Ashing method plastics

Samples of heavy duty and cmde oils, lubricating oils, worn oils, organic polymers, plastics, grease, etc., may be ashed with the retaining acid PTSA using the dry-ashing method up to temperatures of 650°C. This compound will retain most mono- and divalent states of elements in samples. The structure of PTSA is ... 

The metal salts are added to plastic products as organometallic, metallocenes or inorganic salts. The ashing method of sample preparation is only suitable for elements that do not volatilise during the heating cycle. The results obtained and recorded in Table 4.10 are reproducible for most elements with the exception of Pb and Sb in which some loss had taken place using the opened dry ashing method even in the presence of PTSA. 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

For plastics, ISO 3451 Plastics — Determination of Ash describes various methods for determination of the ash content of different types of plastics including those containing glass fibres and/or flame-retardants. 

Molded and Formed Wood. Historically wood has been bent and shaped first by steaming, which plasticizes the wood polymers. The new shape then is set in place by cooling and drying in the desired conformation. However, the curvature possible by this method is limited, and the process is time-consuming. Some chair backs and solid hickory and ash skis still are steam-bent. 

A method has been reported for the determination of calcium, copper, iron, magnesium, potassium, sodium and zinc in cellulose [169]. The sample (10 g) was air-dried and then ashed at 575°C until all the carbon was removed. Hydrochloric acid (5 ml of 6M) was added to the residue and evaporated to dryness twice before taking up the sample in a third aliquot, diluting to 100 ml and aspiration into an air /acetylene flame. It is likely that volatile elements such as cadmium may be lost at such an elevated ashing temperature and temperatures below 500°C may be preferable. Alternatively wet ashing with nitric acid has been proposed for the determination of aluminium, cadmium, potassium and zinc in pressed boards [170] or sodium in gypsum glass board [171]. For the determination of lead in confection wrappers, the sample may be treated with concentrated nitric acid at 70—80°C and diluted for flame analysis [172]. In the full method, the wrapper was wiped clean with a damp tissue, cut up to 0.5 X 0.5 mm pieces and dried at 110°C (for paper, for plastic 80°C) for 1 h. The sample (0.5 g) was heated with concentrated nitric acid (1ml) at... 

Perhaps the simplest test method for the evaluation of antistatic finishes is the ash test. A piece of the fabric to be evalnated is mbbed briskly on a piece of plastic or rubber (the vinyl covered arms of a chair, for example). The fabric is then placed over an ashtray containing cigarette ash. The amount of ash transferred to the fabric is an indication of the amount of static charge imparted to the fabric. Owing to the difficulty in quantifying the results, this test is mainly nsed as a qualitative tool to distinguish between antistatic-treated and untreated fabrics. 

The first step in analysing plastics for metals content in polymers by ICP-AES technique is that they must be prepared in solutions that are suitable for nebulization. There are four general methods applicable for sample preparation for metal analysis by ICP-AES and they are solvent dissolution of some plastics dry ashing using a muffle furnace acid digestion using a microwave oven and oxygen bomb combustion. 

Method. An accurate weight of approximately 2.0 to 3.0 g of each polyurethane listed in Table 6.24 is placed in a clean platinum dish with 0.15 g of PTSA. The samples are ashed using a program of ramping/holding stages similar to methods described for cyanoacrylate adhesives to a maximum temperature of 650 °C. The resulting ashes are contacted with 10.0 ml of 0.1 M HC1 and the suspensions transferred to a Teflon beaker. To each add 2.0 ml of cone. HF and heat to -150 °C on a hot plate to dissolve the SiC>2. The clear solutions are made up to mark in a plastic volumetric flask with deionised water. 

Most of the methods (except for direct dissolution in organic solvents) used to convert the analytes of interest in the plastics to solution involve sample mineralization which results in oxidation of its organic constituents to carbon dioxide and water. The oxidation process can be accomplished as sample combustion (dry ashing) whereby the sample is oxidized in a stream of oxygen or air, or alternatively, strong liquid oxidizers (mineral acids, peroxides, etc.) can be used for the same purpose (wet ashing). 

The first step consists a Soxhlet-extraction of the powdered PVC sample with diethyl ether to separate plasticizer. After evaporation of the solvent, the amount of plasticizer can be determined. The rest of the material is then dissolved in tetrahydrofurane (THF), and, after filtration, the fibrous materials are obtained. The other components, insoluble in THF, are separated in a centrifuge. The remaining residue can be divided to fillers and crosslinked PVC by burning to ashes. By dropping the THF solution in a surplus of methanol the PVC is precipitated. The single components are determined gravimetrically and identified by chemical and spectroscopic methods. Usually the quantitative analysis of the main parts of a PVC sample (plasticizer, fiUer, PVC itself) will... 

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