This Article will Help you Understand Polyurethane Pultrusion!

 

 

1. Introduction to Polyurethane/Glass Fiber Composites

 

In recent years, polyurethane resins have stood out for their toughness, fast curing, and no styrene smoke. With the mastery of polyurethane molding technology and the progress in controlling its reactivity to extend its shelf life, polyurethane has entered the field of composite materials that has long been dominated by unsaturated polyester and vinyl ester resins. In the past, polyurethane composites were mainly automotive interior and exterior parts molded by structural reaction injection method (SRIM), such as pickup truck boxes, floor panels, luggage racks, inner door panels, etc. (polyurethane is foamed). However, in recent years, polyurethane composites have developed technologies such as pultrusion, winding, vacuum infusion and long fiber injection, mainly using non-foamed polyurethane composites to manufacture window frames, bathtubs, light poles and large parts of trucks and off-road vehicles.

 

Polyurethane pultrusion: Polyurethane pultrusion generally has low viscosity, moderate to high reactivity, good impact strength and toughness, and short beam shear performance. Compared with other materials, polyurethane pultrusion can produce multiple benefits. It can increase the glass fiber content in the product and greatly improve the strength of the product. For example, the window frames made of glass fiber and polyurethane resin are 8 times stronger than PVC window frames, and their conductivity is 40 times lower than that of aluminum, so the insulation performance is much better. At the same time, because polyurethane pultruded window frames are less brittle, they will not crack and are durable.

 

High-performance polyurethane/glass fiber composite materials are a kind of high-strength, high-modulus, lightweight polymer composite materials produced by continuous pultrusion process with high-hardness polyurethane elastomer as the matrix material and glass fiber as the reinforcement material.

 

Products made of polyurethane pultrusion technology not only have higher strength and better thermal insulation than traditional materials, but are also lighter and more environmentally friendly. Its application field is very wide. From the original gorgeous bathtubs, to surfing and snowboards, to today’s innovative applications such as window frames and container floors, polyurethane composite materials have been integrated into all aspects of our daily life.

 

According to reports, in the past few years, China’s demand for composite materials has shown a gradual growth trend. Composite materials are a high-tech material that integrates the characteristics of several materials into a comprehensive solution with excellent new performance. It is precisely because of the unique properties of the material, such as light weight, high strength and rigidity, and the ability to help achieve higher cost efficiency and ecological responsibility, that polyurethane composites have attracted much attention from various industries. Especially in the construction and transportation industries, innovative technologies and applications have attracted much attention.

 

2. Performance Characteristics of Polyurethane/Glass Fiber Composite Materials

 

After several years of development, polyurethane pultrusion molding has been commercialized abroad. In the polyurethane pultrusion process, 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 interlaminar shear strength of polyurethane itself, the products can be made thinner and lighter.

 

For example, thinner I-beams can be made with less continuous raw fiber mats and more untwisted rovings, reducing the thickness of the I-beam from 3.3mm to 2.6mm while maintaining its longitudinal stiffness unchanged. In this way, the product reduces 13% weight and 7% cost. In addition, because pultruded polyurethane products are less brittle, they can be assembled in a conventional way without cracking and breaking.

 

Specifically, the use of polyurethane pultrusion technology has the following obvious advantages.

 

(1) Pultruding certain profiles with conventional resins may require the use of up to 4 or 5 different glass mats. These mats must be cut and shaped. With polyurethane pultrusion, glass rovings can often be used in place of glass mats. Eliminating glass mats reduces the cost of raw materials and the labor required to operate the mats. Mats also break easily, and fragments can clog the machine, affecting production. Eliminating mats can increase line speeds in many cases, thereby improving cost effectiveness.

 

On the other hand, replacing mats with rovings can increase the fiber volume content to about 80%, while most non-polyurethane pultrusion products have a fiber content of 60%. This higher glass content combined with a better performing resin creates a polyurethane pultruded profile with greater strength and stiffness.

 

(2) The higher strength properties of polyurethane pultrusion products open up new applications. These products can be used in applications where polyester resins are not suitable, replacing steel and aluminum in the construction, infrastructure and transportation markets.

 

(3) Converting an existing pultrusion system to a polyurethane pultrusion system is relatively simple, convenient and economical, without requiring a large investment. The original die head, heater and unit can still be used.

 

(4) In addition to the above-mentioned physical properties and molding advantages, polyurethane pultruded parts also have assembly advantages, especially convenient fastening. Due to the strength of polyurethane, it is not necessary to pre-drill holes when installing screws in polyurethane pultruded products, which can save time and labor. Conversely, the force required to pull out a screw in a polyurethane pultruded product is more than twice the force required to pull out a screw in a polyester pultruded product.

 

(5) Under the same fiber structure, all properties of polyurethane/glass fiber pultruded products are better than those of ordinary thermosetting resins, with similar bending modulus, greatly improved impact strength, high screw pull-out strength, good crack expansion resistance at the opening, excellent wear resistance, good secondary processing ability, and heat resistance above 240 degrees.

 

Comparison of the performance of major thermosetting resin/glass fiber composite materials

 

 

 

(6) Pure Polyurethane/Glass Fiber is the best Pultruded Composite Material at Present. The material has a complex cross-section, a smooth surface, a fast pultrusion speed, the best resistance to water, acid, alkali and salt, good flame resistance, can be painted, and polyurethane resin is used in automotive applications. It is solvent-free, styrene-free and environmentally friendly.

 

3. 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 and windows, exterior walls, roofs and floors are the four major parts of building energy consumption, and doors and windows have the worst insulation. It is estimated that for typical enclosure components in my country, the energy consumption of doors and windows is about 4 times that of walls, 5 times that of roofs, and more than 20 times that of floors, accounting for about 40% to 50% of the total energy consumption of enclosure components. Therefore, enhancing the thermal insulation performance of doors and windows and reducing the energy consumption of doors and windows are important links in improving the quality of indoor thermal environment and improving the energy conservation level of buildings. The rise of composite materials in applications has brought us new ideas, making it possible to apply them to the transformation of building energy-saving doors and windows.

 

Compared with traditional materials, polyurethane pultruded window frames have stronger dimensional stability, higher lateral mechanical properties, higher specific strength and rigidity, and better thermal insulation effects. Coupled with the unique pultrusion process of polyurethane material technology, the material does not contain volatile organic compounds (VOCs), so it is also very environmentally friendly.

 

Glass fiber reinforced polyurethane pultruded door and window profiles are made of glass fiber as a reinforcing material and polyurethane as a matrix through advanced injection dipping and pultrusion processes. The development of GRPU door and window profiles is to provide high-rise buildings with energy-saving window solutions with a total heat transfer coefficient of K ≤ 2.0 W/(m•K). Polyurethane (PU) has an innate thermal insulation ability and has long been used to manufacture foam sealants, sealing strips, and thermal insulation strips in the energy-saving door and window industry. The use of polyurethane to manufacture the entire window frame of energy-saving windows is a domestic first.

 

 

 

The advantages of GRPU window frames are determined by the performance characteristics of GRPU materials themselves. As a new type of composite material, GRPU window frames are a new growth point. Using this resin, larger, thinner and strong enough profiles can be made for large window frames and even curtain walls. This window frame is said to be much better than aluminum, wood and plastic window frames. It has excellent expansion and contraction properties and can withstand various climatic conditions, from the Arctic cold to the desert heat and the humidity of the seaside. It can be painted or post-processed to form a wooden appearance. Polyurethane composite window frames have the following basic characteristics:

 

High Thermal Insulation

GRPU profiles, like solid wood and PVC, have a very low thermal conductivity of 0.22 W/m•K at room temperature, which is only about 1/700 of aluminum alloy, and is an excellent thermal insulation material.

 

Low Thermal Expansion

GRPU has a linear thermal expansion coefficient of about 7×10-6/K, which is much lower than that of aluminum alloy and is similar to that of the wall; therefore, when the temperature changes, the GRPU frame will not have a gap with the wall, and the sealing is good, while ensuring the thermal insulation of the entire window in an environment with a large temperature difference.

 

Corrosion Resistance

GRPU profiles have strong corrosion resistance to most acids, alkalis, salts, organic matter, as well as seawater and humid air; and they are rust-proof and immortal, and their corrosion resistance is better than other material door and window profiles. It is especially suitable for coastal, corrosive and generally humid places.

 

Good Electrical Properties

GRPU profiles are good insulating materials, are not affected by electromagnetic waves, and do not reflect radio waves; they have special uses for the construction of communication systems.

 

2) Polyurethane/Glass Fiber Composite Materials for Container Floors

 

Lighter and More Durable Containers

 

EKO-FLOR composite floor system developed by Bayer and Conforce. Due to the high pultrusion efficiency, high strength and rigidity of the material, as well as excellent impact resistance and wear resistance, it has added a lot of color to the container transportation industry. Conforce is a partner of the German chemical company Bayer.

 

After years of research and development by developers, this composite reinforcement material is considered to have at least five advantages: first, low weight, which can reduce the amount of energy in transportation; second, it has a complete resistance to all types of products (water, oil, odor, microorganisms); third, the overall energy required for production is very low; fourth, it increases the service life of the container; fifth, it has a reusable and recyclable floor.

 

The new container is particularly particular about the materials used. A 40-foot container can reduce the weight by 550 kilograms, thereby reducing the energy required for transportation.

 

Compared with traditional wood-based materials, materials using polyurethane extrusion technology will reduce the weight by 22%, and the fuel consumption and transportation costs of the entire ship and vehicle container will be greatly reduced. While being lightweight, it also maintains sufficient toughness. This feature also reduces maintenance costs and increases the service life of the container. The service life of traditional container wood floors is only 5 to 10 years, while the service life of EKO-FLOR polyurethane pultruded floors can exceed 20 years.

 

CMA CGM of France recently cooperated with Conforce International of Canada to develop a non-solid wood composite container floor, named Eko-flor, hoping to use the accessories developed by this new technology to replace solid wood flooring to reduce environmental pollution and the felling of rainforest wood.

 

3) Railway Sleepers

 

In Europe, railway builders are increasingly paying attention to replacing wooden or concrete sleepers with FFU (fiber-reinforced foam polyurethane) sleepers pultruded by Sekisui Chemical of Japan. After several successful applications, a line system was recently installed in the Leverkusen Chemical Park in Germany, using a total of 136 FFU sleepers. These sleepers were provided by Sekisui Chemical, and the polyurethane used came from Bayer Material Science’s supplier in Japan. It is said that this sleeper looks like wood and combines 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 compression, tension and bending strength are very high, and its service life is more than 3 times longer than that of traditional sleepers. Due to its closed-cell structure, it absorbs very little water even in heavy rain, which does not affect its excellent electrical insulation properties. The material is also resistant to hydrolysis, grease, seawater, frost and deicing salts, and remains stable under long-term climatic conditions.

 

Its weight and on-site processing performance are much better than concrete, and it can be made into any length without the need to make a separate mold for each length. Its ecological performance is also a major advantage. No solvent is used during manufacturing, and it can be recycled after use. Due to these advantages, FFU sleepers are particularly suitable for use in tunnels and bridges. In Japan, more than 90,000 polyurethane sleepers are laid every year, and more than 1.3 million are now in use. This type of sleeper is used on the rails of Japan’s famous high-speed train “Shinkansen”.

 

4) Other Uses

 

Polyurethane pultruded products include profiles, rods and plates, such as ladder rods, tool handles, pole crossarms, poles, hockey sticks, dock piles, container plates, etc.

4. Raw materials and equipment for the production of polyurethane composite materials

 

1) Main Materials

Polyurethane materials (including polyols, isocyanates, catalysts, defoamers, lubricants, release agents, etc.) and glass fibers, of which glass fibers account for 80%-85%.

 

2) Main Equipment:

Glass fiber yarn guides, polyurethane casting machines, molding traction machines, cutting machines, etc. The cost of pultrusion equipment is about 200,000 yuan (20 tons of traction force), and polyurethane equipment is 100,000-150,000 yuan.

 

5. Polyurethane Composite Material Production Process

 

Process Flow:

 

 

Production Efficiency:

Depending on the specifications, the pultrusion speed varies from 1.2 to 3 m/min. The width is greater than 50 cm.