Dr. Peter Kusch
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Miscanthus crops possess very attractive properties such as high photosynthesis yield and carbon fixation rate. Because of these properties, it is currently considered for use in second-generation biorefineries. Here we analyze the differences in chemical composition between M. x giganteus, a commonly studied Miscanthus genotype, and M. nagara, which is relatively understudied but has useful properties such as increased frost resistance and higher stem stability. Samples of M. x giganteus (Gig35) and M. nagara (NagG10) have been separated by plant portion (leaves and stems) in order to isolate the corresponding lignins. The organosolv process was used for biomass pulping (80% ethanol solution, 170 °C, 15 bar). Biomass composition and lignin structure analysis were performed using composition analysis, Fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis) and nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), size exclusion chromatography (SEC) and pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS) to determine the 3D structure of the isolated lignins, monolignol ratio and most abundant linkages depending on genotype and harvesting season. SEC data showed significant differences in the molecular weight and polydispersity indices for stem versus leaf-derived lignins. Py-GC/MS and hetero-nuclear single quantum correlation (HSQC) NMR revealed different monolignol compositions for the two genotypes (Gig35, NagG10). The monolignol ratio is slightly influenced by the time of harvest: stem-derived lignins of M. nagara showed increasing H and decreasing G unit content over the studied harvesting period (December–April).
Miscanthus x giganteus Stem Versus Leaf-Derived Lignins Differing in Monolignol Ratio and Linkage
(2019)
As a renewable, Miscanthus offers numerous advantages such as high photosynthesis activity (as a C4 plant) and an exceptional CO2 fixation rate. These properties make Miscanthus very attractive for industrial exploitation, such as lignin generation. In this paper, we present a systematic study analyzing the correlation of the lignin structure with the Miscanthus genotype and plant portion (stem versus leaf). Specifically, the ratio of the three monolignols and corresponding building blocks as well as the linkages formed between the units have been studied. The lignin amount has been determined for M. x giganteus (Gig17, Gig34, Gig35), M. nagara (NagG10), M. sinensis (Sin2), and M. robustus (Rob4) harvested at different time points (September, December, and April). The influence of the Miscanthus genotype and plant component (leaf vs. stem) has been studied to develop corresponding structure-property relationships (i.e., correlations in molecular weight, polydispersity, and decomposition temperature). Lignin isolation was performed using non-catalyzed organosolv pulping and the structure analysis includes compositional analysis, Fourier transform infradred (FTIR), ultraviolet/visible (UV-Vis), hetero-nuclear single quantum correlation nuclear magnetic resonsnce (HSQC-NMR), thermogravimetric analysis (TGA), and pyrolysis gaschromatography/mass spectrometry (GC/MS). Structural differences were found for stem and leaf-derived lignins. Compared to beech wood lignins, Miscanthus lignins possess lower molecular weight and narrow polydispersities (<1.5 Miscanthus vs. >2.5 beech) corresponding to improved homogeneity. In addition to conventional univariate analysis of FTIR spectra, multivariate chemometrics revealed distinct differences for aromatic in-plane deformations of stem versus leaf-derived lignins. These results emphasize the potential of Miscanthus as a low-input resource and a Miscanthus-derived lignin as promising agricultural feedstock.
Polyurethane (PU) coatings were successfully produced using unmodified kraft lignin (KL) as an environmentally benign component in contents of up to 80 wt%. Lignin samples were precipitated from industrial black liquor in aqueous solution working at room temperature and different pH levels (pH 2 to pH 5). Lignins were characterized by UV-Vis, FTIR, pyrolysis-GC/MS, SEC and 31P-NMR. Results show a correlation between pH level, OH number and molecular weight Mw of isolated lignins. Lignin-based polyurethane coatings were prepared in an efficient one step synthesis dissolving lignin in THF and PEG425 in an ultrasonic bath followed by addition of 4,4-diphenylmethanediisocyanate (MDI) and triethylamine (TEA). Crosslinking was achieved under very mild conditions (1 hour at room temperature followed by 3 hours at 35 °C). The resulting coatings were characterized regarding their physical properties including ATR-IR, TGA, optical contact angle, light microscopy, REM-EDX and AFM data. Transparent homogeneous films of high flexibility resulted from lignins isolated at pH 4, possessing a temperature resistance up to 160 °C. Swelling tests revealed a resistance against water. Swelling in DMSO depends on index, pH of precipitation and catalyst utilization for PU preparation. According to AFM studies, surface roughness is between 10 and 28 nm.
Gas chromatography with flame-ionization detection (FID) and gas chromatography-mass spectrometry (GC/MS) has been used for structure elucidation of long-chain primary n-alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization- (EI) and positive chemical ionization- (PCI) mass spectra of trifluoroacetylated derivatives of the identified nalkyl amines are presented. The corrosion inhibiting n-alkyl amines were applied in the investigation of a new anticorrosive and antifouling formulation for water-steam circuit of energy systems in the power industry. The presented results are part of an EU-funded international collaboration with partners from research institutes and industry from Poland, Lithuania, Romania, France and Germany (EUREKA project BOILTREAT E!2426).
For the last 20 years, solid-phase microextraction (SPME) in headspace (HS) mode has been used as a valuable sample preparation technique for identifying degradation products in polymers and the determination of residual monomers and other light-boiling substances in polymeric materials. For more than 10 years, our laboratory has been involved in projects focused on the application of HS-SPME-gas chromatography–mass spectrometry (GC–MS) for the characterization of polymeric materials from many branches of manufacturing and building industries. This article describes the application of this technique for identifying volatile organic compounds (VOCs), additives, and degradation products in industrial rubber, car labeling reflection foil, and bone cement materials. The obtained analytical results were then used for troubleshooting and remedial action of the technological processes as well as for the health protection of producers and users.
The criteria for assessing the quality of rubber materials are the polymer or copolymer composition and the additives. These additives include plasticizers, extender oils, carbon black, inorganic fillers, antioxidants, heat and light stabilizers, processing aids, cross-linking agents, accelerators, retarders, adhesives, pigments, smoke and flame retardants, and others. Determination of additives in polymers or copolymers generally requires the extraction of these substances from the matrix as a first step, which can be challenging, and the subsequent analysis of the extracted additives by gas chromatography (GC), GC-mass spectrometry (MS), high performance liquid chromatography (HPLC), HPLC-MS, capillary electrophoresis, thin-layer chromatography, and other analytical techniques. In the present work, nitrile rubber materials were studied using direct analytical flash pyrolysis hyphenated to GC and electrospray ionization MS in both scan and selected ion monitoring modes to demonstrate that this technique is a good tool to identify the organic additives in nitrile rubber.
The criteria for assessing the quality of rubber materials are the polymer or copolymer composition and the additives. These additives include plasticizers, extender oils, carbon black, inorganic fillers, antioxidants, heat and light stabilizers, processing aids, cross-linking agents, accelerators, retarders, adhesives, pigments, smoke and flame retardants, and others. Determination of additives in polymers or copolymers generally requires the extraction of these substances from the matrix as a first step, which can be challenging, and the subsequent analysis of the extracted additives by gas chromatography (GC), GC–mass spectrometry (MS), high performance liquid chromatography (HPLC), HPLC–MS, capillary electrophoresis, thin-layer chromatography, and other analytical techniques. In the present work, nitrile rubber materials were studied using direct analytical flash pyrolysis hyphenated to GC and electrospray ionization MS in both scan and selected ion monitoring modes to demonstrate that this technique is a good tool to identify the organic additives in nitrile rubber.
Pyrolysis–Gas Chromatography
(2018)
The methodology of analytical pyrolysis-GC/MS has been known for several years, but is seldom used in research laboratories and process control in the chemical industry. This is due to the relative difficulty of interpreting the identified pyrolysis products as well as the variety of them. This book contains full identification of several classes of polymers/copolymers and biopolymers that can be very helpful to the user. In addition, the practical applications can encourage analytical chemists and engineers to use the techniques explored in this volume.
The structure and the functions of various types of pyrolyzers and the results of the pyrolysis–gas chromatographic–mass spectrometric identification of synthetic polymers/copolymers and biopolymers at 700°C are described. Practical applications of these techniques are also included, detailing the analysis of microplastics, failure analysis in the automotive industry and solutions for technological problems.
This book chapter describes application examples of gas chromatography/mass spectrometry and pyrolysis – gas chromatography/mass spectrometry in failure analysis for the identification of chemical materials like mineral oils and nitrile rubber gaskets. Furthermore, failure cases demanding identification of polymers/copolymers in fouling on the compressor wall of a car air conditioner and identification of fouling on the surface of a bearing race from the automotive industry are demonstrated. The obtained analytical results were then used for troubleshooting and remedial action of the technological process.
Solid-Phase Microextraction (SPME) is a very simple and efficient, solventless sample preparation method, invented by Pawliszyn and coworkers at the University of Waterloo (Canada) in 1989. This method has been widely used in different fields of analytical chemistry since its first applications to environmental and food analysis. SPME integrates sampling, extraction, concentration and sample introduction into a single solvent-free step. The method saves preparation time, disposal costs and can improve detection limits. It has been routinely used in combination with gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) and successfully applied to a wide variety of ompounds, especially for the extraction of volatile and semi-volatile organic compounds from environmental, biological and food samples.
Since the last twenty years, SPME in headspace (HS) mode is used as a valuable sample preparation technique for identifying degradation products in polymers and for determination of rest monomers and other light-boiling substances in polymeric materials. For more than ten years, our laboratory has been involved in projects focused on the application of HS-SPME-GC/MS for the characterization of polymeric materials from many branches of manufacturing and building industries. This book chapter describes the application examples of this technique for identifying volatile organic compounds (VOCs), additives and degradation products in industrial plastics, rubber, and packaging materials.
According to the International Union of Pure and Applied Chemistry (IUPAC) recommendation, analytical pyrolysis (Py) is defined as the characterization in an inert atmosphere of a material or a chemical process by a chemical degradation reaction(s) induced by thermal energy [1]. Thermal degradation under controlled conditions is often used as a part of an analytical procedure, either to render a sample into a suitable form for subsequent analysis by gas chromatography (GC), mass spectrometry (MS), gas chromatography coupled with the mass spectrometry (GC/MS), with the Fourier-transform infrared spectroscopy (GC/FTIR), or by direct monitoring as an analytical technique in its own right [2].