Low Curing Research Articles

A coupled thermal-analytical and mechanical approach to investigate the behavior of bonded anchors cured at sub-zero temperatures

In post-installed connection in reinforced concrete structures, bonded anchors are commonly adopted when elevated mechanical performances are required. Such performances may be significantly impaired by adverse service conditions, above all temperature variations with respect to room ambient one. It is also generally acknowledged that the curing temperature may impact on the anchor performances, to the extent that all the main existing qualification procedures assess the anchor behavior when cured at different temperatures, in particular below zero Celsius degree. However, among the few investigations focusing on the impact of a low curing temperature on the long term behavior of an anchor, a low effort exists in addressing the relationship between the anchor mechanical behavior and the thermal properties of the bonding agent. The paper proposes a coupled thermal-analytical and mechanical approach to detect potential critical issues in the long term mechanical behavior of the anchor as a function of the adhesive behavior, as investigated by thermal or thermo-mechanical analyses. To the scope, a wide investigation on two adhesives is carried out comprising MDSC, DMA, pull-out and sustained load tests. On the basis of the obtained results, it is concluded that some thresholds in the variations of degree of conversion and phase transition temperatures may indicate a negligible impact of a low curing temperature on the anchor mechanical behavior, but also that existing qualification procedures are not able to capture the anchor behavior, when cured at low temperatures and subjected, during its service life, to temperatures higher than room ambient one.

A comparative study of alkanolamines and inorganic additives on the microstructure development of blast furnace slag blended cement at low curing temperature

The initial reactivity and strength development of blast furnace slag cement (BFSC) are crucial factors that increase its utilization. Therefore, it is important to select the most suitable accelerator. In this study, the impact of four accelerators, namely sodium sulfate (Na2SO4), calcium nitrite (Ca(NO2)2), triethanolamine (TEA), and diethanolisopropanolamine (DEIPA), on the hydration and strength development of BFSC at curing temperatures of 5 and 20 °C was investigated. Isothermal calorimetry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were conducted. The results revealed that Na2SO4 effectively enhanced early age strength by accelerating the hydration of the clinker and slag. Ca(NO2)2 is sensitive to temperature changes. At 20 °C, Ca(NO2)2 promoted the reaction of the aluminates and slag in the initial stage. However, the presence of slag inhibited clinker hydration, and the addition of Ca(NO2)2 exacerbated this effect, resulting in reduced strength at 5 °C. Indeed, the use of TEA and DEIPA at 0.02 % at 5 °C is not recommended. Complex interactions between TEA and Ca2+ may inhibit the formation of calcium hydroxide crystals, further inhibiting aluminate hydration. This may lead to low strength development at low curing temperatures such as 5 °C.

Recent Progress of Low Dielectric and High-Performance Polybenzoxazine-Based Composites.

With the rapid advancement of intelligent electronics, big data platforms, and other cutting-edge technologies, traditional low dielectric polymer matrix composites are no longer sufficient to satisfy the application requirements of high-end electronic information materials, particularly in the realm of high integration and high-frequency, high-speed electronic communication device manufacturing. Consequently, resin-based composites with exceptional low dielectric properties have garnered unprecedented attention. In recent years, benzoxazine-based composites have piqued the interest of scholars in the fields of high-temperature-resistant, low dielectric electronic materials due to their remarkable attributes such as high strength, high modulus, high heat resistance, low curing shrinkage, low thermal expansion coefficient, and excellent flame retardancy. This article focuses on the design and development of modification of polybenzoxazine based on low dielectric polybenzoxazine modification methods. Studies on manufacturing polybenzoxazine co-polymers and benzoxazine-based nanocomposites have also been reviewed.

Fiber-Reinforced Alkali-Activated Cements from Ceramic Waste and Ladle Furnace Slag without Thermal Curing

Alkaline-activated cement, as an alternative to conventional portland cement, is being increasingly studied due to its environmental advantages and engineering properties. However, research on the feasibility of using both uncommon precursors and curing at ambient temperature is still limited. This study aims to investigate the potential of ceramic wastes, specifically from brick and tile production and ladle furnace slag, as precursors in alkaline activated cement reinforced with polyacrylonitrile fibers cured at 20°C. Sodium silicate, in solution form, was used to activate the precursors, and three different fiber contents were tested, namely 0%, 0.5%, and 1%, by volume. Physical properties, such as capillarity and porosity, were assessed. Moreover, the mechanical behavior was thoroughly characterized by uniaxial compressive, flexural, and elasticity modulus tests. In addition, a thorough microstructural characterization, including scanning electron microscopy, X-ray energy dispersive analyzer, X-ray diffraction, and Fourier transform infrared spectroscopy was conducted at 14, 28, and 90 days. The results revealed that environmentally friendly alkali-activated binders were produced from wastes with limited industrial recycling possibilities. The mixture with 0.5% fibers was the one that presented better results, i.e., a flexural strength of 8.84 N/mm2 and compressive strength of ∼29 MPa at 90 days. The mechanical performance of this material is relevant, especially considering that a relatively low curing temperature was applied. The results also showed that calcium aluminum silicate hydrate (C-A-S-H) was detected as the main reaction product.Practical ApplicationsAlkali-activated cement has been identified as a potential alternative to traditional portland cement due to advantages such as the reduction of CO2 emissions to the atmosphere, and the conservation of natural resources, because wastes can be transformed into useful products. All over the world, ceramic materials are widely used in different types of construction, and significant amount (between 30% and 45%), end up as waste. Therefore, this study aims to show the possibility of reusing ceramic waste for the development of a fiber-reinforced alkaline activated cement composite with acceptable physical and mechanical properties that allow it to be used in non-structural applications; for example, bricks, tiles, partition walls, and other building materials. It also is a low-energy consumption process, because curing can be done at ambient temperatures. Finally, the obtained results, e.g., flexural strength of 8.84 N/mm2 and compressive strength of 29 MPa, open the door for several applications in the construction industry.

Efficient Photopolymerization of Dental Resin Composites Using the Photoluminescent Long Afterglow of Sr2MgSi2O7:Eu2+,Dy3.

Dental curing light with blue emission acts as the excitation source for the photopolymerization of the dental composite resin to achieve dental repairing. However, the current repair methods still suffer from a low monomer conversion degree and incomplete resin curing. In this study, novel dental resin composites (DRCs) were prepared by combining Sr2MgSi2O7:Eu2+,Dy3+ (SMSED), a photoluminescent material with a blue long afterglow, and dental resin composites. The curing depth, double bond conversion, elastic modulus, compressive strength, water absorption and solubility, and cytotoxicity were investigated systematically. The results suggest that adding 1 wt % SMSED to dental resin composites can maximize the curing depth and double bond conversion rate of DRCs and reduce its water absorption capacity without affecting the mechanical properties and biological toxicity. This work explores the practical applications of SMSED in dental resin composites, which provides an important reference for further improving the effect of dental caries repair.

(Invited) Improvements in Thermal Budget and Film Properties Using Low Pressure Cure Technology for Advanced 3D Integration Packaging

3D advanced integration with Fan-Out Wafer-Level Packaging (FOWLP) and Fan-Out Panel Level Packaging (FOPLP) offers multiple benefits: heterogenous chip design and stacking, increased interconnect density, and improved performance. However, it also brings new requirements for more compact form factors, low thermal budget materials and processing, and lower cost. The materials, process, and fabrication of heterogenous integration on redistribution layers (RDLs) consisting of metal and polymer dielectrics have become important enablers of the move to advanced packaging applications. To achieve the low-stress and low-cost benefits required by advanced integrated devices, thermal budgets must be reduced throughout the heterogenous integration flow -- including the dielectric curing step, which demands the use of low temperature processing and reduced cure times.In this presentation, the low temperature and low pressure thermal polymerization of dielectric polyimides used for redistribution layers (RDLs) is reviewed. Specifically, this presentation illustrates the significant impact of the low pressure cure process in reducing temperature (20° to 50° lower) and cure times (up to a 50% reduction) while providing better mechanical (elongation%, tensile strength, Young’s modulus), thermal (TG, Td 1%, Td 5%), and electrical (Dk, Df, dielectric breakdown strength - DBS) properties for different types of dielectric polyimides, including the Fujifilm LTC-9300 series, the Asahi BL-300 series, and the Toray LT-8300 and PW-1500 series. The post-curing polymerization ratio (FT-IR) and film stress were studied and are described. Finally, a proposed mechanism for the described dielectric polyimides’ polymerization under reduced pressure is discussed.Ongoing developments in design, materials, process and fabrication for FOWLP and FOPLP devices continue to drive progress in 3D heterogenous integration. This study of thermal processing of dielectric polyimides at low pressure and shorter time demonstrates a promising technique to improve overall process flow by reducing thermal budget, stress, and cost.

Boosting flowability and curing reaction of ultra-fine powder coatings using facile-fabrication Al2O3/C4H6N2 nanocomposite

In recent years, the utilization of fiber-reinforced plastic (FRP) parts has become increasingly widespread in various industries, including aerospace, marine, and automobile industries, as a consequence of their potential to enhance energy efficiency and reduce weight. However, the challenge of meeting the demand for eco-friendly and high-quality coatings on FRPs persists. Ultra-fine powder coatings have emerged as a promising solution, offering a cost-effective and high-quality alternative to traditional solvent paints and emitting zero volatile organic compounds (VOCs). Despite their potential benefits, two main obstacles to applying ultra-fine powder coatings on FRPs exist: low powder flowability and high curing temperature. To address these obstacles, we fabricated a nanocomposite comprising Al2O3 and C4H6N2 (2-methylimidazole) and evaluated its functional properties in ultra-fine powder coatings. Our findings demonstrate that the addition of 0.3–0.5 wt% of the nanocomposite significantly improved static and dynamic powder flowability to qualified grades and effectively boosted curing reactions, consequently reducing the curing temperature by 20 °C. Furthermore, the film thickness decreased by approximately 50 %, and final appearance, roughness and water resistance were enhanced significantly. Overall, our results suggest that the nanocomposite boosted the flowability and curing reaction of the ultrafine powders effectively and successfully obtained thin and qualified films on FRP substrates, which holds great promise for expanding the application of ultra-fine powder coatings in the coating industry.

Low‐Energy Driven Ring‐Opening Behavior of Benzocyclobutene Derivatives

Comprehensive SummaryIt's urgent to develop benzocyclobutene (BCB)‐based polymers with low curing temperature for temperature‐sensitive applications such as liquid crystal displays (LCDs) and flexible electronics. Herein, the effect of substituents on the ring‐opening behavior of BCB derivatives was investigated. The ring‐opening activation energy barriers (ΔGA) of BCB derivatives with one or two substituents on the four‐membered alkyl ring were systematically calculated using the B3LYP function. Both mono‐ and di‐substituted BCBs adopted the conrotatory ring‐opening process, obeying the Woodward‐Hoffmann's Rules upon heating. The mono‐/di‐substituted BCBs exhibited 8.2%—69% lower ΔGA compared with BCB, attributed to the electronic effects of the substituents. Disubstituted BCBs with both electron‐donating and electron‐withdrawing groups, e.g., 1‐NH2‐8‐NO2‐BCB, demonstrated the lowest ΔGA. In addition, BCB derivatives with amide/ester/acyloxy group modified on C1 position were synthesized as model molecules, and their ring‐opening temperature can be decreased by 20 °C compared to the unsubstituted one, also consistent with our calculation results. This work combined theoretical calculation methods with experimental results to provide valuable insights into the design and synthesis of BCB derivatives and next‐generation BCB functional packaging materials with low ring‐opening temperature.

Curing reactions of liquid hydridopolycarbosilanes with vinyl or allyl groups

AbstractLiquid hydridopolycarbosilanes (LHPCS) with vinyl or allyl groups have attracted significant research interest due to their low curing temperature and high ceramic yield. In this study, allyl‐terminated hydridopolycarbosilane (AHPCS) and vinyl‐terminated hydridopolycarbosilane (VHPCS) were prepared by the Grignard coupling reaction and characterized by NMR and Fourier infrared spectroscopy (FTIR). And the curing reactions of AHPCS and VHPCS with or without initiators (dicumyl peroxide [DCP], tert‐Butyl peroxybenzoate [TBPB]) or Karstedt catalyst were investigated using differential scanning calorimetry and in‐situ FTIR. The main curing reactions of VHPCS and AHPCS are the double bond free radical polymerization and hydrosilylation reaction, respectively. The addition of initiators and Karstedt catalyst could promote the corresponding curing reaction and increase the weight residual at 1000°C. The thermal properties of the cured resins were investigated by thermogravimetric analysis. The addition of initiators and catalyst could significantly increase the weight residual of VHPCS and AHPCS, respectively. The addition of the Karstedt catalyst increased the weight residual of AHPCS from 75.6% to 83.1%. In addition, the addition of TBPB and DCP increased the weight residual of VHPCS from 74.2% to 81.2% and 80.2%, respectively.

Improvement of microporous structure and impermeability of cement mortars using fly ash and blast furnace slag under low curing pressures

Low air pressures in high plateau will degrade the impermeability and air void structure of cement mortars. In this study, the feasibility and mechanism of fly ash (FA) and ground granulated blast furnace slag (GGBFS) improving the microporous structure and impermeability of cement mortars under low curing pressure were investigated. Results showed that the slag significantly improved the impermeability and air voids distribution of cement mortars, while the fly ash did not benefit the impermeability, as well as the air void in mixed mortars. The heat releasing rate and hydration product composition of the slag mixed paste were superior to that of the FA. The reduction of Ca(OH)2, gentler hydration rate, and filling effect of fine slag particles are believed to contribute to the improvement of impermeability. The water vapor isotherm sorption test demonstrated that low curing pressure changed the surface characteristics of hydrates, and inhibited the adsorption and desorption process (including the capillary condensation process and ink-bottle effect) with the range of relative humidity (RH) > 40%. Meanwhile, the titting parameters variation certified according to Guggenheim-Anderson-deBoer (GAB) model certified that the addition of slag achieved the same result as increasing curing pressure. Moreover, futher analysis showed that if partial OPC was replaced by slag, it could befinit energy consumption, CO2 emission, and materials cost compared with pure OPC. This study provides an initial evidence for applications of slag in low air pressure conditions.

Low‐temperature synthesis of HfC/HfO2 nanocomposites from a commercial single‐source precursor

AbstractA liquid‐phase polymer‐to‐ceramic approach is reported for the synthesis of hafnium carbide (HfC)/hafnium oxide (HfO2) composite particles from a commercial precursor. Typically, HfC ceramics have been obtained by sintering of fine powders, which usually results in large particle size and high porosity during densification. In this study a single‐source liquid precursor was first cured at low temperature and then pyrolyzed at varying conditions to achieve HfC ceramics. The chemical structure of the liquid and cured precursors, and the resulting HfC ceramics was studied using various analytical techniques. The nuclear magnetic resonance and Fourier transform infrared spectroscopy indicated the presence of partially hydrated hafnium oxychloride (Hf–O–Cl·nH2O) in the precursor. Scanning electron microscopy of the resulting HfC crystals showed a size distribution in the range of approx. 600–700 nm. The X‐ray diffraction of the pyrolyzed samples confirmed the formation of crystalline HfC along with monoclinic‐HfO2 and free carbon phase. The formation of HfO2 in the ceramics was significantly reduced by controlling the low‐temperature curing temperature. Pyrolysis at various temperatures showed that HfC formation occurred even at 1000°C. These results show that the reported precursor could be promising for the direct synthesis of ultrahigh temperature HfC ceramics and for precursor infiltration pyrolysis of reinforced ceramic matrix composites.

Pullout behavior of steel fiber embedded into cement matrix under low humidity curing

An experimental was presented in this article to investigate the impact of the low relative humidity (low RH) on the pullout properties of the straight and hooked-end fibers embedded into cement matrices. It was shown that decrease in curing RH results in a reduction in the interfacial carrying capacity and the pullout energy absorption ability, owing to the microstructure of the fiber-matrix ITZ deteriorating as the humidity decreased for all types of fibers. Besides, a novel model was developed to simulate the bond-slip behaviors of the steel fiber-matrix interface under low RHs, and a theoretical method was carried out to estimate the parameters in the model. Furthermore, various analytical models were proposed based on the bond-slip model to simulate the pullout behaviors of the steel fibers embedded in matrix under low RHs, and the validation results revealed that the suggested model is consistent with the experimental data.

Light-settable polybenzoxazines for marine antifouling coatings

Building benzoxazine coatings on large equipment is of great practical importance and challenging. In this work, a main-chain type benzoxazine (MCBZ) resin that can be quickly shaped under UV light was successfully synthesized and can be directly coated into a film. In addition, it had a wide processing window, low curing temperature, excellent static antifouling effect, and sterilization effect. The d12-DHBP-MCBZ resin was prepared from dodecamine, which ensured the sterilization effect, and 4, 4′-dihydroxy-benzophenone provided the photoinitiation sites and activated the oxazine ring. By adjusting the ratio of d12-DHBP-MCBZ to TMPTMA, hydrophilic benzoxazine coatings can be prepared, suitable for fouling-resisting coatings. The results indicated that the d12-DHBP-MCBZ resin could be quickly shaped under UV light, and the post-curing temperature was only 140 °C. In particular, the coatings' excellent hydrophilicity can effectively prevent fouling organisms' adhesion and improve the static antifouling effect. It was worth mentioning that Poly (BZ/20 %TMA) coating achieved a high sterilization performance of >99 %. These works gave us a new strategy to solve application problems of benzoxazine coatings on large equipment and antifouling coating efficiency problems.

Synthesis and Characterization of an Environmentally Friendly Phenol-Formaldehyde Resin Modified with Waste Plant Protein.

To develop a lower-cost, excellent-performance, and environmentally friendly phenol-formaldehyde (PF) resin, soybean meal was used to modify PF resin, and soybean meal-phenol-formaldehyde (SMPF) resins were prepared. This reveals the effect of soybean meal on the structural, bonding, and curing properties of PF resin, which are very important for its applications in the wood industry. The resins' physicochemical properties and curing performance were investigated, showing that SMPF resins have higher curing temperatures than PF resin. The Fourier transform infrared spectroscopy results indicated that a cross-linking reaction occurred between the amino groups of soybean protein and the hydroxymethyl phenol. Moreover, with the addition of soybean meal, the viscosity of SMPF increased while the gel time decreased. It is worth mentioning that SMPF-2 resin has favorable viscosity, short gel time, low curing temperature (135.78 °C), and high water resistance and bonding strength (1.01 MPa). Finally, all the plywoods bonded with SMPF resins have good water resistance and bonding strength, which could meet the standard (GB/T 17657-2013, type I) for plywood. The optimized SMPF resins showed the potential for application to partially replace PF resin in the wood industry.

Polyurethane powder coatings with low curing temperature: Research on the effect of chemical structure of crosslinking agent on the properties of coatings

Polyurethane powder coatings with low curing temperature: Research on the effect of chemical structure of crosslinking agent on the properties of coatings

Ultra low-temperature fabrication of hollow glass microspheres and polysilazane coating for enhanced thermal protection of carbon/epoxy composites

This investigation was aimed to develop high-temperature resistant coatings suitable for carbon fiber-reinforced epoxy composites at ultra low preparation temperatures. In the organic-inorganic coating, hollow glass microspheres were chosen as the filling phase, and polysilazane was selected as the film-forming material. Fourier transforms infrared spectra showed that polysilazane can be cross-linked and solidified at low temperatures, which provided the possibility for protecting the substrate from high-temperature damage. By modifying the surface of hollow glass microspheres, the coating dispersions were able to maintain good stability within 120 min. The coating exhibited good thermal vibration resistance and could stand at 220 °C for 30 min after 6 cycles without obvious cracking and peeling. After the static thermal test, the coated composites still maintained a flexural strength of 603.7±19.2 MPa (retention rate can reach 86.6%) at 250 °C, which was higher than that (593.3±14.8 MPa) of uncoated samples at 190 °C. The results indicated that the coating has the advantage of low curing temperature, convenient operation, and excellent thermal protection performance, which could further expand the potential application of carbon fiber-reinforced epoxy composites in firefighting unmanned aerial vehicles, hypersonic missiles, and other fields.

Mechanical and microstructural investigations on the low-reactive copper mine tailing-based geopolymer activated by phosphoric acid

This paper presents an experimental study on low-reactive copper mine tailings (MT)-based silicate-aluminate-phosphate (SAP) geopolymer activated by phosphoric acid. First, the effect of liquid to solid ratio (L/S) (0.4, 0.5, and 0.6), acid concentration (30, 40, and 50 wt%), curing temperature (45, 60, 75, and 90 °C), and curing time (3, 7 and 28 days) on the unconfined compression strength (UCS) of the MT-based SAP geopolymer was investigated. Then, to better understand the effect of the different factors, microscale analyses using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) techniques were performed on the MT raw material and the tested SAP geopolymer samples. Finally, durability and leaching tests were carried out on cylindrical samples to investigate the integrity of the SAP geopolymer samples in exposure to harsh environments and the leaching of heavy metals from the SAP geopolymer samples. The results show that the optimum L/S ratio and acid concentration are 0.4 and 40 wt%, respectively, giving an optimum Al/P ratio of 2.21, for the MT-based SAP geopolymer. The geopolymerization of MT at the low curing temperature 45 °C is slow but continuous with time; too high a curing temperature (≥75 °C) adversely affects the geopolymerization process and even induces depolymerization and cracking after a long curing time. Therefore, a curing temperature of 60 °C can be used for the production of the MT-based SAP geopolymer. Moreover, the MT-based SAP geopolymer shows good durability and effective solidification/stabilization of heavy metals within the MT in both neutral and acidic environments.

Design and fabrication of high-performance injectable self-setting trimagnesium phosphate

Magnesium phosphate bone cement has become a widely used orthopedic implant due to the advantages of fast-setting and high early strength. However, developing magnesium phosphate cement possessing applicable injectability, high strength, and biocompatibility simultaneously remains a significant challenge. Herein, we propose a strategy to develop high-performance bone cement and establish a trimagnesium phosphate cement (TMPC) system. The TMPC exhibits high early strength, low curing temperature, neutral pH, and excellent injectability, overcoming the critical limitations of recently studied magnesium phosphate cement. By monitoring the hydration pH value and electroconductivity, we demonstrate that the magnesium-to-phosphate ratio could manipulate the components of hydration products and their transformation by adjusting the pH of the system, which will influence the hydration speed. Further, the ratio could regulate the hydration network and the properties of TMPC. Moreover, in vitro studies show that TMPC has outstanding biocompatibility and bone-filling capacity. The facile preparation properties and these advantages of TMPC render it a potential clinical alternative to polymethylmethacrylate and calcium phosphate bone cement. This study will contribute to the rational design of high-performance bone cement.

Polyurethane powder coatings with low curing temperature: Research on the effect of chemical structure of crosslinking agent on the properties of coatings

This research presents the effect of the chemical structure of new crosslinking agent on the properties of powder coatings. A method of synthesis of blocked polyisocyanates and the formation of powder coatings with low curing temperature are presented. In the synthesis of blocked polyisocyanates (bPIC) TDI, glycerine, xylitol, polyethylene glycol, polysiloxane KF-6000 and butanone oxime were used. By using FT-IR, the chemical structure of the obtained blocked polyisocyanates was confirmed. The thermal behavior and the deblocking process were investigated by means of TGA, DSC and DMA. Performance tests were performed on the obtained coatings to assess their hardness, adhesion to steel, roughness, gloss, scratch resistance, and water contact angle. An accelerated weathering test was also conducted to examine the coatings' resistance to weather conditions (UV radiation, water).

(Invited) Improvements in Thermal Budget and Film Properties Using Low Pressure Cure Technology for Advanced 3D Integration Packaging

This paper reviews the low-temperature and low-pressure thermal polymerization of dielectric polyimides that are used for redistribution layers (RDLs). Specifically, this presentation illustrates the significant impact of the low-pressure cure process in reducing cure temperature (by 20° to 50°C) and cure times (by as much as 25%) while providing better imidization ratio, film stress, mechanical (elongation %, tensile strength, Young’s modulus), thermal (Tg, Td5%, CTE), and electrical (Dk, Df) properties for different types of dielectric polyimides. Among the many low-temperature polyimides we have studied, we focus here on the Fujifilm LTC-9300 series (LTC-9310 and LTC-9320) and the Asahi BL-300 series. The excellent post-curing polymerization ratio (as measured by FT-IR) and film stress results are also described. Finally, a proposed mechanism for these dielectric polyimides’ polymerization under reduced pressure is discussed.