Curing Mechanism Research Articles

Toughened polybenzoxazine coating matrix with improved comprehensive performance through hydrogen bond tuning with new polyurethanes

Polybenzoxazine has been explored in coating applications because of its excellent properties, including good processability, excellent thermal stability, and large water contact angles, but its toughness must be improved without compromising its other properties. Herein, a new serious of polyurethanes with varying numbers of ether groups were synthesized to enhance the toughness of polybenzoxazine via tuning the hydrogen bonds. The curing mechanism, chemical structures, and phase morphology of the blends are discussed. The results show that hydrogen bonding is the main reason for improved properties of the cured products. By varying the hydrogen bond content of the modified system, a champion toughness of 20.4 kJ/m2 without sacrificing processability, thermal stability, and coating performances can be realized, which the char yield is varied between 26.0 % and 28.9 % at 800 °C and corresponding coating hardness and adhesion can reach to 6H and 5B, respectively. Furthermore, the modified system-based coatings exhibit a reversible hydrophobic-hydrophilic state by different stimulus with a champion oil-water separation efficiency of 3379 L·m−2·h−1, illustrating their potential intelligent applications.

Study on Modification and Mechanism of Construction Waste to Solidified Silt

A large amount of silt may be produced in river and lake regulation. It not only occupies land but also pollutes the environment. Therefore, it is urgent to seek effective disposal and utilization methods. Based on the problems of poor stability of stabilized soil and its tendency to soften easily in water, as well as its low strength with low curing agent dosage, this paper proposes a method to improve stabilized soil's solidification effect by adding materials such as cement, lime, fly ash, triethanolamine, sodium hydroxide, sodium silicate, etc., while mixing different grain diameters and quantities of building waste materials and ordinary sand. Using construction waste and ordinary sand as a comparative test, the curing mechanism of construction waste debris on the mechanical properties, permeability, and microstructure of solidified sludge was studied through unconfined compression tests, dry and wet cycle tests, permeability tests, and micro-structure tests such as XRD, MIP, and SEM. The test results show that the strength increases 8.5%~72.1% by adding building waste materials, and it grew with the increase in particle size and amount. It reduced the content of large pore size of solidified sediment and optimized the internal pore structure. At the same time, it formed a new structure filled by rigid skeleton material. Thus, it improved its unit section stress, built up the curing effect and water stability. The findings of this study can be used to modify solidified silt to improve stability and compaction characteristics.

3D Printing Thermally Stable High‐Performance Polymers Based on a Dual Curing Mechanism

AbstractHigh‐performance polymers are an important class of materials that are used in challenging conditions, such as in aerospace applications. Until now, 3D printing based on stereolithography processes can not be performed due to a lack of suitable materials. There is report on new materials and printing compositions that enable 3D printing of objects having extremely high thermal resistance, with Tg of 283 °C and excellent mechanical properties. The printing is performed by a low‐cost Digital Light Processing printer, and the formulation is based on a dual‐cure mechanism, photo, and thermal process. The main components are a molecule that has both epoxy and acrylate groups, alkylated melamine that enables a high degree of crosslinking, and a soluble precursor of silica. The resulting objects are made of hybrid materials, in which the silicon is present in the polymeric backbone and partly as silica enforcement particles.

A facile strategy and mechanism to achieve biobased bismaleimide resins with high thermal-resistance and strength through copolymerizing with unique propargyl ether-functionalized allyl compound

Preparing biobased thermosetting resins with high mechanical properties and superior heat resistance is an important issue for the sustainable development and applications of high performance resins. Herein, a novel biobased allyl compound (DBB) with aryl propargyl ether groups was synthesized from renewable honokiol, which was then used to copolymerize with 4,4′-bismaleimidodiphenylmethane (BDM) to develop new biobased resins (BDM/DBB). The effects of the molar ratio of BDM to DBB on the thermal and mechanical properties were studied. Results show that all BDM/DBB resins possess both high thermal and mechanical properties. Specifically, their glass transition temperatures (Tg > 440 °C) and storage moduli (> 1.3 GPa at 400 °C) are higher than those of biobased allyl compounds modified BDM resins reported so far (SCI database); moreover, their initial thermal decomposition temperatures are about 448 °C and flexural strengths range from 106 to 117 MPa. These excellent comprehensive performances are attributed to the unique crosslinked network resulted from the complex curing mechanism of BDM/DBB, which including the copolymerization between imide groups and allyl groups as well as the additional thermal crosslinking of aryl propargyl ether. This work provides a sustainable and facile strategy to construct high performance biobased resins.

A novel formaldehyde-free wood adhesive synthesized by straw soda lignin and polyethyleneimine

To eliminate toxic formaldehyde from wood-based panels, a new formaldehyde-free wood adhesive (named OL/PEI adhesive) was synthesized by a reaction of oxidized lignin (OL) and polyethylenimine (PEI) reaction in the presence of sodium periodate. The curing mechanism of the OL/PEI adhesive was clarified by Fourier transform infrared spectroscopy (FTIR) and solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS13C-NMR) spectroscopy. The results showed that the sodium periodate could selectively oxidize wheat straw lignin to produce the ortho-quinone, and then the ortho-quinone in OL could further react with amino groups in PEI to form the OL/PEI adhesive. The as-prepared poplar particleboard was investigated with regard to hot-pressing temperature, the hot-pressing time, the OL/PEI weight ratio, and the dosage of OL/PEI adhesive. Under the optimum conditions, e.g., hot pressing temperature of 180 °C, hot pressing time of 13 min, the OL/PEI weight ratio of 1:1, and the dosage of 10%, OL/PEI adhesive was found to disperse evenly into the voids among the shavings of poplar particleboard, followed by the curing of OL/PEI adhesive using hot-pressing to form tightly bonds between the shavings. The resulting particleboard reached the requirement of mechanical properties (GB/T 4897.3-2003), higher water resistance properties, and better heating resistivity. This study demonstrated a new way to produce a formaldehyde-free wood adhesive with unique properties. This material could replace formaldehyde wood adhesive in wood bonding.

Effects of silicone resins on copolymerization of acrylated epoxidized soybean oil

AbstractIn this work, effects of the silicone resins on copolymerization of the acrylated epoxidized soybean oil were investigated. Rheological characteristics, curing behaviors, and thermal properties of acrylate epoxy soybean oil prepolymer (AP), silicone prepolymer (SP), and their hybrids (AP/SP) were studied in detail. Spots in a snowflake pattern were observed on the fracture section surface of cured AP/SP hybrid resins by SEM. According to the change of polymer groups revealed by Fourier transform infrared, a possible reaction between AP and SP was proposed. The curing mechanism of AP/SP hybrids was researched, which was suggested to be an autocatalytic curing process. Furthermore, the degree of cure, the activation energy (Eα) and the reaction frequency factor (A) of the curing reaction were estimated. It was found that the cure kinetic of AP/SP hybrid resins could be well‐described by a Sesthk‐Bergglen model with the numerical optimization based on the Kissinger method and the Malek approach. The experimental results show that the mass retention rates of AP/SP hybrid resins were significantly increased after curing, indicating that the thermal stability of AP was enhanced with the addition of SP.

UV-Curable Polyborosilazane Precursors for SiBCN Coatings under Harsh Environments

UV irradiation is a well-established and effective process for polymer curing. However, it has been largely ignored in the field of polymer-derived ceramics (PDCs) due to its intricate mechanism and strict requirements for the precursor molecular structure. The current work designs and synthesizes a series of UV-curable polyborosilazanes containing various vinyl groups, simultaneously examines the effect of UV curing, and investigates the mechanism of curing. Cyclization mechanisms involving vinyl-free radicals and silyl-free radicals are postulated based on the molecular structure of the precursor before and after curing. The ceramic yield of UV-cured precursors is increased by up to 9.0 wt %. Moreover, SiBCN ceramics, pyrolyzed from UV-cured precursors, exhibit excellent thermal stability and remain amorphous at temperatures of up to 1600 °C. The mechanistic interpretation of UV curing opens horizons for the design and application of UV-curable ceramic precursors.

Activated alkali cement based on blast furnace slag: effect of curing type and concentration of Na20

Recent studies highlight the feasibility of using activated alkali cement (AAC) as a substitute for Portland cement. In this context, the objective of this article is to evaluate the influence of the type of curing on the mechanical properties of ACC based on blast furnace slag. For this, cylindrical specimens measuring 50 × 100 mm were made using blast furnace slag activated by sodium hydroxide with different mass concentrations (2.5–15%). Normal curing at room temperature, thermal curing at 65 °C, solution curing with distilled water (saturated curing), hydrated lime (lime curing) and sodium hydroxide (sodium curing), and compound curing were carried out. The compressive strength results at 7 and 28 days indicate that the AAC presents a superior behavior to the OPC. Regarding the curing mechanisms, the most advantageous were thermal curing, which promoted greater thermal energy, and curing in sodium solution, which prevented the loss of alkaline ions from the AAC. In these types of healing, there was greater formation of tobermorite and hydrotalcite, with an increase in alkaline activation rates, as evidenced by the results of XRD, FTIR and TDG. In situations of inefficient curing, such as saturated and lime curing, ettringite and efflorescence were formed, impairing the mechanical properties of the material. It was concluded that the best AAC cure was thermal or sodium cure depending on the Na2O concentration.

Inexpensive monolithic additive manufacturing of silicone structures for bio-inspired soft robotic systems

In soft robotics, the fabrication of extremely soft structures capable of performing bio-inspired complex motion is a challenging task. This paper introduces an innovative 3D printing of soft silicone structures with embedded shape memory alloy (SMA) actuators, which is completed in a single printing cycle from CAD files. The proposed custom-made 3D printing setup, based on the material extrusion (MEX) method, was used in conjunction with a cartesian pick and place robot (CPPR) to completely automate the fabrication of thick silicone skins (7 mm) with embedded shape memory alloy actuators. These structures were fabricated monolithically without any assembly tasks and direct human intervention. Taking advantage of the capability to 3D print different geometries, three different patterns were fabricated over the silicone skin, resulting in remarkable dynamic motions: an out-of-plane deformation (jumping of the structure from the x-y plane to the x-z plane) was achieved for the first-time employing silicone skin, to the best of the author’s knowledge. In addition, two process parameters (printing speed and build plate temperature) and the extruded silicone curing mechanisms were investigated to enhance the printing quality. This paper aims to advance the role of additive manufacturing in the field of soft robotics by demonstrating all the benefits that a low-cost, custom-made silicone 3D printer can bring to the table in terms of manufacturing soft bio-inspired structures.

Engineering Properties and Microscopic Mechanisms of Composite-Cemented Soil as Backfill of Ultra-Deep and Ultra-Narrow Foundation Trenches

The backfilling of lime soil in ultra-deep and ultra-narrow foundation trenches is a difficult construction link, and ordinary-cemented soil has drawbacks, including poor strength, impermeability, and frost resistance. To solve these problems, fly ash (FA)–water glass (WG)-composite-cemented soil is developed based on a background project. The three-factor orthogonal tests are conducted on the unconfined compressive strength (UCS) of the composite-cemented soil, and the optimal engineering mix proportion is proposed for the FA-WG-composite-cemented soil. Its UCS is compared with that of cemented soil only doped with FA or WG (FA- and WG-cemented soil). In addition, the cyclic wetting–drying tests, cyclic freeze–thaw tests, and impermeability tests are carried out to study the endurance of the composite-cemented soil in cold regions rich in water. The hydration products of the composite-cemented soil are investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, and the curing mechanism of the composite-cemented soil is discussed from the microscopic perspective. The research results indicate that the mixing ratio of cement is crucial to the strength development of the cemented soil; the mixing ratio of FA greatly influences the strength development of the cemented soil in the middle and late stages; the mixing ratio of WG only slightly affects the strength. The ratio of cement, FA, and WG of 9%:12%:3% is the optimal engineering mix proportion of the composite-cemented soil. Compared with ordinary-cemented oil and FA- and WG-cemented soil, the composite-cemented soil shows significantly improved compressive load-bearing capacity. The permeability coefficient of the composite-cemented soil is always obviously lower than that of the ordinary-cemented soil after any curing period. Despite the mass loss, the composite-cemented soil is superior to the ordinary one in overall endurance after wetting–drying and freeze–thaw cycles. Through SEM and XRD analysis, the content of hydration products of the composite-cemented soil is found to be obviously higher than that of ordinary-cemented soil after any curing period, and the hydrates exert stronger cementing action on soil particles in the composite-cemented soil. The contents of C-S-H gel and Aft crystals in the composite-cemented soil are apparently larger than those in the ordinary-cemented soil. Under the alkali activation of WG, the FA produces free SiO32− and AlO2−, which undergo the polymerization reaction with Ca2+ to generate C-S-H gel and C-A-H gel, further promoting the hydration of cement.

ПОЛУЧЕНИЕ СМЕШАННЫХ КОМПОЗИЦИОННЫХ ЦЕМЕНТОВ НА ОСНОВЕ ФЕРРИТНОГО КЛИНКЕРА

The possibility of using ferritic clinker as a component of binders with special performance properties is considered. Such types of cements can solve the problems of providing the construction industry with high-strength, resistant to external aggressive effects and relatively cheap binders. However, the mechanism of hardening and curing of cement stone obtained by using ferritic clinkers is complicated and depends on a number of parameters.
 It was found that the greatest thermal effect (more than 70%) during the hydration of the resulting ferritic clinker with the introduction of various additives (lime and gypsum stone) is achieved up to 4 hours from the moment the binder compositions are mixed by means of a calorimetric analysis carried out during the hydration of the developed special binder compositions. That corresponds to the course of the induction period of hydration of the used Portland cement, at the time of the occurrence of primary contacts between crystalline hydrates and sufficient mobility of the cement mass. In this time interval, the strength of the cement stone is not high enough and the produced iron-containing hydration products are able to fill the space of the cement matrix, making it more dense and less defective. 
 The formation of iron-containing crystalline hydrates from ferritic clinker can proceed in several stages: hydrolysis of dicalcium ferrite at the initial stage of the reaction and further interaction of its products with portlandite in the period from 7 to 14 days from the moment of mixing the binder compositions. The main crystalline hydrates formed from ferritic clinker are iron-bearing ettringite and hydrogarnet.
 The study of the physical and mechanical characteristics of cement stone showed that the optimal content of ferritic clinker in the composition of the binder compositions is 5%. With a given quantity, the strength of the cement stone in compression and bending exceeds that of the control sample by 11.5%. The input of 15 and 30% ferritic clinkers into the composition of special binders reduces the strength characteristics by 15-20%.

Redox cationic frontal polymerization: a new strategy towards fast and efficient curing of defect-free fiber reinforced polymer composites.

Frontal polymerization of epoxy-based thermosets is a promising curing technique for the production of carbon fiber reinforced composites (CFRCs). It exploits the exothermicity of polymerization reactions to convert liquid monomers to a solid 3D network. A self-sustaining curing reaction is triggered by heat or UV-radiation, resulting in a localized thermal reaction zone that propagates through the resin formulation. To date, frontal polymerization is limited to CFRCs with a low fiber volume percent as heat losses compromise on the propagation of the heat front, which is crucial for this autocatalytic curing mechanism. In addition, the choice of suitable epoxy monomers and thermal radical initiators is limited, as highly reactive cycloaliphatic epoxies as well as peroxides decarboxylate during radical induced cationic frontal polymerization. The resulting networks suffer from high defect rates and inferior mechanical properties. Herein, we overcome these shortcomings by introducing redox cationic frontal polymerization (RCFP) as a new frontal curing concept. In the first part of this study, the influence of stannous octoate (reducing agent) was studied on a frontally cured bisphenol A diglycidyl ether resin and mechanical and thermal properties were compared to a conventional anhydride cured counterpart. In a subsequent step, a quasi-isotropic CFRC with a fiber volume of >50 vol%, was successfully cured via RCFP. The composite exhibited a glass transition temperature > 100 °C and a low number of defects. Finally, it was demonstrated that the redox agent effectively prevents decarboxylation during frontal polymerization of a cycloaliphatic epoxy, demonstrating the versatility of RCFP in future applications.

Microbially induced calcite precipitation and synergistic mineralization cementation mechanism of Pisha sandstone components

Soil erosion is a key problem of erosion in Pisha sandstone areas, and microbially induced calcium carbonate deposition is a bioconsolidation technique with soil improvement potential. There is more limited information available on the uniformity of the distribution of microbially induced calcium carbonate precipitation mediated by Pisha sandstone grains and on the influence of mineral composition on calcium carbonate bonding mechanisms. In this study, the curing mechanism of Pisha sandstone particles under the microbially induced calcium carbonate deposition technique was investigated by unconfined compressive strength tests, X-ray diffraction spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the self-adsorption biphasic injection method was effective in regulating the homogeneous distribution of microorganisms, and the addition of an additive solvent promoted the homogeneous distribution of bacteria, but the contribution to the mechanical properties was not obvious when urea was used as an additive solvent. The analysis revealed that montmorillonite on the surface of Pisha sandstone particles had an adsorption effect on the bacteria. In addition, the microorganisms induced the transformation of the montmorillonite phase to the illite phase during the biological treatment. Combined Fourier transform infrared spectroscopy and thermogravimetric analysis revealed that the CO bond in biogenic calcium carbonate, the SiO bond in Pisha sandstone particles, undergoes intermolecular hydrogen bonding under the modulating effect of the metabolites of microorganisms, and the anionic coordinating group of the extracellular polymer can form a stronger electrostatic interaction with calcium ions, requiring more energy for decomposition. This work provides a case study of microbially induced calcite deposition to improve loose Pisha sandstone, and at the same time, it is not difficult to see how Pisha sandstone particles, as weakly cemented sands, could be a suitable vehicle for a potential microbial consolidation process.

Adhesive Bonding of an Aluminum Alloy with and without an Oxide Layer in Atmospheres with Different Oxygen Contents

Aluminum surfaces in a normal atmosphere are always coated with a native oxide layer. To prevent a new layer from forming after this oxide layer has been removed, an environment without oxygen must be created. This work uses a new method of doping an inert gas atmosphere with highly reactive silane to ensure technical freedom from oxygen. The influence of the surrounding atmosphere and the influence of the oxide layer on the tensile strength of an aluminum-aluminum joint are investigated. For this purpose, 2-component adhesives are used whose curing mechanisms are fundamentally not based on the reaction with the surrounding atmosphere. The tests are carried out in normal, pure argon, and an oxygen-free argon/silane atmosphere. The experiments show that the surrounding atmosphere influences the strength of the bonded joint. Compared to the oxidized surfaces, the joints of the deoxidized surfaces show a higher tensile strength under constant ambient conditions.

Thermomechanical Properties and Fracture Toughness Improvement of Thermosetting Vinyl Ester Using Liquid Metal and Graphene Nanoplatelets.

In this study, a eutectic gallium-indium (EGaIn) alloy and graphene nanoplatelets (GnPs) were employed as reinforcements for a comonomer vinyl ester (cVE) resin at different weight fractions up to 2% via a direct polymerization process. First, the effect of EGaIn on the curing kinetics of cVE was evaluated. The thermal and mechanical properties, and the fracture toughness of two types of cVE composites consisting of EGaIn and GnPs were then studied. The results showed that sub-micron sized EGaIn (≤1 wt.%) could promote the curing reaction of cVE without changing the curing mechanism. However, with further increases in EGaIn loading between 1 and 2 wt.%, the curing reaction rate tends to decrease. Both EGaIn and GnPs showed a significant enhancement in strengthening and toughening the cVE matrix with the presence of filler loading up to 1 wt.%. EGaIn was more effective than GnPs in promoting the flexural and impact strength. An increase of up to 50% and 32% were recorded for these mechanical properties, when EGaln was used, as compared to 46%, and 18% for GnPs, respectively. In contrast, the GnPs/cVE composites exhibited a greater improvement in the fracture toughness and fracture energy by up to 50% and 56% in comparison with those of the EGaIn/cVE ones by up to 32% and 39%, respectively. Furthermore, the stiffness of both the EgaIn/cVE and GnPs/cVE composites showed a significant improvement with an increase of up to 1.76 and 1.83 times in the normalized storage modulus, respectively, while the glass transition temperature (Tg) values remained relatively constant. This work highlights the potential of EGaIn being employed as a filler in creating high-performance thermoset composites, which facilitates its widening applications in many structural and engineering fields, where both higher toughness and stiffness are required.

Curing Kinetics of Bioderived Furan-Based Epoxy Resins: Study on the Effect of the Epoxy Monomer/Hardener Ratio

The potential of furan-based epoxy thermosets as a greener alternative to diglycidyl ether of Bisphenol A (DGEBA)-based resins has been demonstrated in recent literature. Therefore, a deep investigation of the curing behaviour of these systems may allow their use for industrial applications. In this work, the curing mechanism of 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan (BOMF) with methyl nadic anhydride (MNA) in the presence of 2-methylimidazole as a catalyst is analyzed. In particular, three systems characterized by different epoxy/anhydride molar ratios are investigated. The curing kinetics are studied through differential scanning calorimetry, both in isothermal and non-isothermal modes. The total heat of reaction of the epoxy resin as well as its activation energy are estimated by the non-isothermal measurements, while the fitting of isothermal data with Kamal's autocatalytic model provides the kinetic parameters. The results are discussed as a function of the resin composition. The global activation energy for the curing process of BOMF/MNA resins is in the range 72-79 kJ/mol, depending on both the model used and the sample composition; higher values are experienced by the system with balanced stoichiometry. By the fitting of the isothermal analysis, it emerged that the order of reaction is not only dependent on the temperature, but also on the composition, even though the values range between 0.31 and 1.24.

Study on the curing mechanism of cemented backfill materials prepared from sodium sulfate modified coal gasification slag

In order to promote the resource utilization of coal gasification slag(CGS) solid waste, the use of modified coal gasification slag (MCGS) to replace the cement in the cemented backfill materials is an effective way to improve the utilization rate of CGS resources, reduce the backfill cost and reduce the environmental pollution of the cement industry. In this paper, the dosage of sodium sulfate (SS) in the MCGS cemented backfill materials (MCGS-CB) system composed of MCGS-cement-aeolian sand is optimized, and the curing mechanism of MCGS-CB under the action of SS is revealed. The results show that the addition of MCGS delays the early hydration reaction process, accelerates the consumption of sulfate in the system, and shows the phenomenon of sulfate deficiency; The pozzolanic reaction of MCGS increased the ratio of Al/Ca, Si/Ca and S/Ca and Na/Ca of hydration products, changed the structure of hydration products, promoted the formation of hydration products such as C-S(A)-H, C-N-S(A)-H and AFt, increased the density of matrix, reduced the pore volume of harmful pores, and increased the compressive strength. Under the action of SS, the hydration reaction process of the early MCGS-CB was accelerated, the time of the sulfate depletion (SD) point was delayed, and the reaction time of the MCGS was advanced; The consumption of Al and Si ions drives the dissolution of the aluminosilicate glass body in the MCGS, thereby further promoting the formation of hydration products such as C-S(A)-H, C-N-S(A)-H and AFt, and increasing its matrix compactness. About 4% SS has a good excitation effect on MCGS, and excessive SS addition will cause microcracks in MCGS-CB, resulting in a reduction in strength. The results of this study can provide theoretical guidance for the ratio design and field application of sulfate-coal gasification slag-cement cementation system. • The solidification mechanism of modified coal gasification slag in MCGS-CB was revealed. • The optimal addition amount of SS in MCGS-CB was determined. • The activation mechanism of SS on modified coal gasification slag is revealed. • The degradation mechanism of compressive strength of MCGS-CB under high SS was revealed.

Effect of pozzolanic reaction of zeolite on its internal curing performance in cement-based materials

In the present study, effect of pozzolanic reaction of zeolite on its internal curing performance in cement-based materials was experimentally investigated. Firstly, the pozzolanic activity of zeolite particles was tested. Then, influences of zeolite pozzolanic reaction on the pore structure, morphology, water absorption and water release performance of zeolite particles were studied. Finally, cement paste specimens with zeolite internal curing were prepared, the hydration degree of cement, pozzolanic reaction degree of zeolite and internal relative humidity were tested, and the internal curing mechanism of zeolite coupling with pozzolanic reaction was discussed. The test results show that, 1) pozzolanic reaction can increase the pore volume and water absorption of zeolite particles, when the reaction degree reaches 10.85%, the pore content increases from 0.030 mL/g to 0.054 mL/g, and the water absorption increases from 3.82% to 5.52%; 2) in zeolite internally cured cement paste with curing age of 28d, when zeolite-cement replacement increases from 10% to 30%, zeolite reaction degree in OPC paste decreases from 22.8% to 20.7%, and that in SAC paste decreases from 20.9% to 19.9%; 3) the humidity saturation period of cement paste is shortened by zeolite internal curing, but the relative humidity is improved after it drops below 95%–96%; 4) when zeolite-cement replacement increases from 0 to 30%, the humidity of OPC paste increases from 87.8% to 92.0%, and that of SAC paste increases from 88.8% to 91.4% at curing age of 28d.

Unlocking the role of lignin for preparing the lignin-based wood adhesive: A review

Adhesives––the resins widely used in particleboards , oriented strength boards, and plywood––are traditionally produced from fossil-based polymers. Owing to the toxicity, environmental pollution, and non-renewable raw materials associated with these polymers, attempts to synthesize environmentally friendly and renewable adhesives from bio-based materials has attracted increasing attention. Lignin is an abundant natural and renewable phenolic polymer with multiple types of functional groups, such as hydroxyl, carboxyl, and aldehyde groups. This has drawn considerable attention to the exploitation of this resource based on these functional groups. Because of the advantages of lignin, continued research efforts have been focused on using lignin to partially or completely replace conventional raw materials for adhesives, such as phenol and melamine. In addition, lignin is also used with other biomass materials to produce formaldehyde-free biomass-based adhesives, such as lignin–furfural, lignin–soy protein, and lignin–tannin adhesives. Despite inspiring progress, the preparation of lignin-based adhesives with performances higher than that of fossil-based adhesives remains a serious challenge. This review summarizes the progress made in recent decades in research and commercial application of lignin-based adhesives for wood products, including lignin-based formaldehyde resins and lignin-based formaldehyde-free adhesives, and proposes perspectives on lignin-based adhesives. • Lignin is an abundant natural and renewable phenolic polymer. • This review summarizes the application of lignin in wood adhesives. • Details of lignin-based adhesives, properties and mechanism are discussed. • More research should be done regarding the chemical structure and curing mechanism. • Challenges and prospects are discussed.

Investigation on stabilization/solidification characteristics of lead-contaminated soil using innovative composite model of cement and soda residue

The cement solidification/stabilization method of heavy metal contaminated soils has been promoted in engineering practice and applied on a large scale for site remediation, but it still reveals some scientific problems in the current complex and variable global extreme climate. To solve these problems, this study used waste soda residue as a composite additive, and established an innovative composite model (cement-soda) to remediate lead-contaminated soil. The innovative composite model for unconfined compressive strength (UCS) and toxic leaching properties under different conditions were investigated As well as curing and leaching mechanisms are discussed, and future industrial practice was evaluated. The results showed that the addition of soda residue improved the early (20 days) UCS of the composite curing agent for lead-contaminated soil by an average of 23.1% MPa. The UCS strength was 0.96 MPa, which was the maximum when the percentage of soda residue composite was 40%. The concentration of Pb2+ in the leachate of the cement-soda residue (CSH) composite curing agent was greatly reduced (average 3.28 times) compared with that of a single cement in the same situation, with an average leached Pb2+ concentration of 1.87 mg·L−1. This finding indicates that the addition of alkali residue improved the curing effect. The curing mechanism was divided into four steps, mainly a complex physicochemical reaction between the CSH composite and soil particles. The leaching mechanism of CSH to aqueous solution is mainly the consumption of acid ions by alkaline substances. Collectively, this study will provide scientific data to support potential lead-containing soil in site remediation technologies and future large-scale engineering applications.