Eco-friendly Plastics – Some developments

All of us know that 99% of the plastics(polyethylene, polypropylene,PET and PVC)) used today are made from fossil fuels. We also know(thanks to all negative publicity) that these plastics are not biodegradable – meaning that the polymer waste after use will remain for centuries without degradation and cause tremendous pollution to our natural resources and to all forms of life(human, animals,marine life etc).
This is the background in which quite a lot of research and technological efforts are being carried out today to come up with solutions to the problem. Isn’t it ironical that the problem was, in the first place created by the scientists or Technologists and now the very same community of scientists are being called upon to find a solution?
One could argue,though,that scientists are only a small link in the chain of events and very often they have very little say in the Science and Technology policies framed by Governments.
Anyway,the purpose of this article is only to briefly highlight certain important scientific and technological efforts that have taken place in the recent past in this field.
Scientists have approached the problem of making plastics eco-friendly by the following broad approaches:
1. Synthesizing biodegradable plastics from natural resources or synthetic materials or a combination of both.

2.Chemically transforming the used commodity plastics into useful fuels.

3.Converting the existing commodity plastics like polyethylene or polypropylene or PVC into biodegradable plastics by incorporation of certain additives / photo-catalysts.

The third approach is still being experimented upon in several laboratories. Therefore I will give a brief account of the first two approaches only here.

The multinational Chemical company (Zeneca) was the first to come up with an elegant solution with a smart piece of chemistry. They invented a polymer called “Biopol”(technically known as ‘polyhydroxybutyrate – valerate’). This is a a polymer built or assembled by certain bacteria and it has excellent film properties similar to our well known Polypropylene. Films,foils,dishes could be made out of it which would degrade within a few months of use and disposal. The original cost of this polymer was prohibitively high at 16 USD/ kg compared to Polypropylene at 0.5 USD. Improvements in technology like genetic engineering,better fermentation and purification technologies brought it down to 4-5 USD,which is still high in comparison to Polypropylene. Due to its high cost it has not come into general use.

Scientists followed another approach to make environment friendly polymers. These are based on a combination of natural and synthetic polymer systems. Following examples illustrate this approach:
1.Polymers based on Corn Starch:
Corn starch was gelatinized(high shear mixing to break crystallinity)and plasticised(admixed with glycerine) to make shopping bags,bread bags,over-wrap,flushable sanitary backing material etc. The cost of the product ,however,is higher than the conventional Polyethylene. In-spite of its higher cost,it has really caught on well in developed countries(Europe,USA and Australia etc). One Australian company has recently licensed this process to a Chandighar based company in India.
2.Starch based polymers are also made in the form of foam to substitute thermocol(technically known as ‘polystyrene’) for loose fill applications.
3. Yet another innovative development reports blends of Starch based polymers with polyesters based on lactic acid (polylactic acid -PLA). These are being used for high quality packaging applications.

While such efforts are continuing,I am quite impressed with certain amazing developments with a totally different approach which should partially mitigate the problem of biodegradability of commodity plastics like polyethylene and polypropylene . I will elaborate the same in some detail below.

Plastic waste transformation to liquid and gaseous fuels:
In this approach scientists have developed a process known as “Pyrolysis” would breakdown polypropylene or polyethylene into useful liquid and gaseous fuels. The conventional pyrolysis process is improved upon by using Catalysts for better and selective conversion efficiencies. Briefly the process has the following features:
1.Plastics are collected by Municipal authorities along with other household waste and segregated.
2.All plastics (PVC,Polyethylene,Polypropylene,Polyester or PET bottles etc) can be mixed together for this technology and there is no need to segregate different plastics which is labor intensive and costly.
3. They are melted and pyrolysed at a high temperature
4. Liquid and gaseous fuels are collected separately
5. Liquid obtained in the process is close to the composition of Diesel and fuel oil used in the industries as fuel, while the gas is close to LPG in composition. Therefore the entire product of pyrolysis is readily usable.
6. Most importantly the conversion of plastics is close to 99% and it has been proven to be economically viable.
7.The fuels produced in the process have also been successfully used to produce electricity.

The last feature gives me an idea that this technology can be used for rural electrification. The only hitch is that more than 95% of the plastics are consumed in the urban areas and therefore Government subsidies may be needed to cover the transportation costs to make it economically viable.


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4 CommentsLeave a comment

  1. Dear Sir/Laddy,

    Really I am looking for a pyrolysys equipment for all kind of thermolastics like polyethylen low and high, polypropylene, pvc, polyestyrene, polyethylene terephthalate, polytetrafluorehylene, etc., but I am concerned about PVC and PTFE, becuse of the chlor and fluor. Where I can find such equipment or equipments, the idea is to put in many city.
    Don’t hesitate to amswer, Thank You.
    Best regards
    Esteban Sperber
    Phone +593 99 130 482

    • For all plastics including PVC,I suppose, Stainless steel (of grade 316L) can be used as the material of construction for pyrolysis.

  2. I want to know if by all plastics pirolysys to get terephthalic acid, please don’t hesitate to answer, thank you.
    Esteban Sperber
    +593 99 130 482

    • Plastics,after pyrolysis produce a mixture of hydrocarbons(liquid and gaseous fuels). Terephthalic is not a product of pyrolysis.

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