Environmental Aspects of
Plastics
Introduction
• Plastics & paper- common materials in
everyday life, often used in disposable
applications – major contributor for solid
waste
• Plastics due to their long life- when not
disposed properly, they are widely seen
and often criticized
Source Reduction
• Refer to a reduction in the amount of
material used in any application
• The simplest methods is to emply source
reduction are
– to use fewer products that cause waste
– to choose size and types of products where
by waste is minimized
– To reduce the material requirements of the
product (for manufacturer)
Source Reduction
• For example;
– The amount of packaging material in 1 liter drink
bottle is 40% less than material in 0.5 liter drink
bottle (larger size are more efficient in using
materials)
– Decrease the thickness of materials in application
• PE Trash bag (when it was first introduced)- thickness
0.08 mm
• LDPE introduced – thickness of trash bag is 0.05 mm
• LLDPE (stronger and tougher material) – thickness is
0.025 mm
• HDPE – thickness of 0.017 is available now
• Plastics have a weight & volume over
many other packaging materials
• Germany Society for Research for
Packaging Market estimates without
plastics, the cost of packaging would be
double and the volume of packaging would
increase by 250%
• The use of plastic packaging raises 3
problem;
– Recycling of plastics
– Resistance of most plastics to most form of
natural degradation
– Potential harmfull off-gases when plastics are
incinerated
Recycling of Plastics
• Refers to the reprocessing and
refabrication of a material by a consumer
or disposal of solid waste
• This type of recycle is called
postconsumer recycle (PCR)- different
with recycle (generally called regrind) of
the scrap from manufacturing process
Recycling of Plastics
• Reprocessing and refabrication of PCR
involves several steps;
– Collection
– Handling/sorting
– Reclamation/sorting
– End-use fabrication
Recycling of Plastics
Collection
• Voluntary recycling by the consumer is the
most single factor in improving recycling of
all materials
• However, consumers do not sort their solid
waste but rather mix all materials together
• For many plastics, the cost of virgin
plastics is about the same as the cost
involve in recycling- create problem in
recycling process (different case with
recycling of aluminium cans)
Handling & Sorting
• Involves conveying materials from the pickup
point (from consumer house) to the reclamation
facility
• Sorting of materials is necessary (PET bottle,
HDPE waste, aluminium alloy, etc) or in broader
material groupings (all metal, all plastics, etc)
• For the highest economy benefit, the HDPE and
PET and other recyclable plastics must be
separated from the plastics that are not to be
recycle- thus considerable labour is required to
pick up the recyclables by hand
Handling & Sorting
• Some sorting can be done by machine, i.e.
based on certain characteristics (light
absorption), various plastic resins can be
distinguish from the other
• Under certain condition, the mixture of several
plastic type can be recycled, called as mixed
recycled or comingled recycle
• To assist consumers and sorters, Society for
plastic Industry (SPI) introduced recycling
symbols
Numbering system for plastic
recycling
Recycling No.
Abbreviation
Polymer Name
PETE or PET
Polyethylene Terephthalate
HDPE
High-Density Polyethylene
PVC or V
Polyvinyl Chloride
LDPE
Low-Density Polyethylene
PP
Polypropylene
PS
Polystyrene
OTHER
Other plastics, including acrylic,
polycarbonate, polylactic acid , nylon and
fiberglass.
Polymer Name
Uses
Polyethylene
Terephthalate
Recycled to produce polyester fibres, thermoformed sheet, strapping, soft
drink bottles, reinforcement for concrete.
High-Density
Polyethylene
Recycled to become various bottles, grocery bags, recycling bins,
agricultural pipe, base cups, car stops, playground equipment, and plastic
lumber, flower pot, toys
Polyvinyl Chloride
Recycled to become pipe, fencing, and non-food bottles.
Low-Density
Polyethylene
Recycled to become plastic bags, various containers, dispensing bottles,
wash bottles,
tubing, and various molded laboratory equipment.
Polypropylene
Recycled into auto parts and industrial fibers.
Polystyrene
Recycled into a wide range of products including office accessories,
cafeteria trays,
toys, video cassettes and cases, insulation board and styrofoam.
The coextruded plastics (more than 1 layers of plastics)….how to
recycle???
Reclamation/Cleaning
• After sorted, the plastics must be chopped
into small flake or shredded for further
process
• Then the flakes are treated with solvents
and wash to remove residual
contaminants (original content & paper
label)
• The flake send to the fabricators to
extrude into pellets
End Uses- Sorted PCR
• The recycled material can be used in the
same applications or other applications
• However, PCR plastic cannot be used in in
medical and food-contacting applications
due to danger of contamination and
desease
• Thermoplastic- can be reheated and
reprocessed many times (with minor
changes in resin properties)
End Uses- Comingled PCR
• They cannot be recycled back into their
original product because they usually
come from different products
• The most common product is plastic wood
• Applications: home fence, park bence and table, gazebo,
etc
• Process (twin screw extruder & ram injection molding):
processing the commingled PCR together at a sufficient
temp (to melt the majority flakes)
• Advantages of Plastic wood
– Absence of the highly toxic antifungi that normally applied to
wood
– Wood normally decay and need maintenance
Problem with plastic wood; the dissimilar hygroscopic
characteristics of some components cause different
water absorption & dimensional change (control the
source stream, where the hygroscopic material should
not mixed with hydrophobic materials), the cost of plastic
wood is higher than untreated lumber.
Degradation
• Means that the plastic can break down into
smaller molecules by natural means, biological
agent or by sunlight
• In reality, some materials degrade very slowly
• Some applications require that the material not
degrade, i.e. packaging material
• Some applications need degradable properties,
i.e. sutures in medical applications
Landfill
• Popular since they are less expansive than other
method of waste disposal
• The rubbish is simply buried in the ground
• Careful control of the landfill process is required
to protect the site and its surrounding from
problems like odor, fire, seepage from
contaminating groundwater, etc.
• Problem with landfill, the limited space of the
landfill, thus alternatives for disposal of waste
are needed
• From the following data, the largest
component of waste is paper product
(34.1% by weight), followed by plastics
(19.9%)
Example of materials in solid waste landfills by (a) volume and (b) weight
(in recent year)
Incineration
• Incineration or controlled burning is
another option for disposing of large
percent of solid waste
• The most common purpose of burning is
to generate electricity
Energy content of various solid waste materials and conventional
fuels burned to generate electricity
Incineration can destroy some types of chemicals that other methods can't.
It is also quicker than many other methods.
Obstacles of Recycling
• Usage of various copolymer blends (i.e. PET) from
different manufacturers do not dissolve into one another
when heated. Instead, they tend to phase-separate, like
oil and water.
• Another barrier to recycling is the widespread use of
dyes, fillers, and other additives in plastics. The polymer
is generally too viscous to economically remove fillers,
and would be damaged by many of the processes that
could cheaply remove the added dyes. Additives are less
widely used in beverage containers and plastic bags,
allowing them to be recycled more frequently.