Thermo-oxidative Stability Research Articles

Ethylene-Vinyl Acetate (EVA) Containing Waste Hemp-Derived Biochar Fibers: Mechanical, Electrical, Thermal and Tribological Behavior.

To reduce the use of carbon components sourced from fossil fuels, hemp fibers were pyrolyzed and utilized as filler to prepare EVA-based composites for automotive applications. The mechanical, tribological, electrical (DC and AC) and thermal properties of EVA/fiber biochar (HFB) composites containing different amounts of fibers (ranging from 5 to 40 wt.%) have been thoroughly studied. The morphological analysis highlighted an uneven dispersion of the filler within the polymer matrix, with poor interfacial adhesion. The presence of biochar fibers did not affect the thermal behavior of EVA (no significant changes of Tm, Tc and Tg were observed), notwithstanding a slight increase in the crystallinity degree, especially for EVA/HFB 90/10 and 80/20. Conversely, biochar fibers enhanced the thermo-oxidative stability of the composites, which increased with increasing the biochar content. EVA/HFB composites showed higher stiffness and lower ductility than neat EVA. In addition, high concentrations of fiber biochar allowed achieving higher thermal conductivity and microwave electrical conductivity. In particular, EVA/HFB 60/40 showed a thermal conductivity higher than that of neat EVA (respectively, 0.40 vs. 0.33 W·m−1 ·K−1); the same composite exhibited an up to twenty-fold increased microwave conductivity. Finally, the combination of stiffness, enhanced thermal conductivity and intrinsic lubricating features of the filler resulted in excellent wear resistance and friction reduction in comparison with unfilled EVA.

Synthesis and antioxidation behavior in EPDM of novel macromolecular antioxidants with crosslinking and antioxidation effects

A novel antioxidant denoted as HVA-2@MB was synthesized through the reaction of N,N'-1,3-phenylene bismaleimide (HVA-2) and 2-mercaptobenzimidazole (MB) catalyzed by triethylamine. This antioxidant had high molecular weight as well as crosslinking and antioxidation functions. Then, the effect of HVA-2@MB on the crosslinking and antioxidation behaviors of ethylene-propylene-diene rubber (EPDM) was investigated. HVA-2@MB greatly reduced the inhibitory effect of antioxidants on rubber vulcanization and improved the crosslinking density of rubber. In addition, due to the reactivity of HVA-2@MB, the antioxidant groups were chemically bonded to the rubber network, which significantly reduced the migration of antioxidants in the thermo-oxidative environment, thereby improving the thermo-oxidative stability of the rubber. Therefore, compared with MB/EPDM composites, HVA-2@MB/EPDM composites exhibited better mechanical properties and thermo-oxidative stability during thermo-oxidative aging.

Performance Enhancement of Degraded Engine Oil with Blends of Neem Oil and Avocado Oil for Lubrication

A blending of different non-edible vegetable oils (Neem and Avocado) with synthetic oil (SAE 20W50) that is commercially available has attracted several studies towards making it sustainable, biodegradable, and environmentally suitable for mineral oil for lubricant production. The physicochemical, thermo-oxidative stability and corrosion properties of Nigerian degraded engine oil (Society of Automotive Engineers SAE 20W50) were studied using mixing ratios of 40/60, 50/50, and 60/40 blends of neem/degrade engine oil and Avocado/degraded engine oil respectively. The study revealed specific gravity values of 0.893, 0.897, 0.901 for neem/degraded engine oil and 0.893, 0.897, 0.901 for avocado/degraded engine oil which fall within SAE standard of 0.901. pH values for neem/degraded engine oil were: 5.83, 5.85, 5.62 and 5.59, 5.49, and 5.71 for avocado/degraded engine oil indicating acidic compared to (SAE 20W50) of 7.12. The viscosity of neem/degraded engine oil and avocado/degraded engine oil was found to be lower compared to the SAE 20W50. The Neem and Avocado oil each has a promising effect on the physicochemical properties of the SAE 20W50 blend.

Reinforced Structure Effect on Thermo-Oxidative Stability of Polymer-Matrix Composites: 2-D Plain Woven Composites and 2.5-D Angle-Interlock Woven Composites.

The thermo-oxidative stability of carbon fiber polymer matrix composites with different integral reinforced structures was investigated experimentally and numerically. Specimens of 2-D plain woven composites and 2.5-D angle-interlock woven composites were isothermally aged at 180 °C in hot air for various durations up to 32 days. The thermal oxidative ageing led to the degradation of the matrix and the fiber/matrix interface. The degradation mechanisms of the matrix were examined by ATR-FTIR and thermal analysis. The interface cracks caused by thermal oxidative ageing were sensitive to the reinforced structure. The thermo-oxidative stability of the two composites was numerically compared in terms of matrix shrinking and crack evolution and then experimentally validated by interlaminar shear tests.

A clean and sustainable strategy to produce bio-lubricant with high-bearing and good anti-oxidation ability from Lanzhou lily

Biolubricants like natural oil or grease are sustainable and renewable alternative to mineral lubricants. Poor thermo-oxidative stability and load-carrying capacity are the main obstacles limiting the application of bio-lubricants. Striving for a plant resource with plentiful ester analogues as base oil and other lubricating-benefit ingredients as natural additives may be a new and clean strategy to produce biolubricants with high-bearing and good oxidation stability. In this work, the bio-lubricant was extracted as Lanzhou lily crude extract (LLCE) from the widely cultivated crop Lanzhou lily (Lilium davidii var. unicolor) in China. Its lubricity, load-carrying capacity, and activity-composition relationship were investigated. LLCE exhibits good lubricity at temperature above 50 °C and extreme load-carrying capacity above 600 N. The friction coefficient at stable stage is about 0.12 and the wear rate of the steel discs is on the order of 10−7-10−8 mm3/Nm. These intriguing properties are attributed to the specific components in LLCE. Phenol esters or glycosides in LLCE is functional as base oil to provide the boundary lubrication, and other plentiful components like phospholipids, alkaloids, and organic sulfides play as natural additives to improve the lubricity and extreme pressure ability by accelerating the formation of tribo-reaction film. This work provides a sustainable and clean feedstock for high-performance bio-lubricants/additives and simultaneously expands the economic utilization of crops, which can be applied in the open lubricating systems like chainsaw, metal-cutting work and food-processing equipment in agricultural, food and manufacturer industries.

Study on aromatic nitrile-based resins containing both phthalonitrile and dicyanoimidazole groups

In order to prepare aromatic nitrile-based resins with improved curing reactivity, thermal and thermomechanical properties, and to clarify the difference in curing activity between dicyanoimidazole and phthalonitrile groups, a novel class of autocatalytic aromatic nitrile-based resins named PNDCI which contains both dicyanoimidazole (DCI) and phthalonitrile (PN) groups were designed and synthesized. A method for evaluating the reactivity of nitrile groups using the absorption wavenumber of FTIR was proposed. PNDCI monomers have demonstrated higher activity for self-promoted curing reactions than benzimidazole-containing phthalonitrile monomers (BIPN). The introduction of DCI can change the curing pathway of PN and inhibit the formation of phthalocyanine ring which is an important cured product of PN resins. The data of TGA, DMA, etc. revealed that the cured products of PNDCIs showed outstanding thermal stability, long-term thermo-oxidative stability at high temperatures (425°C) and thermal mechanical properties, which is favorable for the preparation of high temperature resistant resins. • Aromatic nitrile-based (PNDCI)resins containing both dicyanoimidazole (DCI) and phthalonitrile (PN) were reported. • 2.The difference in curing activity of the nitrile group of PN and DCI was preliminarily investigated. • 3.The cured PNDCI resin exhibits excellent thermal and thermomechanical properties.

Melamine modified phthalonitrile resins: Synthesis, polymerization and properties

Phthalonitrile resin, as a thermosetting resin, possesses high chemical resistance, high thermal resistance, high thermo-oxidative stability and good mechanical properties. However, the extremely high curing temperature needed to achieve high curing degree severely limits its large-scale application. It is found that introduction of benzoxazine moities into phthalonitrile would increase the reactivity and decrease the curing temperature. In this work, phthalonitrile resin with melamine moiety (BAph-m) is synthesized by taking advantage of benzoxazine chemistry using melamine as amine source. Its chemical structure is confirmed by Fourier infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (1H NMR) spectra. Its curing reactivity, polymerization mechanism and the properties of the resultant polymers are systematically studied. It is found that the introduction of melamine reduces the content of oxazine ring, leaving active groups like phenolic hydroxyls and secondary amines as build-in catalysts. Consequently, the modified resins show much higher reactivity. The exothermic peaks corresponding to ROP of benzoxazine ring and curing of phthalonitrile groups of BAph-30 m decreased to 197.4 °C and 278.2 °C, 77.7 °C and 30.1 °C lower than those of neat BAph. The gelation time shortened from 892 s for BAph-2m to 231 s of BAph-30 m. Moreover, it is found that the build-in active groups could catalyze the reaction of benzoxazine moities and phthalonitrile groups to form phenolic Mannich bridge structures, triazine rings, phthalocyanine rings and isoindoline. The modified resins show very high thermal stability with BAph-30m-280 showing initial decomposition temperature (Td5) of 492 °C and char yield (Yc) of 79.9%, which is 35 °C and 6.8% higher than those of BAph-280.

Molecular simulation of the O2 diffusion and thermo-oxidative degradation mechanism of carbon-doped boron nitride nanosheets/BTDA-ODA polyimide composites with high O2 adsorption capacity

Relevant studies have indicated that doping boron nitride nanosheets (BNNSs) into polyimide (PI) can significantly improve the thermal conductivity of composites and that the filling of inorganic nontechnical materials can inhibit the thermo-oxidative degradation of insulating polymer materials. Based on this information, three carbon-doped BNNSs models were obtained by modifying BNNSs. PI formed by the condensation of benzophenone-3,3 ',4,4 '-tetracarboxylic acid dianhydride (BTDA) and 4,4 '-diamino diphenyl ether (ODA) was used as a matrix to construct different composite models. Based on molecular simulation methods such as density functional theory (DFT) and reactive force field (ReaxFF), the diffusion of O2 through different composite systems and the inhibition of thermo-oxidative degradation of PI by different dopants were studied. The results showed that compared with pure BNNSs, the BNCB obtained by substituting carbon atoms for boron atoms on BNNSs better inhibited the thermo-oxidative degradation of PI. The adsorption of O2 and the inhibition of the O2 reaction at 2000 K with BNCB were significant improved compared with those with pure BNNSs. The content of the main products of PI thermo-oxidative degradation in the BNCB doping system was only 16% of that in the BNNSs system and the O2 consumption of the BNCB system was 34% lower than that of pure PI. By inhibiting the diffusion of O2 in PI, C-doped BNNSs reduced the contact between O2 and the PI matrix at high temperature, thus inhibiting the damage of O2 to the imide group and benzene ring in PI chains to improve the thermo-oxidative stability of composites. In this paper, a new C-doped BNNSs/PI model was designed based on the BNNS/PI composite model with high thermal conductivity, which achieved the double improvement of PI thermal conductivity and thermo-oxidative stability.

Effect of the Surface Functionalization of Graphene and MWCNT on the Thermodynamic, Mechanical and Electrical Properties of the Graphene/MWCNT-PVDF Nanocomposites.

The nanocomposites of poly(vinylidene fluoride) (PVDF) with pristine graphene nanoflakes (GNF) and a multi-wall carbon nanotube (MWCNT) were prepared by the solution casting method. Additionally, the GNF and MWCNT were functionalized by acid treatment, and nanocomposites of the acid-treated MWCNT/GNF and PVDF were prepared in the same method. The effect of the acid treatment of MWCNT and GNF on the mechanical, thermal and thermo-oxidative stability and the thermal conductivity of the MWCNT/GNF-PVDF nanocomposites was evaluated, and the results were compared with the untreated MWCNT/GNF-PVDF nanocomposites. In both cases, the amount of GNF and MWCNT was varied to observe and compare their thermal and mechanical properties. The functionalization of the GNF or MWCNT resulted in the change in the crystallization and melting behavior of the nanocomposites, as confirmed by the differential scanning calorimetry analysis. The addition of the functionalized GNF/MWCNT led to the improved thermal stability of the PVDF nanocomposites compared to that of the non-functionalized GNF/MWCNT-PVDF nanocomposites. The thermal and electrical conductivity of the functionalized and non-functionalized GNF/MWCNT-PVDF composites were also measured and compared. The functional groups, crystal structure, microstructure and morphology of the nanocomposites were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

Synthesis of Nanoplatelet Zinc Borate and its Combination with Expandable Graphite and Red Phosphorus as Flame Retardants for Polypropylene

The zinc borate nanoparticles (2ZnO.3B2O3.3H2O) were successfully prepared by precipitation reaction in aqueous solutions of borax and zinc sulfate using oleic acid as a surfactant. The structural, morphological characteristics and the wettability of the particle surface were studied through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the contact angle. The hydrophobic zinc borate (n-ZB) had nanoplatelet morphology with a diameter of 1.0 - 1.5 µm and thickness of about 90 nm. Nano zinc borate showed a synergistic influence with expandable graphite (EG) and red phosphorus (RP) on the flame retardant properties and thermo-oxidative stability of polypropylene (PP). The nanocomposite 7n-ZB/7RP/7EG/PP achieved the V-1 UL94 verticle burning test with a limited oxygen index of 23.7% and the char yield of 14.67 wt.% at 900 oC. Furthermore, the fire retardant performance and the mechanical properties of the nanocomposites loading ZB nanoparticles were improved compared with the composites employing commercial ZB microparticles.

Depolymerisation of kraft lignin to obtain high value-added products: antioxidants and UV absorbers

Abstract This study demonstrates that bio-based products of lignin depolymerisation can potentially replace common antioxidants and UV absorbers in the plastics and cosmetics industries. The kraft lignin Indulin AT was used to obtain low-MW lignin and monomers & oligomers rich in phenolic hydroxyl groups. Both thermo-oxidative stability and antioxidant activity significantly improved upon lignin depolymerisation. The results from oxidation induction time differential scanning calorimetry (OIT-DSC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) measurements show that the lignin based depolymerisation products are comparable with commercial antioxidants like pentaerythritol-tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate) (Irganox 1010). UV/vis spectroscopy was investigated to confirm absorption of the depolymerisation products in the UVA and UVB range (280–400 nm).

A rapid method for approximative evaluation of thermooxidative stability of organic materials.

In this work, a novel procedure for fast assessment of the material residual stability is proposed. The method resides in integral isoconversional kinetic analysis of the thermal oxidation of unaged material employing the Berthelot–Hood temperature function. Subsequently, the obtained conversion-independent kinetic parameter D is also employed for samples aged in various regimes. The value of conversion-dependent parameter A for aged samples is calculated from the oxidation onset temperature measured at 5 °C min−1. The residual stabilities are then calculated as a simple ratio of the parameter A of aged material to that of the unaged one. The method has been applied and verified for the samples of low-density polyethylene aged by thermal, radiation and combined ageing. The method can also be employed for high-throughput screening of the effect of various stabilizers and antioxidants in a given organic matrix.

Synthesis and study of the hydrolytic and thermo-oxidative stability of <i>p</i>-(N-β-D-mannopyranosyl)aminobenzoic acid

The performed condensation of p-aminobenzoic acid with D-mannose produced N-mannopyranosylamine with ? configuration at the anomeric centre, which was confirmed by vibrational spectroscopy. The reactivity of the synthesized product in the processes of acid hydrolysis and thermal oxidation in a freely aerated medium was studied. A hydrolytic stability study showed p-(N-β-D-mannopyranosyl)- aminobenzoic acid, which is stable in ethanolic media, to gradually hydrolyse upon heating (50 °C) in acidic aqueous solutions, as confirmed by FTIR spectroscopy and thin-layer chromatography. Upon thermal oxidation, the synthesized product shows sufficient stability when heated up to 30–50 °C. However, a further increase in temperature to 70 °C accelerates destruction, which is manifested in an increase in the band intensity of 1690 cm-1 (vO=C–C=N) in the spectra of the second derivatives of thermostated samples. This process is assumed to involve direct oxidation of N-glycosylamine, most likely in the acyclic form of enaminol. Additionally, the nature of N-glycosylation by-products was studied by electron and oscillatory spectroscopy. These studies indicated the formation of melanoids – coloured products of deep destruction, which might exhibit growth-regulating and other types of biological activity. The main structural fragments of melanoids are assumed to be formed in solutions through the interaction of enaminol forms with α-dicarbonyl derivatives. Our experimental data obtained earlier also indicate the biological activity of melanoids in arylaminocarbonyl reactions, thereby allowing the technology of obtaining functional products of different stages of sugar-amine interactions to be combined within a single synthesis operation. The feasibility of this approach is determined by the availability of reagents, mild synthesis and product separation conditions, as well as by their environmental friendliness.

Preparation and Properties of Modified Phenylethynyl Terminated Polyimide with Neodymium Oxide.

Modified phenylethynyl terminated polyimides (PIs) were successfully prepared by using neodymium oxide (Nd2O3) via high-speed stirring and ultrasonic dispersion methods. In addition, the structure and properties of the Nd2O3-modified imide oligomers as well as the thermo-oxidative stability of the modified polyimides (PI/Nd2O3 hybrid) and its modification mechanism were investigated in detail. The thermogravimetric analysis (TGA) results indicated that the 5% decomposition temperature (Td5%) of the PI/Nd2O3 hybrids improved from 557 °C to 575 °C, which was also verified by the TGA-IR tests. Meanwhile, the weight loss rate of the PI/Nd2O3 hybrids significantly decreased by 28% to 31% compared to that of pure PI under isothermal aging at 350 °C for 450 h when the added content of Nd2O3 was between 0.4 wt% and 1 wt%, showing outstanding thermo-oxidative stability. Moreover, the mechanism of the enhanced thermo-oxidative stability for the modified PIs was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Sulfur-Containing Silsesquioxane Derivatives Obtained by the Thiol-ene Reaction: Synthesis and Thermal Degradation.

This article presents the synthesis of new derivatives of octa(3-thiopropyl)silsesquioxane (SSQ-8SH) via thiol-ene reaction with simple olefins bearing alkyl groups as well as methoxysilyl, substituted aryl or fluoroalkyl groups. All products were characterized by 1 H NMR, 13 C NMR, 29 Si NMR, FTIR, GPC, MALDI-TOF-MS, as well as thermal analysis (TGA) to confirm their structures, purity and thermal stability, and finally give some insight into their thermal degradation pathway. In some of the structures obtained, the T5% values take place at high temperatures and are close to 230 °C. The thiol-ene reaction allowed to obtain 7 new compounds with high yield (>92 %), no by-products and in a relatively short time (24 h). All products are characterized by high conversion >99 %. New derivatives can find potential use as modifiers of plastics to improve their certain properties for example hydrophobicity or thermo-oxidative stability.

DSC isothermal and non-isothermal assessment of thermo-oxidative stability of different cultivars of Camelina sativa L. seed oils

DSC isothermal and non-isothermal assessment of thermo-oxidative stability of different cultivars of Camelina sativa L. seed oils

Effect of natural carbon filler on thermo-oxidative degradation of thermoplastic-based composites

Thermo-oxidative degradation of thermoplastic-based composites filled with two types of carbon filler including bituminous (Pittsburgh No.8, P8) and sub-bituminous (Powder River Basin, PRB) coals were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. Oxidation induction time (OIT) and activation energy (AE) for coal plastic composites (CPCs), HDPE, and commercially available wood plastic composites (WPCs) were determined using isothermal and isoconversional kinetic methods. OIT values for CPC increased with coal content, indicating higher thermo-oxidative stability. AE values obtained using isothermal method were 52–116 kJ/mol for all CPC formulations, 32 kJ/mol for HDPE, and 33–114 kJ/mol for WPCs. AEs for CPCs obtained using isoconversional methods were not constant but rather dependent on the degree of degradation with CPC/ P8 coal possessing higher overall AE. Incorporating coal into HDPE increased thermo-oxidative stability of the resulting composite, indicating coal potentially acts as a natural primary and secondary antioxidant for polymer materials.

Thermo-oxidative stability of asymmetric distigmasterol-modified acylglycerols as novel derivatives of plant sterols

The study investigated the thermo-oxidative stability of distigmasterol-modified acylglycerols as a new structured acylglycerols. Samples were heated at 60 and 180 °C for 8 h. Their percentage degradation and products formed during heating were compared with free stigmasterol and stigmasteryl esters. The remaining of stigmasterol and fatty acid parts, the formation of stigmasterol oxidation products and the composition of polar and non-polar fractions were analysed using chromatographic methods. The cytotoxicity and genotoxicity were determined with the use of an MTT test and a comet assay, respectively. The highest stability during heating was observed for 2,3-distigmasterylsuccinoyl-1-oleoyl-sn-glycerol (dStigS-OA) and the lowest for 2,3-distigmasterylcarbonoyl-1-oleoyl-sn-glycerol (dStigC-OA). Data showed that the formation of thermo-oxidative degradation products is affected by the temperature and chemical structure of lipids present in the molecule. The dStigMAs bonded by a succinate linker and products formed during their thermo-oxidation showed no cytotoxic or genotoxic activity to normal human cells.

UV-LED Curable Acrylic Films Containing Phosphate Glass Powder: Effect of the Filler Loading on the Thermal, Optical, Mechanical and Flame Retardant Properties.

In this work, we thoroughly investigate the effects of the incorporation of a phosphate glass micrometric powder on the morphology, as well as on the thermal, optical, mechanical and flame retardant properties of UV-LED curable acrylic films. To this aim, the filler loading was changed within 10 and 50 wt.%. UV-LED initiated curing was selected as a fast and reliable system, as the standard UV-curing process was not suitable because of the presence of the glass powder that decreased the quantum efficiency during the UV exposure, hence preventing the transformation of the liquid system into a solid network. The glass powder slightly increased the glass transition temperature of the acrylic network, hence showing a limited effect on the chain segments mobility; besides, increasing filler loadings were responsible for a progressive decrease of the transparency of films, irrespective of a marginal effect on their refractive index. Conversely, the presence of increasing amounts of phosphate glass improved the thermal and thermo-oxidative stability of the cured products. Besides, phosphate glass was capable of remarkably enhancing the flame retardance of the acrylic network at 50 wt.% loading, which achieved self-extinction in vertical flame spread tests (and was V-0 rated). This formulation, as assessed by forced-combustion tests, also displayed a remarkable decrease of peak of Heat Release Rate and Total Heat Release (by 44 and 33%, respectively) and of Total Smoke Release and Specific Extinction Area (by 53 and 56%, respectively). Further, the filler promoted an increase of the stiffness and surface hardness of the films, at the expense of a decrease in ductility. All these findings may justify the potential use of these composite films as flame retardant coatings for different flammable substrates.

Synthesis and characterization of phosphonated polybenzimidazole membranes with improved proton conductivity for high-temperature proton exchange membrane applications

The study has synthesized a novel dicarboxylic acid monomer with phosphonate group, 2-((diethoxyphosphoryl)methyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (PMDA), and then successfully prepared a series of polybenzimidazole polymers containing methyl-phosphonic acid group and ether group (POPBI-x) via the polycondensation between PMDA, 4,4′-oxybis (benzoic acid) (OBBA) and 3,3′-diaminobenzidine (DAB) in polyphosphoric acid (PPA)/phosphorus pentoxide (P2O5). Meanwhile, the smooth membranes were fabricated via the solution-casting method. Results of TGA, the Fenton’s reagent immersing test, and the tensile test showed that the POPBI-x membranes possessed good thermo-oxidative stability and mechanical properties. Moreover, compared to poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI), POPBI-x had a significant enhancement in the phosphoric acid doping level, PA retention ability, and proton conductivity after doped with phosphoric acid (PA) because the methyl-phosphonic acid groups on the backbones enriched the hydrogen bonding interactions between the polymer chain and phosphoric acid. Notably, the POPBI-19 exhibited a high phosphoric acid doping level of approximately 11.3 and excellent proton conductivity of approximately 0.0523 S cm−1 at 180°C under anhydrous conditions.