Moisture Absorption Rate Research Articles

Effect of P/Al ratio on an acid aluminum phosphate solution: Thermal evolution and hygroscopic behavior

Hygroscopicity is an obstacle to the widespread use of aluminum phosphate binders, but there is still a lack of relevant fundamental research on this topic. Here, the curing behavior, thermal evolution, phase development and hygroscopic behavior of acid aluminum phosphate (AAP) solutions with different P/Al ratios (2.50–4.00) have been systematically investigated. We comprehensively elucidate for the first time the hygroscopic mechanism of AAP and its derived aluminum phosphate, and establish a dynamic relationship between hygroscopic mechanism, moisture absorption rate, microstructure and phase composition. AAP and its derived aluminum phosphate, namely Al(H2PO4)3, AlH2P3O10, residual H3PO4, [HPO3]n and hydroxyl groups are all hygroscopic. The hygroscopic properties of AAP depend on the phase composition, which is determined by the P/Al ratio and the calcination temperature. Due to the formation of Berlinite and Al8H12(P2O7)9, the reduced formation of AlH2P3O10 and the absence of H3PO4, [HPO3]n and hydroxyl groups, the AAP solution with a P/Al< 3.00 and its derived aluminum phosphate exhibit relatively lower hygroscopicity. Meanwhile, increasing the calcination temperature can also improve the hygroscopicity resistance characteristics. This work complements the basic knowledge of AAP systems, especially those with a P/Al< 3.00. This sets the stage for the fabrication of aluminum phosphate binders and aluminum phosphate-based composites with excellent hygroscopicity resistance properties.

Hydrothermal Effect on Ramie-Fiber-Reinforced Polymer Composite Plates: Water Uptake and Mechanical Properties.

Ramie-fiber-reinforced polymer composites (RFRP) have the advantages of low price and low energy consumption, but they have high hydrophilicity due to their special chemical composition. In order to study the effect of water absorption on the performance degradation of RFRP in a hydrothermal environment, the authors prepared RFRP sheets by compression molding. Manufactured composites were exposed to a hydrothermal environment with a temperature of 40 °C and a humidity of 50% RH, 85% RH and 98% RH to study the water absorption and diffusion, mechanical properties (tensile properties, flexural properties and shear properties) of the RFRP, and their mechanical properties after drying. The research shows that the equilibrium moisture absorption rate of RFRP is mainly affected by the ambient humidity. The moisture absorption and diffusion of ramie-fiber-reinforced polymer composites (RFRP) in a hydrothermal environment conform to Fick's law. Before reaching the moisture absorption equilibrium (1~2 weeks), the mechanical properties decline rapidly, and then tend to be flat, and the mechanical properties of the RFRP decrease significantly with the increase in humidity; the water molecules reduce the interfacial bonding performance and the modulus degradation degree of RFRP in the hydrothermal environment is greater than that of strength. After the samples were completely dried, the mechanical properties of the RFRP rebounded greatly, but less than the initial value, and the hydrothermal environment produced irreversible changes to the substrates.

Preparation and characterization of sisal fibre reinforced sodium alginate gum composites for non-structural engineering applications

Abstract In this work, untreated/treated sisal fibre (SF)-reinforced sodium alginate composites for three different concentrations (1.5%, 2%, and 2.5%) are fabricated by the hand lay-up method, and the variations in mechanical properties such as tensile strength, flexural strength, and impact strength are studied. The treated and untreated composites are analysed and compared using scanning electron microscope to study the surface morphology. Energy-dispersive spectroscopic analysis is carried out to evaluate the elemental compositions. Fourier transform infrared spectroscopic analysis is conducted to determine the interaction between fibres and matrix material. The thermal observations such as differential scanning calorimetry and thermogravimetric analysis showed only slight variations between the untreated and treated SF composites. The results of this work indicate that untreated sample with the maximum sodium alginate gum concentration had significantly enhanced mechanical properties and low moisture absorption rate. Biodegradation test inferred that it was superior for the treated fibre rather than the untreated fibre composites. The primary objective of this work is to assess the suitability of these composites for non-structural engineering applications.

Study onThe Moisture Absorption Properties of jute Fiber Reinforced Composites

Fiber-reinforced composites (FRP) have gradually become an important direction for the development of new materials due to their various excellent properties since their development. However, traditional glass fibers, carbon fibers, basalt fibers, etc. have various problems such as cost and environmental pollution, in contrast to natural crop fibers which are low-priced, widely available and environmentally friendly. In order to verify the service characteristics of jute fiber, one of the representatives of natural fibers, in complex environments, jute fiber reinforced composite laminates were prepared using Vacuum Assisted Resin Infusion (VARI) process, and the moisture absorption properties of the laminates were investigated and the influence law and mechanism of four temperatures and two fiber plies on the water absorption and diffusion properties of the laminates were analyzed. The results show that: the moisture absorption process of the laminate conforms to Fick’s second law, but the applicability of Fick’s second law decreases as the temperature increases; the moisture absorption rate of the laminate increases exponentially as the temperature increases, but the saturation rate decreases, and the corrosion rate of the laminate increases; the increase in the number of plies of the laminate affects the increase in the time to reach the saturation rate of the laminate, and the diffusion coefficient increases; the service performance of 6-layer laminate is better in the same hygrothermal environment.

Developing multifunctional and environmental-friendly hot-pressed peanut meal protein adhesive based on peanut waste

Hot-pressed peanut meal protein (HPMP) adhesives showed great potential as an alternative to formaldehyde-based adhesives because of their renewability and environmental-friendly, but their practical applications are severely limited by the poor bonding strength, water resistance and anti-mildew properties. Inspired by the spider leg structure, the functional graded peanut shell fiber (Ag/ZnO@APSF) loaded with metal nanoparticles was constructed through the biomineralization strategy as mineralized skeleton; Luteolin Epoxide (LE) as crosslinking agent. We had developed a green strategy for fabricating a novel HPMP adhesive with strong water resistance, high bonding strength, and strong mold resistance was prepared through a steel bars-concrete network structure using peanut waste, Ag/ZnO@APSF and LE. Compared with pure HPMP adhesive, the dry shear strength and wet shear strength of adhesive increased by 114% (2.29 MPa) and 257.9% (1.36 MPa), respectively. The residual rate increased by 43.8%, the moisture absorption rate and viscosity decreased by 48% and 45.4%, respectively. The adhesive had excellent flame retardancy with a reduction of 35.2% in peak heat release rate and 28.4% in total heat release rate, respectively. The antimildew time increased from 1 d to more than 45 d. In addition, the HPMP adhesive exhibited long-term adhesion behavior (pot life of 14 d), the pre-pressing bonding strength increased by 175.7% (1.02 MPa). This strategy had enhanced the added value of peanut waste and contributed to the development of multifunctional new plant protein adhesives.

Anisotropic and high-strength SiO2/cellulose nanofiber composite aerogel with thermal superinsulation and superhydrophobicity

SiO2 aerogel is a promising lightweight and high-efficiency thermal insulation material for applications in construction, industrial, aerospace vehicles, etc., but weak mechanical properties limit its further development and application. In order to overcome this challenge, we combined the design concepts of elastic group's introduction and structural strengthening of cellulose nanofibers with a directed freezing process, and successfully realized an anisotropic and high-strength SiO2/cellulose nanofiber composite aerogel. Under the low density of 0.247 g/cm3, the maximum compression strength of the aerogel in the radial direction is as high as 18.08 MPa, corresponding to a high fracture strain of 75.67%, and it also exhibits an excellent fatigue resistance, with only a slight plastic deformation of 6.5% after 100 load-unload cycles at a high compression strain of 50%. In addition, the aerogel exhibits an ultra-low thermal conductivity (0.01714W/(m·K)) in the radial direction, and also has a superhydrophobicity (water contact angle 150.8°) and a long-term hydrophobic stability (saturated mass moisture absorption rate 0.44%). The combination of these properties makes it an ideal material for thermal superinsulation in environments where both integrated mechanical properties and hydrophobic properties are critical.

Hygroscopic properties of whey protein hydrolysates and their effects on water retention in pork patties during repeated freeze–thaw cycles

The hygroscopic properties, water migration properties and micromorphology of native whey protein (NWP) and whey protein hydrolysate (WPH) under different relative humidity (RH) conditions were assessed in this study. Moreover, their effects on water retention in pork patties during freeze–thaw (F–T) cycles were assessed. The results showed that the moisture absorption rate of WPH was 7.45 percentage units higher than that of NWP after the moisture content balance. When the RH reached 97.0%, the equilibrium moisture content of WPH was 1.81 times that of NWP. Combined with low-field nuclear magnetic resonance and microstructure results, WPH exhibited the strongest moisture absorption and moisturising abilities and was more suitable for addition to meat systems. Furthermore, the addition of WPH effectively improved water retention in pork patties during F–T cycles. After seven F–T cycles, the addition of 15% WPH effectively inhibited myofibrillar protein degradation and microstructural damage, reduced the relative content of α-helix and the water holding capacity loss of pork patties and enhanced proton density. These results indicate that WPH has the potential to be used as a water retention agent candidate to reduce the quality loss of meat products during F–T cycles.

Comparison of biodegradable chitosan-based composite films reinforced by different micron-sized plant fibers for food packaging

To provide a fully degradable food packaging film with excellent performance, a chitosan (CS)-based film containing micron-sized plant fibers was prepared by the casting method. With the addition of different plant fibers—wheat straw fiber (WF), maize straw fiber (MF), rice straw fiber (RF), and sisal fiber (SF), a significant improvement in mechanical, water resistance, water vapor barrier, and thermal properties was observed. By comparison, the most significant enhancement effect was observed in CS/SF-based film. The tensile strength and elongation at break of this film were 58.44 MPa and 14.42%, respectively. Moreover, it exhibited excellent properties such as the highest water contact angle (118°), a moisture absorption rate of 5.14%, a low water vapor transmission rate (110.73 g·m-2·d-1), and high thermal stability. Considering the sustainability and attractive physical properties, the improved films showed great potential for food packaging.

Long-term ageing effect on mechanical properties of polyamide 12 printed by Multi-Jet-Fusion

Multi-Jet-Fusion (MJF) is a relatively new powder-based face-sintering additive manufacturing technique that exhibits great potential in high-volume manufacturing due to its rapid printing speed. Extensive research has been conducted on the mechanical properties of MJF-printed polyamide 12 (MJF PA12) by investigating the powder characteristics and build orientations. However, no work has been conducted to study the effect of humidity and physical ageing on the mechanical performance of MJF PA12 specimens. Here, the physical and mechanical properties of MJF PA12 specimens that were printed in different build orientations and stored under ambient and dryer conditions for 474 days were investigated. It was found that specimens stored under ambient conditions exhibited a drop in glass transition temperature due to moisture absorption followed by an increase, which could indicate that ageing of the specimens occurred. The moisture absorption was also found to have an insignificant effect on the crystallinity and crystallite size of the specimens. The change in mechanical properties, such as the tensile modulus and ultimate tensile strength, was more significant for specimens stored in ambient conditions than those in dryer conditions. It was also found that the build orientation does not have a significant impact on the moisture absorption rate, glass transition temperature, and the change in the trend of mechanical properties. In addition, an artificial neural network was adopted to predict the mechanical properties of the MJF PA12 specimens under the influence of physical ageing, humidity, and build orientations. The neural network adopted in this work can predict the change in the mechanical properties of differently-orientated MJF PA12 with different moisture content over time. The neural network prediction could be useful in providing guidance on the structure and risk assessment of the parts before print.

새싹귀리 분말을 첨가한 생면 파스타의 품질 특성

This study examined the quality characteristics and consumer acceptance of fresh pasta made with various additions of oat sprout powder. Fresh pasta noodle samples were prepared with varying amounts of oat sprout powder added to fresh pasta, ranging from CON (0%), SP2 (2%), SP4 (4%), SP6 (6%), SP8 (8%) and SP10 (10%). The analysis of moisture content, pH, color, moisture absorption rate, texture profiles and sensory evaluations were conducted. The study found that as the percentage of oat sprout powder in fresh pasta increased, the moisture content of raw noodles increased, while that of cooked noodles decreased, and pH also decreased. Hunter L and b values decreased with increasing oat sprout powder, while moisture absorption rate increased. Texture profile analysis showed that the hardness, adhesiveness, springiness, gumminess, and chewiness of raw pasta noodles decreased significantly, but the cooked noodles increased significantly. In the sensory attribute difference test, dark color and green received the highest score in SP10, and oat sprout odor received the highest score, but egg and flour odor received the lowest score. The bitterness and oat sprout taste increased with increasing oat sprout content, but the savory taste showed no significant difference. SP6 had the highest overall acceptance score in consumer acceptance tests. Based on this research, it is expected to be used as meaningful basic data for more diverse studies on the functionality of oat sprout powder in the future.

Highly Deformable High-Strength SiO2 Aerogel Designed with an Alternating Structure of Hard Cores and Flexible Chains for Thermal Insulation.

Thermally insulating aerogels can now be prepared from ceramics, polymers, carbon, and metals and composites between them. However, it is still a great challenge to make aerogels with high strength and excellent deformability. We propose a design concept of hard cores and flexible chains that alternately construct the aerogel skeleton structure. The approach gives the designed SiO2 aerogel excellent compressive (fracture strain 83.32%), tensile. and shear deformabilities, corresponding to maximum strengths of 22.15, 1.18, and 1.45 MPa, respectively. Also, the SiO2 aerogel can stably perform 100 load-unload cycles at a 70% large compression strain, demonstrating an excellent resilient compressibility. In addition, the low density of 0.226 g/cm3, the high porosity of 88.7%, and the average pore size of 45.36 nm effectively inhibit heat conduction and heat convection, giving the SiO2 aerogel outstanding thermal insulation properties [0.02845 W/(m·K) at 25 °C and 0.04895 W/(m·K) at 300 °C], and the large number of hydrophobic groups itself also gives it excellent hydrophobicity and hydrophobic stability (hydrophobic angle of 158.4° and saturated mass moisture absorption rate of about 0.327%). The successful practice of this concept has provided different insights into the preparation of high-strength aerogels with high deformability.

Bio-inspired hydrophobic copper stearate coating to reduce the moisture absorption of fine-grained ammonium perchlorate and improve safety and thermal decomposition performance

Inspired by the superhydrophobic phenomenon in nature, multifunctional fine-grained ammonium perchlorate (F-AP)@copper stearate (CS) core-shell structure composite particles were designed by the in-situ liquid deposition method. Scanning electron microscopy (SEM) characterization proved that raw AP was refined, and a series of in-depth characterizations proved that the core-shell structure of F-AP@CS was prepared. Due to the core-shell F-AP@CS bionic hydrophobic structure and low surface energy, when the CS content is 5%, the moisture absorption rate was reduced from 0.54% to 0.03% within 72 h, and the water contact angle was increased to 126.6°. At room temperature, the safety performance of F-AP is effectively improved because of the barrier effect and melting heat absorption of the CS shell, the impact sensitivity (H50) of F-AP@CS (wt = 5%) was increased from 27.2 cm to 54.2 cm, and the friction sensitivity was reduced from 96% to 0%. As the temperature rises, CS will decompose into CuO with extremely high catalytic activity at 267 °C, the high temperature decomposition peak of F-AP@CS (wt = 5%) was advanced from 423.3 °C to about 305.9 °C, and speculate the mechanism of CS catalyzing the decomposition of AP.

Mechanical and Barrier Properties of Cellulosic Nano-Fibers Reinforced Bionanocomposite

Cellulose is one of the most frequently used and generally available materials on Earth and has been utilized for ages in a variety of applications. Numerous researchers have investigated various lignocellulosic sources for the extraction of cellulose and the author has introduced a new source for the extraction of cellulose and cellulosic nanofibers: fruits or seedpods of Delonix Regia (CNF). The solvent casting process is used to create the PVA/CNF composite after the cellulose and CNF have been removed using a mechano-chemical method. SEM, tensile testing, soil burial testing and moisture absorption tests have all been used to examine the morphological, mechanical, biodegradable and moisture absorption capabilities of pure PVA and PVA/CNF composite with 1, 3, 5, 7 and 9 percentages of CNF. According to SEM findings, agglomeration was seen at higher concentrations but uniform and homogenous distribution of nano-fillers was seen at lower percentages of CNF. It is profusely clear from the results of the tensile tests that the percentage elongation initially decreased and then began to increase at higher concentration, while the Young’s modulus and tensile strength initially increased at lower percentages of CNF rapidly and gradually decreased for higher concentration. Pure PVA had the least resistance to degradation in biodegradability test, while the biodegradability test showed that the inclusion of CNF decreased the composite material’s ability to degrade. With the addition of CNF, the rate of moisture absorption decreased, resulting in a PVA/CNF composite material that will last longer and perform better without material degradation.

Hydrothermal aging of carbon fiber reinforced epoxy composites with different interface structures

Four carbon fiber reinforced epoxy resin composites (CFRPs), CF/EP, CF-COOH-EP, CF-COOH/MXene/EP and CF-CONH-MXene-EP, were prepared and subjected to hydrothermal aging experiments at 55 °C. The changes in structure and mechanical property of these CFRPs, having different interface, before and after the aging were investigated to explore the influence of interface structure on hydrothermal aging of CFRPs. CF-COOH-EP has the highest moisture absorption because of a large number of hydrophilic groups in the interface. The Mxene nanosheets help reduce the moisture absorption rate and equilibrium moisture absorption of CFRPs CF-COOH/MXene/EP and CF-CONH-MXene-EP is similar to that of CF/EP. The aging results in decreases of storage modulus and temperature at maximum tan δ, but the different interface structures show little influence on them. The inter-laminar shear strength (ILSS) presents a fast decline in the early aging and a gradual decrease at the following stage. The interface structure has an influence on the hydrothermal aging of the CFRPs and results in different ILSS changes. Among the four CFRPs, CF-COOH-EP presents the fastest hydrothermal aging corresponding the lowest ILSS retention rate and CF-CONH-MXene-EP keeps the highest ILSS after aging exhibiting the highest reliability.

Performance of clinoptilolite zeolite after milling as a pretreatment on hydration kinetics, shrinkage, and alkali-silica reaction of cementitious materials

Natural clinoptilolite zeolite has been a popular supplementary cementitious material (SCM) due to its acceptable pozzolanic performance and the overall lower environmental footprint. Previous research established that milling is an effective pretreatment technique to further increase the pozzolanic reactivity of zeolitic tuffs leading to an increased specific surface area and amorphous contents. Therefore, the present study characterized the zeolite particles after ball milling for 1 and 3 h using phase analysis by X-ray diffraction (XRD), particle size distribution by laser diffraction, microstructural analysis by scanning electron microscopy (SEM), moisture absorption rate, and relative chemical dissolution. The performance of milled clinoptilolite zeolite as a SCM with the replacement of up to 20% portland cement was evaluated through hydration kinetics (heat of hydration, setting time, chemical shrinkage, degree of hydration), workability, compressive strength, autogenous shrinkage, drying shrinkage, and alkali-silica reaction (ASR). Results revealed that 1 and 3 h of milling led to an increased specific surface area, moisture absorption capacity, and relative dissolution of particles, but had no visible effects on the crystalline structure of zeolite particles compared to the unmilled zeolite particles. For the hydrated system, both 1 and 3-h milled zeolite increased the overall heat of hydration leading to an increased silicate and aluminate reaction along with the acceleration effects in the setting time. The compressive strength of up to 20% milled (1 and 3 h) zeolite samples was increased by about 20 to 25% compared to the unmilled zeolite samples at an early age which suggested an increasing pozzolanic response of milled zeolite particles in the system due to an increased volume of hydrated phases and degree of hydration. Milling slightly decreased the workability by demanding a higher content of fresh water which was released at a later age leading to a higher drying and autogenous shrinkage. In addition, milling reduced the internal curing capacity leading to damage to the porous structure of zeolite particles. The use of up to 20% 3-h milled zeolite reduced the deleterious expansion by about 80% due to ASR compared to the control sample and the overall performance of milled clinoptilolite zeolite as the SCM was satisfactory in the hydrated system.

Study on hygroscopic mechanism and atomic‐scale hygroscopic pathways of polyurethane foams

AbstractMoisture absorption of polyurethane foams (PUFs) lead to its plasticization and swelling deformation, which can affect its precise installation in precision instruments for engineering applications. In addition, changes in mechanical properties after moisture absorption can affect its safety in service in some vibration damping applications. Herein, a series of foams with different compositions were prepared, and the factors influencing the hygroscopicity of polyurethane foams and the mechanism of hygroscopicity were investigated by combining experimental and theoretical simulations to provide data support for the preparation conditions and molecular structure design of foams in this context. The experimental results showed that the adsorption kinetics of the foams were in accordance with FICK's law, and the mechanical properties of the foams were slightly reduced by moisture absorption, Hydrophobically modified PU‐5 has the lowest moisture absorption rate (0.616%) and dimensional change rate (0.118%), but its compressive strength is poor, only 10.548 MPa; PU‐6 with fluorosurfactant has the least reduction in compressive strength after moisture absorption (1.63%), its moisture absorption rate and dimensional change rate are 0.738% and 0.168%, respectively; while PU‐4 with ammonia ether crosslinker has the largest compressive strength with moisture absorption rate and dimensional change rate of 0.818% and 0.150%, respectively, and the compressive strength decreases by 4.6% after moisture absorption. Considering that the application context requires that the changes in dimensional and mechanical properties after moisture absorption are more important, so PU‐4 is the best system. In addition, As the temperature and humidity rise, the moisture absorption increases significantly, when the temperature rises from 25°C to 45°C, the moisture absorption rate is three times the original, when the humidity rises from 40% to 80%, the moisture absorption rate has the same change. More importantly, the moisture absorption mechanism and moisture absorption pathway at the atomic scale were revealed by two‐dimensional infrared (2D IR) and low‐field NMR, and the experimental results were verified by molecular dynamics simulations, and the simulations and experimental results were found to be consistent. It can be seen from low‐field NMR and 2D IR that the foam contains four states of water in the initial stage and the largest proportion is bound water, NH is the most moisture‐sensitive group in the hygroscopic process, OH is the main reason for the increase of bound water, and bound water absorbs moisture earlier than free water. Kinetic simulation shows that hygroscopicity of PUF was primarily attributed to hydrogen bonds between oxygen atoms and water molecules, at the beginning state of moisture absorption the velocity of water accumulation inside of porous PU block is larger than that in the surface of porous PU block. Basing in the detailed hygroscopic data was presented as well as a reliable and conclusive analysis of polyurethane foam, This work screened the optimal foam system with low moisture adsorption and good mechanical properties and elucidated the moisture absorption mechanism of the foam at the molecular scale, providing data to support the selection of foams in the context of precision instrument installation and vibration‐damping applications.

Effects of Hygrothermal and Salt Mist Ageing on the Properties of Epoxy Resins and Their Composites.

Epoxy and epoxide composites have a wide range of outdoor applications wherein they are affected by ageing. In this study, epoxy casting plates and epoxy-based composite rods for use in overhead conductors were prepared. A concurrent investigation concerning the ageing of epoxy resins and their carbon fibre composites was carried out via artificially accelerated experiments under hygrothermal and salt mist conditions. The moisture penetration along the depth, water absorption, appearance, hardness, density of the epoxy resins, and variation patterns of the impact strength and tensile strength of the epoxy-based composites were investigated. The ageing mechanisms were explored using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Both ageing modes had essentially similar influences on the properties of the resins and their composites; moreover, they did not significantly affect the chemical structure and microstructure of the epoxy resin, with the physical adsorption of water primarily observed during the ageing process. The moisture absorption behaviour of the epoxy obeyed Fick's law. Although the water penetration rate in the salt mist ageing mode was slightly higher than that in the hygrothermal ageing mode during the early ageing stage, it was essentially the same during the later stage. The final moisture absorption rate at saturation was approximately 1.1% under both modes. The flexural strengths and impact strengths of the composites in both ageing modes followed a similar trend. They decreased gradually with the ageing time and then stabilized at almost the same value. The flexural strength was reduced from 803 MPa to 760 MPa and the impact strength from 383 J/m2 to 310 J/m2, indicating a decrease of approximately 5.4% and 19%, respectively. The absorbed water during the ageing process caused micro-cracks at the interface between the fibres and resin, weakening the interfacial strength and reducing the mechanical properties of the composites.

Study on the aging properties of 3D woven composites under corrosive conditions

Different aging conditions have an important influence on the performance of carbon fiber composites. In this study, the properties of three-dimensional woven carbon fiber reinforced resin matrix composites were investigated and analyzed in three different aging environments (distilled water immersion, 30% H2SO4 solution immersion, and 10% NaOH solution immersion) at 60°C. Mass change, moisture absorption change, Fourier transform infrared spectra (FTIR), surface morphology before and after aging, glass transition temperature (Tg), compression properties, bending properties, and interlayer shear properties were analyzed. The results showed that the immersion in 10% NaOH solution made the specimens destroyed and the aging process was chemically changed. Distilled water immersion and 30% H2SO4 solution immersion moisture absorption rate to meet the FICK law, the aging process only physical changes. The surface of the composite specimens under the three aging conditions produced different degrees of cracks and different degrees of debonding at the interface between the fibers and the resin matrix. The Tg, flexural properties, interlaminar shear properties, and compressive properties of the aged specimens all showed different degrees of degradation.

Reversible sacrificial hydrogen bonds enhanced ultra-high strength polybenzoxazine aerogel for thermal insulation

Aerogels are a very attractive class of lightweight and high-efficient thermal insulators, but poor mechanical properties have always been the main obstacle restricting their development and application. In order to overcome this problem, we innovatively used the concept of reversible sacrificial hydrogen bondings strengthening, and successfully synthesized a polybenzoxazine aerogel with outstanding mechanical properties and a lightweight structure. The aerogel (density 0.231 g/cm3 and porosity 90.7 %) exhibits a high compression strength of 14.36 MPa with a suitable deformation capacity of 19.6 % fracture strain, and also shows a relatively good fatigue resistance. In addition, the aerogel has outstanding thermal insulation properties [0.03012 W/(m·K) at 25℃ and 0.03486 W/(m·K) at 150℃] and hydrophobic properties (hydrophobic angle 148.7° and saturated mass moisture absorption rate about 0.63 %), thus it has great prospects for a high-efficiency thermal insulator used in buildings, industries, aerospace vehicles, etc.

Effect of tannin on the bonding performance and mildew resistance of soybean meal-based adhesive

For improving the water resistance, bonding performance, and anti-mildew property of the soy protein-based adhesive (SPA), in this research, based on cross-linking enhancement theory, soybean meal flour as the main raw material, self-synthesizing triglycidylamine (TGA), and larch tannin (LT) were used to build efficient crosslinking water-resistant structure and develop SPA. The effect of LT addition on the physical properties, bonding strength, and anti-mildew property of the resultant adhesive was investigated. The results showed that the residual rate of SPA with 4 % LT and 3 % TGA was improved by 2.1 % and the corresponding moisture absorption rate was reduced by 20.1 % compared with the SPA only modified by 3 % TGA. In addition, the SPA with 4 % LT and 3 % TGA had a 42.3 % increase in bonding strength, reaching 1.11 MPa, which satisfied the standard requirements of interior use plywood (≥ 0.7 MPa). The improved water-resistant bonding performance is mainly because interaction forces, such as hydrogen bonds, ionic bonds, and covalent bonds, formed between tannin and protein, and under the cross-linking effect of TGA, the whole cross-linking system forms a dense network structure. LT not only had a reinforcing effect on the SPA but also could prolong the pot life of the adhesive for 60 h due to the phenolic hydroxyl groups of tannin. Compared with the commercial anti-mildew agents, the mildew resistance before and after curing is the following: 1,2-benzisothiazole in-3-one > LT > sodium tetraborate > potassium sorbate. • An easy-to-produce, high-performance, and environmentally friendly bio-adhesive was developed. • The incorporation of larch tannin enhanced the cohesion and mechanical properties of adhesives. • The resultant adhesive has better water-resistant bonding performance and an anti-mildew effect. • Effectively extend durability of plywood prepared by adhesive and storage period of the SPAs.