Environmental Aspects of Plastics

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Environmental Aspects of Plastics
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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

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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)

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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

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• 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

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• 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

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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

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Recycling of Plastics

• Reprocessing and refabrication of PCR involves
  several steps
• Collection
• Handling/sorting
• Reclamation/sorting
• End-use fabrication

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Recycling of Plastics
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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)

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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

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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

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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.
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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???
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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

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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)

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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

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• 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.

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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

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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

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• 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)
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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
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Incineration can destroy some types of chemicals
that other methods can't. It is also quicker
than many other methods.
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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.