12.1 Introduction

Thermosetting resins are the most predominant matrices for high performance composite materials; this is due to their combination of low viscosity for processing and intrinsic high strength and high temperature performance. It is reported that the formation of thermoset resin materials by the reaction of phenols and aldehydes had been known a long time prior to their commercialisation in the early 1900s. Their first reported formulation was in 1872 by Baeyer [1] using phenols and aldehydes. Such work lead to thirty years of trial formulations leading to the polymerisation of phenols with formaldehyde; these were the first commercial formulations. Their synthesis was first patented in 1907 by L.H. Baekeland and became a commercial product in 1910 [1].

The polymerisation of phenol-formaldehyde is a two stage process, which leads to a soluble and fusible intermediate resin by attack of a phenol-derived species on the carbonylderived species. The first phenol-formaldehyde formulation was base-catalysed and is called the resole process and requires molar ratio of less than one, respectively. The second and/or newer formulation involves an acid catalyst and is called the novolak process and requires a molar ratio of greater than one phenol-formaldehyde [2, 3, 4]. The products obtained from these two processes are called resole and novolak resin. The intermediate resins are converted to the final crosslinked solid by acid-catalysed second stages.

Whilst these early polymers used fossil-based raw materials, natural monomers are also in existence. Since the most available of these...