Plastics: Morphology, History, Applications Quiz

Plastics: A Study of Morphology, History, and Applications

• Polymer Families
  • Thermosets: Cross-linked structure, irreversible solidifying upon heating
  • Thermoplastics: Linear or branched structure, can be repeatedly melted and solidified
    • Commodity: High production volume, low cost (e.g., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC))
    • Engineering: Higher performance than commodity thermoplastics (e.g., polybutylene terephthalate (PBT), polycarbonate (PC), polyamide (PA), polyoxymethylene (POM))
    • High Performance: Excellent properties but high cost (e.g., polyetheretherketone (PEEK), polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP))

Glass Transition Temperature (Tg)

• Definition: Temperature at which a polymer transitions from a rigid, glassy state to a flexible, rubbery state
• Importance: Determines if a polymer will behave like a rigid plastic or a flexible rubber at its service temperature
• Factors Affecting Tg:
  • Chain Length: Higher molecular weight = higher Tg
  • Plasticizers: Small molecules that reduce Tg by increasing free volume, effectively making the polymer more flexible.
  • Chain Stiffness and Side Groups: Stiff chains and bulky side groups hinder movement, resulting in higher Tg.
  • Copolymers: Tg is an average between the Tg values of the individual monomers based on their weight percentage in the copolymer.
  • Pressure: Increased pressure reduces free volume, leading to a higher Tg.

Molecular Weight of Polymers

• Polymers are not uniform: Individual polymer chains have a range of lengths, resulting in a distribution of molecular weights.
• Average Molecular Weights: Measures of the overall molecular weight of a polymer sample:
  • Number Average Molecular Weight (Mn): Calculated based on the number of molecules, weighted by their individual molecular weights.
  • Weight Average Molecular Weight (Mw): Calculated based on the weight of each molecule, weighted by their respective molecular weights.
• Degree of Polymerization (DP): Average number of repeat units per polymer chain, calculated by dividing Mn by the molecular weight of the repeat unit.

Plastic Myths and Reality

• Plastic Burning: Burning plastics primarily produces CO2 and water, not toxic gases.
• Plastic Waste Volume: Plastic waste comprises a smaller percentage of Municipal Solid Waste (MSW) compared to paper, metal, and glass, but its low density and visibility make it more noticeable.
• Plastic and Soil Fertility: Improper plastic waste disposal can lead to its accumulation in soil, but plastic itself does not directly reduce soil fertility.
• Food Contact: FDA-approved plastics are safe for food contact applications.
• Animals and Plastics: Animals are generally able to distinguish between food and plastic, but they may be attracted to plastic by food odors.
• Plastic Bags and Drains: Blocking of drains is primarily caused by a mix of waste materials, not solely plastic bags.
• Plastic and the Environment: Plastics can conserve natural resources and energy during production and may have positive environmental impacts in certain applications, but their disposal and potential environmental contamination are concerning
• Paper vs. Plastic: Production of paper requires significantly more natural resources, water, and energy than plastic, generating more solid waste.

Plastics in Infrastructure

• Geosynthetics and Geotextiles: Used in construction for reinforcement, drainage, and filtration.
• Plastic Wire and Cable: Provide electrical power distribution.
• HDPE Ducting: Used for optical fiber cable installations.
• Gas Distribution: Plastic pipes are used for gas distribution, offering corrosion resistance.

Plastic in Healthcare and Safety

• Advantages of Plastics in Medical Products:
  • Flexible and durable
  • Low coefficient of friction
  • Inert to body fluids
  • Cost-effective and recyclable
• Applications:
  • Drug delivery systems
  • Joint replacements (e.g., HDPE)
  • Growing human organs
  • Artificial organs (e.g., kidneys, heart valves)
  • Surgical sutures (e.g., polyglycolic acid, PET, PP)

Plastics in Automobiles

• Interior: Seats, door panels, instrument panels, steering wheels, upholstery, roof liners, air ducts
• Exterior: Bumpers, weather seals, headlamps, reflectors, body paint
• Engine and Powertrain: Engine components, cooling systems, fuel tanks, suspension components
• Electrical: Ignition systems, batteries, electrical and electronic equipment