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Introduction to Polyurethane/Glass Fiber Composite Materials

In recent years, polyurethane resin has stood out in the field of composite materials due to its excellent toughness, rapid curing, and absence of styrene smoke. With advances in controlling polyurethane’s reactivity to extend its applicability and mastery of polyurethane molding techniques, polyurethane has entered the realm of composites traditionally dominated by unsaturated polyester and vinyl ester resins. Previously, polyurethane composites were mainly used in automotive interiors and exteriors manufactured using Structural Reaction Injection Molding (SRIM), such as pickup truck boxes, underbodies, luggage racks, and internal door panels (through foamed polyurethane). However, in recent years, polyurethane composites have developed techniques like pultrusion, filament winding, vacuum infusion, and long fiber spraying, primarily using non-foamed polyurethane composites for manufacturing window frames, bathtubs, lamp poles, and large components for trucks and off-road vehicles.

Polyurethane Pultrusion:

Polyurethane pultrusion typically has low viscosity, moderate to high reactivity, good impact strength, toughness, and short beam shear performance. Compared to other materials, polyurethane pultrusion offers various benefits. It allows for a higher glass fiber content in products, significantly enhancing strength. For example, a window frame pultruded with glass fibers and polyurethane resin is eight times stronger than a PVC frame and has 40 times less conductivity than aluminum, thus offering much better insulation. Additionally, due to their less brittle nature, polyurethane pultruded window frames are more durable and less prone to cracking.

High-performance polyurethane/glass fiber composites are high-strength, high-modulus, lightweight polymer composites produced using continuous pultrusion processes, with high-hardness polyurethane elastomers as the matrix and glass fibers as reinforcement.

Products of polyurethane pultrusion technology not only have higher strength and better thermal insulation than traditional materials but are also lighter and more environmentally friendly. Their application range is vast, from luxurious bathtubs to surfboards and ski boards, and now to window frames and container floors in innovative applications, integrating polyurethane composites into various aspects of our daily lives.

Composite materials, being high-tech materials, integrate several materials’ characteristics into a comprehensive solution with outstanding new properties. Due to their unique properties, such as lightweight, high strength and rigidity, as well as helping achieve higher cost efficiency and ecological responsibility, polyurethane composites have attracted attention across various industries. Particularly in the construction and transportation sectors, innovative technologies and applications are in the spotlight.

Performance Characteristics of Polyurethane/Glass Fiber Composites

In the polyurethane pultrusion process, more reinforcing fibers can be used, greatly increasing the strength of the product. Also, due to polyurethane’s excellent impact strength, tensile strength, and interlaminar shear strength, products can be made thinner and lighter. For instance, I-beams can be made thinner by using less continuous roving and more untwisted roving, reducing thickness from 3.3mm to 2.6mm while maintaining longitudinal stiffness. This results in a 13% reduction in weight and a 7% cost saving. Additionally, because pultruded polyurethane products are less brittle, they can be assembled using conventional methods without cracking or breaking.

Specifically, polyurethane pultrusion technology has several distinct advantages:

  1. When pultruding certain profiles with traditional resins, up to four or five different types of glass fiber mats may be required, which must be cut and shaped. Polyurethane pultrusion often allows the substitution of untwisted roving for glass fiber mats. Eliminating the mats reduces raw material costs and the labor involved in handling them. The mats are also prone to breaking and can clog machinery, affecting production. Eliminating the mats often increases production line speed, thereby improving cost-effectiveness.
  2. The higher strength of polyurethane pultrusion products opens up new applications. These products can be used in construction, infrastructure, and transportation markets to replace steel and aluminum in applications where polyester resins are inadequate.
  3. Converting an existing pultrusion system to a polyurethane pultrusion system is relatively simple, convenient, and economical, requiring no significant investment. Existing dies, heaters, and machine sets can still be used.
  4. In addition to the aforementioned physical properties and molding advantages, polyurethane pultrusion parts also have assembly advantages, particularly in terms of easy fastening. Due to the strength of polyurethane, screws can be driven into polyurethane pultrusion products without pre-drilling, saving time and labor. Conversely, the force required to pull out a screw from a polyurethane pultrusion product is more thantwice that needed for a polyester pultrusion product.
  5. Under the same fiber structure, all properties of polyurethane/glass fiber pultrusion products are superior to ordinary thermosetting resins. They have a similar bending modulus but significantly improved impact strength, higher screw pull-out strength, better resistance to crack propagation, superior wear resistance, excellent secondary processing capabilities, and heat resistance above 240 degrees.
  6. Pure polyurethane/glass fiber is currently the best-performing pultrusion composite material, with complex cross-sections, smooth surfaces, fast pultrusion speed, and the best resistance to water, acids, alkalis, and salts. It has good flame resistance, is paintable, uses aliphatic polyurethane systems, is solvent-free, styrene-free, and environmentally friendly.

Main Uses of Polyurethane/Glass Fiber Composite Materials

1) Used in Building Materials In recent years, building energy conservation has become an important part of China’s sustainable development. In buildings, doors, windows, exterior walls, roofs, and floors are the four major parts of energy consumption, with doors and windows being the least insulated. It is estimated that for typical building envelopes in China, the energy consumption of doors and windows is about four times that of walls, five times that of roofs, and more than twenty times that of floors, accounting for 40-50% of the total energy consumption of envelopes. Therefore, enhancing the insulation performance of doors and windows to reduce their energy consumption is an important link in improving indoor thermal environment quality and building energy efficiency levels. The rise of composite materials in applications has brought us new ideas, making it possible to use them in the transformation of energy-saving doors and windows.

Polyurethane pultruded window frames, compared to traditional materials, have stronger dimensional stability, higher lateral mechanical performance, higher specific strength and stiffness, and better thermal insulation effects. Additionally, the unique pultrusion process of polyurethane materials, which are free from volatile organic compounds (VOCs), makes them very environmentally friendly.

Glass fiber reinforced polyurethane pultruded window profiles, made of glass fiber as reinforcement and polyurethane as the matrix, produced through advanced injection impregnation pultrusion processes. The development of GRPU window profiles aims to provide high-rise buildings with energy-saving window solutions with an overall heat transfer coefficient K ≤ 2.0 W/(m•K). Using polyurethane, which inherently has insulating capabilities, in the energy-saving window industry has long been used to make foam fillers, sealing strips, and insulation bars. Using polyurethane to manufacture the entire frame of energy-saving windows is a first in China.

The advantages of GRPU window frames are determined by the properties of GRPU material itself. As a new type of composite material, window frames are a new growth point. Using this resin, larger and thinner profiles with sufficient strength can be produced for large window frames and even curtain walls. It is claimed that these window frames are much better than aluminum, wood, and plastic frames. They have excellent expansion and contraction properties, can withstand various climatic conditions, from Arctic cold to desert heat and seaside humidity. They can be painted or post-processed to create a wood-like appearance. Polyurethane composite window frames have the following basic characteristics:

  • High Insulation: Like real wood and PVC, GRPU profiles have a very low thermal conductivity of 0.22 W/m•K at room temperature, only about 1/700th of that of aluminum alloys, making them excellent insulating materials.
  • Low Thermal Expansion: The linear thermal expansion coefficient of GRPU is about 7×10-6/K, much lower than that of aluminum alloys, and close to that of the wall body. Therefore, when the temperature changes, the GRPU frame will not create gaps with the wall, ensuring good sealing and insulation of the entire window in environments with large temperature differences.
  • Corrosion Resistance: GRPU profiles are highly resistant to most acids, alkalis, salts, organic substances, seawater, and humid air. They are rust-free and more corrosion-resistant than other door and window materials. They are particularly suitable for coastal, corrosive, and generally humid places.
  • Excellent Electrical Properties: GRPU profiles are good insulating materials, unaffected by electromagnetic waves, and do not reflect radio waves, making them particularly useful for buildings with communication systems.

Other Uses: Polyurethane pultrusion products include profiles, rods, and plates, such as ladder poles, tool handles, crossarms for electrical poles, poles, hockey sticks, dock pilings, container flooring, etc.

We hope the knowledge we have summarized can help you. Thank you.

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