Hot-pressing Conditions Research Articles

Mechanical Properties and Thermal Degradation Behaviour of Polyurethane Composites Incorporating Waste-Glass Particles.

This study investigated the effect of hot-pressing conditions, including the curing temperature, curing time and the applied pressure, on the flexural properties of polyurethane (PU) composites incorporating 88 wt.% (Glass/PU-88/12) and 95 wt.% (Glass/PU-95/5) recycled glass particles. Hot-pressing (cure) temperatures between 100 °C and 180 °C were investigated with the objective to shorten the cure cycle, thereby increasing the production rate of the glass/PU composites to match industrial scales. The hot-pressing time varied between 1 min and 30 min, while the pressure varied between 1.1 MPa and 6.6 MPa. Further to investigating the hot-pressing conditions, the effect of post-curing on the flexural properties of glass/PU composites was also investigated. Microstructural analysis was used to identify the interactions between the glass particles and the PU matrix, explore the void content and establish the relationship between the microstructure and the mechanical properties of the resultant glass/PU composites. Glass/PU composites incorporating 5 wt.% (Glass/PU-95/5), 10 wt.% (Glass/PU-90/10) and 12 wt.% (Glass/PU-88/12) were manufactured under optimised hot-pressing conditions (temperature = 100 °C; cure time = 1 min; pressure = 6.6 MPa) and evaluated under flexural, tensile and compression loadings. Furthermore, the high-temperature stability of the composites was evaluated using thermogravimetric analysis. This study demonstrates the feasibility of upcycling glass waste into value-added materials for potential use in the construction and building industry.

Optimization of semi-wet hot-pressing conditions for Salix psammophila-based mycelium-bound boards via response surface methodology

Optimization of semi-wet hot-pressing conditions for Salix psammophila-based mycelium-bound boards via response surface methodology

Effects of synthesis and hot-pressing conditions on ZrB2-ZrC-SiC eutectic ceramics: Structure formation and properties

Effects of synthesis and hot-pressing conditions on ZrB2-ZrC-SiC eutectic ceramics: Structure formation and properties

Uncovering Key Parameters in Perfluorosulfonic Acid (PFSA) Membrane Fuel Cells to Enhance Performance.

The conversion of chemical energy to electricity in proton exchange membrane fuel cells (PEMFCs) is essential for replacing fossil fuel engines and achieving net-zero CO2 emissions. In the pursuit of more efficient PEMFCs, certain often-overlooked parameters significantly influence cell performance by either weakening the interaction between the catalytic layer (CL) and the membrane or restricting gas access to the CL. This study examines the effects of cell tightening and hot-pressing conditions on three similar-thickness perfluorosulfonic acid (PFSA) membranes: Aquivion®, Fumapem, and Nafion®. The results reveal that the hot-pressing method employing higher pressure and a lower temperature (125C method) yields lower fuel cell performance compared to the method utilizing a higher temperature and lower pressure (145C method). Furthermore, incorporating cellulose paper as a pressure homogenizer in the MEA preparation setup significantly improved current density by approximately 2.5 times compared to the traditional assembly method. Cyclic voltammetry with Ar-feed in the cathode showed that all prepared MEAs exhibited a similar platinum surface area; however, MEAs pressed at higher temperatures displayed slightly lower hydrogen desorption charge values. The torque applied to the bolts does not show a consistent trend in fuel cell performance, but optimal torque values can enhance PEMFC performance under certain conditions.

Lignin-Based Coatings: A Sustainable Approach to Produce Antibacterial Textiles

The growing interest in developing antibacterial textiles using natural functional agents is largely driven by their sustainable and eco-friendly attributes. Lignin, a highly available biopolymer with a polyphenolic structure, has drawn attention due to its potential as a bioactive antibacterial agent. However, its inherent heterogeneity poses challenges, particularly regarding its antibacterial efficacy. In this study, unmodified kraft lignin sourced directly from the paper industry was applied to cotton and polyester fabrics, using a knife-coating technique with varying concentrations (0%, 5%, 10%, 20%, and 30% w/v), to assess its potential as an antibacterial coating. The lignin-coated fabrics demonstrated hydrophobic properties, with water contact angles reaching up to 110.3° and 112.6°, for polyester and cotton fabrics, respectively, alongside significantly reduced air permeability and water vapor permeability indexes, regardless of lignin concentration. Antibacterial evaluations also revealed that lignin-based coatings, with at least 10% w/v concentration, allowed cotton fabrics with a bacterial reduction surpassing 96%, according to ASTM E2149-2013, particularly for Gram-positive S. aureus, highlighting the potential of lignin as an antibacterial agent. Despite their limited resistance to domestic washing, the lignin-coated fabrics demonstrated exceptional stability under hot-pressing conditions. Therefore, this stability, combined with the hydrophobic and antibacterial properties observed, particularly on coated cotton fabrics, highlights the potential application of lignin-based coatings for the development of antibacterial and water-repellent textiles, with these coatings being particularly suited for single-use applications or scenarios where washing resistance is not a requirement. This approach offers a sustainable and efficient method for producing functional textiles while enabling value-added utilization of lignin, showcasing its potential as an eco-friendly solution in textile functionalization.

Improving the fixed charge density of sustainably produced saloplastic anion exchange membranes.

Recent studies have shown that sustainable ion exchange membranes can be fabricated by hot-pressing polyelectrolyte complexes (PECs), resulting in saloplastic membranes. Among these, the anion exchange membrane (AEM) formed from the strongly charged polyelectrolyte pair, poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyl-dimethylammonium chloride) (PDADMAC) stands out due to its excellent chemical stability. However, the performance of this membrane is limited by its comparatively low fixed charge density. To address this limitation, we aimed to enhance the fixed charge density through incremental PDADMAC overcharging during the complexation step, followed by optimisation of hot-pressing conditions to produce dense, freestanding films. This approach allows for precise control over membrane charge and improves the reproducibility of films, thereby overcoming challenges in the processing and handling of non-stoichiometric PECs. NMR spectroscopy was used to quantify the fixed charge of the saloplastic AEMs before and after testing, providing a reliable and time-efficient method for assessing stability. Our results showed that a PDADMAC overcompensation of ∼30 mol% optimised the fixed charge density without compromising membrane stability. The enhanced membrane exhibited an 84% improvement in ionic conductivity (4.3 ± 0.3 mS cm-1 in 0.5 M KCl) compared to the original membrane. Notably, all membranes displayed excellent permselectivity (>90%) in 0.1 M KCl, and at higher electrolyte concentrations, a moderate improvement in permselectivity was observed with the increase in fixed charge density. Overall, this study presents a simple yet effective methodology for quantifying and optimising the fixed charge density of saloplastic membranes, resulting in significantly improved performance.

The impact of hot-press conditions on the durability of polymer electrolyte membrane fuel cells

The impact of hot-press conditions on the durability of polymer electrolyte membrane fuel cells

Electro-Epoxidation of Propylene in the Gas Phase with Solid-Polymer-Electrolyte Water Electrolysis.

The development of a reaction system for direct epoxidation of propylene is an essential topic. Gas-phase electro-epoxidation of propylene to propylene oxide (PO) with water as the oxidant was successfully accomplished by using solid-polymer-electrolyte (SPE) electrolysis without solvents. The oxidized surface of the PtOx anode was essential for propylene epoxidation and oxidation. It was revealed that PO was sequentially oxidized and accumulated on the anode by the interval electrolysis experiment. The formation rate and Faraday efficiency (FE) to PO were improved by applying mild hot-press conditions for the SPE unit because the active phase of the oxide surface of PtOx was maintained and diffusibility of water in the SPE (Nafion) membrane was improved. The FEs to PO are low in this work, but this system is halogen-free.

Thermal Condensation of Dehydrogenation Polymer (DHP) with Xylose.

Conventional adhesives used in wood-based panels typically contain volatile organic compounds, including formaldehyde, which can potentially lower indoor air quality and damage human health. Lignin, a natural adhesive present in wood, offers significant advantages over other materials due to its ready availability, renewable nature, rich aromatic rings, and aliphatic and aromatic hydroxyl groups, as well as quinone groups. However, when modified as an adhesive for wood-based panels, lignin suffers from poor water resistance and formaldehyde release. Dehydrogenation polymer (DHP), as a lignin model compound, possesses a structure similar to lignin and excellent water resistance, making it a potential substitute for lignin as a formaldehyde-free adhesive. A DHP-xylose complex was obtained from a condensation reaction between DHP and xylose in hemicellulose in a simulated hot-pressing environment. The feasibility of DHP bonding with hemicellulose components was verified using FT-IR and NMR spectroscopic methods. In addition, the structure of the adduct and condensation process were also studied. DHP and xylose underwent condensation under simulated hot-pressing conditions. Xylose and DHP may be linked by C-C bonds. The thermal condensation of DHP with xylose was investigated. This may contribute to a better understanding of the adhesive bonding process for xylose during hot-pressing and offer support for practical applications.

Study on the Thermal Condensation Mechanism of Dehydrogenated Polymer (DHP) and Glucuronic Acid.

The preparation of traditional wood-based panels mostly uses adhesives such as urea-formaldehyde resin and phenolic resin, which not only consumes petrochemical resources but also releases formaldehyde, posing potential health risks to the human body. Lignin, a natural adhesive in plant cells, is characterized by high reactivity, and it is expected to aid in the development of a new generation of green formaldehyde-free adhesives. However, current studies of lignin adhesives have revealed that while strides have been made in reducing formaldehyde emissions, its residual presence remains a concern, an issue which is compounded by inadequate water resistance. Dehydrogenated Polymer (DHP) has a lignin-like structure and good water resistance, offering a new option for the development of formaldehyde-free adhesives. In this paper, DHP and glucuronic acid were reacted with each other in a simulated hot-pressing environment to obtain DHP-glucuronic acid complex, and then the structure of the complex was characterized by infrared nuclear magnetic resonance to verify whether DHP can be efficiently connected with hemicellulose components under hot-pressing conditions. The results showed that the thermal condensation reaction of DHP and glucuronic acid can generate ester bonds at the Cα position in a simulated hot-pressing environment. This paper explores the thermal condensation mechanism of DHP and glucuronic acid, which is helpful for understanding the bonding process between adhesives and components of wood-based panels in the hot-pressing process, and provides key theoretical support for the design of more sustainable lignin adhesives.

Self-adhesive fiberboards fabricated from waste bamboo powder through biological pretreatment

Self-adhesive fiberboards fabricated from waste bamboo powder through biological pretreatment

Reprocessable and repairable carbon fiber reinforced vitrimer composites based on thermoreversible dynamic covalent bonding

Reprocessable and repairable carbon fiber reinforced vitrimer composites based on thermoreversible dynamic covalent bonding

Electron Beam Powder Bed Fusion of ATI C103TM Refractory Alloy

The study investigated the use of electron beam powder bed fusion (EB-PBF) to fabricate niobium ATI C103™ alloy articles for microstructural characterization and mechanical testing. The feedstock powder was consolidated into low-porosity articles, and both powder and sample chemistry were monitored. Oxygen uptake in the powder was limited to less than the ASTM B655/B655M (2018) specification limits for 7 uses. Manipulating vacuum chamber pressure showed stable hafnium content but decreasing titanium content with decreasing chamber pressure attributed to evaporation. AM samples were evaluated in the post-processed, as-fabricated, annealed, and hot isostatic pressing (HIP) condition with a maximum yield strength of 287 MPa, UTS of 375 MPa for the HIP, and maximum elongation of 32 pct for the annealed specimens, respectively. Mechanical properties are similar to typical wrought products, with a notable increase in yield strength after post-processing by HIP. The fracture behavior was driven by porosity in the as-fabricated specimens and grain boundary fracture after HIP.

Preparation of Wheat Straw Hot-Pressed Board through Coupled Dilute Acid Pretreatment and Surface Modification.

The production of wheat straw waste board materials encounters challenges, including inadequate inherent adhesiveness and the utilization of environmentally harmful adhesives. Employing a hot-pressed method for converting wheat straw into board materials represents a positive stride towards the resourceful utilization of agricultural wastes. This study primarily focuses on examining the influence of hot-pressing process conditions on the mechanical properties of wheat straw board materials pretreated with dilute acid. Additionally, it assesses the necessity of dilute acid treatment and optimizes the hot-pressing conditions to achieve optimal results at 15 MPa, 2 h, and 160 °C. Furthermore, a comprehensive process is developed for preparing wheat straw hot-pressed board materials by combining dilute acid pretreatment with surface modification treatments, such as glutaraldehyde, citric acid, and rosin. Finally, a thorough characterization of the mechanical properties of the prepared board materials is conducted. The results indicate a substantial improvement in tensile strength across all modified wheat straw board materials compared to untreated ones. Notably, boards treated with glutaraldehyde exhibited the most significant enhancement, achieving a tensile strength of 463 kPa, bending strength of 833 kPa, and a water absorption rate of 14.14%. This study demonstrates that combining dilute acid pretreatment with surface modification treatments effectively enhances the performance of wheat straw board materials, offering a sustainable alternative to traditional wood-based board materials.

Colloidal Photonic Composites with a Long-Range Order by Hot-Pressing Polymer Brush-Grafted Silica Colloids.

Colloidal photonic composites (CPCs) are unique optical materials that combine flexible and responsive polymers with colloidal photonic crystals, and they have promising applications in colorful displays, optical anticounterfeiting, and visual sensors. However, conventional self-assembly strategies for constructing CPCs via solvent evaporation have faced limitations due to the meticulous regulation required during the evaporation process and typically long preparation durations. Here, we present an external force method to achieve a long-range ordered arrangement in CPCs by hot-pressing poly(2-[[(butylamino)carbonyl]oxy]ethyl acrylate (PBCOE)) brush-grafted silica colloidal particles (SiO2-g-PBCOE). We show that the hot-pressing conditions (i.e., temperature and pressure) and the silica volume fraction (φsilica) of the SiO2-g-PBCOE colloidal particles play crucial roles in determining their ordering and optical properties. By optimization of the hot-pressing temperature up to 100 °C and pressure of 5 MPa, a long-range ordered arrangement of SiO2-g-PBCOE colloidal particles with a φsilica of 20.3% can be achieved. For the effect of structural features, our findings reveal that SiO2-g-PBCOE colloidal particles featuring a higher φsilica are more prone to obtain a long-range ordered arrangement compared to a lower φsilica under hot-pressing conditions at relatively low temperature and pressure (50 °C and 5 MPa), which is mainly attributed to the chain entanglement and hydrogen bonding interactions induced by grafted longer polymer brushes, leading to additional energy inputs and weakening the ordering. Significantly, the critical φsilica (φc) of SiO2-g-PBCOE colloidal particles is discerned, strongly influencing the optical properties of the hot-pressed films. Specifically, a hot-pressed SiO2-g-PBCOE film with a critical φsilica of 29.3% displays enhanced optical properties characterized by intensified reflection peaks, narrowed full width at half-maximum (FWHM), and brilliant structural colors. Notably, in this work, we reveal the mechanism of hot-pressing-driven core-shell colloidal particle ordering and the key factors affecting the ordering of colloidal particles, i.e., chain entanglement and hydrogen-bonding interactions, which play a crucial role in obtaining CPCs with controllable structures. Moreover, angle-dependent structural color is observed in the hot-pressed SiO2-g-PBCOE film with a φsilica content of 29.3% due to the unique attributes of the highly ordered arrangement, while the films exhibit mechanochromic properties due to chain entanglement and hydrogen bonding interactions. This work provides valuable insights into the rapid construction of highly ordered CPCs and establishes a solid foundation for external force-assisted ordering of colloidal particles.

Influence of Formulation and Hot-Pressing Conditions on the Performance of Bio-Based Molasses Adhesive for Plywood

Molasses can serve as a natural adhesive for plywood and particleboard. However, several disadvantages remain, including lower dimensional stability and low bonding strength compared to other adhesives. Therefore, modifications are needed to use molasses as an adhesive for plywood. This research aims to improve bio-based molasses (MO) adhesive for plywood using citric acid (CA) adhesive. In addition, this research aims to analyze the effect of adding citric acid and to investigate the optimum hot-pressing temperature to produce the best quality plywood. In the first stage, the molasses and citric acid were combined in a ratio of 100:0, 75:25, 50:50, 25:75, 0:100 w/w%. Then, the second stage focuses on analyzing the influences of pressing temperature based on an optimum first stage. The research demonstrated that the addition of CA altered the gelation time, solid content, viscosity, and pH of the molasses adhesives. In addition, the thermal properties of molasses adhesives were changed after mixing with citric acid. These phenomena indicate changes in characteristics, such as the curing of adhesive. Overall, the characteristics of plywood showed a steady improvement as the CA ratio increased but revealed a significant decline for the 25:75 MO-CA ratio. By raising the pressing temperature from 180°C to 200°C, the quality of plywood was effectively improved. The plywood that was bonded using adhesives with a 50:50 MO-CA ratio exhibited superior mechanical properties and improved dimensional stability compared to the plywood bonded solely with MO. Furthermore, the optimal mechanical and physical properties resulted in plywood bonded with a 50:50 MO-CA ratio when subjected to a pressing temperature of 200°C. The Thermal and FTIR measurements revealed that CA established ester bonds with both the MO and wood veneers. In conclusion, the mechanical characteristics of plywood were improved, while maintaining its excellent dimensional stability.

Exploiting sugarcane waste molasses and dephenolized cottonseed protein as the promising component for eco-friendly wood-based panel adhesive formulation

ABSTRACT In this study, sugarcane waste molasses (SWM) was utilized as a raw component to prepare an eco-friendly plywood adhesive. The optimization of preparation conditions, examination of thermal curing behavior, and exploration of the adhesive's curing mechanism were investigated. Based on the results, the optimal preparation conditions were determined as follows: the SWM is mixed with dephenolized cottonseed protein (DCP), a mass ratio of 2:1 between SWM and DCP, with a concentration of 75% and the addition of 7.5 wt% ammonium dihydrogen phosphate (ADP). Additionally, the optimal hot-pressing condition involved a temperature of 190°C for 10 min. Under these optimized conditions, the adhesive exhibited a maximum wet shear strength of 1.14 MPa, successfully meeting the China National Standard GB/T9846-2015. The curing behavior of the adhesive was investigated by analyzing thermal analysis and measuring the insoluble mass proportion. As the heating temperature and heating time increased, the insoluble mass proportion gradually rose. Thermogravimetric analysis (TG) showed that the thermal decomposition reaction temperature was 146.4°C and 202.05°C, differential scanning calorimetry (DSC) showed that endothermic reaction occurred at 135.8°C, exothermic reaction occurred at 227.8 °C. Through Fourier-transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), it was observed that the addition of ADP promotes the conversion of sucrose hydrolyzed products into furan compounds and reacts with proteins. Moreover, the amino and carboxyl groups of proteins react with the phenol hydroxyl groups of lignin to form C–N and C–O bonds, a polymer with a cross-linked network is formed.

A fully bio-based soy protein wood adhesive modified by citric acid with high water tolerance

A fully bio-based soy protein wood adhesive modified by citric acid with high water tolerance

Glycerol-based liquefied palm kernel shell product and its blend with citric acid as bio-based wood adhesive

Concerns for the environment and for human health have become critical factors that motivate creating bio-based wood adhesives. Therefore, this study proposes replacing toxic chemicals with alternative adhesives. In the first step, glycerol was added to the natural phenolic compounds from liquefaction of palm kernel shell (PKS), having a high content of lignin. The obtained glycerol-based liquefied PKS, and its blend with citric acid, were tested for bonding in a study on the effects of hot-pressing conditions (temperature and time). The results revealed that the liquefaction system in this study achieved an 83% conversion of the PKS components into glycerol-based liquefaction. According to the Fourier transform infrared and carbon-13 nuclear magnetic resonance analyses, the glycerol-based PKS contained lignin derivatives and furan products. This accounted for its great performance in bonding rubberwood veneers. The tensile shear strength was improved by blending with 15% citric acid, especially when applying the high 190 °C pressing temperature for 15 min.

In Situ X-ray imaging of HT-PEMFC hot-pressing using contrast enhancement

A contrast enhancement agent is used to visualise phosphoric acid penetration and distribution in high-temperature polymer electrolyte membrane fuel cells. This new method is demonstrated in the investigation of hot-pressing parameters on phosphoric acid penetration and distribution. In situ radiography of the hot-press process showed acid plumes breaking through the catalyst layer, microporous layer (MPL) and gas diffusion layer (GDL). The phosphoric acid volume and distribution within the MPL and GDL are quantified, and their dependence on hot-press pressure, duration and compression control are analysed. Increasing hot-press pressure and duration was found to increase acid penetration and delamination of the membrane and catalyst layers. The absence of a compression control gasket also led to significant infiltration into the MPL and GDL. Penetration occurred first at the anode for all tests, which was attributed to a higher number of cracks and greater degree of crack connectivity. Phosphoric acid entered the MPL and GDL either through initial breakthrough of the catalyst layer, or from acid pooling on the GDL surface and being compressed into the fibres. This work provides a novel method to improve visualisation of phosphoric acid and highlights the acid loss mechanisms resulting from hot-press conditions.