Low Curing Temperature Research Articles

Performance investigation of blast furnace slag based cemented paste backfill under low temperature and low atmospheric pressure

To promote application of cemented backfill mining in underground mines located at high-altitude regions, there is a necessary to investigate mechanical performance of cemented paste backfill (CPB) under low temperature and low atmospheric pressure. In this study, the orthogonal experiment was first scheduled to synthesize the new cementitious material by combining industrial byproducts of blast furnace slag (BFS), carbide slag (CS), desulfurization gypsum (DG) with cement clinker (CC). Then, CPB samples were prepared with the new cementitious material and cured under different temperatures of 5, 10, 20 ℃ and atmospheric pressures of 50, 75, 101 kPa for 3, 7 14, and 28 days. Unconfined compressive strength (UCS) and microstructural analyses were conducted to evaluate strength and microstructure evolution of CPB. Experimental results indicate that UCS values of CPB increase with BFS, but decrease with CS and DG. The optimal proportion of the new cementitious material is determined as: 70 wt% BFS, 12 wt% CS, 1 wt% DG, and 17 wt% CC. Under curing of low temperature and low atmospheric pressure, CPB samples exhibit lower UCS values than those under 20 ℃ with 101 kPa. Especially, the coupling of low temperature and low atmospheric pressure exerts significantly adverse influence on the later strength of CPB after curing of 14 and 28 days. The declines of 57.99 % and 41.75 % are observed from UCS values of 14-day and 28-day CPB under 5 ℃ with 50 kPa, respectively. Regardless of curing temperature and atmospheric pressure, UCS values increase with the ratio of cementitious material to tailings and curing time. Low curing temperature and low atmospheric pressure reduce the hydration degree of the new cementitious material. The amount of hydration products decreases, the number of micropores (0.1 ∼ 1 μm) and the total porosity increases, as well as more loose microstructure forms among solid particles. This is the underlying reason behind performance degeneration of CPB under low temperature and low atmospheric pressure.

Synthesis and characterisation of cycloaliphatic and aromatic amines based cardanol benzoxazines: A comparative study

In the current study, an attempt has been made to synthesize cardanol-based mono, bi, and tetra-functional benzoxazines by reacting various aryl amines and cycloaliphatic amines with cardanol (C) in the presence of paraformaldehyde under suitable experimental conditions by Mannich condensation. The resultant benzoxazines were characterized using several analytical techniques for their molecular structure, curing behavior, thermal stability, and hydrophobic nature. By using FTIR and 1H-NMR spectroscopic methods, the structure of benzoxazines was ascertained and assessed with benzoxazines based on aryl and cycloaliphatic amines. Using the DSC technique, the curing temperature of benzoxazines was investigated. Tetra-functional benzoxazines have a lower curing temperature than that of other mono- and bi-functional benzoxazines from the various systems of benzoxazines studied. It was also observed that the curing temperature of cycloaliphatic amine-based benzoxazines is also lower than that of aryl amine-based benzoxazines. The low temperature cure behavior of cycloaliphatic amine benzoxazine systems is due to the presence of a tertiary amine group, which contributes to a more basic nature than that of aryl amines. Thermal stability of polybenzoxazines was studied by TGA technique, among the different benzoxazine systems, the poly(C-ap-ddm) has higher char yield (30%) at 850 °C than that of other polybenzoxazines (poly(C-cha), poly(C-a), poly(C-mbch), poly(C-ddm), poly(C-ap-ipda), poly(C-ap-xyda) and poly(C-ap-mbch)). The value of water contact angle of cycloaliphatic amine-based benzoxazineswas found to be higher than that of aryl amines. Among the polybenzoxazines studied, poly(C-ap-mbch) possesses a higher value of water contact angle of 143°. Poly(C-aP-mbch) filled with 10 wt% SBA-15 (Santa Barbara Amorphous-15) possesses a value of lower dielectric constant (1.62) than that of poly(C-aP-ddm) (1.65). Data from different studies, cardanol based tetra functional benzoxazines can be used as sealants, encapsulants, adhesives, and matrices for microelectronics and automotive applications.

Solvent‐free synthesis of phosphate‐containing imidazole fluid for flame retardant one‐component epoxy resin with long pot life, low curing temperature and fast curing rate

AbstractThe design of flame retardant one‐component epoxy resin (EP) with long pot life, low curing temperature and fast curing rate has been challenging in the industry. Herein, we synthesized a phosphate‐containing imidazole fluid (TA) as the thermal latent curing agent of EP. Based on simple structural design, TA endows EP with excellent curing properties, storage properties, and flame retardant properties. According to DSC results, EP/TA systems exhibit low curing temperature and fast curing rate during operation. The rotary rheometer test confirms that the viscosity curve of EP/TA system maintains long‐term stability at 40°C. The X‐ray photoelectron spectroscopy (XPS) data reveals that TA releases imidazole intermediates and phosphorous compounds during curing. The former provides conditions for fast curing of EP, while the latter gives EP intrinsic flame retardant properties. With the addition of 20 wt.% TA, EP/TA‐4 achieves UL‐94 V‐0 rating and 28.5% of LOI value. The study of flame retardant mechanism shows that the flame retardancy of TA mainly comes from the protective effect of phosphorus‐rich char layer, the dilution effect of non‐combustible gas and quenching effect of phosphorous compound. Besides, due to no solvent involved, the synthesis strategy of TA is environmentally friendly, showing a great potential of industrial application.

Analysis of the synergistic effect of particle size of compound mineral admixtures on the hydration properties and porosity of Portland cement under low-temperature conditions

The mechanical properties of cement matrix composites can be severely affected at low temperatures, limiting the environment in which they can be used. To ameliorate this problem, the addition of silica fume and fly ash to the matrix is an effective method. This study used silica fume and flew ash as composite admixtures mixed with Portland cement to characterize the heat of hydration, mechanical properties, and microstructure of the composite cementitious materials. The test results show that the particle size distribution of fly ash and silica fume can influence the hydration reaction rate and the whole hydration process. By adjusting the particle size of the admixtures, the structural loosening and strength attenuation of the concrete caused by low temperatures can be improved. At low temperatures, when cement hydration is low, the coarser the particle size, the better the gradation between silica fume and fly ash and the better the filling of the pores. In addition, the specific surface area of silica fume was fixed at 19.1m 2 /g, and the correlation between fly ash particle size intervals in mineral admixtures was strongest in (30~40μm), (40~50μm) on the total porosity. Silica fume in the (>0.4μm) and (0.25~0.4μm) particle size intervals had the strongest correlation with porosity. Finally, a prediction model between the particle size interval of the mineral admixture and the total porosity of the concrete under standard and low temperature curing conditions was established. • The admixture effectively fills micro-pores • Methods for improving the strength of cementitious materials at low temperatures • The particle size distribution affects the rate of hydration and the hydration process • The hydration rate can be increased by improving the particle size of the admixture.

Low-temperature curable and strong soy protein/allicin adhesive with excellent mildew resistance via a free-radical-polymerization curing system

Epoxide modification effectively improves the water tolerance of soy protein adhesives, showing great potential in the commercial application as alternatives to petroleum-derived formaldehyde-based adhesives. However, epoxide-modified adhesives still present problematic limitations, such as poor mildew resistance and high hot-pressing temperature. In this study, a curing system based on radical polymerization was designed and developed to prepare soy protein adhesives, instead of building a traditional epoxide cross-linking structure. First, allyl glycidyl ether (G) was grafted onto a soy protein (SP) molecule to obtain soy protein with unsaturated double bonds ([email protected]). Allicin (A) was then used as a cross-linker to build a cross-linking structure ([email protected]/A) via free-radical polymerization to enhance the bond performance of the adhesive. Relative to that of pure SP adhesive, the wet shear strength (WSS) and dry shear strength (DSS) of plywood bonded with the [email protected]/A adhesive increased by 108% and 45%, reaching 1.08 MPa and 1.84 MPa, respectively, at 120 °C pressing temperature. Notably, the [email protected]/A adhesive showed superior antibacterial (Escherichia coli and Staphylococcus aureus) activity, high mildew resistance (35 d shelf life), good cytocompatibility, and biodegradability (30 d). Moreover, the WSS of plywood bonded with the [email protected]/A adhesive at 80 °C for 6 min and 20 °C for 72 h reached 1.08 MPa and 1.12 MPa, respectively, indicating the sufficient low-temperature curing ability of the resultant adhesive. Thus, building a cross-linking structure by free-radical polymerization can be extended to improve the performance of film composites, other adhesives, and engineering materials.

Low‐dielectric and low‐temperature curable fluorinated nano carbon/polyimide composites with 6‐aminoquinoline for end capping

AbstractOne challenge in the high‐performance dielectric material of polyimide (PI) is to obtain the excellent comprehensive properties at low curing temperature for advanced IC package. In this work, 6‐aminoquinoline (AQL) is introduced through covalent bonds for end capping to obtain a low‐temperature curable PI at first. The results demonstrate that with very limited introduce (2.76%) of AQL, the imidization index could reach as high as 1.01 at 200°C. Then, fluorinated nano carbon (FC) is further introduced resulting in the fluorinated nano carbon/polyimide (FCPI) composites, which effectively reduces the dielectric constant (1 wt%, 2.75 @ 1 MHz). Besides, the as‐prepared FCPIs also possess excellent thermal property of which FCPI‐0.3 exhibited the 5% weight loss temperature of 540°C and the glass transition temperature is also as high as 385°C. Furthermore, the tensile strength of the film is 127 MPa, the elongation at break is around 15.82%, and the Youngs' modulus is about 3.10 GPa proving the superior mechanical property. As a result, the successful preparation of the FCPI nanocomposites not only possess low‐temperature curing and low‐dielectric performance but also exhibit excellent thermal and mechanical properties, which shows a wide range of application prospects in the field of microelectronics for the advanced electronic package.

A benzimidazolyl‐substituted cyclotriphosphazene and its application in benzoxazine: Curing behaviors, thermal properties, and fire safety

AbstractIn this study, a well‐designed benzimidazolyl‐substituted cyclotriphosphazene (BICP) was used as a versatile additive to enhance the integrated performances of bisphenol A‐aniline based benzoxazine (BA‐a). Our results showed that the BA‐a/BICP systems possessed lower curing temperature than virgin BA‐a due to the catalytic action of tertiary amines in BICP. Moreover, the thermal resistance of BA‐a/BICP thermosets was better than that of BA‐a thermoset because of the rigid structure and high thermal stability of BICP. The introduction of BICP significantly enhanced the fire safety of BA‐a. For instance, the limiting oxygen index and UL‐94 rating of BA‐a/BICP‐11 sample with 11 wt% of BICP were up to 35.2% and V‐0. Compared with BA‐a, the total smoke production and peak smoke production rate of BA‐a/BICP‐17 sample with 17 wt% of BICP were reduced by 36.5% and 39.3%, respectively. The improved fire safety of BA‐a/BICP sample was mainly due to the condensed‐phase effect of BICP. This work provides a simple strategy for the development of advanced benzoxazine resins with low curing temperature, great thermal properties, and superior fire safety.

Bio-based polybenzoxazines coatings for efficient marine antifouling

It is a subject of great practical significance and challenge to endow marine coatings with both excellent bacterial killing and antifouling properties. In this work, a series of bio-based organic coatings demonstrating high antibacterial rate, strong algae-killing ability and satisfied real-sea fouling resistance were reported. The main-chain type benzoxazine (MCBZ) resins were prepared from the renewable daidzein and furfurylamine, together with polyetheramine, long aliphatic chain primary amines, and paraformaldehyde. By adjusting the amines, the overall performance of synthesized MCBZs could be manipulated. Results indicated that the low surface energy of obtained MCBZ could prevent fouling adhesion, and the synergistic effect of long alkyl chains and daidzein led to the efficient anti-fouling. Notably, besides the low curing temperature of 200 °C, excellent processing property and good substrate adhesion (5.02 MPa), poly (12-fu-MCBZ) also possessed 94.5 % antibacterial rate, 100 % algae-killing ability and excellent real-sea antifouling performance. This work provides us a new strategy to solve the marine biological pollution using renewable raw materials.

Recycling of glass fines and plastics in clay bricks at low temperatures

This research study aims to develop a new blend of clay bricks using varying percentages of recycled glass fines and recycled plastics in masonry bricks at low curing temperatures. Alkaline-activated solutions used in this research study were sodium hydroxide and sodium silicate. Having tried various percentages of alkaline activators, the suitable amount of alkaline activator was set at 20%. Brick samples were placed in an oven at a heating temperature of 50°C for 24 h (to reduce the moisture content), followed by a temperature of 155°C for 48 h. Earlier findings demonstrated that the moisture curing for the sample was 50°C for 48 h, and the heating temperature increased to 155°C for 24 h. A series of laboratory tests on the brick samples such as compressive strength, water absorption, linear shrinkage and scanning electron microscopy characterisation were carried out in this study. The examined curing conditions were 7 and 28 days. The results from the experiment revealed that the relationship between water absorption and curing conditions satisfied the minimum requirement of masonry bricks using recycled glass fines and plastics.

Kinetic evaluation of the crosslinking of a low-temperature cured biobased epoxy-diamine structure

Bis(oxiran-2-ylmethyl) adipate, synthesized by adipic acid, was investigated for its capability to polymerize at ambient temperature when blended with 1-(2-aminoethyl) piperazine. The object of the current work is associated to the kinetic analysis of the aforementioned epoxy-amine system, qualifying it as a potential candidate in the adhesion field of manufacturing industries. Polymerization kinetics were followed by Differential Scanning Calorimetry measurements, carried out both under dynamic and constant temperature conditions. The first gave rise to the total heat released through polymerization and the glass transition temperatures of the initial monomers (Tgo) and the crosslinked network (Tgoo), found to be 356 J/g, −69.7°C and 1.8 °C, respectively. The later revealed the effective crosslinking of the system at 25, 40 and 60 °C under reasonable periods of time. Cyclical dynamic-dynamic and isothermal-dynamic DSC experiments were further performed, giving results that follow the Di Benedetto equation, with Tgo and Tgoo values very close to the experimentally calculated. According to Vyazovkin isoconversional method applied on dynamic DSC measurements, the activation energy found to be independent of the conversion degree throughout the curing process and equal to 61.4 kJ/mol, indicating a single-step reaction. Various autocatalytic reaction models were selected to reproduce constant heating rate experiments, all displaying very accurate results, while fitting parameters from the aforementioned simulations, along with kinetic parameters derived from Vyazovkin method, were utilized for the estimation of isothermal curing predictions. Isothermal predictions were validated through comparison to both solely isothermal DSC measurements and data gathered in cyclical isothermal-dynamic experiments. Consequently, the nth order with an autocatalytic constant (Kcat) reaction model Cn was selected for the construction of a Time-Temperature-Transformation plot, revealing optimum curing conditions for the investigated temperature range. The superiority of the present epoxy thermoset system lies in the monomers' organically originated nature, along with its low-temperature curing cycle, enhancing environmental consciousness and saving energy for generations to come.

Eco-, economic- and mechanical- efficiencies of using precast rejects as coarse aggregates in self-compacting concrete

This paper investigates the eco-, economic- and mechanical- properties of self-compacting concrete (SCC) containing recycled coarse aggregates generated from prefabricated concrete rejects (PRA) or construction and demolition wastes (CRA). A total of 720 specimens from 36 unique SCC mixes are prepared and tested. The effects of the key parameters including, water-to-binder ratio (w/b), fly ash replacing ordinary Portland cement weight ratio, recycled coarse aggregate replacing natural coarse aggregate volume ratio, heat curing temperature, mixing method or the addition of steel fibers, on the fresh and hardened properties of SCC are experimentally explored. In addition to the experimental study, cradle-to-gate life cycle cost (LCC) analysis and life cycle assessment (LCA) of the SCC are carried out, where these are done through considering different levels of functional units. Based on the results of the experimental work, LCA and LCC, it is found that the PRA based concrete shows ecological-, environmental- and economic- benefits over conventional SCC with slightly compromised rheological and mechanical properties. When considering only the volumetric equivalence, it is observed that a higher w/b, the inclusion of higher amount of recycled coarse aggregate (RCA), or fly ash, or using a lower curing temperature can efficiently reduce the cost and environmental impacts of SCC with PRA. PRA concrete products are more eco-friendly and less cost intensive than those associated with the CRA ones due mainly to the shorter distance to transport PRA compared to CRA. Beyond the volumetric functional unit, the results of LCC and LCA show that, as indicated by carbon dioxide equivalent-, embodied energy- or cost- intensity, a higher w/b, the incorporation of higher content of RCA or fly ash, and using a lower curing temperature no longer benefit the eco-, environmental and mechanical performance of recycled coarse aggregate SCC (RCASCC) and the effect of curing temperature becomes ambiguous.

Novel multifunctional microcapsule and its cyanate ester resin composites with self‐healing ability and gamma radiation shielding ability

AbstractResin‐based composites used in spacecraft face risks from space debris and high‐energy charged particles during their long‐term service in the space environment. This work proposes a novel microcapsule (MC) and its cyanate ester (CE) resin‐based composites (CE/MCs) with self‐healing ability and gamma radiation shielding ability. The multifunctional epoxy/lead tungstate (EP@PWO) microcapsules are developed through self‐assembly method and in‐situ precipitation method. These microcapsules and curing agent 4,4′‐diaminodiphenylsulfone (DDS) are incorporated into the CE resin to form resin‐based composites with low curing temperature, self‐healing ability, and gamma radiation shielding ability. Various approaches including chemical characterizations (X‐ray diffractometer, fourier‐transform infrared, energy dispersive spectrometer), microscopy (optical microscope, scanning electronic microscope), and thermal analysis (differential scanning calorimeter, thermogravimetric analysis) are utilized to demonstrate the successful encapsulation of the EP resin by PWO shell and good thermal stability of this material. The mechanical property, self‐healing ability, and gamma radiation shielding property are investigated via fracture toughness test and using a NaI (Tl) spectrometer. In comparison with pure CE resin, the fracture toughness of the CE/MCs composites can increase by 66.5%, and the self‐healing efficiency can reach up to 56%, indicating that the microcapsules have good toughening and self‐healing abilities. The microcapsules and their composites also exhibit good gamma radiation shielding properties.

A strategy to construct low temperature curable copolyimides with pyrimidine based diamine

Low temperature curable polyimide (PI) films with outstanding mechanical and thermal properties are highly demanded in advanced packaging. Herein, a flexible diamine with pyrimidine named PMNH2 was synthesized and copolymerized with pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA), which showed significant influences on degree of imidization as well as the mechanical, thermal and dielectric properties of PI films. The copolyimide films have been proven almost complete imidization at 200 °C without any other curing accelerators. Meanwhile, the utilization of PMNH2 improved mechanical properties of copolyimide films greatly without severely sacrificing their thermal stability when curing at 200 °C. Copolyimide films containing 20 wt% and 30 wt% PMNH2 exhibited fairly high tensile modulus of 3.06 and 3.13 GPa, tensile strengths of 120 and 118 MPa, elongations at break of 61.1% and 20.1% and glass transition temperature of 352 and 342 °C, respectively. Moreover, the curable mechanism has been deeply probed by comparing the basicity and electron effects of the different diamine monomers via theoretical calculation, which showed an enlightening result that stronger basicity of pyrimidine-based diamine promoted the low temperature curing process, however the weaker electron-donating ability decreased the reactivity. Hence, both basicity and electron effects are key factors to be considered in designing new diamine monomer for low temperature curable PI films, providing opportunities of application in the advanced microelectronic package.

Bimetal-organic framework-derived nanorod-like FexNi1−x@C, P composites for electrochemical hydrogen evolution

Electrocatalytic decomposition of water using bifunctional catalysts is a potential method for clean hydrogen energy production. In order to solve the weakness of present catalysts, this study rationally designed a novel iron-nickel bifunctional electrocatalyst of FexNi1−x @C, P composites prepared by pyrolysis and phosphorus doping of a FeNi-bimetal-organic framework (FeNi-MOF). The innovative combination of FeNi bimetallic co-doping, low-temperature curing and phosphating has bred an excellent electrocatalyst for the hydrogen evolution reaction (HER) in alkaline solution. When the mass ratio of phosphate to FexNi1−x @C250–800 was 10:1, FexNi1−x @C250–800, P(10:1) showed the highest hydrogen evolution activity, obtaining a low 189 mV hydrogen evolution overpotential with a Tafel slope of 91.9 mV·dec−1 at 10 mA·cm−2 current density. Meanwhile, FexNi1−x @C250–800, P exhibited good stability during HER process. This work would open up a novel pathway for designing efficient and stable bifunctional electrocatalysts for water electrolysis as well as sustainable chemistry applications.

Dicyanoimidazole thermoset derived from [2.2]Paracyclophane: Synthesis, curing behavior and thermal properties

New functionalized cyclophane derivative (DCI-PcP) on the basis of [2.2]paracyclophane and dicyanoimidazole was designed and prepared. Fourier transform infrared spectrometer (FT-IR) suggested triazine and azaporphyrin can be observed in the cured product. DSC showed that DCI-PcP monomer revealed a melting point at 226 °C and exothermic transition at 312 °C. Rheological analysis showed that DCI-PcP possessed outstanding processability (melt viscosity <1 Pa s). DMA and TGA analysis indicated that cured resin showed excellent thermal properties and high glass transition temperature merely by a relatively low curing temperature of 300 °C.

Development of New Simple Compositions of Silver Inks for the Preparation of Pseudo-Reference Electrodes.

Silver materials are known to present excellent properties, such as high electrical and thermal conductivity as well as chemical stability. Silver-based inks have drawn a lot of attention for being compatible with various substrates, which can be used in the production uniform and stable pseudo-reference electrodes with low curing temperatures. Furthermore, the interest in the use of disposable electrodes has been increasing due to the low cost and the possibility of their use in point-of-care and point-of-need situations. Thus, in this work, two new inks were developed using Ag as conductive material and colorless polymers (nail polish (NP) and shellac (SL)), and applied to different substrates (screen-printed electrodes, acetate sheets, and 3D-printed electrodes) to verify the performance of the proposed inks. Measurements attained with open circuit potential (OCP) attested to the stability of the potential of the pseudo-reference proposed for 1 h. Analytical curves for β-estradiol were also obtained using the devices prepared with the proposed inks as pseudo-references electrodes, which presented satisfactory results concerning the potential stability (RSD < 2.6%). These inks are simple to prepare and present great alternatives for the development of pseudo-reference electrodes useful in the construction of disposable electrochemical systems.

Developing intrinsic halogen-free and phosphorus-free flame retardant biobased benzoxazine resins with superior thermal stability and high strength

Endowing intrinsic halogen-free and phosphorus-free flame retardant biobased benzoxazine resins (biobased content > 50 %) with ultrahigh thermal stability and high strength is still an important and challenging issue. Herein, starting from citraconic anhydride and para-aminophenol or ortho-aminophenol, two isomeric phenolic compounds containing citraconimide groups, pCI and oCI, were designed and synthesized, each of which then reacted with furfurylamine and paraformaldehyde to synthesize novel para-functionalized benzoxazine monomer (pCI–fa) or ortho-functionalized benzoxazine monomer (oCI–fa). Results show that pCI–fa and oCI–fa have excellent processability, represented by low melting point (pCI–fa: 150.0 °C, oCI–fa: 127.7 °C) and low curing temperature (pCI–fa: 217.6 °C, oCI–fa: 205.5 °C); moreover, interestingly, there is no Diels-Alder reaction between citraconimide and furan groups. The cured resin from pCI–fa or oCI–fa, coded as poly(pCI–fa) or poly(oCI–fa), has outstanding thermal resistance, tensile properties and flame retardancy. Especially, poly(pCI-fa) has better integrated performance than poly(oCI–fa), and the initial thermal decomposition temperature (Tdi) of poly(pCI-fa) is as high as 391 °C, obviously higher than the those of all halogen-free and phosphorus-free flame retardant biobased benzoxazine resins (the biobased content > 50 %) reported in SCI database by 3 August 2022. The mechanism behind the integrated performances was discussed.

Enhancing the hardened properties of blended cement paste cured at 0 °C by using alkali-treated ground granulated blast furnace slag

The use of high-volume ground granulated blast furnace slag (GGBFS) in cement-based materials significantly reduces CO2 emissions. Nevertheless, low curing temperatures are barriers to using environmentally friendly materials in winter construction works. This is mainly attributed to slow GGBFS's reactivity and blends' strength development due to the low alkalinity offered by the slow hydration rate of Portland cement (PC) at low temperatures. In this study, sodium hydroxide was employed to produce dry reactive pre-alkali-activated GGBFS (A-GGBFS), with an intention to increase the system's alkalinity and reactivity. The blended cement paste was prepared with 50% PC replacement with untreated and treated GGBFS, and cured constantly at 0 °C for 28 days. The A-GGBFS accelerated the hydration rate and enhanced the precipitation of hydration products. By adding an optimal NaOH content during the pre-alkali-activation process, the 3 and 28 days compressive strengths of paste increased by 41% and 37%, respectively, gaining a comparable 28 days compressive strength to that measured in a 100% PC-based binder. The microstructural assessments are consistent with compressive strength measurements.

Low temperature and moisture dependent curing behavior of selected wood adhesives

Curing kinetics of adhesives are a highly influencing factor in the manufacture of engineered wood products. Various parameters such as temperature and humidity can affect the reactivity of the adhesive and thus the curing speed and the resulting adhesive strength. This research investigates the influence of very high and low wood moisture content (MC) and low temperature on the curing kinetics of adhesives. The examined melamine-urea-formaldehyde (MUF) and one-component polyurethane (1C PUR) are used for structural timber products where mechanically stable and durable adhesive bonds are crucial. A rheometer set-up with conditioned poplar plates allowed the interaction of adhesive and substrate to simulate realistic curing conditions. Both adhesives, MUF and 1C PUR, had delayed gel times at lower temperatures and curing slowed down. For 1C PUR water absorption from the wood to the adhesive had a further important role on the curing reaction. For MUF, substrate temperature was the main influencing factor with much longer gel times at low temperatures compared to 1C PUR. Gel times increased to such an extent for a low MC of 5%, as the moisture required was not sufficiently available, that temperature influence became negligible. Resulting tensile shear strength supported the rheological results. Lower substrate temperature affected tensile shear strength of MUF negatively, while 1C PUR kept its tensile strength. Both adhesives retained their tensile properties after water immersion.

Filament stretching during parallel dispensing – A way to reduce silver consumption in SHJ metallization

In the field of silicon heterojunction (SHJ) solar cells, great successes on improving production processes have been achieved in the last years, however further improvements in the case of metallization are required to obtain higher market share. Therefore, lower Ag laydowns and higher process throughput are demanded. This study presents the impact of filament stretching on Ag-electrode shapes and laydown during temperature-controlled micro-extrusion, known as parallel dispensing. Dispensed metal grids ensure higher cell performances than screen-printed grids. It has been discovered that the maximum use of filament stretching benefits the solar cell efficiency due to narrower Ag-electrodes and less silver consumption. We have shown a low Ag laydown per 157.35 mm line of m Ag = 0.27 mg electrode -1 in average. An efficiency gain of Δη A = + 0.26% abs. has been demonstrated by the maximum usage of filament stretching. Further, a novel parameter that values the effectiveness of silver usage and enables the comparison between different printing processes has been introduced. We have demonstrated that silver is used more effectively by up to +74% rel. when the low-temperature curing paste is dispensed compared to screen printing because dispensed electrodes show an almost perfectly homogeneous shape. • Temperature-controlled filament stretching phenomenon during micro-extrusion obtains higher solar cell performances and higher throughput-rates. • Filament stretching phenomenon is process-specific and paste-specific. • Novel parameter is introduced to value the effectiveness of silver usage in printed structures. • Silver is used more effectively in dispensed lines than in screen-printed lines.