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TD-GC/MS · VOC · Polymers · thermal Desorption

Analysis of volatile organic compounds (VOCs) is a useful method for under-standing the chemical processes in-volved in polymer degradation and for the identification of materials. VOCs emitted during thermal treatment of plastics were analyzed to indicate po-tential unpleasant odor issues. In case of analyzing VOCs from ligning and lignin composite was identification fo-cused on comparison emitted sulphuric compounds. Screening analysis were made at 80, 160 and 200°C by different techniques and atmospheres. To con-firm which compounds are emitted from samples, experiments were con-ducted and volatile organic compounds (VOCs) emitted from samples were trapped by Tenax/Carbograph adsorp-tion tubes and analyzed by TD-GC/MS or directly analyzed by py-GC/MS. In the present study, polypropylene (PP), rubber, lignin/PLA/PHB composite and lignin were tested.

Identifizierung non „Vocs“ aus natürlichen und synthetischen Polymeren TD-GC/MS · VOC · Polymere · Thermische Desorption

Die Analyse flüchtiger organischer Stof-fen (VOCs) ist eine nützliche Methode, um chemische Prozesse der Polymer-degradation zu verstehen und Materia-lien zu identifizieren. VOCs, die wäh-rend thermischer Behandlung von Plas-tik emittiert werden, wurden analysiert, um das Potential von unerwünschtem Geruch aufzuzeigen. Bei der Analyse von VOCs aus Lignin und Lignin-Kompo-siten war die Identifizierung auf den Vergleich von emittierten Schwefel- verbindungen fokussiert. Es wurden Übersichtsanalysen bei 80, 160 und 200 °C mit verschiedenen Techniken und Atmosphären durchgeführt. Aus den Proben emittierte Stoffe (VOCs) wurden auf Tenax-Carbograph-Adsorp-tionsröhrchen gesammelt und mit TD-GC-MS oder direkt mit Py-GC-MS analysiert. Es wurden Polypropylen (PP), Gummi, Lignin/PLA/PHB-Komposite und Lignin getestet.

Figures and Tables: By a kind approval of the authors.

IntroductionThermal desorption (TD) is a highly sen-sitive alternative to conventional sample collection procedures for volatile and se-mi volatile compounds, such as solvent desorption tubes. It is more efficient than other extraction methods and al-lows the selective concentration of tar-get analytes, making it ideal for trace-le-vel analysis by gas chromatography (GC/MS) across a wide range of applications. Thermal desorption is a process of collec-tion and desorption of analytes from so-lid sorbents using heat and a flow of in-ert gas, rather than solvent extraction. Analytes are then focused on a cold trap prior to entering the analytical column, resulting in higher responses and nar-row, more symmetric peaks. This is ac-complished by interfacing a thermal de-sorption unit with a GC/MS (Figure 1). TD is highly sensitive and can significantly lower detection limits, by as much as 103, as it allows water to be purged, further facilitating the selective concentration of the compounds of interest. Thermal de-sorption tubes can be sampled actively with a sampling pump, or passively with a diffusion cap, which are also reusable.

Plastics are extremely diverse in terms of chemical composition, properties and possible applications, and are widely dis-tributed in the society and the environ-ment. In the last two decades the global annual production has doubled, reaching 245 million tons in 2008. Several of the chemicals used to produce plastics are hazardous for human health and the en-vironment. These, and their degradation products, may be released during the life cycle of a plastic product. The plastic po-lymers are not considered as toxic, but in plastic products there may be present non-bound residual monomers, polyme-rization chemicals, degradation pro-ducts, and additives which have toxic properties 1-3.

Study of volatile organic compounds (VOCs) brings outputs/outcomes in seve-ral levels:1) Environmental (toxicity, emitted

hazardous compounds)2) Processing (stability, bonding,

efficiency of selected processes)

3) Conversation (preservation of cultural heritage artefacts)

4) Degradation (study of degradation and stabilization process)

5) Recycling (secondary usage of materials, converting waste materials into new materials and objects)

At every level of this distribution is useful VOCs analysis. Dependence of purpose is necessary to change the conditions and process of emitting and collecting VOCs. In case of polymer stability study is necessary to simulate typical conditions of material purpose. A dynamic condition during hea-ting of material leads to identification of products which are emitted during proces-sing. Static conditions bring information about compounds which are emitted du-ring typical conditions in which the materi-als are used. In both cases is possible to use different atmospheres (O2, Air, N2, noble gases, etc.), sorbents and their mixtures (activated carbon, Tenax, etc.).

Sorbent tubes are suitable for ppt to ppm concentrations of volatile organic compounds (VOCs) in ambient, indoor, and industrial hygiene environments. Possible in stainless steel and glass form (for thermally labile VOCs), they fit Mar-kes ULTRA-UNITY, PerkinElmer, and Shimadzu thermal desorbers. Packed tu-bes come with a report detailing the to-tal mass of sorbent in the tube.

Experimental In this article is shown possibilities of using some of capturing and analyzing VOCs from three types of polymers (rub-ber, polypropylene and lignin/PLA/PHB

Identification of Vocs generated by natural and synthetic Polymers

AuthorsAleš Ház, Michal Jablonský, Ivan Hudec, Igor Šurina, Bratislava, Slovakia

Corresponding Author:Aleš HázDepartment of Wood, Pulp and PaperSlovak University of Technology Radlinského 9Bratislava 812 37, Slovakia, E-Mail: ales.haz@stuba.sk

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composite). Capturing right into the ab-sorption tube (Tenax + Carbograph) in first, second and third case was used. In fourth case releasing of VOCs by analyti-cal pyrolysis was used.Conditions at capturing VOC’s from rub-ber: 80°C, atmosphere – air, flow 60ml/min, duration 2hrsConditions at capturing VOC’s from po-lypropylene: 200°C, atmosphere – air, flow 60ml/min, duration 12hrsConditions at capturing VOC’s from composite (lignoplast): 160°C, atmos-phere – CO2, flow 70ml/min, duration 2hrsConditions at capturing VOC’s from lignin: 200°C, atmosphere – He, flow 70ml/min, duration 30sec.

Py-GC/MS and TD-GC/MS analysis The pyrolysis was performed with a Pyro-probe 5150 Series (CDS Analytical Inc.). The pyrolyzer interface temperature was 150°C. Approximately 1.5 mg of sample was inserted into the glass liner and placed immediately in the pyrolyzer pro-be. The Pyroprobe temperature was initi-ally set and held for 5 sec s at 60 °C, and then ramped at 10 °C/ms to a final tem-perature and held for 5 sec.

Sorbent tubes were thermally desorbed by a thermal desorption unit (Unity 2, Mar-kes, UK) coupled to a gas chromatograph (GC 7890A gas chromatograph Agilent Technologies, USA) with ion trap mass spectrometer detector (MSD 5975C, Agi-lent Technologies, USA). Thermal desorpti-on of sorbent tubes was carried out in a two-step mode. In the first step, collected compounds were desorbed from sorbent tubes for 4 min at 320 °C and a flow rate of 50 mL.min-1 of He, carried through a 100 mg Tenax™ TA cryogenic internal trap, cooled at -10 °C. Thereafter, in the second step, the trap was desorbed at 300 °C for 1 min with fast heating (900 °C min-1).

For GC/MS analysis, a GC 7890A gas chromatograph Agilent Technologies was used. The separation was made on a 30 m x 250 µm x 0.25 µm i.d. fused silica capillary column HP-5MS. The oven tem-perature was held at 40°C for 2 min, and then heated by ramp 20 °C/min to 300°C. The final temperature was kept for

5 min. The injector temperature was 250°C with splitless mode. Helium was used as the carrier gas with flow 1,2 ml/min. The end of the column was introdu-ced into the ion source of the Agilent Technologies model 5975C series mass selective detector (MSD) operated in electron impact ionization mode. The

data acquisition system used ChemStati-on E software and analyzed compounds were identified with NIST and Wiley elec-tronic libraries.

Results and discussionIt is possible to focus analyses according to which parameter is desired: for poly-mer stability, identifying toxic or odor compounds, checking polymerization process, identifying of compound which were used as catalyst/antioxidant/plas-ticizer during polymer production.

The main purpose of the analysis of rubber was to identify compounds which can be toxic or may cause unpleasant odor. On the basis of identificated com-pounds it is possible to execute sensoric evaluation of pure compounds and de-terminate compounds which generate unpleasant odor. The toxicity of com-

Fig. 1: VOCs sampling and analysis process.

Fig. 2: TD-GC/MS analysis of VOCs from rubber with addition of stabilizer at 80°C.

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pound can be evaluated according to known properties of each compound. Main emitted compounds from rubber sample were: Aniline, Cyclohexanone, 1,2-Ethandiyl-bis(2-methylacrylat), N-Cyclohexyl-1-phenylmethanimin, N-Ben-zylidenaniline, etc.

The purpose of the analysis of poly-propylene was to identify compounds which can stay in sample after PP proces-sing. Based on identified compounds it is possible to create an assumption that the parameters set up by the producer of VOCs capturing are the parameters un-der which the degradation of PP take place. Wide spectrum of common com-pounds of PP decomposition were identi-fied (Fig. 3).

In case of lignin analysis and biocom-posite material made from lignin it is possible to observe lower emittion of

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PRÜFEN UND MESSEN – PMA 2017 TESTING AND MEASURING – PMA 2017

36 KGK · 05 2018 www.kgk-rubberpoint.de

sulphuric compounds which are undesi-rable by-products of biocomposite pro-duction. Methanethiol, Dimethyl sulfo-ne, Dimethyl sulfoxide were identified in final material.

ConclusionsIt is obvious that different type of prepara-tion and isolation techniques make diffe-rences between lignin and lignin price. A wide range of lignin prices from 50 to

Fig. 3: TD-GC/MS analysis of VOCs from polypropylene at 200°C.

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Fig. 4: TD-GC/MS analysis of VOCs from lignin - LIGNOBOOST at 160°C4.

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Fig. 5: Py-GC/MS analysis of VOCs from Lignoplast at 200°C.

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750$ makes it suitable for further use5. It is important to know which compounds causes unpleasant odors in the virgin plastics or bioplastics created from ligno-sulfonates and biodegradable materials. Parameter as “unpleasantness” depends on subjective evaluation mainly of costu-mer or people which are involved in ma-nufacturing of polymers. Parameters which can be better solved than “unple-asantness” is the type and the amount of toxic compounds emitted from the mate-rial. More VOC and more oxygenated or-ganic compounds considered to be hazar-dous to human health and the cause of malodor were emitted in air atmosphere than in N2. Based on these results, lower temperature and lower oxygen level is re-commended to reduce hazardous or ma-lodor compounds during the plastic mel-ting process of mechanical recycling6.

AcknowledgementThis work was supported by the Slovak Research and Development Agency under the contracts No. APVV-15-0052 and APVV-0393-14. This article was realized al-so thanks to the support for infrastructure equipment by the Operation Program Re-search and Development for the project „National Center for Research and Applica-tion of renewable energy sources“ (ITMS 26240120016, ITMS 26240120028) for the project „Competence center for new mate-rials, advanced technologies and energy“(ITMS 26240220073) and for the project „University science park STU Bratis-lava“ (ITMS 26240220084), co-financed by the European Regional Development Fund. The authors would like to thank for finan-cial assistance from the STU Grant scheme for Support of excellent Teams of Young Researchers under the contract no. 1663.

References[1] A. Ház, M. Jablonský, A. Sládková, J. u. Šurina Fe-

ranc, Key Engineering Materials, 688 (2016).[2] Delilah Lithner, Ph.D. thesis, Environmental

and health hazards of chemicals in plastic polymers and products (2011).

[3] J. Kubačková, J. Ferenc, I. Hudec, Š. Šutý, M. Jablonský, J. Annus, & Pret‘o, J.: Elastomery, 17 (3), 21 (2013).

[4] Šutý, Š., Ház, A., Lauko, T., Feranc, J., Plavec, R.:. Identification of odorous substances in kraft lignin for bioplastics. In PMA 2015 & SRC 2015, 56 (2015)

[5] Hodásová, Ľ., Jablonský, M., Škulcová, A., Ház, A.: Wood Research 60.6: 973 (2015)

[6] Yamashita, K., Kumagai, K., Noguchi, M., Yamamoto, N., Ni, Y., Mizukoshi, A., Yanagisawa, Y.: The 6th International Conference on Indoor Air Quality (2007).

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