Identify plastic

Pattern of Plasticizer Analysis. Use of the analytical methods discussed here allows a general pattern for separating and identifying plasticizers to be designed which allows quick and simple characterization, at least for the more frequently occurring substances. 

Kenneth E. Kolb and Doris K. Kolb, "Method for Separating or Identifying Plastics,"... 

Identifying Plastics by Their Densities Experiments with Films... 

Kolb, K. E., and D. K. Kolb. 1991. Method for separating or identifying plastics. Journal of Chemical Education 58 348-49. 

Identifying Plastics by their Densities Experiments unth Films... 

There are different types of plastics that are usually identified by their composition and/or performance. As an example there are virgin plastics. They are plastic materials that have not been subjected to any fabricating process. NEAT polymers identify plastics with Nothing Else Added To. They are true virgin polymers since they do not contain additives, fillers, etc. They are very rarely used. Plastic materials to be processed are in the form of pellets, granules, flakes, powders, flocks, liquids, etc. Of the 35,000 types available worldwide there are about 200 basic types or families that are commercially recognized with less than 20 that are popularly used. Examples of these plastics are shown in Table 1.1. 

Postforming identifies plastic sheet, rods, tubes, and other profile shapes that are formed into different shapes (coils, corrugated tubings, tubular nets, etc. Its major use is inline with an extruder processing... 

It can therefore be concluded that a steady increase in the use of plastic for packaging materials, components and devices can be envisaged. Any trend to identify plastics suitable for pharmaceuticals (as already exists for foods) could possibly assist the industry, at least in the initial selection of materials. The fact that the quantities used by the pharmaceutical industry will never be large compared with, say, the food industry should make the industry aware that any increase in more stringent standards can only be achieved by an on-cost. Sharing standards with the food industry, whether it is related to materials or converted items, may produce an acceptable compromise. 

The ability of plastics to float on the surface of a beaker of tap water at 20°C is related to their density at that temperature. The density of water at 20°C is approximately 1 g cm-3. If a small sample floats on the surface of the water, it has a density lower or equal to one at the same temperature if it sinks, it has a density greater than one. Polyethylene, polypropylene and polystyrene float on water while other plastics sink, Bakelite and casein having the highest densities. The flotation test is a rough method to identify plastics since results are dependent on the physical form of the plastic. Foams contain cells filled with air, so their densities will be lower than a solid block of the same type of plastic. 

Chapter 5 discusses the reasons and techniques for identifying plastics in collections. In addition to establishing the age and technological history of a plastic, identification indicates the factors and pathways by which degradation is likely to occur and thus helps the conservator to develop a treatment strategy. Simple tests enable identification of the polymer type while instrumental techniques are necessary if the various components are to be characterized. This chapter describes simple and non-destructive tests, simple and destructive tests, chemical spot tests and instrumental analytical techniques which are applied to plastics in collections today. 

Appearance and odour are the major non-destructive simple tests used to identify plastics. 

The flotation test is a rough method to identify plastics since results are dependent on the physical form of the material. Foams contain cells filled with air, so their densities will be lower than a solid block of identical dimensions of the same type of plastic. Water-sensitive or absorbent fillers such as paper... 

Two types of heating test are used to identify plastics. The bum or flame test requires a sample of approximately 2 X 4 cm (Braun, 1996). A Bunsen burner is adjusted to its lowest setting and forceps are used to hold the sample over the flame. The colour of the flame and behaviour of the sample are recorded including its ability to melt or drip and whether it self-extinguishes or continues to burn after removal from the flame. Acrylonitrile-butadiene-styrene, acrylics, cellulose acetate, cellulose nitrate, polystyrene, polyurethane and polyesters... 

The instrumental analytical techniques discussed in this chapter are those used most frequently to identify plastics in collections. There are many techniques that are used in the plastics industry or university research laboratory which provide extensive information about synthetic materials, but which have not yet found a place in the conservation workshop. This may be attributed to the high cost of the instruments and their maintenance. For this reason they have not been included here. High resolution solid state nuclear magnetic resonance spectroscopy is one such technique which may well be found in many museum laboratories by 2015, but is not available to such institutions today (Lambert et al., 2000). Descriptions of instrumental analytical techniques have been divided into those used to identify polymers, those to examine fillers and those to characterize plasticizers, stabilizers and flame retardants. 

Plasticizers are attached to the polymer by weak physical bonds rather than chemical ones, so can be separated readily by solvent extraction. A suitable solvent should selectively dissolve the plasticizer from the polymer. Methanol is frequently employed. Excess methanol should be dried off at 105°C. Infrared spectroscopy can be used to identify plasticizers by smearing the sample on one side of a KBr tablet and running a transmission spectrum or by examining the neat extract by ATR-FTIR spectroscopy. The resulting spectra can be compared with those in a specialized database of additives (Scholl, 1981). 

To increase the precision of quantitative analysis, the plasticizer sample is diluted with carbon disulfide, its infrared absorption measured, and compared with absorptions standard of standard samples prepared also in CS2 to cover the range of concentrations from 0.5 to 3 mg/ml. For each suspected (identified) plasticizer, a series of standards has to be prepared and measured. It is also important to select a suitable wavelength for quantitative analysis. For dioctyl phthalate bands at 1725 and 1121 cm" are usually used. For tricresyl phosphate band at 1191 cm is used. Similar to gravimetric method, the results are subject to various interferences when mixtirres of plasticizers or mixture of plasticizers with other additives ate used. 

Thermal analysis is well suited for characterizing and identifying plastics, as their properties are temperature dependent. It involves methods in which the substance is subjected to a controlled temperature program and the changes in the physical and chemical properties are measured as a function of temperature or time. The ambient atmosphere also influences the properties of plastic. Thermal analysis comprises traditional techniques differential scanning calorimetry (DSC), differential thermal analysis, thermogravimetric analysis, thermomechanical analysis, and more recent methods pressure differential scanning calorimetry, dynamic mechanical analysis, and differential photocalorimetry. 

Automated sorting systems use various technological devices to identify plastics in materials rather than relying on embedded codes. Capital investment is generally higher... 

Various systems are now available to quickly and automatically identify plastics by resin type—or at least to distinguish between desired and undesired materials. Many of these rely on differences between resins in absorption or bransmission of various wavelengths of electromagnetic radiation. Many can also separate plastics by color or color family in addition to sorting by resin type. Most of these systems work well with whole containers but are not effective in separating chipped plastics or multilayer materials. 

Encoded particles identify plastic parts. Plastics News, Oct. 4, 2004, p. 12. 

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