Hot-pressing Pressure Research Articles

The potential of using agricultural waste: Corn husk for particleboard raw material

The development of manufactured particleboard using non-wood raw materials has been significant due to the decrease of wood as the main raw material for the particleboard industry. In this study, corn husk, an agricultural waste, was used for experimental manufacturing of particleboard bonded with natural and synthetic adhesives. The influence of adhesive types and concentration on the physical and mechanical properties of particleboard were investigated. The synthetic adhesive types used were urea-formaldehyde (UF) and phenol-formaldehyde (PF) with 8,10 and 12 wt% adhesive concentration. The natural adhesive used was citric acid with 15, 20, and 25 wt% adhesive concentration. The target density of particleboard was set at 0.80 g/cm3. The boards were manufactured at a pressing temperature of 130°C for UF, 150°C for PF and 200°C for citric acid, pressing time of 10 minutes, and 2.5 MPa for hot-pressing pressure. Generally, this study confirms that types of adhesive and adhesive concentrations influence the properties of particleboard. Results show that particleboard with citric acid adhesive has better physical and mechanical properties than particleboard bonded with UF and PF adhesives.

Effect of viscoelastic thermal compression (VTC) treatment on density and moisture content of laminas from Paraserianthes falcataria

ABSTRACT Paraserianthes falcataria, a low-density wood species underwent viscoelastic thermal compression (VTC) treatment, which was the combination of pre-steaming and compression by hot-pressing, in order to increase its density and mechanical performance. The aim of this study was to evaluate the impact of VTC treatment on the density and moisture content of Paraserianthes falcataria laminas. Several process conditions which consisted of pre-steaming duration (0–30 minutes) and hot-pressing pressure (0–8 MPa) were applied on Paraserianthes falcataria laminas. Density and moisture content of Paraserianthes falcataria laminas were measured for 7 days. This study found out that process condition of 30 minutes pre-steamed combined with 8 MPa pressing pressure obtained the highest percentage of densification degree (83.71%) based on time period of before the treatment until the next 7 days after VTC process; and the lowest percentage of density improvement was recorded on non-pre-steamed combined with 4 MPa pressing pressure (54.23%). In terms of moisture content, process condition of non-pre-steamed combined with non-hot-pressed recorded the highest equilibrium moisture content (9.5%); while non-pre-steamed combined with 4 MPa pressing pressure had the lowest equilibrium moisture content (6.3%).

TO THE COMPARISON OF TWO METHODS OF MANUFACTURING NEW DRY FRICTION PRODUCTS

The technological indicators of manufacturing methods and the physicotechnical and tribotechnical properties of new dry friction friction products made of friction powder materials based on Fe , two different methods, are used: separate pressing and sintering under pressure and dynamic hot pressing. Approximate dependencies of effect of porosity of friction materials on their tribotechnical properties are obtained.

Multilayer polyethylene/ hexagonal boron nitride composites showing high neutron shielding efficiency and thermal conductivity

Abstract Polymer composites show huge potential as high efficiency neutron shielding and thermally conductive materials applying in aerospace, nuclear reactors, medical treatment fields, where neutron radiation is inevitable. Designing multilayer structure with concentrated filler in one layer is an effective strategy for achieving high neutron shielding efficiency at low filler loading. Herein, multilayer composite films with alternating high density polyethylene/hexagonal boron nitride (HDPE/hBN) layers and low density polyethylene (LDPE) layers were prepared by stacking hot-pressing. By selecting suitable hot-pressing temperature and pressure, multilayer composite films with highly oriented hBN sheets were successfully fabricated, and confirmed by the morphology and structure characterizations. As a result, the multilayered PE/hBN films show excellent neutron shielding performance through multiple repeated scattering, absorption, and dissipation between multilayers. At the filler content of 30 wt%, the ratio of transmitted neutrons to incident ones decreases to 4.16%, which is much lower than that with random PE/hBN composite (14.95%). Meanwhile, the concentrated and oriented hBN results in multilayer PE/hBN composite with a higher in-plane thermal conductivity than random one. Such the high thermal conductivity can contribute to the rapid dissipation of heat converted by neutron energy. Therefore, the superhigh neutron shielding efficiency and excellent thermally conductivity, as well as the simple and scale preparation process, mean our multilayer PE/hBN films with a huge application prospect.

Oscillatory pressure sintering of Al2O3 ceramics

Herein, Al2O3 ceramics are sintered by oscillatory pressure sintering (OPS) and hot pressing (HP) at different temperatures. The density and grain size of OPS- and HP-processed Al2O3 ceramics are measured and analyzed using existing models. Results reveal that OPS-processed Al2O3 ceramics exhibit high density and small grain size likely due to plastic deformation. Moreover, OPS-sintered Al2O3 ceramics render higher hardness and fracture strength than HP-sintered Al2O3 ceramics, which can be ascribed to high density and small grain size, respectively. These results demonstrate that sintering behavior and mechanical properties of Al2O3 ceramics can be improved by OPS.

Effect of oscillatory pressure on the sintering behavior of ZrO2 ceramic

Zirconia ceramics were prepared by oscillatory pressure sintering (OPS) and hot pressing (HP). The result revealed that OPS could enhance densification compared to HP when sintering temperature was higher than a critical value. The onset temperature for rapid grain growth was found to be same for both techniques. However, rate of grain growth in OPS was lower than that in HP. Furthermore, the result also showed that samples prepared by OPS exhibited higher hardness than those prepared by HP when sintering temperature was higher than the critical value. The improved hardness was solely due to the higher density of the samples prepared by OPS.

Mechanical and Thermal Properties of All-Wood Biocomposites through Controllable Dissolution of Cellulose with Ionic Liquid.

All-wood biocomposites were prepared with an efficient method. The ionic liquid of 1-butyl-3-methylimidazolium chloride (BMIMCl) was used to impregnate manchurian ash (MA) before hot-pressing, and the all-wood biocomposites were prepared by controllable dissolving and regenerating the cellulose in MA. The Fourier transform infrared analysis suggested that all the components of MA remained unchanged during the preparation. X-ray diffraction, thermogravimetric and scanning electron microscope analysis were carried out to study the process parameters of hot-pressing pressure and time on the crystallinity, thermal properties and microstructure of the all-wood biocomposites. The tensile strength of the prepared all-wood biocomposites reached its highest at 212.6 MPa and was increased by 239% compared with that of the original MA sample. The thermogravimetric analysis indicated that as the thermo-stability of the all-wood biocomposites increased, the mass of the residual carbon increased from 19.7% to 22.7% under a hot-pressing pressure of 10 MPa. This work provides a simple and promising pathway for the industrial application of high-performance and environmentally friendly all-wood biocomposites.

Thermoelectric Properties of BiTe

Research on crystal structures and thermoelectric properties has been carried out using BiTe material. The sintering method used is hot press. Hot press pressure comes from the bottom up. Temperature variations used in hot press are 400, 450, and 500°C. Analysis of crystal structure used XRD. Based on the XRD results, the result is that the crystal structure of BiTe bulk is hexagonal. Thermoelectric properties measurements used ZEM-3. The sample is measured in a temperature range of 50–200°C. Based on the measurements, the sample with hot press 500°C has the highest Seeback coefficient and power factor values which are –71µV/K and 3.6 x 10–4 W/mK2, respectively. The sample has the best performance at room temperature and has decreased performance with increasing temperature. While, the best electrical resistivity value is owned by the sample with hot press 450°C with a value of 1.28 mΩ cm at room temperature. Overall, the higher the temperature used when sintering, the better the performance produced. Thus, the BiTe material can be considered as a thermoelectric material.

Glue wood veneer to wood-fiber–high-density-polyethylene composite

Wood-fiber-reinforced thermoplastic plastic composite is a type of environmentally friendly material. However, its application in furniture and interior decoration is limited due to its lack of wood texture. In this work, wood-veneer-facing decoration was explored to beautify the composite's appearance. Surface planning and slight sanding were applied to wood-fiber–high-density-polyethylene (WF-HDPE) composite. Polyvinyl acetate emulsion was used as adhesive, and the veneer-faced WF-HDPE composite floor was prepared by the hot-pressing method. The bonding line was analyzed with Fourier-transform infrared spectroscopy and scanning electron microscopy. Planning plus sanding treatment removed the HDPE film on the composite surface and exposed the wood fibers to react with the adhesive. The rough surface provided all decorative samples bonding strengths higher than 0.9 MPa. The bond line could stand 63 °C water soaking for 3 h without delamination. The hot-pressing temperature exhibited a significant effect on surface bonding strength. The optimized hot-pressing technique included a hot-pressing temperature of 80 °C, a hot-pressing time of 10–20 min, and a hot-pressing pressure of 0.2 MPa. With this combination, the surface-decorative veneer retained the beauty of its original color.

Удосконалення сенсорів з призмовим типом збудження поверхневого плазмонного резонансу на полімерній основі

The means related to the improvement of a sensor device on plastic substrate with the prism type of surface plasmon resonance (SPR) excitation in the Kretschmann configuration and with the scanning of the incidence angle of monochromatic light aimed for decreasing of production costs and increasing of sensitivity as well as productivity are considered. It has been shown that application of the laminar polymer substrates after hot press processing, under (180-210 °С) temperature and (300-500 kg/cm 2 ) pressure, will provide disappearance of double refraction and high level in SPR sensor sensitivity because of smoothing surface microrelief. Analysis of the operational characteristics of SPR sensors based on Au and Ag resonant metallic films is performed. Gold displays higher shift of the resonance angle to changes of ambient refraction index and is chemically stable. Silver posses narrower resonance curve thus providing a higher signal/noise ratio of SPR chemical sensors, but has a poor chemical stability. In order to improve sensitivity, measurement accuracy and stability of the SPR instruments operation, two variants for the active metallic coating preparation are proposed: employment of bimetallic Ag/Au (Au as an outer layer) structure in 2:1 ratio that combines the advantages of both layers, as well as pure gold film with subsequent annealing at 120 oC that smoothes the surface microrelief thus stabilizing the sensors characteristics and increasing sensitivity. The main challenge for increasing of productivity consist in the determination of the easiest and most cost-effective way to achieve a high degree of parallelization for high throughput SPR-based analysis. We propose a construction of the sensor in disk format on the basis of the prism scheme of excitation of SPR in the Kretschmann configuration with optical scanning over angles, where a planar chip with integrated gratings for the input-output of light was used as a sensor unit. Thus, the traditional prism and the focusing optics are integrated in a planar sensor unit of the SPR transducer. The unit is placed on a rotating disk, which increases essentially the number of sensitive elements of a sensor. Cheap one-time SPR disks can be produced already now in series with the use of available materials, technologies, and facilities, which opens possibility for the large-scale application. Fig.: 5. Refs: 92 titles.

Preparation of large-scale Ti3SiC2 ceramic impeller with complex shape basing on the optimization of sintering manner

In order to manufacture large-scale Ti3SiC2 impeller, three techniques including pressureless sintering (PLS), hot pressing (HP) and ultrahigh pressure sintering (UHP) were adopted to prepare Ti3SiC2 bulks, and the phase stability, microstructure and properties of the sintered Ti3SiC2 was evaluated. The results showed that the stable Ti3SiC2 blocks can be obtained by PLS, HP, UHP methods at 1550 °C. Furthermore, the HP Ti3SiC2 exhibited excellent strength of 520.46 MPa and toughness of 7.62 MPa m1/2 owing to the prominent lamellar grains with large aspect ratio of 3.63. In this case, large-scale Ti3SiC2 bulks of Φ 120 mm × 29 mm were prepared via HP technique and then subjected to precision machining to manufacture the centrifugal pump impeller with complex shape. All the machining dimensions including outer diameter, inner diameter, keyway depth, keyway width and blade thickness completely met the design precision.

Reuse of reclaimed tire rubber for gas-separation membranes prepared by hot-pressing

Abstract Waste tires are mainly composed of natural rubber, synthetic rubber, carbon black, steel wires, and fibers. Rubber, which is a valuable resource, is one of the raw materials used for membrane preparation. In this study, a convenient and environmentally friendly synthetic technology, hot-pressing method was developed for reusing reclaimed tire rubber to prepare gas-separation membranes. The effects of the preparation conditions, including hot-pressing temperature, pressure, and time on the membrane structure and separation performance, were investigated. Thermogravimetric analysis and field-emission scanning electron microscopy were carried out. The Thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cross-linking degree results showed that the reclaimed tire rubbers used in this study consisted mainly of styrene-butadiene rubber and polybutadiene rubber. Reclaimed tire rubbers with low carbon contents and low degrees of cross-linking are beneficial for fabricating membranes by hot-pressing. The hot-pressing technique proposed in this study yielded dense gas-separation membranes from the reclaimed tire rubbers, proved to be an efficient approach for simplified recycling of waste tires and can in fact inspire the development of new recycling routes. The hot-pressed membranes derived from reclaimed tire rubber showed competitive results with a CO2/N2 selectivity of 12.8 and CO2 permeability of 161 Barrer.

Experimental Investigations of Drilling Silicon Carbide Using Brazed Diamond Tools

Abstract This article mainly studied the machining efficiency and service life of a brazed diamond tool for drilling silicon carbide (SiC). Firstly, the influence of process parameters (spindle speed [ss], axial pressure [ap], feed rate [fr]) on the drilling efficiency was researched. Then, the orthogonal analysis was carried out to study the influence of tool structural parameters (wall thickness of tools [wtt], diamond grit size [dgs], working layer thickness [wlt], and outer diameter of tools [odt]) on the drilling efficiency and tool life. Eventually the effects of solder composition on the drilling performance were investigated. The results show the following: (1) the optimal drilling efficiency can be obtained under the condition of ss of 83π rad/s, ap of 800 N, and fr of 4/100π mm/rad. (2) The influence degree of tool structure on the drilling performance is wtt > dgs > wlt > odt; the optimal tool structural parameters are wtt of 1 mm, dgs of 250 μm, odt of 10 mm, and wlt of 0.8 mm. (3) For SiC ceramics prepared by hot pressing and hot isostatic pressure sintering, diamond tools with nickel-chromium alloy solder should be chosen; whereas for SiC ceramics prepared by pressure-free and reactive sintering, diamond tools with copper-based solder should be chosen.

Prevention and Control Measures for Vertical Spread of Fire along the External Wall of High-rise Buildings

 In the analysis and research of few cases on the characteristics of vertical "burning" and spreading of fire in high-rise buildings in China and overseas, the mechanism of vertical spreading of fire along external wall is caused by hot pressing and wind pressure existing in high-rise buildings. The use of external wall combustible materials and near-window combustible items resulted in the formation of high temperature pyrotechnics and the burning of the external wall. Besides, due to the lack of fire-fighting measurements in high-rise building, it is recommended that the external wall of the high-rise building should be equipped with vertical fire-proof partitioning and non-combustible materials by setting up an automatic fire-fighting water curtain system along the vertical section of the external wall and above the indoor window. Therefore, the automatic sprinkler can be set up to prevent the fire from spreading vertically along the external wall of the building effectively.

Environmentally-Friendly High-Density Polyethylene-Bonded Plywood Panels.

Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with traditional UF and PF adhesives, even though the adhesive dosage and pressing pressure were lower than when UF and PF adhesives were used. The obtained bonding strength values of HDPE-bonded alder plywood panels ranged from 0.74 to 2.38 MPa and met the European Standard EN 314-2 for Class 1 plywood. The optimum conditions for the bonding of HDPE plywood were 160 °C, 0.8 MPa, and 3 min.

Response Surface Methodology as an Approach to Optimize the Preparation of Maize Straw Panels Applying Soy-based Adhesives

In this study, maize straw was used to prepare formaldehyde-free panels with soy-based adhesives. Influences of adhesive amount, hot-pressing time, temperature and pressure on the internal bonding strength were optimized by applying response surface methodology (RSM). The results showed that based on experimental mathematical model, the optimum hot-pressing conditions were obtained. Adhesive amount was 14%, hot-pressing pressure was 3.0 MPa, hot-pressing temperature was 126 °C, hot-pressing time was 28 s/mm. The actual internal bonding strength was 0.52 MPa while the predicted value was 0.51 MPa, indicating that the experimental mathematical model was accurate and reliable.

Preparation and process optimization of randomly oriented C/C composites by a novel method

Conventional ways of fabricating C/C composites are unable to achieve wetting in the core of the carbon fiber tow by molten pitch because a single tow has thousands of fibers. Pitch stabilization after infiltration into the carbon fiber preform results in local oozing of the pitch and a non-uniform microstructure due to non-uniform pitch stabilization in the preform. The objective of this research was to devise a method by which complete wetting of fibers in the tow with mesophase pitch is attained by mixing stabilized pitch and chopped and scattered carbon fibers, followed by hot-pressing and carbonization. The influence of process parameters on the carbon yield of the stabilized mesophase pitch is evaluated. The carbon yield divided by processing time and the carbon yield multiplied by the ratio of the apparent density to real density of the C/C composites are used to optimize process parameters. Results show that complete wetting of fibers with mesophase pitch is attained by this method. The carbon yield of the stabilized mesophase pitch decreases with heating rate and the mass ratio of stabilized pitch to carbon fibers, and increases with hot-pressing pressure. At high pressures and high mass ratios, local oozing of the stabilized pitch occurs. The optimum C/C composite was prepared under a hot-pressing pressure of 15 MPa, a heating rate of 0.2 °C/min and a mass ratio of stabilized pitch to carbon fibers of 1:1.

The use of cellulose nanofibrils to enhance the mechanical properties of graphene nanoplatelets papers with high electrical conductivity

Mechanically flexible and high electrically conductive multilayered graphene nanoplatelets (GnP)/cellulose nanofibrils (CNF) composite papers were successfully fabricated through a vacuum-assisted self-assembly technique. The morphology observation showed that highly disassembled CNF were achieved by high-pressure homogenization of water-based cellulose slurry, and the homogenized CNF uniformly interpenetrated within the microporous GnP paper network. The analyses of mechanical properties and morphology suggest that the CNF effectively bridged the adjacent GnP sheets and efficiently strengthened the GnP papers by producing strong GnP/CNF interfacial interactions resulting from mechanical interlocking, van der Waals forces and hydrogen bonds between the GnP and the CNF. Moreover, it was noticed that hot-pressing pressure is necessary to be applied on samples to produce stronger papers with higher electrical conductivity. As the CNF loading reached 60 wt%, the Young’s modulus and tensile strength of the hot-pressed GnP/CNF hybrid paper were significantly increased to 9.1 GPa and 57.7 MPa, respectively. In addition, a high electrical conductivity of 26.8 S/cm was retained for the paper with 30 wt% CNF. Our approach provides a facial and eco-friendly fabrication route to produce strong and highly conductive GnP/CNF papers which are of great practical appeal as a new type of nanomaterials in various fields.

A Thermoplastic Multilayered Carbon-Fabric/Polycarbonate Laminate Prepared by a Two-Step Hot-Press Technique.

Carbon fiber (CF) reinforced thermoplastic composites have gradually become increasingly popular in composite production owing to their lower hazard level, good structural flexibility and recyclability. In this work, a multilayered carbon–fabric/polycarbonate laminate (multi-CFPL) was fabricated by a two-step hot-press process, mainly based on the thermoplastic properties of its polycarbonate (PC) matrix. Different from the conventional one-step method, the two-step hot-press process was composed of two separate procedures. First, a unit-hot-press operation was introduced to prepare a single-layered carbon–fabric/PC laminate (simplified as unit-CFPL). Subsequently, a laminating-hot-press was employed to compress several as-prepared unit-CFPLs bonded together. This combined process aims to reduce the hot-press temperature and pressure, as well as facilitate the structure designability of this new composite. Several mechanical investigations were conducted to analyze the effect of the hot-press parameters and unit-CFPL numbers on the performance of this multi-CFPL material, including flexural, uniaxial tensile and impact tests. The results reveal that the multi-CFPL exhibits a good stability of flexural and tensile properties in terms of strength and modulus. Furthermore, during impact tests, the multi-CFPL presents an accelerated growth of peak force and energy absorption capability with increasing unit-CFPL layers.

Densification, microstructure and properties of mechanically alloyed and hot-pressed Cu–15 wt% Al alloy

In the present work, hot press of Cu–15 wt% Al alloys was carried out in a vacuum environment at a sintering temperature of 500 °C for 30 min with varying pressure (100–500 MPa) to densify the alloys. Both the density and hardness of Cu alloys were significantly increased with increasing the hot press pressure. A maximum density of ~ 94.5% ρth (theoretical density) and microhardness of ~ 6.2 GPa was achieved for Cu–Al alloy after hot press at 500 °C with 500 MPa pressure application. The XRD, SEM-EDS analysis confirms the presence of solid solution α (Cu0.78Al0.22) and γ (Cu9Al4) inermetallic phases in the sintered samples. Maximum hardness of 7.88 GPa and elastic modulus of 177.35 GPa was measured for Cu–Al alloy using nano-indentation test. It must be noted that so far in the literature a maximum hardness of 4.9 GPa was reported for Cu-based materials. The alloy was also measured with a moderately high compressive yield strength (1019 MPa), compressive strength (1106 MPa), and a reasonable amount of strain (6.6%). The wear tests revealed that the Cu–15 Al alloy hot pressed at 500 MPa pressure can exhibit better wear properties. Low coefficient of friction (COF) of 0.15 and wear rate of 0.71 × 10−5 mm3/N-m was observed at a sliding speed of 0.25 m/s and high COF of 0.20 and wear rate of 4.33 × 10−5 mm3/N-m were noted with further increasing the sliding speed (1.25 m/s). Further microstructural characterization of worn surfaces reveals abrasion wear as the major dominant wear mechanism. The present work clearly demonstrates the use of a high amount of hot press pressure in achieving good sinter density for Cu–15 wt% Al alloys with superior hardness, better wear and compressive strength properties.