Model-free Isoconversional Method Research Articles

Effect of ethanolysis on the structure evolution, pyrolysis kinetics, and volatile products of waste poplar sawdust

Ethanolysis had been the promising approach for the deoxygenation of waste poplar sawdust (WPS), and its effect of structure variation and pyrolysis behaviors on the WPS was investigated in present research. The decreasing of C–O chemical bonds and the increasing of C content was typical phenomenon during the ethanolysis of WPS. The pyrolysis behaviors of sample were performed by thermogravimetric analyzer at three different heating rates. The pyrolysis kinetics and thermodynamics of WPS, residue230 (R230), and residue260 (R260) were well determined on the basic of three model-free iso-conversional methods. Average activation energy derived from the Kissinger-Akahira-Sunose (KAS) method of R260 displayed the high value (445.06 kJ/mol), followed by 224.88 kJ/mol for R230, then 200.68 kJ/mol for WPS. Thermodynamics data suggested that R260 required more total energy consumption for the breakage of chemical bonds. Additionally, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) results showed that the highest relative content of volatile products compound derived from the flash pyrolysis of R230 and R260 was 47.12 % (d-Allose) and 38.69 % (Phenols), respectively, and RC value of arenes significantly increased to 15.82 % after ethanolysis. The findings would significantly contribute to the valuable utilization of waste biomass and its residues.

Fabrication of Polycaprolactone-Based Polyurethanes with Enhanced Thermal Stability.

The benefit of being acquainted with thermal properties, especially the thermal stability of polyurethanes (PU), and simplified methods for their improvement is manifold. Considering this, the effect of embedding different amounts of unmodified and surface-modified TiO2 nanoparticles (NPs) within PU, based on polycaprolactone (PCL) and Boltorn® aliphatic hyperbranched polyester, on PU properties was investigated. Results obtained via scanning electron microscopy, swelling measurements, mechanical tests and thermogravimetric analysis revealed that TiO2 NPs can be primarily applied to improve the thermal performance of PU. Through surface modification of TiO2 NPs with an amphiphilic gallic acid ester containing a C12 long alkyl chain (lauryl gallate), the impact on thermal stability of PU was greater due to the better dispersion of modified TiO2 NPs in the PU matrix compared to the unmodified ones. Also, the distinct shape of DTG peaks of the composite prepared using modified TiO2 NPs indicates that applied nano-filler is mostly embedded in soft segments of PU, leading to the delay in thermal degradation of PCL, simultaneously improving the overall thermal stability of PU. In order to further explore the thermal degradation process of the prepared composites and prove the dominant role of incorporated TiO2 NPs in the course of thermal stability of PU, various iso-conversional model-free methods were applied. The evaluated apparent activation energy of the thermal degradation reaction at different conversions clearly confirmed the positive impact of TiO2 NPs on the thermal stability and aging resistance of PU.

Exploring New Schiff Bases: Synthesis, Characterization, and Multifaceted Analysis for Biomedical Applications.

The current work aims to generate novel Schiff bases by reacting substituted aldehydes with amine derivatives catalyzed by a natural acid. The developed compounds underwent diverse physicochemical analyses including liquid chromatography-mass spectrometry, Fourier transform infrared spectroscopy, scanning electron microscopy, 1H- and 13C-nuclear magnetic resonance, and X-ray diffraction. Furthermore, differential thermogravimetric, thermogravimetric, and differential thermal analysis techniques were employed in a nitrogen-free environment to determine kinetic parameters. These data were then used in model-free isoconversional methods (e.g., Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa). The Schiff bases were evaluated for their in vitro and in silico α-amylase inhibitory activity. Schiff base-2 displayed the highest inhibition compared with the reference drug acarbose. In comprehensive MTT assay cytotoxicity investigations, both Schiff bases showed strong anticancer capabilities against the human lung cancer cell line (A549). Moreover, this study demonstrated effectiveness of synthetic compounds in screening Caenorhabditis elegans for anti-Alzheimer's and stress resistance properties. The simplicity of its biology allowed precise evaluation of the effect of compounds on neuronal function and stress response. This research enhances drug discovery efforts for Alzheimer's and stress-related disorders, potentially improving patient outcomes.

Co-pyrolysis of chrome-tanned leather shavings with wheat straw: Thermal behavior, kinetics and pyrolysis products

The thermal behavior and kinetics of chrome-tanned leather shavings (CLS)/wheat straw (WS) blends at different mass ratios during co-pyrolysis were investigated, and the pyrolysis products were characterized. Model-free isoconversional and master-plots methods were applied to determine kinetic triplet of the pyrolysis/co-pyrolysis of CLS, WS and their blends based on thermogravimetric (TG) analysis. Results showed that the activation energy for CLS pyrolysis was reduced by the addition of WS, and a synergistic promoting effect predominated across the majority of temperature ranges and feedstock compositions during the co-pyrolysis process. TG-Fourier transform infrared spectrometry-Mass spectrometry analysis showed the changes in evolution profiles of H2O, CO, CO2, HNCO and pyrrole during pyrolysis. The pyrolysis solid residues were characterized and results indicated that the addition of WS to CLS can increase solid residue yield and potentially inhibit the formation of hexavalent chromium during pyrolysis. This study helps to foster a promising solution for the valorization and safe disposal of chromium-containing solid wastes from leather industry.

Comprehensive investigation of almond shells pyrolysis using advance predictive models

This research focused on comprehensive characterization and assessment of almond shells pyrolysis for bioenergy potential through thermogravimetric analysis from ambient temperature to 900 °C at different heating rates of 10, 15, and 20 °C/min in inert environment. Iso-conversional model-free methods like Friedman, Ozawa-Flynn-Wall (OFW), and Kissinger-Akahira-Sunose (KAS) were used for kinetic analysis. Average activation energies (Ea) evaluated using Friedman, OFW, and KAS methods were 198.45 kJ mol−1, 204.43 kJ mol−1, and 204.97 kJ mol−1, respectively. The evaluation of thermodynamic parameters, including ΔH‡, ΔG‡, and ΔS‡, was also assessed. The average values of ΔH‡, ΔG‡, and ΔS‡, were found to be 199.4 kJ mol−1, 172.17 kJ mol−1 and 42.60 kJ mol−1 respectively. The reaction mechanism was obtained from combined kinetics. A high R2 value of 0.9933 demonstrates strong agreement between the combined kinetic analysis results and the experimental data. The distribution activation energy model was assessed employing four pseudo elements identified as PC1, PC2, PC3, and PC4. Artificial Neural Network (ANN) and Boosting regression trees (BRT) were used for the prediction of Ea of almond shells pyrolysis. The detailed understanding of thermokinetics and creating customized predictive and innovative modelling techniques like ANN and BRT sets a new benchmark for developing customized models for thermochemical conversion of varieties of almond shells.

Size-dependent thermal oxidation kinetics in Sm2(Co, Fe, Cu, Zr)17 alloy powder

This study investigates the interrelationship between the oxide growth kinetics and the microstructural changes induced by dry, thermal oxidation in Sm2(Co, Fe, Cu, Zr)17 alloy powder (of varying particle sizes and compositions). Whereas, model-free iso-conversional methods are used to determine the kinetic-triplets during the non-isothermal oxidation stage, power-law dependent kinetic model is considered during the entire oxidation process to calculate the reaction order, rate constant and the apparent-activation energy. A distinctly different oxide growth kinetics, with strong dependency on the initial particle size(s) and the alloy composition-induced oxide microstructure is seen here.

Study on non-isothermal pyrolysis of Azadirachta Indica for kinetic triplets and thermodynamics evaluation

Exploring kinetics and thermodynamics of biomass pyrolysis process is imperative for optimizing the process. This study employs various model-free iso‐conversional methods and a model-fitting method to investigate the kinetics and thermodynamics of non-isothermal pyrolysis of Azadirachta indica biomass under four distinct heating rates of 10, 20, 30 and 40 °C/min. Average values of activation energy and pre-exponential factor ranged from 187.613 to 196.635 kJ/mol and 5.068×1014 − 1.178×1022 min−1, respectively, indicating an endothermic and complex nature of reaction. Integral master plots proved superior in revealing the reaction mechanism, although Criado's master plot unveiled a combination of reaction models, aligning with the intricate degradation mechanisms of biopolymers. The average enthalpy change, Gibbs free energy change and entropy change values spanned from 182.425 to 191.638 kJ/mol, from 167.288 to 173.742 kJ/mol and from 0.014 to 0.039 kJ/mol·K, respectively.

Model-free isoconversional methods to determine the intrinsic kinetics and thermodynamic parameters during pyrolysis of boiled banana peel: influence of inorganic species

Raw banana peel was hydrolyzed to produce boiled banana peel (BBP) that exhibited enhanced volatile matter, calorific value; and lower ash content. BBP was analyzed for proximate, ultimate, TGA, DTG, SEM-EDX and FTIR. TGA and DTG curves exhibited variation in thermal lag at higher heating rates. XPS studies confirmed the dominance of inorganic species in BBP. The activation energy computed using isoconversional models increased with increasing conversion up to 60 %. Beyond that, activation energy suddenly decreased due to the influence of potassium, chlorine, and calcium containing compounds which lowered thermal stability of lignin which decomposed at a faster rate. The average activation energy (Eav) using isoconversional models such as KAS, Starink, FWO, Tang and Friedman are 457.75, 458.16, 468.01, 470.67, and 488.20 kJ/mol, respectively. Enthalpy, entropy, and Gibbs free energy were computed. Reaction mechanism during pyrolysis of BBP at various heating rates was predicted using Criado method (Z-master plots).

Catalytic Pyrolysis of Hydrochar by Calcined Eggshells for Bioenergy Production: Improved Thermo-Kinetic Studies and Reduced Pollutant Emissions

Bioenergy production from hydrochar via catalytic thermal conversion is of increasing importance to easing the energy shortage. The catalytic pyrolysis characteristics of hydrochar derived from sawdust (HSD) with calcined eggshell (CES) were investigated by the thermogravimetric–Fourier transform infrared spectroscopy–mass spectrometry (TG-FTIR-MS) method. Kinetic and thermodynamic parameters were determined by two iso-conversional model-free methods, namely, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). The results demonstrated that HSD exhibited a high fuel quality, with elevated carbon content (54.03%) and an increased high calorific value (21.65 MJ Kg−1). CES significantly enhanced the pyrolysis behavior of HSD by promoting the secondary cracking of organic vapors under the synergistic effect of CaO and mineral elements. Compared to non-catalytic pyrolysis, the residual mass and average activation energy of HSD-CES decreased by 29.61% and 14.10%, respectively, and the gaseous products of H2 and CO from HSD-CES increased by 26.14% and 22.94%, respectively. Furthermore, the participation of CES effectively suppressed the emission of pollutants in the HSD pyrolysis process, with a 27.13% reduction in CH4, a 22.76% reduction in HCN, and a 20.28% reduction in NH3. This study provides valuable guidance on the potential use of hydrochar for renewable energy production.

Kinetic and Thermodynamic Analyses of Co-Pyrolysis of Nylon-Polyethylene Pouch Wastes.

In this study, thermogravimetric measurements of nylon-6/polyethylene double-layer pouch wastes were conducted in N2 under a constant heating-rate mode, and the multiple heating-rate results were analyzed in terms of degradation features and specific temperatures. Experimental results show that the waste pyrolysis involves one reaction stage, and all specific parameters appear to increase with the heating rate. Kinetic analysis of non-isothermal data was thoroughly performed using various isoconversional model-free methods for the calculations of the activation energy, resulting in 143~215 kJ/mol over the whole pyrolysis process. By means of the model-fitting method, the reaction mechanism model g(α) and pre-exponential factor lnk0 are concurrently determined with the aid of the linear compensation effect. With such methodology proposed, the Avrami-Erofeev kinetic model A3/2 of g(α) = [-ln(1 - α)]2/3 is found to be the most appropriate mechanism function for describing the pyrolysis of the nylon-6/polyethylene waste along with lnk0 of 23.14 to 34.26 min-1. With the Arrhenius parameters thus obtained, the predictions were made and performed very satisfactorily to correlate experimental results. Additionally, the service life and thermodynamic parameters over the entire pyrolysis process were also estimated.

Investigation of thermodynamic and kinetic parameters of Albizia lebbeck seed pods using thermogravimetric analysis

Thermodynamic and kinetic studies are very necessary to evaluate the conversion efficiency of biomass to energy. Therefore, this current work reported the thermodynamic and kinetic parameters of Albizia lebbeck seed pods through thermogravimetric analysis, which was carried out at temperatures from 25 °C to 700 °C, and heating rates of 5, 10, 15, and 20 °C/min. Apparent activation energies were determined by applying three iso-conversional model-free methods including Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW), and Starink. Resultantly, average apparent activation energy values for the three models of KAS, OFW, and Starink were found to be 155.29, 156.14, and 155.53 kJ/mol, respectively. In addition, thermodynamic triplets such as enthalpy, Gibbs free energy, and entropy were obtained as 151.16 kJ/mol, 150.64 kJ/mol, and −7.57 J/mol·K, respectively. The above results suggest Albizia lebbeck seed pods could become a potential source for bioenergy production aiming to achieve the sustainable goal and waste-to-energy strategy.

Phenolic resin/coal char composites: Curing kinetics and thermal/mechanical performance

Curing behavior plays a key role in determining the ultimate properties of thermosetting polymers. With the use of fillers, curing behavior and reaction kinetics are affected. Here, we report the study of the curing process and thermal and mechanical behaviors of phenolic composites reinforced with 50 wt% of an economic filler, coal char. Curing kinetics were investigated using non-isothermal differential scanning calorimetry (DSC) measurements and analyzed by model-free isoconversional methods for determining kinetic parameters. The study revealed that the coal char had a retarding effect on the curing of the phenolic resin. The curing reaction was also influenced by the processing method of the composite. Mixing of the char in tetrahydrofuran (THF) led to higher activation energies than via dry mixing. The mechanical properties and thermal stability of the phenolic resin were significantly improved in the presence of the filler. The information reported in this work can be used for optimal curing of phenolic resin/coal char composites as well as tuning performance by choosing an appropriate processing technique.

Synergistic interactions between sewage sludge, polypropylene, and high-density polyethylene during co-pyrolysis: An investigation based on iso-conversional model-free methods and master plot analysis

Sewage sludge (SS) is a hazardous by-product of wastewater treatment processes that requires careful management for minimal environmental impacts and effective resource recovery. Through thermochemical processes such as pyrolysis, clean energy is recovered from SS in the form of bio-oil, biogas, and biochar. To improve the yield and quality of products, the co-pyrolysis of more than two materials is increasingly gaining interest. Here, the thermal behaviour, kinetics, and synergistic interactions during the co-pyrolysis of SS with polypropylene (PP) and high-density polyethylene (HDPE) were comparatively evaluated with thermogravimetric analysis at different mixing ratios and heat rates. Activation energies and reaction mechanisms were determined through iso-conversional model-free methods and master plot analysis. Evolved gases were monitored with thermogravimetric-mass spectrometry. Increased volatile conversion and degradation rates, and reduced activation energies during co-pyrolysis were mediated by synergistic interactions between H-radicals of PP/HDPE and oxygenated intermediates of SS. Contrary to the pyrolysis of SS, PP and HDPE, the co-pyrolysis processes are predominantly diffusion-controlled. Insights into the co-pyrolysis processes of SS/PP and SS/HDPE gained from this work provide the theoretical support for subsequent investigation, facilitate design of waste-to-energy reactor, and aid the adoption of the technology to harness the bioenergy potential of the feedstocks.

Thermal degradation study of natural fibre through thermogravimetric analysis

Thermogravimetric analysis was performed to understand the thermal degradation characteristics of natural fibre (bhimal). The objective of the study was to evaluate the suitability of fibre as an alternative to synthetic fibre for reinforcement in polymer composite synthesis. The thermal degradation study was conducted at three heating rates, 10, 15 and 20 °C/min from room temperature to 800 °C. The highest weight loss (65–71 wt%) was observed in the temperature range of 200–435 °C. Three model-free isoconversional methods, FWO, KAS, and Friedman, were applied to estimate the kinetic parameters (activation energy and pre-exponential factor). Average activation energies of 115.96 ± 30.89, 111.08 ± 33.01, and 112.67 ± 41.87 kJ/mol were calculated by FWO, KAS, and FR methods, respectively. The respective estimated pre-exponential factors were 1.41E + 11, 6.62E + 10, and 4.49E + 13 min−1. The kinetic parameters varied substantially with the conversion level, which shows the multi-step reaction mechanism of bhimal fibre thermal degradation. The present study suggests the apparent activation energy of bhimal fibre in the range of 108–120 kJ/mol for polymer composite synthesis.

Pyrolysis and co-pyrolysis of Egyptian olive pomace, sawdust, and their blends: Thermal decomposition, kinetics, synergistic effect, and thermodynamic analysis

The pyrolysis and co-pyrolysis kinetics of two Egyptian olive-pomace (Kroneiki and Shamlali), wood dust, and their blends were investigated by advanced isoconversional model-free methods (Vyazovkin and Senum-Yang) and model-fitting methods (Coats and Redfern integral method) using different integrated reaction mechanisms g(α) through TGA/DTG, and DTA techniques. Master Plot's method was applied to determine the best reaction mechanisms for the pyrolysis of the tested materials. The synergistic effect of co-pyrolysis on kinetics and the role of biomass were examined. The average values of activation energy estimated from VYA and SY kinetic methods, respectively, for KROP, SHOP, FSSD, Blend (1), and Blend (2) were 90.57 and 85.67 kJ/mol, 70.05 and 65.26 kJ/mol, 131.66 and 126.71 kJ/mol, 66.73 and 62.09 kJ/mol, and 113.12 and 108.21 kJ/mol. The co-pyrolysis of KROP, SHOP, and FSSD at a heating rate of 10 °C/min showed the best synergistic pyrolysis performance. The diffusional reaction mechanisms are the most likely reactions to describe the pyrolysis process of the first conversion stage (α = 0.1–0.5), while the reaction mechanism C8 and the reaction order model (F4) are the most likely reactions to describe the second stage (α = 0.5–0.9) pyrolysis process. The higher ΔH and ΔS values for the FSSD and Blend (2) signify that these materials consumed more energy during the pyrolysis process, while the lower ΔH and ΔS values for the KROP, SHOP, and Blend (1) showed the opposite. A blending ratio of 50% KROP, 25% SHOP, and 25% FSSD showed the best performance at a heating rate of 10 °C/min. The obtained kinetics parameters and the solution of the master plots method were validated by solving the Coats and Redfern integral method based on the reaction mechanism function g(α) that showed the best fit in the master plots method.

Thermal decomposition study of cadmium telluride (CdTe)

Pure CdTe crystalline material is synthesized at 1073 K temperature in a closed tube under vacuum in horizontal tubular furnace. The synthesized material is found to be stoichiometric having atomic % of Cd: 49.31 and Te: 50.69 as determined by energy dispersive analysis of X-ray. The material is CdTe phase with cubic unit cell structure possessing lattice parameters of a = b = c = 6.48 Å as determined by X-ray diffraction. The morphology of the as-synthesized material is studied by scanning and transmission electron microscopy. The morphology showed clusters of varying sizes ranging from sub-micron to nano having stacked layers. The Raman spectroscopy showed three peaks positioned at 91, 120 and 140 cm−1, corresponding to CdTe. The thermogravimetric, differential thermogravimetric and differential thermal analysis curves of synthesized CdTe are recorded in the temperature range of ambient to 1233 K for three heating rates of 10, 15 and 20 K⋅min−1. The thermocurves demonstrated one-step decomposition of the as-synthesized CdTe material. The thermodynamic parameters, such as activation energy (Ea), activation enthalpy change (ΔH*), Gibb’s free energy change (ΔG*), activation entropy change (ΔS*) and phonon frequency factor (A) are calculated by model-free isoconversional methods. The obtained data and outcomes are discussed thoroughly.

Exploring the potential of fish waste (Sardinella fimbriata) through pyrolysis: A study of kinetics and thermodynamics using isoconversional methods

The growing global demand for fish has led to an increase in fish waste (FW) production, necessitating efficient waste management strategies. Pyrolysis is a promising way to convert fish waste into high-value products. To achieve optimal waste mass reduction and gain insights into the pyrolysis process, estimating kinetic parameters is essential. This study investigated the pyrolysis of FW, Sardinella fimbriata, a previously unexplored waste source, using a thermogravimetric analyser. The study determined an average activation energy value of 84–124 kJ/mol using model-free isoconversional methods including Flynn-Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink, whereas pre-exponential factor values were predicted to be between 102 and 1011 s−1. Further analysis using Criado's reduced master-plot approach showed that the experimental curves for pyrolysis coincided with many different theoretical plots for reaction mechanisms, with a concentration on reaction-order models. The analysis of thermodynamic parameters showed positive values of enthalpy change and Gibbs energy change for S. fimbriata FW pyrolysis, suggesting that the process is endothermic and non-spontaneous, while negative values of entropy change were observed across all conversion degrees as a result of the breakdown of complex organic molecules into simpler compounds. This study provides insights into the feasibility of thermal processes and offers new guidance for FW waste management and resource recovery, expanding the understanding of pyrolysis kinetics and thermodynamics for fish waste treatment.

Analysis and distribution of volatile gases from catalytic pyrolysis of Sulcis low-rank coal

Catalytic pyrolysis of Sulcis low-rank coal over naturally occurring olivine, and home-made 15 wt%Ni/γ-Al2O3 catalyst was conducted for the upgrading of coal pyrolysis volatile gases in the temperature range ambient-900 °C under atmospheric pressure. Raw coal and mixtures of coal-additive (90:10 wt%) were slowly heated in temperature programmed mode using a laboratory-scale quartz furnace coupled in parallel to Fourier transform infrared (FTIR) spectrometer and GC chromatograph for quantitative analysis of flue gas. Coal pyrolysis with and without additives was also conducted by TG/DTG/DSC analysis at different heating rate (β = 15, 20, 30 °Cmin−1). DSC results clearly indicated some extra exothermic events during catalytic coal pyrolysis. Quantitative gaseous products distribution with temperature showed yields significantly and selectively improved with additives. Generally, more CO and CO2 were emitted under catalytic coal pyrolysis. Meanwhile, nickel catalyst exerted a marked positive effect on H2 yield overall in the temperature range 400–500 °C. The light hydrocarbons such as methane, ethane, propane and n-hexane substantially remaining unchanged, whereas a remarkable increase of emitted ethene was originated from catalytic pyrolysis. A deeper SO2 evolution was observed over olivine, whereas the N-containing compounds (NH3, NOx) were also modified in catalytic pyrolysis. Formaldehyde was also monitored, which represents a fragment originating from polycyclic aromatic side chains. Reaction kinetic study by a model-free isoconversional method indicated a complex multiple-step mechanism of coal pyrolysis, exception made for conversion values between 5% and 50% where a single-step reaction path was operating. The calculated average Ea and the pre-exponential factor were markedly reduced by the presence of additives. Meanwhile the compensation effect was also existing.

Investigation of combustion performance of tannery sewage sludge using thermokinetic analysis and prediction by artificial neural network

The disposal and the management of sewage sludge from tanneries is a challenging issue for the leather industries because of their adverse effect on the environment. In this study the detailed characterization and assessment using kinetic and thermodynamic parameters of the tannery sewage sludge in combustion environment was employed. Isoconversional model-free methods like Ozawa-Flynn-Wall (OFW), Friedman and Kissinger-Akahira-Sunose (KAS) were employed to investigate the kinetics and the thermodynamic parameters in the air environment. Activation energies (Ea) for the Friedman, KAS and OFW were reported. The DTG curves at the heating rate of 5, 10, 20 and 40 °C/min show the diversified conversions in three major stages. The Ea values for the model ranges are Friedman (148.96 kJ/mol-395.23 kJ/mol), KAS (169.65 kJ/mol-383.75 kJ/mol) and OFW (176.44 kJ/mol-377.85 kJ/mol). The average Ea for the Friedman is 226.04 kJ/mol while for KAS and OFW the average Ea is 230.71 kJ/mol and 230.11 kJ/mol. Moreover, the values of ΔH, ΔG, and ΔS were analysed. Furthermore, the frequency distribution by applying the DAEM model is investigated, and there are six pseudo-components involved in the frequency distribution for combustion. For the thermal degradation prediction of the sewage sludge from the tannery, an artificial neural network (ANN) of the MLP-3-7-1 model was used. This model shows that there is good agreement between the experimental and the predicted values. Overall, this study highlights the importance of the ANN for the prediction of combustion behaviour of biomass with more accuracy.

Tack of epoxy resin films for aerospace-grade prepregs: Influence of resin formulation, B-staging and toughening

Aerospace-grade prepreg resin films based on multifunctional tetraglycidyl-4,4′-methylenedianiline (TGMDA), triglycidyl p-aminophenol (TGAP), Bisphenol A diglycidyl ether (DGEBA) and curing agent 4,4'diaminodiphenyl sulfone (DDS) are investigated in terms of tackiness by probe testing. The model epoxy systems are modified regarding the thermoplastic toughener content (polyethersulfone, PES) and the B-stage level, which is adjusted by cure prediction based on a model-free isoconversional method (Flynn-Wall-Ozawa). Additional DSC and rheological analysis are performed to study the thermal and viscoelastic material behavior in conjunction to its impact on temperature-dependent tack. Maximum achievable tack is found to decrease as a function of both degree of conversion and toughener content. Meanwhile, both influencing factors shift the tack maximum towards higher temperatures corresponding to increased flow characteristics attributed to evolving network formation and the incorporation of high molecular weight PES. In terms of absolute tack level and corresponding temperature, probe tack values similar to commercial prepreg systems (∼100 μJ mm−2) are recorded for TGMDA-based formulations containing 10 wt% PES at 20% pre-cure. Model formulations, which have neither been exposed to B-staging nor toughened, show exceptionally high tack below room temperature for all investigated epoxy prepolymers and are therefore not considered processable by automated fiber placement.