CE 527 Solid Waste Management
Plastic Recycling
 Dr. S.K. Ong
Plastics
- Plastics make up ≈ _________ percent of our trash by weight as compared to paper, which constitutes ≈ ________
percent. Glass and metals make up ≈ _________ percent by weight.
- Plastics are polymers, i.e., made of chains of a basic unit that is usually made of carbon, hydrogen, oxygen, and/or
silicon. The chain consists of many links or "-mers", hooked or polymerized together
- Natural polymers include tar and shellac, tortoise shell and horns, as well as tree saps that produce amber and latex.
Natural polymers were first chemically modified during the 1800s to produce many materials. The most famous of
these were vulcanized rubber, gun cotton and celluloid. The first truly synthetic polymer produced was Bakelite in
1909 and was soon followed by the first synthetic fiber, rayon, which was developed in 1911.
Structure of Polymers
- Many common classes of polymers are composed of hydrocarbons. Carbon makes up the backbone of the
molecule and hydrogen atoms are bonded along the backbone. Below is a diagram of polyethylene, the simplest
polymer structure.
- The polymer contains only carbon and hydrogen. Other examples include polypropylene, polybutylene,
polystyrene, and polymethylpentene.
- Other elements such as _________________________________________________________________________
may be found in the molecular makeup of polymers.
Polyvinyl chloride (PVC) contains _________________.
Nylon contains _________________.
Teflon contains _________________.
Polyester and polycarbonates contain ____________________.
- Some polymers, instead of having a carbon backbone, have _________________________ backbone. These are
considered inorganic polymers. One of the most famous silicon-based polymers is _________________.
Molecular Arrangement of Polymers
- Controlling the polymerization process can result in ________________ organization, i.e., no long-range order or
form in which the polymer chains arrange themselves. Amorphous polymers are generally ________________.
This is an important characteristic for many applications such as food wrap, plastic windows, headlights, and contact
lenses.
- The polymer chains in objects that are _____________________ are in a _________________ arrangement. The
higher the degree of crystallinity, the less light can pass through the polymer. Therefore, the degree of translucence
or opaqueness of the polymer is directly affected by its crystallinity.
- Manufacturers and processors introduce various fillers, reinforcements, and additives into the base polymers,
expanding product possibilities.
General Classification of Plastics
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- Polymers are divided into two distinct groups: ___________________ and ______________________.
- The majority of polymers are _______________________, meaning that once the polymer is formed it can be
heated and reformed over and over again. This property allows for easy processing and facilitates recycling.
- The other group, the thermosets, can not be ____________________. Once these polymers are formed, reheating
will cause the material to scorch.
- ____________________ (a single linear chain of monomers) and _____________________ (linear with side
chains) are thermoplastic, that is they soften when heated.
- ___________________ (two or more chains joined by side chains) are thermosetting, that is, they harden when
heated.
Total amount of plastics produced in 2002
Resin
Thermosets
Thermoplastics
Production (x 106 lbs)
660
3220
4440
Epoxy
Urea and Melamine
Phemolic
TOTAL
LDPE
LLDPE
HDPE
PP
ABS
SAN
Other Styrenics
PS
Nylon
PVC
Thermoplastic Polyester (PET)
TOTAL
8040
11330
15,970
1660
1,320
130
1,600
6,670
1,270
15,300
7,250
Thermoplastics make up ______________% of the plastics produced today. Examples of thermoplastics
include;
________________________ (HDPE) used in piping, automotive fuel tanks, bottles, toys, (density range
> 0.941 g/cm3)
________________________ (LDPE) used in plastic bags, cling film, flexible containers; (density range
0.910 – 0.925 g/cm3)
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______________________________ (PET) used in bottles, carpets and food packaging;
________________________ (PP) used in food containers, battery cases, bottle crates, automotive
parts and fibers;
___________________________ (PS) used in dairy product containers, tape cassettes, cups and plates;
___________________ (PVC) used in window frames, flooring, bottles, packaging film, cable insulation,
credit cards and medical products.
- There are hundreds of types of thermoplastic polymer, and new variations are regularly being developed.
- Thermosets make up the remaining 10% of plastics produced. Because they hardened by curing and cannot be remelted or re-molded, they are therefore difficult to recycle. They are sometimes ground and used as a filler material.
- They include:
____________________ (PU) –coatings, finishes, gears, diaphragms, cushions, mattresses and car
seats;
__________________ –adhesives, sports equipment, electrical and automotive equipment;
________________________ – ovens, handles for cutlery, automotive parts and circuit boards.
Resin Identification Code
- The Society of the Plastics Industry, Inc. (SPI) introduced its voluntary resin identification coding system in 1988
at the urging of recyclers around the country. The SPI code was developed to meet recyclers' needs while providing
manufacturers a consistent, uniform system that could apply nationwide.
- Because municipal recycling programs traditionally have targeted packaging - primarily containers - the SPI
coding system offered a means of identifying the resin content of bottles and containers commonly found in the
residential waste stream.
Plastic Packaging Resins
Descriptions
Properties
Polyethylene Terephthalate (PET,
PETE).
- clear, tough, good gas and moisture
barrier properties.
- Commonly used in soft drink bottles
and many injection molded consumer
product containers.
- Other applications - strapping and
both food and non-food containers. - Cleaned, recycled PET flakes and
pellets are in great demand
Nickname: Polyester.
High Density Polyethylene (HDPE)
- make bottles for milk, juice, water
and laundry products.
- Unpigmented bottles are
translucent, have good barrier
properties and stiffness, and are well
suited to packaging products with a
short shelf life such as milk.
- good chemical resistance, used for
packaging many household and
industrial chemicals such as
detergents and bleach.
- Pigmented HDPE bottles have
better stress crack resistance than
unpigmented HDPE bottles.
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Packaging
Applications
Plastic soft drink,
water, sports
drink, beer,
mouthwash,
catsup and salad
dressing bottles.
Peanut butter,
pickle, jelly and
jam jars.
Ovenable film
and ovenable
prepared food
trays.
Milk, water, juice,
cosmetic,
shampoo, dish
and laundry
detergent
bottles; yogurt
and margarine
tubs; cereal box
liners; grocery,
trash and retail
bags.
Recycled
Products
Fiber, tote bags,
clothing, film and
sheet, food and
beverage
containers,
carpet,
geotextiles,
strapping, fleece
wear, luggage
and bottles.
Liquid laundry
detergent,
shampoo,
conditioner and
motor oil bottles;
pipe, buckets,
crates, flower
pots, garden
edging, film and
sheet, recycling
bins, benches,
dog houses,
plastic lumber,
floor tiles, picnic
tables, fencing.
Vinyl (Polyvinyl Chloride or PVC)
- stable physical properties,
excellent chemical resistance, good
weatherability, flow characteristics
and stable electrical properties.
- broadly divided into rigid and
flexible materials.
- Bottles and packaging sheet are
major rigid markets, also widely used
in the construction market for such
applications as pipes and fittings,
siding, carpet backing and windows.
- Flexible vinyl is used in wire and
cable insulation, film and sheet, floor
coverings synthetic leather products,
coatings, blood bags, medical tubing
and many other applications.
Low Density Polyethylene (LDPE).
- predominately in film applications
due to its toughness, flexibility and
relative transparency, making it
popular for use in applications where
heat sealing is necessary.
- used to manufacture some flexible
lids and bottles and it is used in wire
and cable applications
Clear food and
non-food
packaging,
medical tubing,
wire and cable
insulation, film
and sheet,
construction
products such as
pipes, fittings,
siding, floor tiles,
carpet backing
and window
frames..
Packaging,
loose-leaf
binders,
decking,
paneling,
gutters, mud
flaps, film and
sheet, floor tiles
and mats,
resilient flooring,
cassette trays,
electrical boxes,
cables, traffic
cones, garden
hose, mobile
home skirting
Dry cleaning,
bread and frozen
food bags,
squeezable
bottles, e.g.
honey, mustard.
Shipping
envelopes,
garbage can
liners, floor tile,
furniture, film
and sheet,
compost bins,
paneling, trash
cans, landscape
timber, lumber
Polypropylene (PP).
- good chemical resistance, is strong,
and has a high melting point making
it good for hot-fill liquids.
- found in flexible and rigid packaging
to fibers and large molded parts for
automotive and consumer products.
Catsup bottles,
yogurt containers
and margarine
tubs, medicine
bottles
Polystyrene (PS).
- a versatile plastic that can be rigid
or foamed.
- General purpose polystyrene is
clear, hard and brittle. It has a
relatively low melting point.
- Typical applications include
protective packaging, containers,
lids, cups, bottles and trays.
Compact disc
jackets, food
service
applications,
grocery store
meat trays, egg
cartons, aspirin
bottles, cups,
plates, cutlery.
Automobile
battery cases,
signal lights,
battery cables,
brooms,
brushes, ice
scrapers, oil
funnels, bicycle
racks, rakes,
bins, pallets,
sheeting, trays.
Thermometers,
light switch
plates, thermal
insulation, egg
cartons, vents,
desk trays,
rulers, license
plate frames,
foam packing,
foam plates,
cups, utensils
Bottles, plastic
lumber
applications.
Other.
- Use of this code indicates that the
package in question is made with a
resin other than the six listed above,
or is made of more than one resin
listed above, and used in a multilayer combination.
Dependent on resin
or combination of
resins
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Three and five
gallon reusable
water bottles,
some citrus juice
and catsup
bottles.
Identification of different types of plastics
- There are several simple tests that can be used to distinguish between the common types of polymers so that they
may be separated for processing.
- _____________________ After adding a few drops of liquid detergent to some water. put in a small piece of
plastic and see if it floats.
- ________________________ Hold a piece of the plastic in a tweezers or on the back of a knife and apply a flame.
Dose the plastic burn? If so, what color?
- ____________________________. Can a sample of the plastic be scratched with a fingernail?
Test
Water
Burning
PE
PP
PS
PVC
______ flame with
yellow tip, melts and
drips
__________ flame
with blue base
________, sooty
flame – drips
Smell after burning
Like candle wax
Like candle wax –
less strong the PE
Sweet
_______, sooty
smoke, Does not
continue to burn if
flame is removed
Hydrochloric acid
Scratch
To confirm PVC, touch the sample with a red-hot copper wire and then hold the wire to the flame. A green flame
from the presence of chlorine confirms that it is PVC (source: Volger, 1984)
- To determine if a plastic is a thermoplastic or a thermoset, take a piece of wire just below red heat and press it into
the material. If the wire penetrates the material, it is a thermoplastic; if it does not it is a thermoset.
Plastics for recycling
- Not all plastics are recyclable. There are 4 types of plastic which are commonly recycled:
- Polyethylene terephthalate (PET)
- Polyethylene (PE) - both high density and low-density polyethylene.
- A common problem with recycling plastics is that plastics are often made up of more than one kind of polymer or
there may be some sort of fiber added to the plastic (a composite) to give added strength. This can make recovery
difficult.
- The number of companies handling and reclaiming post-consumer plastics in 1999 (___________________) was
nearly six times greater than in 1986 (___________________).
- Only _________ % of the virgin production is recycled in the US compared to about _______% in Netherlands
and _________% in Germany.
- In 1999, over ______________ tons of plastic bottles were recycled. Each year the amount of plastic bottles
recycled increases while the recycling rate has stabilized around ____________%.
- Markets for recycled plastics are stable in most areas and the American Plastics Council's recently updated
Recycled Plastics Products Source Book lists over 1,300 plastic products with recycled content. The primary market
for recycled PET bottles continues to be fiber for carpet and textiles, while the primary market for recycled HDPE is
bottles.
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- Development of new end uses for recycled PET bottles (like coating for corrugated paper and other natural fibers
to make waterproof products like shipping containers) will fuel the demand for more post-consumer plastics in the
future. For HDPE, a similar situation exists for recycled-content landscape and garden products, including
everything from lawn chairs to garden edging.
- The plastic lumber industry is also beginning to hit its stride, and new ASTM (American Society for Testing and
Materials) standards and test methods are paving the way for use of these materials in structural applications. Even
recycled plastic railroad ties and marine pilings are being field tested. For many products the switch to plastic
means longer life and less maintenance, which translates to lower cost over the life of the product.
Comsumer Plastic Bottle Recycling
- Total plastic bottle recycling was approximately _________________ million pounds in 2001. In 1990, the
amount was 400 million pounds.
- More than 20,000 communities, 63 percent of the nation's total, are estimated to have access to a community
recycling program (curbside or drop-off) that collects plastics.
- Almost all major urban areas in the U.S. have recycling collection programs resulting in approximately 80 percent
of the U.S. population (over 148 million people) having convenient access to a plastics recycling collection program.
- PET and HDPE bottle recycling programs represent ____________percent and _________ percent of plastic bottle
recovery, respectively. Plastic bottles production were 51% PET and 44% HDPE.
- In total, ______ U.S. companies reclaimed U.S.-generated post-consumer plastic bottles during calendar year
2001. Of these, 18 domestic reclaimers reported recycling PET bottles, and 35 companies reported recycling HDPE
bottles. Five companies, that together recycle 75 percent (450 million pounds) of the recovered postconsumer PET
bottle resin in the country, dominate the PET recycling industry.
- Domestically, nearly _________ million pounds of PET and ___________ million pounds of HDPE were recycled.
The difference between domestic recycled pounds and the total recycled pounds shown in Table 1 is the amount of
material that was exported to recyclers in other countries (234 M lbs. for PET and 94 M lbs. for HDPE).
- Almost __________ million pounds of PVC, LDPE/LLDPE, PP and PS from bottles were recycled during 2001.
The majority of these recycled bottles were polypropylene. These bottles accounted for less than 5 percent of all
plastic bottles manufactured during 2001.
Domestic Markets for Recycled PET bottles
- As illustrated in Figure 6, there are five primary markets for recycled PET bottles. The fiber market continues to
be the largest domestic end-market for post-consumer recycled PET bottles. Strapping, food and beverage
containers, and film/sheet applications represent other major markets for recycled PET bottles.
- Pigmented PET bottles are continuing to expand into the national packaging markets. Tests on the use of these
bottles recovered from the post-consumer stream are progressing in several new applications. One such market
mentioned in last year’s report, a paper fiber coating for moisture-resistant corrugated packaging continues to
expand its potential. Other markets involve non-wovens, sheet, and foamed molded products.
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Markets for Recycled HDPE Bottles
- As shown in Figure 7, over one-third of all HDPE plastic bottles recycled in the United States were
remanufactured into HDPE bottles.
- Other major HDPE end-markets include pipe, lawn and garden (e.g., products such as edging and flower pots);
film and sheet; injection molded products (e.g., applications such as buckets, crates, and automobile parts) and
plastic lumber. Plastic lumber, manufactured from either 100% recycled plastic or from a combination of recycled
plastic and wood fiber, represents a rapidly growing product line with many manufacturers now in the industry.
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Effect of Contaminants on PET Processing
- a major concern during the reprocessing of PET is to remove all contaminants that can ______________________
__________________ of PET
- the use of _______________ or alkaline detergent containing _____________ is avoided since they may be
entrapped in the PET granules and promotes hydrolysis
- most troubling contaminants present in PET bottles are the _________________ used for the label and base cup.
Most commercial washing systems used to recover PET from bottles inevitably leave traces of adhesives (typically
hot melt adhesives such as rosin acids and esters) in the PET. These rosin acids can catalyze the ______________
of PET.
- Adhesives also __________ the PET at extrusion temperatures making the recycled PET becomes discolored and
hazy.
- ink from labels can leach out in the hot washing step and produce a faintly colored recycled PET resins
- as low as _______________ ppm of PVC can discolor PET
Reprocessing technologies for PET and PE
- equipment design and process details for reclaiming PE items are determined in part by the physical form of the
feedstock such as rigid containers, films, foamed sheets, wire jacketing and battery cases
- generally processing of PET and PE are similar
Process
Sortation of dirty baled bottles – by
color, polymer type
Shredding
Granulation
Air classification
Items removed
Comments
Washing/rinsing
Flotation or Hydrocyclone
Dewatering/Drying
Electrostatic separator/Metal
detector
Product High Purity PET
flake, moderate purity
HDPE (contaminated with
PP and adhesive)
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Glass
- In US, _______ billion glass containers are manufactured annually (1995)
- 33% food containers
- 31% beer bottles
- 9% wine and liquor bottles
- 22% bottles for other beverages
- 5% for cosmetics, pharmaceuticals
- By color – ________% clear, ________% amber, _________% in shades of green and blue
In 1995, _______________ million tons of glass were discarded nation wide
- Only ____________% if glass containers are recycled nation wide
- constitutes about 6 - 8% by weight of MSW
- __________% is flint (clear), green or amber bottle and container glass
- remaining __________% is mostly glassware and plate glass
- all recycled glass is used to produce new glass containers and bottles, some for glass wool or fiberglass insulation
and part of building materials (ceramic, tiles)
Glass bottles and containers
- manufacturers prefer to use cullet (crushed glass) with raw materials because of energy savings. Recycled glass
melts at lower temperatures (about ______________ % less total energy needed)
- disadvantage is that contaminants in the cullet nay alter product color quality
- in-house cullet, off specs products, is always preferred
Fiber glass
- most of the recycled materials come from in house operations of other glass manufacturers because of the stringent
specifications for the manufacture of fiberglass.
Specifications of Color Sorted Glass
___________________________________________________________________________________
Color
Permissible color mix levels, %
Flint
Amber
Green
Other
___________________________________________________________________________________
Flint (clear)
______
0–3
0–1
0–3
Amber (brown)
0–5
_____
0–5
0- 5
Green
0 – 10
0 – 15
______
0 – 10
________________________________________________________________________________
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