Understanding Plastic Materials and Their Properties
Plastic Materials
Materials: These are materials made of polymers consisting of long chains of molecules containing carbon.
- Natural: Obtained directly from plant materials (pulp) or animals (casein).
- Synthetic or Artificial: Elaborated from compounds derived from petroleum, natural gas, or coal.
Polymerization
Consists of joining small molecules together to form large ones.
Thermoplastic Materials
Compounds obtained from petroleum products. Chains are weakly bound together, soften when heated, and can be molded.
- PVC (Polyvinyl Chloride):
- Properties: Very hard, impermeable.
- Uses: Pipes, gloves.
- Polystyrene (PS):
- Hard: Transparent, pigmented.
- Expanded Polystyrene:
- Properties: Fluffy and soft.
- Polyethylene (PE):
- High Density: Rigid, resistant, and transparent.
- Low Density: Soft, lightweight, and transparent.
- Methacrylate: Transparent.
- Teflon: Slippery and non-stick.
- Cellophane Bags: Transparent, flexible, resilient, brilliant.
- Nylon: Translucent, bright, strong, flexible, and waterproof.
Thermoset Plastics
Derived from petroleum. Formed by strongly bound chains. If subjected to heat, they become rigid.
- Polyurethane: Spongy, flexible, soft, solid, elastic.
- Melamine: Light, resistant, odorless, tasteless, and thermal insulator.
Elastomers
Obtained by vulcanization (consisting of mixing sulfur and rubber at 160ยบ). When force is applied, the chains stretch, exhibiting great elasticity.
- Natural Rubber: Resistant.
- Synthetic Rubber: Resistant to chemical agents.
- Neoprene: Harder, more resistant, and impermeable.
Plastic Shaping Techniques
Extrusion
Thermoplastic material in the form of granules is introduced through a funnel and falls into a heated cylinder. The molten material is forced through an exit nozzle or mold, where it cools and solidifies.
Vacuum Forming
Thermoplastic foil is clamped to a mold. The foil is heated with a radiator to soften the material. Air is sucked from beneath the foil by a vacuum, adapting the material to the walls of the mold and taking its shape.
Blow Molding
A process through which hollow plastic objects, such as bottles, are produced. It includes two steps: extrusion of a molten polymer through a special die and inflation of the tube in a mold, where it takes its final form.
Injection Molding
Thermoplastic material is injected into a mold, where it cools and solidifies. The mold is then opened, and the piece is removed.
Compression Molding
Thermosetting material is introduced in powder or granule form into a female mold. Another male mold compresses the material, which is heated and softened to make it malleable, taking the form of the internal cavity of the two molds. Afterward, it is cooled, and the piece is removed.
Natural Fibers
Raw materials are extracted from plants, animals, or minerals.
Vegetable Fibers
- Cotton: Comes from the fruit of a plant in the Malvaceae family. It is white, flexible, elastic, and a thermal insulator.
- Linen: Obtained from a plant in the Linaceae family. Its color is white or tan. It is a good conductor of heat and is resistant.
- Esparto: A herbaceous plant with tough, tenacious leaves.