Processing and Applications of Thermoset Polymers

Processing and Applications of Thermoset Polymers

Introduction

Thermoset polymers are a class of materials that, once cured, form an irreversible chemical network, giving them superior dimensional stability, thermal resistance, and mechanical strength compared to thermoplastics. Unlike thermoplastics that soften upon reheating, thermosets undergo permanent cross-linking during the curing process (Strong, 2016). This property makes them ideal for high-performance applications such as aerospace components, automotive parts, electrical insulation, and coatings.

The purpose of this report is to discuss the primary processing techniques of thermoset polymers and critically analyse their applications across industrial sectors. Additionally, it explores the advantages, limitations, and technological developments influencing their current and future use.

Processing of Thermoset Polymers

Polymerisation and Cross-Linking

Thermoset polymers are typically produced through step-growth or chain-growth polymerisation, leading to a highly cross-linked network. Common examples include epoxy resins, phenolics, melamine-formaldehyde, and unsaturated polyester resins. During processing, these polymers transition from a liquid or malleable prepolymer into a rigid three-dimensional structure under heat, pressure, or radiation (Kim and White, 2019).

Moulding Techniques

The most common thermoset processing techniques include compression moulding, transfer moulding, and reaction injection moulding (RIM).

• Compression Moulding: The prepolymer or moulding compound is placed in a heated mould, compressed, and cured to shape. This method is ideal for phenolic and melamine resins due to their flow characteristics before gelation (Rosato et al., 2018).

• Transfer Moulding: Used for more complex geometries, where the preheated resin is transferred into a closed heated mould cavity through a sprue and runner system. It provides improved surface finish and dimensional accuracy (Ibeh, 2017).

• Reaction Injection Moulding (RIM): Commonly used for polyurethane and epoxy systems, RIM involves mixing two liquid components that react and cure inside the mould. This method allows for lightweight and intricate parts with short cycle times (Rahman et al., 2020).

Curing Process

Curing converts the prepolymer into an infusible, insoluble material through heat or chemical initiators. The curing temperature and time directly affect the degree of cross-linking and mechanical properties. Over-curing may cause brittleness, while under-curing leads to incomplete network formation. Modern advancements include microwave-assisted curing and UV curing, which reduce processing time and energy use (Chen et al., 2018).