Thermo-oxidative Stability Research Articles

Physicochemical characteristics of cold-pressed blackcurrant-, strawberry-, and raspberry seed oils during storage and its influence on thermo-oxidative stability

The storage characteristics of cold-pressed blackcurrant-, strawberry- and raspberry seed oils and the factors influencing thermo-oxidative stability during storage were determined. It was established that throughout one year there were no significant (p ≤ 0.05) changes of thermo-oxidative stability (OIT at 120 and 140 °C) and fatty acid composition in all berry seed oils (BSO), despite a minor reduction in antioxidant activity (DPPH radical scavenging) and tocopherol content, and an increase in acid value, p-anisidine value, and K232, K268 values. Pigment degradation became noticeable after 6 months, resulting from a decrease in chlorophyll and carotenoid content, and observed in changes of colour parameters (angle hue, chroma, ΔE). The study also showed that many compositional factors play an important role in maintaining the thermo-oxidative stability of berry seed oils at a constant level over a period of one year, among which the most significant parameters influencing OIT values were the content of fatty acid c18:1, tocopherols and carotenoids, as revealed by the multiple linear regression analysis (MLR).

Enhancement of thermo-oxidative stability of polyimide composites by functionalized polyimide film surface modification

Polyimide (PI) resin-based composites exhibit excellent high-temperature resistance, solvent resistance, and mechanical properties, making them have broad application prospects in various fields such as aviation, aerospace, and transportation. With the continuous development of new devices, the requirements for the service temperature and service life of materials are improved, so there is an urgent need to improve the thermo-oxidative stability of polyimide composites. In this work, PI films, aluminum-coated PI film, and copper-coated PI film with low oxygen permeability were used as surface oxygen barrier materials, and surface film modified polyimide composites were prepared. The results show that, compared with the unmodified composite materials, after aging at 350°C for 400 hours, the weight loss rates of the composites modified by three kinds of surface films all increased by more than 50%, and the bending strength retention rates of the composites respectively increased by 47%, 51%, 45%, and the interlaminar shear strength retention rates respectively increased by 107%, 82%, 78%, showing excellent thermo-oxidative stability.

Wave-transparent and eco-friendly flame-retardant phosphorus-based phthalonitrile/quartz composites by a synchronized self-curing strategy with cyano and alkynyl groups

The robust human–machine interaction systems of the aerospace industry necessitate the development of thermal resistant wave-transparent composites, with a pivotal focus on organic resin matrix. However, enhancing the heat resistance of such materials while preserving other critical attributes has been a formidable challenge. In this study, a novel designed strategy of a dual-curing functional phosphorus-based phthalonitrile monomer (P-ALK-PN) has been proposed. The optimized curing temperatures for intra- or intermolecular Diels-Alder reactions of alkynyl groups and polyaddition reaction of cyano groups resulted in a homogeneous and highly crosslinked N-enriched phthalonitrile system. After curing at 450 °C, the resin, namely P-ALK-PN-450 °C, demonstrated exceptional thermal stability (T5% = 644 °C), thermo-oxidative stability (T5% = 554 °C), and char yield at 800 °C (90.7 % in N2 and 67.5 % in air). Their quartz fiber reinforced composites (P-ALK-PN/QFs) were subsequently fabricated by the hot-pressing process. Upon post-curing at 420 °C, P-ALK-PN-420 °C/QF displayed elevated glass transition temperature (550 °C), flexural strength (319 MPa), and relatively low dielectric properties with a dielectric constant (Dk) of approximately 4.2 and a dissipation factor (Df) less than 0.02 across a wide temperature ranging from 25 °C to 600 °C. Especially, it exhibited excellent flame retardancy (only a 6.7 % weight loss at ambient temperatures exceeding 1300 °C for 200 s) as well, stemming from release of eco-friendly inert gases (NH3) and formation of a graphitized protective layer during pyrolysis. These promising results highlight the potential applications of P-ALK-PN resins in aerospace and high-performance engineering fields.

Development of polyols analogous to neopentyl glycol and trimethylolpropane for the production of oleic acid-based biolubricants

Vegetable oils and animal fats have been known and used as lubricants and fuels since ancient times. However, the chain structure of the triacylglycerols (TAGs) generate limitations that discourage the use of these raw materials as lubricants. As an alternative to improve the physicochemical and thermo-oxidative characteristics of natural oils, the use of polyols without the β-hydrogens in the triacylglycerols structure is an efficient solution for the production of biolubricants. In this context, a series of polyols, analogous to trimethylolpropane (TMP) and neopentyl glycol (NPG) was synthesised and applied in the synthesis of polyol esters based on oleic acid. These esters were prepared by homogeneous catalysis using p-toluenesulfonic acid (p-TSA) and are intended for use as biolubricants. The synthesised polyols were characterized by one and two-dimensional NMR. The derived polyol esters were purified and had their structure confirmed by 1H and 13C NMR, infrared spectroscopy, and mass spectrometry. The polyol esters showed high viscosity index (189 – 222), thermo-oxidative stability (Tonset between 258 and 285 °C), and low melting points (between –19.4 and –47.6 °C). Furthermore, polyol esters showed reduced friction coefficients (0.021 – 0.041) and scar wear diameter on the metallic surface (0.274 – 0.448 mm). In addition to the satisfactory results of thermal stability and lubricity, which suggest the potential of these molecules as lubricants, all molecules were considered environmentally safe when evaluated through the Zebrafish toxicity model.

Kinetics and mechanism of thermal and thermo-oxidative degradation for high-density polyethylene modified by fullerene and its derivative

To investigate the effect of fullerene (C60) and its iron compound (C60-Fe) on the thermal and thermo-oxidative degradation mechanism of high-density polyethylene (HDPE), the Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern methods are used. The data of thermal and thermo-oxidative degradation are achieved through the thermogravimetric (TG) analysis, and the trapping free-radical ability and the dispersion of C60 or C60-Fe in matrix are characterized by the electron spin resonance (ESR) and transmission electron microscopy (TEM). C60 and C60-Fe improve effectively the thermal and thermo-oxidative stability of HDPE. In N2, C60 and C60-Fe do not change the degradation mechanism of HDPE, and the degradation rate is determined by the random generation and growth of free-radicals. In air, C60 changes the reaction order (n) of HDPE at the oxidation stage and the degradation mechanism at the random fracture. C60-Fe changes the thermo-oxidative mechanism of HDPE due to the formation of cross-linked network.

Study on Thermal Oxygen Aging Characteristics and Degradation Kinetics of PMR350 Resin.

The thermal stability and aging kinetics of polyimides have garnered significant research attention. As a newly developed class of high thermal stability polyimide, the thermal aging characteristics and degradation kinetics of phenylene-capped polyimide prepolymer (PMR350) have not yet been reported. In this article, the thermo-oxidative stability of PMR350 was investigated systematically. The thermal degradation kinetics of PMR350 resin under different atmospheres were also analyzed using the Flynn-Wall-Ozawa method, the Kissinger-Akahira-Sunose method, and the Friedman method. Thermogravimetric analysis (TGA) results revealed that the 5% thermal decomposition temperature (Td5%) of PMR350 in a nitrogen atmosphere was 29 °C higher than that in air, and the maximum thermal degradation rate was 0.0025%/°C, which is only one-seventh of that observed in air. Isothermal oxidative aging results indicated that the weight loss rate of PMR350 and the time-dependence relationship follow a first-order exponential growth function. PMR350 resin thermal decomposition reaction under air atmosphere includes one stage, with a degradation activation energy of approximately 57 kJ/mol. The reaction model g(α) fits the F2 model, and the integral form is given by g(α) = 1/(1 - α). In contrast, the thermal decomposition reaction under a nitrogen atmosphere consists of two stages, with degradation activation energies of 240 kJ/mol and 200 kJ/mol, respectively. The reaction models g(α) correspond to the A2 and D3 models, with the integral forms represented as g(α) = [-ln(1 - α)]2 and g(α) = [1 - (1 - α)1/3]2 due to the oxygen accelerating thermal degradation from multiple perspectives. Moreover, PMR350 resin maintained high hardness and modulus even after thermal aging at 350 °C for 300 h. The results indicate that the resin exhibits excellent resistance to thermal and oxygen aging. This study represents the first systematic analysis of the thermal stability characteristics of PMR350 resin, offering essential theoretical insights and data support for understanding the mechanisms of thermal stability modification in PMR350 and its engineering applications.

UV‐cured epoxy‐acrylate interpenetrating polymer networks with different contents of epoxidized soybean oil

AbstractThis work aims to study the effect of epoxidized soybean oil (ESO) concentration on the process of formation and characteristics of UV‐cured ternary epoxy‐acrylate interpenetrating polymer networks (IPNs). Whereas the amount of triethylene glycol dimethacrylate (TEGDMA) keeps constant, the one of ESO incorporated to substitute the respective quantity of diglycidyl ether of bisphenol A (DGEBA) is equal to 10, 20, and 30 parts by weight (pbw). A total of 30 pbw of ESO is found to be the most effective content for altering the conversion degree of epoxy groups and for enhancing the impact resistance of cured materials while providing their transparency. The addition of ESO induces the decrease in cross‐linking density and in the values of glass transition temperature. The samples exhibite good water and chemical resistance with some variations dependent on their composition. Thermooxidative stability of the specimens gradually reduces as the content of aromatic epoxy decreases. Overall, the introduction of ESO into epoxy‐acrylate IPNs not only lessens the fraction of synthetic epoxide but also facilitates the photopolymerization process of DGEBA and diminishes its brittleness. Considering fine atmospheric resistance testified by accelerated weathering test, given materials may be purposed as transparent films or protective coatings for both indoor and outdoor applications.

In English

Biopolymer matrices has been synthesized on the basis of ED-20 epoxy resin and soybean oil (SbO) bearing cyclocarbonate and epoxy groups. Mono(cyanoethyl)diethylenetriamine (UP) and tris(2-hydroxyethyl)amine (TEA) were used as hardeners. Chemical structure, mechanical properties, thermo-oxidative resistance of the samples and their changes after contact with distilled water, alkaline or acidic environment were studied. By means of ATR-FTIR the possible formation of H-NIPU (hybrid non-isocyanate polyurethane) fragments between cyclocarbonate groups of SbO and amino groups of the hardener was demonstrated. Influence of the curing mode and the type of hardener on water absorption, chemical and thermal oxidation resistance of the developed biopolymer matrices was thoroughly investigated. UP-based biopolymer matrices showed water and alkali resistance similar to the ones of neat epoxy polymers, while TEA-based biopolymer matrices showed better resistance to the acidic medium. The thermo-oxidative stability of the chosen samples was revealed by the TGA method in an air atmosphere. It was demonstrated that epoxy polymer cured with TEA hardener were more stable than the one cured with UP hardener. The similar dependence is observed for biopolymer matrices based on TEA hardener. At the same time, the curing mode has almost no effect on ultimate tensile strength value of the samples with ED-20/UP composition. However, the addition of functionalized SbO to the epoxy matrix cured with both TEA and UP hardeners increases the ultimate tensile strength values regardless of the type of oil functionalization. As expected, all biopolymer matrices exhibited higher ultimate tensile strength compared with unmodified epoxy polymers, which provides the possibility of their further application to obtain multi-layered bioplastics.

Aromatic nitrile resins with improved processability and thermal properties prepared by collaborative design of structure and blending strategy

The contradiction between processability and thermal properties has been limiting the development of high-performance thermoset resins, especially aromatic nitrile resins (AN). A new AN resin blend of 2-(3-(3,4-dicyanophenoxy)phenyl)-1H-imidazole-4,5dicarbonitrile (PNDCI) and 4-(4-aminophenoxy) phthalonitrile (APN) named PAB based on Brønsted acid-base blending strategy and introduction of asymmetric structure was designed and prepared in this paper. A series of characterizations showed that the PAB has not only excellent processability with a diminished melting point (118°C), wider processing window (90°C), and high curing reactivity, but that the cured PAB resins (C-PAB) also possessed high glass transition temperature (477°C), excellent long-term thermo-oxidative stability, thermomechanical properties and dimensional stability. The present design strategy of blending resins provides PAB as a good reference material for achieving a good balance between processability and high-temperature resistance.

Selection of antioxidants for capacitor grade polypropylene film: Insights into electrical performance of the oil-film system.

High voltage power capacitors employ the oil-impregnated polypropylene film as the insulation. The swelling phenomenon might drive the antioxidants and small molecules within the film to migrate into the oil. It is necessary to comprehensively investigate the physical migration mechanism of antioxidants and their impact on the electrical performance of the oil-film combination insulation system and, consequently, formulate the proper selective prescription of antioxidants. Theoretical elucidation of the competitive interaction mechanism between the film and the oil in attracting antioxidant molecules was achieved through the calculation of inter-molecular binding energy, and the migration coefficient ηm was introduced to quantify the migration characteristics of antioxidants. Experimentally, the effects of antioxidants on the space charge distribution of the film, the dielectric properties of the oil, and the breakdown characteristics of both the film and oil were investigated. The experimental conclusions are consistent with theoretical analysis. The lamellar structure antioxidant molecules with ηm > 1 tend to migrate from the film to the oil, which results in increased dielectric loss and decreased breakdown strength of the insulating oil. In addition, the presence of phosphorus atoms in phosphite antioxidants contributes to a reduction in the breakdown strength of the film. For capacitor grade polypropylene film, in addition to the synergistic effect between different types of antioxidants on the thermo-oxidative stability, the structure of the antioxidant molecules and its influence on the electrical performance of the oil-film systems should also be taken into account.

Synthesis of polyol esters of estolide and evaluation of their tribological properties

Polyol esters of oleic acid estolides with propylene glycol (PG), neopentyl glycol (NPG), trimethylolpropane (TMP), and pentaerythritol (PE) were synthesized. A qualitative analysis of the role of the structure of various physicochemical and tribological properties was carried out. The synthesized esters were evaluated based on physicochemical properties like pour point (PP), kinematic viscosity (KV), viscosity index (VI), surface tension, and thermo-oxidative stability with commercial and reported data of esters. To gauge the potential of the esters as a lubricity additive, the esters were blended with SN 500 base oil. The tribological assessment showed the ability of the esters to reduce wear & friction and increase the load-carrying capacity.

Rheological insights into the degradation behavior of PP/HDPE blends

The (re-)processing and degradation behavior of polypropylene (PP) blends with high-density polyethylene (HDPE) is a crucial topic in mechanical recycling due to the prevalence of PP/HDPE mixtures. In particular, small amounts of cross-contamination (below 10.0 wt.%) between these polyolefins are quite common. While much empirical data is available, systematic studies on such blends are scarce and rarely account for the polymers’ chain structure. This study employs time-resolved rheology, atomic force microscopy (AFM), differential scanning calorimetry (DSC) and chemiluminescence techniques to study the degradation of different PP types containing 0.5 to 10.0 wt.% of HDPE. It is observed that the addition of small amounts of HDPE can result in a prominent change in the viscoelastic properties of PP during the thermo-oxidative degradation. The substantial evolution of elasticity in the blends is mainly related to the gelation of fine PE particles dispersed within the PP matrix. It is also shown that a smaller viscosity ratio between the blend components can lead to a more significant degradation through morphology alterations. Remarkably, time-resolved rheology studies revealed that even a small amount of HDPE (2.5 wt.%) can lead to a reduction in the thermo-oxidative stability of the PP/HDPE blend through excessive branching/crosslinking of the HDPE phase. This effect was particularly more pronounced when the PP contained an ethylene comonomer in its backbone. The finer morphology of PE particles in PP copolymer can exacerbate the thermo-oxidative stability of the blend. These insights are essential in designing new life cycles for recycled PP cross-contaminated with HDPE, typically found in the light fraction of municipal solid plastic waste.

Improvement of the oxidative stability of edible oils through enzymatic esterification with hydroxytyrosol‐rich extract

AbstractOxidative degradation is a common issue of commercial edible oils that results in rancidity, downgrading the organoleptic characteristics of food matrices. The aim of this study was the enzymatic modification of common vegetable oils (pomace olive and sunflower oil) with polyphenolic extract to prepare functional oils enriched with bioactive phenolipids. Under that scope, an agro‐industrial effluent, olive mill wastewater, was used as source to recover phenolic compounds. The recovery of hydroxytyrosol and tyrosol reached up to 81.2% ± 0.3% and 98.3% ± 0.2%, respectively. Further, immobilized lipase was used to catalyze the one‐step acylation of these phenolic antioxidants into the oils with the aim of enhancing their stability under accelerated oxidation conditions. The optimum parameters of the bioconversion were found to be 0.1% (w/w) immobilized lipase, 24h of incubation at 50°C under orbital shaking reaching high conversion yields for both phenolic compounds (≥94%). The results also highlighted that the extract‐modified oils presented notable thermooxidative stability at 60°C for 28 days compared to the control and synthetic antioxidant‐enriched oils, as demonstrated by several analytical (conjugated dienes, thiobarbituric reactive substances), chromatographic (solid‐phase microextraction gas chromatography/mass spectroscopy), and spectroscopic (fluorescence, attenuated total reflectance) techniques, giving new insights regarding the preservation of edible oils.Practical Application: Htyr has recently gained much attention as an active ingredient of food matrices for industrial applications due to its high antioxidant/antiradical activity. A major drawback of Htyr exploitation is the high market price and its solubility. Meanwhile, several edible oils are prone to autooxidation during transport, stock management, and household storage. The proposed one‐step biocatalytic process aims to enhance the lipophilicity and bioactivity of Htyr in bulk oil systems, making the use of this potent antioxidant compound feasible. This approach shows promise in extending the shelf life of common oils and highlights the advantages of by‐product management. Moreover, these functional oils can be applied for the preparation of sauces, bakery products, food supplements, and so on, as the bioactive ingredients that are present in them can delay the oxidative cascade reactions and, thus, the spoilage of the products, whereas the whole process meets the requirements of circular economy and green chemistry.

Synthesis and characterization of a high-temperature polycyanophosphate resin

A phosphorus-containing polymer with very high thermo-oxidative stability was synthesized for the first time by addition of silver nitrate to tricyanophosphine (P(CN)3). By optimizing the reaction time and silver nitrate concentration to a 1:1 molar ratio, a new polycyanophosphate [p(CP)] was formed as the primary phosphorus-containing product over the competing species, P(CN)3. The reactions and products were monitored by FT-IR, ICP-OES, NMR, and XPS spectroscopic techniques, which indicated a complicated oxidation reaction that converted the P(III) precursor species to P(V) polyphosphate species with pendant cyano- and isocyano- moieties. The p(CP) resin was found to contain a high (17.6 at.%) amount of phosphorus by ICP-OES, which contributed to its excellent thermo-oxidative resistance with a high char yield of over 60 wt.% at 1000 °C (1273 K) in air, indicating that the material could be particularly useful for high-temperature applications.

Development of MWCNTs@PDMS nanocomposites with enhanced hydrophobicity and thermo-oxidative stability

This paper presents the fabrication of hydrophobic polymer nanomaterials with improved thermal characteristics based on MWCNTs and poly(dimethylsiloxane). The samples were synthesized by physical adsorption of poly(dimethylsiloxane) onto P-MWCNTs surfaces in the amount from 5 to 20 wt%. The effect of different content of adsorbed polymer on the structure and properties of the prepared nanocomposites was studied in detail using ATR-FTIR, SEM, TEM, XRD and RS techniques. XPS results showed that with the increase of adsorbed PDMS onto the MWCNTs surfaces, the Si 2p atomic percentage increased from 1.5 to 5.0 at.%. The investigation of thermal properties using TGA/DSC techniques in air atmosphere revealed that polymer adsorption on the MWCNTs surfaces enhances the thermo-oxidative stability of the nanocomposites to a great extent. The WCA of MWCNTs@PDMS-1000(20) nanocomposite reached 138.9° while this value was 81.8° in the case of the P-MWCNTs. The electrical characterization of the examined samples demonstrated a non-linear current–voltage behaviour and the invariance of the electrical current value with the increasing polymer content in the nanocomposites. The results suggest that the obtained nanocomposites have multi-functional surfaces and are promising for integration into a silicon-based polymer matrix for the development of new materials for electronic devices.

Rheological and Functional Properties of Mechanically Recycled Post-Consumer Rigid Polyethylene Packaging Waste.

The properties of recycled post-consumer rigid polyethylene packaging waste were studied, using sorted waste washed in the laboratory with water alone and with added detergent, and compared with large-scale high-intensity washed flakes. The washed flakes were compounded using three different temperature profiles in a twin-screw extruder and then injection molded. A higher compounding temperature reduced the thermo-oxidative stability, the average molecular mass, and the viscosity of the samples. Rheological measurements suggested that changes in chain branching occurred at different compounding temperatures. The strength and the elongation at break were also influenced by the compounding temperature in both the molten and solid states. Detergent washing maintained the thermo-oxidative stability in contrast to washing with water. The large-scale washed samples had a relatively high thermo-oxidative stability, a higher melt elasticity, and a lower elongation at break in both the molten and solid states than the laboratory-scale washed samples. The thermal properties, melt elasticity, Young's modulus, yield stress, and yield strain of the samples were not, however, significantly affected by either the compounding temperature or the washing medium and intensity. The results indicated that recycled post-consumer rigid polyethylene packaging waste has properties that can support further applications in new products.

Preparation and Characterization of Bismaleimide-Resin-Based Composite Materials.

This study utilized bismaleimide (BMI) resin, reinforced with introduced ether bonds, as a binding matrix, in combination with silicon carbide (SiC), for the fabrication of composite materials. A thorough investigation was conducted to assess the influence of diverse processing parameters on the mechanical properties and high-temperature thermo-oxidative stability of these composites. Experimental results indicate a notable improvement in the mechanical properties of the composites upon the incorporation of ether bonds, in contrast to their unmodified counterparts. The variation in performance among composites with different ratios and molding densities is apparent. Within a certain range, an increase in resin content and molding density is correlated with improved bending strength in the composites. With a resin content of 27.5 vol% and a molding density of 2.31 g/cm3, the composite achieved a maximum flexural strength of 109.52 MPa, representing a 24% increase compared to its pre-modification state. Even after exposure to high-temperature heat treatment, the composites displayed commendable mechanical properties compared to their pre-ether bond modification counterparts, maintaining 74.5% of the strength of the untreated composites at 300 °C. The scanning electron microscopy (SEM) microstructures of composite materials correlate remarkably well with their mechanical properties.

Synergism between α-amino acid-derived polyamidoamines and sodium montmorillonite for enhancing the flame retardancy of cotton fabrics

Polyamidoamine (PAA)/sodium montmorillonite (MMT) nanocomposite coatings were investigated as flame retardants for cotton to ascertain whether the addition of clay improved the efficacy of PAAs thanks to its ability to act as insulating shield during combustion. Three amphoteric PAAs were obtained by reacting N,N’-methylenebisacrylamide with natural α-amino acids, namely glycine (M-GLY), arginine (M-ARG) and glutamic acid (M-GLU). These PAAs act as intumescent flame retardants for cotton performing well in horizontal flame spread tests (HFSTs) but failing to inhibit combustion in vertical flame spread tests (VFSTs). All three PAAs have been proven to form strong interactions in water with MMT via their protonated tert‑amine groups. The presence of 12.5 % MMT did not significantly change the thermal and thermo-oxidative stability of PAA coatings, while 2 % MMT add-on affected those of both untreated and PAA-treated cotton fabrics. In HFSTs, substituting 2 % MMT for PAA did not significantly change the flame retardant efficacy of the coatings. In VFSTs, the 2 % MMT/14 % PAA combination inhibited cotton ignition, regardless of the PAA structure, while in the 2 % MMT/11 % PAA combination M-GLU protected cotton from ignition, M-ARG extinguished the flame and M-GLY burned completely. By further reducing the PAA content to 8 %, only M-GLU quenched cotton combustion, leaving an RMF of 82 %. The fact that neither MMT nor PAAs alone induced flame extinguishment at the same add-ons used in the adopted formulations suggests a synergistic behavior of MMT and PAAs.

In English

Natural fibre reinforced polymer composites nowadays are considered to be attractive cheap, safe and eco-friendly materials. The main problem of such composites related to the hydrophilicity of plant fibres may be successfully solved by chemical modification of their surface. However, some characteristics of the materials may be suppressed after this procedure. Therefore, the aim of the research is to find out the impact of chemical modification of filler on thermooxidative stability, tensile and flexural strength, as well as on biodegradability of polymer composites. The novelty of this work is in the examining new materials on the basis of Si-containing epoxyurethanes and chemically treated hemp woody core (HWC). Woody core that is the side product of hemp industry requiring its apropriate utilization was exposed to mercerization with sodium hydroxide solution and to further functionalization with epoxidized soybean oil (ESO) or 3-aminopropyltriethoxysilane (APS). Raw and surface treated HWC was used as reinforcement for two types of organic-inorganic epoxyurethane matrices made from sodium silicate, polyurethane prepolymer based on polyisocyanate and castor oil, and either diglycidyl ether of bisphenol-A (DGEBA) or ESO as epoxy component. Functionalization of HWC led to better mechanical properties of composites. Compared to the corresponding materials including untreated filler, maximum increase in flexural strength (26 %) was observed for the samples with ESO-containing epoxyurethane and silanized HWC, while maximum increase in tensile strength (53 %) was revealed for the ones with DGEBA-containing epoxyurethane and oil treated HWC. Thermooxidative stability was also higher for composites reinforced with functionalized HWC. The specimens with APS-treated HWC performed the best at thermal decomposition. The values of their T50% were up to 68 °C more than those for composites with unmodified filler. At the same time, the samples based on APS- or ESO-treated HWC were the most resistant to biodegradation, which may be concluded from their smallest weight loss during soil burial test.

The Roles of Impurities and Surface Area on Thermal Stability and Oxidation Resistance of BN Nanoplatelets.

This study considers the influence of purity and surface area on the thermal and oxidation properties of hexagonal boron nitride (h-BN) nanoplatelets, which represent crucial factors in high-temperature oxidizing environments. Three h-BN nanoplatelet-based materials, synthesized with different purity levels and surface areas (~3, ~56, and ~140 m2/g), were compared, including a commercial BN reference. All materials were systematically analyzed by various characterization techniques, including gas pycnometry, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared radiation, X-ray photoelectron spectroscopy, gas sorption analysis, and thermal gravimetric analysis coupled with differential scanning calorimetry. Results indicated that the thermal stability and oxidation resistance of the synthesized materials were improved by up to ~13.5% (or by 120 °C) with an increase in purity. Furthermore, the reference material with its high purity and low surface area (~4 m2/g) showed superior performance, which was attributed to the minimized reactive sites for oxygen diffusion due to lower surface area availability and fewer possible defects, highlighting the critical roles of both sample purity and accessible surface area in h-BN thermo-oxidative stability. These findings highlight the importance of focusing on purity and surface area control in developing BN-based nanomaterials, offering a path to enhance their performance in extreme thermal and oxidative conditions.