Polymer Properties and Processing: A Detailed Look

Posted on Feb 25, 2025 in Technology

Copolymerization

Copolymerization is the chemical modification of polymer properties resulting from the polymerization of two or more monomers.

Long-Term Mechanical Behavior

When a material is subjected to tension, it undergoes elastic deformation, but simultaneously begins a slow, permanent plastic deformation. This phenomenon is known as Creep.

  • Creep Modulus Curves: Defined as the ratio of constant voltage applied to the material and the increasing deformation experienced over time.
  • Relaxation Modulus Curves: Defined as the ratio between the voltage at a given time and the initial deformation imposed on the material.
  • Isochrones Curve: Represents a constant time.
  • Permanent Tension Resistance Curve: Indicates no breakage.

Short-Term Mechanical Behavior

Polymers can be classified into five types based on their short-term mechanical behavior:

  1. Fragile-plastic
  2. Deformable plastic
  3. Plastic-plastic
  4. Flexible plastic
  5. Expandable elastomers

Polymer Degradation

Factors affecting polymer degradation include:

  • Water absorption
  • Aging
  • Chemical attack
  • Flame behavior

Processing Levels

There are three levels of processing:

  1. Material Preparation: Using special extruders with multiple entries, materials are dosed out where filaments are sliced into granular form (pellets).
  2. Fabrication of Intermediate Products: This involves processes like extrusion, blow molding of plates, coextrusion, and calendering.
  3. Fabrication of Parts: Main manufacturing processes include injection molding, reaction injection molding, blow molding, injection blow molding, sandwich injection, foam injection, rotational molding, press molding, transfer molding, heat forming, and thermoforming.

Plastics

Plastics, characterized by low density, high coefficient of thermal expansion, and low thermal conductivity, are divided into thermoplastics and thermosets.

Plastic Groups

  • Consumer Plastics: Low cost, moderate mechanical and thermal properties, and a service temperature limited to 100°C. They account for over 80% of global plastic consumption.
  • Engineering Plastics: Higher cost, superior mechanical and thermal properties, a service temperature ranging from 80 to 150°C, and good abrasion and slip resistance.
  • High-Performance Plastics: (e.g., PMMA – Polymethyl Methacrylate) High cost, excellent mechanical properties beyond 150°C.
  • Special Plastics: Moderate to very high cost.

Consumer Plastics

  • Polyethylene (PE-LD, PE-LLD, PE-HD): The cheapest and most used plastics, with low densities, good chemical resistance, low water absorption, and good friction behavior. Applications: films, shopping bags.
  • Polypropylene: The lightest polymer, low cost, good balance between thermal and mechanical properties, odorless, tasteless, and harmless.
  • Chlorinated Plastics: Good strength, stiffness, and moderate toughness. Applications: construction (doors, windows, roofs).
  • Styrene Polymers: High strength and rigidity, low water absorption, and good dimensional stability.

Technical Plastics (Thermoplastics)

Examples include Acrylonitrile Butadiene Styrene (ABS), Polyamides, Polyacetals (POM), Polycarbonates, Unsaturated Polyesters, and Poly(phenyl ethers).

Technical Plastics (Thermosetting)

Examples include Phenolic Resins, Amino Resins, Unsaturated Polyesters, Epoxy Resins, and Polyurethanes.

High-Performance Plastics

Examples include Polysulfones, Poly(phenylene sulfide), Polyaryletherketone, Polyimide, and Liquid Crystal Polymers.