Plastics identification

Details Plastics identification Plastics identification

1995-07-21

1997-03-04

Regan, Maura K.

Electricity: measuring and testing

A material property using electrostatic phenomenon

Frictionally induced

324452, 324 711, G01R 2726

Patent

active

056083262

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for identifying different plastics materials. The apparatus and method are particularly (but not exclusively) suitable for use in the plastics industry, for separating plastics components into chemically similar groups, as a first stage in, for instance, the recycling of the plastics materials. In this specification, "plastics" includes both thermoplastic and thermoset materials, whether in the form of solid or foamed material and also includes natural and synthetic rubbers and any composite material which is a combination of any of these materials. The invention is also applicable to such materials in which additives (plastics or non-plastics) have been included.
One field of application is the recycling of motor car components. When a motor car is scrapped, its saleable components such as battery, tyres or radio are removed, usually for use in other vehicles. The metal parts of the scrap car are generally recycled, and what remains is shredded and used as landfill.
The remainder that is used for landfill consists principally of a mixture of plastics materials. For environmental and/or economic reasons it is desirable to be able to recycle such waste plastics material. However, it is not possible effectively to recycle mixtures of waste plastics without first separating the plastics into chemically similar groups or families. Failure to achieve this separation would mean that unknown proportions of different plastics were incorporated in the melt during the reclaim process. The presence of other plastics components in a blend may necessitate changes in processing conditions or lead to unacceptable changes in the physical properties of the finished recycled material.
A requirement for any industrial method of identifying plastics materials for recycling is that the identification is made quickly, preferably in less than one minute per sample. Slow identification speeds would slow down the rate at which components could be grouped according to plastics type, and this can have a significant effect on the economics of any recycling process. In the recycling of motor car components, it is conventional to identify components of value before they are stripped from the car, and if identification of plastics types takes too long, the process of motor car disassembly is slowed down, making it less economic. Currently, however, there is no quick and simple method for identifying the chemical constitution of a plastics component, and therefore no simple method of separating such plastics materials is available.
The number of families of plastics materials which are in common industrial use is relatively small, and in practical terms it is likely to be necessary only to distinguish between about seven or eight different families of plastics. In this specification, the plastics discussed will be referred to by their common acronyms, which are identified as follows:


______________________________________ PP Polypropylene PA Polyamide (nylon) PBT Poly (butylene terephthalate) POM Polyoxymethylene/Polyacetal ABS Acrylonitrile butadiene styrene PET Poly(ethylene terephthalate). PC Polycarbonate PVC Polyvinylchloride PE Polyethylene ______________________________________
The physical properties of plastics from any one family can vary considerably depending on the addition of additional components such as fillers and plasticisers, but for the purposes of recycling of plastics, it is of most importance just to be able to identify the plastics family to which a piece of material belongs.


SUMMARY OF THE INVENTION

According to the present invention, there is provided a method for identifying plastics materials, the method comprising the steps of preparing a clean, substantially charge-free surface on a piece of unidentified plastics material, rubbing different areas of the surface with different reference materials, each reference material being of a known, different position in a triboelectric series, and measuring the polar

REFERENCES:
patent: 3733544 (1973-05-01), Petrick
patent: 4685569 (1987-08-01), Osaki
patent: 5341103 (1994-08-01), Dasgupta et al.
patent: 5455514 (1995-10-01), Pazda et al.
Journal of Physics vol. 9, No. 3, pp. 226-229 Mar. 1976; Ohara et al.; Apparatus for Simultaneous Measurements of Static Electricity and Friction of Polymer Films.
Textile Research Journal, vol. 24, No. 9; Sep. 1954 Kirkwood et al.; Measurement of Triboelectric Response of Raw Cottons.

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