Curing System Research Articles

Novel Weigh-in-Motion Pavement Sensor Based on Self-Sensing Nanocomposites for Vehicle Load Identification: Development, Performance Testing, and Validation.

The development of the transportation industry has led to an increasing number of overloaded vehicles, which reduces the service life of asphalt pavements. Currently, the traditional vehicle weighing method not only involves heavy equipment but also has a low weighing efficiency. To deal with the defects in the existing vehicle weighing system, this paper developed a road-embedded piezoresistive sensor based on self-sensing nanocomposites. The sensor developed in this paper adopts an integrated casting and encapsulation technology, in which an epoxy resin/MWCNT nanocomposite is used for the functional phase, and an epoxy resin/anhydride curing system is used for the high-temperature resistant encapsulation phase. The compressive stress-resistance response characteristics of the sensor were investigated by calibration experiments with an indoor universal testing machine. In addition, the sensors were embedded in the compacted asphalt concrete to validate the applicability to the harsh environment and back-calculate the dynamic vehicle loads on the rutting slab. The results show that the response relationship between the sensor resistance signal and the load is in accordance with the GaussAmp formula. The developed sensor not only survives effectively in asphalt concrete but also enables dynamic weighing of the vehicle loads. Consequently, this study provides a new pathway to develop high-performance weigh-in-motion pavement sensors.

Synthesis and characterization of stereolithography3Dprinting fluorescent resin

AbstractIn this study, bisphenol A epoxy resin, 1,6‐Hexanediol diacrylate (HDDA), and 2,4,6‐Trimethylbenzoyl‐diphenylphosphine oxide (TPO) were utilized as a prepolymer, diluent, and photoinitiator, respectively, to prepare a light curing system with different amount of phosphor, which was used in place of conventional inorganic fillers. Phosphor was utilized to improve the precision of the material molded parts during the light curing process and enhance the mechanical properties of the molded parts owing to the ultraviolet (UV) absorption properties of phosphor, which prevented UV damage to the material, thus improving the light aging resistance and stability of the molded parts. Results revealed that the addition of 3% phosphor optimized the mechanical properties of the material (a maximum tensile strength of 42.43 MPa). Additionally, the material achieved the lowest linear (4.1%) and volumetric (0.58%) shrinkage at a phosphor content of 6%. This study provides a new insight into three‐dimensional (3D) printing resin for stereolithography and provides a reference for the improvement of 3D printing products.

Isothermal curing analysis and properties of ultra heat‐resistant polyimide composites by DMA method

AbstractThe isothermal curing process of T700 carbon fiber/P450 polyimide prepreg is characterized by dynamic mechanical analysis method and the gelation points are analyzed by torsional braid analysis theory. The growth mechanisms of the mechanical property at different constant temperatures are investigated by the relative mechanical growth rate of storage modulus and the curing kinetics models are established. The theories of Flory and Hsich are used to calculate the activation energy during the curing reaction of prepreg. The results indicates that the gelation times which are detected by the method of torsional braid analysis at 300, 310, 330, and 350°C were 293.7, 213.8, 104.1, and 45.4 min, respectively. The activation energies of curing reaction are calculated by Flory theory and Hsich theory, they are 112.35 and 119.96 kJ/mol, respectively. The feasibly of curing system 300°C × 4 h + 330°C × 2 h + 350°C × 2 h + 370°C × 2 h is verified by the mechanical properties and the heat resistance of polyimide composite.

The impact of accelerated maintenance system on alkali-activated mortar incorporating ultra-fine dredged sand

Alkali-activated concrete mixed with waste dredged sand (DS) is a new type of green concrete. In addition to reducing resource consumption and CO2 emissions, this approach is also cost-effective. Therefore, the ongoing research on its application in real industrial production is of great importance. This study examined the impact of the steam curing system on the mechanical properties and microstructure of alkali-activated dredged-sand concrete (AADSC). Different alkali equivalents and DS contents were used to produce AADSCs, and such AADSCs were cured using different steam curing schemes. The results show that steam curing significantly improves the early strength and 28-day strength under low alkali equivalent. The curing promotes the 1-day strength at 3% alkali equivalent from 2.1 MPa to 27 MPa after steam curing, and the 28-day strength increase was 7.8%. It is also found that the rise in compressive strength does not have a direct correlation with the energy consumption of steam curing. Even though the energy consumed by steam curing at 40 °C was 67% more than that at 60 °C, the 1 d strength under 40 °C steam curing was 7.5% lower. However, low-temperature steam curing retains more room for concrete strength increase. These results indicate the importance of a reasonable steam curing regime for the strength of AADSC.

Synthesis of 1‐Methyl‐4‐methoxyethyl‐1,2,4‐triazolium Dicyanamide and Its Plasticizing Behavior on HTPB/TDI Curing System**

AbstractIn this paper, a novel ionic liquid plasticizer, 1‐methyl‐4‐methoxyethyl‐1,2,4‐triazole dicyanamide ([MMET][DCA]), was synthesized and characterized. The effect of [MMET][DCA] on the viscous flow properties of HTPB was studied, and then the effect of [MMET][DCA] on the mechanical and thermal properties of the HTPB/TDI curing system was further explored. The results show that the hydrogen bond between [MMET][DCA] and HTPB has a significant effect on the viscosity of HTPB. In the HTPB/TDI curing system, when the di(2‐ethylhexyl)adipate (DEHA) was replaced by an equal amount of [MMET][DCA], the glass transition temperature did not change significantly; the tensile strength of the curing system increased from 0.436 MPa to 0.474 Mpa; the elongation at break increased from 506.2 % to 700.4 %, and the decomposition temperature at 5 % and 10 % mass loss increased by 32 °C and 70 °C, respectively.

Impact of carbamate formation on the surface tension of epoxy‐amine curing systems

AbstractEpoxy‐amine reactive systems, including their surface tension, have been studied due to their use and importance in composites and adhesives in laboratory and industrial applications. Understanding how the system's surface tension changes during curing could help target applications for tailored composites. Using the Wilhelmy plate method, surface tensions for epoxy‐curing agent systems were investigated under different environments. While the epoxy exhibited an expected negative temperature coefficient of −0.096 mN/m/°C, the curing agent exhibited a positive temperature coefficient of 0.073 mN/m/°C, which is due to the curing agent reacting with atmospheric CO2 to form carbamate through a zwitterion pathway and functional groups accumulating at the surface of the reacting systems. Carbamate formation results in a surface tension below that of the individual constituents in the epoxy‐amine curing agent system. Fourier transform infrared (FTIR) spectroscopy was used to verify in situ formation of carbamate, and by reducing the system's temperature, it was demonstrated that the system surface tension profiles displayed micellar surfactant‐like characteristics. FTIR was used to explore the difference in composition between the surface and the bulk, in particular carbamate formation at the surface, resulting in a lowering of the surface tension of reacting systems.

Synthesis and properties of silicone‐epoxy polymer with long silicone chain

AbstractSilicone‐epoxy polymers (SEP) with different n(SiH)/n(CC) ratios were synthesized through the hydrosilylation reaction of diallyl bisphenol A epoxy resin (DADGEBA) and hydrogen‐containing silicone oil (HS) with long silicone chain. The structure of SEP was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC), and the compatibility of the curing system was studied by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA and SEM results showed that after curing with epoxy curing agent, the compatibility of the curing system was excellent. The mechanical, bonding, and thermal properties of the cured product were also measured. The cured product exhibited superior thermal stability and mechanical properties. High toughness of SEP was provided by the long silicone chain, and high mechanical strength was provided by the cross‐linking networks. The maximum tensile strength was 15.64 MPa, the maximum elongation at break was 62%, and the maximum tensile lap‐shear strength was 8.89 MPa. The silicone‐epoxy polymers can be widely used in electronic packaging in the future.

Effects of Message Framing and Information Source on Consumers’ Attitudes toward an Amino Acid-Based Alternative Meat Curing System

Recently, meat scientists have developed an innovative amino acid-based alternative meat curing system (AAACS). However, consumer skepticism toward novel foods presents challenges regarding the acceptance of food innovations like the AAACS. Effective communication about this and other food technologies is critical. Our study was a 2 × 4 randomized factorial between-groups experiment that investigated how two peripheral cues-message frame and information source-impact attitudes toward the AAACS. We used Qualtrics to randomly assign participants to one of eight treatment groups. Each group viewed a different video about the AAACS. Then, all participants were asked about their attitudes toward the alternative meat curing system. Data were analyzed using a two-way multivariate analysis of variance (MANOVA). The two-way MANOVA determined concurrently the experimental effects of message frame and information source on information recall, trust, source expertise, source credibility, and anticipated consumption behavior. A significant MANOVA was followed up using Discriminant Function Analysis (DFA). A significant main effect was found for information source. The DFA revealed only one significant underlying function and that source expertise was the most powerful discriminating variable for information source.

Curing light-curable materials – sustainability benefits of using UV LEDs

Light-curable materials are employed in a range of applications in the automotive and aerospace industries, and in electronics manufacturing. They can be used to create form-in-place and cure-in-place gaskets that adhere to glass, plastics, ceramics and metals – sealing complex assemblies and preventing leakage of gas or liquids. In this article, Simon Gibbs, Technical Sales Executive, UK-based Intertronics – which supplies sealants, coatings, adhesives and dispensing equipment – explains the sustainability advantages of using curing systems that are based on ultraviolet light-emitting diode (UV LED) technology rather than UV spot-curing lamps that use a mercury arc bulb.

High-Branched Organosilicon Epoxy Resin with Low Viscosity, Excellent Toughness, Hydrophobicity, and Dielectric Property

Rapidly developing technology places higher demands on materials, thus the simultaneous improvement of materials' multiple properties is a hot research topic. In this work, a high-branched silicone epoxy resin (QSiE) was synthesized and applied to the curing system of bisphenol A epoxy resin (DGEBA) for modification investigations. When 6 wt% QSiE was added to the system, the viscosity dropped by 51.8%. The mechanical property testing results indicated that QSiE could significantly enhance the material's toughness while preserving good rigidity. The impact strength was enhanced by 1.31 times when 6wt% of QSiE was introduced. Additionally, the silicon skeleton in QSiE has low surface energy and low polarizability, which could endow the material with good hydrophobic and dielectric properties. This work provided a new idea for the preparation of high-performance epoxy resin additives, and provided a broad prospect for cutting-edge applications of epoxy resins.

An Easy Method to Determine the Effective Conductivity of Carbon Fiber Composites Using a Wall Perturbation Approach

Carbon-fiber-reinforced plastics (CFRPs) are of increasing popularity in a wide range of applications, and microwave curing promises significant reduction in processing times. However, for the design of an efficient microwave curing system, the composites' effective material parameters must be known. This work presents a measurement system using a wall perturbation approach with a coaxial cavity to determine the effective conductivity of a CFRP along the fiber direction.

Binary Resin-Curing Agent Systems for Fabricating Epoxy and Graphene Oxide-loaded Epoxy Films

In this research, diglycidyl ethers of bisphenol-A (BADGE) and polyethylene glycol (PEGDGE) were binarily cured with a mixture of diamine curing agents including isophorone diamine and polyethylene glycol diamine (PEGDA) in the absence/presence of aminated graphene oxide nanoplatelets (AGNPs, 0.5 wt.%). Four molar ratios of diglycidyl ethers and curing agents were used stoichiometrically in isothermal curing systems. The films prepared from the epoxy networks were entirely strong and pliable. All epoxy thermosets were evaluated using field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and diffuse reflectance-ultraviolet/visible spectroscopy (DR-UV/vis). The absorption coefficients of the epoxy and AGNPs-loaded epoxy materials decreased with increasing the molar ratio of PEGDGE resin and polyethylene glycol diamine curing agent. According to dynamic mechanical analysis no phase heterogeneity occurred in the structure of the prepared thermostats. When the thermoset materials were loaded by AGNPs filler, the peaks associated with alpha relaxations shifted to higher temperatures. Moreover, thermogravimetric analysis demonstrated that the thermal stability of the prepared epoxy thermosets slightly increased after the addition of the nanoplatelets. In addition, the thermal resistance of the prepared thermosets decreased to some extent by increasing the participation rate of monomers containing polyoxyethylene.

Preparation and properties of p-coumaric acid epoxy resin co-cured by a novel fluorinated diamine curing agent based on bisphenol AF in electronic materials

The epoxy resin based on p-coumaric acid and fluorine-containing diamine curing agent based on bisphenol AF were synthesized. The chemical structure was confirmed by FTIR, 1H NMR, 13C NMR and 19F NMR. Using HCA-EP as the epoxy resin matrix, methyl hexahydro phthalic anhydride as the curing agent and BAFFP as the co-curing agent, the performance differences were investigated for different curing systems, including HCA-EP-BAFFP-0/10/20/30. The results show that the increase of BAFFP content can improve the mechanical properties and dielectric properties of HCA-EP. In particular, HCA-EP-BAFFP-30 exhibited the highest impact and flexural strengths (7.14 KJ/m2 and 142 MPa), exceeding HCAP-EP-BAFFP-0 (2.9 KJ/m2 and 113 MPa) by 147% and 26%. In addition, HCA-EP-BAFFP-30 has the lowest dielectric constant and dielectric loss (Dk = 3.61 and Df = 0.00243 at 10 MHz). Therefore, we believe that HCA-EP cured with BAFFP has great potential for application in the field of electronic packaging materials.

Catalyst-free reprocessable, degradable and intrinsically flame-retardant epoxy vitrimer for carbon fiber reinforced composites

Fire risk and waste disposal are two major conundrums for carbon fiber reinforced composites (CFRCs), particularly for the thermoset-based ones; and it is beset with difficulties to solve them simultaneously. In this work, a phosphorus-containing diol with tertiary amine structure named 2-(bis(2-hydroxyethyl)amino)ethyl diphenylphosphinate (DPEA) was synthesized and successfully used as a transesterification modifier in an epoxy-anhydride curing system to construct epoxy vitrimers with dynamic ester networks, which further served as matrix for CFRCs. The phosphinate structure in DPEA was covalently bonded into the epoxy, endowing the vitrimers and CFRCs with intrinsic flame retardancy. With 0.30 mol% DPEA, both achieved a UL-94 V-0 rating with enhanced LOI value and reduced heat release. Meanwhile, thanks to the self-catalytic tertiary amine and highly reactive primary hydroxyls from DPEA, the transesterification within the dynamic ester networks was accelerated, endowing reprocessibility of the vitrimers as well as healing and recycling capacity of the relevant CFRCs. Killing two birds with one stone, this work provided a promising and feasible way to make sustainable and flame-retardant CFRCs with comprehensive properties.

Influence of curing system on static and dynamic mechanical properties of fly ash concrete

This paper investigates the effect of curing conditions on the static mechanical properties of fly ash concrete such as compressive strength and stress–strain behavior, and utilizes the split Hopkinson pressure bar (SHPB) device to characterize the dynamic mechanical responses of steam-cured concrete under different strain rates. Experimental results reveal that the strength of static concrete decreases with the increase of fly ash (FA) content and increases first and then decreases with the increase of steam curing temperature. The substitution of fly ash for cement reduces water consumption, weakens the hydration degree of cement, and affects the development of static concrete strength. The steam curing temperature plays a role in promoting cement hydration within a certain range, but high temperature leads to the destruction of concrete microstructure, thus inhibiting the development of strength and leading to the instability of concrete performance. The steam curing temperature effects on the dynamic compressive strength of concrete is receded with the increase of strain rate. When the steam curing temperature is constant, the dynamic compressive strength of concrete increases gradually with the increase of strain rate, and the influence of strain rate on the dynamic compressive strength of concrete is greater than that of steam curing temperature. The analysis of the scanning electron microscope (SEM) confirmed that the decrease of concrete strength was due to the change of temperature and fly ash content, which increased microstructure pores, thus affecting the development of strength. This study has important guiding significance to improve the safety of engineering facilities and adapt to the development of modern engineering towards heavy load, long span, and harsh environment.

Influence of accelerators and curing system composition on the cure characteristics, crosslinks structure and properties of acrylonitrile‐butadiene elastomer

AbstractThe goal of this work is to study the influence of the type of vulcanization accelerator and the quantitative composition of the curing system on the cure characteristics, morphology of elastomer network, crosslink density and physico‐chemical properties of acrylonitrile‐butadiene rubber (NBR) composites. Sulfur curing systems are investigated, which consist of various types of accelerators, that is, sulfenamide, guanidine and thiuram, applied in various proportions to sulfur. The type of accelerator and the sulfur/accelerator ratio significantly affect both the cure rate and the structure and number of crosslinks resulting from the vulcanization. The highest cure rate and the lowest content of polysulfidic crosslinks are exhibited by rubber composites with efficient (EV) curing systems due to the highest content of accelerators compared to semi‐efficient (SEV) and conventional (CV) systems. The structure of crosslinks strongly affect tensile properties and hardness of the vulcanizates as well as their solvent resistance, thermal stability and resistance to thermo‐oxidative aging.

Simultaneously improving fracture toughness and impact resistance of the rapid-curing CFRP via insert with MAM/EP resin film

In this research, a resin film of the MAM/EP blend curing system containing the triblock copolymer polymethyl methacrylate- b-poly-n-butyl acrylate- b-polymethyl methacrylate (MAM) was prepared. Such resin film was inserted into the interlaminar of rapid-curing composites to simultaneously improve both mode I, mode II fracture toughness and impact resistance. Both the Mode I and Mode II interlaminar fracture toughness of the composites were carefully investigated as a function of MAM content of the MAM/EP resin film (0, 20 and 40 phr@50 μm). A maximum improvement up to 109% and 70.2% on Mode I and Mode II fracture toughness, respectively was obtained with the introduction of the 40 phr@50 μm compared to the laminates with the introduction of the 0 phr@50 μm. Analysis of the fracture surfaces of the laminates elucidated that the distinctive improvement of the interlaminar fracture toughness could be attributed to the characteristic interlaminar structures of MAM in epoxy resin by self-assembly. The interleaved laminates also displayed an increase of 26.7% for the compression after impact (CAI) properties, and showed excellent impact resistance. The interlaminar shear strength (ILSS) of the composite was thereafter explored, which indicated slight enhancements to the strengths.

Preparation and characterization of high damping poly(epichlorohydrin) and poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) elastomers: I. Effect of curing system and blending on the damping properties

In this study, the effect of curing system on the rheological, network structure, mechanical and damping properties of poly(epichlorohydrin) (CO) and poly (epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO) elastomers and also blend of CO and GECO were investigated. To identify the curing system's effect on elastomers damping behavior, ethylene thiourea (ETU) and 2,4,6-Trimercapto-s-triazine (TMT) were used as curing agents. To determine the impact of blending on the damping properties of epichlorohydrin-based elastomers, the homopolymer of epichlorohydrin (CO-DP5245) and the terpolymer of epichlorohydrin (GECO-T3108) was mixed in equal proportions. It has been observed that with the use of TMT instead of ETU for both CO and GECO elastomers, the mechanical properties can be significantly increased without changing the damping behavior. CO-DP5245, which has a much higher long chain branching value than GECO-T3108, shows effective damping (tanδ > 0.3) at particularly high temperatures (between −1.7oC to +70oC), while GECO-T3108 has been found to show effective damping at low temperatures (between −41.6oC and − 8.3oC). By blending the homopolymer DP5245 and terpolymer T3108 of epichlorohydrin, it has been proven that elastomers with high damping properties can be easily prepared for moderate temperatures where these elastomers have relatively low damping properties. As a result of these studies, it has been proven that the mechanical, dynamic-mechanical, damping, and energy dissipation properties of ECH-based elastomers can be changed in a controlled manner by changing the type of curing agent by preparing compounds in the presence or absence of resin or by using high damping ECH homo and terpolymer blends.

Flexible canvas produced from uncured-natural rubber composites filled with high calcium oxide fly ash/cement hybrid filler

Concrete canvas (CC) is an attractive composite based on a combination of textile and cement, applying for the slope protection and ditch lining. However, there is no binder between both the materials and its high thickness causes a strong detachment of cement particles, and the complex designing of CC shapes is limited. Therefore, the possibility of incorporating natural rubber (NR) as a binder for extending the applications of cement-based composites has been considered. In the present work, NR composites with fly ash (FA) and cement (CM) are prepared through an internal mixer and a two-roll mill with a total filler concentration of 1000 phr. It can be found that, FA/CM hybrid filler is successfully adhered together through the NR matrix, and it promotes the flexible canvas composites with controlled thickness and provides complex shapes. The existing calcium oxide (CaO) present in the filler reacts with water molecules, and the NR composites become hardened and restrict the deformation and decomposition. The optimum ratio of FA/CM hybrid filler has been fixed at 300/700 phr, which has recognized as the product-like concrete canvas. Tensile properties, dynamic properties and thermal stability are improved upon the incorporation of hybrid fillers and its flexibility is found to be sustained on soaking with water. The structural changes are confirmed from the infrared spectrum which clearly explains the transformation of CaO to the CSH network structure in the NR composites. Un-crosslinked composites exhibited similar mechanical properties compared to the chemically crosslinked NR with sulfur curing system. Thus the composites can be used as the flexible canvas, although it has not been vulcanized. To clarify this statement, tensile properties, abrasion resistance and bending propagation of NR composites, NR vulcanizates and commercial concrete canvas are compared. The composites exhibited comparable properties with superior flexibility performance. Along with the waste utilization, the uses of FA, provides an opportunity of using FA/CM as the flexible canvas.

Cationic Polymerized Epoxy and Radiation Cured Acrylate Blend Nanocomposites Based on WS2 Nanoparticles—Part A: Curing Processes and Kinetics

Cationic photo-initiated and polymerized epoxies are characterized by good adhesion, high modulus, zero volatiles, low shrinkage and living polymerization characteristics. Radiation—cured acrylate resins are characterized by rapid initial curing with increased initial strength. The combination of radiation-cured acrylates and epoxies may present advantageous attributes. Thus, the system investigated is a hybrid epoxy/methyl acrylate and three different initiators for cationic polymerization of epoxies, the radical reaction of acrylates and the thermal initiator. When incorporating additives like opaque WS2 nanoparticles (NPs), absorption of the photo radiation takes place, which may lead to low photo activity. Curing kinetics measurements revealed that the absorbing/masking effect of WS2 was insignificant, and surprisingly, the level of curing was enhanced when the WS2 NPs were incorporated. FTIR results demonstrated that covalent bonds were formed between the inorganic fullerenes (IF-WS2) and the crosslinked matrix. Viscosity measurements showed a surprising reduction of five to ten times in the low-shear viscosity upon NPs incorporation compared to neat resins. It was concluded that the decrease of viscosity by the inorganic NPs, in addition to the enhanced level of conversion, has profound advantages for structural adhesives and 3D printing resins. To the best of our knowledge, this investigation is the first to report on a radiation-induced curing system containing opaque WS2 NPs that leads to an enhanced degree of curing and reduced shear viscosity.