Technologies for the Identification, Separation and Recycling of

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Technologies for the Identification, Separation and Recycling
of Automotive Plastics
by
Joerg Hendrix*, Kevin A. Massey*, Eric Whitham* and Bert Bras**
Systems Realization Laboratory
The George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, Georgia 30332-0405
U.S.A.
Mark D. Russell+
Chrysler Corporation
800 Chrysler Drive East
Auburn Hills, Michigan 48326-2757
U.S.A.
ABSTRACT
Virtually all of the material in today's automobiles can technically be recycled. The challenge
facing engineers is making this recycling process economical, especially for the materials in such
components as seats and instrument panels. Recycling these components requires the different
materials to be separated so that each can be recycled individually. This separation can be
accomplished either manually, where workers disassembly and sort the vehicle components by
hand, or mechanically, where the vehicle is shredded and the materials sorted by properties such
as conductivity and density. In this paper, we provide an overview of efforts and technologies
which primarily support automated separation and recycling. Although the paper is focused on
*
**
+
Undergraduate research assistant
Assistant Professor, corresponding author
Supervisor Quality Planning and Recycling, Large Car Platform
Submitted to International Journal of Environmentally Conscious Design and Manufacturing,
March 1996.
automotive applications, many of the technologies are applicable to white goods and consumer
electronic products as well.
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1
OUR FRAME OF REFERENCE
Whether motivated by recent legislative efforts or by a moral sense of obligation, automotive
manufacturers are attempting to reduce the environmental impacts of the entire life cycle of their
vehicles. Specifically, the manufacturers are attempting to improve the recyclability of their
vehicles and therefore reduce the percentage of each car which must be disposed of in a landfill.
In Europe, legislation has been proposed that requires car manufacturers to be responsible for
comprehensive recycling and material recovery from their vehicles. The increased emphasis on
recyclability has among others led to the establishment of the Vehicle Recycling and Development
Center (VRDC) in Detroit which serves as the headquarters of the Vehicle Recycling Partnership
(VRP), a cooperative effort among Chrysler, Ford, and General Motors as part of the USCAR
initiative. Since most of the steel and metals from these vehicles (which constitute about 75% of a
vehicles weight) are already recycled (see, e.g., [1]), the concentration of recent efforts has been
on the vehicle sub-systems which are mostly non-metal - for instance, the polymers in the bumper
systems, the instrument panel, the seats, and other interior trim components.
The need to focus on non-metal parts is emphasized by the undeniable shift towards a lower metal
content in most cars. Over the last 20 years, the metal percentage has dropped approximately
10% of the weight of the car - from about 85% to about 75%. This has translated to cars which
are less recyclable, since the only well developed recycling infrastructure is for steel and other
metals. However, the change has resulted in lighter, cheaper, more fuel efficient vehicles.
Currently, automobiles are recycled aproximately 75 percent by weight and mainly the ferrous and
non-ferrous metals are recycled from the discarded vehicle by shredding the vehicle and
magnetically sorting the metals. The remaining 25 percent is known as automobile shredder
residue. This residue contains potentially recycleable materials including polyurethane foams and
thermoplastics. Currently the residue is landfilled. However as tipping fees increase, legislative
recycling recycling targets increase, and the use of plastics in automobiles also increases, it will
become necessary to find ways to divert this material from the landfill and utilize it in a profitable
manner, either through energy recovery, or by separating the different types of plastics, removing
contaminants, and recycling different plastics contained in the shredder residue.
In recent years, a great number of publications are available which deal directly with “designing
for disassembly”. However, it must be emphasized that disassembly is only one step in the
recycling process. In the German recycling guideline VDI 2243 [2], three generic sub-processes
are identified which typically occur in a material recycling process, namely:
• material separation,
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• material sorting, and
• material reprocessing.
In addition, practical experiments and findings indicate that although it is theoretically possible to
dismantle and recycle a vehicle completely (100 %), it is not economically feasible. In
promotional videos on automobile recyclingBMW and Mercedes both cite that it costs money to
recycle cars. Studies at the VRDC and independent research on recycling cost assessments tend
to confirm this (see, e.g., [3-5]).
In this context, the objectives of the work presented in this paper were to catalog different types
of plastic-from-plastic and plastic-from-metal separation technologies that exist in the recycling
industry which may lead to economically feasible recycling. In addition, we investigated whether
these technologies were commercially available or still under development. A number of plasticfrom-plastic and plastic-from-metal separation technologies were identified, as well as at least
some of the companies/institutions which are either using or researching these technologies. The
technologies and researchers/institutions were identified through an extensive literature search in
both academic and trade literature, as well as through personal conversations and interviews.
Though it is unlikely that all existing technologies have been identified, we feel that those
technologies which were identified represent the majority of those in existence. Also, many of the
companies and institutions identified are considered to be the prime movers and developers of
such technologies in both the United States and Europe. In this paper, we will discuss
• the role of manual dismantling,
• mechanical separation technologies,
• plastic identification technologies,
• chemical recycling technologies.
Prior to discussing the various technologies, we will first give an overview of the current vehicle
recycling practice and recycling guidelines.
2
CURRENT AUTOMOBILE DISMATLING AND RECYCLING PRACTICE
Recycling efforts in the U.S. exist because a profit can be made; without this incentive vehicles
would simply be sent to landfills. Current recycling efforts for a vehicle consists of manual and
mechanical separation (Figure 1). Reusable/remanufacturable components (such as engines and
alternators) are manually removed from the car by dismantlers. These components are resold in a
market limited to other vehicles of the same model, and often limited to the same year of
manufacture. The vast majority of reusable/remanufactured items are powertrain components.
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When all these components are removed, materials with high value are removed by the
dismantlers. For the most part, this consists of aluminum, magnesium, and other large pieces of
pure metal. These materials are removed by hand because separate piles of aluminum and steel
are worth significantly more than a commingled pile of the two metals.
Vehicle
Reusable/Remanufacturable Parts
Dismantler
Easily Accessible Pure Materials
Hammer Mill or other Shredder
Magnet
Eddy Current
Separator
Ferrous Metals
Non-ferrous metals
Automotive
Shredder
Residue
Figure 1 – Current Vehicle Dismantling and Separation Process
Following this, the vehicle is sent to a shredder, shredded, and the pieces mechanically
separated based on the properties. The only requirements for shredding are that the tires and gas
tank (and preferably also other fluids like oils) are removed; the rest of the car (or whatever
portions have not been removed by a dismantler) will be sent into a hammer mill or similar piece
of equipment which reduces the vehicle to fist-sized pieces. The ferrous metals are magnetically
separated into one pile, and the non-ferrous metals are generally separated using an eddy-current
machine into another pile. The ferrous metals are then sold to a smelter. The non-ferrous metals,
which are worth significantly more, are then separated into specific types of metal, either by the
shredder or another company. The remainder of the car, about 25% by weight currently, is
generally called Automotive Shredder Residue (ASR) or “fluff”. This ASR, which consists of
plastics, rubber, glass, dirt, fluids, and other materials, is currently sent to a landfill.
3
VEHICLE RECYCLING GUIDELINES
Due to the increased emphasis on product take-back and recycling, a wide variety of guidelines
and methods for designing for recycling have been proposed in recent years. It would go beyond
of the scope of this paper to provide a comprehensive list. The German national standard VDI
2243 represents a good example of the state of the art in design for recycling [2, 6]. Admittedly,
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the standard is still evolving and not completely applicable to US situations. To our knowledge,
VDI 2243 has not been officially translated into English yet, but Beitz provides a general
overview [6]. Many researchers have placed high emphasis on Designing for Disassembly (DFD).
Boothroyd and Alting provide a good overview [7]. Extensive overviews are given in [8, 9].
Noller states some of the differences between design for disassembly and DFA [10]. For example,
complete nesting can slow disassembly by not providing a location for the disassembler to reach,
grasp, or otherwise handle. Other sources for design guidelines and efforts facilitating recycling
are, e.g., [11-19]. However, many of the DFD guidelines focus on manual disassembly and fail to
take destructive disassembly through automated processes into account. In [5], the argument is
made that a component designed for manual disassembly is not necessarily easy to disassemble
mechanically.
In the U.S., two major organizations which are very involved in the development of automotive
dismantling technology are the American Plastics Council (APC) and the Vehicle Recycling
Partnership (VRP). The VRP is managed by the United States Council for Automotive Research
(USCAR) [1]. One APC project involved the collection of automotive plastic from both new cars
and older cars dating from the 1970’s. The cars were manually disassembled and the plastics
were sorted by resin type before being sent to the wTe Corporation’s Multi-Products Recycling
Facility (MPRF) recycling operation for processing. The APC noted that newer cars required
significantly less effort in the removal of the plastic, and that almost 40% of the parts recovered
from newer cars had some sort of resin identification [20]. This is in part due to the increase in
attention that vehicle recycling has gotten from automobile manufacturers and suppliers. Most
automobile manufacturers have established vehicle recycling guidelines. In the U.S., Chrysler,
Ford and General Motors each have their own recycling guidelines. Although slightly different in
detail, they are very similar and all focus on the following issues:
• material selection, e.g., reduce overall material diversity, avoid the use of laminates or
make them out of compatible materials which can be recycled as a mixture,
• fastener selection, e.g., reduce fastener count and diversity, avoid incompatible adhesives
which degrade recyclability of materials, use snap fits where appropriate, and
• component design issues, e.g., avoid paints and laminates, build in planes for easy
separation and access.
GM also includes packaging issues in their GM-520M recycling standard. It should be noted that
all auto-makers are emphasizing the link between use of regulated substances and recycling and
refer from their recycling guidelines to appropriate regulated substance elimination guidelines
(e.g., Chrysler’s CS9003 and GM’s 1000M standards) because many components with regulated
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substances will have to be recycled, whether it is profitable or not. For example, chromium plated
plastics may not be landfilled in Europe. Although many suppliers have been exposed to the
various recycling standards, these recycling guidelines are not (yet) disseminated on a large scale
by the automakers.
4
MANUAL DISASSEMBLY AND ITS ROLE IN PLASTIC RECOVERY
In the automobile industry, an extensive infrastructure for ferrous and non-ferrous metal recycling
is present, but no such infrastructure exists yet for plastics. It is only recently in the context of
European take-back legislation that recycling of plastics embedded in products is being pursued in
order to meet the stringent recycling levels set by those legislative initiatives. In this context, a
report published by the American Plastics Council in August of 1994 [21] states that, “Hand
removal today is the only demonstrated technology for recovery of plastic parts or assemblies
from vehicles”. A year later, our survey of the industry indicates that the same is still true. So
although a number of sophisticated automated separation techniques are currently being
developed, it is useful to examine current manual disassembly practices and what technologies are
being developed to facilitate economical manual disassembly.
The advantage of manual separation over many other techniques is that the material recovered is
more pure, and thus higher value. The disadvantage is that the cost is also high due to the worker
labor cost. As the mechanical separation techniques are improved, the disadvantages of manual
recycling will become overwhelming for materials used in small quantities or with low weight.
However, the presence of dirt, oil, and other contaminants which are not completely removed by
mechanical separation techniques make manual separation a viable, and even preferable, option.
In the automotive industry, a large number of metal and plastic parts, from taillight assemblies to
fenders, are removed and resold into the used parts market. Plastic parts which are components
of larger assemblies (such as doors, front ends, seats, etc.) are typically sold as part of the
complete assembly. Other plastics remain in the stripped vehicles, which are stored in outside
yards. Mechanics and the general public remove specific parts, as needed, from the vehicles while
stored in the yards. In preparation for shredding, dismantlers usually remove tires, exhaust
systems including the catalytic converter, batteries, and fuel tanks and recover fluids (anti-freeze,
oils, and air conditioner refrigerant) [14].
Visual identification of plastic type for purposes of recycling is possible by labeling of the
individual parts. This practice is only partially established in industry. Although (inter)national
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labeling standards exists (e.g., SAE J1344 and ISO 1043), there is no uniform enforcement on
labeling parts for identification for recycling. In the absence of such labeling, another means of
identification of plastic type which we found was infra-red (IR) spectrometry (discussed in more
detail later in this paper). This method is applied by the Appliance Recycling Centers of America,
Inc., where an employee manually “guns” the parts which are still on the appliance to determine if
they are of a type of plastic which is economical to remove and recycle.
A major factor which facilitates economic manual removal is the use of fewer varieties of plastic
in a single assembly. Large, single-polymer components and assemblies such as dashboards,
consoles and bumpers offer better opportunities for economic recycling. European companies
have been giving attention to this point for some time. As of 1991, the German Association for
Research in Automotive Engineering had commissioned Porsche to investigate a scheme for
designing a vehicle that would lend itself to easy dismantling [19]. Also in 1991, BASF was
developing a dashboard constructed entirely of polypropylene. At that time it was anticipated that
the development process would take some time due to problems related to installation. BASF
also found that if the entire bumper system consisted exclusively of a single polymer such as
polypropylene, recovery was facilitated and usually economic. BASF has developed (1991) a
bumper/grill/spoiler system constructed entirely of polypropylene. Also in 1991, Dutch State
Mines (DSM) in Europe was processing bumpers from Volkswagen and Audi cars to produce
material which Volkswagen molded into new bumpers [19]. As of 1993, the Porsche 911 had a
bumper made from 100% bumper scrap. BMW was using wheel arch and luggage component
liners made from recovered polycarbonate/ polyester blends. DSM had designed an allpolypropylene dashboard for easy disassembly and recycling, and was still actively involved with
Volkswagen/Audi in recovery of bumper plastics. Door panels in polypropylene can be developed
more easily and the technique is already at an advanced stage [19]. [17, 22] provide additional
information on European initiatives in plastics recycling.
It is difficult to find instances of successful large scale recovery of single-polymer automotive
components in the United States. However, a program has just been initiated by GE Plastics and
Ford Motor Company in which GE Plastics will buy intact Ford bumpers made of XENOY resin
from auto dismantlers. GE Plastics has officially announced that they will buy the bumpers, and
now it will be up to the auto dismantlers to take advantage of the infrastructure which has been
created. GE will remove the paint from the XENOY resin using a water-based process developed
with funding from GE and Ford [23].
Another promising development is the recycling of polyurethane foam recovered from automobile
seats. The recycling of polyurethane foam into carpet padding is already an established practice in
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the carpet industry, and all that remains to link this infrastructure with the automotive recycling
industry is an economical means of removing the seats from the vehicles and separating the foam
from the other seat components. Research on manual removal of the foam is underway at the
University of Illinois, and wTe Corporation’s pilot recycling facility in Boston is investigating
automated separation of the foam from other seat components [24].
An example of a more established plastic recycling process in the automotive industry is the
separation of the polypropylene battery case from the battery’s lead is an established practice in
the battery lead recovery industry. Reference [25], an English publication, says that the recovery
of polypropylene battery cases has been a profitable activity when linked with the associated
recovery of lead. The polypropylene is recovered and converted back into battery cases or other
items like horticultural containers. Exxon Chemical in the United States and the C2P (Cookson
Penarroya Plastics) subsidiary of Metaleurop Group in Europe are both major recyclers of leadacid batteries. Reference [26] describes the battery composition and the recycling and separation
process used by C2P. C2P the European leader in the recycling of polypropylene from
automotive battery cases produces more than 40 tons of polypropylene chips daily resulting from
the crushing of fifty thousand batteries.
5
PLASTIC IDENTIFICATION TECHNOLOGIES
The identification of plastics prior to recycling is of crucial importance in order to avoid
contamination of plastic batches to be recycled. Standards exist for labeling plastic components
(e.g., SAE J1344). These labels and markings are intended to be read by human dismantlers.
However, there is a need for more advanced identification technologies because:
• Even though plastic parts may be labeled by the generally preferred practice of molded in
markings, these markings may be incorrect. For example, a company may change the resin
type used for an injection molded component, but may not change the mold used and, hence,
the molded in plastic identification will be incorrect for the newer components.
• Human labor is expensive and automation of plastic identification is preferred, especially when
large scale recycling is sought.
In the following, we will discuss some plastic identification technologies that are available in
addition to visual markings.
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5.1
FT-IR, FT-NIR, FT-Raman, and X-Ray
Because different plastics have distinguishable light absorption spectra, a simple way to sort them
out is accomplished by electromagnetic absorption and reflectance measurements. The plastic
specimen is illuminated by infrared, YAG laser, or X-ray light and the reflected spectrum is
detected and analyzed to determine the type of plastic. This is possible because each type of
plastic has its own “fingerprint” in the electromagnetic spectrum [27]. FT-IR stands for Fourier
Transform - Infrared. FT-NIR uses Near Infrared light. FT-Raman uses a YAG laser.
This means of identifying and separating mixed plastics is the only plastic-from-plastic
identification technology we found in wide use in the plastics recycling industry. As mentioned
before, Appliance Recycling Centers of America, Inc., makes limited use of IR spectrometry to
identify plastic resin type before manual disassembly. A more sophisticated application that is
widespread in the plastic bottle recycling industry is in the automated separation of bottles of
different resin types, and even different colors, in preparation for recycling. We found no other
industry application of this separation technology. The reason given by the companies with whom
we spoke was that no one perceives a market for any other recycled plastics.
FT-IR, FT-NIR, FT-Raman, and X-Ray identification are means of identifying polymer type, after
which some action must be taken to actually separate the different types. Current industry
separation practice is either to eject the discovered plastic type via air jet or to route the detected
plastic via an actuated gate in the material flow path. Though the theory of operation of each of
these identification methods is similar, the capabilities of each vary. Some of the differences are
shown in Table 1.
[30] is a June, 1993 report on the operation of an installed identification/separation system by
Magnetic Separation Systems (Nashville, TN) at Eaglebrook Plastics, Inc. This system, designed
for recycling of plastic bottles and containers, began operation in January of 1992. The system
uses FT-NIR and X-ray sensing, and is capable separation into the following categories:
• PVC - colored: up to seven different color classifications
• PET - clear
• PET - colored: up to seven different color classifications
• HDPE - natural
• HDPE - colored: up to seven different color classifications
• PP
Overall accuracy of the system under production conditions was found to be 85% to 95%, except
for PVC, which was detected (via X-ray) with an accuracy of 99.3 to 99.5%. Sources of
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inaccuracy are detailed in [30]. [30] also acknowledges APC and Exxon Chemical Company for
received funding. In August of 1994, [21] recommended to the APC that funding be given to
support Magnetic Separation Systems (MSS) in the further development of this system. APC
contracted with MSS to construct a bottle separation system in late 1994. [31], a more recent
(November, 1994) report from MSS, contains detailed descriptions of a number of domestic and
overseas systems designed and installed by MSS. All are centered around the recycling of plastic
bottles. Specific volume and efficiency figures are given, but are not included in this report as
they are similar to the figures for the Eaglebrook installation. According to [30], other companies
involved in this technology are:
• Automation Industrial Control
• National Recovery Technologies
• Buhler AG (Uzwil, Switzerland)
Table 1 - Distinctions Between Different Spectrographic Identification Methods
FT-IR
Reference [27] indicates that FT-IR has greater discriminative power than FT-NIR and Xray techniques, and can discriminate between “a diversity of engineering plastics”. [27]
discusses the principles of FT-IR in great detail.
FT-IR is very sensitive to the condition of the surface being identified [28]. Because most
consumer plastics carry different types of commercial labeling, it is often not possible to
obtain any surface IR spectral measurement reliably [29]. Problems may arise with
stickers, lacquers, contaminations, etc. on the surface of the plastic products. The IR
spectra have to be recorded from “clean” surfaces [27].
FT-IR has difficulty identifying very thin plastic such as for plastic bags, and cannot
identify blown polystyrene (PS).
FT-NIR
Unlike FT-IR, the FT-NIR reflection technique cannot identify black materials [27]
[30] goes into some detail on the identification process using FT-NIR.
FT-Raman
FT-Raman has no difficulty identifying very thin plastic such as plastic bags. FT-Raman is
able to identify rough surfaces and powders, can accommodate almost any shape, color, and
surface condition, and is at least 50 times faster than FT-IR. However, FT-Raman cannot
identify black or darkly-colored surfaces [28].
We have found no use of FT-Raman in industry, and the only research we found was being
conducted in France as of April 1994.
X-Ray
The use of X-ray techniques is restrict to specific problems, like the separation of PVC and
PET (plastic bottles) [27].
[30] goes into some detail on the identification process using X-ray.
[31] also says that sensing units based on FT-NIR were introduced by the following companies:
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• Buhler AG (Uzwil, Switzerland), developed by Optan (Switzerland) - 1993
• Laser Labor Adelshof GmbH (Berlin, Germany) - 1994
• Massen Machine Vision Systems GmbH (Konstanz, Germany) - 1994
[31] says that processing lines using the Laser and Massen sensors respectively are being offered
by Mashcinenfabrik Bezner GmbH based in Ravensburg, Germany and Binder & Company AG in
Gleisdorf, Austria. According to Joe Taylor of Carpco Inc., Simco-Ramic and Buhler AG were
developing optical and NIR systems.
[32] indicates that research is underway (June 1994) at Rutgers University in New Brunswick, NJ,
as well as in Europe, on detection-and-route systems based on electromagnetic spectra. Bruker
Instruments, in conjunction with the APC, recently developed an infrared identification instrument
that can distinguish between 23 different types of plastic, including black plastics. As of August,
1995, this device was scheduled to be evaluated at the Vehicle Recycling Development Center in
Highland Park, MI, which is managed by the Vehicle Recycling Partnership (VRP).
Perhaps the most interesting information in [31] is the development of new sensor technology for
separation on the flake level. Separation of granulated plastic is now operating on a commercial
basis. Simco-Ramic of Medford, Oregon has installed several systems capable of separating
colored HDPE from natural HDPE, green PET from clear PET and PP and mixed color HDPE.
Flake sorter volumes of up to 6,000 pounds per hour are available. One such system is in use at
Productivity Corporation (Richmond, Indiana) sorting PET and PP flakes by color. The quality
of these systems is reported as “quite good”. MSS also offers an automated system for the
separation of PVC flakes from mixed plastics flake streams. Flakes down to 3/16” are removed
with typical removal efficiencies of greater than 98% and a throughput of up to 4,000 lb/hr. [31]
indicates that there are 23 multi-resin processing lines operating world wide, 20 of which were
provided by MSS. Of the non-MSS lines, one is a prototype system installed by NRT and Sorema
in Italy, and two lines are provided by Govoni, one in Japan and one in France.
5.2
Photoacoustics
As with FT-IR and similar techniques, photoacoustics is only a means of identification after which
some action must be taken to separate the material. In 1994, researchers in the Department of
Chemistry at Queen’s University in Kingston, Ontario conducted a small-scale study to
demonstrate the application of photoacoustics to on-line sorting of waste plastics. This material
identification process is generally similar to the use of IR in that the sample is exposed to a light
of known frequency and a reaction of the material is observed. The differences are that the green
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light of a Nd:YAG laser is used and that it is an acoustic emittance, not a light
reflectance/absorbance, that is measured. The advantage is that the identification of the material
is not limited by surface modifications such as color, printed labels, etc. Other incidental
advantages over IR include lower cost and portability. The plastics tested in the study were
HDPE #2, HDPE #7, and PP #5. As of 1994, this process was still very much in the research
stage [29].
6
MECHANICAL PLASTIC SEPARATION TECHNOLOGIES
Mechanical separation has a relatively lower cost than manual separation. Mechanical
separation, however, requires significant differences in easily measurable properties of the
materials. For instance, ferrous metals are very easy to separate from other materials with a
simple magnet. Non-ferrous metals can be separated with an eddy current separator with
somewhat less accuracy. In this section, we will highlight a number of separation technologies
that are under development and show promise. It should be emphasized that most are in a
prototypical stage and are not commercially available yet for plastic recycling.
6.1
Float-Sink Method Using Supercritical Fluids
This plastic-from-plastic separation technique was developed in the Department of Chemical
Engineering, University of Pittsburgh, PA. Reference [33] is the original proposal to begin the
research, and discusses theory in detail. Reference [34] is the first report on the findings of the
research.
This method involves placing the mixed waste to be separated into a sealed pressure vessel with
CO2 or a mixture of CO2 and SF6. The pressure inside the vessel is varied so as to vary the
density of the fluid over the range of the mixed waste ingredients. This control over the fluid
density gives the operator the ability to float different materials in stages, removing the floating
material before proceeding to the next density. Density can be closely controlled, allowing the
process to closely discriminate between types of plastics. Additional details of this process are
contained in [34].
Several thermoplastic mixtures have been tested, including HDPE/LDPE/PP and PVC/PET. The
purity of the separated homopolymers ranged from 77% to 100% by weight, with most runs
yielding 96%-100% purity [34]. As of 1993, this process was still very much in the research stage
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[34]. In August of 1994, [21] recommended that funding be given to support the continuation of
this research. That is the most recent information we have found.
6.2
Float-Sink Using Other Fluids
According to Joe Taylor of Carpco, Inc., float-sink with brine solutions is established practice in
wire industry. [31] indicates that Rensselaer Polytechnic Institute recently installed a float-sink
system for separation of granulated PVC from PET. wTe Corporation’s Multi-Products
Recycling Facility uses float-sink classifiers as one of its many stages of separation. wTe was
reluctant to release any details to us due to funding received from the APC [20].
6.3
Air Classification
Conventional air classification uses a steady, rising current of air to separate lighter particles from
heavier ones. An example of such a process is found in the food industry in the separation of
wheat from chaff in a grainery [32].
However, the separation is affected by both density and particle size. Thus a less dense, larger
particle can be mistaken to be equivalent to a smaller, more dense one [34]. Clear separation can
never be achieved by steady airflow because separation occurs by aerodynamic lightness, not
density [32] .. Thus, although air classification has been shown to effectively remove the
polyurethane foam component of ASR [35], discrimination between plastics with similar densities,
such as PET and PVC, cannot be achieved at all [34].
Stessel is developing an air classifier that uses pulsed airflow, as opposed to continuous airflow,
to overcome the above-mentioned disadvantage [32]. It is recommended as an inexpensive
preliminary step to more sophisticated and costly separation technologies. Separation of plastics
from other materials and perhaps even separation into different plastic types is expected. This
method has received only limited testing due to lack of funding.
The APC and MBA Polymers, Inc. have opened a new recycling facility in Berkeley, CA, which
focuses on identification and development of new mechanical recycling technologies. The facility
is said to incorporate some of the most advanced plastics recycling technologies in the U.S.
Among the many separation processes employed at the facility is a three-stage air classification
system [20]. MBA was reluctant to release details on its operations for proprietary reasons.
Air classification has the advantage over hydrocycloning of being a dry operation [32].
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6.4
Hydrocycloning
Hydrocycloning is similar to air classification, except that the fluid medium is a liquid, not a gas.
Hydrocylconing is also plagued by the same shortcomings as air classifiers [34]. Although several
hydrocylone manufacturers may be found in the Thomas Register [36], we have found only one
confirmed application of hydrocyclones in the recycling industry; the new recycling facility
opened by the APC and MBA Polymers, Inc. discussed under air classification. It is said to be
much faster than float-sink methods [20].
6.5
Electrostatic Separation
This plastic-from-metal separation technology is discussed in the May 1994 issue of Wire Industry
[37] in the context of recycling cable scrap. First, the cable is finely shredded to free the copper
from the insulation. Then the shredder output is fed onto the top of a horizontal, rotating drum in
the presence of a high electrostatic field which charges the particles. As the drum revolves, the
particles are brought out of the electrostatic field and begin to lose their charge to the grounded
drum. The copper, being a metal, loses its charge first and is flung quickly off the barrel due to
the barrel’s rotation. The plastic insulation loses its charge more slowly, and clings to the barrel a
little longer before it too is flung outward. In this way the copper and insulation are thrown in
different directions and collected in separate containers. This technique has proven to be highly
effective in this context. This process is in use by Hamos Elektronik, Ruhe am Bach 5, D-82377
Penzberg, Germany [37]. In August of 1994, [21] recommended that funding be given to support
research by Kali and Salz of BASF.
Carpco, Inc., located in Jacksonville, Florida, is a manufacturer of a great variety of separation
devices for a great variety of applications. They are currently manufacturing electrostatic
separators for cable recycling and fiber removal, and indicated that they had plastic-from-plastic
separation technology under development that would be ready for sale towards the beginning of
1996.
6.6
Magnetic Separation
Magnetic separation is currently used in industry to separate both ferrous and non-ferrous metals
from the light fraction of ASR, as well as in many other industrial applications. Ferrous metals
may be separated via a simple magnet mounted over a moving conveyor belt. Non-ferrous metals
are separated by rapidly spinning magnetic pulleys in close proximity to the metal particles, which
– 15 –
induce eddy currents in the metals which can physically move the particles.
separation is often referred to as “eddy current separation”.
This type of
According to the Thomas Register an extensive number of manufacturers are involved in magnetic
separation. Because of this, and because the emphasis of this report is plastic-plastic separation,
we have neither tried to locate current research nor included a listing of relevant manufacturers.
6.7
Paint/Coating Removal
The removal of paint and other surface coatings from the plastic resins is one of the larger
obstacles to overcome in the development of automotive plastics recycling. Two companies
which have developed processes which appear to be economically viable are GE Plastics [23] and
MBA Polymers, Inc. [20]. GE Plastics plans to use their process in the XENOY bumper recovery
program in conjunction with Ford Company. MBA Polymers will use their process in their new
plastics recycling pilot plant constructed in conjunction with the APC. Though we know that
both process are “water-based”, we have been unable to obtain substantial amounts due to the
proprietary nature of the technology.
6.8
Selective Solvent Extraction
Argonne National Laboratory published a paper in 1991 summarizing the results of an endeavor
to extract and separate plastics from ASR. The ASR was first sifted through a screen and then
the plastics-rich stream was treated using acetone, xylene, and ethylene dichloride to obtain good
recovery of an ABS/PVC blend and separate PP. Since 1991, a larger-scale testing of the process
was undertaken [35]. According to Sam Jody of ANL, the process was successful with
separating Polyethylene, Polypropylene, ABS and PVC. Due to market conditions, the recovery
of ABS was emphasized. Results have been successful with 98% pure ABS being produced with
less than 1% PVC contamination. [38] and [39] give detailed descriptions of the selective solvent
extraction process developed at Argonne. [39] also indicates that the process is not only
technically feasible using commercially available equipment and material, but is also potentially
economical. In August of 1994, [21] recommended that funding be given to support research on
solvent extraction at the Rensselaer Polytechnic Institute in Troy, New York.
6.9
Melt Temperatures
[32] indicates that, as of June 1994, research was under way at the University of Tennessee in
Knoxville on a separation technology using melt temperatures.
– 16 –
6.10
Dielectric Characteristics
[32] indicates that, as of June 1994, research was under way at Gannon University in Erie, PA on
a separation technology using dielectric characteristics.
6.11
Separation in an Oxygen-free, Vacuum Oven
This plastic-from-metal separation process had no formal name and was found in only one source,
Wire Industry, where it was cited as being used in the recycling of cable scrap. The cable scrap is
taken directly from the production line and placed in the self-contained separation device. The
device is sealed, nitrogen is used to drive any oxygen from the system, and a vacuum is applied.
The device takes over, heating its contents, and at the end of the run the copper and plastic are
completely separated and in separate containers. Both he plastic and copper are immediately
suitable for mixing with the virgin material at the head of the production line [40]. This process is
in use by Swisscab in Yvonand, Switzerland.
7
CHEMICAL RECYCLING PROCESSES
In addition to mechanical separation and recycling processes there exists a large body of chemical
recycling processes that can be applied. In the following we will outline some important
technologies and their current state of application in the recycling industry.
7.1
Pyrolysis
Pyrolysis is a chemical process which is currently being developed by a number of U.S. and
European companies. In pyrolysis, mixed plastics can be decomposed into energy sources or
monomers by ultrahigh temperature in the absence of oxygen [41]. This eliminates the need for
separation of the plastics in the recycling process.
In [19], it is stated that pyrolysis can reduce ASR to combustible gas, carbon black, and aromatic
oils for petrochemical use. At that time, pyrolysis had been used to recover poleofins from
scrapped cars but the process was then uneconomic because of the relatively low price of
petroleum. According to [19] it is anticipated that if the price of crude oil were to rise by a factor
of three, the process could be developed to provide a successful means of material recovery.
– 17 –
The January 1994 issue of Modern Plastics indicates that, as of January 1994, five European resin
makers, Petrofina, DSM, Elf Atochem, Enichem, and BP, were pooling resources to
commercialize a BP pyrolysis process [41]. [41] also says that, as of January 1994, the APC was
funding several pyrolysis efforts.
A project by Conrad Industries (Chehalis, WA) that converts comingled plastics into fuels. Early
in 1994, Conrad was to have started operation of a 2000-lb/hr continuous pyrolysis unit that
converts plastics into hydrocarbons.
General Motors owns technology that converts ASR into energy and filler. The ASR is pyrolyzed
at 1400 degrees Fahrenheit, converting organics into a carbon-rich stream of gases or liquids.
Kadar Agarwal, sr. Project engineer at GM who holds patents on the process, says it has a higher
energy value (15,000-18,000 BTU/lb) than No. 2 heating oil (13,000 BTU/lb). Inorganics
undergo an added step that renders heavy metals inert for reuse in steel reinforcing rods. [41]
said that some auto-shredder firms in Canada and the U.S. were considering using this
technology, however, we did not encounter any such process in use in industry.
7.2
Glycolysis
Glycolysis is a process that breaks down PET into short-chain oligomers. Ashland Chemical
Company has developed a chemical process for the recycling of thermoset polyester composites.
The composite is broken down into raw materials using heated glycols (glycolysis), and the
resulting polyols have been used successfully in automotive sheet molding composite applications
on a laboratory scale [23].
7.3
Hydrolysis
Polyurethanes, polyesters and polyamides can be treated by hydrolysis. Hydrolysis is similar to
pyrolysis, with the plastics being disassociated at high temperatures in the presence of water [19].
We did not encounter either research on, or industry use of, hydrolysis for recycling purposes.
7.4
Methanolysis
Polyesters can be treated by methanolysis. Methanolyisis is similar to pyrolysis and hyrdrolysis,
with the plastic being disassociated at high temperature and pressure in the persence of methanol.
The polymer is broken down into individual monomers and can remove all colorants and
impurities. According to [42], Hoechst Celanese was using methanolysis to process post– 18 –
consumer PET flakes and was completing (winter 1992) completion of an ultra-modern recycling
complex at its Spartanburg, South Carolina plant.
7.5
Waste-to-Energy Conversion
Waste-to-energy conversion varies from pyrolysis and hydrolysis in that the process simply uses
the mixed plastics as fuel for combustion. This combustion generates heat which can be used to
power both the combustion process itself and external devices such as steam turbines. Processes
of this type appear to be more common outside the U.S. because of environmental issues.
Because of this, it was difficult to obtain details of the many varieties of combustion systems. The
only manufacturer located in the U.S. was Vortec Corporation, which is proposing to use its
system in the recycling of automobile shredder residue (ASR). The solid byproduct of this system
is a glass which can be used in the production of asphalt, brick, and mineral wool. [43] also
discusses recent advances in energy recovery.
8 NON-SEPARABLE PLASTICS
Even with all the preceding technologies available, there may still be components made out of
thermo-plastic and thermo-set laminates that cannot be separated. The two main uses of such
mixed plastics are energy recovery via combustion processes such as pyrolysis, and plastic
lumber/concrete filler materials used in construction. One company involved in plastic lumber is
Urban Resource Technologies in Canada. They are able to create a variety of products by varying
the concentrations of plastics, paper, cardboard, and wood by-products which are ground, mixed,
melted, and shaped in a “floating mold”. Another company involved in plastic lumber is
Eaglebrook Products Inc. of Chicago IL. Eaglebrook has an integrated sortation, purification and
extrusion capability which has been successful with post consumer HDPE that has been cleaned of
contaminants.
Though we know of the existence of concrete filler technologies in industry (see [34], [44]), we
have been unable to locate specific companies involved in these technologies. In [20], it is
indicated that the Department of Civil and Environmental Engineering at Michigan State
University has done research on the practicality and environmental impact of using ASR as
concrete filler. It is also known to us that thermo-set composite suppliers, like Premix, Inc. who
is a Sheet Molding Compound (SMC) manufacturer, are actively pursuing ways to recycle/reuse
their products. Chemical recycling processes are mostly favored for thermo-sets. [44-46]
– 19 –
describe some options for SMC scrap recycling. It should be noted that reuse of plastics as filler
for construction material is often a downgrading of the material, especially for thermo-plastics.
9
SUMMARY AND CLOSURE
In this paper, we discussed a number of (future) technologies which may provide not only
technically feasible, but also economically feasible options to separate, identify, and process
plastic-metal and plastic-plastic automotive materials. It should be clear that a great variety of
technologies are being developed. In order to summarize some of our findings, we have given a
summary of companies, organizations and institutions that we have come accross who are actively
working on applicable recycling technologies in Table 2. In Table 2, we have also indicated, to
the best of our knowledge, the technological focus of each company, organization and institution,
as well as the level of maturity of their technology ranging from laboratory, to pilot and
commercial scale. Despite all these efforts and technologies, the only established commercial
usage of those technologies in the automotive recycling industry is of manual disassembly and of
plastic-from-metal separation via magnetic separators. At this stage, automated plastic-fromplastic separation technologies, though under development, are not used commercially in
automobile recycling. However, given the increased interest from the automotive manufacturers
in light of European take back legislation, we may see a move towards a greater
commercialization and usage of these technologies in the next five to ten years. It should be
pointed out that electronic and white good manufacturers who may also be subject of similar take
back legislation are also pursuing many of the same technologies.
Table 2 - Summary of Applicable Recycling Technologies and Associated Parties
Company / Organization / Institution Name
Technology
BASF
Hoechst Celanese Corp Fibers and Film
Bayer (Miles Inc Polymers Div. is US
Subsidiary)
Huls (Huls America Inc.)
BASF
GE Plastics
American Plastics Council
Ashland Chemical Company (General
Polymers Div.)
Phoenix Fiberglass
Owens-Corning (Composites Div)
Dupont Automotive
Appliance Recycling Centers of America, Inc.
Porsche
BASF
Dutch State Mines
Porsche
BMW
Recycling of Automotive Plastics
Recycling of Automotive Plastics
Recycling of Automotive Plastics
Laboratory / Pilot /
Commercial Scale
Laboratory
Laboratory
Laboratory
Recycling of Automotive Plastics
Composite Separation
Recycling of Automotive Plastics
Many different technologies
Composite Separation
Laboratory
Laboratory
Laboratory
Composite Separation
Composite Separation
Nylon Carpet Recycling
Electromagnetic Spectrum Identification
Manual Disassembly
Manual Disassembly
Recycling of Automotive Plastics
Recycling of Automotive Plastics
Recycling of Automotive Plastics
Laboratory
Laboratory
Pilot
Commercial
Laboratory
Laboratory
Commercial
Commercial
Commercial
– 20 –
Laboratory
Dutch State Mines
Vehicle Recycling Partnership
GE Plastics
GE Plastics
Urban Resource Technologies
Dept. of Civil and Environmental Engineering
at Michigan State Uni.
Petrofina (FINA Inc)
Dutch State Mines
Elf Atochem North America Inc.
Enichem Elastomers America Inc.
BP
Conrad Industries
General Motors
Energy and Environmental Research Center
Magnetic Separation Systems
Eaglebrook Plastics, Inc.
Automation Industrial Control
National Recovery Technologies (National
Recovery Systems Inc.)
Buhler
Laser Labor Adelshof GmbH
Massen Machine Vision Systems GmbH
Maschinenfabrik Bezner GmbH
Binder & Company AG
Simco-Ramic
Rutgers University
Bruker Instruments
Dept,. of Chemistry at Queen's University
Dept. of Chemical Engineering at University of
Pittsburg
Rennselaer Polytechnic Institute
wTe Corporation
Dept. of Civil Engineering and Mechanics at
the University of Florida
MBA Polymers, Inc.
MBA Polymers, Inc.
MBA Polymers, Inc.
Argonne National Laboratory
Argonne National Laboratory
Rennselaer Polytechnic Institute
University of Tennessee
Gannon University
Swisscab
Hamos Elektronik
BASF
Carpco, Inc.
Custom Cryogenic Grinding Corporation
VKE
Polymer Products
Vortec Corporation
University of Illinois
Automobile Dismantlers and Recyclers
Association
STIBA
C2P Cookson Penarroya Plastics a Div of
Metaleurop Group
Manual Disassembly
Manual Disassembly
Recycling of Automotive Plastics
Paint/Coating Removal
Plastic Lumber
Concrete Filler
Laboratory
Pilot
Commercial
Commercial
Commercial
Laboratory
Pyrolysis
Pyrolysis
Pyrolysis
Pyrolysis
Pyrolysis
Pyrolysis
Pyrolysis
Pyrolysis
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Commercial
Commercial
Commercial
Commercial
Commercial
Pilot
Laboratory
Pilot
Commercial
Commercial
Commercial
Commercial
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Electromagnetic Spectrum Identification
Photoacoustics
Float-Sink
Commercial
Commercial
Commercial
Commercial
Commercial
Commercial
Laboratory
Pilot
Laboratory
Laboratory
Float-Sink
Float-Sink
Air Classification
Laboratory
Pilot
Laboratory
Air Classification
Hydrocycloning
Paint/Coating Removal
Float-Sink
Solvent Extraction
Selective Solvent Extraction
Melt Temperatures
Dielectric Characteristics
Oxygen-free Vacuum Oven
Electrostatic Separation
Electrostatic Separation
Electrostatic Separation
Cryogenic Grinding
Pyrolysis
Plastic Lumber
Waste-to-Energy Conversion
Manual Disassembly
Manual Disassembly
Pilot
Pilot
Pilot
Laboratory
Pilot
Laboratory
Laboratory
Laboratory
Commercial
Commercial
Laboratory
Commercial
Commercial
Pilot
Commercial
Commercial
Laboratory
Commercial
Manual Disassembly
Lead-Acid Battery Recycling
Commercial
Commercial
– 21 –
ACKNOWLEDGEMENTS
This paper is based on a report commissioned by the Chrysler Corporation and compiled in
September 1995 by Joerg Hendrix, Kevin A. Massey, and Eric Whitham of the George W.
Woodruff School of Mechanical Engineering at the Georgia Institute of Technology under the
guidance of Dr. Bert Bras. We gratefully acknowledge the technical support of Susan Yester of
the Chrysler Corporation and would like to thank all other persons who have helped us to compile
the information presented in this paper. We gratefully acknowledge the funding and donations
from the Chrysler Corporation and the National Science Foundation under grant number DMI9410005 and DMI-9414715.
REFERENCES
1.
Klimisch, R. L., “Designing the Modern Automobile for Recycling” in The Greening of
Industrial Ecosystems, B. R. Allenby and D. J. Richards Ed., National Academy of
Engineering, Washington, D.C. (1994), pp. 165-170.
2.
VDI, “Konstruieren Recyclinggerechter Technischer Produkte (Designing Technical
Products for ease of Recycling)”, VDI 2243, VDI-Gesellschaft Entwicklung Konstruktion
Vertrieb (1993).
3.
Emblemsvåg, J. and Bras, B., “The Use of Activity-Based Costing, Uncertainty, and
Disassembly Action Charts in Demanufacture Cost Assessments”, 1995 ASME Advances in
Design Automation Conference, DE-Vol. 82, Boston, Massachusetts, September 17-21,
ASME, (1995), pp. 285-292.
4.
Chen, R. W., Navin-Chandra, D. and Prinz, F. B., “Product Design for Recyclability: A
Cost Benefit Analysis Model and its Application”, IEEE International Symposium on
Electronics and the Environment, Arlington, Virginia, IEEE, (1993), pp. 178-183.
5.
Coulter, S. L., Bras, B. A., Winslow, G. and Yester, S., “Designing for Material Separation:
Lessons from the Automotive Recycling”, 1996 ASME Design for Manufacturing
Symposium, ASME Design Technical Conferences, Advances in Design Automation
Conference, Irvine, California, August 22-24, ASME, (1996).
6.
Beitz, W., “Designing for Ease of Recycling - General Approach and Industrial
Applications”, 9th International Conference on Engineering Design, The Hague, August 1719, Heurista, Zurich, Switzerland, (1993), pp. 731-738.
7.
Boothroyd, G. and Alting, L., “Design for Assembly and Disassembly”, Annals of CIRP,
Vol. 41, 2 (1992), pp. 625-636.
8.
Scheuring, J. F., Bras, B. A. and Lee, K.-M., “Effects of Design for Disassembly on
Integrated Disassembly and Assembly Processes”, Fourth International Conference on
Computer Integrated Manufacturing and Automation Technology, Rensselaer Polytechnic
Institute, Troy, New York, October 10-12, IEEE, (1994), pp. 53-59.
9.
Scheuring, J. F., “Product Design for Disassembly”, M.S. Thesis, Georgia Institute of
Technology, Atlanta, Georgia (1994).
10. Noller, R. M., “Design for Disassembly Tactics”, Assembly, January (1992), pp. 24-26.
11. Babyak, R., “Design for Disassembly Focuses on Fastening”, Appliance Manufacturer, June
(1991), pp. 26-28.
– 22 –
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
Berko-Boateng, V. J., Azar, J., De Jong, E. and Yander, G. A., “Asset Recycle
Management – A Total Approach to Product Design for the Environment”, International
Symposium on Electronics and the Environment, Arlington, VA, IEEE, (1993), pp. 19-31.
Burke, D. S., Beiter, K. and Ishii, K., “Life-Cycle Design for Recyclability”, Fourth
International Conference on Design Theory and Methodology, Miami, Florida, American
Society of Mechanical Engineers, (1992), pp. 325-332.
Hock, H. and Maten, M. A., “A Preliminary Study of the Recycling and Recovery of
Automotive Plastics”, Automobile Life Cycle Tools and Recycling Technologies SP-966,
Society of Automotive Engineers, March (1993), pp. 59-71.
Kuuva, M. and Airila, M., “Design for Recycling”, 9th International Conference on
Engineering Design, The Hague, August 17-19, Heurista, Zurich, Switzerland, (1993), pp.
804-811.
Matysiak, L., “Design For Recycling: A New Corporate Strategy in the Automotive
Industry”, International Journal of Environmentally Conscious Design & Manufacturing,
Vol. 2, 1 (1993), pp. 5-12.
Seegers, H., “Automotive Design for Recycling in GE Plastics”, 9th International
Conference on Engineering Design, The Hague, August 17-19, Heurista, Zurich,
Switzerland, (1993), pp. 812-819.
Spath, D., Hartel, M. and Tritsch, C., “Tools to Support Environmental Product Design and
Economical Disassembly of Technical Consumer Products”, 10th International Conference
on Engineering Design (ICED 95), Praha, Czech Republic, August 22-24, Heurista, Zurich,
Switzerland, (1995), pp. 1066-1072.
Wood, R., Automotive Engineering Plastics, Pentech Press, London (1991).
Jost, K., “American Plastics Council Technology Update”, Automotive Engineering, August
(1995), pp. 49.
APC, “Sorting and Processing Automotive Plastics – Emerging Technologies”, Automotive
Report Series, American Plastics Council (1994).
Weber, A., “Plastics in Automotive Engineering: Use and Re-use”, Materials and Design,
Vol. 12, 4 (1991), pp. 199-208.
Jost, K., “Recycling Processes and Products: A Quick Read”, Automotive Engineering,
August (1995), pp. 43.
Jost, K., “Recycling Polyurethanes”, Automotive Engineering, August (1995), pp. 36.
Matthews, V., “Overview of Plastics Recycling in Europe”, Plastics, Rubber, and
Composites Processing and Applications, Vol. 19, (1993), pp. 197-204.
Jolly, R. and Rhin, C., “The Recycling of Lead-Acid Batteries: Production of Lead and
Polypropylene Resources”, Resources, Conservation, and Recycling, Vol. 10, September
(1994), pp. 137-143.
Jansen, J. and Hastenberg, C. V., “Identification of Plastic Parts”, Kunstoffe Plast Europe, 1
(1994), pp. 22-23.
Florestan, J., Lachambre, A., Mermilliod, N., Boulou, J. C. and Marfisi, C., “Recycling of
Plastics: Automatic Identification of Polymers by Spectroscopic Methods”, Resources,
Conservation, and Recycling, Vol. 10, April (1994), pp. 67-74.
Wan, J. K. S., Vepsalainen, K. P. and Ioffe, M. S., “Time-Resolved, Pulsed Laser Sensitized
Acoustic Technology: Application to On-Line Sorting of Waste Plastics”, Journal of
Applied Polymer Science, Vol. 54, 1 (1994), pp. 25-31.
Kenny, G. R. and Bruner, R. S., “Experience and Advances in Automated Separation of
Plastics for Recycling”, Survival Tactics Thru the ‘90’s, Chicago, Illinois, June 14-16,
Society of Plastics Engineers, (1993), pp. 83-90.
– 23 –
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
Kenny, G. R. and Vaughan, D., Optimization of Plastic Bottle Sorting, Magnetic Separation
Systems, Inc., Nashville, Tennessee (1994).
Stessel, R. I. and Pelz, S., “Air Classification of Mixed Plastics”, Proceedings of the 1994
National Waste Processing Conference, Boston, Massachusetts, June 5-8, American Society
of Mechanical Engineers, (1994), pp. 333-339.
Super, M. S., Enick, R. M. and Beckman, E. J., “Separation of Thermoplastics by Density
Using Near-Critical and Supercritical Carbon Dioxide and Sulfur Hexafluoride” in Emerging
Technologies in Plastics Recycling, (1991), pp. 172-185.
Super, M. S., Enick, R. M. and Beckman, E. J., “Density-Based Separation of
Thermoplastics in the Post-Consumer Waste Stream”, Resources, Conservation, and
Recycling, Vol. 9, (1993), pp. 75-88.
Bonsignore, P. V., Jody, B. J. and Daniels, E., “Separation Techniques for Auto Shredder
Residue” in Designing for Recyclability and Reuse of Automotive Plastics SP-867, Society
of Automotive Engineers, Warrendale, Pennsylvania (1991), pp. 59-63.
Anonymous, Thomas Register of American Manufacturers and Thomas Register Catalog
File, (1995).
Elektronic, H., “Copper Separation from Cable Scrap”, Wire Industry, May (1994), pp.
342-343.
Jody, B., Daniels, E., Bonsignore, P. and Brockmeier, N., “Recovering Recyclable Materials
from Shredder Residue”, Journal of Minerals, February (1994), pp. 40-43.
Jody, B., Daniels, E. and Brockmeier, N., “Recovering Car Plastics”, CHEMTECH,
November (1994),
Kertscher, E., “Recycling of Cable Waste”, Wire Industry, January (1994), pp. 40-41.
Leaversuch, R. D., “Industry backs pyrolysis as a recycling option”, Modern Plastics,
January (1994), pp. 93.
Anonymous, “PET Tech – The Latest Technical News in PET Recycling”, National
Association for Plastics Container Recovery (1992).
Menges, G., “New Developments in Chemical Recycling as a Sink for Problematic Waste
from Fiber-Reinforced Plastics”, Journal of Thermoplastic Composite Materials, Vol. 7,
January (1994), pp. 64-74.
Watt, D. F. and Xu, J. Z., “On the Use of Pyrolysed SMC as a Concrete Additive”,
Advanced Composite Materials:
New Developments and Applications Conference
Proceedings, Detroit, Michigan, , (1991), pp. 615-619.
Godlewski, R. and Herdle, W., “Recycling of Ground SMC into Polyptopylene and
Recovery of Scrap Azdel to Produce Quality Molded Parts”, Proceedings of 8th Advanced
Composite Conference, Chicago, Illinois, (1992), pp. 239-246.
Agarwal, K., “Pyrolysis of Sheet Molding Compound Scrap” in Sheet Molding Compounds:
Science and Technolohy, H. G. Kia Ed., Hanser/Gardner Publications, Inc., Cincinnatti,
(1993), pp. 235-246.
– 24 –
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