Recycling of plastics that used to end up only at city landfills or incinerators is increasing around the world. As with any technological trend, the engineering profession plays an important role. Discarded plastic products and packaging make up a growing portion of Municipal Solid Waste(MSW). The Environmental Protection Agency (EPA) estimates that by the year 2000, the amount of plastics throw away will be 50 percent greater than at the beginning of the 1990s. EPA also says that plastic waste accounts for about one-fifth of all waste in the waste stream. Over the past two decades, recycling of plastics has dramatically increased. After years of predictions that plastics recycling would never be widespread because processes were inefficient, too expensive or not practical, the tide of waste headed to the landfill is slowly being turned.
The difference between a polymer and a plastic
The term “plastics” is used to describe a wide variety of resins or polymers with different characteristics and uses. Polymers are long chains of molecules, a group of many units, taking its name from the Greek “poly” (meaning “many”) and “meros” (meaning “parts” or “units”).
The term “polymer” is often used as a synonym for plastic, but many other types of molecules — biological and inorganic — are also polymeric. While all plastics are polymers, not all polymers are plastic. Polymers are rarely useful in themselves and are most often modified or compounded with additives (including colours) to form useful materials. The compounded product is generally termed a plastic. Most people have little contact with "polymers" because most articles that they come across are actually modified and coloured and therefore are actually plastics. Polymers can be classified in many ways, based on how they are developed and perform. For this discussion of recycling, an understanding of two basic types of polymers is helpful:
- Thermoplastic polymers can be heated and formed, then heated and formed again and again. The shape of the polymer molecules are generally linear or slightly branched. This means that the molecules can flow under pressure when heated above their melting point.
- Thermoset polymers undergo a chemical change when they are heated, creating a three-dimensional network. After they are heated and formed, these molecules cannot be re-heated and re-formed.
Plastic identification; recycling code
When working with plastics there is often a need to identify which particular plastic material has been used for a given product. Most consumers recognize the types of plastics by the numerical coding system created by the Society of the Plastics Industry in the late 1980s. There are six different types of plastic resins that are commonly used to package household products. The identification codes listed below can be found on the bottom of most plastic packaging.
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HDPE High-Density Polyethylene - Milk, detergent & oil bottles, Toys and plastic bags. HDPE is called natural since that is it's natural color, and it is the most valuable because it can be made into any color when it is recycled. Other products are often packed in brightly colored bottles whiched are mixed together at recycling plants into mixed color or rainbow bales. Most of this material is later dyed black after it is processed. -
V Vinyl/Polyvinyl Chloride (PVC) - Food wrap, vegetable oil bottles, blister packages.
PETE Polyethylene Terephthalate (PET) - Soda & water containers, some waterproof packaging. Recycling PET is similar to the polyethylenes (PE). Bottles may be color sorted and are ground up and washed. Unlike polyethylene, PET sinks in the wash water while the plastic caps and labels are floated off. The clean flake is dried and often repelletized. Recycled PET has many uses and well established market for this useful resin. By far, the largest usage is in textiles. Carpet companies can often use 100% recycled resin to manufacture polyesther carpets in a variety of colors and textures. PET is also spun like cotton candy to makr fiber filling for pillows, quilts and jackets. PET can also be rolled ito clear sheets or ribbon for VCR and audio cassettes. In addition a substantial quantity goes back into the bottle market.
Recycling HDPE is a pretty simple process. The bales are broken aprt and ground into small flakes. These flakes are then washed and floated to removed and heavy (Sinkable) contaminants. This cleaned flake is then dried in a stream of hot air and may be boxed and sold in that form. More sophisticated plastic plants may reheat these flakes, add pigment to change the color and run the material through a pelletizer. This equipment forms little beads of plastic that can then be reused in injection molding presses to create new products. Some end uses for recycled HDPE are plastic pipes,lumber, flower pots, trash cans, or formed back into non food application bottles.
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LDPE Low-Density Polyethylene - Many plastic bags. Shrink wrap, garment bags. It ic chemically similar to HDPE but it is less dense and more flexible. Most polyethylene film is made from LDPE which you often see as plastic bags and grocery sacks. This scrap may be clear or pigmented and it is hand sorted and baled at recycling processing
plants.
Recycling LDPE is verry similar to HDPE except special grinders are used to handle the thin films. The films are often washed and repelletized or used directly to make new products. Some end uses for recycled LDPE are plastic trash bags and grocery sacks, plastic tubing, agricultural film, and plastic lumber.
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PP Polypropylene - Refrigerated containers, some bags, most bottle tops, some carpets, some food wrap. -
PS Polystyrene - Throwaway utensils, meat packing, protective packing. -
OTHER Usually layered or mixed plastic. No recycling potential - must be landfilled.
Plastic consumer goods not identified by code numbers are not usually collected. Plastic tarps, pipes, toys, computer keyboards, and a multitude of other products simply do not fit into the numbering system that identifies plastics used in consumer containers. There are actually thousands of different varieties of plastic resins or mixtures of resins. These are developed to suit the needs of particular products. There is limited recycling of some of these specific plastic products in truckload quantities from industrial sources. No one has entered the business of collecting a variety of these plastics in small quantities.
The Problem with Plastics Recycling
When glass, paper and cans are recycled, they become similar products which can be used and recycled over and over again. With plastics recycling, however, there is usually only a single re-use. Most bottles and jugs don't become food and beverage containers again. For example, pop bottles might become carpet or stuffing for sleeping bags. Milk jugs are often made into plastic lumber, recycling bins, and toys.
A recent development has been the bottles-to-bottles recycling of "regenerated" pop bottles. Though it is technologically possible to make a 100% recycled bottle, there are serious economic questions. Also, some critics claim that the environmental impact of the regeneration process is quite high in terms of energy use and hazardous by-products.
Currently only about 3.5% of all plastics generated is recycled compared to 34% of paper, 22% of glass and 30% of metals. At this time, plastics recycling only minimally reduces the amount of virgin resources used to make plastics. Recycling papers, glass and metal, materials that are easily recycled more than once, saves far more energy and resources than are saved with plastics recycling.
Consider this example: polyvinyl chloride (PVC) bottles are hard to tell apart from PET bottles, but one stray PVC bottle in a melt of 10,000 PET bottles can ruin the entire batch. It's understandable why purchasers of recycled plastics want to make sure that the plastic is sorted properly. Equipment to sort plastics is being developed, but currently most recyclers are still sorting plastics by hand. That's expensive and time consuming. Plastics also are bulky and cumbersome to collect. In short, they take up a lot of space in recycling trucks.
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PVC is used for packaging and other short-life consumer products, furnishings and long-life goods, mostly construction material such as window frames and pipes. Short-life products, disposed of within a few years, have caused serious PVC waste problems, especially when incinerated. The average life span of the long life products is around 34 years. Long-life PVC goods produced and sold since the 1960s are now just starting to enter the waste stream. We are now only seeing the first stages of an impending PVC waste mountain.
There are currently over 150 million tonnes of long-life PVC materials in existence globally, used mostly in the construction sector, which will constitute this waste mountain in coming decades. Taking into account the ongoing growth in production, by the year 2005 this amount will double and the world will have to deal with approximately 300 million tonnes of PVC starting to enter the waste stream. The amount of PVC waste arising in industrialised countries is already expected to grow faster than PVC production. Of even more concern is the fact that the PVC industry is rapidly expanding in Latin America and Asia, so that eventually a growing waste mountain will be generated in these parts of the world.
In the late 1980s, PVC recycling was promoted by the vinyl industry in order to make PVC more acceptable to the public and to prevent government action to limit PVC production and use. As a result, the general public and decision-makers are now accepting recycling as a technical solution to the environmental problems associated with PVC. This is especially the case in countries with advanced recycling policies, like Denmark, Germany, the Netherlands and the USA.
As a result, PVC requires separation from other plastics and sorting before mechanical recycling. PVC recycling is particularly problematic because of high separation and collection costs, loss of material quality after recycling, the low market price of PVC recyclate compared to virgin PVC and, therefore, the limited potential of recyclate in the existing PVC market. Feedstock recycling of PVC is hardly feasible at present, from an economic or an environmental perspective, and it is doubtful whether it will ever play a significant role in PVC waste management. The PVC industry seems to acknowledge that PVC recycling is no solution for PVC waste and it therefore is not surprising that industry is now lobbying for PVC incineration as a recovery option (for energy, hydrochloric acid and/or salt) in Western Europe and Japan and for landfilling in the USA and Australia. This forces local authorities to shoulder the burden of pollution and costs from PVC consumption.
Incineration is not a sustainable option for dealing with waste. Less energy is generated from burning the plastic than was used to make it, and incineration also means that the carbon contained within it is emitted as CO2 - a greenhouse gas. Toxic substances are also emitted, and large amounts of solid wastes are produced as slag, ash, filter residues and neutralisation salt residues. Part of this needs to be disposed of as hazardous waste.
Despite these concerns, PVC production is still increasing, especially in developing economies where PVC consumption is being encouraged. PVC waste is exported from the USA, Europe and Australia to developing countries, often for recycling into lower quality products such as shoes and low quality pipes, or ‘downcycling’. According to the Indonesian Environment Minister, up to 40% of the plastic waste imported into Indonesia is not recycled but directly disposed of, partly as hazardous waste. Downcycled products will eventually be dumped or burned since downcycling simply delays the inevitable need to dispose of PVC plastic waste. In light of the large volume of long-life PVC products due to become waste in the coming decades, and the projected increase in PVC production, it becomes apparent that an international PVC phase-out is urgently required. Only this will put a halt to a growing, dangerous and intractable waste problem.
Political frameworks for PVC phase-outs already exist. The North Sea Ministers Conference agreed in 1995 to stop environmental emissions of hazardous substances within one generation. According to the Swedish Chemical Committee, PVC has no place in a sustainable society and should be phased out for all uses by the year 2007. Denmark has proposed restrictions on the use of softeners, lead and other additives used in PVC plastic and is questioning the recycling potential claimed by the PVC industry. The Czech Republic agreed to phase-out production, imports and use of PVC packaging from 2001 onwards and Switzerland has banned PVC drinking bottles in 1991.
Biodegradable polymers, By Dr P. J. Barham, University of Bristol
In Europe and Japan there are few sites left which can be used for landfill. Since the main bulk of domestic waste is made up of plastics there is a great deal of interest in recycling plastics and in producing plastic materials that can be safely and easily disposed of in the environment.
One option is to produce polymers that are truly biodegradable, and which may be used in the same applications as existing polymers. The requirements for such materials are that they may be processed through the melt state, that they are impervious to water, and that they retain their integrity during normal use but readily degrade in a biologically rich environment.
Polyhydroxyalkonates are a family of naturally occurring polyesters, produced in the form of carbon storage granules by many bacteria. Zeneca Bioproducts is currently producing these polymers on a pilot plant scale under the trade name BIOPOL TM. The Bristol Polymer group has been actively involved in the development of these polymers, especially in determining optimum processing conditions.
Solid-State Shear Pulverization: A New Technology for Plastics Recycling and Powder Production
At Polymer Technology Center (PTC), Department of Chemical Engineering,Northwestern University, a patented, breakthrough technology for plastics recycling has been developed that eliminates sorting by type or by color. This technology, called Solid State Shear Pulverization (S3P), is a continuous one-step process for recycling unsorted pre- or post-consumer plastic waste. Unlike conventional recycling, S3P produces uniform powders that can be used to make a variety of high-quality products.
S3P subjects polymers to high shear and high pressure while rapidly removing frictional heat from the process to prevent melting. S3P can convert multi-colored, unsorted (commingled) waste, industrial plastic scrap, and virgin resins to a uniform, light-colored, partially reactive powder of controlled particle size and particle size distribution. These powders are suitable for direct melt conversion by all existing plastic processing techniques. This energy-efficient process pulverizes it into powders of particle sizes ranging from coarse (10 mesh/2000microns) to very fine (635 mesh/20microns). The resulting powders can be used in a variety of consumer goods and special products. Non-food applications are seen throughout industry in everything from automotive and appliance parts to business equipment and furnishings. Samples made from either single polymers or from commingled mixtures with the S3P process often shows enhanced mechanical properties (e.g. elongation, tensile strength and flexural strength) as compared to samples which did not undergo the S3P process.
Near Infrared Spectroscopy
A. Fiber Optics for Absorption and Reflexion Measurements - Fraunhofer-Institut für, Chemische Technologie ICT
An integral recycling operation for mass consumer electronic and electric products has to be based on large scale disassembly processes. In order to reuse polymeric materials for high-class products and to minimize the amount of chemical waste, polymer identification and analysis of additives are required. Economic aspects demand fast response times (< 1 s), easy handling and integration in automated or at least semi-automated systems. As macroscopic physical methods, e.g. based on density measurements, are not sufficient to separate polymers, identification has to use methods monitoring structural or molecular properties of the plastic under investigation.
The near-infrared (NIR) spectral range allows to monitor structural or molecular properties of the plastic under investigation. At the Fraunhofer-Institute for Chemical Technology (ICT) the application of near-infrared spectroscopy (NIRS) for identification of polymers has been studied widely. The presented spectrometer system is based on fiber optics for absorption and reflexion measurements, an acoustooptic tunable filter (AOTF) and a transputer system. It is able to detect 1,000 spectra/s and to identify 20 pieces/s.
In the near-infrared (NIR) spectral range (700 to 2,500 nm) molecules absorb light by overtone or combination vibrations. Registration of spectra of bulky samples which are of practical interest in recycling processes is possible. C-H, O-H, N-H and C-O bands observed in NIR spectra are characteristic of polymers and enable identification of most commonly used materials.
Results
Polymeric samples differ in structural composition of aromatic or aliphatic groups, as can be seen from the spectra. Plastics, especially when applied in mass consumer products, contain fillers, plasticizers, dyes and additives. These components, as well as processing and surface treatment strongly influence the spectra obtained from plastic materials. Especially carbon black absorbs all light and even small amounts (> 0.1 %) reduce NIR light reflexion or transmission to levels which are not sufficient for identification. Nevertheless identification of non-black polymers is almost always possible.
The identification of plastics requires the wavelength range of 1,000 to 1,800 nm if the plastic materials are from a similar type of material like the references (e.g. household waste or glass fiber reinforced plastics of cases and parts from electronic products). Therefore, in this application, an uncooled Ge detector can be used.
In case of household waste mainly PE, PP, PET, PS and PVC are of interest. So, the range could be reduced to 1,600 to 1,800 nm. In electronic products ABS, PA, PP, PBT, PC and PMMA are found in larger quantities. N-H groups in PA require an extension of range to below 1,400 nm.
Household waste gives spectra of sufficient quality so that the range of 1,600 and 1,800 nm can be scanned in 1 ms or less. Glass fiber reinforced materials of technical products need longer scan times or spectra averaging.
| samples (uncleaned, not black) | Household waste | Technical plastics |
|---|---|---|
| spectral range | 1,600 - 1,800 nm | 1,300 - 1,800 nm |
| scan speed | 200 nm/ms | 300 nm/ms |
| spectra averaged | 1 | 200 |
| spectra/identification | 20 during moving | 1 |
| detector head | enlarged area | small fixed area |
| sample position | moving ca. 2 m/s | fixed |
B. Spectroscopic Infrared Focal Plane Array (FPA) - Applied Spectroscopy June 1997
A spectroscopic near-infrared imaging system, using a focal plane array (FPA) detector, is presented for remote and on-line measurements on a macroscopic scale. On-line spectroscopic imaging requires high-speed sensors and short image processing steps. Therefore, the use of a focal plane array detector in combination with fast chemometric software is investigated. As these new spectroscopic imaging systems generate so much data, multivariate statistical techniques are needed to extract the important information from the multidimensional pectroscopic images. These techniques include principal component analysis and (PCA) and linear discriminant analysis (LDA) for supervised classification of spectroscopic image data. Supervised classification is a tedious task in spectroscopic imaging, but a procedure is presented to facilitate this task and to provide more insight into and control over the composition of the datasets. The identification system is constructed, implemented, and tested for a real-world application of plastic
identification in municipal solid waste.
Polymer Crackin - Please see COGSYS
While old plastics can be re-cycled by melting and reforming into new uses, as volumes get larger, it gets harder and harder to find enough outlets. The solution is to break the plastics down, extract the valuable hydrocarbon portion and use this to make fresh plastics and other valuable feedstocks.
BP Chemicals in Grangemouth has a lead technology in this area which it calls Polymer Cracking. This has reached metal development rig stage with a throughput of 1 kg/hr with a 20 kg/hr unit for scale-up tests currently being commissioned. This will be followed by a 100 kg/hr unit with all the envisaged design features.
The plant is monitored using an integrated Real-Time Database (RTD) system developed by BP Chemicals themselves.
The requirement was for a sophisticated and flexible display system that could be easily augmented with intelligent rules, for assisting in the control of the process. It was important that the solution could be easily integrated into RTD.
As in any research and development environment, the plant may change several times during its lifetime, and this demands a large degree of flexibility in the operator interface. It was important that the system could be developed and maintained by technologists such as development chemists.
The requirement for rules or intelligence stems from the need to design a commercial plant that is robust and easy to operate so that the plant can be operated by non-specialist personnel. Full scale plants will be located with Polymer Production, Petrochemical Refineries or Recycling Complexes. In most cases, and especially the Recycling Complexes, in depth knowledge of the process is unlikely to be available on demand. This could have consequences in terms of the overall running of the plant, both in terms of maintaining efficiency and product quality, but perhaps more importantly in terms of diagnosing and rectifying problems.
In the United States 75 billion pounds of plastic are produced every year, unfortunately the majority of this plastic ends up in landfills. When plastic is dumped into landfills the decomposition process can take anywhere from 10 to 30 years. Recycling has therefore become a reasonable solution to the landfill problem.
There are five factors that are necessary in order for the recycling of plastic to be a successful process. First, the supply of used plastic has to be of a large quantity. This large quantity of plastic is collected at certain areas, which is the second step. Once the plastic is collected, the sorting and separating process begins; this is the third step in the process. The sorting and separating process depends upon the type of polymers that make up the plastic. Plastic products are given codes to help the sorting and separating process. The fourth step in plastic recycling is reprocessing. The reprocessing of polymers includes the melting process, the melting process can be accomplished if the polymers have not been widely cross-linked with any synthetics. If the cross-linking of polymers contain too many synthetics, the polymers will be difficult to stretch and less pliable. The final step is the manufacturing of the melted plastic into new products.
The codes on plastic recyclable containers are what help most in the sorting and separating process. The six categories of plastics are separated into two areas: polyethelyne plastics and polymer plastics. The polyethelyne plastics are labeled HDPE, for high density polyethelyne; or LDPE, for low density polyethelyne. The four polymer plastics that are recycled include polyvinyl chloride, labeled V; polystyrene, labeled PS; polypropylene, labeled PP; and polyethylene terephthalate, labeled PETE. These names and labels can seem confusing, but they are a necessity in the recycling process.
There are four types of recycling processes that usually occur: primary, secondary, tertiary, and quaternary. The primary recycling process is recycling materials and products that contain similar features of the original product. This process is only feasible with semi-clean industrial scrap plastics, therefore this process is not widely used. Secondary recycling allows for a higher mixture of combination levels in plastics. When the secondary process of recycling is used it creates products such as fenceposts and any products that can be used in the substitution of wood, concrete, and metal. The low mechanical properties of these types of plastics are the reason why the above products are created. Tertiary recycling is occurring more and more today because of the need to adapt to the high levels of waste contamination. The actual process involves producing basic chemicals and fuels from plastic. The last form of recycling is the quarternary process. This quarternary process uses the energy from plastic by burning. This process is the most common and widely used in recycling. The reason this process is widely used is because of the high heat content of most plastics. Most incinerators used in the process can reach temperatures as high as 900 to 1000 degrees Celsius. For the sake of the environment the new techniques being used with the incinerators have decreased the amount of air pollutants being released.
The use of incineration in the quarternary process is most beneficial because through the high temperature heating process the incoming waste is reduced by 80% in weight and 90% in volume. The materials left over form this process are then placed in landfills.
Why Worry About Recycling Plastics?
A current promotional program sponsored by the plastics industry emphasizes the positive contributions that plastics make. And claims listed in those advertisements are accurate.
But as shown in the article on the preceding page, the largest single use for plastics is packaging. Because packaging has a short lifespan, it makes up a large portion of the plastics waste stream. But where does that “waste stream” lead?
In general, the Environmental Protection Agency says that in the early 1990s about 80 percent of all municipal solid waste was sent to landfills, 10 percent was incinerated and 10 percent was recycled. While more and more plastic is being recycled, the EPA estimates that plastics make up about 20 percent of the solid waste that is landfilled.
Most consumers think that the slow degradation of plastics is the primary reason that plastics should be recycled. However, research has shown that other waste, such as paper, wood and food wastes, also degrade very slowly in landfills.
The more serious problem with plastic waste concerns the additives contained in plastics. These additives include colorants, stabilizers and plasticizers that may include toxic components such as lead and cadmium. Studies indicate that plastics contribute 28 percent of all cadmium in municipal solid waste and about 2 percent of all lead. Researchers don’t know whether these and other plastic additives contribute significantly to products leached from municipal landfills.
How toxic are plastics that are burned? Researchers don’t know that, either. Plastics that contain heavy-metal-based additives may also contribute to the metal content of incinerator ash. The EPA is looking for substitutes for lead- and cadmium-based additives.
One additional concern relates to use of petroleum products. All plastics began their lives as petroleum. By increasing plastics recycling, scientists and engineers are able to reduce dependence on petroleum.
Before plastic waste can be converted into new products, the various types of plastics must be separated. Initially plastic reclamation companies relied on manual sorting — either by consumers themselves or by paid workers — but manual sorting is considered too unreliable and too expensive.
At least two organizations have developed systems for automated plastics sorting. National Recovery Technologies received the EPA’s Small Business of the Year National Award in 1991 for its efforts in developing and marketing a high-speed, automated system that efficiently separates vinyl containers (those marked #3) from mixtures of whole or crushed post-consumer plastic containers. NRT says that the presence of chlorine atoms within vinyl resins triggers a computer-timed air burst that separates vinyl containers from the mixed plastic stream. The company also developed a system that optically scans mixed plastics to separate PET soda bottles from HDPE milk jugs, green PET
from clear PET, as well as other specifications.
Sandia National Laboratories, which works with the U.S. Department of Energy, has designed a device to classify plastic waste into one of the seven plastics categories. Near-infrared light is used to distinguish one plastic from another using the vibrational characteristics unique to each. Sandia engineers report that the device can classify many types of plastics with a success rate of 98 to 100 percent. The laboratory has issued a license for commercial development of this new device.
Old ABS Phone Housings Recycled Into Innovative Mounting Panels
Seeking new uses for recycled plastic from old telephones, AT&T Bell Laboratories engineers are remolding discarded phone housings into mounting panels for AT&T’s business telephone systems and improving service to business customers as well.
“Until now, when a telephone reached the end of its life, AT&T would sell the plastic to a recycler who would grind it up and resell it into the secondary market, where it was made into products ranging from tape cassettes to park benches,” said Werner Glantschnig, a member of Bell Laboratories technical staff and the project’s leader.
“However, we wanted to see if we could close the loop ourselves and re-use these millions of pounds of ‘ABS plastic flake’ in a way that makes both environmental and business sense.”
ABS — or acrylonitrile-butadiene-styrene — plastic flake can’t be made into new telephones because colors change during re-melting, and the plastic loses the smooth, glossy finish AT&T requires for its phone housings.
“When we mold the ABS into telephone system mounting panels, the colors disperse nicely into a uniform gray and the finished product meets all of our requirements,” said Louis D’Anjou, another Bell Laboratories engineer and the panel’s designer.
With these ABS panels, AT&T’s supply centers can now assemble and test business telephone systems before delivery to the customer’s premises. Previously, these panels had to be custom-made from plywood and the system assembled and tested at the customer’s location. In addition to reducing the use of wood, the new method is far more efficient, reducing both the time and cost of installation.
AT&T engineers and designers are looking into other possible uses for the ABS plastic flake, including spools for copper and fiber optic telephone cables.
“This is encouraging evidence that environmental awareness and the concept of ‘design for environment’ are spreading through the AT&T design community,” said John C. Borum, AT&T environment and safety engineering vice president. “Our goal is to remain in the vanguard of environmentally responsible corporations by recycling as many of our products as we can.”
Junk Car Seats Lead To New Technology
Throughout the environmental movement, researchers are concerned with products that are discarded in large quantities. Junk cars are one such product. But junk cars pose unique problems because of the combination of products used in automaking. Used metals from junk cars have long been recycled, and now many researchers are turning their attention to other auto components.
The Center for Excellence in Polymer Science and Engineering at the Illinois Institute of Technology has focused one project on the 400 million pounds of polyurethane foam scrapped each year from junk cars. IIT has patented a solid state sheer extrusion process and apparatus that could be used to recycle that waste, along with a broad range of other polymer wastes and rubbers.
IIT’s system, known by the acronym SSSE, pulverizes polymeric material, producing fine powders that have numerous applications for industry. The advantage of SSSE is that it can be applied economically to many types of natural and synthetic polymer wastes. The Center for Excellence in Polymer Science and Engineering points out that many recycling processes developed to date have been limited to certain types of waste. Most processes have not been economical, especially in the amount of energy needed, they add, and the reclaimed materials have not been produced in forms that are needed and usable for re-manufacturing.
The SSSE technology has been optioned to a New York firm for possible development. More information is available through IIT’s Office of Public Relations, (312) 567-3104, or at IIT’s web site, www.iit.edu.
Research Into Chemical Recycling Could Open New Opportunities
The U.S. Department of Energy conducts on-going research on plastics recycling. This report highlights new approaches to chemical recycling. Recycling of plastics can be costly and difficult because of constraints on waste contamination and inadequate separation prior to recycling. Chemical recycling could remove some of those restraints.
Pyrolysis and hydrolysis are two processes that have shown promise in the recovery of basic chemicals and fuels from waste plastics. Pyrolysis is a process in which plastic wastes are heated in the absence of oxygen in a closed chamber. The products of pyrolysis may be used as a chemical feedstock or fuel. Hydrolysis decomposes plastic wastes through a series of chemical reactions.
Research sponsored by the U.S. Department of Energy’s Office of Industrial Technologies at the National Renewable Energy Laboratory has led to the development of a new process based on the pyrolysis of certain waste streams. This process retrieves monomers, the basic building blocks of a polymer, and high-value chemicals that are sufficiently pure to use in making new plastics. The advantage of this process is that the waste plastics do not have to be separated ahead of time, thereby eliminating a labor-intensive step in current processes. It also will reduce the cost of the monomers and chemicals and will reduce consumption of petroleum, the source of chemical feedstocks used to produce plastics.
In the new process, monomers and high-value chemicals are retrieved from manufacturing or post-consumer wastes through sequential pyrolysis. The reaction products undergo detailed chemical analysis to determine conditions that allow control of pyrolysis reactions. This allows the design of a process to collect the desired products in high yields, reducing requirements for subsequent separation and purification of the target product. NREL has filed patent applications to cover the process for a total of seven mixed plastic waste streams.
For example, NREL has demonstrated the new process of waste carpet recycling. Caprolactam, the valuable monomer of Nylon 6 used in about half of all carpet fibers, can be isolated with yields of 85 percent. This can be done without separating the nylon from the backing material.
An economic evaluation of recycling caprolactam performed by an independent economic firm shows the applications to be promising. Those findings project that a commercial-size plant recycling 100 million pounds of waste carpet could produce high-grade caprolactam for about 15-50 cents per pound. The chemical currently sells for 90 cents to $1 per pound. In other words, recycling caprolactam could reduce its cost by 50 percent or more.
Other applications of the chemical recycling process include recovering terephthalic acid from polyethylene terephthalate, or PET, in mixed plastic bottles and recovering styrene from mixed residential plastics. PET recycling does not have as favorable economics as the polyurethane application because of the lower value of plastic bottles but the potential volume of the waste stream is very large. Researchers estimate that 900 million pounds of thermoplastic polyester resin, of which PET is a major component, could be recycled each year.
Researchers are expanding the technology base for the chemical recycling process and are identifying new, promising applications for specific waste streams. Experiments are currently underway using engineering-scale reactors to confirm process reactions and to refine operating conditions.
Here’s a simple activity to share with students to help them understand some characteristics of plastics and other polymers. It was developed for the Sandia National Laboratory “Science and Math Carnival.” This activity is suggested for students in third through eighth grade.
Gluep is a polymer made from borax (sodium tetraborate) and white glue. Each of these materials is a polymer already. Glue is a mixture of polyvinyl acetate and polyvinyl alcohol. Borax forms long borate chains in an aqueous solution. When the two materials are mixed together and the mixture is kneaded by hand, crosslinking of the polymer chains occurs as a result of hydrogen bonding with water molecules which links the two polymer chains. The physical properties of the mixture are quite different from the properties of the individual compounds. The resulting Gluep is a semi-solid plastic-like material.
Materials
4 percent borax solution (1/4 cup of borax dissolved in 1 quart of tap water)
White glue mixture (50:50 mixture of glue and water, mixed well)
Food coloring
Ziploc plastic bags
Procedure
1. Pour 15 ml (1 tablespoon) of the borax solution into the bag.
2. Add three drops of food coloring.
3. Add 60 ml (4 tablespoons) of the white glue mixture.
4. Zip the plastic bag tight.
5. Knead thoroughly until the color is uniform and water is no longer visible. Consistency should be reached within 10 minutes.
6. Remove Gluep from the bag by turning the bag inside out and rubbing the Gluep from the sides.
7. Store the Gluep in the plastic bag.
Questions
How is Gluep like a solid? Like a liquid? What happens if you leave Gluep out of the bag? What happens if you freeze it?
Extension
Try other experiments with the Gluep. What happens when extra borax solution is added? What happens when extra glue is added? What happens if a base or acid is added during mixing? After the Gluep has hardened?
For a complete lesson plan for this activity, visit Sandia’s web site at www.ca.sandia.gov/outreach /htm/gluep.html.
The PET bottle — the bottle consumers know as #1 soda bottles — was patented in 1973 by chemist Nathaniel Wyeth, brother of distinguished American painter Andrew Wyeth.
The first PET bottle was recycled in 1977.
The average household generates about 17 pounds of used PET bottles each year. That is equal to the amount of used aluminum.
Eight two-liter bottles equals about a pound of PET.
When PET bottles are crushed and tied into 48-inch bales, one bale can hold about 4,800 bottles and weighs about 1,200 pounds.
How is PET recycled?
Five PET bottles yield enough fiber for one extra-large T-shirt or one square foot of carpet. (Half of all polyester carpet manufactured in the United States is made from recycled plastic bottles.)
Twenty-five two-liter bottles can make one sweater.
Five two-liter PET bottles yield enough fiberfill for a ski jacket.
It takes 35 two-liter PET bottles to make enough fiberfill for a sleeping bag.
Used milk jugs (#2 HDPE) become:
Lumber substitutes (like those green plastic park benches)
Base cups for soda bottles
Flower pots
Pipe
Toys, pails and drums
Traffic barrier cones
Trash cans
The American Plastics Council reports that consumers recycled almost half of all PET soda bottles produced in 1994. About one-quarter of all milk jugs were recycled.
Recycling: The Next Generation?
No one can predict what the next generation of recycling research and engineering will bring. Young engineers — really young engineers — are already contemplating the question. If this report from eighth-grader Nick Gidzak of Polar Bay, Manitoba, Canada, is any indication, the sky’s the limit.
Recycling Plastics and Mixing It With Cement to Make Bricks
This year, I entered my school science fair and got a silver medal for this project. I went to the divisional science fair and got a gold medal and the engineering award. When I went to the Manitoba Schools Science Symposium, I got an outstanding project award by the Professional Engineering Society of Manitoba.
For my project, I cut up plastic milk cartons and plastic two-liter pop containers and mixed this with cement to make bricks. I made three bricks with different amounts of plastic mixed with cement. The first brick was made with the most plastic. The second had half as much. The last brick had no plastic.
After I made the bricks, I left them outside for four months. It snowed, rained and was sunny. After four months, I brought them inside. I then pumped water over the bricks for two weeks. The water wore away the bricks and show how much erosion effect it did. The results were that the brick with the most plastic mixed in showed the least amount of erosion.
European Union Legislation - April 14, 1998
A European Union legislative target to recycle a minimum of 15 percent of plastic packaging waste by 2001 is close to being achieved, judging by the latest annual figures released by the Association of Plastic Manufacturers in Europe (APME).
The recycling rate for plastics packaging in the European Union (EU) rose from 14 percent in 1995 to 14.7 percent in 1996 as a proportion of the total plastics packaging waste generated, while the proportion of the waste incinerated - with energy recovery - dropped from 18 to 16 percent. The total amount of plastic packaging waste generated in Europe during this period increased.
Under a 1994 EU directive on packaging, member states are required to recover at least 50 percent and recycle at least 25 percent of all packaging waste by mid-2001. A minimum of 15 percent recycling for each packaging material must also be achieved.
EU member states have already begun considering the next set of targets under the directive although the European Commission is not expected to produce proposals before the end of the year. According to industry sources, some member states have already indicated that they want the target raised to a minimum 25 percent recycling rate for each packaging material. Other governments are reported to be opposed to setting new targets until data on the recovery and recycling of packaging waste are improved.
A prominent packaging industry spokesman last month called on governments to postpone discussionof post-2000 targets under the packaging directive until better data is available. Julian Carroll, director of the Brussels-based packaging organisation, Europen, said the packaging directive was in "danger of failing" because of a lack of understanding of the industry.
APME's figures also show that total plastics waste rose 5 percent from 16.05 million tonnes in 1995 to 16.87 million tonnes in 1996. While the material recycling rate rose for the third year running, from 8 to 9 percent, the proportion incinerated with energy recovery fell slightly from 17 to 15 percent. The overall recovery rate dropped from 26 to 24.5 percent. Austria recorded the highest rate for mechanical recycling of 20 percent, followed by Germany with 15 percent.
Feedstock recycling of plastics, where materials are broken down chemically and thermally into their constituent molecules and reprocessed, increased by 150 percent from 99,000 tonnes to 251,000 tonnes.
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