In this section :- (click below)
(B) Types of Recycling
(C) Recycling of used containers for liquids
(D) Effects of contamination
(E) Different Post Consumer Plastics for
(F) Flow Diagram for Recycling
(G) News Items / Special Information
Recycling plastics significantly reduces
energy and GHG emissions
A new study using life cycle inventory (LCI) conclusively shows that the
recycling of plastics, specifically PET and HDPE, translates into significant
savings in energy and greenhouse gas (GHG) emissions. Source :Canadian Plastics Industry Associations (CPIA)
For More Details....Click Here
The most environmentally friendly alternative for plastic waste disposal
- is the process by which we can re-utilize the energy content of
the polymer in an ecologically acceptable way. The other two alternatives
are Land filling, and Incineration, which have, amongst others, the
following constraints, especially because of increasing rapid accumulation
of plastic wastes:
||Lack of adequate and suitable sites for landfilling.
||The feared toxic emissions from inadequate equipment and
inappropriate incineration conditions, and the resultant public
Types of Recycling
Material Recycling - This practice of recycling post-manufacturing
waste has been in vogue since the last many years. But problems
are encountered in case of post consumer waste such as great
inhomogeneity of different polymers present such as PE/PP,
PS, PVC etc. Further the incompatibility of the components
mixed, chemically different polymers present pose difficulties
in processing and inferior material properties. It is therefore
necessary to separate various polymers to boost their value.
The separation works based on the principle of sorting by
a centrifugal force field, using density difference of the
various polymers is one possible solution. Prior to separation,
it will be necessary to clean the polymer waste to remove
contamination like dirt, food leftovers, paper etc.
||Chemical Recycling - Converting polymers back into short
chain chemicals for re-use in polymersation or other petro-chemical
processes: e.g. - Cracking, Gasification, Hydrogenation and
Pyrolysis. Investigations and studies are going on.
Recycling of Heterogeneous Plastics
Degradation of polymers during different processing steps is the
main problem in post consumer plastics recycling. Incompatibility
among the different phases also poses major difficulty in the recycling
of heterogeneous waste.
Recycling of used plastic containers for liquids
Incompatibility between component polymers (PE, PVC and PF) and
degradation of components during the heterogeneous reprocessing
results in poor quality of mechanical properties of such secondary
The use of different classes of additives, such as stabilizers,
inert fillers, elastomeric modifiers and compatibilizers can improve
the processability enhancing the thermo-mechanical resistance of
the polymers and the mechanical properties.
To reduce cost, inert fillers can be used, by which mechanical
properties will be enhanced, though not to the expected level.
Elastomers will improve mechanical properties substantially. Functionalised
polyethylene and styrene butadiene-styrene rubber and CaO coated
with organo - titanates will help in some compatibilising actions.
For blends produced from this mixture and recycled polyethylene
good results can be expected.
Recycling - Effects of contamination
In polymers used for recycling, contamination is omnipresent,
resulting in reduction of the quality of recycling. It can be in
the form of dirt, printing inks, paper, metals, foil, additives,
pesticides, partially oxidized polymers, contamination by foreign
bodies can be noticed even in PET and HDPE bottles collected from
roadsides. In very old scraps of building products, electrical
and electronic system, vehicles, furniture etc., which now come
for recycling may contain very high concentration of additives
in particular, fire retardants, which are now banned. Contamination
can be reduced if consumers can be organized to segregate polymer
products before disposal. However accidental or unintentional mixtures,
multi-component products etc do pose problems.
Common contaminants in recycled polymers:
|| Beverage bottles
PVC, green PET, Al, water,
|| Milk/water bottles
PP, milk residue, pigments,
paper, EPS, cork
|| Greenhouse films
Insecticides, soil, Ni, oxidation
|| Shopping bags
Paper receipts, printing ink,
|| Battery cases
Pb, Cu, acid, grease, dirt
|| Detergent bottles
Paper, glue, surfactants, bleach,
|| Photographic film
Silver halides, gelatin, caustic
|| Circuit boards
Cu, tetrabromobisphenol A
|| Multilayer film
Ethylene vinyl alcohol, polyamide,
|| Beverage bottles
PET, PE, paper, Al foil, PP
|| Appliance housings
Polybrominated flame retardants
|| Automobile tires
Steel wire, fiber, oil extender
|| Mulch film
Soil (up to 30%), iron (up
to 3% in soil)
The simple and widely used process for separation is by using
differences in density, e.g. HDPE cups and PET bottles.
Separation and purification by chemical reaction process will give
Mixtures of solvents allowing selective dissolution can be used
for multi component plastic products.
Different Post Consumer Plastics for Recycling
In the plastic industry, in terms of volume, polyethylenes are
the largest group, followed by PVC (Poly vinyl chloride) in the
HDPE (High density Polyethylene) products:
Generally available in bales, low cost.
Products: milk jugs and detergent bottles. High-density polyethylene
- almost as dense as water, natural in colour, transparent, white,
without any pigment. During recycling any colour can be mixed.
Process of recycling is very simple - Grind into small flakes
approx. 1 cm., wash, float and remove heavy contaminant, dry the
clean flakes in a stream of hot air, pack in boxes - ready for
Reheat the flakes, add pigments of choice, colour and run through
a pelletizer. By using injection moulding presses new products
can be made out of the little beads that may be formed in the process
End uses: Pipes, lumber, flowerpots, trashcans, and non-food application
LDPE (Low Density Poly Ethylene)
LDPE available in bales - low cost. Chemically similar to HDPE
but less dense and more flexible., e.g. Polyethylene films used
for plastic bags and in grocery sacks.
Process is similar to HDPE, and special grinders are used when
thin films are required.
End use - Plastic trash bags grocery sacks, tubing, agricultural
films and lumber.
PET (Poly Ethylene Terephthalate)
A thin strong polyester film, extremely tough. Used for softdrink
and water bottles, jars, clamshell packages like cooking containers
or trays etc.
Process: - Similar to the process for Polyethylene. Sort out based
on colour, grind & wash. PET sinks in the wash water when plastic
caps and labels will float. The clean flake is dried and often
End use: Largest usage is in Textiles. Carpet companies often
use 100 % recycled resin to manufacture Polyester carpet in different
colours and textures, fibre filling for pillows, quilts and jackets
clear sheets or ribbon for VCR and audio cassettes. A good quantity
goes back into the bottle market. Cost varies widely with supply.
PVC (Poly Vinyl Chloride):
PVC is a versatile and universal polymer, low cost.
PVC can be compounded with variety of additives to make wide range
of flexible and rigid forms and hence versatile. PVC is a universal
polymer because it can be processed by various techniques like
calendering, extrusion, injections, moulding and plastosol. Physical
chemical, weathering properties of PVC are excellent.
End uses: - Pipes, Profiles, Floor coverings, cable insulation,
roofing sheets, packaging foils, bottles and medical products,
Advantages: Easy to clean, Water proof and resistant to corrosion.
Recycling of Plastics: Indian Context
Recycling of Plastics has been classified into 4 main categories:
- Primary Recycling – conversion of waste
plastics into products having performance level comparable to
that of original products made from virgin plastics.
- Secondary Recycling – conversion of
waste plastics into products having less demanding performance
requirements than the original material.
- Tertiary Recycling – the process of
producing chemicals / fuels / similar products from waste plastics.
- Quaternary Recycling – the process of
recovering energy from waste plastics by incineration.
The present article deals with the first two categories of Recycling.
The process of recycling of waste plastics into products of varying
usefulness mostly involves the following essential steps:
- Collection Segregation.
- Cleaning & Drying.
- Sizing / Chipping.
- Agglomerating / Colouring
- Extrusion / Palletisation
- Fabrication into end Product.
Each of the above steps involves a series of operations.
Collection / Segregation:
The basic principle of plastic / polymer processing is that the
polymeric materials under process are required to be compatible
with each other, if more than one type of plastic materials are
Certain polymeric materials are compatible with each other at
all proportions.For example LDPE and Lldpe are generally compatible
to each other at all proportions.
However, it is to be remembered that even differing molecular
weight variety of the same polymer may not be compatible for useful
purpose. For example phase separation may occur if a high molecular
weight (low Melt Flow Index) grade of LDPE (e.g. heavy duty film
grade) is processed with a very low molecular weight (high Melt
Flow Index) grade of LDPE (e.g. high flow Injection Moulding grade).
The advanced technology of separating / segregating different
types of waste plastics involves ‘Floatation Process’.
In this process the property of the varying densities of different
plastics is made use of for segregating different types of plastics.
However in the Indian Context, this separation or segregation
process, in many cases, are done by manual process utilizing the
availability of cheap and expert labour force.In case the waste
is contaminated with embedded metals, proper method of separating
the metals / other contaminants, is required.
Cleaning & Drying:
The scale of cleaning depends on the type of waste.
Generally, Industrial waste does not require significant cleaning
operation, whereas, post-consumer waste requires proper cleaning.
Whenever a cleaning operation is involved, it is to be ensured
that the water or any other cleaning material used, should be discharged
after ascertaining that the discharge does not contain any objectionable
substance. A proper Treatment Device may have to be deployed – like
a water treatment plant / effluent treatment plant.
For drying, a suitably designed drier is used.
Many industries situated out side the metropolises, use open space
for natural drying of the cleaned waste.
Sizing / Chipping:
The cleaned plastics waste is then required to be properly sized
so that those may be fed into the extruders for processing and
palletizing. The sizing operation depends on the type and shape
of the waste plastics.
During this process, attention is required to separate any powdery
material from the sized / chipped plastics.
Agglomerating / Colouring
In the next operation the sized plastics waste is mixed with colour
master batch in high-speed mixers / agglomerators and the output
is ready for extrusion into pellets.
Extrusion / Palletisation
This is the most important part of the process wherein the sized
/ chipped plastics are plasticised and regranulated to make the
plastics material ready for fabrication next.
The type and size of the Extruder depend on the type and volume
of the plastics waste.
Fabrication into end Product
Finally the reprocessed plastics granules are used as raw material
for producing end products using similar fabrication machines like
Injection Moulding / Extrusion etc., depending upon specific requirement.
Flow diagram for Recycling
Status of Plastic Recycling in Japan as presented
PWMI Japan, in December 2006.
Of Polyurethane In European Countries
A deck, Chair or even railroad ties made out of Plastic
Eurobodalla Recycling in good hands (Narooma
News - Narooma,New South Wales,Australia).
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