Recycling of plastics – A Solution to waste Management

Dr. Mrs.G.D.SHAH (Ph.D. Chemical Engg., M.E. PolymerTech.)  

I/C HEAD OF PLASTICS ENGG.DEPT.
GOVT. POLYTECHNIC, AHMEDABAD
GUJARAT, INDIA.

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ABSTRACT
Plastics consumption has grown at a tremendous rate over the past two or three decades. In the 'consumer' societies scarce petroleum resources are used for producing an enormous variety of plastics for an even wider variety of products. Many of the applications are for products with a life-cycle of less than one year and then the vast majority of these plastics are discarded. In most instances reclamation of this plastic waste is simply not economically viable. In industry (the automotive industry for example) there is a growing move towards reuse and reprocessing of plastics for economic, as well as environmental reasons, with many praiseworthy examples of companies developing technologies and strategies for recycling of plastics. Plastics are made from a non-renewable resource and it is generally non-biodegradable (or the biodegradation process is very slow). Hence plastics litter is often the most objectionable kind of litter and will be visible for weeks or months, and waste will sit in landfill sites for years without degrading. There is a much wider scope for recycling in developing countries like India.
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Plastics are unique, remarkable versatile material having fantastic properties to fulfill the need of our modern society. The plastic age arrived in 1868 with the invention of “CELLULOID” by Alexander Park to replace billiard ball previously made of ivory. In 1909 Leo Backeland derived “BACKELITE” i.e. phenol formaldehyde – a thermo set material. The other plastics like PP, PS, PC, PVC, NYLON, TEFLON POLYSULFON, and other engineering plastics were derived in the last 100 years.
Virtually every known plastics material is used in some aspect of packaging. After using packaged item the plastics wrapper, bag, or container is merely a waste. During plastics processing also some portion of material is in the form of waste along with the finished products. But such fresh waste is reprocessed or converted in to scrap form and is reused along with virgin materials up to 15%. But the huge amount of waste generated by industry and the consumer can not be ignored. Plastics waste becomes nuisance for human beings. Environmentalists and regulatory authority are thinking that plastics are not environment friendly and cause health hazards.
THIS IS NOT TRUE:
Actually implementation of eco friendly waste disposal management system should be developed to solve this problem. Plastics waste itself is not at all dangerous to human being but the unscientific manner of waste disposal creates the danger.
WASTE DISPOSAL MANAGEMENT SYSTEMS:
To reduce the problem of ecological imbalance, due attention must be given to waste managements systems like:

1. Recycling
2. Combustion or incineration (5%)
3. Land filling (40%)
4. Source reduction
5. Repairs
6. Reuse
7. Degradation of polymers
8. Use as fillers

TYPES OF WASTE:

1. Waste products – defective products
2. Industrial waste
3. Post consumer waste- packaging films, damaged moldings etc.
4. Nuisance waste- thermo set waste
5. Scrap waste- feed system, flash, finishing scrap etc.



Fig. 1 use of plastics in various sectors Fig. 2 plastics waste through various industries

DEFINITIONS:
REGRIND MATERIAL: The plastics scrap obtained from grinding machine in form of coarse powder is known as regrind material.
REGRIND MATERIAL: the regrind material obtained in the form of pellets from granulation line of extruder is known as reprocess material.
RECYCLE MATERIAL: The regrind material compounded with suitable additives so that the quality of reprocess material approaches to that of virgin material.
PROCESS OF RECYCLING:
The manufacture of recycle material involves five steps:

1. Separation from Municipal solid waste
2. Grinding the plastics waste material
3. Reprocessing material
4. Testing for quality reduction
5. Compounding to attain virgin quality


SEPARATION FROM MUNICIPAL SOLID WASTE:
The municipal waste is reduced in size mechanically by tension, compression, shear using crushers, shears, chippers, drum pulverizers, disc mills, pulpers and hammer mills.
After making small particles each individual particles are separated by:

1. density-floating in water
2. magnet-ferrous particles
3. Manual- glass, paper etc.
4. gravity- fluidized bed separation
5. electrostatic- charged particles by attraction to a charged roll
6. color- different colored particles
7. air separation- paper and light weight material by blowing air
8. heat separation- hot roll or doctor blade
9. solvent extraction- dissolution in solvent


GRINDING:
The plastics waste material is obtained in various forms viz. the feed system, flash, film, molded product etc. all these forms must be sorted out and possibly cleaned. These materials are now cut to suitable size so that they can be fed to the grinding machine. The regrind material obtained from various forms of scrap is collected separately.
REPROCESSING:
The regrind material is then fed to the hoper of an extruder which is previously prepared for processing. While using the film material as regrind material, care should be taken for positive feeding because the film has high bulk density.
After the material is melted to the required melt temperature, the material extruded from the granulation die of the extruder in the form of a long, continuous strands. These strands after cooling are cut to the required pellet size. The pellet size i.e. length and diameter can be varied to some extent by varying the take off speed of the cutter.
TESTING:
The reprocess material always involves quality reduction. The reason is:
The processing of plastics involve the melting of material to required processing temperature and then cooling this melt so as to obtain required shape. While melting the material, the heat is imparted to that material and while cooling the material, the heat is extracted from the material.
While heating the material the bond in the polymer chain expand and the molecular distance is increased. While cooling the bonds contract and the molecular distance is reduced. While reprocessing these steps are repeated. Due to these expansion and contraction, some of the heat energy is absorbed by the bonds so the bond strength is reduced. Due to this reduction this reduction in bond strength, now less energy is required to break this bonds i.e. the strength of the material or resistance towards load is reduced. Also during these heating and cooling process, some of the bonds break. Thus there is reduction in molecular weight and corresponding strength.
This reduction is tested by measuring melt flow index of the reprocess material, because MFI is inversely proportional to the molecular weight of the material and corresponding melt viscosity.

Table: Effect of molecular structure on various properties of plastics material

Sr. No. Property Linear chain Polymer Branched chain Polymer
1 Density More Less
2 Permeability Less More
3 Tensile strength More Less
4 % elongation Less More
5 Stiffness More Less
6 Crystallinity More Less
7 HDT Less More
8 Softening temperature Less More
9 Hardness More Less
10 Creep resistance More Less
11 Flow ability Less More
12 Compressibility Less More
13 Impact strength Less more
COMPOUNDING:
This step involves the addition of suitable additives to improve particular quality of the material. The material and additives are then mixed into a homogeneous mass with the help of suitable compounding methods. The selection of compounding method depends upon the additives added and the mixing quality required.
MODES OF RECYCLING:
Depending on the products obtained after recycling it can be explained as:

1. Primary recycling
2. Secondary recycling
3. Tertiary recycling
4. Quaternary recycling
PRIMARY RECYCLING:
It is the processing of scrap plastics into the same or similar type of product from which it has been generated using standard plastics processing methods.
Uniform, uncontaminated plastics waste reprocessed directly after scrapping particularly thermoplastic waste.
Plastics waste is ground to a particle size close to that of virgin material. The size reduction is done in scrapping machine consisting of a hoper, cutting chamber (rotor knives), fixed and rotating cutters, screen and drive. The knife arrangement may be parallel, slanted, V type, etc. Counter rotating rotors or two step rotors are also designed for scrapping. Cryogenic grinders are available for difficult material. For film type material waste plunger type or screw type stuffer is used.
SECONDARY RECYCLING:
Secondary recycling utilizes plastics waste unsuitable for direct reprocessing using standard plastics processing equipments.
Plastics waste feedstock from:
1. Post consumer plastics waste recovered from municipal refuse.
2. Post consumer plastics waste obtained from returnable packages (milk pouches, jars, soft drink bottles etc.)
3. Industrial plastics waste consisting of a single type of plastics material.
Reverser machines are used to manufacture products from contaminated and/or mixed thermoplastic waste. It can employ as feed stock such as PVC, PE, Nylon and used bottles and drums. It can handle contaminated scrap- pieces of copper, sand, glass etc. Waste plastics are pulverized in a crusher, dried and conveyed to large extruder and from extruder the material is delivered to accumulator; from accumulator a vertical screw plunger discharges the material into the mould. Final products can be formed by intrusion (flow molding), compression molding or extrusion.
TERTIARY RECYCLING:
It is the pyrolysis of post consumer waste. In this process the physical and chemical decomposition of organic materials caused by heating in an oxygen free atmosphere. This process is used for manufacturing charcoal, acetic acid and turpentine.
Pyrolysis is an endothermic reaction and heat must be supplied to distill off the volatile components.
PRIMARY REACTIONS:
Organic material → gases + liquid + char
SECONDARY REACTIONS:
CO2 + H2O → CO2 + H2 + 
C + H2O → CO + H2 + 
C+CO2 → 2CO + H2 + 
C + O2 → CO2 + 
C + 2H2 → CH4 + 
As shown, the products of pyrolysis of solid waste are in the form of gases, liquids and char.
The solid residue from the process was in the form of a light weight, flocky char, which could be coarsely sieved to remove extraneous materials such as bottle caps and lids.
The liquid portion of the pyrolysis products consists of tar, light oils and liquor.
QUARTERNERY RECYCLING: (Energy from plastics waste)
Incineration pf refuse is done to reduce combustible waste to inert residue by controlled high temperature combustion. The main reason for incineration is reduction in the volume of waste. Incineration is capable of reducing the weight of refuse by 80% and the volume by over 90%. The residue from the refuse is inert and may be disposed off in land fill.
ENERGY RECOVERY:
1. By burning refuse in steam generating incinerators to generate electricity.
2. Pouring refuse in existing heat exchangers as a fuel in power boilers.
3. Pyrolysis of refuse can be employed to produce a transportable fuel.
4. Refuse can be converted to heavy oil by hydrogenation by heating under pressure in the presence of carbon monoxide and steam.
5. In anaerobic digestion the organic portion of the refuse is decomposed in the absence of oxygen. Methane produced has the potential of being used as a natural gas substitute.
At present time, burning refuse in steam generating incinerators and its use as supplemental fuel are the most advanced waste energy utilization technologies.
An incinerator consists of:
1. Scale → To measure the weight of feed
2. Storage pit → To collect feed stock
3. Cranes → To handle waste from storage t o furnace
4. Charging/ Feeding mechanism/ Hoper → For furnace
5. Furnace → Where combustion occurs
6. Boilers → For generating steam
7. Steam turbines → To convert heat energy to mechanical energy
8. Generators → To convert mech. energy to electrical energy
Lastly, the environmental attack on the plastics industry is not justified because of the small contribution of solid waste (2-4% only). Also the large portion of waste generated by industry is reprocessed or recycled in the industry it self.
Not all plastics waste can be easily recycled. At present a considerable portion of plastics waste is still being disposed off without the recovery of cost incurred in production. However rising material and energy costs, govt. regulations and awareness of the consumer exert a pressure on the industry to change the situation. New separation techniques, incinerators and technology will make more recovery of energy and chemically possible scientific waste disposal management.

WASTE MANAGEMENT OF PLASTICS MATERIAL

                                                                       

The World Environment Day is observed on 5^th June every year, to conserve our environment. Plastic waste remains one of the biggest headaches globally. Piles of plastic waste have become a common site in towns, and the menace is rapidly spreading to the countryside. Plastics have become an indispensable part of our daily life. But repeated reprocessing of plastic waste, and its disposal creates environmental problems, pose health hazards, although plastics pose a hazard to the environment because they do not decay, plastics are preferred because they are cheap and versatile.

Health impacts of solid waste

The unhygienic use and disposal of plastics and its effects on human health has become a matter of concern. Colored plastics are harmful as their pigment contains heavy metals that are highly toxic. Some of the harmful metals found in plastics are copper, lead, chromium, cobalt, selenium, and cadmium. In most industrialized countries, colour plastics have been legally banned. Until recently no legislation was framed to deal specifically with issues connected with plastic waste management. The Government of Himachal Pradesh was one of the earliest to introduce legislation prohibiting the throwing or disposing of plastic articles in public places. The Union Ministry of Environment and Forests has recently notified the "Recycled Plastic Manufacture and Usage Rules, 1999''. These rules require that carry bags or containers used for purposes of storing shall be made of virgin plastic and be in natural shade or white. These items when made of recycled plastic and used for purposes other than storing and packaging of foodstuffs shall use pigments and colorants as per Indian Standards. Recycling of plastics shall also be undertaken strictly in accordance with specifications prescribed by the Bureau of Indian Standards, and shall carry a mark that the product is manufactured out of recycled plastic. The thickness of carry bags shall not be less than 20 microns. Finally and most importantly, Rule 4 prohibits all vendors from using carry bags or containers made out of recycled plastics for storing, carrying, dispensing or packaging of foodstuffs. In other words all vendors are required to use carry bags and containers manufactured to specifications prescribed in the 1999 Rules.

Sorting Of Wastes

Waste is separated into the following categories:

1.      kitchen wastes

2.      paper and cardboard

3.      glass

4.      aluminium

5.      other metals

6.      oils, fuels, other liquids

7.      wood

8.      batteries

9.      other materials, plastics, construction materials and obsolete items

Preventive measures

Proper methods of waste disposal have to be undertaken to ensure that it does not affect the environment around the area or cause health hazards to the people living there. At the household-level proper segregation of waste has to be done and it should be ensured that all organic matter is kept aside for composting, which is undoubtedly the best method for the correct disposal of this segment of the waste. In fact, the organic part of the waste that is generated decomposes more easily, attracts insects and causes disease. Organic waste can be composted and then used as a fertilizer.

Waste Disposal Options:

Plastics material offer many waste disposal options because they are usually solid, handleable materials. They are recoverable in most cases after use for several disposal options. This includes:

1.                  Incineration

2.                  Recycling

3.                  Land fill

4.                  Composting

5.                  Reuse

6.                  Source of energy

7.                  Reclamation

Incineration

Qualified staff operate high-temperature two-chamber incinerators at all stations. Incinerator ash and residues are returned to disposal. Kitchen and medical waste, low grade paper and cardboard, contaminated low density polythene (rubbish bags) and solid human waste from field camps are incinerated. All fats and oils, plastics (including polyurethane foam, polystyrene), large quantities of timber boxing and out-of-date food are returned for waste management.

Disadvantages of incineration:

1. Incineration destroys valuable resources.
2. Burning fossil fuels like coal, oil and gas is causing increasing levels of carbon dioxide in our atmosphere, leading to climate change. Incineration contributes to climate change, because when materials are burnt more fossil fuel energy is used to replace them through mining, manufacturing, and transportation around the world. Energy from burning waste is not renewable.
3. Incinerators need a steady stream of waste to keep them going. This means there is no incentive to reduce waste or recycle it.
4. Incineration causes pollution from air emissions and toxic ash.
5. Incineration is worse for climate change than recycling because new products have to be made to replace those destroyed.
6. Incineration does not provide the thousands of new job opportunities that recycling does.

Re-Cycling

Many items are re-used on station, e.g. packing materials such as cardboard boxes and plastic sheeting, packing crate timber, 200 L drums either with the lid part opened (for metal waste, glass or incinerator ash) or intact for returning chemical waste (e.g. photographic chemicals). Official photography on stations is now substantially electronic (i.e. no wet processing). All stations sort wastes as indicated above for disposal to recyclers. Recycling is one of the most immediate and effective ways to protect the environment. By recycling instead of producing goods from raw materials, substantial amounts of energy and raw materials are saved. 40% of local authorities now provide facilities for recycling plastics, with a quarter of these involved in doorstep collection schemes which are the most successful in recovering plastic waste. The six most common types of plastic can all easily be recycled and have a much higher value than most recyclable materials. As the volume of recycled material increases markets will expand, making the material more attractive to industry and the benefits of recycling more apparent. Recycling and waste minimization businesses could employ over 100,000 more people than the landfill and incinerator businesses would make redundant. Hence we can:

• Buy products made of recycled plastic wherever possible.

• Recycle plastic plants can be established.

• Set up a community scheme. The Community Recycling Network can help

• Encourage recycling in your workplace/school/church, etc.

Landfill:

Friends of the Earth wants a ban on new landfill capacity until policies are in place to achieve the 60-80 per cent recycling rates achieved in other countries, because:

• Landfill waste valuable resources.

• Landfill contributes to climate change, because when materials are buried more fossil fuel energy is used to replace them through mining, manufacturing, and transportation around the world.

• Landfill produces methane, a powerful greenhouse gas which contributes to climate change.

• Landfill creates water pollution as liquid from landfill sites leaks into our water supply.

• Landfill can lead to land contamination.

• Landfill leads to increased traffic, noise, smell, smoke, dust and litter.

Composting:

Composting is predominantly biodegradation with the possibility of oxidation and hydrolysis. There is an opportunity for environmentally degradable plastics which are used in food application such as wrappers and utensils in these uses, plastics are contaminated with food residues and are suitable for composting without separation. Where recovery of current plastics is not economically feasible, viable, controllable or attractive, the plastics remain as litter and may be discarded at sea from naval vessels, may be used in farm and agricultural application such as pre emergency plant protection or  in hygienic application such as diapers, hospital garments and swabs etc.

Re-use

It makes sense and it saves energy to re-use rather than recycle, but it is currently more economical for manufacturers to produce new product rather than wash and re-fill packaging. The Body Shop will re-fill plastic bottles with the same product, and many small producers across the country also do this, showing that re-use can make economic sense.

• Re-use plastic bags, or better still avoid them by using a sturdy bag that will last for years.

• Re-use pots with lids for storage rather than buying new ones.

• In the garden, re-use plastic pots for raising seedlings and cut-down plastic bottles to protect them from slugs

• Give usable goods to charity shops, or hold car boot sales for charity with any plastic items that can be re-used.

• Ask suppliers if they will take back plastic items for re-use: for example, plant pots in garden centers.

• Use refillable toner cartridges.

A Source of Energy

Material recovery is by no means the only way to recycle plastics. Another option is to recover their thermal content, providing an alternative source of energy. An average typical value for polymers found commonly in house hold waste is 38 mega joules per kilogram (MJ/kg), which compares favorably to the equivalent value of 31 MJ/kg for coal. This represents a valuable resource raising the overall calorific value of domestic waste which can then be recovered through controlled combustion and re-used in the form of heat and steam to power electricity generators. Successful ventures in this field include plants, such as a major incinerator, which produces steam to power an electricity turbine. Waste containing plastics can also be reprocessed to yield fuel pellets, which have the added advantage of being storable.

It is sometimes claimed that incineration of municipal waste poses an environmental problem in the shape of atmospheric pollutants. Although the potential is there, modem incineration techniques ensure that actual emission levels are kept with-in internationally accepted safety limits. In fact, several countries, such as Sweden, Germany and the Netherlands, have recently affirmed their confidence in incineration by announcing plans to expand existing capacity.

Reclamation

The majority of municipal waste is still used as land fill, due to the very high cost of facilities for the sorting, separation and recycling of waste. As plastics are stable, both physically and chemically they in turn provide stability to the tips. This provides a safe and solid foundation upon which to build; thereby releasing land for development.

Conserving the Environment

The plastics industry is concerned that it should take appropriate care of resources and the environment. The advantages of plastics over other raw materials are apparent from the beginning of their life-cycle. Research shows that it often takes less energy to make products in plastics, and although most plastics depend on oil, coal or gas they are responsible for only a small fraction of the national consumption of these fuels. Energy savings can be made easily with plastics because plastics are lighter, easier to store and transport. Also the developments in the recycling of plastics, there are interesting advances in the production of degradable plastics for products which need only a limited life.

The Future

Plastics recycling are in the growth phase as the whole industry is still relatively young. A further development in recycling, which is being researched, is the recovery of the individual chemical components of plastics for re-use as chemicals, or for the manufacture of new plastics.

 

FAILURE ANALYSIS

To learn from every failure is the way to success. Every well experienced person is the one who learns maximum out of the failure by analyzing the cause of failure and exploring suitable remedy for each cause. Sir Thomas Alva Edison explored 1000 of procedures through which light bulb could not glow. Learning out of each way he found his way to glow the bulb. Thus learning from each failure and not repeating the same mistakes/blunders one can achieve the success.    

How to analyze the failure? One has to perform quick immediate postmortem on a project that has failed so as to prevent future failure as well as to get guideline for future testing and quality control.

Some of the areas to cover are:

1.       Scope:

The goals must be set on the basis of available infrastructure and all surrounding parameters influencing the project. Higher target or over ambitions may describe the feeling of failure. In other words, higher expectations than what is been deserved cannot be called failure.  

2.       Money:

Sufficient funding and that to when required is necessary for a project to be successful.

3.       The team of project:

The team members who have shared the experience of failure of the previous project should be given chance to try again because they also have learnt from the failure. If the project is launched for the first time just select the persons having experience of analyzing the failure in a positive manner.

4.       Vendors/suppliers:

The raw material should be of the desired quality. Raw material should be supplied in right quantity and at the right time. Supplier should be able to identify the problem and be able to troubleshoot them.  

5.       Structure:

The structure of the project should be simple and easily understood by the persons who have to execute it. Over complicated and messy project will fail due to its own complexity. The goals should not be intangible and imponderable.

6.       Timing:

There must be a right time to launch a new project. A team of fresher/trainees members cannot handle all to gather a new project. OR A rain water harvesting plant may not run in a desert or in summer. The environment surrounding the project, the people affected by or can affect the project, system; business conditions should be properly evaluated.   

7.       Information/data:

The reliability of the data used during the planning and goal setting of a project must be checked. Precise, recent, valid and timely data are useful for a project to be successful. If the data is collected especially for setting a goal for a project may be biased and the goals set on the basis of such data may be exaggerated.  

8.       Salvaging:

The previous failed project may be assessed for the extent of failure. Whether the project is a total failure and should be started from the beginning or can be started from a point where the situation went out of control should be analyzed.  

9.       Graphics:

Graphs and charts can be used to identify problems easily. Graphs and charts help to analyze the failure easily and promptly.

10.   Comparisons:

Comparison with a successful project of a similar kind may help to identify and rectify the problems causing failure.

11.   Motivation:

The project under consideration should have new idea or plan i.e. it should be profitable or of some benefit to the the people affected by or can affect the project. In other words there must be some motivational value of the project so that the people affected by or can affect the project will endeavor for its success. Nobody is willing to work on a futile project.   

12.   Use failure to be successful:

Planning a failure may be beneficial for further planning of a successful project at a low cost. When we are aware of causes of failure we are sure to take remedial actions against those causes. This in turn results in a full proof planning of a successful project.