Plastics

Nature of Plastics' Design

• Most plastics are produced from petrochemicals.
• Bio-plastics are being developed due to:
  • The finite nature of oil reserves
  • The threat of global warming
• Bio-plastics degrade upon exposure to factors such as:
  • Sunlight, water, or dampness.
  • Bacteria, enzymes, wind erosion, and, in some cases, consumption by insects.
• In most cases, degradation does not lead to the complete breakdown of plastic.
• Designers must consider the moral, ethical, and environmental implications when selecting materials.

Examples of Plastics

Purpose and Properties of Plastic

• Many plastics were invented, often by accident, to meet specific needs:
  • Withstand pressure, heat, transport, skin contact, acids, and impacts.
• Plastic introduced possibilities not achievable with traditional materials (wood, iron, stone).
• Plastics have become integral to daily life.

Categorizing Plastics

Thermoplastics

• Thermoplastics are chemically recyclable and can be melted and cooled into a new form.

• Thermoplastics are the most commonly used type of plastic.
• They are composed of long linear chains of molecules, called polymers.

• The main feature that sets them apart from thermosets is their ability to go through numerous melt and solidification cycles without significant degradation.

• Thermoplastics are usually supplied in the form of small pellets or sheets that are heated and formed into the desired shape using various manufacturing processes.
• The process is completely reversible, as no chemical bonding takes place, which makes recycling or melting and reusing thermoplastics feasible.

• Features of thermoplastics:
  • Can be reheated and reshaped.
  • Good impact resistance and toughness.
  • Easily processed by injection molding, blow molding and vacuum molding.
  • Lower thermal resistance
  • Can be easily recyclable.

• Examples of thermoplastics:
  • Acrylic (PMMA)
  • Acrylonitrile butadiene styrene (ABS)
  • Polyamide (PA)
  • Polylactic acid (PLA)
  • Polycarbonate (PC)
  • Polyether ether ketone (PEEK)
  • Polyethylene (PE)
  • Polypropylene (PP)
  • Polyvinyl chloride (PVC)

Thermosetting Plastic

• In contrast with thermoplastics, thermosetting plastics (also referred to as thermosets) remain in a permanent solid state after curing.
• Polymers in thermosetting materials cross-link during a curing process that is induced by heat, light, or suitable radiation.
• This curing process forms an irreversible chemical bond.
• Thermosetting plastics decompose when heated rather than melting, and will not reform upon cooling.
• Recycling thermosets or returning the material back into its base ingredients is not possible.

• Examples of Thermoset Plastics:
  • Cyanate ester
  • Epoxy
  • Polyester
  • Polyurethane
  • Silicone
  • Vulcanized rubber

Single-Use Plastics

• Single-use plastics, as per their name, are only used once.
• They have very short product lifespans and are generally thrown away once it is over.
• Common in packaging and targeted for replacement by alternative materials (supported by global legislation).

• Features of thermosets:
  • Set permanently when heated, cannot be remolded.
  • Very high thermal resistance.
  • Strong and durable.
  • Good electrical insulators.
  • Difficult to recycle.
  • Excellent dimensional stability.
  • Chemical resistance.

• Examples of applications of single-use plastics include:
  • Plastic cups
  • Plastic straws
  • Grocery bags
  • Bubble wrap
  • Packaging peanuts

Durable Plastics

• Used in long-lasting applications like furniture and are harder to replace in daily life.

• Examples of applications of durable plastics:
  • Furniture
  • Toys
  • Car interiors

Future Challenges with Plastic

• Petrol-based virgin plastic is a finite resource:
  • The question is how society will perceive plastic: as waste or as a resource?
  • A shift is required from a make-use-dispose mindset to rethink and reuse, which is difficult due to existing habits.

Recycling Complexities

• Plastics may appear similar but differ chemically, making recycling challenging:
  • Mixing chemically unrelated materials (e.g., wood and glass) results in unusable resources, as with plastics.
  • Some plastics are chemically related and recyclable, while others are not.

Recycling challenges

Issues with Recycling

• Recycling does not fully address the issue of virgin material dependency.
• The invention of mixed plastics creates additional complexity in achieving chemical purity for reuse.
• There is a significant challenge for humanity and the industry to innovate sustainable plastic solutions.

Properties and Uses of Various Thermoplastics

• You don't need to memorize all these.

Acrylic (PMMA)

Physical

• Transparent
• Rigid
• Lightweight

Mechanical

• Moderate hardness
• Moderate impact resistance

Uses

• Displays
• Signs
• Optical lenses
• Automotive lights

Advantages

• Excellent clarity
• UV resistant
• Weatherproof

Acrylonitrile Butadiene Styrene (ABS)

Physical

• Rigid
• Tough

Mechanical

• Strong impact resistance
• Moderate hardness

Uses

• Consumer electronics
• Automotive parts
• Plumbing

Advantages

• Easy to mold
• Tough at low temperatures
• Good dimensional stability

Polyamide (PA) / Nylon

Physical

• Strong
• Durable
• Somewhat flexible

Mechanical

• Excellent wear resistance
• High strength

Uses

• Gears
• Automotive parts
• Clothing
• Electrical components

Advantages

• High toughness
• Wear-resistant
• Can be reinforced with fibers

Polylactic Acid (PLA)

Physical

• Rigid
• Biodegradable
• Semi-transparent

Mechanical

• Moderate strength
• Low impact resistance

Uses

• 3D printing
• Food packaging
• Disposable items

Advantages

• Made from renewable resources
• Biodegradable
• Low environmental impact

Polycarbonate (PC)

Physical

• Transparent
• Tough
• Impact-resistant.

Mechanical

• Very high impact resistance
• Moderate hardness.

Uses

• Eyewear lenses
• Optical discs
• Automotive parts
• Safety gear.

Advantages

• Extremely strong
• Optical clarity
• Flame retardant

Polyether Ether Ketone (PEEK)

Physical

• Rigid
• High-temperature resistance

Mechanical

• Very high strength
• Tough
• Low friction

Uses

• Aerospace
• Automotive
• Medical implants
• Electrical insulation

Advantages

• Extremely high heat resistance
• Excellent chemical resistance
• Wear-resistant

Polyethylene (PE)

Physical

• Flexible
• Lightweight
• Low-density

Mechanical

• Moderate strength
• High impact resistance

Uses

• Packaging
• Pipes
• Toys
• Containers

Advantages

• Easy to process
• Resistant to chemicals
• Low moisture absorption

Polypropylene (PP)

Physical

• Lightweight
• Flexible
• Resistant to fatigue

Mechanical

• Moderate strength
• Good impact resistance
• Uses: Packaging, automotive parts, textiles, medical supplies.
• Advantages: Low density, high chemical resistance, easy to mold.

Polyvinyl Chloride (PVC)

Physical

• Rigid or flexible, depending on the formulation

Mechanical

• Moderate to high strength
• Can be either flexible or rigid

Uses

• Pipes
• Flooring
• Medical tubing
• Electrical insulation

Advantages

• Versatile
• Resistant
• Chemicals
• Cost-effective

Properties and Uses of Various Thermosetting Plastics

Cyanate Ester

Physical

• Rigid
• Thermoset resin
• Highly resistant to heat and chemicals

Mechanical

• Very high strength
• Excellent dimensional stability
• Low moisture absorption

Uses

• Aerospace components
• High-performance electronics
• Automotive parts

Advantages

• Superior thermal stability
• High electrical insulation properties
• Resistant to harsh environments

Epoxy

Physical

• Hard, rigid, and tough
• Can be formulated for flexibility

Mechanical

• Excellent bonding strength
• Good fatigue resistance
• High tensile strength

Uses

• Adhesives
• Coatings
• Composite materials
• Electrical encapsulation
• Structural components

Advantages

• Superior adhesion
• High mechanical properties
• Chemical resistance
• Excellent durability

Polyester

Physical

• Rigid
• Lightweight
• Somewhat flexible

Mechanical

• Moderate strength
• Impact resistance
• Less durable compared to epoxy

Uses

• Fiberglass-reinforced composites (boats, car parts)
• Resin for molds
• Surface coatings
• Clothing

Advantages

• Cost-effective
• Easy to process
• Good corrosion resistance

Polyurethane

Physical

• Can be rigid or flexible depending on formulation, durable.

Mechanical

• Excellent abrasion resistance, high strength, and flexibility.

Uses

• Foam (e.g., mattresses, insulation), coatings, adhesives, automotive parts, footwear.

Advantages

• Versatile (rigid or flexible), high wear resistance, impact resistance, good thermal insulation.

Silicone

Physical

• Flexible
• Heat-resistant
• Rubber-like, but can also be rigid.

Mechanical

• Low tensile strength
• Excellent elongation and flexibility.

Uses

• Seals
• Gaskets
• Medical implants
• Electronics
• Kitchenware

Advantages

• Extremely heat-resistant
• Flexible
• Chemically inert
• Non-toxic
• Great for sealing and insulation