Decomposition Of Polymers Research Articles

Supercritical Hydrothermal Reactions for Material Synthesis

Abstract Since the early 1990s, Adschiri and his colleagues have performed research on the use of supercritical water in diverse applications, including heavy oil reforming, waste polymer decomposition and chemical raw materials recovery, cellulose hydrolysis and sugar recovery, lignin decomposition and chemical raw materials recovery, and nanoparticle synthesis. Regarding inorganic materials synthesis, they invented supercritical hydrothermal synthesis for the continuous flow synthesis of metal oxide nanoparticles, which has already found worldwide industrial applications. They proposed a two-fluid mixing flow system where an aqueous metal salt solution is mixed with supercritical water to heat the solution to the supercritical state within a very short time, that is not attainable by conventional reactor systems. Organic-inorganic hybrid nanoparticles synthesis was demonstrated in the supercritical state, realizing homogeneous phase formation of organic molecules at high loadings. By optimizing the reaction conditions, small facet-controlled nanoparticles with narrow particle size distribution can be obtained. Organic modification of nanoparticles is shown to be effective for fabricating highly concentrated nanohybrid polymers or nano inks. Furthermore, these synthesized facet-controlled nanoparticles show high catalytic activities. Indeed, it is demonstrated that steam reforming of heavy oils or biomass wastes (black liquor) can occur in water even at low temperatures.

Polymer‐Derived High‐Temperature Nonoxide Materials: A Review

This review is focused on an attractive class of polymer‐derived high‐temperature ceramics, namely, polymer‐derived nonoxide materials. With a brief introduction of high‐temperature nonoxides, the origin of using polycarbosilane (PCS) polymer melt spinning to synthesize silicon carbide (SiC) fibers is traced back. For SiC formation, the four stages for the conversion from polymer precursors to microcrystalline ceramics are examined first: crosslinking, polymer decomposition, ceramic formation, and crystallization. Also, the important parameters related to PCS pyrolysis are explained, and polymer‐derived SiC microstructures and compositions are evaluated. Solid‐solution carbides and transition metal carbides are further reviewed. For boride materials, the discussion is focused on transition metal borides and boride composites. Similar to PCS conversion to SiC, nitride materials mostly start with polycarbosilazane (PSZ) precursors and form into the final materials through pyrolysis. With different carbide and nitride precursors mixed and pyrolyzed together, high‐temperature nonoxide composites are formed. Such molecular‐level intermixing and versatile capability of forming different shapes enable many exciting properties. Among these are mechanical and thermal properties, along with electrical conductivity, electromagnetic shielding, and charge storage capability. An overview of applications of polymer‐derived nonoxides is provided, followed by a summary and outlook.

Spectral properties inspired image enhancement for crystalline polymer powder impurity detection

Crystalline polymer powder inevitably incorporates certain impurities, including decomposed polymers or foreign particles. An essential criterion for assessing the quality of polymers is the quantity of contaminants in the powder. However, it is challenging to discern powder contaminants through machine vision due to the poor quality of images taken at production sites. Inspired by the spectral properties of crystalline polymers, this paper proposes an efficient image-based impurity detection method, which seeks to precisely and robustly detect contaminant content. Based on the changes in absorbance during polymer decomposition, a highly selective channel-weighted image enhancement approach is designed to emphasize the difference between impurities and normal particles. Then, using the prior information on the powder’s attributes, an adaptive thresholding method is employed to categorize pixels belonging to impurities. Finally, a dataset of 119 12-megapixel photos from a chemical facility, where the average size of contaminants in images is 43 pixels, is used to evaluate the performance of the proposed algorithm. The results of the detection demonstrate that the proposed strategy for image enhancement has better selectivity to impurities than typical image enhancement methods.

Sewage sludge valorisation by hydrothermal carbonization: A new method to enhance nitrogen removal in hydrochar catalyzed with Ni–Mg–Al layered double oxides

Hydrothermal carbonization is a technology that can quickly treat sludge. However, the high nitrogen content of the sludge hydrochar will produce NOx and pollute the environment, which influences the utilization of hydrochar as a fuel. Therefore, the calcined Ni–Al and Ni–Mg–Al layered double hydroxides (LDH) catalyst, named layered double oxides (LDO), were used for catalytic nitrogen removal during hydrothermal carbonization. Compared with the sample without catalyst, the layered double oxides catalyst showed excellent nitrogen removal capability, which can reach more than 57.00% at 240 °C. LDH catalyst enhanced the destruction of sludge structure to effectively realize the transfer of nitrogen-containing substances from solid phase to aqueous phase, which decreased the content of organic-N in hydrochar and increased the content of ammonia nitrogen and total nitrogen in aqueous phase to 4184 and 6463 mg/L, respectively with Ni–Mg–Al LDO at 240 °C. Moreover, this study also adjusted the acid-base sites by changing the metal ratio of catalysts, which was the key to produce the low nitrogen hydrochar. The acid sites were beneficial to inhibit the Maillard reaction and the basic sites can promote the decomposition of extracellular polymer (EPS). The possible removal pathways were proposed in this study.

Формирование молекулярных кластеров серебра полимерно-солевым методом в пористых стеклах

A methodology for the formation of molecular clusters of silver in silicate nanoporous glasses has been developed. Composite materials containing molecular clusters of silver, silver nanoparticles and zinc oxide have been synthesized. The synthesis was carried out by impregnation of porous glasses in aqueous solutions of silver and zinc nitrates stabilized with high-molecular polyvinylpyrrolidone, followed by heat treatment of samples for decomposition of metal nitrates and polymer. Spectral-luminescent properties of composites have been investigated.

Formation of molecular clusters of silver by polymer-salt method in porous glasses

A methodology for the formation of molecular clusters of silver in silicate nanoporous glasses has been developed. Composite materials containing molecular clusters of silver, silver nanoparticles and zinc oxide have been synthesized. The synthesis was carried out by impregnation of porous glasses in aqueous solutions of silver and zinc nitrates stabilized with high-molecular polyvinylpyrrolidone, followed by heat treatment of samples for decomposition of metal nitrates and polymer. Spectral-luminescent properties of composites have been investigated. Keywords: porous glass, zinc oxide, silver molecular clusters, silver nanoparticles, spectral-luminescent properties.

Heat-set supramolecular polymer gel and decomposition by guests

A degradable, heat-set fibrillar gel by supramolecular polymer in DMF based on stearic acid appended l-lysine, β-cyclodextrin and potassium carbonate has been developed. The heat-set stable, irreversible gel decomposed by aromatic guest molecules.

Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development.

Processing of Biomass Prior to Hydrogen Fermentation and Post-Fermentative Broth Management.

Using bioconversion and simultaneous value-added product generation requires purification of the gaseous and the liquid streams before, during, and after the bioconversion process. The effect of diversified process parameters on the efficiency of biohydrogen generation via biological processes is a broad object of research. Biomass-based raw materials are often applied in investigations regarding biohydrogen generation using dark fermentation and photo fermentation microorganisms. The literature lacks information regarding model mixtures of lignocellulose and starch-based biomass, while the research is carried out based on a single type of raw material. The utilization of lignocellulosic and starch biomasses as the substrates for bioconversion processes requires the decomposition of lignocellulosic polymers into hexoses and pentoses. Among the components of lignocelluloses, mainly lignin is responsible for biomass recalcitrance. The natural carbohydrate-lignin shields must be disrupted to enable lignin removal before biomass hydrolysis and fermentation. The matrix of chemical compounds resulting from this kind of pretreatment may significantly affect the efficiency of biotransformation processes. Therefore, the actual state of knowledge on the factors affecting the culture of dark fermentation and photo fermentation microorganisms and their adaptation to fermentation of hydrolysates obtained from biomass requires to be monitored and a state of the art regarding this topic shall become a contribution to the field of bioconversion processes and the management of liquid streams after fermentation. The future research direction should be recognized as striving to simplification of the procedure, applying the assumptions of the circular economy and the responsible generation of liquid and gas streams that can be used and purified without large energy expenditure. The optimization of pre-treatment steps is crucial for the latter stages of the procedure.

Simulation of the thermal degradation kinetics of biobased/biodegradable and non-biodegradable polymers using the random chain-scission model. Capabilities and limitations

In literature, several models have been applied in the simulation of the thermal degradation of polymers. Often, the models used were taken from solid-state physics and found to simulate very well the experimental data, though without any real physical meaning. In this investigation, a systematic approach is carried out regarding the simulation of the thermal decomposition of polymers using the random chain-scission model. Specifically, the model developed by Sánchez-Jiménez, P é rez-Maqueda and Criado based on the original idea of Simha and Wall is analyzed and applied to several polymers including polyolefins, styrenics, aromatic or aliphatic polyesters both biobased/biodegradable and non-biodegradable. The aim is to compare the thermal stability of several polymers and provide kinetic parameters having physical meaning based on a meaningful kinetic model. In order to estimate the kinetic parameters independently and consistently, the following procedure is proposed: initially, one has to perform experiments at several heating rates in order to estimate the activation energy of the reaction using a differential or an advanced integral isoconversional approach. Following, a system of differential equations is set and solved based on the random scission model, using only one adjustable parameter, i.e. the pre-exponential factor. It was found that using the same set of parameters, thermogravimetric data for all these polymers at several different heating rates can be simulated very well in the range of relative degree of degradation from 30% to 90%. This observation verified the hypothesis that at this region of degradation the dominant mechanism for several polymers is that of random scission. The best set of kinetic parameters is proposed for several polymers with the activation energy mainly ranging in between 160 and 210 kJ/mol.

Trends for the Thermal Degradation of Polymeric Materials: Analysis of Available Techniques, Issues, and Opportunities

This paper examines the degradation trends of polymeric materials during heat conversion and solvolysis processes. The presence of different fractions of polymeric materials, such as PET, PP, SBR, ABS, resin, and tier waste, necessitates the use of different procedures for degradation, transformation, and further elimination from the natural environment. A significant part of the work was devoted to discussing the issue of thermal pyrolysis, taking into account the chemical composition and the possible impact of the process reaction mechanism, the type of raw material used, and the influence of the process temperature on the yields of low, medium, and high boiling products. The issue was extended to the possibility of decomposition of polymers based on the use of catalytic additives for the improvement and efficiency of the process and the structural modification of reactors. The major goal of this investigation of these various options was to generate a spectrum of accessible strategies for polymeric material degradation. The optimal technique depends on the polymer type and predicted final product qualities. Different catalysts, such as ZSM-5 (Zeolite Socony Mobil-5 one of the most efficient catalysts), ZSM-5 with ammonium groups, and ZSM-5 with 10% Ni, improved the efficiency of several heating processes. The final products after polymeric material degradation were determined by the type and conditions of the degradation processes, results of the materials characterisation, and the scale of the reactors utilised.

Effects of polyphenols on the thermal decomposition, antioxidative, and antimicrobial properties of poly(vinyl alcohol) and poly(vinyl pyrrolidone)

Thermal stabilizers are frequently employed to increase the thermal stability of polymers. Among the thermal stabilizers, the polyphenols and related molecules have been widely used as thermal stabilizers of polymers. However, the effect of the number of their phenolic hydroxyl groups on the thermal decomposition of polymers was relatively less studied. In this study, three phenolic compounds with different numbers of phenolic hydroxyl groups (phenol, pyrocatechol, and pyrogallol) were incorporated in water-soluble poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) to fabricate the polymer/phenolic additive composite films. The effects of the phenolic additive on the thermal decomposition of PVA and PVP were investigated through thermogravimetric analysis. The results suggested that the phenolic additive is effective as a thermal stabilizer, owing to its radical-trapping action, when its boiling point is higher than the thermal decomposition temperature of the polymer (PVA and PVP) and the polymer decomposition follows a radical pathway. In addition, to compare the effect of the number of phenolic hydroxyl groups in the phenolic additive on the properties of the composite films, their antioxidative and antibacterial activities were evaluated using the α,α-diphenyl-β-picrylhydrazyl assay and disk diffusion test, respectively.

Simple Method to Analyze Degradation of Nonaqueos Polymers

Polymers are one of the most important materials used in our daily life. Polymers are mainly synthesized from monomers through a process called polymerization, and most synthesized polymers change their state over time. For example, some polymers are continuously decomposed after the polymerization is finished. Gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), and viscometry are commonly used for analyzing the polymers. Each of these methods has their own advantages and disadvantages. However, in common, these methods have disadvantages in that analysis takes a long time and requires a large number of samples. In this study, we have developed an electrochemical method based on cyclic voltammetry to measure the degradation of polymers. To validate our work, we measured the CV under the conditions of polymers degradation. As a result, it was possible to measure different current values in samples in which large amounts of polymers was decomposed. We believe that the method presented here is a sensitively measure the degree of decomposition of polymers, and this method will be of great help in analyzing and maintaining the properties of polymers.

지르코니아 나노입자 기반 나노패턴 금속 몰드 제작과 열가소성 재료의 복제성형 응용

Fabrication of a durable and strong nanopatterned mold insert using metal sheet and plate is important for molding of thermoplastic materials. Conventionally, the nickel stamper replicating a master pattern by electroforming process has been used for injection molding of nanotextured products such as Blu-ray media. However, a more facile and cheaper mold fabrication process is highly required for manufacturing of functional products based on nanostructured surface. In this study, zirconia nanoparticles were blended with UV curing polymer to fabricate a polymer nanocompositebased nanopattern mold. Compared to the cured pure Ormostamp, the modulus of elasticity of the nanocomposite filled with approximately 54 vol% of zirconia nanoparticles increased by 160 times. Additionally, the modulus of elasticity reached 197 ㎬ by thermal decomposition of the UV-Cured polymer and post-annealing at 800°C of the nanoparticle layer. The nanopatterns were formed on stainless steel sheet and block, and applied to hot embossing of the PMMA films and injection molding of the COC materials, respectively. No deterioration of the mold occurred during the hot embossing 30 times and the injection molding 600 shots. Nanoparticle-enhanced UV curing nanocomposites or post-heat treatment methods are cost-efficient and easy, because many molds can be manufactured from one master pattern.

Upcycling Polytetrahydrofuran to Polyester

Upcycling Polytetrahydrofuran to Polyester

Catalytic Activation of Polyethylene Model Compounds Over Metal-Exchanged Beta Zeolites.

Decomposition of polymers by heterogeneous catalysts presents a promising approach for reuse of waste plastics. We demonstrated non-hydrogenative decomposition of model polyolefins over proton-form and metal (Cu, Ni) ion-exchanged beta (BEA) zeolites at moderate temperatures (around 300 °C). Near complete polyolefin decomposition was observed in batch reactions monitored by thermogravimetric analysis, while decomposition at partial conversion was studied in flow reactions. Ni-exchanged zeolites produced H2 at substantially higher rates (>10x) than other catalysts while also uniquely resisting deactivation over time. Application of the delplot formalism offered insights into the reaction network for polyolefin decomposition over Ni/BEA most notably that H2 is solely a primary product. We deduce that H2 production is catalyzed by activation of C-H bonds at ionic Ni sites, and H2 prevents buildup of polyaromatic coke species in Ni-exchanged zeolites that deactivate Cu-exchanged and protonic zeolites.

Self-heating evaluation on thermal analysis of polymethyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE)

Thermal analysis has been proven to be an efficiently technique to analyse thermal decomposition reactions of different type of materials. This technique is widely used in different fields. Among them, fire science, where polymeric materials are very common, has a particular issue, being the combustion reactions recurrent on these analyses. Thermal analysis has different particularities depending on the studied material. For instance, polymeric materials could undergo different decomposition reactions that are highly dependent on definition of the thermal analysis boundary conditions. The International Confederation for Thermal Analysis and Calorimetry (ICTAC) (Vyazovkin et al. in Thermochim Acta 590:1–23, 2014) and standards (ISO 11358-1. Plastics—Thermogravimetry (TG) of polymers—Part 1: General principles. ISO. 2014; https://www.iso.org/standard/59710.html. Accessed 31 Jan 2022), (ISO 11357-1. Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles. ISO. 2016; https://www.iso.org/standard/70024.html. Accessed 31 Jan 2022) stablish how to set-up these boundary conditions in the thermogravimetric (TG) and differential scanning calorimetry (DSC) standards. As far as initial amount of sample mass is concern, some discrepancies can be found between the standards. For instance, the standards suggest a sample mass between 10 and 100 mg for TG and between 2 and 40 mg for DSC, whereas the ICTAC recommendations suggests that the sample mass times the heating rate should not exceed 100 mg K·min−1 in thermo-oxidative decomposition analysis, which is equivalent to samples masses lower than 10 mg for heating rates of 10 K·min−1, or lower than 5 mg for heating rates of 20 K·min−1. This discrepancy may lead to obtain different results from the tests. Additionally, according to the thermal and thermo-oxidative decomposition of polymers, the ICTAC remarks the influence on the results of the sample thicknesses, carrier gas and heating rates, but it does not analyse the influence of self-heating as it does for the hazardous materials. This work presents a study of the self-heating influence in the thermal decomposition processes of two widely used polymers as poly methyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE). TG/DSC tests are used to evaluate the thermal decomposition processes. Boundary conditions of the tests definition as sample mass, atmospheres, and heating rate are considered to evaluate its influence on the polymers self-heating effect on the thermal decomposition. It also includes how to check if TG/DSC tests follows the theoretical principles of the thermal analysis, or if the results are affected by the self-heating. In the present study, a series of 32 experimental tests has been performed, analysing 16 boundary conditions. These experimental tests allow evaluating the influence of selected boundary conditions on the mass loss, the heat flux, and the materials decomposition reactions. Additionally, we analyse the effect of the boundary conditions on the temperature of the sample. Results show the impact of each different boundary conditions of the self-heating effect, and its influence in the final thermal decomposition measured and they represent an aid to define the suitable conditions to perform TG/DSC test on PMMA and LLDPE, or similar polymer materials. This is done by the evaluation of the influence of the self-heating in parameters as the sample temperature lags defined in [1], the reactions heat fluxes, and the difference between the sample and the programmed temperature. It is also analysed the influence of the auto-ignition temperature in the thermal analysis. It is remarkable the PMMA auto-ignition temperature effect on the TG/DSC results. Finally, some useful recommendations have been defined.

Design of Zr- and Al-Doped *BEA-Type Zeolite to Boost LDPE Cracking.

Nowadays, the increase in plastic waste is causing serious environmental problems. Catalytic cracking has been considered a promising candidate to solve these problems. Catalytic cracking has emerged as an attractive process that can produce valuable products from plastic wastes. Solid acid catalysts such as zeolites decompose the plastic waste at a lower temperature. The lower decomposition temperature may be desirable for practical use. Herein, we synthesized both Zr- and Al-incorporated Beta zeolite using amorphous ZrO2–SiO2. The optimized Zr content in the dry gel allowed the enhancement of Lewis acidity without a significant loss of Brønsted acidity. The enhancement of Lewis acidity was mainly due to Zr species incorporated into the zeolite framework. Thanks to the enhanced Lewis acidity without any significant loss of Brønsted acidity, higher polymer decomposition efficiency was achieved than a conventional Beta zeolite.

The development of 3D technology for the creation of glass sealants for tubular oxide fuel cells

AbstractThe creation of gas‐tight connections in solid oxide fuel cells (SOFCs) requires finding a suitable glass sealant composition and developing high‐tech approaches to sealant molding. 3D printing has been used successfully to mold SOFC functional materials (anode, electrolyte), and this study tests its applicability to glass sealant printing. We have found the composition of the glass‐filled polymer compound to print glass sealants for tubular SOFCs: the polycaprolactone/filler ratio is 60/40 wt%. Silica has been shown to be a good model filler to polish the 3D printing technology. Polymer decomposition during sealing leads to the formation of voids and seal failure, which indicates that the filler content of 40 wt % is insufficient for such purposes.

Measurement of organic and elemental carbon in the char deposits from the combustion of permitted and undesirable fuels in domestic boilers

Burning solid fuels in domestic boilers during the heating season increases the concentrations of dust containing carbonaceous particles that exist as organic carbon (OC) and elemental carbon (EC). For economic reasons, plastic wastes are also incinerated with traditional energy fuels. In this study, fossil fuels (bituminous coal and lignite) and biomass (softwood and hardwood) together with an addition of different types of plastics (HDPE, LDPE, PP, and PET) were combusted in domestic boilers. Carbonaceous matter in deposits (char and soot) from the combustion of fuels and fuels with added plastics has been examined by the thermo-optical method using an OCEC Lab analyser. The addition of plastics significantly changes the concentrations of individual carbon forms. The temperature range of the EC2 fraction (740 – 840 °C) includes the charring of plastics and OC3 (480 – 580 °C) and corresponds to the temperature range for polymer decomposition. Deposits from bituminous coal combustion contained EC2 = 10.28 mg/kg of combusted fuels, and OC3 = 1.25 mg/kg of combusted fuels. After the addition of plastics to bituminous coal, the concentrations of EC2 = 23.91 mg/kg, OC3 = 3.13 mg/kg of combusted household fuels increased. Similar changes in the concentrations of the EC2 and EC3 fractions were found after adding plastics to biomass and lignite. The method can be used for the preliminary identification of “banned fuels” in domestic boilers.