Some Analytical Methods Developed for Risk Assessment of Polymer-Based Materials

Polymer-based materials are widely used as raw and semi-finished materials in the production of many materials used in daily life. Being both economically viable and easy to apply, polymers have rapidly increased consumption compared to other materials, and high plastic consumption is considered an indicator of countries' development levels. In Turkey, the main sectors driving plastic consumption are packaging and construction materials, as is the case worldwide. The most commonly used commercial polymeric materials include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). In polymer production, various additives are used to meet desired requirements, increase quality and ease of use. Through these substances, desired properties can be imparted to plastics. Additives and auxiliary chemicals commonly used in polymer production include: antiblock and slip agents, antioxidants, antistatic agents, plasticizers, foaming agents, fillers, flame retardants and smoke suppressants, heat stabilizers, lubricants and process aids, plasticizers, ultraviolet and visible light stabilizers. Metals and non-metals can be added to plastic products through the additives mentioned above. Examples of these include; catalysts used in plastic production, flame-retarding chemicals, antimicrobial agents, plasticizers, heat stabilizers containing Pb and Cd, and dyes. For example; in PVC production, cadmium and lead can be used as colorants. In polystyrene (PS) and acrylonitrile/butadiene/styrene (ABS), PBDE is used as a flame retardant, and in red/orange/yellow plastics, cadmium, lead and chromium (VI) are used as lead chromate colorants [1].

International restrictions have been imposed on metal values found in plastic materials. These are directives issued by the European Union;

• Restriction of Hazardous Substances (RoHS), Waste Electrical and Electronical Equipments (WEEE) and Directive on Energy Using Products (EuP). • In China: "Management Methods on the Prevention and Control of Pollution Caused by Electronic information Products (Chinese RoHS)" and in the United States: US (California) Electronic Waste Recycling Act (S.B. 20), Electronic Waste, Advanced Disposal Fees (S.B. 50). • According to the European Union RoHS directive, electrical and electronic equipment put on the market from 1 July 2006 onwards must not contain components such as lead, mercury, chromium (VI), cadmium, polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE). The maximum concentration of these prohibited substances in the product is 0.1% for Pb, Cr (VI), Hg, PBDE and PDE and 0.01% for Cd (EPCEU, 2003a). Products covered by the RoHS directive include: small and large household appliances, IT/communication devices, consumer equipment, lighting devices, electric and electronic hand tools, toys, hobby and sports equipment, medical devices, monitoring and control devices, automatic dispensers. If the requirements of these two directives are not met, manufacturers face various sanctions such as fines, imprisonment, and bans on importing the product to that country. Some standard test methods used during RoHS compliance assessments are shown in Table 1.

Table 1. Some standard test methods.

Analytical methods frequently used in metal analysis include: Atomic absorption spectrophotometry (AAS), X-ray fluorescence spectrophotometry (XRF), inductively coupled plasma (ICP) techniques and scanning electron microscopy - energy dispersive X-ray analysis (SEM/EDX). The methods used have advantages and disadvantages relative to each other. A comparison of the methods is given in Table 2. However, the analytical methods used in standards for analyzing these metals are open to improvement in both sensitivity and accuracy.

Table 2. Comparison of methods used

In AAS and ICP measurement techniques, polymeric material is generally decomposed with an acid or acid mixture, metals are made soluble, and the liquid sample is measured by the device. Although ICP techniques, which have lower sensitivity and can perform simultaneous multi-element analysis, appear superior to AAS, AAS techniques are more advantageous in terms of equipment investment, ease of use and consumables consumption. In a study conducted by our group, a sample preparation method was developed for Pb and Cd analysis in PVC-based samples using AAS technique. In the sample preparation process, a Kjeldahl unit, a simple open system wet digestion apparatus, was used, and the acid mixture (H₂SO₄ and HNO₃) used for solubilization and the sample amount were optimized by statistical methods to find suitable conditions. Since each polymeric structure has different chemical composition and different additives, the optimization of procedures in the sample preparation stage for each sample type is quite important in terms of accuracy and sensitivity. Thus, the sensitivity values of the method for Cd and Pb were determined as 1.6 and 6.4 mg kg⁻¹ respectively [2]. In XRF and SEM/EDX techniques, simultaneous multi-element analysis can be performed directly on polymeric material without any sample preparation methodology. However, sensitivity values are not as good as AAS and ICP techniques. In XRF technique, the penetration of X-rays to approximately 0.1-1 mm depth at a small point of the sample necessitates working with homogeneous samples. For this reason, avoiding direct measurement on non-homogeneous samples leads to the need for a homogeneous sample preparation with simple sample preparation. In a different study conducted by our group in this direction, a solvent-based sample preparation technique was developed for the determination of Cr, Cd, Hg and Pb levels in plastic bag samples made of polyethylene and polypropylene using XRF.

Polymeric samples were homogenized by thermal treatment in xylene, an organic solvent, and metal levels were determined with high accuracy. The sensitivity values of the method used were found to be 12, 24, 12 and 12 mg kg⁻¹ for Cd, Cr, Hg and Pb, respectively [3].

Although AAS methods have better sensitivity, the time required for analysis is longer. Although data were collected for PE and PP materials, the proposed method can be applied to different types of plastic materials and to all light organic and soluble matrices such as pharmaceuticals, agricultural chemicals, organic dyes and pigments. Phthalate esters, which fall into the class of endocrine-disrupting chemicals, constitute another important risk group. Phthalates are added to plastic materials, resins, adhesives to impart properties such as flexibility, softness, durability and the like. The sources through which people are most exposed to phthalates are those related to materials (construction materials, furniture, electronic appliances), cosmetics, packaging, paints, textiles and medical device products, industrial products, agricultural products (insecticides, pesticides and medicines) and waste [4]. Exposure of humans to phthalates can occur either through direct contact or through the use of phthalate-containing products. Exposure to phthalates occurs through oral ingestion, inhalation, injection from PVC-made devices and skin absorption. The amounts present in the final product are limited by regulations. In Turkey, taking into account Commission Decision No. 2004/781/EEC, within the scope of harmonization with European Union legislation, the Ministry of Health published in the Official Gazette in 2006 the "Notification on Phthalates in Toys and Child Care Products," which introduced some restrictions on the use of phthalates in children's toys and child care products. This Notification covers toys and child care products made of partially or fully soft PVC where more than 0.1% by weight of certain phthalates (DINP, DEHP, DnOP, DDP, BBP, DBP) are likely to be placed in the mouths of children under three years of age. Considering all of these factors, sensitive and accurate analytical techniques need to be developed both for determining the levels of phthalates in plastics and for determining their migration. The techniques used in sample preparation and determination of phthalates are summarized in Figure 1.

Figure 1. Process steps in phthalate analysis

In our study, phthalate esters in some packaging and toy samples were determined by gas chromatography-mass spectrometry (GC-MS) following ultrasonic solvent extraction. First, solutions of standards at specific concentrations were injected into GC-MS under suitable conditions and operated in scanned ion mode, and the retention times and mass spectra of the standard peaks were determined. The mass spectra of peaks in the total ion chromatograms of standards were compared with NIST and WILEY libraries, and mass/charge (m/z) ratios were determined for selective ion mode studies of standards. Using the obtained m/z values, calibration curves for six standards in the concentration range of 1-10 mg/L were obtained in selective ion mode studies and are shown in Figure 2. Analytical parameters for the calibration graphs are summarized in Table 3. During ultrasonic extraction of phthalate esters from packaging materials, operations were performed simultaneously with different solvents to select the appropriate solvent. To calculate extraction efficiency, mixed standards were added to vials containing packaging material before extraction at 2 mg/L. Table 4 shows the effect of solvent selection on recovery in packaging materials.

Figure 2. GC-MS calibration graphs for phthalate esters

Table 3. Analytical parameters for calibration graphs.

Table 4. Recovery values obtained for different solvents in the ultrasonic extraction process of packaging material (n=3).

Looking at the recovery values, it was found that chloroform could be the most suitable solvent for extraction. However, the recovery values for other solvents are also in the range that can be used for quantitative evaluation. In extraction efficiency studies from solid samples, the recovery percentages found for the liquid standard added to the medium are usually high if there are no species that could show interference effects by providing complexation, precipitation, and polymerization of the analyte in the medium. In such extraction efficiency studies, the use of certified reference material would be more beneficial for analytical evaluation. However, since a commercially available certified reference material containing phthalate esters in plastic materials is not available, this approach was followed. In addition; when looking at phthalate esters in toy samples, it stands out that DEHP is found at the highest rate. For toy samples, the values for DEHP in extraction with different solvents are shown in Figure 3.

Figure 3. Solvent selection in DEHP extraction from toy sample.

In toy samples, chloroform was also found to be the suitable solvent providing the highest extraction. However, the standard deviation values for DEHP values related to chloroform solvent were found to be higher than other solvents. Phthalate ester values obtained for four toy and two different packaging material samples with ultrasonic extraction performed using chloroform solvent are given in Table 5.

Table 5. Phthalate ester values for samples (n=3).

The multipurpose use of plastics and the continuation of research and development activities in this field place the sector face to face with many analytical problems. Frequently encountered analytical problems include: plastic recycling limitations, detection of conditions that could pose health risks in packaging and toy applications, etc. In our study, as an example of solving analytical problems related to improving product quality; for the detection of metal levels that may be encountered in recycling; we developed methods with AAS and EDXRF, and also developed analytical methods for monitoring phthalates by GC-MS in identifying risks that harmful components could create. In conclusion; in solving analytical problems in this sector, in addition to the use of various analytical surface techniques and effective chromatographic and spectroscopic techniques in structure characterization; we can emphasize that the importance of appropriate solvent selection in the solubilization of polymers remains significant. Assoc. Prof. Dr. Elif Tümay Özer Faculty of Arts and Sciences, Department of Chemistry Uludağ University Prof. Dr. Şeref Güçer Faculty of Arts and Sciences, Department of Chemistry Uludağ University

References [1] İ. Baylakoğlu, European Union Electronics Sector Directives. Eco-Friendly Electronics Design Conference Paper. Gebze, 15-16 June 2006, pp. 9-14. [2] Elif Tümay Özer, Şeref Güçer, Central Composite Design to the Optimization of Cd and Pb Determination in PVC Materials by Atomic Absorption Spectrometry after Kjeldahl Digestion, Polymer Testing, 30:7 (2011) 773-778. [3] Elif Tümay Özer, M. Akif Çimenoğlu, Şeref Güçer, Determination of Cadmium, Chromium, Lead and Mercury in Polyethylene and Polypropylene, after Xylene treatment, by Energy Dispersive X-Ray Fluorescence Spectrometry, Instrumentation Science & Technology, 39 (2011) 357–367. [4] C. F., Wilkinson, J. C. Lamb, The potential health effects of phthalate esters in children's toys: a review and risk assessment. Regulatory Toxicology and Pharmacology (1999) 140–155.