Pultrusion processes

Figure 7.87 Schematic diagram of a typical pultrusion process. Reprinted, by permission, from M. Schwartz, Composite Materials Handbook, 2nd ed., p. 4.46. Copyright 1992 McGraw-Hill.

Among the more common thermoplastics from ring opening polymerization of interest in composite processing are polylactams, polyethers, polyacetals, and polycycloolefins. It has also been shown that polycarbonates can be produced from cyclic carbonates [22], Anionic ring opening polymerization of caprolactam to nylon 6 is uniquely suited to form a thermoplastic matrix for fiber-reinforced composites, specifically by the reaction injection pultrusion process [23-25]. The fast reaction kinetics with no by-products and the crystalline... 

Pultrusion is a steady-state process in which the fiber-resin mass changes its properties as it moves from the entrance to the exit of the die. In order to track the temperature, polymer conversion, and other properties of the fiber-resin mass as it moves along the die, it is useful to define a representative volume element (RVE) that rides along the fiber at the line speed of the pultrusion process. An RVE is defined such that it will contain both the solid phase (i.e., fibers and resin), irrespective of its location in the composite. In real-life pultrusion, a thermocouple wire that passes through the pultrusion die tracks the temperature of an RVE in the composite. 

As pointed out in the beginning of the chapter—and perhaps also noticeable from the process description earlier—the pultrusion process at first appears rather simple and straightforward however, several intricacies arise on closer inspection. The key technology issues of pultrusion of thermoset-matrix composites are usually considered to be resin formulation, temperature control, material guidance, and die design (not in order of importance). It is typically the skill in these areas that distinguishes a successful pultruder from his hapless competitor. 

In the pultrusion process, continuous fibers are impregnated by the thermoset precursors and are pulled through a heated die where the cure takes place this produces continuous profiles of different shapes at a rate of the order of 1 m min-1. 

Figure 6. Schematic of the pultrusion process for continuous production of polymer composites.

Batch, G. L., and Macosko, C. W., Computer Aided Analysis of Pultrusion Processing. AIChE Conference on Materials in Emerging Technologies, Minneapolis, August 1987. 

To produce pultruded products with consistent and high quality, it is important to tailor and control the pultrusion process. To achieve a uniform degree of cure in the cross-section of a product, control of the temperature profile inside the pultrusion die is an essential aspect. Also, to achieve consistent fibre wetting, controlled flow and pressure build-up must... 

Initial modelling on predicting velocity profiles in pultrusion dies was carried out by Gorthala et al. (1994). Here a two-dimensional mathematical model in cylindrical co-ordinates with a control-volume-based finite-difference method was developed for resin fiow, cure and heat transfer associated with the pultrusion process. Raper et al. 

Development of Long-Fibre Prepreg via Pultrusion Process. 453... 

The simplest of them is the solvent based pultrusion process. Furthermore it does not require specially prepared resin normally confined to resin suppliers, albeit sometime... 

---