Thermoset Composites / Pultrusion


Pultrusion is a process that enables continuous production of composite profiles with constant cross sections and material properties tailored to specific purposes. The difference with the extrusion process in which material is pushed/pressed through the process, in pultrusion it is pulled (see pullers in picture below). There is no molding involved in shaping the article.

Materials used in pultrusion are very similar to those used in SMC and BMC. 

A composite used in the pultrusion process is a combination of two materials:

  1. The matrix (formulation containing the polymer/resin)
  2. A fibrous material (in case of pultrusion continious glass-fibres or even textiles). 

The main reason to make composites is to get mechanically stronger (reinforcement) materials by establishing a strong interaction between the resin and the fibre. For this reason composites are sometimes also referred to as FRP’s (Fibre Reinforced Plastics). While the resin can be of any kind, most often they are thermoset resins (like polyester, vinyl-esters and epoxies). What sets composites aside from “compounds” is the fact that unlike “compounds” the individual components (matrix and fibrous material) remain separate and visibly distinct within the finished structure/composite.

Composites are often used as a replacement of metal to reduce the overall weight of e.g. a car or plane leading to better fuel economics.

To get the best properties for the composite the matrix needs to be fully wetted (impregnated to saturation) with the formulation containing the polymer. In the case of the pultusion process the viscosity/rheology of the formulation can be more critical. 

Fillers are added to the composite and Sibelco offers mineral fillers that can further improve the properties (beyond reinforcement) of the article made by the pultrusion process, by providing 

  • Flame-retardancy (ATH)
  • Dimensional Stability (Silica)
  • lower cost (Silica)
  • better heat conductivity (ATH)

The combination of two different (coarse and fine) ATH-grades offered by Sibelco can lower the viscosity of the formulation and improve processing and final product properties.