Curing System Research Articles

Influence of Mixed Sulfur and Peroxide Curing Systems on Cross‐Linking and Properties of Rubber Compounds Based on EPDM

AbstractIn this work, sulfur vulcanization system, peroxide vulcanization system, and combined sulfur and peroxide curing systems are applied for cross‐linking of rubber compounds based on ethylene propylene diene monomer rubber. The goal is to investigate the influence of curing system composition on cross‐linking and properties of rubber formulations. The combination of both vulcanization systems in cross‐linking of rubbers combines the pattern of carbon–carbon linkages and sulfidic bridges, which gives the real presumption to modify physical–mechanical properties of final vulcanizates. The results reveal that the combination of vulcanization systems affects the curing characteristics, cross‐link density as well as physical–mechanical properties of tested materials. In comparison with vulcanizates cured only with sulfur or peroxide system, rubber compounds cross‐linked with mixed sulfur and peroxide curing systems exhibite higher tensile strength and elongation at break.

Water-resisting performances and mechanisms of magnesium phosphate cement mortars comprising with fly-ash and silica fume

Design of hydraulic structures using magnesium phosphate cement (MPC) composites is a still challenging issue because of the volume instability of MPC matrices in water environment. In this research, an attempt was taken to progress the water-resistance performance of MPC blended with fly ash (FA) and silica fume (SF). The FA was introduced as one third of magnesia in the mortar specimens, where SF dosages were 5%, 10% and 15% as the substitution of magnesia. Physico-mechanical and microstructural properties of mortar samples were examined considering the air and water curing systems. The analytical results bared that compressive strength (CS) and flexural strength (FS) of specimens composed with MPC + FA+5%SF were observed about 25% higher as compared to control. Both strength properties having the optimized content of SF (i.e. 5%) was reduced close by 3–4% in water system, whereas the pure MPC matrix exhibited around 20% less at 28 d. In addition, mass loss (ML) was found nearby 1.56% at 28 d. Moreover, SEM, EDS and XRD tests were detected that intermediate minerals namely Berlinite, Mullite, Lizardite and Enstatite were formed in the microstructures, and micro-cracks and micro-pores were significantly reduced. Consequently, compact microstructure was obtained that resulted the well water-resistant of proposed MPC mortar. The outcomes of this research might be a potential information for constructing the MPC-based water structures.

Rapid ultraviolet curing of epoxy acrylate films with low refractive index and strong interfacial adhesion

The low refractive index of coatings for optical fiber helps to reduce the information loss in optical transmission. However, previous studies focused on decreasing refractive index by adding fluorine-containing monomers into the curing system, ignoring the effect of the functional monomer on the adhesion of the coating onto the optical fiber. To address this limitation, this paper established a rapid light-curing system that reduced the refractive index of the cured film while enhancing the interfacial adhesion between optical fiber and coatings. Based on the Lorentz equation, the low molar refractive index of fluorine atoms was utilized to reduce the refractive index of the light-cured films. Simultaneously, the bisphenol A epoxy acrylate, as an oligomeric main resin, was highly active in cationic photoreaction and can effectively enhance interfacial adhesion. Moreover, the methyl methacrylate was applied to increase the compatibility of epoxy resins and fluorine-containing monomers. The experimental data indicated that the refractive indices of the cured films with fluorine-containing monomers were adjustable from 1.4930 to 1.5576, and the light transmittance was greater than 90%. The curing rate of the sample containing 11.3 wt% of fluorine (F-11.3%) was 26.26 J∙cm−2, which was 28.6% higher compared to that without fluorine. Intriguingly, in terms of molecular dynamics simulations, the interfacial interaction between fluorine-containing monomers and SiO2 crystalline surfaces was modeled. As a result, the interfacial energy between the curing system F-11.3% and SiO2 was −1879.91 kcal/mol, which was 1.16 times higher compared with the cured system without trifluoromethyl methacrylate, proving that increasing the fluorine content is profitable to promote the adhesion force in this system. This paper provided a design method of optical fiber coatings with strong interfacial adhesion, low refractive index and rapid light curing.

Influence of curing system composition and aging on the performance of rubber magnets based on NBR and EPDM

ABSTRACT Rubber magnetic composites were fabricated by incorporation of strontium ferrite in constant loading level in ethylene propylene diene monomer rubber and acrylonitrile butadiene rubber. Different curing additives based on peroxide, sulfur and combined sulfur/peroxide systems were introduced for cross-linking of rubber matrices. Both sulfur and peroxide curing systems lead to the formation of cross-links with different length and structure, which subsequently results in different properties of rubber products. Moreover, due to various bonding energies of the formed cross-links, rubber articles exhibit different propensity to degradation factors as to thermo-oxidative aging. Therefore, the work was aimed at the investigation of curing system composition and aging on cross-link density and properties of rubber magnetic composites. The achieved results point out to close correlation between cross-link density and physical-mechanical characteristics with exception of tensile strength, which showed increasing tendency with increasing amount of peroxide in combined vulcanization systems. It can be stated that no significant changes in physical-mechanical and magnetic properties were recorded during aging.

Optimization of Mineralization Curing System for Efficient and Safe Utilization of Steel Slag Wastes

Optimization of Mineralization Curing System for Efficient and Safe Utilization of Steel Slag Wastes

Heterogeneous Coordination Environment and Unusual Self-Assembly of Ionic Aggregates in a Model Ionomeric Elastomer: Effect of Curative Systems

Heterogeneous Coordination Environment and Unusual Self-Assembly of Ionic Aggregates in a Model Ionomeric Elastomer: Effect of Curative Systems

Impact properties of Ultra High Performance Concrete (UHPC) cured by steam curing and standard curing

In order to study the effects of steam curing system, silica fume and steel fibre on the impact resistance of UHPC, the split Hopkinson pressure bar tests were used in the study. Two curing regimes were considered in the test, steam curing at 90 ℃ for 3 days and standard curing. The amount of silica fume replacement of cement was 0 % and 20 %, and the volume content of steel fibre was 0 % and 1 %. In order to study the crystal and pore structure of UHPC, XRD and MIP tests were utilised.The test results demonstrate that the failure mode of UHPC after SHPB test can be studied by the concept of the fineness modulus of residue (). Silica fume has little influence on the integrity of UHPC after impact, while steam curing and steel fibre improves the integrity of the UHPC after impact. The increasing of Mr value of UHPC under steam curing at strain rates around 80 s−1 is 26.0 %.The Mr value of UHPC with the addition of steel fibre was greater than 1.25 times that of plain concrete. Steel fibre can lead to the redistribution of the internal stress of UHPC after impact, and change the propagation paths of cracks, so as to improve the energy absorption capacity of UHPC. Under dynamic load, the ultimate strength of UHPC increased by 10.6 %, 15.7 % and 25 % after steam curing at 90 ℃ for 3 days, silica fume (under steam curing condition) and steel fibre, respectively. E, DIF, and EA of UHPC all have a significant strain rate effect. Strain rate sensitivity of UHPC prepared by steam curing for 3 d is stronger than that prepared by standard curing for 28 d, especially for the concrete mixed with silica fume and steel fibres.The hydration degree of UHPC after steam curing for 3 d using the steam curing system in this study was slightly higher than that of standard curing for 28 d. Steam curing can reduce the porosity by 34.4 %, while silica fume can reduce the porosity by 15.3 % compared to benchmark group under steam curing. The addition of silica fume changes the probable diameter of UHPC while steam curing reduces it.

Improvement of Mechanical Properties and Microstructure of Cementitious Materials in a Hot-Dry Environment

The hot-dry environment in high geothermal tunnels negatively affects the development of properties of cementitious materials. In order to improve the mechanical properties of cementitious materials in such environments, a proper curing system was developed, the material compositions were taken into account, and the related mechanism was analyzed by microscopic tests. The results showed that the mechanical properties and microstructure of cementitious materials can be improved effectively by adopting film curing and an adequate dosage of fly ash in a hot-dry environment. Compared with standard curing, a hot-dry environment accelerates the evaporation of water in fresh cementitious materials and the early hydration rate of cementitious materials, resulting in lots of unhydrated cement particles and an uneven distribution of hydration products, seriously decreasing the properties of the cementitious materials. Film curing keeps the water from evaporating and ensures enough water is available for hydration at an early age. The addition of FA reduces the amount of cement clinker and decreases hydration reaction rate in high temperature environments at an early stage, avoiding the unevenness of hydration products. High temperatures stimulate the pozzolanic activity of fly ash and promote the degree of secondary hydration reaction, producing more hydration products, as well as contributing to the improvement of the mechanical properties and microstructure of cementitious materials. In this study, in a hot-dry environment, the mechanical properties of mortar with 25% fly ash and 2–3 d film curing are better than those of other experimental groups, including those of standard curing.

Performance Evaluation of Green Cushion Gum Composite Formulated Based on Hybrid Filler and Curing System

Cushion gum is a type of rubber composite material used as adhesive in the manufacture of retread tires. Therefore, cushion gum should have good processability and mechanical characteristics, particularly tensile property, and adhesion strength. The effect of hybrid filler and curing system on the performance of green cushion gum composite was investigated to determine the appropriate green cushion gum formula designed at a laboratory scale. The content of CB N330/lignin in hybrid filler was arranged at 40/10 phr and 50/10 phr. Meanwhile, the curing system was performed semi-efficient (CBS/S 1.6/1.6 phr) and conventional (CBS/S 1.6/2.2 phr). Green cushion gum composite was also formulated using pine tar oil as a bio plasticizer. Referred to the curing characteristic and mechanical property test result, it showed that green cushion gum composite formula coded by RF1 which composed of CB N330/lignin as 50/10 phr and applied conventional curing system which ratio of CBS/S as 1.6/2.2 phr was regarded as the acceptable combination in designing green cushion gum composite formula. Higher CB N330 loading in hybrid filler composition and conventional curing system attributed to the relatively high crosslink density indicated by MH-ML value. Consequently, green cushion gum composite was obtained using the RF1 formula that has a better optimum curing time accompanied by good tensile property and adhesion strength. The composite was also comparable to conventional commercial cushion gum.

Mechanical properties and efficiency of SIFCON samples at elevated temperature cured with standard and accelerated method

This research shows the results and conclusions of an experimental study that aims to shed light on the mechanical performance of Slurry Infiltrated Fiber Concrete (SIFCON) (i.e. compressive strength, splitting tensile strength, flexural strength, Poisson's ratio, elastic modulus, and ultrasonic pulse velocity (UPV) and explore its efficiency at elevated temperature (i.e. 200, 400 and 600 °C) with different steel fiber ratios of 5 %, 7.5 %, and 10 % cured standard and in boiling water (accelerated curing). Hence, sets of cylinders and prisms are cast and tested under ASTM standard conditions. The results indicate that mechanical properties improve by increasing the steel fiber ratio up to 7.5 % in the case of a standard curing system, but more improvement is achieved with a steel fiber ratio up to 10 % in case of accelerated curing with boiling water. Also, the results indicate the superiority of the accelerated curing method for flexural and splitting tensile strength. Fly ash has a good contribution to the enhancement of mechanical performance of SIFCON with high steel fiber ratios. A decreasing and drastic reduction in compressive strength with increasing temperature above 200 and 400 °C for control specimens and SIFCON specimens with fiber ratios of 5 %, respectively are observed. While a dramatic gain in the strength of SIFCON samples with fiber ratios of 7.5 % and 10 % is concluded. High ratios of steel fiber can retard the spalling of concrete; hence it makes SIFCON the unique material for resisting explosive loads.

Unfilled Natural Rubber Compounds Containing Bio-Oil Cured with Different Curing Systems: A Comparative Study

This study focuses on the properties of unfilled natural rubber compounds containing bio-oils cured with a peroxide curing system and then discusses the comparisons to those cured using the sulfur system from our previous work. Two types of bio-oils, i.e., palm oil and soybean oil, were used, and distillate aromatic extract (DAE)-based petroleum oil was employed as a reference. The bio-oils caused no significant change in the vulcanization of rubber compounds cured using peroxide. However, the compounds containing bio-oils and cured with sulfur showed a faster vulcanization than the ones with DAE. The bio-oils strongly affected the crosslink density of rubber compounds in both curing systems. The use of bio-oils caused a low crosslink density due to the possible implication of curing agents to bio-oil molecules. The properties of rubber compounds dependent on the different levels of crosslink density were also investigated. The results revealed that when the crosslink density increased, the modulus, tensile strength, and hardness of the rubber compounds increased and the elongation at break and compression set decreased. The use of bio-oils in the rubber compounds cured with different curing systems gave low modulus at 300% strain, tensile strength, and hardness but high elongation at break and compression set when compared to the ones with DAE. However, no significant change was observed for the compression set of the rubber compounds cured using sulfur. With the presence of bio-oils, the properties of rubber compounds cured with sulfur system deteriorated less than those of the ones cured with peroxide.

Investigation of Curing Mechanism and Mechanical Properties of Polypropylene/Aliphatic Epoxy Composites

Temperature-sensitive cure kinetics based on bisphenol A oligomeric diglycidyl ether and branching diphenylmethane di-isocyanate, polymer aliphatic or lower molecular weight aromatic amines, and polypropylene and epoxy composites were examined. Polypropylene networks are formed initially, followed by amine hardeners interfering with epoxy oxirane rings to frame linear oligomers. Finally, the system is formed by a reaction between amines obtained in the second phase and epoxy oxirane rings during the curing step. This three-stage treatment was illustrated. The activation energy was calculated using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose isoconversational approaches to cure degree. The Ea-to-αcorrelation was determined using these approaches, revealing that the research curing systems exhibited autocatalytic effects. Among the materials studied, compounds with low molecular weight aromatic amines had the strongest and longest-lasting tensile characteristics. There are numerous advantages to slow curing and discrete stages of composite creation, including better mechanical properties.

Room temperature Self-healable and extremely stretchable elastomer with improved mechanical Properties: Exploring a simplistic Metal-Ligand interaction

The dynamic supramolecular crosslinking reactions like imine bond formation, disulfide metathesis reactions, Diels Alder reactions, metal–ligand interactions, H-bonding, and ionic interactions are broadly used for the self-healing application of elastomers. Herein, we have developed a new self-healable and extremely stretchable elastomer based on robustness and dynamic metal–ligand coordination bonds between the API ligand and the Zn2+ metal ion moieties incorporated onto the XNBR rubber backbone. The FT-IR analysis confirmed the formation of amide linkage and metal–ligand coordination bonds into the XNBR rubber backbone. The healing performance and mechanical properties of various rubber compounds depend on the dosages of metal ions and the type of crosslinking systems. The metal–ligand crosslink compounds exhibit excellent healing performance over the sulfur crosslinking system. Differential scanning calorimetry, rubber process analyzer, crosslinking density, and morphology studies are indicated to characterize the metal–ligand interactions in the XNBR rubber matrix. The metal–ligand cross-linked XNBR rubber with 3 parts of Zn2+ metal ion demonstrates an excellent healing performance of 91.2%, with the tensile strength of 5.7 ± 0.8 MPa at room temperature for 24 h is much higher than the covalently cross-linked elastomers. The metal–ligand coordination bonds are entirely dynamic and thermoreversible during the rebuilding process and obtain an excellent self-healing property than the sulfur curing system.

Impact of magnetic ionic liquids as catalystson the curing process of epoxy/anhydride system: Mechanistic investigation and dynamic‐mechanical analysis

AbstractCyclic acid anhydride – based hardeners provide excellent physic‐mechanical and thermal properties to epoxy networks. However, the curing process takes place at relatively high temperature, thus limiting the applications as coatings and free‐heating devices. The present work describes for the first time the efficient catalytic action of imidazolium‐ and phosphonium‐ based ionic liquids (IL) bearing iron tetrachloride (FeCl4) as counteranion for the curing process of epoxy prepolymer (EP)/methyl tetrahydrophthalic anhydride (MTHPA) even at room temperature. Indeed, both differential scanning calorimetry and rheological analysis revealed that the addition of 5 phr of trihexyl (tetradecyl)‐phosphonium iron tetrachloride (P66614. FeCl4) resulted in faster curing process when compared with systems cured with conventional tertiary amine. The gelation at room temperature occurred before 24 h with this magnetic IL. Moreover, the systems catalyzed by P66614. FeCl4 presented higher glass transition temperature, higher storage modulus and higher crosslink density as indicated by dynamic‐mechanical analysis (DMA). A mechanism for the curing process was proposed based on DSC and Fourier transform infrared analysis. These results highlight the importance of magnetic ILs as catalysts for the curing process of EP/MTHPA system and open new avenues for applications of this system as a room temperature‐based curing system.

Improve the long-term property of heat-cured mortars blended with fly ash by internal curing

Due to the satisfactory property and high productivity, heat-cured concretes have been widely used in engineering practice. However, heat curing process also brings some drawbacks that are detrimental to the long-term property of this material. To address this issue, lightweight fine aggregate (LWFA) was employed to provide internal curing (IC) for a heat-cured mortar (HCM) blended with fly ash (FA). The influences of LWFA on the interior relative humidity of HCM and the reaction environment and behavior of FA were measured. It was found that IC of LWFA could mitigate the drop of interior humidity and enhance the reaction degrees of cement and FA. This contributed significantly to the microstructure densification of HCM, higher compressive strength and better resistance to chloride ion. The results indicate that LWFA benefits to enhancing the efficiency of FA in a heat curing system and the combination of LWFA and FA contribute to improving the long-term property of HCM.

Application of Sulfur and Peroxide Curing Systems for Cross-Linking of Rubber Composites Filled with Calcium Lignosulfonate.

Calcium lignosulfonate in different loadings was applied to the rubber matrix based on EPDM. A sulfur curing system, organic peroxide, and a combination of organic peroxide with two coagent types were used for cross-linking of rubber compounds. The work was focused on the investigation of filler content and curing system composition in the curing process, cross-link density, morphology, and physical–mechanical properties of composites. The achieved results demonstrated that the curing parameters of rubber compounds cured with the sulfur system were significantly different from those cured with peroxide systems. There was also an observed different influence of curing systems composition on cross link density, though in all cases, the degree of cross-linking showed a decreasing trend with increasing content of lignosulfonate. The tensile strength of the composites cured with sulfur system and organic peroxide was comparable, regardless of lignosulfonate loading. This points to the application of both curing systems in cross-linking of rubber compounds with biopolymer filler. However, the introduction of coagents in peroxide vulcanization led to the improvement of adhesion and compatibility between the rubber and the filler on the filler–rubber interface. This subsequently resulted in the improvement of the tensile characteristics of composites. The introduction of organic peroxide in combination with coagent seems to be a very simple and efficient way for the preparation of biopolymer-filled composites with applicable physical–mechanical properties.

Study on Nitrile Oxide for Low-Temperature Curing of Liquid Polybutadiene.

As a significant component of composite solid propellants, the cross-link alkenyl polymers need to cure at high temperatures and the current isocyanate curing systems are highly humidity sensitive. This paper presented a low-temperature curing method for a cross-linked polymer (polybutadiene) with stable wettability by using cycloaddition of the nitrile oxide of tetramethyl-terephthalobisnitrile oxide (TTNO) and the C=C group of liquid polybutadiene (PB). The TTNO was synthesized in four steps from 1,2,4,5-tetramethylbenzene and evaluated as a low-temperature hardener for curing liquid PB. To characterize the reaction ability of TTNO at 25 °C, the cross-linked rubber materials of various contents (8%, 10%, 12%, 14%, 16%) of curing agent TTNO were prepared. The feasibility of the curing method can be proved by the disappearance of the absorption peak of the nitrile oxide group (2300 cm−1) by FT-IR analysis. Contact angle, TG-DTA and tensile-test experiments were conducted to characterize the wettability, thermo-stability and mechanical properties of the obtained cross-linked rubber materials, respectively. The results showed that the curing agent TTNO could cure PB at room temperature. With the growing content of the curing agent TTNO, the tensile strength of the obtained cross-linked rubber material increased by 260% and the contact angle increased from 75.29° to 89.44°. Moreover, the thermo-stability performances of the cross-linked rubber materials have proved to be very stable, even at a temperature of 300 °C, by TGA analysis.

Structural stability of thin overhanging walls during material extrusion additive manufacturing of thermoset-based ink

Recent developments have enabled material extrusion additive manufacturing of thermoset-based composite inks on the large scale. In addition, printing out-of-plane components is of broad interest to the polymer material extrusion community. This work addresses some of the challenges associated with both large-scale and out-of-plane thermoset material extrusion additive manufacturing by studying the height at which thin overhanging walls collapse. Walls at a range of overhang angles were printed until they collapsed. An optical camera captured the profile of each wall throughout the print, allowing the collapse height to be identified and the geometric fidelity to the programmed angle to be evaluated. Using previously measured rheological properties, predictive models were generated to approximate the collapse height and profile of the deflected walls. First, an analytical model was created to predict the height at which the walls would yield. The analytical model assumes the walls exhibit a perfectly linear profile; however, experiments proved this assumption to be false. Therefore, a finite element simulation was developed to account for the elastic deflection that occurs during printing. The finite element simulation predicts both the yield height and the deflected profile after the deposition of each layer. For the properties of the thermoset ink used here, the yield height predicted by the analytical model and finite element simulation are virtually identical. These predictions match experimental data reasonably well, but minor errors are observed. Accounting for the fully plastic moment appears to explain the small mismatch between experimental data and predictions. Additionally, the finite element simulation provides an excellent prediction of the deflected profile before the wall begins to collapse. By demonstrating that the collapse height and deflected profile of thin overhanging walls can be predicted, this work illustrates how the soft viscoelastic properties of thermoset-based composite inks limit the scale of a key feature required to print some nonplanar components. It also provides a basis to tailor in-process curing systems to suppress deflection and collapse of thin overhanging walls.

Repair of Wind Turbine Blades: Costs and Quality

Repair and maintenance operations of wind turbines constitute a significant part of costs of wind energy. In this paper, technologies of structural repair of damaged wind turbine blades are reviewed. Costs of repair, and technological contribution to the costs are discussed. Technologies of repair are compared, including hand layup lamination, vacuum repair with hand layup and infusion, ultraviolet curing and high temperature thermal curing systems. Computational models of repaired blades, and curing as kinetic process are presented. Void formation during repair and curing, and the void influence on the post-repair reliability of blades is discussed.

Multifunctional benzoin derivatives based macrophotoinitiators: Synthesis, inorganic fillers modification, and fabrication of composite materials

AbstractPhotopolymer composites are the materials with wide application potential in paints and varnishes, diverse lithographic processes, electronics, medicine, and so forth. Here a new approach to the synthesis of macrophotoinitiators (MPIs) were developed and their effective application for curing polymer composites after immobilization on the surface of diverse mineral fillers was demonstrated. The MPIs were synthesized by reaction of benzoin or 3‐hydroxy‐1,2‐diphenyl‐2‐(propan‐2‐yloxy)propan‐1‐one as a photodissociating species with a copolymer of maleic anhydride with methyl methacrylate as carrier. Chemical structure of MPIs and the content of the tethered photoinitiating moieties were determined using 1NMR‐, IR‐, and UV‐spectroscopies. Photolysis of MPIs was investigated in details using a spot‐light curing system. It was demonstrated that MPIs are effective surface modifiers of mineral fillers, such as titanium dioxide, zinc oxide, and nanohydroxyapatite; and behave as effective photoinitiators. The benefits of using the fillers surface‐modified by MPIs in photo‐curable polymer composites were discussed.