Thermoplastics are permanently fusible and can be melted down and recycled. The reason why thermoplastics melt down so easily is because the molecules have a relatively weak attraction between the chains of molecules. Thermoplastic resins have molecules that are generally not cross-linked, meaning, the resin can be repeatedly melted and reused. Usually, no chemical change occurs when thermoplastic is cured. Thermoplastic resin usually starts out in solid pellet form, and changes shape with the addition of heat and pressure. Thermoplastic polymers are more widely used because of their flexibility, so there are, therefore, more of them. Thermoplastic polymers are known as acrylics (Polymethyl methacrylate), fluorocarbons (PTFE or TFE), nylons, polycarbonates, polyethylene, polypropylene, polystyrene, vinyls and polyester.

Features of thermoplastic resins:

• Pros
• High Impact Strength
• Attractive Surface Finish
• Recyclable / Scrap is Reusable
• No Emissions
• Can bond to other thermoplastics
• Can be molded or shaped with reheat
• Cons
• Generally softens with heat
• More difficult to prototype

Common types of Thermoplastic Resins

• Polyamide (PA or Nylon)
• Polybutylene terephthalate (PBT)
• Polyethylene terephthalate (PET) as Polyester.
• Polycarbonate (PC)
• Polyethylene (PE)
• Polypropylene (PP)
• Polyvinyl chloride (PVC)

What are thermoset plastics?

Thermosets are cured and will only char and break down. Thermoset molecules are formed by cross-linked chains of molecules further strengthened by chemical bonds. A thermoset is essentially one large molecule, without a crystalline structure. Thermoset resins generally come in liquid form, and when mixed with a catalyst, a chemical reaction occurs forming a solid. Thermoset molecules crosslink with each other during curing, thus once cured, they cannot change. Thermoset polymers do not equal thermoplastic polymers in quantity but they remain present within the manufacturing market. Thermoset polymers are known as epoxies, polyesters, silicones and phenolics.

Features of thermoset resins:

Pros

Easy to process and laminate Does not necessarily need pressure or heat to form Generally inexpensive Generally stronger than thermoplastics Generally better suited to higher temperatures then thermoplastics

Cons

• Often release emissions known as volatile organic compounds (VOCs)
• Cannot be recycled or reclaimed easily
• Short workable pot life, with some exceptions
• Less-than-perfect surface finish

Common Types of Themoset Resins

Epoxy

Polyester (Not PET) Vinylester

Polyurethane

Phenolic