Invited review
‘Green’ polymers

https://doi.org/10.1016/S0141-3910(99)00182-2Get rights and content

Abstract

The utilisation of waste polymers by mechanical recycling and incineration have ecological limitations. Consequently, degradable polymers are gaining acceptance in biological recycling in areas of agricultural technology and packaging where the waste product is located in a microbially active environment. The ecological benefits of the synthetic polymers, particularly the polyolefins, are compared with hydro-biodegradable polymers made from renewable resources with emphasis on energy utilisation, environmental pollution and land utilisation. It is concluded that polymers that degrade by peroxidation followed by bioassimilation of the oxidation products (oxo-biodegradable polymers) are in general more environmentally acceptable (‘green’) than the the biologically produced hydro-biodegradable polymers.

Section snippets

Environmental impact of the synthetic polymers

The synthetic polymer industry has brought great benefits to modern society. For example in the packaging and distribution of foodstuffs and other perishable commodities the commercial thermoplastic polymers are hydrophobic and biologically inert and this has made them essential to modern retailing [1].

Similarly in agriculture, plastics have largely replaced glass in greenhouses and cloches and they have gained a unique position in the growing of soft fruits and vegetables over very thin

Mechanical recycling

Experience in the reprocessing of industrial wastes in the traditional materials industries suggested to polymer technologists in the 1970s that similar procedures might be used to recover materials suitable for second use from polymer wastes. However, this proposal overlooked the fact that industrial polymers are organic materials and whereas glass and metals can be recycled to products with properties essentially similar to the primary materials, this is not so with polymers. In particular,

Waste to energy

Energy generation by incineration of plastics waste is in principle a viable use for recovered waste polymers since hydrocarbon polymers replace fossil fuels and thus reduce the CO2 burden on the environment. The calorific value of polyethylene is similar to that of fuel oil (Table 2) and the thermal energy produced by incineration of polyethylene is of the same order as that used in its manufacture (Table 1).

Incineration is the preferred energy recovery option of local authorities because they

Biological recycling

Nature's waste is returned to the natural carbon cycle by biodegradation. The primary product is biomass which acts as a seed-bed for new growth [8].

Biomass formation is also beneficial to the environment since it ‘ties up’ the carbon for a more extended period compared with incineration. The importance of making use of this natural process by controlled composting of organic wastes has been recognised by waste disposal authorities and a combination of mechanical recycling, energy recovery by

Applications of biodegradable polymers

Two different applications have emerged over the past two decades for degradable polymers. The first is where biodegradability is part of the function of the product. Examples of this are temporary sutures in the body or in controlled release of drugs where cost is relatively unimportant. Similarly in agriculture, very thin films of photo-biodegradable polyethylene are used to ensure earlier cropping and to reduce weed formation [1], [2]. By increasing soil temperature they also increase crop

Biodegradable polymers derived from renewable resources

We have seen that polymers based on biological resources are perceived as being ‘greener’ than synthetic polymers even although the latter may also be biodegradable. The argument for using renewable resources is that the carbon dioxide burden in the environment is neutral for biologically-based polymers but is positive for polymers based on mineral oil. However, this ignores the oil-based energy that goes into the growing, transport and processing of biological materials to produce polymers.

‘Green’ polymers in the twenty-first century

The above discussion illustrates conceptually different approaches to ‘green’ polymer development. Bio-based polymers are based on natural products which are bioassimilated by hydro-biodegradation. However, they have to be made technologically acceptable by chemical modification. The commodity plastics already have satisfactory technological properties but must be modified to become oxo-biodegradable. During manufacture and post-consumer disposal, polyolefins appear to be ‘geener’ materials

References (30)

  • R. Wasserbauer et al.

    Biomaterials

    (1990)
  • R. Arnaud et al.

    Polym. Degrad. Stab.

    (1994)
  • G. Scott

    Polym Degrad. Stab

    (1990)
  • G. Scott

    J. Photochem. Photobiol. (A Chemistry)

    (1990)
  • Scott G. Polymers and the environment. Royal Society of Chemistry,...
  • Scott G, Gilead D, editors. Degradable polymers: principles and applications. Kluwer Academic Publishers/Chapman and...
  • Showmura RS, Godfrey ML, editors. Proceedings of Second International Conference on Marine Debris, Honolulu, 2–7 April...
  • A.G. Sadun et al.

    Breaking down the degradable plastics scam

    (1990)
  • Scott, G. Antioxidants in science, technology, medicine and nutrition. Chichester: Albion Publishing, 1997 (Chapter...
  • Scott G. Antioxidant control of polymer biodegradation. In: Albertsson A-C, et al., editors. 5th International Workshop...
  • Scott G, Gilead D. In: Scott, G, Gilead, D, editors. Degradable polymers, principles and applications. Kluwer Academic...
  • Scott G. Wastes Management, May,...
  • C. Sadrmohaghegh et al.

    Polym. Plast. Technol. Eng.

    (1985)
  • J. Brandrup

    Müll and Abfall

    (1998)
  • Sadrmohaghegh C., Scott G. Polym Degrad Stab...
  • Cited by (338)

    • Bioloop: The circular economy

      2023, Rethinking Polyester Polyurethanes: Algae Based Renewable, Sustainable, Biodegradable and Recyclable Materials
    View all citing articles on Scopus

    Adapted from a lecture given at the UNIDO International Workshop on ‘Polymeric Materials and the Environment’ at Doha, 21–25 March 1999.

    View full text