Determination of Inorganic Constituents and Polymers in Metallized Plastic Materials

Journal of Radioanalytical and Nuclear Chemistry, Vol. 264, No. 1 (2005) 9–13 Determination of inorganic constituents and polymers in metallized plastic materials E. P. Soares,1,2 M. Saiki,1* H. Wiebeck3 1 Neutron Activation Analysis Laboratory, IPEN/CNEN-SP, Avenida Lineu Prestes, 2242, Cidade Universitária, CEP 05508-000, São Paulo, SP, Brazil 2 Escola SENAI “Fundação Zerrenner”, Rua Serra de Paracaina, 132, Cambuci, CEP 01522-020, São Paulo, SP, Brazil 3 Chemical Engineering Department, Escola Politécnica, USP, Caixa Postal 61548, CEP 05424-970, São Paulo, SP, Brazil (Received April 6, 2004) This work presents results obtained in the analyses of metallized plastics by neutron activation analysis (NAA) and results of polymer identification by infrared spectroscopy (IR) and differential scanning calorimetry (DSC). Metallized plastics of packagings, automobile accessories, toys, house wares, cards and compact discs were selected for these analyses. Toxic elements such as As, Cd, Cr, Ni, Sb and Sn as well as Ba, Br, Ca, Co, Fe, Sc, Se, and Zn were determined and their concentrations presented great variability. IR and DSC assays indicated that polyethylene, polypropylene, poly(ethylene terephthalate), polycarbonate, acrylonitrile-butadiene-styrene terpolymer are main types of polymers used in metallized plastics. Introduction In a previous work, plastic materials originated from household and hospital wastes were analyzed.4 This In the past years, polymers have been applied in work presents results obtained in the analyses of several fields of state of art technology, such as civil metallized plastics by neutron activation analysis (NAA) constructions, automotive industries, electro-electronic and in the identification of polymers by infrared productions and packagings.1 There is also an increasing spectroscopy (IR) and differential scanning calorimetry use of metallized plastics, since they cost less than (DSC). casting metals and present light weight, high resistance to corrosion, and versatility.2,3 Experimental Although many improvements in life quality can be attributed to plastics, it seems to be considerably less Samples of metallized plastics attractive as the accumulation of solid waste becomes a major environmental issue because of problems Samples of metallized plastics were from food associated with its disposal. Plastic products could (appetizers, fried potatoes, smoke-dried meat), cosmetics contain heavy metals originated from both additives (lipsticks, perfumes) packagings, automobile accessories used as polymer stabilizers, coloring agents, catalysts or (headlights, horn ornaments, wheel hub and logotypes), filling materials and from contamination during toys, house wares, identification and phone cards and manufacturing and recycling. Plastics are becoming an compact discs. For NAA, these samples were cut or environmental issue regarding solid waste incineration. smashed into chips or strips smaller than 10 mm × At present, solid waste disposal is an increasing 10 mm and then they were wiped with a cotton pad problem all over the world and in order to solve the soaked with hexane p.a. grade and distilled water and problem, incineration and recycling are being proposed finally dried at room temperature. For IR and DSC as a feasible solution to reduce the great quantity of analyses, the samples were cleaned the same procedure urban solid waste. Besides, plastics are being used for NAA. extensively used in food, drink, blood, and medicine packaging storage. As toxic compounds may migrate Standards from plastic to stored materials, there is also great concern regarding health hazards. Standard solutions of As, Ca, Ba, Co, Cr, Fe, Ni, Sb, Consequently, toxic element determination and Sc, Se and Sn from Spex Certiprep Chemical were used polymer identification in plastic materials are of great to prepare synthetic standards of elements for interest. From the environmental monitoring point of comparative neutron activation analysis. The standard view, elemental analyses of plastics may contribute to stock solutions of Br, Cd and Zn were prepared the identification of possible sources of heavy metals dissolving the element in the metallic form or its salt of present in incinerated solid waste and its gas emission. high purity with adequate reagents. Concentrations of all Polymer identification is also vital for selecting types of this elements in the stock solutions were higher than plastics to be recycled. * E-mail: [email protected] 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2005 Akadémiai Kiadó, Budapest Springer, Dordrecht E. P. SOARES et al.: DETERMINATION OF INORGANIC CONSTITUENTS AND POLYMERS 1.0 mg.ml–1. Some of these stock solutions were diluted procedure described in Reference 6. These samples and used to prepare single or multielemental standards. without metallic surface were washed with deionized 50 or 100 µl of these solutions were pipetted onto sheets water, dried at room temperature before the of Whatman No. 41 filter paper and after drying at room measurements. Some metallized plastics were dissolved temperature in a desiccator, these sheets were placed in using organic solvent, such as chloroform, ethyl methyl clean polyethylene bags and irradiated with the samples. ketone or ethyl acetate or some of them were also The quantity of each element in the standards varied submitted to a pyrolysis. The organic solvent was from 0.06 to 500 µg. evaporated and a film was obtained for IR measurements. When the pyrolysis process was applied, Procedure for NAA the vapor formed was collected on a surface of KBr crystal and analyzed, afterwards. The equipment used About 120–180 mg of the sample weighed and heat- was a Fourier transform infrared spectrophotometer, sealed in polyethylene bags were irradiated at the IEA- Nicolet IR 550 series II, with a resolution of 4.0 cm, R1 research nuclear reactor for a period of 16 hours and beamsplitter of KBr and DTGS/KBr detector. The under a thermal neutron flux of 5.1012 n.cm–2.s–1, with function “find peaks” was used to obtain absorption elemental synthetic standards. After about five days of bands. The polymers identification was carried out decay time, samples and standards were fixed onto comparing a sample spectrum with standard spectra,7 stainless steel planchets for the gamma-ray and then the interpretation of absorption bands was measurements. The measurements were carried out performed. using a Canberra system, consisting of a Model GX2020 hyperpure detector, which is connected to a Model 1510 Procedure for DSC analysis integrated processor and S100 card. The resolution of the system (FWHM) used was of 0.80 keV for Samples were cut in small pieces to be analyzed in a 121.97 keV of 57Co photopeak and 1.80 keV thermal analyzer model DSC 910 from TA Instruments 1331.49 keV of 60Co photopeak. Counting times varied and using a heating rate of 10 °C.min–1 for temperatures from 6,000 to 50,000 seconds, depending on the half- ranging from 20 to 350 °C. For peak identification, the lives or activities of the radioisotopes considered. The DSC curves obtained for the samples were compared gamma-spectra were processed using VERSAO2 with those presented by BRANDUP.8 computer program.5 The radioisotopes measured were identified according to their half-lives and gamma-ray energies. The radioisotopes and their respective gamma- Results and discussion ray energies (in keV) utilized were: 76As (559.1), 31Ba (383.2); 82Br (776.5); 47Ca (1297.5); 115Cd (336.2 and Table 1 presents the concentration ranges of As, Ba, 527.9); 60Co (1332.2); 51Cr (320.0); 59Fe (1099.2); 58Co Br, Ca, Cd, Co, Cr, Fe, Ni, Sb, Sc, Se, Sn and Zn (810.8); 122Sb (564.2); 46Sc (889.3); 76Se (264.7); 113Sn determined in metallized plastics of computer discs, (391.7) and 65Zn (1115.5).The elemental concentrations telephone and identification cards and automobile were calculated by comparative method. accessories. As can be seen in this table, not all the Quality control of the results was evaluated by elements were detected in some samples and the range analyzing certified reference materials NIST-1577b of elements is varying from few ppb to percentage levels Bovine Liver of National Institute of Standards and in samples of same type. The compact discs presented Technology and IMEP-10 Polyethylene of the Institute the lowest concentrations of most elements presented in for Reference Materials and Measurements, this table, and in metallized plastics of telephone and Commission of the European Communities (IRMM). identification cards were found toxic elements such as As, Cd, Sb and Sn. In metallized plastics of telephone Procedure for IR analysis cards, the highest concentration of Ni found was of 0.1% and for Sn was of 7.8% and in identification cards the First, the plastic was isolated from the metal concentration of Cd found was 761 µg.g–1. The high excepting in the case of plastic films samples that were concentrations of these elements are due to a thin layer measured directly. Plastic samples free of metal part of metal present inside these cards. High concentrations were obtained by immersing them in concentrated nitric of Ca were detected in some metallized plastics from or hydrochloric acid for a time enough to dissolve the automobile accessories since compounds of this element metal without affecting the polymer according to the are used to improve their properties and make it cheaper. 10 E. P. SOARES et al.: DETERMINATION OF INORGANIC CONSTITUENTS AND POLYMERS Table 1. Range of elemental

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