields and fenders.
4. Pultrusion
In recent years, polyurethane pultrusion has been commercialized. North American pultrusion manufacturers see the fierce competition in the Chinese pultrusion product market, hoping to seek development opportunities through higher toughness and strength of polyurethane.
In the process of polyurethane pultrusion, more reinforcing fibers can be used to greatly increase the strength of the product. At the same time, due to the excellent impact strength, tensile strength and interlayer shear strength of polyurethane itself, products can be made thinner and lighter. For example, less continuous strand mat can be used, and more untwisted rovings can be used to make thinner I-beams while maintaining their longitudinal rigidity, which not only reduces weight but also reduces costs. In addition, the polyurethane pultrusion material is less brittle and can be assembled in a conventional manner without cracking and breaking.
Polyurethane pultrusion materials include profiles, rods and plates, such as ladder poles, tool handles, telephone pole crossarms, telephone poles, hockey sticks, container plates, etc.
The latest application of polyurethane pultrusion materials is the door and window system, which can make larger, thinner and strong enough profiles for large window frames and even curtain walls. This window frame is better than aluminum, wood and plastic window frames, has good expansion and contraction performance, good weather resistance, and the appearance can be painted to form a wooden appearance.
Another new use is railway sleepers. Japan's Sekisui Chemical has successfully used it for railway construction, and the polyurethane resin used is from Covestro. This sleeper looks like wood, combining all the advantages of natural products and modern design. It can be sawed, planed, nailed, screwed and glued with ordinary woodworking tools. Its thermal expansion coefficient and thermal conductivity are very low. Due to fiber reinforcement, its compressive, tensile and flexural strengths are very high, and its service life is more than 3 times longer than traditional sleepers. Used for its closed-cell mechanism, even if it absorbs very little water in heavy rain, it will not affect its electrical insulation performance. Its weight and on-site processing performance are also much better than concrete, can be made into any length, without the need for another mold for each length. In addition, it is very environmentally friendly, does not use solvents during manufacturing, and can be recycled after the end of its life cycle. This type of sleeper is used on the rails of Japan's famous high-speed train "Shinkansen".
5. Winding
In winding molding, the replacement of polyester with polyurethane has caused great interest from polyurethane suppliers. A major breakthrough is the use of proprietary polyurethane resin and fiber winding patented technology to manufacture assembled composite poles. This is the first polyurethane composite pole. Polyurethane composite materials can make longer telephone poles, while polyester composite materials are mostly used for smaller telephone poles. This utility pole uses aromatic polyurethane for the inner layer and aliphatic polyurethane for the outer two layers. This resin system has higher strength and toughness, reducing the weight by 45%.
BASF has been very active in polyurethane winding molding, especially in Europe, and its target use is corrosion-resistant "long-term infrastructure".
Another potential application area is corrosion-resistant pipes and drinking water facilities in the Middle East and Southeast Asia. The hot water tank is also very promising. Using the winding molding process, the water tank made of polyurethane composite material is 40%-50% higher than the burst strength of the polyester water tank.
6. Resin transfer molding (RTM)
For decades, the resin transfer molding (RTM) process has been used to manufacture composite parts. The resins used in this process include polyester, vinyl ester and epoxy resin. Covestro is committed to the development of polyurethane resins in the RTM process. In the RTM process, the fiberglass mat is placed in a double-sided mold. The polyurethane resin is injected into the mold when the mold is closed. After the part is cured, the mold is opened again to obtain the final part.
Vacuum infusion molding is a form of RTM that allows resin to be drawn into the mold by vacuum through the fiber penetration, rather than injected into the mold. Vacuum infusion molding ensures complete wetting of the fiberglass mat and eliminates drying points that can cause component defects.
It is reported that the progress of extending the pot life of polyurethane to more than 30 minutes makes various infusion molding processes possible. Huntsman and Covestro have developed polyurethane resins suitable for vacuum infusion molding.
Polyurethane composite materials manufactured by the RTM process have better physical properties than other resins such as unsaturated resins or vinyl esters. They are often used in fields such as explosion-proof bulletproof and sports equipment.
Polyurethane composites: some promising fields of application
1. Wind power blades
Process used: vacuum infusion molding
In April 2016, successfully trial-produced the world's first 1.5MW new high-performance polyurethane resin system fan blade. This polyurethane blade, which is 37.5 meters long and weighs about 6 tons, uses glass fiber cloth, and was successfully trial-produced at the Shanghai Fiberglass Research Institute through the online polyurethane casting equipment. The success of polyurethane in the large blade infusion process has caused a stir in the industry. Compared with traditional epoxy resin-based composite materials, polyurethane composites have more excellent mechanical properties, faster curing speed, and their lower organic volatiles are more environmentally friendly. Lighter and longer blades mean higher power generation efficiency and lower power generation costs, which is the development trend of the global wind power industry. Polyurethane composites break through the limitations of existing materials and bring new solutions to the industry.
In October 2018, the first fan blade made of polyurethane resin was successfully installed and put into operation. The fan blade (model WB113-PU) installed this time is 55.2 meters long and has a power of 2 MW. Both the main beam and the web are made of polyurethane Made of resin material. The wind turbine was installed at a wind farm in Tieling City, Liaoning Province. In order to obtain relevant certifications, new fan blades must pass various strict third-party tests. In order to ensure that the fan blades can achieve long-term stable operation in harsh environments, Covestro conducted a comprehensive test of the fan blade performance and successfully passed the (CGC) static and fatigue tests (including swing and swing direction) .
With this, a strong signal is sent to the industry that the era of using polyurethane to make longer and stronger fan blades has arrived.
2. Door and window profiles
Process used: pultrusion
Huntsman and partners jointly launched doors and windows of polyurethane composite material full-break bridge system. The doors and windows of the polyurethane composite material full-broken bridge system use lightweight, high-strength polyurethane composite materials, and use resource- and energy-friendly materials. This system also has excellent fire resistance, with fire-resistant glass and hardware accessories, the whole window can be fire-resistant for up to 1 hour. Therefore, since entering the market, this system doors and windows have been well received by the industry.
In August 2019, we will create a customized Baiduo® glass fiber reinforced polyurethane energy-saving fireproof window solution for the "Future Residential Energy and Environment Experimental Platform" project. The profile is made of alkali-free glass fiber yarn as the reinforcing material and polyurethane resin as the matrix resin. It is formed by the closed-mold injection pultrusion process, which combines energy saving, fire resistance and high strength.
In response to the energy and environmental requirements of the project for "future buildings", through the application of this material, the following three door and window solutions were jointly customized:
For the requirement that the K value (heat transfer coefficient) of the entire window is less than 1.5, two solutions are provided. Among them, the "pure heat insulation 65 flat open series" adopts all polyurethane profiles, suitable for various doors and windows projects. This profile has the advantages of ultra-low heat conduction, reliable low temperature resistance, superior mechanical properties and longer service life. At the same time, because the linear thermal expansion coefficient of the material is very close to concrete, it can avoid the gap between the window frame and the wall due to the difference in thermal expansion and contraction.
The "Big Broken Bridge 65 Swing Series" doors and windows use polyurethane profiles as heat-insulating broken bridges, and are covered with aluminum profiles on the surface. Polyurethane composite material as the inner heat insulation core is sufficient to bear the fixing force of the upper wall and the weight of all glass layers, ensure the wind pressure resistance of the entire window, and integrate the heat insulation and the load bearing.
In order to meet the requirement that the K value of the whole window is less than 0.8, the "85 flat open series" full polyurethane profiles are customized. The profile adopts polyurethane composite material as a whole, which can meet the energy saving requirements of "passive house". The outer window is made of glass fiber reinforced polyurethane, equipped with double Low-E argon-filled insulating glass, and the K value of the whole window is as low as 0.77W/(m2•K). In addition, the program uses a dedicated sub-frame, which has good energy saving, corrosion resistance and waterproof sealing functions.
3. Telephone pole
Process used: winding forming
Attempts have been made to use polyurethane composite materials for telephone poles.
Polyurethane composite poles were adopted by a large Japanese pole dealer in July this year. The telephone poles are made of polyurethane and use fiber winding technology, which can withstand extremely severe weather conditions and maintain a reliable power supply for the affected areas. The weight of the telephone pole is only 220 kg, and the bending strength is 10 times its weight. Telephone poles can be customized for length, strength and hardness according to the different needs of telephone pole dealers and energy suppliers. The length varies from less than 8 meters to 12 meters, and the breaking strength ranges from less than 4 to more than 20 kilonewtons (kN). Telephone poles are also fireproof and can self-extinguish quickly.
4. 5G communication tower
Process used: winding forming
With the advent of the 5G era, polyurethane composite materials can be applied to 5G communication towers. Compared with traditional concrete or steel-based materials, communication towers made of polyurethane composite materials are lighter in weight and can be quickly installed even in remote areas, while being able to withstand severe weather such as heavy snow and strong winds.
The 35-meter-high communication tower made of polyurethane composite material weighs about 1,500 to 1,800 kilograms, and its breaking strength is ten times its own weight. Not only that, communication towers made of polyurethane composites are more cost-effective than traditional steel towers. It has rust and corrosion resistance characteristics and requires less maintenance. The surface is covered with a specially formulated UV-resistant coating, which can extend its service life. At the same time, it is fireproof and can self-extinguish quickly.