Process Innovation and High-Performance PU Composites for Advanced Applications
2025/08/20
The development of the composite materials industry is advancing with each passing day. Polyurethane resins, leveraging their outstanding advantages such as excellent toughness, rapid curing properties, and environmental friendliness without volatilization, are constantly breaking through the boundaries of traditional materials. In many application fields that have long been dominated by unsaturated resins and epoxy resins, polyurethane composite materials are demonstrating strong substitution potential, continuously driving the upgrading and transformation of material systems.
Resin
Advantages
Disadvantages
Unsaturated resin
Easy to operate
Low price
Medium strength
Styrene evaporates seriously
Large shrinkage during curing
General weather resistance and chemical resistance
Vinyl ester
Relatively high mechanical properties and good chemical resistance
Good weather resistance
Post-curing required
High styrene content
Higher price than unsaturated resin
Large shrinkage during curing
Epoxy resin
Ideal mechanical and thermal properties
Good water resistance
Longer pot life
Can work in hot and humid environments
Small shrinkage during curing
Expensive
Relatively difficult to operate
Curing agent is corrosive
Phenolic resin
High Tg
Fireproof
Corrosion resistance
Difficult to operate
Many pores in the resin
Very brittle
Polyurethane resin
High strength
Good toughness
Good impact strength
Wear resistance
Short pot life
Water sensitive
Two-component dosing machine required
The market is relatively unfamiliar with polyurethane resin
Advantages of Polyurethane Composites
Value Created
High strength
Better product designability and weight reduction effect
Excellent tear and impact resistance
Good secondary processability and weather resistance
Low-pressure molding
Low investment in equipment and molds
Rapid curing
High production efficiency
No styrene volatilization
Good production environment
Development of Polyurethane Composites
♦ In 1937, Otto Bayer of Germany invented polyurethane.
♦ In the 1960s, Bayer and CIBA Corporation of Switzerland developed RIM (Reaction Injection Molding process).
♦ In the 1970s, General Electric Company of the United States launched the RIM automatic production line; glass fiber began to be used for RIM reinforcement.
♦ In the 1980s, S-RIM (Structural Reaction Injection Molding process) emerged; China introduced RIM technology.
♦ For more than 20 years since the 1980s, RIM has been the main process for FRSP polyurethane composite materials.
♦ Up to now, fiber-reinforced polyurethane composites have developed processes such as Long Fiber Injection (LFI), pultrusion, winding, and resin transfer molding. Non-foaming polyurethane composite materials are mainly used to produce products such as window frames, telephone poles, bathtubs, and large auto parts.
Process development has expanded the applicability of polyurethane composites.
R-RIM (Reaction Injection Molding)
Standard RIM is not reinforced. Reinforced RIM is divided into R-RIM and S-RIM according to different reinforcing materials.
R-RIM (Reinforced Reaction Injection Moulding): Reinforced with powdered materials such as ground glass fibers.
S-RIM (Structural Reaction Injection Moulding): Reinforced with glass fiber fabrics, chopped mats/continuous mats, and preforms.
VFI (Variable Fiber Injection): To address the limitations of SRIM, such as the limited addition of pre-placed glass fiber mats (increased glass fiber content leads to decreased resin fluidity and the formation of small bubbles), Germany and Italy developed VFI. This process involves directly chopping and dispersing glass fiber rovings into a mixing chamber, which are then injected into the mold together with polyurethane for curing and molding. Compared with the S-RIM process, VFI produces high-density products with better performance.
2.Long Fiber Injection (LFI)
Long Fiber Injection (LFI) is a production process for polyurethane composites, mainly used to manufacture large automotive interior parts and semi-structural components with relatively low mechanical performance requirements but complex shapes, such as instrument panels, interior door panels, and vehicle floor panels.
In this process, a fiber cutting device cuts continuous glass fiber strands into 25–50 mm segments of fixed length, which are then directly fed into a temperature-controlled mold. Simultaneously, mixed components such as polyol, isocyanate, and catalysts are precisely proportioned via metering equipment and injected into the mold, where they mix, infiltrate, and cure to form the final product. The LFI process not only efficiently produces lightweight and high-strength polyurethane composite components but also offers significantly greater process flexibility compared to traditional SRIM (Structural Reaction Injection Molding).
LFI is widely regarded as a strong alternative to SRIM technology. Unlike SRIM, which requires multi-step operations such as pre-laying glass fiber mats followed by closed-mold injection, LFI enables synchronous feeding of fibers and resin, drastically shortening the molding cycle and improving production efficiency. Additionally, LFI supports higher glass fiber addition levels and a wider range of polyurethane formulation options, allowing the manufacture of lighter composite products with superior mechanical properties.
The automotive industry was one of the earliest application fields for LFI technology, with typical applications including structural and semi-structural plate-like components such as roof modules. Reports indicate that the roof of a certain sports car model, manufactured using LFI polyurethane composites, is over 20% lighter than traditional steel roofs, while its stiffness is more than twice that of aluminum roofs or other fiberglass roofs.
Furthermore, in the fields of agricultural machinery and commercial vehicles, LFI is widely used in the manufacturing of large components such as tractor hoods, heavy-duty truck body panels, bulldozer exterior covers, and bus luggage compartment lids, to meet the demands for lightweight design, high strength, and integrated structure.
bulldozer
3.Fiber Composite Spraying (FCS)
Fiber Composite Spraying (FCS) is an emerging polyurethane composite molding process that provides an innovative solution for the efficient manufacturing of large fiber-reinforced products. This technology is particularly suitable for producing large-area or structurally complex products, such as body covers for general-purpose vehicles like buses and tractors, as well as components like truck deflectors and cab enclosures. Meanwhile, FCS technology also shows broad application potential in the construction and infrastructure fields, including the rapid 成型 of non-load-bearing or secondary load-bearing structural parts such as large thermal insulation panels, sound insulation barriers, and construction formworks.
The hand lay-up method is still common in the production of composite products. Its obvious advantage is the lowest equipment cost, and it can manufacture products with very complex shapes. However, it has disadvantages such as high labor costs, long cycles, and unstable product quality. In addition, styrene emitted during production is harmful to health, and additional operating costs are required to reduce this risk. The fiber composite spraying technology, while meeting the product manufacturing requirements, can avoid certain adverse factors in the hand lay-up process to a certain extent and produce products with superior quality.
3.Fiber Composite Spraying (FCS)
The 4-component mixing head used in the FCS process provides the possibility of selecting multiple materials. For example, by choosing different polyols (up to 3 types), both dense layers and foam layers can be integrated into the same product. The foam layer can reduce the product weight and improve acoustic performance. Another variation is to use two different polyols and two isocyanates. In other words, the system can be configured into two completely different polyurethane systems. For instance, the outer layer of the product can be an ultraviolet-resistant skin made of aliphatic polyurethane, while the inner layer can be a general polyurethane.
Baypreg Method
This is a manufacturing process for sandwich panels. Core materials such as paper honeycomb are embedded between two layers of glass fiber mats, impregnated with two-component polyurethane through spraying, and then compression-molded in a closed mold and cured by heating. This type of panel is lighter than other sandwich products, thus being highly attractive for applications such as automobiles. Typical applications include car floor panels, luggage compartment floors, spare tire covers, and sunroof panels.
Baypreg can be reinforced with various fiber materials such as glass fiber, carbon fiber, or natural fibers. It is suitable for various compression molding processes, compatible with different types of core materials, and no solvents are used in the entire process.
Multitec Method
This is an updated open-mold spraying technology. Chopped glass fibers and fast-curing polyurethane mixtures are sprayed into the mold at room temperature and cured in the open mold.
For small-volume production, manual spraying can be used, while for mass production, robotic automatic spraying is applicable. Typical products of this process include spa equipment, fish tanks, shower trays, recreational vehicle components, tractor guards, and fenders.
4.Pultrusion Molding
In recent years, polyurethane pultrusion technology has successfully achieved commercial application. Faced with increasingly fierce competition in China’s pultrusion product market, North American pultrusion manufacturers are actively leveraging the advantages of polyurethane resin’s higher toughness and strength to explore new market opportunities through a differentiation strategy.
In the polyurethane pultrusion process, a higher proportion of reinforcing fibers can be incorporated, thereby significantly enhancing the mechanical properties of the final products. Meanwhile, the polyurethane resin matrix itself exhibits excellent impact strength, tensile strength, and interlaminar shear strength, enabling products to maintain high load-bearing capacity while being thinner and lighter. For example, when producing I-beams, more glass fiber rovings can be used to replace part of the continuous strand mat. On the premise of keeping longitudinal stiffness unchanged, a thinner cross-section and lighter weight are achieved, which not only improves material efficiency but also reduces overall costs. In addition, the toughness of polyurethane pultruded materials is significantly better than that of traditional resin systems. Products are less likely to crack or chip during subsequent assembly processes such as drilling and cutting, making them easy to process and install using conventional methods.
Polyurethane pultruded materials include profiles, rods, and plates, such as ladders, communication steel towers, railway fish plates, solar photovoltaic frames, door and window frames, and modular housing panels.
ladder
The latest application of polyurethane pultruded materials is in door and window systems.
They can produce larger and thinner profiles with sufficient strength, which are used in large window frames and even curtain walls. Such window frames are superior to aluminum, wood,
and plastic window frames,featuring good expansion and contraction performance, excellent weather resistance, and a wooden appearance after being painted.
Polyurethane Doors and Windows
Another new application is railway fish plates. Polyurethane fish plates (often also referred to as composite fish plates or connecting components in synthetic sleepers) are high-performance composite products used in the rail transit field. They are particularly suitable for harsh working conditions such as heavy loads, high speeds, and high corrosion. They are important innovative products that improve railway operation efficiency and safety.
Characteristics
Polyurethane Fish Plate
Traditional Steel Fish Plate
Weight
Extremely light
Heavy
Corrosion resistance
Excellent, maintenance-free
Poor, requires regular rust prevention and maintenance
In 2019, the flame-retardant pultrusion resin independently developed by Nanjing Jufa New Material Co., Ltd. was successfully applied to the manufacturing of equipment
compartment components for high-speed EMUs (Electric Multiple Units) with a speed of 400 km/h. This marked a major technological breakthrough for the company in the field of
high-end rail transit composite materials. This flame-retardant resin system not only meets strict flame-retardant standards (such as EN 45545) but also combines excellent mechanical
properties with efficient adaptability to the pultrusion process. It ensures that the equipment compartment components possess high impact resistance, low smoke and non-toxic
properties, and structural reliability under ultra-high-speed operation conditions. It provides key material support for the lightweight design and safety protection of China’s
new-generation high-speed rail technology, demonstrating the strong competitiveness of domestic high-end composite materials in the field of top-tier equipment.
High-speed rail with a speed of 400 km/h
5.Filament Winding Molding
In filament winding molding, the replacement of polyester with polyurethane has attracted great interest from polyurethane suppliers. A major breakthrough was achieved by Canada’s RS Technologies, which used its proprietary polyurethane resin and patented filament winding technology to manufacture assembled composite utility poles. These are the first polyurethane composite utility poles. Polyurethane composites can be used to produce longer utility poles, while polyester composites are mostly used for smaller ones. The inner layer of these poles is made of aromatic polyurethane, and the outer two layers are made of aliphatic polyurethane. This resin system offers higher strength and toughness, reducing weight by 45%.
Hunan Qiangtai New Material Co., Ltd. holds a significant market share in China’s communication tower field and is one of the important new material solution providers in this domestic sector.
Leveraging its leading technology in composite materials (especially polymer materials such as polyurethane), the company continuously provides high-performance, corrosion-resistant, and lightweight alternative products for the communication tower market. Its composite towers exhibit weather resistance and structural durability that traditional metal towers lack in 5G base station construction, coastal areas, and harsh environments. In line with the strategic needs of communication infrastructure upgrading and "new infrastructure," they have won wide customer recognition and rank among the top in market share in the industry.
In the future, with the in-depth coverage of 5G networks and forward-looking layout of 6G technology, the demand for lightweight, low-loss, and maintenance-free towers will further grow. Hunan Qiangtai is expected to continuously consolidate and expand its market leadership by virtue of its material and technological advantages.
Nanjing Jufa New Material Co., Ltd. has always maintained high activity and technological leadership in the field of polyurethane pultrusion technology and is one of the important promoters of the industrial application of this process. Through continuous technological research and development as well as process optimization, the company is committed to addressing bottlenecks in traditional pultruded materials in terms of toughness, fatigue strength, and lightweight performance. Making full use of the excellent impact resistance and high fiber impregnation of polyurethane resin, its products have successfully produced composite profiles with high strength, lightweight properties, and excellent durability.
Nanjing Jufa New Material Co., Ltd. and its innovative achievements have been deeply reported by major central mainstream media such as CCTV and People's Network on multiple occasions. They have frequently shone in the public eye, with their brand influence and social recognition continuously improving.
6. Resin Transfer Molding (RTM) and Vacuum Infusion Process
Resin Transfer Molding (RTM) is a closed-mold composite molding process with decades of application history, traditionally using unsaturated polyesters, vinyl esters, and epoxy resins. With the development of material technology, the polyurethane RTM system has gradually matured.
In the polyurethane RTM process, pre-laid fiber-reinforced materials (such as glass fiber mats) are placed in a closed mold. After injecting polyurethane resin, it is heated and cured, and finally demolded to obtain composite products with high surface quality.
Vacuum Infusion, as a derivative technology of RTM, enables resin to fully penetrate the fiber reinforcement through the action of vacuum negative pressure, achieving better impregnation effect than traditional injection, effectively avoiding defects such as dry spots, and significantly improving product consistency and reliability.
In recent years, advancements in polyurethane resin curing systems—especially the extension of the pot life to more than 30 minutes—have greatly promoted the feasibility of processes such as vacuum infusion. Enterprises like Nanjing Jufa have developed long-operation-window polyurethane resin products specifically for vacuum infusion molding.
Compared with traditional unsaturated polyester or vinyl ester resins, polyurethane RTM composites exhibit superior mechanical strength, impact resistance, and fatigue performance. They have been widely used in fields with stringent material performance requirements, such as bulletproof and explosion-proof equipment and new energy vehicle components.
Wind Turbine Blades
In 2022, the vacuum infusion resin system developed by Nanjing Jufa New Material Co., Ltd. was successfully applied to the manufacturing of 84-meter ultra-large wind turbine blades. This marked that the company’s technical strength in the field of high-performance composite resin has reached the industry-leading level.
This landmark application fully demonstrates the excellent process adaptability and reliability of its resin products in the molding of ultra-large fiber-reinforced structures. The resin system features low viscosity, a long operation period, high impregnation, and excellent cured mechanical properties, which can meet the extreme requirements for material mechanical strength, structural stiffness, and fatigue life during the integral molding of ultra-long blades. It provides key material support for the development of larger and lighter wind turbine blades in China, helping the offshore wind power industry reduce costs and increase efficiency.
7.Successful Development of Aliphatic Polyurethane Nanjing Jufa New Material Co., Ltd. has achieved a major breakthrough in the field of high-performance composite resins. Its aliphatic polyurethane resin system, specially developed for high-speed pultrusion processes, has successfully obtained TÜV international certification. This achievement signifies that the material has gained recognition from a global authoritative institution in meeting the requirements of efficient production and ultra-long weather resistance for photovoltaic frames.
Characteristic Dimension
Core Advantages
Typical Application Fields
Application Value
Weather Resistance and Aging Resistance
Resists erosion from ultraviolet rays, humidity, and temperature changes, with stable performance, comparable to polyurethane paint
Photovoltaic equipment (such as supports, frames)
Ensures long-term stable operation of photovoltaic equipment in harsh climates, improving power generation efficiency and equipment service life
Excellent Mechanical Properties
Superior tensile strength, flexural strength, and impact resistance, on a par with aromatic polyurethane
Marine engineering (such as offshore wind power facilities, marine platform protective structures)
Resistant to seawater corrosion, sea wave impact, and complex marine climates, providing reliable material support for marine resource development and infrastructure construction
UV Resistance and Moisture - Heat Resistance
Not prone to yellowing, with stable performance when exposed to sunlight for a long time
Outdoor signage
Maintains long-term aesthetics and functionality
Process Adaptability
Suitable for pultrusion process
Automotive paint (potential application)
(Inferred based on its weather resistance) Provides long-term weather protection
