Vacuum Pressure Impregnation Research Articles

Preliminary investigation on the vacuum pressure impregnation performance of flame retardant for larch (Larix kaempferi) depending on grooving type

Due to wood’s susceptibility to fire, it is crucial to treat wood-based materials with flame retardants, especially in construction applications. This study investigated the effectiveness of various grooving types, including transverse, longitudinal, both transverse and longitudinal, and surface grooving, in enhancing the vacuum pressure impregnation of larch wood. The results revealed that transverse grooving provided a slightly greater impregnation advantage than longitudinal grooving. Moreover, exceptional impregnation performance was observed in larch samples subjected to threefold longitudinal, transverse, and surface grooving, exhibiting a remarkable improvement of 215% compared to untreated larch. However, a limitation of this study is that only one wood species and one flame retardant formulation were used. While it is meaningful as a preliminary investigation into the vacuum pressure impregnation performance of flame-retardant wood based on groove processing, further studies using various wood species and flame retardants.

Enhanced SiC/NFG/Ni ternary composite microwave absorbing materials with micro-network structures produced by selective laser sintering

In this paper, a ternary composite wave-absorbing material consisting of silicon carbide (SiC), natural flake graphite (NFG) and nickel (Ni) has been successfully fabricated through a combined process of selective laser sintering (SLS) and vacuum pressure impregnation. The study investigated how the content of SiC powder affected the absorption capacity and mechanical performances of the composites. The findings indicate that as the proportion of SiC powder rises, the porosity of the composites diminishes, while the bending strength increases. As the content of SiC is 40 wt%, the porosity is 52.14 % and the flexure strength is 9.58 MPa, approximately five times greater than that of graphite-type ceramic preforms. The composite’s electromagnetic wave-absorbing capability initially improves and then declines with the increase of SiC content. When the SiC content is 10 wt% and the thickness is 1.5 mm, the composite absorbing material exhibits optimal electromagnetic absorption performance, with a minimum reflection loss (RLmin)of −44.04 dB and an effective absorption bandwidth (EAB) of 5.42 GHz (8.24–13.66 GHz). The composite material, characterized by its lightweight, high strength, and broad frequency range, shows promise for applications in microwave absorption technology.

Characteristics of Fast-Growing Wood Impregnated Using Monoethylene Glycol and SiO Nanoparticles Against Fungal Attacks

Jabon (Anthocephalus cadamba) and Sengon (Falcataria moluccana) were fast-growing wood species widely planted in the community forest. Both kinds of wood have low durability even though they can potentially be used in the carpentry material industry. Therefore, this research aimed to analyze the vacuum-pressure impregnation effect using monoethylene glycol (C2H6O2) or MEG and silica dioxide (SiO2) nanoparticles on wood resistance to fungal decay. The results showed that impregnation treatment with MEG and SiO2 nanoparticles significantly improved the durability of Jabon and Sengon against fungal attacks. Furthermore, MEGSiO2 with 24-hour polymerization had a better impact on durability compared to both the control and MEGSiO2 with 12-hour polymerization. The 24-hour polymerization using 1% SiO2 nanoparticles resulted in the lowest weight loss for Jabon (5.86% ) and Sengon (5.21%). In addition, the variation of SiO2 nanoparticle concentration did not significantly affect the weight loss and durability of Jabon and Sengon against fungal decay.

Study on the physico-mechanical properties and mechanisms of poplar wood co-modified by anoxic high-temperature heat treatment and impregnation with silica sol/phenolic resin

Addressing the challenges of fast-growing poplar wood in construction, decoration, and furniture, including low density, insufficient strength, poor toughness, and suboptimal dimensional stability, this study introduces an innovative organic/inorganic impregnation-heat treatment technique. This method significantly enhances the physico-mechanical properties of poplar wood and overcomes issues associated with thermosetting resin modification, such as reduced impact toughness, uneven resin penetration, and wood swelling. Utilizing in situ polymerization with silica sol and phenolic resin, specifically with particle sizes between 8 and 15 nm, the process markedly improves wood permeability and overall properties through vacuum pressure impregnation and heat treatment. The findings indicate a 54.42 % increase in the wood's density. Optimized heat treatment at 180 °C for 1 h significantly enhances dimensional stability and reduces water absorption, with the ASE value reaching up to 69.3 %. Furthermore, the impregnation-heat treated wood exhibits a 50.19 % increase in bending strength to 81.6 MPa, a 103.93 % increase in modulus of elasticity to 16.5 GPa, and a 29.42 % increase in impact toughness to 92.5 kJ/m2, demonstrating substantial improvements over the raw material. FT-IR analysis reveals the presence of Si-O-Si vibration peaks, indicating the effective penetration of silica sol. TGA analysis displays the treated material's superior thermal stability compared to the raw material. XRD analysis confirms that the impregnation and heat treatment processes have not adversely affected the wood's crystalline regions but have instead reduced hygroscopicity and enhanced stability. SEM analysis showed that the composite impregnation liquid effectively penetrated and distributed within the wood cells. These results open new theoretical and technical pathways for enhancing the physico-mechanical properties of fast-growing poplar wood.

Preparation and drying characteristics of poplar wood modified by hexacyclite

In recent decades, wood drying has emerged as an important method to ensure wood quality and improve wood utilization. However, the addition of modifiers to wood can hinder the transfer of moisture, making the drying process difficult. Therefore, the drying of modified wood is challenging. This study focuses on poplar wood and reports the preparation of modified wood capable of releasing health-beneficial negative oxygen ions. In particular, this study examined the effect of hexacyclite on the transfer of internal moisture and heat in wood. Hexacyclite was dispersed using sodium hexametaphosphate as a dispersing agent, and the modified poplar wood was prepared via vacuum pressure impregnation. The process involved six cycles of the following treatments: a vacuum treatment (−0.08 MPa, 20 min), followed by a pressure treatment (1 MPa, 120 min), and a final atmospheric treatment (5 min). The modified wood was dried via kiln drying, during which the overall wood temperature rapidly increased, with the total drying rate also increasing by 1.05%/h. The introduction of hexacyclite potentially altered the way modified wood bound with moisture, leading to permanent changes in the porosity of cell walls and the structure of polymers and thus altering the movement of water molecules. The modified wood continuously emitted far-infrared rays with a wavelength of 8–15 μm. In some large water clusters, after the far-infrared energy was absorbed, the movement of water molecules accelerated, thereby increasing the drying rate in the wood below the fiber saturation point. Ultimately, this resulted in the modified wood drying faster and thus exhibiting a better quality.

Preparation of a graphite / SiC composite casting material and study of its performance

The inferior mechanical properties and thermal conductivity of carbon graphite materials are attributed to the presence of pores and cracks. The integration of graphite with ceramics has been proposed as a method to enhance these properties; however, graphite/ceramic composites fabricated through pressureless sintering often exhibit inadequate integration. In this paper, a diffuse-continuous network dual-reinforced graphite/silicon carbide(SiC) ceramic composite was prepared by integrating the graphite powder micro-thermal press forming technology with the fused deposition modelling(FDM) technology and combining the pressureless sintering and vacuum pressure impregnation processes. It was found that the addition of high purity silicon powder to the material formulation reacts with the resin carbon to form silicon carbide particles (SiC-p), which can play a role in diffusion enhancement. However, the addition of excessive silicon powder can have a detrimental effect, and the performance of diffusion enhanced graphite/silicon carbide composites is positively correlated with the density of billet formation, and the effect of diffusion continuous network dual enhancement is more obvious, and the performance of the composites is better compared to that of single diffusion enhancement. The compressive and flexural strengths of the graphite/SiC composites finally obtained reached 59.47 MPa and 44.25 MPa, respectively, and the thermal conductivity was 43.62 W/m·K, and the porosity and open porosity were 29.62 % and 20.48 %, respectively, which are comparable to those of manmade graphite castings, and have better gas permeability, which is expected to be applied in the casting field.

Leach-resistant modified bamboo with fire-retardant and anti-mildew properties via in situ synthesis

To ensure the long-term fire-retardant (FR) and anti-mildew (AM) of bamboo materials when employed in outdoor settings susceptible to rainfall exposure, high durability is essential. In this study, we achieved water-leaching resistance of FR and AM bamboo through the in situ synthesis of phosphotungstic acid (PW) and silver nitrate (AG) via vacuum-pressure impregnation. The successful synthesis of the nanospheres within the bamboo (referred to as PWAG-B) was confirmed by TEM, FTIR, and XPS. These nanospheres remained intact within the bamboo cell wall after being subjected to a leaching test, with only a negligible mass loss of 0.88% and virtually no traces of Ag and W in the leachate for PWAG-B1. Furthermore, the treated bamboo exhibited superior AM properties, with complete resistance against two types of mildew, namely Botryodiplodia theobromae and Alternaria alternate, as well as stain fungi including Aspergillus niger and Penicillum citrinum. Notably, the treated bamboo displayed reduced thermal and smoke parameters in comparison to untreated bamboo, along with a delayed ignition time. This long-term AM and FR bamboo has the potential for the development of eco-friendly outdoor building materials.

Superhydrophobicity wood with reversible photoresponsive property

Superhydrophobic photoresponsive wood (HPW) was synthesized through the vacuum pressure impregnation process with octadecyltrimethoxysilane (OTS), spiropyran, and polyvinyl alcohol (PVA). The process endowed the wood with photostimulation responsiveness and superhydrophobic characteristics. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Fourier transform infrared spectroscopy (FTIR), and a contact angle meter were analyzed to determine the micromorphology, chemical composition, and hydrophobicity of the modified wood. The modified wood had a micro-nanometer mastoid structure at the microscopic level, with a large number of hydrophobic groups. The static water contact angle of the modified wood reached 153°, the water absorption rate decreased from 123.28 % to 19.29 %, and the anti-swelling rate was only 1.69 %, showing good hydrophobic and anti-swelling performance. At the same time, color values of the wood L*, a*, b*, and total color difference ΔE*, it was found that spiropyran made the modified wood have a rapid response to light stimulation.

Cell wall water induced dimensional changes of beech and pine wood

Hygroexpansion in timber construction is a phenomenon that occurs as a result of changes in the cell wall structure of wood caused by water. In this study, beech (Fagus sylvatica) and pine (Pinus taeda L.) wood were conditioned at different relative humidities with saturated salt solutions and saturated through vacuum pressure impregnation. The moisture content and dimensions of the samples were evaluated under various adsorption equilibrium states, as well as during drying from water saturation to an air-dried state. The results obtained using the two-dimensional time-domain nuclear magnetic resonance technique revealed two distinct types of cell wall water in both wood species, designated as B-water and C-water, as they displayed different mobilities. With increasing moisture content, the mobility of cell wall water increased; however, B-water maintained a constant level of mobility and formed water clusters when it accumulated in the high humidity region and at slightly above the fiber saturation point (FSP), which is evidence of the occurrence of free-bound water. The B-water, located in the amorphous region of microfibrils and their surrounding hemicellulose, exerted a predominant influence on the dimensional changes of the wood both under equilibrium and nonequilibrium conditions, in comparison to the C-water which located in the matrix of hemicellulose and lignin.

Effect of the second curing cycle on performance of superconducting magnet insulating system

In large-scale, high-field superconducting magnets used for magnetic confinement fusion, high energy accelerators, and magnetic resonance imaging, the insulating system made from glass fiber reinforced resin-based composites is the key component, which mainly plays the role of mechanical support, fixing and protecting superconducting conductors, as well as electrical insulation. Vacuum Pressure Impregnation (VPI) approach is widely used in the manufacturing of the insulation system. The second curing cycle is generally required after the first VPI and curing process. For example, after the superconducting coil is cured in the mold, the de-molding process requires the superconducting coil to be reheated according the curing temperature. Moreover, for large-scale superconducting magnets, the superconducting coil needs to undergo a second VPI process after the first VPI process to fix the coil in the coil case. In this work, the tensile and shear properties of pure epoxy resin and the glass fiber reinforced resin-based composite, were investigated at both room and cryogenic temperatures and the effect of the second curing cycle on the mechanical properties was analyzed. Additionally, the strain evolution of the Nb-Ti superconducting coil during the second curing cycle was measured using the Fiber Bragg Grating (FBG) sensors embedded in the composite. The results indicate that the second curing cycle will not introduce additional strain to the previously cured resin matrix, but the defective or weak parts of the resin matrix may be affected by the new added epoxy resin and a little extra strain has been observed.

Construction and mechanism analysis of flame-retardant, energy-storage and transparent bio-based composites based on natural cellulose template

With the proposal of sustainable development strategy, bio-based energy storage transparent wood (TW) has shown broad application value in green buildings, cold chain transportation, and optoelectronic device fields. However, its application in most fields is limited due to its own flammability. In this study, epoxy resin, triethyl phosphate (TEP) and polyethylene glycol (PEG) were introduced into delignified balsa wood template by vacuum pressure impregnation, and bio-based TW/PEG/TEP integrating flame retardant, high strength and phase-change energy-storage performance was prepared. TW/PEG composites have no leakage during phase change process and their transparency is up to 95 %. Compared with TW/PEG, the shielding effect of char layer and the inhibition effect in condensed and gas phase significantly decrease the total heat release of TW/PEG/TEP. TW/PEG/TEP biocomposites still maintained a high enthalpy of phase change and a low peak melting temperature, which was conducive to its application around the area of low temperature phase change energy storage. In addition, the tensile strength of TW/PEG/TEP was nearly 4 times higher than that of DW, and its toughness was obviously enhanced. TW/PEG/TEP biocomposites conformed to the current concept of energy-saving and green development. It has the potential to replace traditional petrochemical-based materials and shows excellent application prospects in emerging fields.

Utilizing pyrolysis cleavage products from softwood kraft lignin as a substitute for phenol in phenol-formaldehyde resins for modifying different wood species

Phenol-formaldehyde resins can be used for wood modification through an impregnation process and subsequent curing within the wood cell wall. Phenol is gained from non-renewable resources, and its substitution by renewable chemicals has been a research goal. A promising example for renewable phenol substituents are lignin-derived organic chemicals. Phenol-formaldehyde resins with such substitutions have been studied, however, knowledge of their application for wood modification is deficient. While there are attempts to modify pine and beech wood with this method, studies on other wood species are scarce. Considering the increasing use of different wood species in wood industry, determining the influence of the wood species on the modification quality is an important research goal. Therefore, in this study, vacuum-pressure impregnation of five wood species – Scots pine sapwood (Pinus sylvestris), Norway spruce (Picea abies), European beech (Fagus sylvatica), Silver birch (Betula pendula), and European aspen sapwood (Populus tremula) – with phenol-formaldehyde resins is described. Here, up to 45% of the phenol in the synthetic resin is substituted by vacuum low-temperature microwave-assisted pyrolysis cleavage products from commercial softwood kraft lignin. The solution uptake, weight% gain, leaching, and anti-swelling efficiency of the modified wood are analyzed and compared. The results indicate that up to 30% of the phenol can be substituted without significant decreases in the performance of the modification. The method gives comparable results for most of the wood species described herein, with exception of beech wood, for which the modification had a lower quality. The results could help to develop more environmentally friendly wood modification methods for several common European wood species.

Performance of demountable solder joints for no-insulation superconducting coils produced by vacuum pressure impregnation

No-insulation high temperature superconductor (HTS) stack coils show both increased thermal and electrical stability, and present a simplified geometry for the integration of demountable joints. Demountability is a desirable feature for many superconducting applications including fusion magnets, which motivate this research. In this work, a novel vacuum pressure impregnation (VPI) solder process was developed to couple superconducting paths via a low resistance, mechanically simply, demountable joint for a non-insulated coil design. The three low temperature solders considered were (mp = 118 C), (mp = 156.6 C), and (mp = 29.8 C), all with a lower melting point than the (mp = 183 C) used to solder the HTS tapes into the coil, thus allowing for the advantages of solder in the joint, yet facilitating demountability without disturbing the primary solder in the non-insulated coil stack. A multidisciplinary campaign was undertaken to design, build, test and identify the major challenges with these small-scale demountable solder joints. A multi probe voltage tap system was used to infer the effective resistances to exit a superconducting stack, cross the solder layer, and enter the second superconducting stack, at 77 K. The experimental resistivities show good agreement with a newly developed finite element model that breaks down domains to the level of individual layers of an HTS tape. When taking into account the thermal degradation that can occur to the HTS stacks during the VPI processes, the normalized joint resistances are found to be 528, 668, and 671 for the , and solders, respectively. The benchmarked finite element model is used to predict normalized joint resistivities for fusion-relevant temperatures and magnetic fields using a 100 µm solder layer thickness, finding 38, 125, and 103 for the respective solders; these results are competitive with the lowest resistance cable joints presented in the literature.

Densification of SiCf/mullite composite via vacuum pressure impregnation process towards excellent mechanical and microwave absorbing performance

A simple and low-cost method for preparing SiCf/mullite composites with high density, mechanical, and absorbing performance using a vacuum pressure impregnation (VPI) system has been developed. The densification mechanism of the mullite matrix was investigated, and the effects of impregnation pressures on the flexural strength, interfacial bonding strength, and the electromagnetic wave (EMW) absorbing performance of SiCf/mullite composites were also studied. The dense composite was prepared under 3 MPa pressure with a porosity of 6.23 % and median pore diameters (MPDs) of 13.02 nm. The preparation efficiency was improved with the impregnation circles decreased from 20 times to 13 times. The flexural strength of SiCf/mullite composites prepared by VPI is 297 MPa, which is improved 230 % of the one prepared by the traditional vacuum impregnation method. Benefiting from the synergistic effects of appropriate impedance matching and multiple polarization loss, the effective absorption bandwidth (EAB, RL < −10 dB) of the SiCf/mullite composites increases from 2.17 GHz to 2.80 GHz in the X band.This work has a positive application value for the manufacture of high-strength EMW absorbing composites in terms of significantly reducing the preparation cost and cycle duration.

Silver Nanoparticles and Chitosan Oligomers Composites as Poplar Wood Protective Treatments against Wood-Decay Fungi and Termites

This study focuses on Populus ×euramericana (Dode) Guinier, a globally distributed fast-growing tree. Despite its valuable wood, it exhibits low durability. The aim of this study was to assess the efficacy of a binary composite comprising silver nanoparticles (AgNPs) and chitosan oligomers (COS) in protecting P. ×euramericana ‘I-214’ wood against degradation caused by xylophagous fungi and termites through vacuum-pressure impregnation. The test material was carefully selected and conditioned following the guidelines of EN 350:2016, and impregnation was carried out in accordance with EN 113-1:2021. Five concentrations of AgNPs–COS composites were utilized. Biodeterioration resistance was evaluated based on EN 350:2016 for white (Trametes versicolor (L.) Lloyd) and brown (Coniophora puteana (Schumach.) P.Karst.) rot fungi, and EN 117:2012 for subterranean termites (Reticulitermis grassei Clément). The durability class and use class were assigned following EN 350:2016 and EN 335:2013, respectively. In comparison to the untreated control, the binary solution at its highest concentration (AgNPs 4 ppm + COS 20 g·L−1) demonstrated a notable reduction in weight loss, decreasing from 41.96 ± 4.49% to 30.15 ± 3.08% for white-rot fungi and from 41.93 ± 4.33% to 27.22 ± 0.66% for brown rot fungi. Furthermore, the observed termite infestation shifted from “heavy” to “attempted attack”, resulting in a decrease in the survival rate from 53.98 ± 10.40% to 26.62 ± 8.63%. Consequently, the durability classification of P. ×euramericana I-214 witnessed an enhancement from “Not durable” to “Slightly” and “Moderately durable” concerning decay fungi and termites, respectively. These findings expand the potential applications of this wood and substantiate the advantages of employing this environmentally friendly treatment.

The Effect of Joint Thickness on Intermetallic Growth in the In52Sn48(Liquid)/Cu(Solid) Diffusion Couple

Intermetallic growth can simultaneously enable low-resistance electrical pathways and determine the lifetime of a solder joint. Motivating this work is a demountable linear bilateral solder joint application, enabled via a vacuum pressure impregnation process. The effect of the initial solder joint thickness δj=25-125\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta _j = 25 - 125$$\\end{document}μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu $$\\end{document}m on intermetallic growth in this configuration is investigated for the In52Sn48\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{In}_{52}\ ext{Sn}_{48}$$\\end{document}(liquid)/Cu(solid) diffusion couple for temperatures T = 393, 413 and 433 K, in the range just above the In52Sn48\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{In}_{52}\ ext{Sn}_{48}$$\\end{document} melting temperature of 391 K. It was found that beyond a critical time ∼1-15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1-15$$\\end{document} min into the kinetic reaction, thicker solder joints had more intermetallic growth. There are two intermetallic phases identified in this temperature range: Cu6(In,Sn)5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{Cu}_{6}\ ext{(In,Sn)}{_5}$$\\end{document} closer to the Cu substrate, and Cu(In,Sn)2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{Cu(In,Sn)}_{2}$$\\end{document} closer to the solder bulk. The intermetallic growth fits give temporal growth exponents between n=0.25-0.29\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n = 0.25 - 0.29$$\\end{document}, indicating that grain boundary diffusion rather than volume diffusion is the predominant growth mechanism. Growth in thicker joints is associated with higher temporal growth exponents; this is attributed to suppressed grain coarsening, as there is Cu dissolution from the intermetallic into the solder bulk in the early stages of the reaction, in more highly unsaturated environments. In addition, there is on average a decrease in the intermetallic phase activation energy with increasing joint thickness. In combination with the literature, the results suggest the linear bilateral joint geometry has a growth constraining effect, and the liquid solder phase state strongly affects the morphology and coarsening of grains, leading to the intermetallic growth trends observed.

Research on the Impregnation Process and Mechanism of Silica Sol/Phenolic Resin Modified Poplar Wood

Phenolic resin-modified materials partially reduce the toughness of the wood. In this study, organic–inorganic composite modifiers were used to modify the wood. Silica sol/phenolic resin was prepared through in-situ polymerization, and poplar wood was modified using a vacuum pressure impregnation process, enhancing its toughness. Orthogonal experiments were conducted, and the impact toughness of the modified poplar wood was used as the evaluation index. Through orthogonal experiments, using the impact toughness of modified poplar as the evaluation indicator, it was found that when the average particle size of the silica sol is 8–15 nm, the pressure is 1.2 MPa, and the pressurization time is 3 h, the impregnation-modified poplar’s impact toughness reaches its optimum, improving by 84.1% and 135.4% compared to the raw material and phenolic resin impregnated wood, respectively. The Fourier Transform Infrared Spectroscopy (FT-IR) results indicated that the characteristic absorption peak of Si-O-Si appears in the poplar wood after impregnation, confirming the formation of new silicon-oxygen (Si-O) chemical bonds. X-ray Photoelectron Spectroscopy (XPS) analysis revealed that a chemical reaction occurs between the impregnation liquid and the wood, generating Si-O-C. Subsequently, through Dynamic Mechanical Analysis (DMA) and Thermogravimetric (TGA) analysis, it was understood that this chemical reaction significantly enhances the thermal stability and toughness of the impregnated material, making it superior to the original poplar material. The TGA further unveiled that, compared to untreated poplar, the thermal stability of the impregnated material has been notably improved. Lastly, Scanning Electron Microscopy (SEM) analysis demonstrated that the composite impregnation liquid successfully permeates and fills the interior of the poplar cells.

Flame-retardant smoke-suppressing and antibacterial poplar wood enabled by a bio-based flame retardant containing transition metal

Utilizing bio-based flame retardants like chitosan (CS) and tannic acid (TA) is an effective way to enhance the flame retardancy of wooden products. In this work, the poplar wood was impregnated with composite flame retardants containing CS, TA, Cu (CH3COO)2·H2O and silane coupling agent (KH550). When KH550 bound these substances together to form a stable compound, a highly efficient flame-retardant wood (wood/CTA-Cu-Si) was prepared under vacuum pressure impregnation. The results of the functional group test show that bio-based flame retardants have been successfully synthesized. The limiting oxygen index (LOI) of the treated sample was reached 31.5%, the sample also passed the V-0 grade in the UL-94 vertical burning test, and in the Cone colorimeter test, the total smoke release was reduced by 50.2% compared to that of the Control. The energy dispersive spectroscopy proved that Cu and Si elements were evenly distributed in the wood before and after combustion. Raman spectra of the residues after the burning of treated wood were compared and it was found that the degree of graphitization of wood/CTA-Cu-Si was significantly increased, which ID/IG reached 1.85. After impregnation, the flame-retardant treated wood sample exhibited no negative effect on mechanical properties. The flame-retardant mechanism was probed and summarized as the Cu and Si synergistic promotion on charring and suppression on heat and smoke release. Simultaneously, the existences of Si-C, Si-O and Si-N strengthened the char layer and enhanced flame retardancy of poplar wood. Such resulted poplar wood with flame retardancy will be an excellent application prospect as engineering biomaterial.

Numerical Simulation and Experimental Validation of Internal Heating in Vacuum Pressure Impregnation Process for High Field Coil

An experimental system has been built to explore the vacuum pressure impregnation (VPI) technique and internal heating method. The mold with coil and support part is put into the vacuum tank and a novel type of epoxy resin IR-3 is applied for impregnation. The heat transfer models is built to simulate the heating process and calculate the radiation heat leakage and heating power. A shield is made to reduce the radiation heat leakage and two preliminary experiments without impregnation are carried out to verify the thermal insulation effect of the radiation shield. An experiment with impregnation and shield is carried out to identity the temperature rise, the magnitude of current and heating power applied to the coil. The numerical and experimental results showed that the radiation heat leakage is the main way of heat loss during curing process, and the shield can reduce radiation heat leakage effectively, thereby heating power consumption is reduced, meanwhile the coil and resin could not reach the setting temperature when shield is absent. The results obtained in this paper will helpful to manufacture of superconducting coils using VPI technique and internal heating method.

Investigation of winding cooling enhancement and thermal modelling of large‐power high‐torque‐density direct‐drive PMSM

AbstractLarge‐power high‐torque‐density direct‐drive permanent magnet synchronous motors (LHDPMSM) are more and more frequently used to drive ball mills, belt conveyors, scraper conveyors, etc. Aiming at the characteristics of large copper loss and high winding temperature rise of the LHDPMSM, an effective winding cooling enhancement technology based on winding overall potting (WOP) is presented. The manufacturing process and cooling principle of WOP is described in detail and compared with the traditional vacuum pressure impregnation (VPI). In order to solve the problem of complex modelling process and long calculation time of LHDPMSM thermal field caused by large volume and asymmetric fluid cooling structure, the lumped parameter thermal network (LPTN) considering both fluid cooling and winding potting is proposed. Then, the cooling capacity of WOP and VPI are compared by LPTN, and the influence of some major cooling system parameters on LHDPMSM temperature rise are also researched. Finally, in order to verify the correctness of the theoretical calculation results, two 450 kW LHDPMSM prototypes adopt WOP and VPI are manufactured, tested and compared. The theoretical and experimental results are highly consistent, which proves the effectiveness of WOP in winding cooling enhancement of LHDPMSM.