“What is the difference between plastic injection molding thermoplastic and thermoset polymers?”
This is a question our customers often ask, so today we are taking a closer look at the subject. As the prefix “thermo” suggests, the differences in these polymers lie in how they react when exposed to heat. While both thermoset and thermoplastic materials have wide applications, their unique properties make them better suited for some applications over others.
Thermoset materials begin in a liquid state and become solid when heated. This curing (or hardening) process permanently changes the material through chemical reactions that create “cross-links” (permanent connections between molecular chains). These cross-links make the cured material strong, dimensionally stable, highly resistant to heat and chemicals, and give a higher degree of rigidity than it possessed before curing.
As a result, thermoset polymers outperform other materials in several areas, including chemical resistance, thermal stability, mechanical properties an overall durability. However, the chemical reaction is permanent, meaning thermoset polymers cannot be melted and reformed. They are also not as impact resistant as plastic injection molding thermoplastics in harder forms and thus can tend to shatter.
Thermoplastics commonly start in pellet form that becomes more liquidy and pliable as heat is applied. This allows the material to be injected from a heated cavity into a cool mold. The thermoplastic hardens into the shape of the mold as it cools, but it does not “cure” and create cross-links like thermoset materials do. Therefore, the changes in the thermoplastic are purely physical and completely reversible with the reapplication of heat.
Plastic injection molding thermoplastic polymers can be reheated and reprocessed many times before the material’s properties begin to suffer. They are therefore easier to recycle and repair. This elastic, highly flexible and versatile material is useful in a variety of industries.
Cooking with Polymers
To help clarify the difference between plastic injection molding thermoplastic and thermoset polymers, let us take a trip to the kitchen. Imagine making a delicious egg and cheese sandwich for breakfast. You crack the egg in the pan and the liquid egg white and yolk pour out. As you apply heat, the egg cooks and solidifies. Next you grab a block of solid cheese and cut some slices. When you add the cheese to the hot eggs, they quickly liquify. If you allow the cheese to cool, it will return to a hardened state.
While the egg and cheese were both altered by the heat, they had two different reactions. Once cooked, an egg will never return to its pre-cooked, liquid state. The cheese, however, can be reheated to a liquid state and cooled to a hard state over and over. The same is true of thermosets (eggs) and thermoplastics (cheese).
Proto-Cast: Experts in Plastic Injection Molding Thermoplastics
At Proto-Cast, we have extensive experience with thermoplastic materials and can meet all your plastic injection molding needs, from overmolding to plastic part machining. Call us today at 610-326-1723 to learn more about our services.