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Primary Raw Materials For Pultrusion Of Fiberglass Reinforced Plastics

Pultrusion stands as a continuous production process, instrumental in the fabrication of fiber-reinforced plastic profiles with consistent cross-sections. At the heart of the pultrusion process lies the pulling of fibers and resins through a heated die, where the resin undergoes a polymerization reaction, solidifying the profile into its final shape. The selection of raw materials in the pultrusion process is paramount, directly impacting the final product’s mechanical properties, durability, and applicability.

Resins: The Binding Force

Resins play a pivotal role in the pultrusion process, acting as the matrix that binds the reinforcing fibers together. Various types of resins are utilized, including:

  • Unsaturated Polyester Resins (UP): Known for their ease of handling and good mechanical properties. However, they may release moisture during curing, potentially leading to cracks and voids.
  • Vinyl Ester Resins: Renowned for their excellent moisture and chemical resistance.
  • Epoxy Resins: Characterized by superior strength, stiffness, and temperature resistance.
  • Phenolic Resins: The oldest resin system, known for their very low flammability but higher smoke emissions and lack of color.
  • Methacrylate Resins: Noted for their high filler content, flame retardancy, high reactive activity, low shrinkage, and ease of coloring.
  • Polyurethane (PU): A two-component thermoset resin, celebrated for its impact resistance, fatigue resistance, low shrinkage, and structural integrity. Polyurethane resins are increasingly used in pultrusion processes for their superior mechanical properties and productivity advantages.

Reinforcing Fibers: The Backbone

Fibers provide the composite material with strength and stiffness. The most commonly used fibers in pultrusion include:

  • Glass Fibers: Including E, C, or S glass types, these fibers are bundled into rovings and serve as a crucial component of the reinforcement. They are treated with silanes to enhance adhesion with the resin matrix.
  • Carbon Fibers: Employed in situations where high strength and stiffness are required.
  • Aramid Fibers: Occasionally used in scenarios demanding very high strength and impact resistance.

Fillers and Additives: Performance Enhancers

Fillers and additives are incorporated to enhance specific properties of the pultruded profiles, such as flame retardancy, surface quality, and mechanical performance:

  • Fillers: Such as kaolin, chalk, and alumina trihydrate (ATH), are added to the resin to improve flame retardancy and mechanical properties.
  • Additives: Include wetting and dispersing agents to reduce viscosity and improve filler dispersion, degassing agents to eliminate voids, and coupling agents to enhance the adhesion between fibers and the matrix.

Reinforcement Forms: Tailoring Performance

To achieve desired mechanical and surface properties, different forms of reinforcing materials can be utilized:

  • Rovings: Smooth, textured, or single-end rovings for unidirectional reinforcement.
  • Continuous Filament Mat (CFM): Provides multi-axial glass strands arrangement to improve surface smoothness.
  • Surface Mats: Polyester or glass mats used as a covering layer for profiles to enhance weatherability, UV resistance, and surface quality.


The pultrusion process employs a variety of raw materials, each selected based on the performance required for the final product. Resins, reinforcing fibers, fillers, and additives are meticulously chosen to ensure that the pultruded profiles meet specific performance standards, including mechanical strength, durability, and resistance to environmental factors.

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