Pultruded FRP mainly uses unsaturated polyester resin and vinyl ester resin, and other resins also use phenolic resin, epoxy resin, methacrylic acid, and other resins. In recent years, due to the advantages of phenolic resins such as fire resistance, phenolic resins suitable for pultrusion of FRP have been developed, called second-generation phenolic resins, and have been widely used. In addition to thermosetting resins, thermoplastic resins are also selected as required.
Fiber Reinforced Material
The fiber-reinforced materials used in pultrusion of FRP are mainly E glass fiber roving. According to the needs of the product, C glass fiber, S glass fiber, T glass fiber, AR glass fiber, etc. In addition, synthetic fibers such as carbon fiber, aramid fiber, polyester fiber, nylon, etc. can also be selected for the needs of special-purpose products. In order to improve the transverse strength of hollow products, continuous fiber mats, cloths, belts, etc. can also be used as reinforcing materials.
The characteristics of initiators are usually expressed in terms of active oxygen content, critical temperature, and half-life.
The commonly used initiators are:
- MEKP (methyl ethyl ketone peroxide)
- TBPB (tert-butyl peroxybenzoate)
- BPO (benzoyl peroxide)
- Lm-P (special curing agent for pultrusion)
- TBPO (tert-butyl peroxyisooctanoate)
- BPPD (diphenoxyethyl peroxydicarbonate)
- P-16[ Peroxydicarbonate bis (4-tert-butyl cyclohexyl ester) ]
In practical applications, one-component is rarely used, and usually two-component or three-component are used in combination with different critical temperatures.
2. Epoxy resin curing agent
Commonly used are acid anhydrides, tertiary amines, imidazole curing agents.
Colorants in pultrusion typically come in the form of a pigment paste.
The filler can reduce the shrinkage rate of the product, improve the dimensional stability, surface finish, smoothness, and flatness of the mattress of the product; it can effectively adjust the viscosity of the resin; can meet different performance requirements, improve wear resistance, improve electrical conductivity and Thermal conductivity, etc. Most fillers can improve the impact strength and compressive strength of the material, but not the tensile strength; can improve the coloring effect of the pigment; some fillers have excellent light stability and chemical resistance; can reduce costs. When choosing the particle size of the filler, there should be a gradient in order to achieve the best use effect. There are also surface treatments for fillers to increase the amount.
5. Release agent
The release agent has very low surface free energy and can evenly wet the surface of the mold to achieve the release effect. Excellent demoulding effect is the main condition to ensure the smooth progress of the pultrusion profile process.
The early pultrusion process used external mold release agents, such as silicone oil. However, the dosage is large and the surface quality of the product is not ideal, so an internal release agent has been used.
The internal release agent is directly added to the resin, and at a certain processing temperature, it oozes out from the resin matrix and diffuses to the surface of the cured product, forming a layer of isolation film between the mold and the product, which plays the role of mold release.
Internal release agents generally include phosphate, lecithin, stearate, triethanolamine oil, etc. Among them, the release effect of zinc stearate is better. In pultrusion production, people usually prefer to use internal mold release agents that are liquid at room temperature. The internal mold release agents currently available in the market are mostly mixtures of primary amines, secondary amines and copolymers of organic phosphates and fatty acids.