What are Engineering Plastics and Their Characteristics

Engineering plastics refer to a class of high-performance polymer materials that can be used as structural materials, capable of withstanding mechanical stress over a wide temperature range and in harsh chemical and physical environments. Generally, these plastics can endure certain external forces, exhibit excellent mechanical properties and dimensional stability, and maintain their superior performance under high and low temperatures, making them suitable for engineering structural components. Examples include Ultra-High Molecular Weight Polyethylene (UHMWPE), Nylon PA66, Nylon MC, and Polyacetal.

These high-performance plastics are primarily used in industrial applications due to their high heat resistance (above 100°C) and include:

1. **Thermal Properties**:

   - High glass transition temperature (Tg) and melting point (Tm)

   - High heat deflection temperature (HDT)

   - High long-term use temperature (UL-746B)

   - Wide range of operating temperatures

   - Low thermal expansion coefficient

2. **Mechanical Properties**:

   - High strength

   - High mechanical modulus

   - Low creep

   - Wear resistance

   - Fatigue resistance

3. **Other Properties**:

   - Chemical resistance

   - Excellent electrical insulation

   - Flame resistance

   - Weather resistance

   - Good dimensional stability

Common engineering plastics include:

- **Ultra-High Molecular Weight Polyethylene (UHMWPE)**: Known for its excellent wear resistance.

- **Polycarbonate (PC)**

- **Polyamide (Nylon, PA)**

- **Polyacetal (POM)**

- **Modified Polyphenylene Oxide (Modified PPE)**

- **Polyesters (PETP, PBTP)**

- **Polyphenylene Sulfide (PPS)**

- **Polyarylates**

Thermosetting plastics include unsaturated polyesters, phenolic plastics, and epoxy plastics. These materials typically have tensile strengths exceeding 50 MPa, tensile strengths over 500 kg/cm², impact resistance above 50 J/m, flexural modulus around 24,000 kg/cm², and load deflection temperatures over 100°C. They also exhibit excellent hardness and aging resistance.

Polypropylene can also be classified as an engineering plastic if its hardness and cold resistance are improved. Additionally, there are specialized plastics like fluoroplastics known for their chemical resistance, and high-temperature resistant silicones, polyamide-imides, polyimides, polybismaleimides, polysulfones (PSF), PES, acrylate plastics, modified melamine plastics, BT resins, PEEK, PEI, and liquid crystal polymers. Due to their differing chemical structures, these materials have varying chemical resistance, frictional characteristics, and electrical properties. Their forming processes also differ, leading to certain application limitations.

Thermosetting engineering plastics often have poor impact resistance and usually require the addition of glass fibers. Engineering plastics, excluding highly impact-resistant ones like polycarbonate, typically have low elongation and are hard and brittle. Adding 20-30% glass fiber can improve these properties.