Assessing thermal behaviours of cellulose and poly(methyl methacrylate) during co-pyrolysis based on an unified thermoanalytical study

Synergistically improve the strength and porosity of carbon paper by using a novel phenol formaldehyde resin modified with cellulose nanofiber for proton exchange membrane fuel cells

To optimize the imbalance between the interfacial bonding and porosity properties of carbon paper (CP) caused by phenol formaldehyde resin (PF) impregnation, and therefore improve the performance of proton exchange membrane fuel cells (PEMFCs), a new approach through cellulose nanofibers grafted with methyl methacrylate (CNFM) as a modified reinforcement and pore-forming agent for PF is investigated. Through suppressing the methylene backbone fracture of CNFM-modified PF during its thermal depolymerization, the interfacial bonding between PF matrix carbon and carbon fibers is enhanced. Compared with unmodified CP, the in-plane resistivity of CNFM-modified CP is reduced by 35.78 %, while the connected porosity increases to 82.26 %, and more homogeneous pore size distribution (PSD) in the range of 20-40 μm is obtained for CNFM-modified CP. Besides, the tensile strength, flexural strength, and air permeability of CNFM-modified CP increase by 72.78 %, 298.4 %, and 103.97 %, respectively. In addition, CNFM-modified CP achieves the peak power density of PEMFCs to 701.81 mW·cm-2, exhibiting 10.98 % improvement compared with commercial CP (632.39 mW·cm-2), evidently achieving an integral promotion of CP and comprehensive performance.

Effect of different thermoplastics on the thermal degradation behavior, kinetics, and thermodynamics of discarded bakelite

In this work, the kinetics, thermodynamics, and mechanism for co-pyrolysis of thermoplastic (PP, HDPE, PS, PMMA) blended bakelite (BL) (1:1 by weight) are explored utilizing different kinetics models like model-fitting and KAS model-free method. The thermal degradation experiments of each sample are conducted from ambient to 1000 °C temperature at 5, 10, 20, 30, and 50 °C/min heating rates in an inert environment. Thermoplastic blended bakelite is degraded in four steps, including two significant weight loss steps. A significant synergetic effect was observed by the addition of thermoplastics, which is reflected in the change in the thermal degradation temperature zone and the weight loss pattern. Among the four thermoplastics blended bakelites, the promotional synergetic effect is more pronounced for PP addition, causing an increase in the degradation of discarded bakelite by 20%, whereas the addition of PS, HDPE, and PMMA enhances the degradation of bakelite by 10%, 8%, and 3% respectively. Again, the activation energy of the thermal degradation of PP blended bakelite is found lowest followed by HDPE blended bakelite, PMMA blended bakelite, and PS blended bakelite. The mechanism of thermal degradation of bakelite changed from F5 to F3, F3, F1, and F2.5 by the addition of PP, HDPE, PS, and PMMA respectively. A significant change in the thermodynamics of the reaction is also found in the addition of thermoplastics. The kinetics, degradation mechanism, and thermodynamics for thermal degradation of the thermoplastic blended bakelite contribute to the optimization of pyrolysis reactor design to increase valuable pyrolytic products.

A Study of Parallel and Competitive Reaction Schemes in Kinetic Modeling of Plastic Pyrolysis

Pyrolysis is a technology capable of harnessing energy from challenging-to-recycle plastics, thus mitigating the necessity for incineration or landfill disposal. To optimize the plastic pyrolysis process, reliable models for product yield prediction are imperative. This study endeavors to determine the suitability of lumped models, a widely used approach for modeling biomass and coal pyrolysis, in accurately estimating product yields in the context of plastic pyrolysis. To address this question, three lumped models with parallel and competitive reaction mechanisms were compared and fitted to experimental data collected across a broad temperature range. The aim is to identify which models can elucidate the most appropriate reaction pathway for the plastic pyrolysis process. The first model in this study assesses whether the commonly employed wood pyrolysis kinetic models can effectively fit the experimental data from plastic pyrolysis. Subsequently, the final two models introduce additional reactions into the pyrolysis process, prompting the authors to investigate the necessity of these supplementary reaction pathways for accurately predicting plastic pyrolysis outcomes. This investigation seeks to pinpoint the essential terms and discern which ones may be safely omitted from the models. The results of the study reveal that the model incorporating secondary tar reactions with gas, tar, and char is the most precise in predicting the products of plastic pyrolysis, surpassing all other combinations evaluated in this research.

Research and application of surface heat treatment for CO2 continuous laser ablation of polymeric methyl methacrylate materials

Based on the influence of a filamentous laser Gaussian heat source and its movement speed on Polymeric Methyl Methacrylate materials (PMMA sheets), the physical model of heat transfer of PMMA materials by CO2 continuous laser ablation was established. Numerical simulation research on heat transfer in CO2 continuous laser processing of PMMA sheets was carried out by applying the heat transfer model, and experiments on continuous laser processing of PMMA sheets were conducted on the basis of the numerical simulation results. Theoretical and experimental research indicated that under relevant conditions, when the laser power was 20 W, the maximum surface temperature of PMMA sheet was approximately 520 K, which was higher than the melting temperature of the PMMA material, achieving the transformation of the PMMA material from solid to liquid phase in the laser ablation area. When the laser power was 40 W, the CO2 continuous laser could vaporize the PMMA material, cracking the polymer structure of polymethyl methacrylate. When the laser power was 80 W, the maximum surface temperature of the PMMA sheet was approximately 1300 K, and the processing efficiency of CO2 continuous laser ablation of the PMMA material was the highest. The above research provided theoretical guidance and process optimization for the research of CO2 continuous laser ablation of PMMA sheets. The consistency between the experimental results and the numerical simulation results demonstrated the correctness and feasibility of the theoretical model, which has certain universality and reference value for the optimization research of laser processing non-metallic materials and polymer materials.

Sustainable Polyhydroxyalkanoate Production from Food Waste via Bacillus mycoides ICRI89: Enhanced 3D Printing with Poly (Methyl Methacrylate) Blend

In view of implementing green technologies for bioplastic turning polices, novel durable feedstock for Bacillus mycoides ICRI89 used for efficient polyhydroxybutyrate (PHB) generation is proposed herein. First, two food waste (FW) pretreatment methods were compared, where the ultrasonication approach for 7 min was effective in easing the following enzymatic action. After treatment with a mixture of cellulase/amylases, an impressive 25.3 ± 0.22 g/L of glucose was liberated per 50 g of FW. Furthermore, a notable 2.11 ± 0.06 g/L PHB and 3.56 ± 0.11 g/L cell dry eight (CDW) over 120 h were generated, representing a productivity percentage of 59.3 wt% using 25% FW hydrolysate. The blend of polyhydroxybutyrate/poly (methyl methacrylate) (PHB/PMMA = 1:2) possessed the most satisfactory mechanical properties. For the first time, PHB was chemically crosslinked with PMMA using dicumyl peroxide (DCP), where a concentration of 0.3 wt% had a considerable effect on increasing the mechanical stability of the blend. FTIR analysis confirmed the molecular interaction between PHB and PMMA showing a modest expansion of the C=O stretching vibration at 1725 cm-1. The DCP-PHB/PMMA blend had significant thermal stability and biodegradation profiles comparable to those of the main constituent polymers. More importantly, a 3-Dimetional (3D) filament was successfully extruded with a diameter of 1.75 mm, where no blockages or air bubbles were noticed via SEM. A new PHB/PMMA "key of life" 3D model has been printed with a filling percentage of 60% and a short printing time of 19.2 min. To conclude, high-performance polymeric 3D models have been fabricated to meet the pressing demands for future applications of sustainable polymers.

Pyrolysis activation energy of cellulosic fibres investigated by a method derived from the first order global model

The pyrolysis kinetics of cellulosic fibres, a natural cotton yarn (NCY) and a mercerized cotton yarn (MCY), has been explored with a modified first order global analysis method (FOG), via a series of non-isothermal experiments, using thermogravimetric analysis (TGA). The modified FOG analysis routine was developed to overcome discrepancy in heating rate and the difference between exact results and approximations in integrals. The intrinsic pyrolysis activation energy, with temperature range tending to zero, was found to be independent of heating rate and approximation used, giving average values of 153 ± 2 kJ/mol for NCY and 192 ± 7 kJ/mol for MCY. This proves the applicability of the reported analysis routine under the conducted TGA measurements. The reasons for different values were hypothesized to be the difference in chemical composition and crystalline structure. The findings provide a new approach in the investigation on pyrolysis kinetics of biomass and factors impacting their pyrolytic behaviour.

Process Analysis of PMMA-Based Dental Resins Residues Depolymerization: Optimization of Reaction Time and Temperature

This work aims to optimize the recovery of methyl methacrylate (MMA) by depolymerization of polymethyl methacrylate (PMMA) dental resins fragments/residues. In order to pilot the experiments at technical scale, the PMMA dental resins scraps were submitted by thermogravimetric analysis (TG/DTG/DTA). The experiments were conducted at 345, 405, and 420 °C, atmospheric pressure, using a pilot scale reactor of 143 L. The liquid phase products obtained at 420 °C, atmospheric pressure, were subjected to fractional distillation using a pilot scale column at 105 °C. The physicochemical properties (density, kinematic viscosity, and refractive index) of reaction liquid products, obtained at 345 °C, atmospheric pressure, were determined experimentally. The compositional analysis of reaction liquid products at 345 °C, 30, 40, 50, 60, 70, 80, and 110 min, at 405 °C, 50, 70, and 130 min, and at 420 °C, 40, 50, 80, 100, 110, and 130 min were determined by GC-MS. The morphology of PMMA dental resins fragments before and after depolymerization was performed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The experiments show that liquid phase yields were 55.50%, 48.73%, and 48.20% (wt.), at 345, 405, and 420 °C, respectively, showing a first order exponential decay behavior, decreasing with increasing temperature, while that of gas phase were 31.69%, 36.60%, and 40.13% (wt.), respectively, showing a first order exponential growth, increasing with temperature. By comparing the density, kinematic viscosity, and refractive index of pure MMA at 20 °C with those of liquid reaction products after distillation, one may compute percent errors of 1.41, 2.83, and 0.14%, respectively. SEM analysis showed that all the polymeric material was carbonized. Oxygenated compounds including esters of carboxylic acids, alcohols, ketones, and aromatics were detected by gas chromatography/mass spectrometry (GC-MS) in the liquid products at 345, 405, and 420 °C, atmosphere pressure. By the depolymerization of PMMA dental resins scraps, concentrations of methyl methacrylate between 83.454 and 98.975% (area.) were achieved. For all the depolymerization experiments, liquid phases with MMA purities above 98% (area.) were obtained between the time interval of 30 and 80 min. However, after 100 min, a sharp decline in the concentrations of methyl methacrylate in the liquid phase was observed. The optimum operating conditions to achieve high MMA concentrations, as well as elevated yields of liquid reaction products were 345 °C and 80 min.

Thermodynamics, kinetics and thermal decomposition characteristics of sewage sludge during slow pyrolysis

Pyrolysis has shown great potential for sewage sludge valorisation and management by producing value-added chemicals. Although the product process yields are extensively studied, a few studies exist without consensus on the kinetic properties of sewage sludge pyrolysis. As a result, a study to investigate the thermal decomposition characteristics of Gauteng sewage sludge (GSS) at various heating rates (10, 20, and 30 °C/min), its pyrolysis kinetic parameters, reaction mechanism and thermodynamic properties was meticulously conducted. The results show that sewage sludge decomposition occurs in three stages, whereby the main decomposition (active pyrolysis) takes place at 150-570 °C. Fourier transform infrared spectroscopy (FTIR) analysis results confirm progression of thermal decomposition of GSS and drive off volatile compounds and formation of aromatic structures during TGA studies of GSS. An increase in heating rate shifts the characteristic temperatures towards higher temperatures with the highest decomposition rate of 1.10%/min.mg at 30 °C/min. The activation energies of GSS pyrolysis were calculated using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Starink methods and averaged as 225.92, 218.04 and 218.97 kJ/mol, respectively. GSS pyrolysis involves complex reaction chemistry with high reactivity whereby reactions that follow third order and three-dimensional diffusion-reaction mechanisms dominated the process. However, these mechanisms cannot be used explicitly to define the global pyrolysis kinetics due to the occurrence of multiple simultaneous reactions. The obtained thermodynamic and kinetic data will advance and amplify the design, simulation and optimisation of global energy pyrolysis units for production of value-added chemicals.

Microwave-assisted synthesis of β-cyclodextrin functionalized celluloses for enhanced removal of Pb(II) from water: Adsorptive performance and mechanism exploration

Herein, β-cyclodextrin (β-CD) was efficiently grafted onto rice husk-based celluloses using different cross-linking agents of epichlorohydrin (EPI) and glutaraldehyde (GA). By feat of microwave irradiation, the functionalization procedure was completed in 17 min, and the synthesized RHEPIMWβ-CD and RHGAMWβ-CD exhibited fast adsorption equilibrium for Pb(II) within 20 min, excellent monolayer adsorption capacities of 216.06 and 279.08 mg g^-1 across an extensive pH scope of 3.0-6.0, unaffected affinity to Pb(II) during the existence of co-existing ions, superior reusability with over 81% and 87% of Pb(II) uptake sustained for four adsorption-desorption cycles. Thermodynamic parameters implied that the uptake process of Pb(II) occurred spontaneously (-ΔG⁰) with an endothermic characteristic (+ΔH⁰). Furthermore, electrostatic attraction and complexation were demonstrated to enhance the Pb(II) uptake onto the RHEPIMWβ-CD and RHGAMWβ-CD. In fix-bed columns, these two adsorbents also efficiently eliminated Pb(II) under various flow rates with experimental breakthrough curves well simulated by Thomas and Yoon-Nelson models. Significantly, the RHEPIMWβ-CD and RHGAMWβ-CD could effectively purify acid battery effluent containing Pb(II) for meeting regulatory requirement. Overall, the fast fabrication, excellent adsorption and recycling performance facilitate the development of tailored adsorbents for Pb(II) elimination in wastewater.