Non–biodegradable fossil-based polymers
The term non-biodegradable describes polymers that do not break down to a natural, environmentally safe condition over time by biological processes. Most plastics are non-biodegradable mainly because plastic is widely used because of its low cost, versatility and durability. This durability is partially based on plastic being an uncommon target for bacteria, which makes it non-biodegradable. However, plastics can be made biodegradable with the addition of certain chemicals that breakdown the structure of the polymer.
Below is the list of conventional fossil-based plastics and their properties and applications –
|Code & Symbol||Name||Properties||Applications|
|Polyethylene Terephthalate (PET or PETE)||Clarity, strength / toughness, barrier to gas and moisture, resistance to heat.||Plastic soft drink and water bottles, beer bottles, mouthwash bottles, peanut butter and salad dressing containers, ovenable film, ovenable pre-prepared food trays.|
|High Density Polyethylene (HDPE)||Stiffness, strength / toughness, resistance to chemicals and moisture permeability to gas, ease of processing and forming.||Milk, water, juice, cosmetic, shampoo, dish and laundry detergent bottles; trash and retail bags, yogurt and margarine tubs, cereal box liners.|
|Polyvinyl Chloride (V or Vinyl or PVC)||Versatility, ease of blending, strength / toughness, resistance to grease/oil, resistance to chemicals, clarity.||Toys, clear food and non-food packaging, shampoo bottles, medical tubing, wire and cable insulation, film and sheet; construction products such as pipes, fittings, siding, flooring, carpet backing, window frames.|
|Low Density Polyethylene (LDPE)||Ease of processing, barrier to moisture, strength / toughness, flexibility, ease of sealing.||Dry cleaning, bread, and frozen food bags; squeezable bottles (i.e., honey, mustard).|
|Polypropylene (PP)||Strength / toughness, resistance to chemicals, resistance to heat, barrier to moisture, versatility, resistance to grease/oil.||Ketchup bottles, yogurt containers and margarine tubs, medicine bottles.|
|Polystyrene (PS)||Versatility, insulation, clarity, easily foamed (“styrofoam”).||Compact disc cases, foodservice applications, grocery store meat trays, egg cartons, aspirin bottles, cups, plates, cutlery.|
|Others||Nylon (PA) Acrylonitrile butadiene styrene (ABS) Polycarbonate (PC) Layered or multi-material mixed polymers||Custom products, bottles, plastic lumber|
Oxo-biodegradable and Enzyme mediated plastics
- They are based on conventional plastics, like polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET), to which additives, that should cause the plastic to degrade by a process initiated by oxygen and accelerated by light and/or heat, are added.
- The additives are typically metal salts of carboxylic acids or dithiocarbamates based on cobalt (Co), iron (Fe), manganese (Mn) or nickel (Ni), with Co being used more for packaging and Fe and Ni more for mulch film. Other transition metals like Cerium (Ce) have also been reported to exhibit strong pro-oxidative effects.
- Similar to oxo-degradable plastics, conventional plastics can also be enriched with organic additives, resulting in so called “enzyme-mediated degradable” plastics.
- The degradation process is claimed not to be initiated by heat, UV light, mechanical stress or oxygen, but by the micro-organisms themselves.
- According to the producers of “enzyme-mediated degradable” additives, the organic additive, together with its carrier material (in most cases this is ethylene vinyl acetate), is consumed by the micro-organisms, during which these excrete acids and enzymes that should break down the plastic into materials that are easily consumed by microbes.
Oxo-biodegradable and Enzyme-mediated are not Bioplastics. Why?
These plastics are made from fossil based polymers and combined with specific additives in order to follow a similar end-of-life as bioplastics i.e. biodegradation. However, these additives will enable only fragmentation of the plastics and not degradation, which results in very small fragments that still remains in the environment.
Both OXO and Enzyme-mediated degradable plastics cannot biodegrade as defined in industry accepted standard specifications such as ASTM D6400, ASTM D6868, or EN 13432
Plastic pollution and their main causes
Plastics are used because they are easy and cheap to make and they can last a long time. Unfortunately these same useful qualities can make plastic a huge pollution problem. Because the plastic is cheap it gets discarded easily and its persistence in the environment can do great harm. Some of the common causes of plastic pollution –
- Plastic bags from shopping (LDPE, HDPE)
- Plastic toys (PP, PVC)
- PET Bottles (PET)
- Plastic disposables (PE, PS)
- Plastic fishing nets (HDPE)
Some of these products can be made from biodegradable alternatives thereby achieving a reduction in the pollution caused by them.