Random Scission Model Research Articles

Understanding the kinetics of waste plastic catalytic pyrolysis under microwave irradiation for enhanced resource valorization

The increasing accumulation of ABS plastic waste poses significant environmental challenges, necessitating efficient methods for its disposal and recycling. The pyrolysis of the ABS plastic waste was performed under various heating programs including constant heating rate (27.5, 42.2 and 65 K min−1), and sample-controlled reaction rate (0.01 min−1) to obtain the TG curves using the in-house developed microwave assisted thermogravimetric analyzer. Fe-impregnated SiC was used as thermal and chemical catalyst, while neat SiC played only thermal catalyst role. The modified Sestak-Bergren equation used to model the TG data by Pearson’s linear correlation and associated parameters n = 1.129 and m = 0.27 was achieved. The comparison of normalized form of the conversion function (f (α)/f (0.5)) with the most common models of solid-state reactions showed that random scission model (L2) was the most suitable approach to physically explain the pyrolysis of ABS plastic waste. Furthermore, by applying isoconversional kinetic analysis, the variation of activation energy (Eα) with conversion value was approximately constant. The Eα obtained was 140.5 and 63.7 kJ/mol with SiC and Fe/SiC, respectively. These findings hold practical implications for industrial applications or waste management strategies, particularly when considering the developed microwave-assisted real-time TGA-pyrolysis, which can enhance the efficiency and sustainability of plastic waste recycling processes.

Insight into the pyrolysis of bamboo flour, polylactic acid and their composite: Pyrolysis behavior, kinetic triplets, and thermodynamic parameters based on Fraser-Suzuki deconvolution procedure

Kinetic triplets and thermodynamics are important in the design of pyrolysis processing. In this study, the non-isothermal kinetics and thermodynamics of pseudo components of bamboo flour (BF), Polylactic acid (PLA), and the resulting BF/PLA composite were investigated using Fraser-Suzuki deconvolution. Fourier-transform infrared spectra (FTIR) was used to characterize the gaseous products. Results showed the Fraser-Suzuki deconvolution curves fitted well to the experimental data. For pseudo hemicellulose and pseudo components in PLA, common kinetic models were applied. The pyrolysis of pseudo cellulose met the random scission model and pseudo lignin need to be described with empirical model. The Kinetic models were verified and shown to be in good agreement with the experimental results FTIR results indicated that more radical reactions occur in PLA during co-pyrolysis with BF.Thermodynamic results indicated the pyrolysis of pseudo components were non-spontaneous reactions except lignin. These results will contribute to reactor design and scale-up in future.

Preparation and evaluation of effective thermal decomposition of tetraamminecopper (II) nitrate carried by graphene oxide

Graphene oxide (GO) was investigated in this paper as a promising catalyst for the effective thermal decomposition of tetraamminecopper (II) nitrate coordination complexes. CuC has been synthesized by doping GO nanoparticles in a one-step method and it demonstrates a uniform deposition of the produced nanocomposites onto the surface of the complex. The kinetics of decomposition and underlying mechanisms of GO on CuC have been studied using a Differential Scanning Calorimetry (DSC) technique and Thermal Gravimetric Analysis (TGA) coupled Fourier-Transform Infrared Spectroscopy (FTIR) technique and relevant theories. Under the effect of GO, the release of heat from the decomposition process is significantly increased from 97.1 J·g-1 to 69.2 J·g-1. Under the effect of GO, the activation energy of the CuC decreased from 94.3 to 82.2 ± 0.5 kJ·mol−1 (for endothermic reaction). The significance of this discovery is due to the reactive sites and great thermal conductivity of the GO. By FTIR analysis, GO affected by the formation of NH3 and N2O; and the decomposition of CuC complex in cooperation with the GO may follow a random scission model (A2) since it highly depends on the edge defects of GO as well as coordination center reactive sites (scission sites). In addition, the combustion behavior of CuC and CuC–GO in the physical mixture with B/KNO3 has been investigated. The results show that the pressure exponent “n” samples (CuC: n = 0.621 vs. CuC–GO: n = 0.703) can be stable and investigated composites are available for successful application as energetic materials.

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.

Catalytic Effect of Ferrocenyl Energetic Catalysts for N-Guanylurea Dinitramide (GUDN or FOX-12) Decomposition.

Four N,N-dimethylaminomethylferrocene polynitrogen catalysts were applied to the thermal decomposition of FOX-12, and their catalytic effect on FOX-12 was investigated by TG-DSC. The kinetic parameters and kinetic model of the mixed system were revealed by the Kissinger method, Freidman method, and combined kinetic analysis. The results showed that MAFcTAZ is the catalyst with the strongest effect on FOX-12, the decomposition peak temperature of FOX-12 is reduced, and the decomposition weight loss is higher than those for other catalysts, which prove that the decomposition of FOX-12 is more thorough under the catalysis of MAFcTAZ. The introduction of the four catalysts reduced the thermal decomposition peak temperature of FOX-12. MAFcTAZ was the most active catalyst for the decomposition of FOX-12, and the maximum heat release of catalyzing the decomposition of FOX-12 can reach 1236.76 J·g–1. The activation energy (Ea) of FOX-12 decomposition decreased from 217.91 to 128.19, 137.85, 157.65, and 151.91 kJ·mol–1 under the effect of MAFcNO3, MAFcPA, MAFcNTO, and MAFcTAZ. The Freidman analysis illustrated that MAFcTAZ reduced the activation energy during the entire decomposition process of FOX-12. The physical model of the decomposition reaction of FOX-12 transformed from the random nucleation and two-dimensional growth of nuclei model (A2) to the random scission model (L2) in the presence of MAFcNO3 and two-dimensional diffusion (D2) under the effect of MAFcPA, MAFcNTO, and MAFcTAZ. By analyzing the molecular structures, MAFcTAZ has a higher iron content and nitrogen content, which are the essence of its excellent catalytic performance. From the perspective of interaction energy, the strong catalytic effect of MAFcTAZ is attributed to its large interaction energy with FOX-12 by energy decomposition analysis.

Changes in molecular weight distribution caused by main-chain scission of electron beam resists

Main-chain-scission-type resists have attracted much attention as the next-generation electron beam (EB) resist used for photomask fabrication. In this study, the gel permeation chromatography (GPC) charts of irradiated EB resists (ZEP series of ZEON) were analyzed by simulation to clarify the changes in the molecular weight distribution caused by the main-chain scission of a resist polymer. In the low-exposure-dose region, the molecular weight distribution obtained by GPC was well reproduced by the simulation using a random-scission model. In the high-exposure-dose region, the calculated molecular weight distribution deviated from the experimental one because of crosslinking and the generation of stable components.

Kinetics and mechanism of thermal degradation of vegetable-tanned leather fiber

Thermal degradation of vegetable-tanned leather fiber (VLF) was investigated by thermogravimetric analysis aiming to know the exact kinetics and degradation mechanism. The thermogravimetric (TG) and differential thermogravimetric (DTG) curves showed that decomposition of the VLF occurs mainly in the range of 150–600 °C, and the latter exhibits asymmetrical peak with a pronounced shoulder. The decomposition process was first analyzed by deconvolution of the experimental DTG curves, followed by reconstruction of the weight loss profiles of two individual processes. Several common isoconversional approaches were applied to calculate the activation energy over a wide range of conversion for the sample, including modified Kissinger-Akahira-Sunose (MKAS), Friedman, and Flynn-Wall-Ozawa. The average activation energy of vegetable-tanned leather fiber was found to be 241.9 kJ mol− 1 by MKAS method. The activation energy values obtained for the pseudocomponents representing highly-crosslinked and low-crosslinked collagen in VLF were given as 190.6 and 124.8 kJ mol− 1, respectively. Generalized master plots results suggested that the reaction mechanism for highly-crosslinked collagen follows the random nucleation and growth process at conversion values lower than 0.5. When the conversion is higher than 0.5, the mechanism tends to random scission model. For low-crosslinked collagen, the degradation is mainly governed by random nucleation and nuclei growth. The gaseous products of VLF thermal degradation were analyzed with an online-coupled TG-Fourier transform infrared spectroscopy system.Graphical abstract

Kinetic analysis of thermal and catalytic degradation of polymers found in waste electric and electronic equipment

Thermo-chemical recycling of plastics originating in waste electric and electronic equipment (WEEE) is always a challenge due to the production of secondary value-added compounds or energy from obsolete materials. The dominant step for a suitable design of any pyrolysis reactor is to understand the kinetics of thermal degradation of the input materials. Therefore, in this investigation thermal and catalytic degradation of several polymers found in WEEE, such as High-Impact Polystyrene (HIPS), polypropylene (PP), and polycarbonate (PC) as well as PC/MgO and PP/MCM-41 was investigated. The random scission model developed by Sanchez-Jimenez et al., with L = 2 was used for the simulation of the degradation of all systems at several heating rates. The activation energy was estimated using an isoconversional approach. A system of differential equations were set and solved using as an adjustable parameter only the pre-exponential factor. It was found that using the same set of parameters, thermogravimetric data at different heating rates can be simulated very well in the range 0.3 < α < 0.9. This observation verified the hypothesis that at this region of degradation the dominant mechanism is that of random scission. Better simulation was obtained at higher heating rates. Using catalysts of variable acidity, it was verified that the activation energy of the catalytic was decreased compared to the conventional thermal degradation.

A modified kinetic analysis method of cellulose pyrolysis based on TG–FTIR technique

The pyrolysis characteristics of cellulose was investigated using TGA and TG–FTIR. An modified reaction model was proposed to study cellulose pyrolysis. In this model, the active cellulose (E=137 kJ/mol) and dehydrocellulose (E=91.3 kJ/mol) were formed by parallel mechanism. The degradation of the active cellulose was followed by two competitive pathways, this is, one that formed levoglucosan (E=159.2 kJ/mol) and another that formed furan and some low molecular weight products (E=203.5 kJ/mol). The random scission model was used to describe the kinetics of cellulose pyrolysis. The same kinetic parameters were used for different linear heating rates (10–100 °C/min) and isothermal segment conditions. By successfully modeling non-isothermal and isothermal segment data, the model was proved to be credible in describing cellulose pyrolysis.

Pyrolysis mechanism and thermal degradation kinetics of poly(bisphenol A carbonate)-based polymers originating in waste electric and electronic equipment

Poly(bisphenol A carbonate) or polycarbonate (PC) constitutes a significant fraction of the Waste Electrical and Electronic Equipment, mainly due to its high production and consumption rate and its variety of applications. Traditional methods for its treatment no longer appear to provide long-term solutions and for this reason, the investigation of thermochemical methods and more specifically pyrolysis as a potential recycling method took place in the current study. In the first part of this study, pyrolysis studies of polycarbonate have been performed in a Pyrolizer equipped with GC–MS, at five different reactor temperatures, in order to facilitate the understanding of the degradation mechanism. Higher pyrolysis temperatures were found to be more suitable for PC pyrolysis, since they increased the volatile fractions (liquid and gaseous). The gaseous fraction consisted mainly of CO2, CH4 and CO, whereas in the liquid fraction a large amount of different phenolic compounds, including the monomer bisphenol A was recorded. Based on the findings, it has been suggested that the main degradation pathway follows a chain scission mechanism and that the scission of the isopropylidene linkage is the first step. Phenols and phenolic compounds were formed through a series of scission and hydrolysis reactions. In the second part, pyrolysis kinetics of PC are investigated in detail using thermogravimetric experimental data, collected at several heating rates and several either model-free (isoconversional) or model-fitting models. From the isoconversional kinetic analysis the effective activation energy was fund to increase with the extent of conversion, ranging from 146 to 189 kJ/mol and from 154 to 215 kJ/mol, when using the integral method of Tang (similar to the KAS) or the differential method of Friedman, respectively. A simple first order kinetic model was found to simulate excellent the experimental data, though predicting different activation energies and pre-exponential factors at each heating rate employed. The random scission and the autocatalytic models were investigated in detail and the best fit to the experimental data at all different heating rates was found to be the autocatalytic model with n = 1.15 and m = 0.46 (values close to those considered for the random scission model with L = 2, i.e. n = 1.119 and m = 0.4) using an average activation energy, E = 195.9 kJ/mol and pre-exponential factor A = 6.06 1012 min−1. Having a detailed knowledge of the PC degradation kinetics and mechanism will help in better design of large scale process for the recycling of such material originating in WEEE and provide targeted value-added products.

Development of a microwave thermogravimetric analyzer and its application on polystyrene microwave pyrolysis kinetics

To study pyrolysis kinetics inside a microwave environment, a microwave thermogravimetric analyzer was developed. A sample mass as low as 0.3 g can be studied along with silicon carbide as the microwave receptor. The temperature is measured with a custom-made infrared thermopile equipped with different optical filters specific to this application. Validation of the microwave thermogravimetric analyzer features showed that the measured data can be used as is for kinetic development. Different heating profiles can be achieved by modulating the microwave power. The microwave thermogravimetric analyzer was then used for the kinetic development of polystyrene microwave pyrolysis. Polystyrene was chosen because of its low recycling rate and its great potential to produce high-valued products, like styrene. Three heating rates (24.5, 38.5 and 49.5 °C min−1) were used to estimate the kinetic parameters. By comparing several reaction models, a random scission model was found to best explain the experimental data. The choice of the reaction model was made based on two statistical tests: the coefficient of determination R2 and the residual sum of squares RSS. With this reaction model, an activation energy of E = 45 kJ mol−1 and a pre-exponential constant of ln(A) = 3.6 were found for polystyrene microwave pyrolysis.

Ultrasound degradation of xanthan polymer in aqueous solution: Its scission mechanism and the effect of NaCl incorporation

Degradation of xanthan polymer in aqueous solution by ultrasonic irradiation was investigated. The effects of selected variables i.e. sonication intensity, irradiation time, concentration of xanthan gum and molar concentration of NaCl in solution were studied. Combined approach of full factorial design and conventional one-factor-at-a-time was applied to obtain optimum degradation at sonication power intensity of 11.5Wcm−2, irradiation time 120min and 0.1gL−1 xanthan in a salt-free solution. Molecular weight reduction of xanthan gum under sonication was described by an exponential decay function with higher rate constant for polymer degradation in the salt free solution. The limiting molecular weight where fragments no longer undergo scission was determined from the function. The incorporation of NaCl in xanthan solution resulted in a lower limiting molecular weight. The ultrasound-mediated degradation of aqueous xanthan polymer chain agreed with a random scission model. Side chain of xanthan polymer is proposed to be the primary site of scission action.

Thermogravimetric kinetics of lignocellulosic biomass slow pyrolysis using distributed activation energy model, Fraser–Suzuki deconvolution, and iso-conversional method

Pyrolysis kinetics of pine wood, rice husk and bamboo (Bambusa chungii) were studied via thermo-gravimetric analysis technique under low heating rates. The result of model-free procedure showed that the lignocellulosic pyrolysis according to one-step reaction model is dominated by the diffusion effects. However, the complex features of variations are caused by the mechanism changes, which are hard to be determined. The distributed activation energy model (DAEM) kinetic results indicated that the activation energy distribution for pseudo components follows the orders of: E0(lignin)>E0(cellulose)>E0(hemicelluloses), σ(lignin)>σ(hemicelluloses)>σ(cellulose). The Fraser–Suzuki deconvolution fits better with the experimental data than DAEM. The pyrolysis mechanism of pseudo components after deconvolutions follows the theoretical models: third order model f(α)=(1−α)3 for hemicelluloses and lignin, random scission model f(α)=2(α1/2−α) for cellulose. The apparent activation energy for pseudo hemicelluloses is 162.84±26.45kJ/mol for pine wood, 168.63±28.47kJ/mol for rice husk and 154.55±26.49kJ/mol for bamboo, respectively. The Eα value increases with the conversion with little deviation to its mean value. Similar Eα vs. α dependencies also are observed for pseudo celluloses, which has Eα of 188.14±24.42kJ/mol for pine wood, 206.71±24.88kJ/mol for rice husk and 190.45±23.79kJ/mol for bamboo, respectively.

Polysaccharides modification through green technology: Role of ultrasonication towards improving physicochemical properties of (1-3)(1-6)-α-d-glucans

Ultrasonication was applied to modify the structural and physicochemical properties of the (1 → 3)(1 → 6)-α-d-glucans from Leuconostoc citreum SK24.002. Upon ultrasound treatment, both the UV absorption at 220 nm and number-average molecular weight decreased substantially in the first 20 min, and then incrementally decreased to a plateau value after 160 min. The molecular weight distribution curves gradually shifted to the low molecular weight region with a narrower distribution and the chain degradation reaction followed the random scission model. NMR results showed that the partial consecutive α-1,6 linkages in the limited regions were ruptured by acoustic cavitations. The viscosity of modified glucan solution dropped remarkably and the glucan after ultrasonication for more than 20 min was dissolved in water to give solutions of 30 g/100 ml or greater. The Newtonian plateaus for sonicated glucan solutions were observed at the high shear rates (1–100 1/s).

Factors Affecting Enzymatic Degradation of Microgel-Bound Peptides

Proteolytic degradation and release of microgel-bound peptides was investigated for trypsin, poly(acrylic acid-co-acrylamide) microgels (70-90 μm in diameter), and oppositely charged polylysine, using a method combination of confocal microscopy and micromanipulator-assisted light microscopy. Results show that trypsin-induced release of polylysine increased with increasing trypsin concentration, decreasing microgel charge density and decreasing peptide molecular weight. While the microgel offered good protection against enzymatic degradation at high microgel charge density, it was also observed that the cationic peptide enabled trypsin to bind throughout the peptide-loaded microgels, even when it did not bind to the peptide-void ones. With the exception of highly charged microgels, proteolytic degradation throughout the peptide-loaded microgel resulted in the generation of short and non-adsorbing peptide stretches, giving rise to the concentration and peptide length dependence observed. A simple random scission model was able to qualitatively capture these experimental findings. Collectively, the results demonstrate that microgel charge density, peptide molecular weight, and enzyme concentration greatly influence degradation/release of microgel-bound peptides and need to be considered in the use of microgels, e.g., as carriers for protein and peptide drugs.

Efficient Reduction of Chitosan Molecular Weight by High-Intensity Ultrasound: Underlying Mechanism and Effect of Process Parameters

The degradation of chitosan by high-intensity ultrasound (HIU) as affected by ultrasound parameters and solution properties was investigated by gel permeation chromatography coupled with static light scattering. The molecular weight, radius of gyration, and polydispersity of chitosan were reduced by ultrasound treatment, whereas chitosan remained in the same random coil conformation and the degree of acetylation did not change after sonication. The results demonstrate that (1) the degradation of chitosan by ultrasound is primarily driven by mechanical forces and the degradation mechanism can be described by a random scission model; (2) the degradation rate is proportional to M w (3); and (3) the degradation rate coefficient is affected by ultrasound intensity, solution temperature, polymer concentration, and ionic strength, whereas acid concentration has little effect. Additionally, the data indicate that the degradation rate coefficient is affected by the degree of acetylation of chitosan and independent of the initial molecular weight.

31: Upregulation of IL-21 gene expression by HHV-6: contribution of CD4+ T cells to host's anti-viral innate immune response

Ultrasonication was applied to modify the structural and physicochemical properties of the (1 → 3)(1 → 6)-α-d-glucans from Leuconostoc citreum SK24.002. Upon ultrasound treatment, both the UV absorption at 220 nm and number-average molecular weight decreased substantially in the first 20 min, and then incrementally decreased to a plateau value after 160 min. The molecular weight distribution curves gradually shifted to the low molecular weight region with a narrower distribution and the chain degradation reaction followed the random scission model. NMR results showed that the partial consecutive α-1,6 linkages in the limited regions were ruptured by acoustic cavitations. The viscosity of modified glucan solution dropped remarkably and the glucan after ultrasonication for more than 20 min was dissolved in water to give solutions of 30 g/100 ml or greater. The Newtonian plateaus for sonicated glucan solutions were observed at the high shear rates (1–100 1/s).

Enzymatic hydrolysis by Humicola lanuginosa lipase of poly(lactic acid)-poly(glycolic acid) monolayers

The enzymatic hydrolysis by Humicola lanuginosa lipase (HLL) of spread insoluble monolayers of poly (α-hydroxy acid)s with various molecular weights and various lactic–glycolic molar ratios was studied using a barostat surface balance. The interfacial hydrolysis under enzyme action leads to the progressive fragmentation of the polymer molecules. The appearance at the interface of charged insoluble fragments was detected by measuring the surface potential, while the solubilization of the small soluble fragments was detected by measuring the decrease in the surface area. The data obtained were used to test the mode of fragmentation: either random or chain-end scission. The catalytic specific activity of HLL was estimated in the framework of the random scission model and compared with the activities obtained for the hydrolysis of simple molecules of di- and tri-glycerides organized as monolayers or emulsion.

Role of the molecular weight and the composition on the hydrolysis kinetics of monolayers of poly(α-hydroxy acid)s

The hydrolysis kinetics of spread insoluble monolayers of poly(α-hydroxy acid)s with various molecular weights and lactic acid–glycolic acid molar ratios was followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. The interfacial hydrolysis at alkaline pH leads to the progressive fragmentation of the polymer molecules and the appearance of charged insoluble products (detected by measuring the surface potential) and small soluble fragments (detected by measuring the decrease in the surface area). The data obtained by both approaches were interpreted in the framework of the random scission model. The rates of hydrolysis are larger for polymers with smaller initial polymerization numbers and increase with the decrease in the molar ratio of lactic acid units.

Ion beam effects on the surface and on the bulk of thin films of polymethylmethacrylate

Poly(methyl methacrylate) (PMMA) is a prototype polymer for positive resist (scission rate higher than cross linking rate). Notwithstanding its importance the literature studies on the chemical effects induced by energetic beam irradiation on this polymer are relatively scarce. The interest for PMMA is considerable also because it has been reported in literature that beyond a given threshold fluence (that in turn depends on the ion) the resist turns negative: i.e. the cross linking rate becomes higher than the scission rate. No explanation has been reported till now in literature for this behaviour. In this paper we report a study on the molecular weight distribution (MWD) of thin PMMA films irradiated with energetic beams. In addition we have also performed a study of the effects induced by the bombardment on the surface of the polymer by using the XPS (X-ray photoelectron spectroscopy) technique. The main results are: i) There is a strong evidence of contemporary scission and cross linking events. The first ones predominate at low fluences, the second ones at high fluences. ii) While at low fluence there is a good agreement between the experimental results and a simple equation based on random scission model, with increasing fluence one observes larger and larger deviations from this equation. These results will be discussed and compared with the existing literature reports.