Measuring and testing – Vibration – By mechanical waves
Patent
1994-10-12
1996-09-24
Williams, Hezron E.
Measuring and testing
Vibration
By mechanical waves
73599, 73646, G01N 2908
Patent
active
055592929
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for the identification of a target species in a sample, in particular a method which involves the use of ultrasonic vibrations. The invention also relates to apparatus for use in such a method.
BACKGROUND TO THE INVENTION
It is often necessary to identify the type and concentration of various species present in an unknown sample. This is especially so when it is desired to reclaim or recycle materials for re-use. In this case, it is necessary to be able to test a product to identify the presence of recyclable species in it and their relative concentrations.
When recycling materials, it is especially important to be able to detect the presence and concentration of contaminants which would otherwise adversely affect the recycling process. Even a small level of contaminant can often greatly affect the properties of a recyclable material. However, often the physical properties (including visual) of a likely contaminant are very similar to those of a target species to be recycled. For instance, polypropylene and polyethylene have very similar properties. It may be desired to recycle polypropylene from a product. A concentration of any more than about 1% of polyethylene contaminating that product can adversely affect the moulding and other properties of the recycled polypropylene.
Thermoplastic waste is also widely perceived to be a major environmental problem. Approximately 85% of the polymers used in the EC are thermoplastics and the volume of waste materials continues to rise commensurate with materials consumption. Attention has focused on the economic treatment and disposal of waste materials from both commercial and domestic products, including packaging, white goods, scrapped automotive components and textiles.
Reclamation of plastics compositions and recycling of polymeric materials is of increasing interest to the industrial sector which includes materials waste collectors and separators, materials processors, product users, materials suppliers and processing equipment suppliers. However, with the inherent limitations in current identification and separation technology, it is inevitable that a relatively high percentage of recycled materials will contain contaminants.
Plastic bottle collection and recycling has also made considerable advances in recent years. However, to date sorting of PET (polyethylene terephthalate), PVC (polyvinyl chloride) and PE (polyethylene) bottles has been achieved mainly by hand, using unskilled labour. It is imperative that the reclaimed PET does not contain PVC, as a contaminant, in amounts greater than 50 ppm, because this results in the formation of low molecular weight degradation products which make processing of the material extremely difficult to control and can result in serious impairment of mechanical properties. In addition, the reclamation process can result in partial depolymerisation of the PET which also causes major processing problems.
In the UK, most plastics waste (90%) is disposed of in landfill sites, where it is hoped that the inert nature of plastics will have no long term harmful effects. Until recently, this approach was viewed as the optimum method of plastics waste disposal by the Waste Management Sector. However, rising costs per tonne of plastic disposed of in landfill has promoted a search for more economical solutions.
Incineration with energy recovery has been postulated as an alternative way of dealing with the waste problem. This approach, however, is viewed by many as both wasteful of a diminishing natural resource and environmentally unfriendly because of the potential impact of gas emissions. Another option is to recycle and reuse plastic waste directly.
Direct reclamation is thus increasingly viewed as the best approach to retaining the many benefits of plastics whilst minimising the impact associated with waste disposal.
However, increasing use of a wider range of thermoplastics and polymer blends with additives has made the identification and separation of waste materials an
REFERENCES:
patent: 4773267 (1988-09-01), Abts
patent: 5255564 (1993-10-01), Glad et al.
patent: 5305239 (1994-04-01), Kinra
patent: 5433112 (1995-07-01), Piche et al.
"Ultrasonic pulse spectroscopy of a solid inclusion in an elastic solid" by F. Bifulco and W. Sachse, Ultrasonics, vol. 13 No. 3 May 1975 p. 113.
Hull John B.
Langton Christian M.
Finley Rose M.
Schindler Edwin D.
University of Bradford
Williams Hezron E.
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