Comprehensive Notes on Plastic Recycling and Innovations in Design

VCAA Study Design

  • The VCAA study design includes:
    • Categorization of different plastics as fossil fuel-based.
    • Categorization as bioplastics.
    • Plastic recycling (mechanical, chemical, organic).
    • Compostability.
    • Circularity and renewability of raw ingredients.
    • Innovations in polymer manufacture using condensation reactions.
    • Breakdown of polymers using hydrolysis reactions.
    • Transition from a linear economy towards a circular economy.

Plastic Types and Recycling

  • Australasian Recycling Label: Indicates the type of plastic and provides instructions on how to recycle it.
  • Recycling labels are not recycling symbols, they indicate the type of plastic.

PETE (Polyethylene Terephthalate)

  • Most used consumer plastic.
  • Mainly for single-use products.
  • Not heat resistant.
  • Difficult to clean properly, should not be reused.
  • Examples: Textiles (fleece garments, carpets, stuffing for pillows), soft drink and water bottles.
  • Widely recycled.

HDPE (High-Density Polyethylene)

  • Hard wearing, does not break down.
  • Stronger than PET.
  • Reusable.
  • Suitable for freezing.
  • Examples: Compost bins, detergent bottles, pipes, plumbing fittings, household bags, irrigation pipes, milk, juice, water, and detergent bottles.
  • Easily recycled.

PVC (Polyvinyl Chloride)

  • Can leach toxins.
  • Not suitable for food and drinks.
  • Useful for outdoor products because it doesn't break down.
  • Produces toxic chemicals when heated, limiting recyclability.
  • Examples: Juice bottles, detergent bottles, PVC piping, credit cards.
  • Not easily recycled, but can be made into more PVC products such as flooring.

LDPE (Low-Density Polyethylene)

  • Thin and flexible.
  • Easy and inexpensive to produce.
  • Safe to use with food.
  • Examples: Frozen food bags, bin liners, squeezable bottles, flexible container lids, cling film, carry bags, packaging film, bubble wrap.
  • Soft, scrunchable plastics can be returned to the supermarket for recycling.

PP (Polypropylene)

  • Hard and lightweight.
  • Withstands heat.
  • Resistant to grease and chemicals.
  • Safe to reuse.
  • Examples: Reusable microwave containers, kitchenware, nappies, yoghurt containers, straws, disposable cups and plates, landscaping border stripping, battery cases, margarine tubs.
  • Can be recycled, but depends on the local council.

PS (Polystyrene)

  • Lightweight and soft.
  • Flammable.
  • Inexpensive to make.
  • Easily molded.
  • Can release harmful chemicals, particularly if heated.
  • Examples: Packing 'peanuts', disposable cups, plates and trays, insulation, disposable takeaway containers.
  • Not easily recycled and must be disposed of in general waste; avoid use if possible.

OTHER

  • Strong and tough.
  • Includes polycarbonates and other plastics.
  • Possible release of hazardous BPA.
  • Examples: Beverage bottles, baby milk bottles, electronic casing, lenses for sunglasses and safety goggles.
  • Generally not recyclable.

Bioplastics

  • Sourced from biomass (e.g., agricultural, cellulose, and corn starch waste).
  • Not necessarily biodegradable.
  • Environmental impact depends on the type and end-of-life disposal.
  • Degradable: Broken into smaller fragments or simpler chemical structures but may never degrade into simple molecules.
  • Biodegradable: Broken down completely by natural means (i.e., water, carbon dioxide, and compost by microorganisms).
  • Compostable: Degraded by microorganisms in a moist, warm environment to produce matter that can support plant life in a relatively small amount of time (approximately 180 days).
  • Recyclable: Materials which can be reprocessed into new materials.

Polylactic Acid (PLA)

  • Formula: (C3H4O2)n
  • Thermoplastic polymer obtained from plant products (e.g., corn starch, maize, sugar cane).
  • Soluble in some organic solvents.
  • Relatively low heat resistance, thus easy to melt and manipulate.
  • Applications: Bottles, food packaging, shrink wrap, plastic bags, 3D printing, PPE.

Formation of PLA

  1. Starch extracted from plant material.
  2. Sugar dextrose is processed from the starch.
  3. Dextrose is converted to lactic acid by fermentation.
  4. Lactic acid undergoes condensation reaction to form PLA.

Advantages of PLA

  • Relatively low heat resistance, easy to melt and manipulate.
  • Biodegradable and cost-efficient to produce.
  • Degradation rates depend on additives, pH, molecular weight, and crystallinity.

Disadvantages of PLA

  • Unsuitable for high-temperature applications.
  • Fertilizers are required to grow the plants used in production.
  • Land used for crops may be needed for food.
  • Specialized facility is required for composting.
  • Water usage (although less than for synthetics).
  • Additives may not break down.
  • May contaminate the recycling process if mixed into general plastic waste.

Biopolyethene (BioPE)

  • Thermoplastic polymer.
  • Can be melted, remoulded, and recycled.
  • Made from raw materials (e.g., sugar cane, sugar beet, and wheat grain).
  • Not biodegradable and cannot be composted.
  • Chemically identical to polyethene made from fossil fuel-based feedstocks.
  • Used to manufacture shopping bags, films, bottles, and car parts.

Formation of Bio-PE

  1. Yeast is used to ferment the sugars in the plant biomass into ethanol.
  2. The ethanol is distilled and dehydrated to form ethene.
  3. The ethene undergoes addition polymerization to form polyethene.

Bio-Based Polypropene (Bio-PP)

  • Thermoplastic polymer.
  • Similar properties to bioethene but harder and more resistant to heat.
  • Applications: Injection moulding, textiles, film, ropes.

Formation of Bio-PP

  1. Raw materials are sourced from biomass.
  2. Biomass is fermented to produce propan-2-ol.
  3. The propan-2-ol is then dehydrated to obtain propene.
  4. The propene undergoes addition polymerization to produce biopolypropene (polypropylene).

Plastics Recycling

Current Challenges

  • Most feedstocks are still sourced from fossil fuels.
  • Most plastics at the end of life are sent to landfill or incinerated (not yet recycled).
  • Biodegradable plastics in landfill can lead to methane emissions, contributing to global warming.

Current Treatment for Plastics

  • Mechanical recycling.
  • Chemical recycling.
  • Organic recycling.

Mechanical Recycling

  • Physical recycling where the plastic is shredded and melted, and converted into pellets.
  • Produces plastic granules with the same structure as the original plastic but with shorter chains.

Chemical Recycling

  • Recycling using heat or chemicals to convert the polymer's chemical structure into monomers that can be reused in chemical processes.

Organic Recycling

  • Waste material is treated using microorganisms in humid, warm conditions.
  • Composting facility produces carbon dioxide, water, inorganic compounds, and biomass without toxic residue.

Plastic Products and the Circular Economy

  • Towards a circular economy:
    1. Eliminate use where possible.
    2. Reuse items.
    3. Recycle plastics.
    4. Make recycling easier.
    5. Use compostable plastics.
    6. Develop innovative design.
    7. Use renewable energy.
    8. Use renewable raw materials.
    9. Use less hazardous chemicals.

Examples

  • Avoid packaging for items such as clothing, toys, and sporting equipment.
  • Use cloth shopping bags instead of plastic.
  • Consider the need to purchase plastic items or packaging.
  • Use reusable coffee cups, water bottles, etc.
  • Use refillable containers for bulk goods.
  • Make bottles, furniture, shoes, and clothing from recycled plastics.
  • Use deposits for containers to facilitate collection.
  • Make collection and recycling centres more accessible.
  • Collect more plastics so they do not end up in waterways and oceans.
  • Use clear labels on containers to inform consumer choices.
  • Automate sorting of plastics at waste collection facilities for appropriate treatment.
  • Design products that last longer and are less likely to be disposed of.
  • Develop effective and economical methods of sorting and recycling.
  • Design plastics for easier degradation.
  • Use renewable energy for manufacture, recycling, and transport of plastics.
  • Use biomass to produce plastics to replace fossil fuel-based plastics.
  • Ensure chemicals used in manufacturing, use, and recycling are safe for living organisms and the environment.

Innovations in Polymer Manufacture

  • More efficient and sustainable design of chemical recycling using catalysts to reduce energy usage.
  • Use different bacteria or fungal enzymes to break down plastics such as PET into reusable monomers.
  • Many polymers are manufactured by condensation reactions and broken down by hydrolysis reactions.