A Comprehensive Guide to Plastics, Fibers, and Modern Materials
Plastics and Polymers
Introduction
Plastics, or polymers, are synthetic materials created through chemical reactions, often with additives to enhance their properties. These materials offer numerous benefits such as corrosion resistance, thermal and acoustic insulation, electrical shock resistance, and aesthetic appeal.
Raw Materials
The raw materials used in plastic production have evolved over time:
- 19th Century: Primarily animal and vegetable sources.
- Until ~1930: Coal tar, a byproduct of coal transformation.
- Present Day: Oil and natural gas.
Components of Plastics
- Base Materials (Monomers): The primary building blocks of the plastic.
- Fillers: Added to reduce cost and improve physical, chemical, or mechanical properties.
- Additives: Enhance specific qualities of the polymer.
- Catalysts: Initiate and accelerate the curing process.
Types of Plastics
- Thermoplastics: Become moldable when heated to temperatures between 50 and 200°C.
- Fibers: Exhibit a preferential direction in their molecular structure, making them resistant to tension, washable, and wrinkle-resistant.
- Thermosets: Harden permanently after being shaped by heat and cannot be remolded.
- Elastomers: Highly resilient, allowing for significant deformation without permanent change. Cannot be melted again.
Plastic Forming Processes
- Pressing: Granulated material with fillers and additives is placed in a mold, heated, and pressed to shape.
- Injection Molding: Plasticized material is injected into a mold under pressure.
- Thermoforming: Rigid sheets are heated and formed over a mold using vacuum or pressure.
- Extrusion Blow Molding: Tubular plastic is inflated inside a cooled mold.
Reinforced Plastics and Composites
These materials combine a reinforcing element for strength with a plastic matrix.
- Kevlar: Exceptionally strong and difficult to machine.
- Carbon Fiber: Derived from polyacrylonitrile mixed with other polymers.
Laminated Plastics
Composed of two or more layers of material bonded together.
- Plastic-Glass: Glass coated with a thin plastic layer.
- Plastic-Metal: Metal coated with plastic (e.g., food cans).
- Plastic-Paper/Cardboard: Cardboard coated with plastic for moisture resistance (e.g., Tetra Pak).
- Plastic-Woven Fabric: Used in synthetic leather and canvas.
- Plastic-Plastic: Multiple layers for enhanced protection and properties (e.g., food packaging).
Fibers
Mineral Fibers
Extracted from fibrous ores. Handling may pose health risks.
- Fiberglass: Used for thermal and acoustic insulation.
- Metallic Fibers: Gold and silver can be spun into threads for decorative purposes.
Vegetable Fibers
- Cotton: Composed of 91% cellulose.
- Linen: Strong, less elastic, and more expensive than cotton.
- Esparto: Primarily used for crafts.
Animal Fibers
- Wool: Obtained from sheep, elastic but sensitive to moisture and heat.
- Silk: Produced by silkworms, elastic but a poor heat conductor.
- Leather: Animal hide treated through tanning to remove hair and enhance durability and flexibility.
Artificial Fibers
- Cellulosic Fibers (Rayon): Derived from chemically treated cellulose.
- Protein Fibers: Less common, examples include fibrolana and lanital (made from milk casein), vicara (corn protein), and alginate (seaweed).
Elastomers
Highly elastic materials that undergo vulcanization (treatment with sulfur, heat, and pressure).
Types of Elastomers
- Natural Rubber: Obtained from latex, primarily used in mattresses and pillows.
- Neoprene: A synthetic rubber resistant to combustion and deterioration, used for cable insulation.
- Silicone: Highly resistant to external agents.
- Synthetic Rubber: Resistant to heat, abrasion, and aging, commonly used in tires.
Cork
Harvested from the bark of cork oak trees every nine years.
Glass
Produced by melting quartz sand with salt and sodium carbonate. Other compounds like lead oxide may be added.
Gypsum
A white material derived from calcium sulfate dihydrate. Hardens quickly after mixing with water.
New Materials
• Structural materials: Its usefulness lies in their mechanical properties • Functional Materials: Their usefulness lies not in its mechanical properties if not chemical, magnetic, electronic, optical. • functional materials, phosphorescent materials, alloys of neodymium iron boron or samarium cobalt, liquid crystals and biomaterials • Organic Materials: Produced by genetically modified virus used optical systems, electronic • Smart materials: Be self-repairing, with a behavior similar to our body, which is able to repair damaged tissue. • Nanocomposite Materials: A hybrid base for electronic components with higher capacity, lower volume and faster • Gels : respond to stimuli such as temperature or pH changes.