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Environmental Aspects of Plastics

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Title: Environmental Aspects of Plastics


1
Environmental Aspects of Plastics
2
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

3
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)

4
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

5
  • 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

6
  • 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

7
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

8
Recycling of Plastics
  • Reprocessing and refabrication of PCR involves
    several steps
  • Collection
  • Handling/sorting
  • Reclamation/sorting
  • End-use fabrication

9
Recycling of Plastics
10
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)

11
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

12
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

13
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.
14
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???
15
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

16
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)

17
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

18
  • 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.

19
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

20
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

21
  • 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)
22
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
23
Incineration can destroy some types of chemicals
that other methods can't. It is also quicker
than many other methods.
24
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.
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