Polymer Materials: Types, Properties, and Applications
Polymer Materials
Introduction
Polymers are large molecules (macromolecules) primarily composed of carbon, derived from natural or synthetic sources. These macromolecules are also known as plastics. Polyaddition involves the joining of monomer units without the loss of any atoms. Polycondensation, on the other hand, results in the formation of a polymer along with small byproduct molecules like water or alcohol. When different monomers are polymerized together, the process is called copolymerization, and the resulting macromolecule is a copolymer.
Polymer Bonds
The molecular weight of a polymer isn’t always uniform and increases as the polymerization process continues. There are two types of forces that link polymers: intramolecular forces, which hold the atoms within a molecule together, and intermolecular forces, which are weaker bonds between polymer molecules.
Types of Polymers
Thermoplastics
Thermoplastics are linear or branched polymers. When heated, the weak intermolecular bonds break, allowing the polymer chains to slide past each other. Most polymers are thermoplastics formed by addition polymerization.
Thermosets
Thermosets are characterized by strong covalent bonds between their molecules, forming a giant, cross-linked network. They are insoluble in most organic solvents and decompose at high temperatures.
Elastomers
Elastomers are formed by long, loosely connected polymer chains. They are very elastic and can be stretched without breaking. Vulcanization, the process of adding sulfur, increases the number of intermolecular bonds, making the elastomer more rigid.
Common Polymers
Polyethylene
Polyethylene is one of the most stable and inert polymers. It has excellent mechanical and electrical properties, is transparent, and has a low density. There are two types: low-density polyethylene (LDPE), which is branched, and high-density polyethylene (HDPE), which has fewer branches and higher crystallinity.
Polypropylene
Polypropylene has a lower density than polyethylene (0.9). Its main limitation is its fragility at low temperatures, which can be addressed by using copolymers. It is resistant to aging, light-colored, resistant to traction, and has good electrical properties.
Polystyrene
Polystyrene is a rigid, brittle, and amorphous material with low heat resistance. It is used in household accessories and toys. Expanded polystyrene (EPS), used in packaging and insulation, is created by adding volatile substances during polymerization.
Polyamide (Nylon)
Nylon is known for its elasticity, high tensile strength, and ability to be spun into fine threads, making it a major synthetic fiber.
Polyesters
Polyesters are formed by the polycondensation of a dicarboxylic acid and a di-alcohol. Terylene, a common polyester fiber, is highly resistant to traction and wrinkles.
Polycarbonates
Polycarbonates are crystalline thermoplastics used in housings, office machinery, gears, and boat propellers.
Polyacetals
Polyacetals have a regular linear structure, high melting point, and excellent mechanical properties. They are resistant to abrasion and corrosion.
Fluoroplastics (Teflon)
Fluoroplastics, like Teflon, are derived from acetylene. They have high thermal stability, are resistant to abrasion, and have excellent electrical insulation properties.
Thermoset Polymers
Thermoset polymers have three-dimensional structures, making them tough and brittle.
Epoxy Resins
Epoxy resins are initially liquid and poisonous but become hard, odorless, and harmless once cured. They are resistant to chemicals and heat and are good electrical insulators.
Elastomers (Rubber)
About 68% of elastomer production is used in tires. Elastomers have long, linear chains and are typically soft and elastic. Oxygen and heat can cause aging, reducing elasticity and increasing rigidity.
Glass Ceramics
Glass ceramics combine the crystalline nature of ceramics with the formability of glass. They are resistant to mechanical impact and thermal shock.
Amino Resins
Amino resins include urea-formaldehyde and melamine-formaldehyde (Formica) products. They have similar properties to phenolic resins and are used in decorative panels, adhesives, and kitchen countertops.
Polyurethane Resins
Polyurethane resins are formed from isocyanates and alcohols. They are commonly used in low-density foams for insulation, pillows, mattresses, and other applications.