Curing Behavior Research Articles

Effects of curing, temperature, pressure, and moisture on the surface-figure of a high-precision bonded mirror

Adhesive bonding is widely used in the assembly of high-precision optomechanical products. However, of the curing and relaxation behaviors as well as environmentally sensitive features of adhesives, the surface-figure accuracy of bonded mirrors is often attenuated, which greatly degrades the performances of the optomechanical system. This paper developed a comprehensive finite-element model for understanding the evolution of surface figure in a high-precision bonded mirror. For the used optical adhesive, its cure kinetics was experimentally examined by differential scanning calorimetry and then modeled based on a modified Kamal kinetic model, and its mechanical behaviors were described by a viscoelastic constitutive model including temperature, moisture, and degree of cure. Additionally, time-temperature/moisture/curing superposition principles for the adhesive were experimentally determined and embedded into the constitutive model. The comprehensive finite-element model was verified and then applied to simulate the surface-figure evolution of the bonded mirror. The effects of environmental factors, such as temperature, environmental pressure, and moisture, on the surface-figure accuracy and stability were further understood.

Melamine as cross‐linking agent for mono‐cyclic benzoxazine with aldehyde groups: higher crosslinking density and thermal properties

AbstractBenzoxazine resin shows great potential as matrix for high performance composites, possessing good processabilty, dielectric property, mechanical property, and thermal properties, but its further application is limited by low crosslinking density and poor curing activity, especially for mono‐cyclic benzoxazines. In this work, melamine, a tertiary amine with a stable triazine structure, was introduced into the aldehyde‐containing mono‐cyclic benzoxazine, in order to achieve higher crosslinking density, higher curing activity, and better thermal properties. The chemical structure of prepolymers was verified by Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR) spectra, the curing behavior was investigated by differential scanning calorimetry, the thermal properties of polymers were studied by thermogravimetric analysis (TGA) and thermal mechanical analysis (TMA). It was found that the introduction of trifunctional melamine (MA) could lower curing temperature and promote the curing degree. Additionally, a proper amount of MA could increase the crosslinking density and thermal properties of the resultant polybenzoxazine. For example, poly(BZ‐3MA) showed the highest thermal stability with the temperature at 5% weight loss (Td5) of 415°C, carbon residue (Yc) of 67.7%, 23°C, and 2.9% higher than those of poly(BZ). Moreover, the glass transition temperature of poly(BZ‐5MA) reached 204.06°C, 36.51°C higher than that of poly(BZ).

Enhanced dielectric and hydrophobic behaviour of aurin based polybenzoxazine dye composites

Herein, three novel bi-functional benzoxazines were synthesized using aurin as the precursor phenol with three different aromatic amines (i.e.) aniline, fluoroaniline, and trifluoromethylaniline with paraformaldehyde through Mannich condensation. The structural confirmation was done using FTIR and proton NMR. The effects of substituents present in the amines on the curing behaviour and thermal stability were studied using DSC and TGA. The aurin based trifluoromethyl substituted benzoxazine shows better thermal stability than that of the other two benzoxazines and it was selected for the preparation of composites with varying weight percentages of graphitic carbon nitride derived from dicyandiamide (Dicy-GCN) to utilize them for high k applications. The dielectric behaviour and thermal properties of both neat polymer matrix and composites were studied and compared. The 15 wt% Dicy-GCN reinforced composite shows the highest dielectric constant value of 10.25, with a low dielectric loss value of 0.046 at 1 MHz frequency. The polybenzoxazine composites developed show better thermal stability and superhydrophobic behaviour than those of neat polybenzoxazine matrix. These properties ascertain that the aurin based bifunctional polybenzoxazines and its composites can be considered for high-performance high k applications.

Synthesis of sustainable curcumin based photo-crosslinkable benzoxazines: Thermal, hydrophobic and anti-corrosion properties

Bifunctional polybenzoxazines have been developed using sustainable bio-phenol curcumin, paraformaldehyde with varying nature of monofunctional amines through Mannich condensation. The molecular structure of synthesized benzoxazines were confirmed by ATR-FTIR, 1HNMR and 13CNMR and high-resolution mass spectroscopic (HRMS) analyses. DSC thermograms were used to ascertain the curing behaviour of curcumin-based monomers. Thermal curing of Cu-api occurs at 192 °C and that of Cu-aa undergoes dual curing at 177 °C and 209 °C due to its inherent molecular structure. The thermal stability of synthesized polybenzoxazines was studied using TGA, Cu-a exhibits higher char yield of 63% due to higher aromatic content than that of other polybenzoxazines. The occurrence of dimerization (2π+2π cycloaddition) of curcumin based benzoxazines proceeds through conjugation present in the main chain of curcumin when exposed to UV irradiation, and was monitored through UV–visible spectroscopy. All the synthesized benzoxazine monomers were excited within the wavelength of UV range with occurrence of photoluminescence behaviour in visible region ranges between 448 nm and 530 nm. The value of band gap calculated for the curcumin-based monomers ranged from 3.55 to 3.77 eV. The explicit character of curcumin based benzoxazines can be exploited in the field of optical applications. The hydrophobic behaviour of polybenzoxazines was also studied and the highest water interface angle value of 146° was observed for poly(Cu-tfma) due to the presence of fluorine groups. Furthermore, the Cu-tfma coated cotton fabric was tested for its durability and the results indicated that these materials coated cotton fabrics are better suitable for sustainable high performance hydrophobic applications. The anti-corrosion studies indicated that the poly(Cu-api) coated on mild steel exhibits greater resistance towards corrosion amongst the other polybenzoxazines which can be potentially employed as coating in marine environments.

Curing kinetics study of chemically modified pineapple leaf fiber/epoxy composite

Agricultural by-products have long hinder farmers, and subsequently, the food supply chain. Making use of their natural by-products will both reduce waste and increase industrial production. In particular, pineapple leaf fibers (PALF) can be extensively studied. Here, the curing kinetics of chemically modified PALF/epoxy resin crosslinked by an anhydride hardener was investigated by non-isothermal and isothermal methods with the differential scanning calorimetry technique. In this study, the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods, as well as Kamal's model, were employed to analyze the curing behavior of epoxy in non-isothermal and isothermal processes, respectively. The highest activation energies for pure epoxy and PALF/epoxy composite calculated differ when using the methods. Additionally, a decreasing trend in the activation energy values during the late stages of epoxy curing was observed. The results from Kamal's model indicate that the k1 values of the PALF/epoxy composite are only greater than those of pure epoxy at 100°C and 110°C. However, all the k2 values of PALF/epoxy are greater than those of pure epoxy. Additionally, the m value of the PALF/epoxy composite is lower than that of pure epoxy only at 100°C, while the n and m+n values of the PALF/epoxy composite are all greater than those of pure epoxy. Moreover, the results reveal that the Cure Index of the PALF/epoxy composite was larger than ΔH* and smaller than ΔT*. With PALF, it was found that the epoxy resin’s curing rate was increased and the activation energy was reduced. Meanwhile, the degree of crosslinks was less than that of the virgin resin. It is speculated that the hydroxyl groups on the plant fibers and the amine groups on the coupling agent-modified fibers can promote the cross-linking reaction. However, the curing reaction of the composite is affected by steric obstacles and high viscosity resulting from the addition of PALFs.

The roles played by anionic and cationic species in the curing process of aromatic nitrile resins

Understanding the curing mechanism of aromatic nitrile (AN) resins is crucial for improving their curing efficiency. Blending the Bronsted acid-containing aromatic nitrile monomers (ACN) and Bronsted base-containing aromatic nitrile monomers (BCN) is a novel approach that simultaneously lowers the melting point and rapid curing reaction temperature of AN resins. To investigate the impact of anionic and cationic species on the curing behavior of ACN-BCN blends, a series of ACN-BCN blends were designed and synthesized. DSC and TGA results demonstrated a significant improvement in the curing efficiency when ACN and BCN blended, the curing temperature decreased by more than 50 ℃, accompanied by a decrease in melting point. According to the DMA results, the Tg of the cured substance of the system can reach 405 ℃ at the curing temperature of 325 ℃. The curing behaviors of ACN-BCN blends were studied through thermal analysis and spectroscopic analysis, which indicates that cationic species can polarize the cyano rather than attack the cyano groups, promoting their curing reaction. Moreover, it was determined that while cationic species play a polarizing role on the cyano, active anionic species attack the cyano, serving as the rate-determining step in the curing process of ACN-BCN blends.

The synergistic impacts of hybrid nanofillers of graphene nanoplatelets/carbon nanotubes on curing behavior of an epoxy‐vinyl ester interpenetrating polymer network nanocomposite coating

AbstractThis study investigated the synergistic effects of hybrid graphene nanoplatelet (GnP)/multi walled carbon nanotube (MWCNT) nanofillers at various loadings on the kinetics of curing of the epoxy (EP)/vinyl ester (VE) interpenetrating polymer network (IPN) system, with a mass ratio of 1:1. Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analyzer (DMTA) and differential scanning calorimetry (DSC) were used to monitor the interpenetration process of EP and VE and likely interactions between the components of the different resin systems in IPN. The curing behavior of all prepared samples under non‐isothermal conditions was studied using DSC at four heating rates. Two different isoconversional approaches were applied to evaluate the reaction kinetics, that is, the Friedman and the advanced Vyazovkin methods. The obtained activation energy curves for all samples revealed a complex curing behavior involving three stages; early IPN stage, IPN growth stage, and late IPN stage. Then, the activation energy values for each reaction step were determined based on the Friedman method. The presence of GnP/MWCNT nanoparticles showed no catalytic effect on the reaction of VE with methyl ethyl ketone peroxide (MEKP). In contrast, incorporating GnP/MWCNT nanoparticles significantly decreases the activation energy values of the reaction of ring opening of epoxides with methyl tetrahydrophthalic anhydride (MTHPA) 1‐methyl imidazole (‐Mi) and the reaction of esterification of the hydroxyl groups of VE with MTHPA.Highlights Model‐free methods used to curing study of epoxy‐vinyl ester IPN nanocomposites FTIR, DSC and DMTA used for evaluation IPN formation of EP/VE It showed that the improvement of dispersion and compatibility by using of GnP/MWCNT hybrid Frideman and Vyazovkin methods used to calculate Ea of nanocomposites DSC thermograms were deconvoluted into three individual peaks.

Synthesis and characterization of low dielectric constant polybenzoxazines with different fluorine contents

AbstractThe rapid development of integrated circuits puts forward higher requirements for low dielectric constant polymers. In this study, two fluorinated benzoxazine monomers, bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isopropane (BA‐ftfa) and bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isoperfluoropropane (BAF‐ftfa), were successfully synthesized. Differential scanning calorimeter (DSC) was used to monitor the thermal curing behaviors of the monomers and their mixtures. Five groups of polybenzoxazine samples with different fluorine content (25% ~ 35%) were obtained by copolymerizing the two monomers with different mass ratios. The effects of fluorine content on dielectric properties were investigated and the results show that PBAF‐ftfa with the highest fluorine content has the lowest dielectric constant of 2.53 at 1 MHz. Furthermore, the results of thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) show that all polymers possess excellent thermal stability and exhibit high glass transition temperatures over than 180°C.

An Investigation of the Dynamic Curing Behavior and Micro-Mechanism of a Super-Tough Resin for Steel Bridge Pavements

To overcome challenging service conditions, a groundbreaking thermoset, “Super-Tough Resin” (STR), has been specifically designed for steel bridge deck paving. Currently, investigations of paving thermosets mainly focus on cured materials. Detailed investigations of the curing process and its impact on the evolving properties of STR are lacking. Therefore, this study aims to explore the curing kinetics and the performance evolution of STR. Specifically, spectroscopy test, time sweep, linear viscoelastic region, and weight loss tests were conducted. Our results show that the curing degrees increase significantly with the curing durations and temperatures at the initial stage. When cured for 10 h, the curing degrees at four temperatures all exceed 80%. Then, a kinetic model with an nth-order of 1.551 was established. Upon increasing the temperature from 35 to 80 °C, the gel point time decreases from 480 to 189 min but the corresponding curing degree remains constant at 75.73%. When curing time is increased from 2.5 to 4 h, the linear viscoelastic regions decrease from 20% to 3%. Finally, after 400 h, the weight losses of STR at 35 and 80 °C are about 8% and 20%, respectively. These outcomes are beneficial to understanding the dynamic curing behaviors of STR and similar thermosets.

Cure behavior and mechanism of cyanate ester with aromatic amines at room temperature

Herein, the catalytic effects of aromatic amines with different structures on the room temperature curing of bisphenol E cyanate (BECy) have been studied using differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. Our results revealed that the mixed amine comprised of aniline and N,N-dimethyl-p-phenylenediamine (AN/NNDPA) bearing primary amino groups in its structure was a highly effective catalyst for the room temperature curing of cyanate esters. When the cyanate ester and mixed amine were combined at a molar ratio of 100:5 and cured at room temperature for 5 days, the curing degree of BECy resin reached 79.7%. The room temperature curing mechanism of the BECy-AN/NNDPA system was investigated using pyrolysis gas chromatography-mass spectrometry (PY GC-MS). Our results showed that the formation reactions of the intermediate structure and cyclotrimerization reactions occurred during the room-temperature curing process. The activation energies of BECy and different aromatic amine systems at different heating rates were determined using non-isothermal DSC. The results further demonstrated the catalytic effect of AN/NNDPA on the cyanate ester curing reaction. BECy-AN/NNDPA cured at room temperature has suitable heat resistance and a 5% weight loss temperature (Td5) of 361°C.

Effect of particle size on rheology, curing kinetics, and corresponding mechanical and thermal properties of aluminum nitride (AlN) ceramic by digital light processing (DLP)-based vat photopolymerization

In this work, the influence of AlN particle size (250 nm, 1.2 µm, and 5 µm) on the curing behavior, stability and viscosity of ceramic suspensions was evaluated. It was revealed that an increase in the particle size of AlN powders reduced the stability and viscosity of the suspension. For curing behavior, the ceramic suspension prepared with 250 nm AlN powder exhibited the smallest curing depth and excess width, whereas the 5-μm ceramic suspension had the largest curing depth. The analysis of the scattering length revealed that a decrease in AlN powder particle size reduced the scattering length. After sintering, both the 250-nm and 1.2-μm samples could be sintered densely at temperatures more than 1800 °C with the relative density greater than 99%. Finally, following a 5 h sintering at 1850 °C, the 250-nm and 1.2-μm samples obtained thermal conductivities of 171 and 174 W/mK, respectively.

Study of the Self-Polymerization of Epoxy/Phthalonitrile Copolymers and Their High-Performance Fiber-Reinforced Laminates.

Self-polymerization epoxy/phthalonitrile (APPEN) pre-polymers were studied systematically, and then, gelation time and differential scanning calorimetry (DSC) were employed to investigate their curing behaviors. Taking advantage of orthogonal test analysis, the key factors that affected the co-polymerization of APPEN were defined and the appropriate pre-polymerization conditions were analyzed. A possible curing mechanism of APPEN was proposed. Then, the thermomechanical and mechanical properties of glass-fiber-reinforced APPEN laminates (APPEN/GF) prepared at 180 °C were analyzed to understand the cross-linked and aggregation structures. Fracture surface of the composite laminates was also investigated to reveal the copolymerization degree and the interfacial binding. The results indicated that APPEN/GF composites exhibit outstanding mechanical and thermomechanical properties (flexural strength, 712 MPa, flexural modulus, 38 GPa, and Tg > 185 °C). The thermal stability (T5% > 334 °C and IPDT reached 1482 °C) of APPEN/GF composites was also investigated to further reveal the copolymerization between epoxy resin and aminophthalonitrile, which may be beneficial to the application of epoxy-matrix-based composites in the field of high-performance polymer composites.

Synthesis of acetone-fractionated hardwood kraft lignin-based adhesive crosslinked with epichlorohydrin

Studies on lignin have garnered great interest for increasing the value of lignin-added products, especially lignin-based adhesives. However, even with the advantage of abundant aromatic materials in lignin, its aromaticity and heterogeneity require its fractionation with various solvents. This study used hardwood kraft lignin (HKL) extracted from black liquor and was acetone-fractionated to produce acetone-soluble HKL (AS-HKL) and acetone-insoluble HKL (AI-HKL). The lignins were crosslinked with different amounts of epichlorohydrin (ECH; 5%, 10%, and 15%) for the synthesis of lignin-based adhesives with a three-dimensional network. The crosslinked HKLs were characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), nuclear magnetic resonance (13C-NMR), and differential scanning calorimetry (DSC) to investigate their molecular weight, chemical structure, and thermal curing behavior. AI-HKL exhibited higher molecular weight than that of AS-HKL. As expected, the FT-IR and 13C-NMR spectra showed successful crosslinking of HKL by ECH with the intensity reduction of − OH, increased C–O stretching, and new peak appearance. From the DSC results, the exothermic peak temperature for crosslinking was 100 °C–130 °C. HKL and AI-HKL plywoods showed good tensile shear strength with minimal variations when they were crosslinked with 10 and 15% ECH. These results suggest the potential of high molecular weight HKL as lignin-based adhesives for wood bonding.

Low dielectric constant and high thermal stability of liquid crystal epoxy polymers based on functionalized poly(phenylene oxide)

Epoxy resins exhibit poor thermal and dielectric properties because of the disordered entanglement of the chain segments and a large number of hydroxyl groups generated after curing by diamine curing agents. Herein, to prepare high-Tg and low-dielectric epoxy thermosets, two functionalized poly(phenylene oxide) (PPOs) were synthesized by redistribution and esterification reactions and used as curing agents to cure liquid crystal epoxy (t-BPDGE). The modified PPOs (TMPA and TMBPA) contain six active ester functional groups, which not only improved the compatibility and the degree of cross-linking of the PPOs with the epoxy monomers but also avoided the generation of hydroxyl groups after curing. The curing mechanism was investigated using TBB cured glycidyl phenyl ether as a model reaction, and the effects of TMPA and TMBPA on the curing behavior and performances were also studied. Due to the ordered arrangement of the liquid crystal epoxy resins and the presence of PPOs, the overall performances of PPOs-based/t-BPDGE are significantly improved. Specifically, the results showed that TMPA/t-BPDGE possessed a high glass transition temperature (Tg) of 199.47 °C and a char rate of 21.84%, which was 77.09 °C and 3.63 times higher than that of the DDM/t-BPDGE, respectively. Moreover, TMPA/t-BPDGE exhibited a lower moisture absorption (0.23%), dielectric constant and loss (2.94 and 0.00815 at 1 GHz) compared to the DDM/t-BPDGE (0.48%, 3.95 and 0.01898, respectively). The findings provide a new design strategy for preparing high-Tg and low-dielectric epoxy thermosets.

Preparation and characterization of the bonding performance of a starch-based water resistance adhesive by Schiff base reaction

Starch is one of the important raw materials for the preparation of biomass adhesives for its good viscosity and low-cost properties. However, the drawbacks of poor water resistance and bonding performance seriously restrict its application in the wood industry. To resolve those problems, an environment-friendly renewable, and high water resistance starch-based adhesive (OSTH) was prepared with oxidized starch and hexanediamine by Schiff base reaction. In order to optimize the adhesive preparation process, the effect of different oxidation times and oxidant addition on the mechanical performance of plywood were investigated. In addition, the curing behavior characteristics, thermomechanical properties, and thermal stability of the OSTH adhesives were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TG). Fourier-transform infrared (FTIR) spectrometry and Liquid Chromatography-Mass Spectrometry (LC-MS) were used to explain the reaction mechanisms involved. The results show this adhesive has an excellent bonding performance at the oxidation time of 12 h with 11 % (w/w, dry starch basis) NaIO4 as an oxidant. The dry shear strength, 24-hour cold water, and 3-hour hot water (63 °C) soaking shear strength of the plywood bonded with this resin were respectively 1.87 MPa, 0.96 MPa, and 0.91 MPa, which satisfied the standard requirement of GB/T 9846-2015 (≥0.7 MPa). Thus, this study provided a potential strategy to prepare starch-based wood adhesives with good bonding performance and water resistance.

Synthesis and characterization of cyano-terminated bisphenol AF-type polyarylene ether nitrile

Four novel phthalonitrile-capped polyarylene ether nitrile oligomers containing trifluoromethyl groups (FPEN-Ph) with different molecular weight were designed and synthesized by adjusting the ratio of bisphenol AF (BPAF) and 2,6-dicholorobenzonitrile (DCBN). The molecular structure of FPEN-Ph oligomers were characterized and analyzed by FTIR, 1HNMR and Gel permeation chromatography. Their curing behaviors were studied by Differential scanning calorimetry and rheological tests, and curing kinetics were also discussed by gel method in detail. The glass fiber cloth reinforced FPEN-Ph composites (FPEN-Ph/GF) had flexural strengths of 415.9–497.5 MPa, shear strengths of 34.5–50.5 MPa, and glass transition temperatures ( Tgs) in the range of 211.3°C–416.6°C. The initial thermal decomposition temperatures ( T5%) of various FPEN-Ph cured products were higher than 500°C under nitrogen. Meanwhile, Fracture morphologies showed that the GF/FPEN-Ph composites had excellent interfacial adhesion between FPEN-Ph matrix and GF reinforcement. Herein, the FPEN-Ph resin could be a good candidate for high-performance polymeric composites and the advanced FPEN-Ph/GF composites can be used under high temperature environment.

Enhanced mechanical properties and biological responses of SLA 3D printed biphasic calcium phosphate bioceramics by doping bioactive metal elements

Favorable mechanical properties and outstanding bioactivity are necessary for bioceramics used for bone defect repair. The doping of Mg2+ and Fe3+ can improve the mechanical properties and bone regeneration capacity of calcium phosphate ceramics. In this study, magnesia oxide (MgO), ferric oxide (Fe2O3), and iron (Fe) powders are chosen as dopants to enhance biphasic calcium phosphate (BCP) bioceramics, and the MgO-BCP, Fe2O3-BCP, Fe-BCP bioceramics are prepared by stereolithography (SLA) for the first time. The effects of these dopants on the curing behavior of bioceramic slurries, mechanical properties, biodegradation, and cytocompatibility of BCP bioceramics are studied. The addition of 1 wt.% Fe well enhances the flexural strength of BCP from 91.61 MPa to 122.60 MPa sintered at 1250 oC. The addition of 1 wt.% MgO effectively promotes the biodegradation of BCP in simulated body solution (SBF), and enhances the proliferation of mouse pre-osteoblast (MC3T3-E1) cells in vitro. In addition, Fe powder is more suitable as a dopant for SLA 3D printed BCP than Fe2O3 powder, and all the performances of Fe-BCP are better than those of Fe2O3-BCP. The less microstructure defects and slower Fe3+ release rate make Fe-BCP have higher flexural strength and less cytotoxic compared with Fe2O3-BCP. This novel way exhibits beneficial effects of bioactive metal elements on mechanical properties and bioactivity, and indicates SLA 3D printed BCP bioceramic doped with MgO, Fe can be promising candidates for bone defect repair.

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.

Stabilizing cohesive soils with Micro- and Nano- fly ash as Eco-friendly Materials: An experimental study

Soil stabilization is a popular technique for improving soil properties and creating sustainable and green buildings using rammed earth walls. Nano materials are a new type of additive that can enhance soil performance. Laboratory tests were performed to examine the geotechnical properties of clay mixed with nano fly ash. Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray powder diffraction (XRD) were used to analyze the nature and changes of the particles before and after the grinding process. The effect of time and different dosages of nano fly ash (3%, 5%, and 7%) on the curing behavior was also investigated. The test results showed that the optimal amount of nano fly ash and fly ash added to soil was 7% by weight of soil after 28 days. This increased the unconfined compression strength of clay from 50 kPa to 410 kPa (8.2 times) and the triaxial strength of clay from 65, 80, and 90 kPa to 520, 640, and 720 kPa (8 times) respectively. The results showed that nano-fly ash as a nano soil-improvement suspension significantly improved the strength and stiffness of the soil-fly ash mixture by forming gel that filled the pores and bonded the soil particles. Nano-fly ash also acted as a nucleation site, enhancing the durability and strength of the mixture.

A highly-crosslinked phthalonitrile modified bismaleimide-triazine resin for PCB substrates: The synergistic effect on curing behavior and properties

In view of the problems of difficult processing and poor toughness, bismaleimide-triazine (BT) resin was modified by the 4-(4-amino-phenoxy)phthalonitrile (4-APN). The effect of 4-APN on the curing behavior of BT resin was investigated, followed by the calculated activation energy. The possible curing mechanism of this ternary system was also proposed, with the further study of the relationship between chemical structures and properties. The results showed that 4-APN can increase the reactivity and decrease the curing temperature of BT resin. Meanwhile, due to the fact that 4-APN exerted a thermal synergistic curing effect on the BT resin, poly(BT/APN)s with a high crosslinking density exhibited the superior overall performance. Concretely, the high heat-resistance of poly(BT/APN)s was displayed, especially the glass transition temperature up to 347 ℃ of poly(BT/30APN). More intriguingly, poly(BT/APN)s with a high breakdown strength possessed better insulation properties, and the dielectric constant and loss reduced to 3 and 0.005 (1 MHz), respectively, while remaining a good stability at high temperature. Additionally, the moisture resistance and toughness of poly(BT/APN)s were also significantly improved. Based on these merits, poly(BT/APN)s can be considered as an ideal material for microelectronics.