Curing System Research Articles

Surface characterization of polyimide and polyethylene terephthalate membranes toward plasma and UV treatments

This study is to bring an overview on various methods regarding the surface treatment performed on different polymeric membranes in relation to a deference between the treatment mechanism and their chemical structure. Herein, plasma and UV surface treatments (PST and UST) were utilized to treat the surfaces of two commercial membranes, i.e., aromatic polyimide and polyethylene terephthalate for various durations using a discharge electrode and an UV LED curing system, respectively. Based on the effects of PST and UST processes on the surface of these membranes, their surface properties have been characterized to surface morphology and hydrophilicity (or wettability), at same time the changes have probably occurred on their surface during the PST and UST processes. As a result, their hydrophilic behavior was significantly enhanced after conducting these treatment processes based on the investigation of water contact angle. Moreover, Fourier-transform infrared and Raman spectroscopy manifested the changes in the chemical bonds, interactions and orientations of molecules, which confirmed the apparition and insertion of polar functional groups after the surface treatments, and accordingly, their wettability was enhanced significantly. Also, optical microscopy images showed direct impactions on their surface and the evidence of slight surface aging/damage during the treatment processes based on the presentation of the strange streaks on the treated surfaces. In particular, the peel forces exhibited an increase comparing to the initial membranes, which is characteristically for enhancing their adhesion behavior. Hence, these results are needful for improving the surface properties of a material, and obtaining better adhesion behavior on the membrane-like materials and recycling polymer materials.

Effect of Different Cavity Dimensions and Curing Systems on Cuspal Deflection of some types of Composite Resin Restorations

The cuspal deflection of different composite resin restorations cured with different systems and restoring different cavity dimensions were investigated using a total 60 freshly extracted human maxillary premolars. These teeth were divided into three main equal groups, based upon the tested restorative materials. Group (I) used T-Econpm Plus, Group (A1) (II) used Filtek Z250 XT (A2), and Group (III) used Filtek P90 (A3). Each group was subdivided into two subgroups based upon the prepared cavity dimensions. Each subgroup was further subdivided into two groups whether cured with Halogen (C1), or LED (C2). MOD cavity with two different dimensions, each restorative material was packed according to the manufacturer's instructions and cured. Dye penetration technique was used and specimens were sectioned in mesiodistal direction and examined by stereomicroscope. Collected data was statistically analyzed. The result showed T-Econom plus had statistically significant higher microleakage value, while Filtek P90 had statistically significant lower microleakage value. There was no statistically significant difference between groups cured with Halogen and LED. It can be concluded that silorane based composite, LED curing system, and smaller cavity dimension could significantly decreased cuspal deflection.

Effect of different cure systems on natural rubber/nanocellulose nanocomposites in rheological, physical-mechanical, aging, and mechanical properties

The effect of different crosslink structures was studied in nanocomposites obtained by co-precipitation of natural rubber (NR) latex and aqueous solution of cellulose xanthate for obtaining nanocellulose. Cure systems characterized as conventional (CV), semi-efficient (SEV), and efficient (EV) were used in compositions of NR and also in natural rubber/cellulose (NR/CEL) nanocompositions with 15 phr of cellulose. The characterization of the developed compositions was based on rheological, physical-mechanical, aging, and mechanical properties. The obtained results allowed the conclusion that cellulose is a reinforcing filler as it promoted a significant increase in all these properties, that were sensitive to the cure systems used and protects NR from accelerated aging. The experimental results are presented and discussed also by Payne effect, entropy (ΔS), and Gibbs free energy (ΔG) to enable an understanding on cellulose distribution throughout NR influenced by the different cure systems.

Study on the compounding of a new type of trimer epoxy resin curing agent

AbstractIn this paper, bisphenol A (BPA), epichlorohydrin (ECH), and isocyanate trimer (TDI‐T) are used as raw materials to synthesize a high toughness/trimer epoxy resin by graft copolymerization. It was cured at room temperature with low molecular weight polyamide 650 (PA650)/isophorone diamine (IPDA) and low molecular weight polyamide 650/triethylene tetramine (TETA) composite curing system respectively. The cured products of the two compound systems were studied by Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC), thermogravimetry (TG), and mechanical property testing. The results show that with the increase of TETA and IPDA curing agents, the heat released during the curing process of the two systems also greatly increases, and the temperature rises from the initial 33.9–69.7°C and 52.8°C. The curing time is shortened from a few days to a few hours, and the controllability of the curing time is effectively realized. When the ratio of triethylene tetramine to low molecular weight polyamide 650 is 2.86:100, the compressive strength is the best, reaching 112.7 MPa, 12% higher than pure polyamide as curing agent, and the specimen can be completely restored to its original shape in a few minutes. When the ratio of TETA to PA650 is 2.86:100, the elongation at break reaches 21.4%.

A Study on Temperature Distribution within HVDC Bushing Influenced by Accelerator Content during the Curing Process

Power transmission technology plays an important role in energy sustainability. Bushing is an indispensable type of equipment in power transmission. In production, the accelerator changes the temperature distribution during the curing process, influencing the formation of defects and thus the safety output of renewable energy. In this study, uncured epoxy resin samples with different accelerator contents were prepared and measured by differential scanning calorimetry (DSC). The obtained heat flow curves were analyzed for curing kinetics. Then, the curing process of large length–diameter ratio bushings was simulated by using the finite element method combined with a curing kinetics model, transient Fourier heat transfer model, and stress–strain model. The study reveals that the curing system can be established by the Sestak–Berggren autocatalytic model with different accelerator contents. The overall curing degree and the maximum radial temperature difference of the capacitor core tend to increase and then decrease with the accelerator content. This is mainly attributable to the rapid exotherm excluding the participation of some molecular chains in the reaction, resulting in permanent under-curing. As the accelerator content increases, the strain peak decreases and then increases. This paper provides guidance for the comprehensive evaluation and manufacturing of the low-defect capacitor cores of large-size high voltage direct current (HVDC) bushings.

3D printing of cell-laden visible light curable glycol chitosan bioink for bone tissue engineering

Although chitosan is the second most abundant natural polymer on earth, with a wide range of biomaterial applications, its poor water solubility limits general printing process. We selected water-soluble methacrylated glycol chitosan (MeGC) as an alternative and prepared a MeGC-based MG-63 cell-laden bioink for 3D printing using a visible light curing system. Optimal cell-laden 3D printing of MeGC was completed at 3% using 12 μM of riboflavin as a photoinitiator under an irradiation for 70 s, a 26-gauge nozzle, a pneumatic pressure of 120 kPa, and a printing speed of 6 mm/s, as confirmed by printability, protein adsorption, cell viability, cell proliferation, and osteogenic capability. In addition, in vitro tests showed that MeGC-70 has a viability above 92%, a proliferation above 96%, and a hemolysis level below 2%. The results demonstrate the potential for MeGC-70 bioinks and 3D printed scaffolds to be used as patient-specific scaffolds for bone regeneration purposes.

The Effect of pH Water on the Concrete Mixtures and Curing Condition on the Compressive Strength of Concrete

This research examined the effect of acid water as a concrete mix material and as a curing system on the compressive strength of concrete. The effect of wet-dry curing conditions in normal and low pH water on the concrete compressive strength was also evaluated. The water pH of 3 and 7 was conducted in this research. Water pH of 3 was obtained by diluting the HCl solution with tap water. The result showed that the concrete compressive strengths with normal water were 26.23, 26.61, 28.31, and 28.31 MPa at 28, 56, 90, and 120 days, respectively. In comparison, concrete mixed with low pH water was 25.48, 26.04, 26.42, and 26.42 MPa at 28, 56, 90, and 120 days, respectively. The wet-dry curing system for normal water concrete mixed reduced the compressive strength at 28 days by 14.39%, 56 days by 18.44%, 90 days by 14.00%, and 120 days by 10.00%. The wet-dry curing with acidic water also decreased the concrete compressive strength. The wet-dry condition breaks the hydration process between concrete and acid water. Wet-dry curing decreased the compressive strength of concrete. The compressive strength at 28, 56, and 90days decreased 16.30, 12.32, and 7.86%, respectively. While at 120 days, the compressive strength on wet-dry curing slightly increased by 1.43% by 0.01%. Wet-dry curing breaks the concrete hydration process with acid water.

Preparation of hexamethylol melamine resin with low crystallization water and low viscosity for hexamethylol melamine/polyvinyl alcohol composite membrane

Abstract Hexamethylol melamine resins (HMM) with low crystallization water content and low viscosity were prepared by inhibiting the condensation polymerization of low hexamethylol melamine. The effects of catalyst, pH, formalde-hyde/melamine ratio, reaction temperature and time on the synthesis parameters of HMM were investigated. The results showed that the sample (HMM8) synthesized with Na2CO3-NaHCO3 as catalyst had the crystallization water content lower than 10%, being with a viscosity of about 0.26 Pa·s. The melting temperature of HMM8/polyvinyl alcohol (PVA) curing system was about 164.3 °C. It was found that the higher the amount of formaldehyde, the greater the hydroxyl methyl bounded to each triazine ring. Compared with the traditional melamine formaldehyde resin which had the crystallization water content of about 20–30%, the production of this resin was expected to reduce the energy consumption of industrial reaction, while the resin with 10% crystallization water content was more conducive to the development of alloying HMM/PVA composite membrane.

Glycidate as a High-Strength Epoxy Adhesive Curable with Amine under Ambient Conditions.

This paper reports that glycidates bearing epoxy moieties with adjacent ester can be cured with diethylenetriamine (DETA) under mild conditions and exhibit high adhesiveness. Curing of bifunctional glycidates with DETA gave cross-linked products. The curing started at a lower temperature (7 °C) than the analogous glycidyl ether (27 °C), while the rate of the curing was slower due to the lower activation energy (Ea = 57 kJ/g) and exothermicity (ΔH = 58 J/g) as confirmed by DSC analysis. The curing system of neopentyl glycol diglycidate and DETA effectively adhered aluminum plates by curing at 25 °C, and the strength was more than five times higher than the curing with analogous glycidyl ether. The higher adhesive strength under curing of ambient conditions and facile preparation of monomers are the significant advantages of this curing.

Experimental study on compressive strength and frost resistance of steam cured concrete with mineral admixtures

The study of frost resistance and mechanical properties of steam cured concrete is helpful to understand the state of precast concrete elements in a complex environment. In this paper, the compressive strength of concrete under 10 working conditions, such as standard cured system, steam cured system, no mineral admixtures, single ground granulated blast furnace slag (GGBS) and fly ash (FA) mixed with GGBS, was tested at the age of 180d. It is found that the compressive strength of concrete under standard cured system is 4.71% to 18.46% higher than that under steam cured system, although steam cured improves the strength at the initial stage. The addition of FA and GGBS can make up 14% to 16% strength defects caused by steam cured system. The compressive strength of steam cured concrete (ZF40℃) is the highest when the steam cured temperature is 40℃ and the mixture ratio of FA and GGBS is 2:3. On this basis, the frost resistance of ZF40℃ specimens was studied. The results showed that the surface degradation degree of steam cured concrete gradually deepened with the increase of freeze–thaw (F-T) cycles, and the extracted surface roughness ranged from 0.066 ∼ 0.505 mm. The relative dynamic elastic modulus and mass loss rate decreased with the increase of F-T cycles, and the maximum loss rate were 69.4% and 1.41%, respectively. In addition, the compressive strength test, acoustic emission (AE) signal monitoring and acquisition of pore structure characteristics were carried out to understand the mechanical properties of steam cured concrete under F-T cycles conditions. The results show that the compressive strength decreases with the increase of F-T cycles, and the strength loss rate is within 10% per 50 cycles. The overall activity of AE signal decreases with the increase of F-T cycles, andthe damage form gradually changes from the initial tensile damage to the later shear damage. Porosity and pore size range basically increase with the increase of F-T cycles. Pore deterioration is the main reason for the decrease of compressive strength of steam cured concrete under F-T environment.

In-Situ Polymerization of Maleic Acid in Presence of Aloe vera Gel for Development of Eco-Friendly Eri Silk-based Handlooms

In this study, eri silk-based handloom fabrics were finished with Aloe vera gel employing maleic acid as a cross-linking agent using a pad-dry-cure method. Water-soluble Aloe vera gel of varying concentrations of 5 to 15% (w/v) was also used in the finishing bath for imparting antibacterial property to the finished fabric along with the anti-crease properties. Assessment of changes in the properties of finished fabric shows substantial improvement in wrinkle recovery of the finished silk fabric achieved at the expense of strength and flexibility at moderate levels. Changes in the chemical nature of silk fabric on such modifications have been studied by infrared (IR) spectroscopy and reported also in this research article. The study proposes a thermal curing system that is conducive to in-situ polymerization of maleic acid in presence of Aloe vera for the development of eco-friendly eri silk-based handlooms with antibacterial and anti-crease properties, without a significant loss in strength. The antimicrobial property appears to remain significant even when the fabric is subjected to wash up to 10 wash cycles.

Photoactive Fe Catalyst for Light-Triggered Alkyd Paint Curing.

Herein, we show that the photoactive complexes [(Cp)Fe(arene)]+ (Cp = cyclopentadienyl; arene = C6H6, C6H5Me) act as latent catalysts that allow for photochemical control over the onset of alkyd paint curing, without the need for antiskinning agents such as the volatile 2-butanone oxime normally used to prevent curing during paint storage. The highly soluble neutral complexes [(Cp)Fe(Ch)] and [(Cp)Fe(Ch′)] (Ch = cyclohexadienyl, Ch′ = methylcyclohexadienyl) readily convert to the photoactive complexes [(Cp)Fe(arene)]+ upon oxidation in alkyd, allowing the latter to be dosed in a wide range of concentrations. Infrared and Raman studies show similar spectral changes of the alkyd paint matrix as have been observed in alkyd curing mediated by well-known, industrially applied cobalt- and manganese-based catalyst Co(neodecanoate)2 and [(Me3TACN)2Mn2(μ-OOCR)3](OOCR). The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ system performs equally well as these cobalt- and manganese-based catalysts in terms of drying time and outperform the manganese catalyst by showing a hardness development (increase) similar to that of the cobalt-based catalyst. Based on electron paramagnetic resonance and light–activity studies, we propose that photolysis of [(Cp)Fe(arene)]+ generates short-lived active FeII species, explaining the desired latency. The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]+ alkyd curing systems presented herein are unique examples of intrinsically latent paint curing catalysts that (1) are based on an abundant and harmless transition metal (Fe), (2) do not require any antiskinning agents, and (3) show favorable performance in terms of drying times and hardness development.

REMOVED: Catalysis of reduced tin oxide in various epoxy resins

Epoxy resins are the most widely used thermoset materials for various applications, including electronic devices such as semiconductor packaging. In this study, tin (Sn) catalysis in diverse epoxy binary systems containing amine, acid or anhydride was explored by using various differential scanning calorimetry (DSC) techniques and rheological properties. Catalytic effects of Sn were observed in epoxy–anhydride and epoxy–diacid systems but not in epoxy–amine systems. For instance, the incorporation of 1 vol% Sn into the epoxy–succinic anhydride and epoxy–pimelic acid systems reduced the DSC exothermic peak temperature from 295 °C to 202 °C and 243–196 °C, respectively. By contrast, Sn presented no catalytic effect in epoxy–amine systems. Sn catalysis was investigated using isothermal curing temperatures and time. The onset temperature during viscosity measurements for the epoxy–anhydride and epoxy–diacid systems substantially decreased as a function of Sn concentration. These catalytic effects of Sn metal particles (oxidized in air) in the epoxy–anhydride and epoxy–diacid systems can be utilized to accelerate the reactions of epoxy resins and to anticipate the reaction conditions in various applications such as electronic devices involving Sn and epoxy resins. • Sn catalysis was observed in epoxy-anhydride and epoxy-diacid curing systems. • Epoxy-amine curing system did not show the Sn catalytic effect. • Various DSC and rheometry measurement techniques were used. • Latent catalytic effects were also examined.

Design of a Prototype Solar Thermal Tobacco Curing Barn

A feasibility study survey held in July 2020 had tobacco farmers agreeing that there was strong need to move away from using firewood for tobacco curing. It became necessary to develop alternative renewable energy systems. Prototyping takes precedence before introducing the renewable energy tobacco curing system for use by farmers. The initiative is to design a prototype tobacco curing barn for use with solar thermal collector tobacco curing energy systems tests. The design accommodates dimensions of maximum cross-section of a tobacco leaf at 65 centimetres long and 40 centimetres wide. Prototype roof rail sustains tobacco mass of 100 kilogrammes. Barn mobility is enabled by mounting 4 roller wheels sustaining a gross weight of 500 kilogrammes. A barn handle is at one narrow side. The paper explains a detailed design process and sketches of the prototype tobacco curing barn as well as presents a lifecycle costing of the project’s investment in Zimbabwe.

Structure, preparation and properties of liquid fluoroelastomers with different end groups.

In order to design and prepare liquid fluoroelastomers with different end groups, and reveal the relationship between the molecular chain structure and properties, we studied on the oxidation degradation method and functional group conversion method to prepare carboxyl-terminated and hydroxyl-terminated liquid fluoroelastomers, respectively. The reaction mechanisms were also deduced. Furthermore, the curing system was created for liquid fluoroelastomers, and systematically analyzed their properties. The sequence type and content of the –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C– and oxygen-containing groups in the samples were measured and characterized by attenuated total reflectance/Fourier transform infrared (ATR-FTIR) spectroscopy, 1H nuclear magnetic resonance (1H-NMR), 19F-NMR spectroscopy and chemical titration, the molecular weights of liquid fluoroelastomers were measured by gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the thermal properties, while a viscometer was used to measure the dynamic viscosity of the liquid fluoroelastomers. Then the mechanical and surface properties of the cured samples were examined by universal testing machine and contact angle measurement instrument, respectively. The results show that carboxyl-terminated liquid fluoroelastomer with 2.71 wt% carboxyl terminal groups can be prepared by oxidation degradation method. When lithium aluminium hydride (LiAlH4) was used as the reducing agent, it can efficiently convert carboxyl group to hydroxyl group with a conversion rate of more than 95%. In addition, it can be seen that the dynamic viscosity of the liquid fluoroelastomers were all decreased with the increase of temperature, and it is similar to about 10 Pa s at 70 °C. Compared with carboxyl-terminated liquid fluoroelastomers, hydroxyl-terminated liquid fluoroelastomers has higher curing reactivity, higher glass transition temperature (Tg) and thermal decomposition temperature (Td), and better mechanical properties of cured samples. The two types of liquid fluoroelastomers with distinct end groups presented distinct hydrophilicity.

Renewable green reactive diluent for bisphenol a epoxy resin system: curing kinetics and properties.

Hydrosilylation epoxidized eugenol (HSI-EP-EU) is successfully synthesized and used as a reactive diluent for epoxy/anhydride (marked as P) and epoxy/imidazole (marked as I) curing systems. The reactive bio-based diluent HSI-EP-EU has an excellent dilution effect on petroleum-based epoxy resin (E44). The curing kinetics of P + HSI-EP-EU and I + HSI-EP-EU are studied by a non-isothermal DSC method. The kinetics parameters are calculated by using the Kissinger model, Crnae model, Ozawa model and β-T (temperature-heating speed) extrapolation, respectively, to determine theoretically reasonable curing conditions. In addition, the effects of HSI-EP-EU on the antibacterial properties, thermo-mechanical properties and thermal stability of P + HSI-EP-EU and I + HSI-EP-EU systems are also studied. It is found that HSI-EP-EU possessed obvious antibacterial properties and could effectively improve the mechanical properties for the I + HSI-EP-EU.

Композиция на основе линейно-лестничного силоксанового блок-сополимера для получения защитных покрытий с улучшенными физико-химическими свойствами

A one-component organosilicon composition based on a solution of the Lestosil SM-NT block copolymer containing an optimal ratio of linear polydimethylsiloxane and ladder phenylsilsesquioxane units in an organic solvent has been developed. As a curing system, a solution of heterosiloxane containing boron and zirconium atoms in the siloxane chain in alkoxysilane and special additives that improve the performance properties of coatings were used. The composition is intended for production of heat-resistant electrically insulating and moisture-resistant coatings with enhanced physical-chemical properties, used as protective materials in microelectronics and electronic products.

Physical-mechanical behavior of nitrile rubber-synthetic mica nanocomposites

Nitrile rubber (NBR) nanocomposites with different contents of synthetic Somasif ME-100 mica (sodium-fluorohectorite) were obtained by melt compounding using a Semi Efficient curing system. The effect of curing on the nanocomposties was evaluated through rheometric properties, crosslink density (CLD) and mechanical properties. The ME-100 mica dispersion in NBR was assessed by transmission electron microscopy (TEM), the Payne effect and thermodynamic properties (ΔS and ΔG). Both the curing parameters and CLD pointd out that the addition of ME-100 directly affects crosslinks formation. It could also be observed that the nanofiller dispersion state is complex, exhibiting exfoliated and agglomerated structures (TEM); besides, agglomerations rose linearly as the nanofiller was added (the Payne effect). Notwithstanding these findings, and on the basis of unfilled formulations, NBR20 nanocomposite showed improvement in mechanical properties (tensile and tear strengths) which suggests that ME-100 might be considered a semi-reinforcing filler.

New<i> Bacillus subtilis</i> vector, pSSβ, as genetic tool for site-specific integration and excision of cloned DNA, and prophage elimination

Site-specific recombination (SSR) systems are employed in many genetic mobile elements, including temperate phages, for their integration and excision. Recently, they have also been used as tools for applications in fields ranging from basic to synthetic biology. SPβ is a temperate phage of the Siphoviridae family found in the laboratory standard Bacillus subtilis strain 168. SPβ encodes a serine-type recombinase, SprA, and recombination directionality factor (RDF), SprB. SprA catalyzes recombination between the attachment site of the phage, attP, and that of the host, attB, to integrate phage genome into the attB site of the host genome and generate attL and attR at both ends of the prophage genome. SprB works in conjunction with SprA and switches from attB/attP to attL/R recombination, which leads to excision of the prophage. In the present study, we took advantage of this highly efficient recombination system to develop a site-specific integration and excision plasmid vector, named pSSβ. It was constructed using pUC plasmid and the SSR system components, attP, sprA and sprB of SPβ. pSSβ was integrated into the attB site with a significantly high efficiency, and the resulting pSSβ integrated strain also easily eliminated pSSβ itself from the host genome by the induction of SprB expression with xylose. This report presents two applications using pSSβ that are particularly suitable for gene complementation experiments and for a curing system of SPβ prophage, that may serve as a model system for the removal of prophages in other bacteria.

Influence of the curing system on the physical-mechanical, dynamic properties, and aging resistance of ethylene–propylene–diene monomer formulations for applications at high temperatures

The effects of three curing systems on rheometric, morphological, physical-mechanical, thermal, and dynamic properties of ethylene–propylene–diene monomer (EPDM) composites was investigated. The influence of thermo-oxidative aging on crosslink density and physical-mechanical properties was studied. Based on a standard composition for application at high temperatures, EPDM formulations with semi-efficient vulcanization systems (ES), efficient vulcanization systems (ED), and peroxide curing systems (EP) were prepared. Experimental results indicated that EPDM compounds cured with efficient vulcanization systems exhibit the highest scorch time with an intermediate maximum torque value at 150°C. The filler dispersion in the elastomeric matrix was greater than 94%; however, the ED formulation showed a more pronounced decrease, with the increase in deformation indicating a greater filler–filler interaction. In comparison with those cured with peroxide and semi-efficient systems, EPDM formulations cured with an efficient system presented better thermal resistance and the crosslink density was sufficient to maintain the mechanical integrity, leading to an intermediate hardness value, tensile strength, modulus, and greater elongation at breaking. In summary, the results indicated that the efficient curing system was the most appropriate to be used in the envelope’s manufacture, due to the better performance of the mechanical properties associated with the better resistance to thermal aging.