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Electrolyte-filled subnanometre pores exhibit exciting physics and play an increasingly important role in science and technology. In supercapacitors, for instance, ultranarrow pores provide excellent capacitive characteristics. However, ions experience difficulties in entering and leaving such pores, which slows down charging and discharging processes. In an earlier work we showed for a simple model that a slow voltage sweep charges ultranarrow pores quicker than an abrupt voltage step. A slowly applied voltage avoids ionic clogging and co-ion trapping—a problem known to occur when the applied potential is varied too quickly—causing sluggish dynamics. Herein, we verify this finding experimentally. Guided by theoretical considerations, we also develop a non-linear voltage sweep and demonstrate, with molecular dynamics simulations, that it can charge a nanopore even faster than the corresponding optimized linear sweep. For discharging we find, with simulations and in experiments, that if we reverse the applied potential and then sweep it to zero, the pores lose their charge much quicker than they do for a short-circuited discharge over their internal resistance. Our findings open up opportunities to greatly accelerate charging and discharging of subnanometre pores without compromising the capacitive characteristics, improving their importance for energy storage, capacitive deionization, and electrochemical heat harvesting. Narrowing pores filled with an electrolyte usually slows down their charge-discharge dynamics. Here the authors demonstrate through molecular dynamics simulations and experiments with novolac-derived carbon electrodes how non-linear voltage sweeps can accelerate charging and discharging of subnanometer pores.

Phenolic novolac-type epoxy (EPN) resin composites were fabricated by reinforcing with cotton waste (CtW), along with aluminum hydroxide (AH), and boric acid (BA) particles under different filler loadings. For characterization, thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry, and water sorption tests were performed on the composites. The effects of the CtW, AH, and BA contents on the thermal, flame-retardant, and mechanical properties of the composites were investigated. The triple hybrid additive (CtW:BA:AH) with a ratio of 20:5:10 wt% exhibited the best mechanical and combustion properties. The tensile strengths of this composite and the neat EPN were determined as 95.7 ± 6.92 and 96.6 ± 4.77 MPa, respectively. The T50 temperatures of the BA- and AH-doped composites were higher than that of neat EPN. The highest char percentages were observed in the triple composites, while the lowest were observed in the EPN/CtW composites. The combustion of the triple composite with a CtW:BA:AH ratio of 20:5:10 wt% was spontaneously extinguished in 37 s. Horizontal flammability testing also showed better fire resistance for the CtW/BA/AH composites over their CtW counterparts, with the highest estimated limiting oxygen index of 32.3 obtained for the 20:5:10 wt% composite. The water sorption test results show that the CtW composites had the highest hydrophilicity, especially those with 30 wt% CtW or higher, in the presence of water at room temperature.Graphic abstract

Phthalonitrile resins (PN) are known for their incredible heat resistance and at the same time poor processability. Common curing cycle of the PN includes dozens hours of heating at temperatures up to 375 °C. This work was aimed at reducing processing time of phthalonitrile resin, and with this purpose, a novolac oligomer with hydroxyl groups fully substituted by phthalonitrile moieties was synthesized with a quantitative yield. Formation of the reaction byproducts was investigated depending on the synthesis conditions. The product was characterized by 1H NMR and FT-IR. Curing of the resins with the addition of different amounts of novolac phenolic as curing agent (25, 50 and 75 wt.%) was studied by rheological and DSC experiments. Based on these data, a curing program was developed for the further thermosets’ investigation: hot-pressing at 220 °C and 1.7 MPa for 20 min. TGA showed the highest thermal stability of the resin with 25 wt.% of novolac (T5% = 430 °C). The post-curing program was developed by the use of DMA with different heating rates and holding for various times at 280 or 300 °C (heating rate 0.5 °C/min). Carbon and glass fiber plastic laminates were fabricated via hot-pressing of prepregs with Tg’s above 300 °C. Microcracks were formed in the CFRP, but void-free GFRP were fabricated and demonstrated superior mechanical properties (ILSS up to 86 MPa; compressive strength up to 620 MPa; flexural strength up to 946 MPa). Finally, flammability tests showed that the composite was extinguished in less than 5 s after the flame source was removed, so the material can be classified as V-0 according to the UL94 ratings. For the first time, fast-curing phthalonitrile prepregs were presented. The hot-pressing cycle of 20 min with 150 min free-standing post-curing yielded composites with the unique properties. The combination of mechanical properties, scale-up suitable fast-processing and inflammability makes the presented materials prospective for applications in the electric vehicle industries, fast train construction and the aerospace industry.

The encapsulation of active components is currently used as common methodology for the insertion of additional functions like self-healing properties on a polymeric matrix. Among the different approaches, polyurea microcapsules are used in different applications. The design of polyurea microcapsules (MCs) containing active diisocyanate compounds, namely isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI), is explored in the present work. The polyurea shell of MCs is formed through the interfacial polymerization of oil-in-water emulsions between the highly active methylene diphenyl diisocyanate (MDI) and diethylenetriamine (DETA), while the cores of MCs contain, apart from IPDI or HDI, a liquid Novolac resin. The hydroxyl functionalities of the resin were either unprotected (Novolac resin), partially protected (Benzyl Novolac resin) or fully protected (Acetyl Novolac resin). It has been found that the formation of MCs is controlled by the MDI/DETA ratio, while the shape and size of MCs depends on the homogenization rate applied for emulsification. The encapsulated active compound, as determined through the titration of isocyanate (NCO) groups, was found to decrease with the hydroxyl functionality content of the Novolac resin used, indicating a reaction between NCO and the hydroxyl groups. Through the thorough investigation of the organic phase, the rapid reaction (within a few minutes) of MDI with the unprotected Novolac resin was revealed, while a gradual decrease in the NCO groups (within two months) has been observed through the evolution of the Attenuated Total Reflectance—Fourier-Transform Infrared (ATR-FTIR) spectroscopy and titration, due to the reaction of these groups with the hydroxyl functionalities of unprotected and partially protected Novolac resin. Over longer times (above two months), the reaction of the remaining NCO groups with humidity was evidenced, especially when the fully protected Acetyl Novolac resin was used. HDI was found to be more susceptible to reactions, as compared with IPDI.

This research aims to make a polymer composite of polydimethylsiloxane (PDMS)/Novolac base reinforced by B 4 C particles. The hot press method was used to produce a polymer composite with an optimum ratio of 85/15 PDMS/Novolac and 7, 12, 15, 20, and 30% B 4 C. The impact of variation in the set values of B 4 C concentration on the physical, mechanical, and shielding properties of polymer composite was examined through a variety of analytical techniques, including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hardness testing, tensile bending strength testing, Fourier transform infrared spectroscopy (FTIR), neutron radiography, and scanning electron microscopy (SEM). The mechanical properties findings revealed that the B15 sample with a concentration of 15% wt. B 4 C had the highest hardness, tensile and bending strength, which were 109 shore A, 203 MPa, and 74 MPa, respectively. Additionally, the SEM images exposed the equilibrium between porous structure and agglomeration of B 4 C particles in B15 sample. Besides, adding 15–20% B 4 C increased shielding properties by 9–10%. Moreover, the results of TGA demonstrated better thermal stability of polymer composites, with weight loss of less than 30% at 500 °C after adding up to 30% B 4 C.

In this paper, in order to further improve the heat resistance of UV-curing epoxy cresol novolac (EOCN), 2,2-bis(hydroxymethyl)propionic acid (DMPA) was firstly introduced to open epoxy groups in EOCN and then the hydroxyl groups reacted with acryloyl chloride to make sure the resin has sufficient UV-curing double bonds. Compared with the system that uses acrylic acid to open epoxy group and the secondary hydroxyl group reacting with unsaturated anhydride, up to 1.5 times double bonds were potentially introduced. The structure of the resins was characterized by FT-IR and 1H-NMR. Influences of double bond content on thermal behavior, photopolymerization kinetic behavior, and basic properties of the cured films were investigated. Thermal performance analysis demonstrated that the glass transition and the initial decomposition of the cured films were increased with the rising proportion of acryloyl group. Moreover, doping of abundant acryloyl chloride caused a significant increase of unsaturated double bond conversion, though the initial photopolymerization rates declined. Cured films with less acryloyl chloride modified showed better adhesive. For solvent-resistant test, with the increase of the acryloyl group, the cured film displayed good resistance to strong acids and alkalis. These attractive features give this process potential applications in soldering ink and protective coatings.

In light of the significant impact of climate change, it is imperative to identify effective solutions to reduce the environmental burdens of industrial production and to promote recycling strategies also for thermosetting polymers. In this work, the mechanical recycling of phenolic resins, obtained from industrial production scrap of plastic knobs for household appliances, was optimized. The feasibility of a partial substitution of virgin materials with recycled ones was investigated both at a laboratory and industrial scale. Finally, the environmental benefits arising from the use of recycled material were quantified through a life cycle assessment (LCA). The results of laboratory characterization demonstrated that the thermal properties of the phenolic resins were not influenced by the presence of recycled material, and the mechanical performances were not significantly impaired up to a recycled content of 30 wt%. The industrial production trials demonstrated the feasibility of replacing up to 15 wt% of virgin material without any influence on the aesthetical features of the produced components. Finally, LCA of industrially produced knobs highlighted a limited benefit of virgin material substitution in the case of novolac chromium-plated samples, while an overall environmental impact reduction of around 7–10% was detected in the case of resol-based materials.

The novolac/polyester blend to coat the glass enhances the characteristics (transmittance, absorbance, reflectance, extinction coefficient, and energy gap of glass) by coating it with a polyester/novolac blend for use in the detector. Spin coating is utilized to coat the glass with novolac/polyester blend at various volume ratios 1:1, 1:2, 1:3 of polyester. The optical properties of novolac: polyester blended film 10 µm thickness have been considered depending on the wavelength of absorbance, transmittance, and reflectance spectra in the range 300-900 nm. The optical parameter includes calculation (absorption coefficient α, extinction coefficient, energy gap). The result showed that the absorption, extinction coefficient, and reflectance decrease with the increase in polyester content, while transparency and transmittance increase. The absorption coefficient increases with wavelength to 365 nm, then decreases. Transmittance decreases with wavelength increase. The reflectance increases with wavelength increase. The energy gap does not affect the increase in the polyester content, so the conductivity will not change with the change in the polyester concentration. Fourier transform infrared spectroscopy (FTIR) analysis was utilized to distinguish bond absorption around 2900-3550 cm-1, and the aromatic C-H groups stretched due to vibration from medium to weak bands within 3090-3020 cm-1. The intensity of the ester group bonds and other bonds increased in the samples due to increased polyester content. FTIR showed physical interaction between novolac and polyester due to Van der Waals bonds.

In this study, the flame-retardant, thermal and mechanical properties of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and nano-SiO2 modified epoxy novolac resin is evaluated, and the combinational effects of both additives are verified. As a hardener, an isophorone diamine (IPDA) and polyetheramine blend is stoichiometrically added to obtain a low viscous epoxy resin system, suitable for resin injection and infusion techniques. The glass transition temperature (Tg) and the silica dispersion quality is affected by the DOPO modification and the nano silica particles. The flame-retardant (FR) and mechanical properties of the additives are investigated separately. The fracture toughness could be increased with the incorporation of both FR additives; however, the effect is deteriorated for higher DOPO amount which is referred to silica particle agglomeration and consequently reduced shear yielding mechanism. Flame-retardant properties, especially the peak heat release rate (pHRR) and the total heat release (THR) could be decreased from 1373.0 kW/m2 of neat novolac to 646.6 kW/m2 measured by resins with varying phosphorous and silica content. Thermogravimetric analysis (TGA) measurements show the formation of a high temperature stable char layer above 800 °C which is attributed to both additives. Scanning electron microscopy (SEM) images are taken to get deeper information of the flame-retardant mechanism, showing a dense and stable char layer for a certain DOPO silica mixture which restrains the combustible gases from the burning zone in the cone calorimeter test and influences the fire behavior of the epoxy resin.

This study investigates the impact of an increased bio-content on the mechanical properties of bio-based epoxy resins. Cardanol-based epoxy and novolac resins (65% and 84% bio-content, respectively) were combined with two commercial cardanol-based epoxy systems to achieve higher total bio-contents. Quasi-static tensile tests showed that resin blends with up to 40% bio-content maintain tensile properties comparable to traditional formulations, with a glass transition temperature (Tg) suitable for automotive requirements. The results highlight that an increased bio-content enhances flexibility and viscoelastic behavior. Additionally, the tests showed that epoxy resins with a high bio-content represent a sustainable alternative with reduced environmental impact. This work benchmarks novel cardanol-based epoxy formulations with existing bio-based systems, supporting their industrial application.