Thermal degradation mechanism and thermal degradation rate constants of poly(epichlorohydrin-co-ethylene oxide) derived from GC-MS pyrolysis studies (2023)

Hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated polyether (HTPE) are used as binders for rocket fuels, while the mechanisms of their pyrolysis processes are still unclear. In this work, the slow and fast pyrolysis behavior of HTPB and HTPE was investigated using a combination of single photoionization mass spectrometry (SPI-MS) and GC-MS, respectively. SPI-MS allowed online study of the dynamics of volatile formation as a function of the pyrolysis process, and GC-MS was used to characterize the condensed products. In addition, heavy products (m/z>300) in the condensed liqs. were also characterized by Fourier transform cyclotron resonance mass spectrometry (FT-ICRMS). Based on the experimental results, a complete picture of the pyrolysis product distributions of HTPB and HTPE has been described. In the meantime, degradation pathways have been proposed and thoroughly discussed. The results showed that the radical addition reaction dominated the HTPB decomposition pathways, where the six-membered ring products were easily formed. HTPE was mainly converted to ethers or aldehydes during the pyrolysis process, and the cyclic products mainly consisted of tetrahydrofuran and its derivatives.

A new poly(epichlorohydrin-)plus-ethylene oxide)-G-Poly(methyl methacrylate)-Copolymer (ECO-G-PMMA) was successfully synthesized from a commercially renewable elastomer using the ATRP method. The graft copolymer was investigated as a curing and compatibilizing agent for polylactide (PLA) and PLA/ECO blends. Binary blending of PLA with the copolymers (5-15% by weight) significantly improved the tensile strength of PLA to over 200% without any significant loss of strength. Most importantly, PLA/ECO/ECOG-PMMA copolymer blends showed remarkably high impact strength of 96.9 kJ/m²with unbroken behavior. An interesting phase structure transformation from a typical sea island structure to a unique quasi-continuous lattice structure has been observed in different ECOG-PMMA from 0 to 15% by weight in ternary mixtures. Analysis of the physical hardening mechanism showed the synergistic hardening effect of good interfacial adhesion and the unique quasi-continuous morphology gave the ternary blends excellent mechanical performance.

Thermal degradation of PLA is a complex process as many reactions take place simultaneously. The use of analytical techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TGA) provides useful information, but a more sensitive analytical technique will be required to identify and quantify PLA degradation products. In this work, the thermal degradation of PLA at elevated temperatures was studied using a pyrolyzer coupled to a gas chromatograph with detection by mass spectrometry (Py-GC/MS). The pyrolysis conditions (temperature and time) were optimized to achieve sufficient chromatographic separation of the compounds formed during heating. The best resolution of the chromatographic peaks was obtained by pyrolyzing the material from room temperature to 600°C for 0.5 seconds. These conditions allowed the identification and quantification of the main compounds formed during the thermal degradation of PLA in an inert atmosphere. The strategy for selecting these operating parameters was sequential cracking based on fitting mathematical models. Using this strategy, it could be shown that PLA degrades at high temperatures following a non-linear behavior. Application of the logistic and Boltzmann models lead to good fits of the experimental results, although the Boltzmann model provides the best approximation for calculating the time required for 50% of PLA to degrade. In summary, the Boltzmann method can be used as a tool to simulate the thermal degradation of PLA.

The photodegradation of polyglycidol in aqueous solution was investigated at a UV wavelength of 254 nm. Experiments were performed in air at a constant temperature and the photodegradation of polyglycidol (PGl) was compared with that of polyethylene oxide (PEO), the most commonly studied polyether. Size exclusion chromatography with multi-angle light scattering detection (SEC-MALLS) was used to measure changes in molecular weights and molecular weight dispersions of polymers during degradation. The molecular mass of PGl decreased dramatically during the first UV exposure period and gradually approached the limit of 17,000 g/mol, regardless of the initial polymer concentration. PEO was less sensitive to UV radiation than polyglycidol, however, both polymers are degraded mainly by chain scission. The degradation of PGE and PEO leads to acidification of their aqueous solution. The photooxidation products were analyzed by FTIR and NMR spectroscopy, and the spectrophotometric results showed that the irradiation of the polymers led to the formation of carbonyl groups in the macromolecular chains. A mechanism responsible for the main photooxidation pathways of PGl is proposed.

Plastics have become an integral part of human life. Its massive use is a major environmental and economic concern, which has prompted researchers and technologists to induce varying degrees of degradation in plastics. These degradation processes can be better elicited if their mechanistic implications are properly understood. A better understanding of the mechanisms of these damages is also suggested to facilitate the proper development of alternative waste management strategies. Given the facts about the degradation of plastics, in this review article we discuss different types of polymer degradation and their mechanisms, including photooxidative degradation, thermal degradation, ozone-induced degradation, mechanochemical degradation, catalytic degradation, and biological deconstruction. This article also reviews the various methods used to study these changes and the factors that influence these changes.

Materials Today Communications, Band 3, 2015, S. 36–42

Nitrogen-enriched carbons with hierarchical pore structures were prepared by direct pyrolysis of melamine resin and poly(vinylidene fluoride) (PVDF) in an inert atmosphere. Our fabrication method produced carbons with a micropore surface of up to 966 µm²G⁻¹, with a maximum micropore width of about 0.5–0.6 nm and mesopore channels of 3–4 nm without the need for patterning or activation after carbonization. Carbons were characterized as N₂and companies₂Absorption analysis, X-ray photoelectron spectroscopy and elemental analysis. Nitrogen concentrations on the carbon surface ranged from 3.1-4.5 atomic %. The electrochemical performance of the carbon electrodes was evaluated by cyclic voltammetry, galvanostatic charge-discharge techniques and impedance spectroscopy at 1 M H₂AFTERWARD₄e 1M TEABF₄/acetonitrile. Electrochemical tests in aqueous electrolyte showed excellent rate performance with capacitive behavior up to 500 mVs⁻¹and specific capacitance of 125Fg⁻¹at a current density of 0.05 Ag⁻¹in a two-electrode cell. Good cycle performance is achieved in both aqueous and organic electrolytes, with 96% and 77% of initial capacity after 10,000 and 5,000 cycles, respectively.

Journal of Bioscience and Bioengineering, Band 121, Ausgabe 6, 2016, S. 631-637

yeastCandida guilliermondiiFTI 20037 is known for its ability to produce xylitol from xylose. Recently, this strain was found to produce more than 5% (w/v) ethanol from glucose. This ethanol content does not exceed normal wild-type strains of other natural pentose-fermenting yeasts. This prompted the current study to examine the ability to do soC.guilliermondiiFTI 20037 allows the use and fermentation of high concentrations of all hexoses commonly found in lignocellulosic hydrolysates. In defined media, FTI 20037 fermented 14.4–25.9% (w/v) glucose, mannose, or galactose separately in ethanol at concentrations ranging from 6% to 9.3% (w/v). Fermentation was completed within 36 hours (for glucose) to 100 hours (for galactose). At 25.9% (w/v) glucose, FTI 20037 produced 9.3% (w/v) ethanol in 40 h. FTI 20037 produced only xylitol when xylose was provided as the sole carbon source. The strain utilized arabinose poorly. Under the same fermentation conditions, aSaccharomyces cerevisiaeCepa produced slightly higher amounts of ethanol [9.9% (w/v)] than 25.0% (w/v) glucose. Another pentose fermenting yeastPachysolen tannophilusIt also fermented high concentrations of glucose and mannose to produce relatively high peak concentrations of ethanol. However, this yeast took much longer to fully consume these exosomes. The ability of FTI 20037 to rapidly produce a high percentage of ethanol from glucose is remarkable. To our knowledge, this is the first known example of an unmodified natural xylose-fermenting yeast strain capable of producing high levels of ethanol from glucose as rapidly as possible.Bier St.in a specified medium.

Systematic Biochemistry and Ecology, Volume 63, 2015, pp. 98-108

Matudaeais the only genus of Hamamelidaceae found in South America. The genus includes two extant species,M. trinervia, from Mexico and Costa Rica, andColombian Matudaea, from the Colombian Andes. There are other fossils in Central Europe. Approaches from population genetics, molecular phylogenetics and niche modeling were used to explain trans-Panama processesM. trinervia/M. colombianadivision and the alleged colonization of the latter north of the Andes. The separation between the twoMatudaeaThe species was estimated during the middle Miocene. the colonization ofMatudaeain South America may have been facilitated by the closure of the Isthmus of Panama and the fall in global temperature during the Miocene. Five haplotypes ofM. colombianawere identified that show an eastward decrease in genetic diversity and suggest a founding effect in the colonization of the eastern Cordillera of the Colombian Andes. We see a sign of specialized conservatism between the twoMatudaeaspecies related to the bioclimatic variables temperature of the coldest month and average temperature of the driest quarter; this sign is probably related to the narrow altitude of both species.

Composites Part A: Applied Science and Manufacturing, Τόμος 114, 2018, σελ. 97-106

Epoxy resin (EP) modified with non-polar rubbers has the potential to achieve simultaneous improvement in mechanical and dielectric properties if the EP-rubber interface is properly handled. Here we investigate rubber-cured EP based on a nonpolar hydroxyl-terminated polybutadiene (HTPB) and an adhesion promoter, dimeric fatty acid diisocyanate (DDI), in which the rubber is covalently bonded to the epoxy resin. Mechanical and dielectric properties can be improved by adding HTPB and are maximized with 15 phr of elastomer inclusion. The improved mechanical toughness is due to the extensive shear flow caused by a large amount of uniformly distributed rubber particles. The same morphology can also combine the good insulating properties of HTPB and dielectrically favorable interfaces. These facts together with the reduced dielectric constant and loss of the modified EP suggest that HTPB-DDI-EP can be used as a promising insulating packaging material for microelectronic applications.

Chemosphere, Band 145, 2016, S. 17-24

The properties of a packed bed bioreactor (PBB) for the continuous removal of Victoria Blue R (VBR) from an aqueous solution were determined. The effects of various factors, including liquid retention time (RT), RBV concentration, shock load, and co-compounds, on the removal of RBV and bacterial community in a continuous system were examined. Degraded RBV intermediates and acute toxicity of PBB effluents were analyzed. If the VBR concentration was less than 400 mg/L at a retention time (RT) of two days, 100% removal was achieved. In continuous operation, performance initially fluctuated with VBR and RT concentration, but gradually increased over the course of a day or two. In addition, the acute toxicity of the effluents was reduced by 21.25 to 49.61, suggesting that PBB can function successfully even under turbulent environmental conditions. VBR degradation involved stepwise demethylation and generated partially deacylated VBR species. Phylogenetic analysis showed that Proteobacteria were the dominant strain in PBBAeromonas hydrophiladominated throughout the season. The properties of the identified species showed that PBB is suitable for processes such as demethylation, aromatic ring opening, carbon oxidation, nitrification and denitrification.

Bioresource Technology, Band 188, 2015, S. 65-72

An absolute biological microbial electrolytic cell (ECM) was operated for a longer time under different applied potentials (m_Application, −0.2 V to −1.0 V) and hydrogen (H₂) was observed in acidic wastewater. Below these potentials, an optimum voltage of -0.6 V affected the biocathode through which the maximum H₂A production of 120 ± 9 ml was detected. This finding was confirmed by dehydrogenase activity (1.8 ± 0.1 μg/ml), which is the key enzyme for H₂Production. ISLANDno partBiocathode-regulated buffer overpotential observed specifically by changing the dissociation value (pKa) peak heights of the titration curve. Analysis of substrate degradation gave an estimated Coulombic efficiency of approximately 72 ± 5% when operating at the optimal voltage. Apparently, electron transfer from the solid carbon electrode to the biocathode was analyzed by cyclic voltammetry and its derivatives showed the involvement of redox mediators. However, MEC supports some activation overpotentials estimated by Tafel slope analysis.