Study On The Determination Of Toxic Heavy Metals In The Decorative Materials Of Wood-Based Panel

Wood-based panels are widely used in decoration or manufacture of woodenproducts.Toxic heavy metals are mainly in the surface decorative materials of wood-basedpanels.But there is no limitation for total content of the toxic heavy metals such as leadcadmium chromium(including hexavalent chromium) mercury in our national limitationstandard of indoor decorating and refurbishing materials.A method was developed fordetermining trace metals lead cadmium chromium(including hexavalent chromium) mercuryin decorative paint,polyvinyl chloride,melamine-impregnated paper. The microwave-digestiontechnique was used in the decomposition of the samples. The content of the four metals weredetermined by atomic absorption spectrometry and induce coupled plasma atomic emissionspectrometry.Diphenyl hydrazine spectrophotometric was adopted for determining thehexavalent chromium content. The conclusions are as follows:1. Scrapping off the decorative coating from the test sample with a suitable blade,collecting the scraps into a mortar and mixing them as proportioned samples.Taking off thepolyvinyl from the surface of the panel,and scrapping off all the fibers adhered to the reversesides of the penal,then cut the PVC samples into small pieces.2. It was adopted microwave digestion to decompose the samples,and confirmed thecondition of microwave digestion.The sample mass for digestion is0.1g,the temperature is225centigrade,the pressure is55bar.Adding7.5ml nitrid acid and2.5ml hydrogen peroxidebefore the digestion process.3. The detection limit of the four elements by atomic absorption spectrometry is0.00003mg/L~0.15mg/L.The recovery rate is from95.52%to106.30%.The liner range is0~5μg/ml. The relative standard deviation of lead and chromium is less than10%while theRSD of cadmium is less than1.5%,and the RSD of mercury is less than50%,when testsamples. 4. The detection limit of the method as determined by ICP-AES is among0.0006mg/L and0.003mg/L.The standard curves were linear over the range of0to5μg/ml. The recovery rangedfrom93.8%to109.19%. The relative standard deviation of lead cadmium and chromium is lessthan1.5%,and the RSD of mercury is less than5%,when test samples.5. Samples for detect Hexavalent chromium was digested with alkali digestion anddetermined by UV-vis spectrophotometric analysis.Sieving the PVC with a500μm sieve,andsieving the paint and the membrane coating with250μm sieve. After the alkali digestion,separate the sample's emulsion with high-speed centrifuge.With a color reagent (DPC) tochelated with Cr(VI), the solution was finally detected by a UV–vis spectrophotometer at awavelength of540nm which is the basis of analyzing Cr(VI) quantitatively.The linear range isfrom0mg/L to1.5mg/L,the correlation coefficient is up to0.9995,the relative standarddeviation is less than1.1%.6. Through the analysis of27samples of wood-based panels' surface decorativecoatings,it was determined that the concentration of lead cadmium chromium is less than100mg/kg in more than80%of the samples,and a small proportion of the samples were detectedwith high concentration metals.The concentration in samples was very a little.It was knownthat the migration of heavy metals from material in solution was greatly influenced by thesolution temperature,acidity grade and soaked time.By comparison of the total content and thecondition migration amount of heavy metal,it was concluded that the heavy metals inmelamine-impregnated paper were more capable to remove into solution and the lead in fourmetals elements was more likely to move into the solution.