Putting it to the test - polymer analysis in the laboratory

Research and development and quality control rely heavily on accurate analytical measurements. Now identifying recycled materials and verifying compliance for increasingly stringent regulations are also proving just as important areas for polymer analysis. Jennifer Markarian reports on some of the major issues in analytical techniques in the laboratory.

Analytical measurement of compounds and components in polymers is important for research and development and quality control. It is increasingly being used for identifying recycled material and ensuring regulatory compliance. Users of analytical instruments want increased detection sensitivity as well as easy-to-use methods and greater automation, agree suppliers. “Our customers want instrument manufacturers to supply method development and automation. They want to be able to drop in a sample and push a button,” notes Mark Taylor, product manager at Shimadzu Scientific Instruments. Customers also want to be able to integrate instrument data into information management systems. In several areas, from polymer characterization to element identification, new instruments with improved technology and user-friendly features address these needs.

Thermal analysis

Thermal analysis is used widely in polymer research and development to examine properties such as melting, crystallization, and decomposition behaviour under various conditions or formulations. PerkinElmer recently introduced the DMA (Dynamic Mechanical Analyzer) 8000, which is designed to meet customer needs for both high quality results and ease of use, explains Mike DiVito, Thermal Analysis business unit manager at PerkinElmer. The technology was part of the acquisition of specific DMA technologies from UK-based Triton Technology Ltd. in December 2006, says PerkinElmer.

IR

Infrared (IR) spectroscopy can be used to identify the bulk material of a sample, as well as identify and quantify components such as additives. IR can also be used on a microscopic level, to identify defects or inclusions, and to identify thickness and composition of multilayer samples. Attenuated total reflectance (ATR) is a surface measurement technique that can enable users to scan samples ‘as is’, which is useful for samples that are difficult to prepare for traditional transmission or reflectance measurement. One common use for ATR surface measurement is in verification of plastics for recycling, notes Dr. Simon Wells, Molecular Spectroscopy business unit manager at PerkinElmer. PerkinElmer’s Spotlight™ FT-IR 400 imaging system now has an ATR imaging accessory. Using ATR allows spatial resolution as low as 3 microns, compared to standard transmission that has resolution down to 10 microns, says Dr. Wells. This feature is particularly useful in analyzing laminates and in looking at very small defects. PerkinElmer recently introduced the Spectrum™ 400, which combines near-infrared (NIR) and optimized mid-infrared (MIR) spectroscopy, allowing more versatility to provide more information. The instrument can also be used with the Spotlight 400. The dual range Spectrum™ 400 complements the single range Spectrum™ 100. Both new Spectrum instruments feature ATR capabilities with improved reproducibility over previous designs, ensuring measurement consistency in both the short and long term and between instruments, says the company.

Regulatory compliance analysis

Regulatory compliance is becoming an increasing concern for the polymer industry, especially with implementation of the European Union’s RoHS regulations. The trend towards increased testing is expected to continue with regulations governing other regions, such as RoHS regulations in the state of California in the USA and in China. With OEMs requiring proof of compliance from the supply chain, testing and record keeping is critical. RoHS restricts six substances in electrical and electronic products: lead, mercury, hexavalent chromium, polybrominated biphenyls (PBBs), and polybrominated diphenyl ethers (PBDEs) other than deca-BDE are restricted to less than 0.1% by weight (1000 ppm); and cadmium is restricted to less than 0.01% by weight (100 ppm). Elements can be identified and quantified with analytical techniques such as inductively coupled plasma mass spectrometry (ICP) and X-ray fluorescence (XRF). GC-MS is typically used to identify and quantify organic compounds, including distinguishing between types of bromine containing species. Official test method standards from ASTM and IEC for RoHS analysis are still being worked on.

ICP and AA

Inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and flame atomic absorption (AA) spectroscopy are used to analyze elements in polymers. ICP-OES is particularly useful for quickly identifying multiple elements down to levels less than 1 part per million (ppm) in laboratories with high sample throughput, explains Ian Shuttler, inorganic business manager at Perkin Elmer. PerkinElmer’s 2006 model of its Optima™ 5000 Series ICP-OES instruments has enhanced electronics and software for improved productivity. AA instrumentation is less expensive than ICP, but has lower sample throughput, adds Mr. Shuttler.

XRF

X-ray fluorescence (XRF) spectrometry is also used to quantify elements in polymers, including additives, catalyst residue and impurities. Advantages of XRF over other methods include lower operation cost and non-destructive analysis, in which samples can be run quickly ‘as-is’, without preparing a solution from the sample. XRF technologies include wavelength dispersive (WD) XRF and energy dispersive (ED) XRF. Although EDXRF are not as effective for trace elements as WDXRF, many EDXRF systems are significantly less expensive, and are being increasingly used in the polymer industry, notes Alexander Seyfarth, North American product manager for elemental and process analysis at Bruker AXS. “The trend is to use smaller instruments with lower operational cost and easy-to-use methods,” he says. EDXRF is agreed to be a good screening tool for regulatory compliance. “Detection limits of EDXRF are sufficient to certify levels of regulated elements in homogenous raw materials, such as compounded polymers,” claims Dr. Stan Piorek, principal research scientist for handheld NITON XRF analyzers at Thermo Fisher Scientific. However, he explains that in finished products, the sample may have coatings or other components that make it inhomogeneous from a measurement standpoint, lowering the accuracy of XRF ‘as-is’ measurement and possibly requiring verification by another method, especially if the measurement is close to the regulatory level. Preparing samples for analysis that are representative of inhomogeneous electrical and electronic parts is a need in the industry, says Taco van der Martin, product manager for XRF at PANalytical, who notes that PANalytical provides solutions for this analysis to its customers.

XRF requires matrix-specific reference standards, which have been in short supply, note industry experts. “The utmost need of the industry is for traceable reference material that can be used to set up an XRF system,” says Mr. Seyfarth. Primary, rigorously characterized reference standards from the U.S. National Institute of Standards and Technology (NIST) and the EU’s Institute for Reference Materials and Measurements (IRMM) are for the most part still being worked on. Standards are available from additive suppliers for their customers, and other secondary reference standards have only relatively recently become commercially available. PANalytical’s ADPOL standards were developed in conjunction with DSM Resolve, ASTM, and major polymer producers. ADPOL standards cover ten of the more commonly used elements – F, Na, Mg, Al, Si, P, S, Ca, Ti and Zn – in polyethylene, says the company. PANalytical’s TOXEL standards, developed with DSM Resolve and introduced in 2005, are used to test low concentrations of toxic heavy metals like Cr, Ni, Cu, Zn, As, Br, Cd, Ba, Hg and Pb in polyethylene and polypropylene. PANalytical is working on a new set of standards specifically for RoHS analysis of end-product or downstream products, targeting the RoHS restricted elements at the higher concentrations (1000 ppm range) of the RoHS regulations. These reference standards are expected to be released in mid-June this year. Bruker AXS supplies standards for toxic elements and RoHS-QUANT™ for RoHS elements for use commercially or with their XRF instruments. The standards were developed with Texas-based Analytical Services Inc. Bruker is currently testing a set of standards for common additives in PE, PP, and PVC.

Instrument suppliers have introduced new and improved XRF technology. While high powered, WDXRF instruments use high heat that can potentially damage samples and affect measurements, Bruker’s lower power (1 kW) S4 EXPLORER system is non-destructive to samples, says Mr. Seyfarth. PANalytical’s Axios-Poly can be operated at various power levels, allowing the user to operate at the optimum power and to give low detection limits and accuracy while minimizing polymer degradation, says the company. EDXRF systems also use lower power. Bruker recently introduced an enhanced bench-top S2 RANGER™. EDXRF spectrometer with a fourth generation silicon drift detector from the XFLASH family, new software, and touch-screen interface for easy use. PANalytical introduced the MiniPal 4 compact, bench-top EDXRF in 2005. The company says that the MiniPal4 has a new silicon drift detector for better resolution, with improved accuracy and precision and much lower detection limits than previous models. Shimadzu’s EDX series enables simple, rapid screening of substances regulated under the WEEE and RoHS directives at parts-per-million levels without pretreatment, notes the company. Large sample compartments on bench-top instruments are useful for measuring samples 'as-is', says Shimadzu. Thermo Fisher recently added a new model of handheld EDXRF to its Thermo Scientific NITON Analyzer product line. Handheld XRF is typically used outside the laboratory for on-site testing of end-products or for auditing incoming raw materials, says Dr. Piorek.

GC-MS

Gas chromatography (GC) and mass spectrometry (MS) are typically combined in polymer analysis of organic components. Pyrolysis or solvent extraction is used to digest a polymer sample for analysis. GC then separates and identifies the relative amounts of components, such as monomers, additives and impurities. MS identifies unknown components by comparing the spectra to a library of known spectra. Suppliers are seeing increasing GC-MS use in regulatory compliance work, such as identifying the presence of or quantifying polybrominated flame retardants for RoHS compliance. Shimadzu’s QP 2010 Plus GC-MS system was introduced in 2006, with improved sensitivity that allows lower detection levels and improved software with additional user-friendly, set-up wizards. The instrument uses a new automatic adjustment of retention time (AART) software function that improves inter-instrument repeatability and shortens the re-validation time needed after column replacement or routine maintenance. AART adjusts all retention time information for as many as 1000 compounds from a single analysis of one n-alkane solution, explains the company.

Contacts:
Bruker AXS GmbH; www.bruker-axs.com
Thermo Fisher Scientific Inc.
Thermo Scientific NITON Analyzers; www.thermo.com/niton
PANalytical; www.panalytical.com
PerkinElmer; www.perkinelmer.com
Shimadzu Scientific Instruments; www.ssi.shimadzu.com