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MEEF - Recycling Technologies  - previous page

 


The Problem with PVC

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.

Independent research shows that by the year 2005, it will only be possible to mechanically recycle 15-30% of PVC consumed, and at a very high cost. It is virtually impossible to separate, collect and recycle the remaining 70-85%. Thus for 70-85% of PVC waste, recycling is not even an option for the mid- to long-term. A major problem in the recycling of PVC is its high chlorine content of raw PVC - 56% of the polymer’s weight - and the high levels of hazardous additives added to the polymer to achieve the desired material quality. Additives may comprise up to 60% of a PVC product’s weight. Of all plastics, PVC uses the highest proportion of additives.

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.

New Developments

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.



At ICT a fast scanning AOTF-NIR-spectrometer has been developed for this purpose. Scan speed of the spectrometer can reach 1,000 nm/ms with a time delay of 0.01 ms between two spectral scans. More than 100 spectra can be stored. At lower scan speeds wavelength resolution reaches 2 to 3 nm. For identification two systems have been developed, used for identification of technical plastics in mass consumer products (cases of tools, electronic products etc.) and of plastics in household waste (bottles, cups etc.).








 


Two detector heads were developed. One detector head has a fixed measuring plane and can be operated manually or automatically. The second detector head has an enlarged measuring plane and allows simultaneous observation of reflected and transmitted light of moving samples.




 

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.

 

Parameters for Identification

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

A statistical study of samples (not dyed black) from real uncleaned plastic waste showed that more than 95  % of the samples were identified. Labels, dyes and inscriptions on household waste did not disturb  identification significantly. Erroneous identifications lay below 0.1 %.

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 Cracking

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.
 

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