In injection molding, two primary material categories dominate the industry: thermoset and thermoplastic. Both of them have distinct characteristics that affect their performance during the injection molding process. Understanding the differences between these materials can help manufacturers make informed decisions about which type of plastic material to use based on performance requirements, production scale, and other factors.
What Are Thermoset Plastics?
Thermoset plastics are polymers that undergo an irreversible chemical reaction (cross-linking) during curing. Once the cross-links form under heat and pressure, the material cannot be melted or reshaped. Common thermoset resins used in injection molding include:
- Epoxy resins
- Phenolic resins
- Unsaturated polyesters
- Polyurethanes (in reaction injection molding)
- Silicone
- Melamine formaldehyde
Advantages of Thermoset Plastics:
- High Strength and Durability: Thermosets are known for their robust mechanical properties and creep resistance.
- Great Heat Resistance: These materials maintain their integrity at higher temperatures
- Chemical Resistance: Thermosets are highly resistant to chemical degradation.
- Dimensional Stability: Thermoset plastic parts have great dimensional stability under load and heat.
Disadvantages of Thermoset Plastics:
- Irreversible Molding: Once thermosets are set, they cannot be reshaped or recycled, which limits their flexibility in manufacturing.
- Higher Manufacturing Costs: The molding process for thermosets is more complex and time-consuming, which can increase production costs.
- Limited Recycling: Due to their permanent structure, thermoset plastics cannot be easily recycled, posing environmental challenges.
What Are Thermoplastic Plastics?
Thermoplastic materials consist of linear or branched polymer chains that soften when heated and harden when cooled. They can be reheated and remolded without undergoing any chemical change. Widely used thermoplastics in thermoplastic injection molding service include:
- Polyethylene (PE)
- Polypropylene (PP)
- Acrylonitrile butadiene styrene (ABS)
- Polycarbonate (PC)
- Polyamide (Nylon 6, Nylon 66)
- Polyvinyl chloride (PVC)
- Polyetheretherketone (PEEK) and other engineering grades
Advantages of Thermoplastic Plastics:
- Recyclable: Thermoplastics can be reheated and reprocessed, which makes them recyclable and environmentally friendly.
- Ease of Processing: These materials are easier to mold and shape compared to thermosets, allowing for faster production cycles.
- High Flexibility: Thermoplastics offer excellent flexibility and can be made into a variety of shapes, making them suitable for complex designs and structures.
Disadvantages of Thermoplastic Plastics:
- Lower Heat Resistance: Thermoplastics generally have lower heat resistance compared to thermosets, making them less suitable for high-temperature applications.
- Weaker Mechanical Properties: While thermoplastics are flexible, they are not as strong as thermosets and can deform under stress.
- Limited Chemical Resistance: Thermoplastics are more susceptible to chemical degradation compared to thermosets, particularly in harsh chemical environments.
Thermoset vs Thermoplastic Material Performance Comparison
Thermoset and thermoplastic materials have different material characteristics. Below is a comparison of the performance characteristics of both materials:
Heat Resistance
- Thermoset Plastics: Offer superior heat resistance and can withstand higher temperatures without losing their shape or mechanical properties.
- Thermoplastic Plastics: Have a lower heat resistance and tend to soften or deform at higher temperatures, making them less suitable for high-heat applications.
Mechanical Properties
- Thermoset Plastics: Known for their high strength and hardness, thermosets are ideal for applications that require durability and resistance to wear and tear.
- Thermoplastic Plastics: Generally more flexible and impact-resistant, but lack the strength and rigidity of thermosets, making them less suitable for high-stress applications.
Chemical Resistance
- Thermoset Plastics: Have excellent chemical resistance, which makes them ideal for use in environments exposed to aggressive chemicals, oils, and solvents.
- Thermoplastic Plastics: While thermoplastics offer some chemical resistance, they are more likely to degrade when exposed to harsh chemicals compared to thermosets.
Recyclability
- Thermoset Plastics: Cannot be recycled or reused once they have been molded, leading to environmental concerns about waste and disposal.
- Thermoplastic Plastics: Can be recycled and reprocessed multiple times, making them a more sustainable choice for many industries.
Key Process Differences in Injection Molding
| Aspect | Thermoset Injection Molding | Thermoplastic Injection Molding |
|---|---|---|
| Size | Size |
78.74in. x 59.05in. x 39.37in. 2000mm x 1500mm x 1000mm |
| Mold Cavities | Mold Cavities | Single-cavity molds, multi-cavity molds, family molds |
| Mold Life | Mold Life | Unlimited (We will open a new mold if the old one worn out) |
| Material feed | Liquid resin + hardener or powder | Solid pellets |
| Mold temperature | Hot mold (150–200 °C) for curing | Cold mold (20–120 °C) for cooling |
| Injection pressure | Lower (5–50 MPa) | Higher (80–200 MPa) |
| Cycle time | 60–300 seconds (curing dominates) | 15–90 seconds |
| Scrap handling | Cannot be reused | Can be reground and reused |
| Cost | Higher due to complex processes and slower cycle times. | Lower cost due to quicker production cycles and simpler processing. |
Thermoset and Thermoplastic Injection Molding Applications
Both thermoset and thermoplastic injection molding are used across a wide range of industries. However, the material choice depends on the specific requirements of the application.Thermoset Plastic Injection Molding Applications
- Automotive Industry: Parts like electrical connectors, bumpers, housings, brake components, and clutch parts.
- Electronics: Components such as circuit board enclosures and electrical connectors.
- Household: kitchenware handles.
Thermoplastic Plastic Injection Molding Applications
- Consumer Goods: Products like containers, packaging, and household appliances.
- Medical Devices: Syringes, IV components, and diagnostic equipment.
- Automotive: Parts like dashboards, door panels, and interior trims.
