Thermo-oxidative Stability Research Articles

Enhancement of cardanol-loaded halloysite for the thermo-oxidative stability and crystallization property of polylactic acid

A natural antioxidant, cardanol (CA), was loaded on halloysite nanotube (HNT) to fabricate a dual-functional green additive cardanol-loaded halloysite (HNT-CA) for the preparation of fully green polylactic acid (PLA) composites with improved thermo-oxidative stability and crystallization property. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) measurements confirmed that cardanol was loaded in the lumen and attached on the outer surface of halloysite with approximately 22.9 wt% loading efficiency. The anti-aging behavior of HNT-CA was evaluated by the change of oxidation onset temperature (OOT) and weight-average molecular weight (Mw) of PLA composites stabilized by this additive after a 12-day aging test at 120 °C. The results showed that the OOT values of PLA composites with CA dropped from 298.2 °C to 279.0 °C, whereas the PLA composites with HNT-CA decreased from 292.2 °C to 281.5 °C, showing a higher retention. Similarly, the PLA stabilized by HNT-CA presented a higher retention of Mw than that stabilized by CA after thermal oxidation aging. For the PLA composites with HNT-CA, the migration of cardanol in PLA was inhibited by the restriction of halloysite to cardanol, thus showing long-term thermo-oxidative stability. Moreover, the analyses of polarized optical microscope (POM) and differential scanning calorimetry analysis (DSC) showed that HNT-CA increased the crystallization rate of PLA compared to HNT further due to the improved dispersion in PLA. These results indicated that HNT-CA exhibited excellent performance in improving the thermo-oxidative stability and crystallization property of PLA.

Friction and Wear Performance Evaluation of Bio-Lubricants and DLC Coatings on Cam/Tappet Interface of Internal Combustion Engines.

The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative stability, are suitable substitutes to conventional lubricant base oils. The research presented in this manuscript was undertaken to experimentally investigate the wear and friction performance of a possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W) tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve train assembly of an internal combustion engine. The tribological correlation between DLC-coated engine components, lubricant base oils and lubricant additives have been thoroughly investigated in this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines (PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were used in this investigation. Real-time drive torque was measured to determine the friction force, detailed post-test analysis was performed, which involved the use of a specialized jig to measure camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution scanning electron microscopy was employed to study the wear mechanism and energy-dispersive X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet interface. The presence of additives further improved the friction characteristics of TMP, resulting in reduced average friction torque values. A tremendous enhancement in wear performance was recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little or no delamination.

Distigmasterol-Modified Acylglycerols as New Structured Lipids-Synthesis, Identification and Cytotoxicity.

Plant sterols, also referred as phytosterols, have been known as bioactive compounds which have cholesterol-lowering properties in human blood. It has been established that a diet rich in plant sterols or their esters alleviates cardiovascular diseases (CVD), and also may inhibit breast, colon and lung carcinogenesis. Phytosterols, in their free and esterified forms, are prone to thermo-oxidative degradation, where time and temperature affect the level of degradation. Looking for new derivatives of phytosterols with high thermo-oxidative stability for application in foods, our idea was to obtain novel structured acylglycerols in which two fatty acid parts are replaced by stigmasterol residues. In this work, asymmetric (1,2- and 2,3-) distigmasterol-modified acylglycerols (dStigMAs) were synthesized by the covalent attachment of stigmasterol residues to sn-1 and sn-2 or sn-2 and sn-3 positions of 3-palmitoyl-sn-glycerol or 1-oleoyl-sn-glycerol, respectively, using a succinate or carbonate linker. The chemical structures of the synthesized compounds were identified by NMR, HR-MS, and IR data. Moreover, the cytotoxicity of the obtained compounds was determined. The dStigMAs possessing a carbonate linker showed potent cytotoxicity to cells isolated from the small intestine and colon epithelium and liver, whereas the opposite results were obtained for compounds containing a succinate linker.

An easy-to-process poly(silylene-acetylene) terminated by reactive ethynylphenyl: Synthesis, properties and composites

A series of telechelic silicon-containing hybrid polymers with reactive ethynylphenyl terminals were synthesized using the Grignard reagent method. The structure, processability, curing behavior, thermal stability and dielectric properties of the polymers, as well as the mechanical properties of carbon fiber reinforced composites at room temperature and high temperature, were well characterized. The results indicate that the ethynylphenyl-terminated poly(silylene acetylene)s (EPTSAs) have wide processing window and stable viscosity for 6 h at 70 °C. The cured EPTSAs exhibit excellent thermooxidative stabilities with temperatures of 5% weight loss (Td5) and the residues at 800 °C (Yr800). The thermal stability of the cured EPTSAs can increase markedly with incorporation of Si-H groups. The Td5 and Yr800 of the cured EPTSAs could reach to 601 °C and 52% in air, respectively. The pyrolysis behavior of cured EPTSAs elucidates the cure reactions and cross-linked networks. The cured resins show excellent dielectric properties in the frequency range of 10–106 Hz. Furthermore, the glass transition temperature of the cured EPTSAs do not arise before 500 °C. The flexural strength and modulus of the carbon fiber cloth (T300CF) reinforced EPTSAs composites could reach 252 MPa, and 42 GPa. The retention of mechanical properties of the composite at 300 °C can reach to 89%.

Enhanced thermo-oxidative stability of polydicyclopentadiene containing covalently bound nitroxide groups

The antioxidant 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group was covalently introduced into polydicyclopentadiene (PDCPD) through ring-opening metathesis polymerization (ROMP) copolymerization of dicyclopentadiene (DCPD) with a TEMPO-derived norbornene comonomer. The thermal oxidation of the resulting thin films was monitored by ThermoGravimetric Analyses (TGA) and Fourier-Transform Infra-Red spectroscopy (FT-IR). This new PDCPD stabilized by immobilization of the TEMPO antioxidant shows a better thermo-oxidative stability at 60 °C under air than an industrial formulation of PDCPD stabilized with 2,6-di‑tert‑butyl‑4-methylphenol (BHT). Impact of thermal oxidation on mechanical behaviour of both formulations have been studied by tensile tests and fracture tests, based on the essential work of fracture (EWF) concept. The TEMPO-functionalized PDCPD offers a promising alternative to BHT-stabilized PDCPD with comparable ductility but slower decay and better cracking resistance, confirming the benefit of the TEMPO antioxidant in PDCPD formulation when chemically bound to the matrix.

Degradation of engine components upon exposure to chemically modified vegetable oil - Based automotive lubricant

The present investigation examines the corrosion behavior of vegetable oil-based engine oil-biodiesel environment against automotive engine components, viz., cylinder liner, crankshaft, camshaft, journal bearing and timing gear as a counteractive measure. The biodegradable engine oil was formulated via chemical synthesis route and the thermo-oxidative stability of the biodegradable engine oil was analysed using thermogravimetric analysis. A high-temperature corrosion test rig was developed for the purpose of evaluating the corrosion behavior of biodegradable engine oil and the corrosion results were compared with those of synthetic engine oil SAE20W40 under similar test conditions. The corrosion penetration rate (CPR) of the journal bearing is 0.03270 ​mm/year and 0.0163 ​mm/year for biodegradable and synthetic engine oil respectively and the CPR of crankshaft, cylinder liner, camshaft and timing gear in biodegradable engine oil is 0.0120, 0.0156, 0.0127 and 0.0119 ​mm/year respectively, conversely in SAE20W40, the respective CPR is 0.0110, 0.0133, 0.0117 and 0.0109 ​mm/year. The scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy analysis of post corrosive surfaces revealed that biodegradable engine oil is prone to corrosion against various lubrication system components as compared to SAE20W40.

Structure, thermal and mechanical properties of copoly(ester amide)s based on 2,5\u2010furandicarboxylic acid

In this work, new bio-based copoly(ester amide)s were synthesized by a two-step melt polycondensation process, using 2,5-furanedicarboxylic acid dimethyl ester (DMFDC), 1,3-propanediol (PDO), and 1,3-diaminopropane (DAP), with different DAP content. The chemical structure of the obtained poly(trimethylene 2,5-furandicarboxylate)-co-poly(propylene furanamide) (PTF-co-PPAF) copolymers was confirmed by nuclear magnetic resonance (1H NMR) and Fourier-transform infrared (FTIR) spectroscopy. Gas chromatography/mass spectrometry was used to provide more details of the polycondensation process. Thermal properties of the obtained materials were characterized by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic–mechanical thermal analysis (DMTA). The copolymers were amorphous and their glass transition temperature increased with the increase in the poly(propylene furanamide) (PPAF) content. The synthesized PTF-co-PPAF copolymers exhibited improved thermal and thermo-oxidative stability up to 300 °C. In addition, from the performed mechanical tests, it was found that along with the increase in PPAF content, Young's modulus increased, while at the same time, the value of elongation at break decreased.Graphical

Antibacterial LDPE-based nanocomposites with salicylic and rosmarinic acid-modified layered double hydroxides

Polymer nanocomposites, prepared by dispersing layered nanofillers bearing active and natural compounds in a polymer matrix, offer a tunable way to confer antibacterial activity to traditional polymers for packaging materials. Antibacterial host-guest systems were prepared by intercalation of mono-deprotonated rosmarinic and salicylic acid (RA and SA), with recognized antibacterial and antioxidant properties, into a nitrate-intercalated MgAl layered double hydroxide (LDH) via anion exchange reaction. The structural, morphological, and thermal properties of the modified LDHs (i.e., MgAl-RA and MgAl-SA), compared with those of a fully exchanged ZnAl-SA, indicated the successful immobilization of the functional molecules. Linear low-density polyethylene (LDPE)/antibacterial-LDH nanocomposites were prepared by a two-step melt compounding procedure. X-ray diffraction analysis and scanning electron microscopy showed that MgAl-RA was better dispersed than ZnAl-SA and MgAl-SA. LDPE nanocomposites containing the highest filler content showed increased thermo-oxidation stability, with a marked effect for LDPE/MgAl-RA due to the antioxidant power of RA. Furthermore, the antibacterial activity of LDPE/MgAl-RA was high and selective toward Staphylococcus aureus. Finally, the overall migration of RA and SA from films of polymer nanocomposites immersed in ethanol solution was followed by fluorescence spectroscopy evidencing a controlled release of the active compounds.

Lignin-Based Additives for Improved Thermo-Oxidative Stability of Biolubricants

There is an environmental concern regarding the use of petroleum-based lubricants, which are generally toxic and nonbiodegradable. Biobased lubricants, such as vegetable oils, are the alternative: they show excellent lubricity, are readily biodegradable and nontoxic. However, a major disadvantage of using vegetable oils in lubricant applications is their lack of thermo-oxidative stability, which can be improved by antioxidant additives. Here, we propose the use of lignin-based additives in biolubricant formulations to improve this feature, based on lignin’s known antioxidant properties. To ensure a stable dispersion in vegetable oil, lignin was partially esterified. Antioxidant properties of lignin before and after palmitoylation were demonstrated in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Four different lignin-based fractions, commercial Protobind P1000 soda lignin from straw, solvolytically fractionated Protobind P1000 lignin and two lignin fractions from reductively catalyzed fractionation (RCF) of native birch wood, were tested in biolubricant formulations with castor oil as base oil. Those lignin fractions exhibited excellent performance compared to butylated hydroxytoluene (BHT), a commonly used petroleum-based antioxidant. Formulations of modified lignin in castor oil possess improved thermo-oxidative stability, as illustrated by their increased oxidation induction time. Additionally, rheological and tribological tests demonstrate similar, or in some cases improved, lubricating properties compared to castor oil. This study showcases the successful incorporation of lignin-based antioxidants in biolubricant formulations, tackling the major disadvantage of vegetable oils as environment-friendly lubricants.

Exploration of the H2O2 Oxidation Process and Characteristic Evaluation of Humic Acids from Two Typical Lignites.

To study the effect of H2O2 on the content and properties of humic acids (HAs) in lignites, the experimental conditions including oxidation time, H2O2 concentration, and the solid–liquid ratio were investigated. Under the optimum oxidation conditions, the contents of HAs of YL and HB lignite were 45.4 and 40.9%, respectively. The HAs extracted from oxidized and raw lignites were characterized and compared. The results showed that the HAs extracted from oxidized lignites contain more total acidic groups, carboxyl groups, and aliphatic carbon than that in HAs extracted from raw lignites, and their hydrophilic–hydrophobic index value is higher and thermooxidative stability is better than those in HAs extracted from raw lignites. In addition, the composition of polycyclic aromatic hydrocarbons and fluorophore types in HAs extracted from oxidized lignites are similar to the HAs extracted from raw lignites. The results indicated that the oxidation operation can increase the content of HAs in lignites, and simultaneously increase the content of oxygen-containing functional groups and biological activity of HAs, which provided a reference for the subsequent application of HAs.

Influence of Rigid Segment Type on Copoly(ether-ester) Properties.

The growing ecological awareness of society created the tendency to replace petrochemically based materials with alternative energy carriers and renewable raw materials. One of the most requested groups of polymer materials with significant technological importance is thermoplastic elastomers (TPE). They combine the properties of elastomers such as flexibility with the typical properties of thermoplastics, like easy processing. Herein, one compares the influence of rigid segments on the properties of copoly(ester-ether). Thermoplastic polyesters based on bio-1,6-hexanediol and terephthalic (T), furanic (F), and napthalate (N) diesters, i.e., PHT, PHF, and PHN, were obtained employing melt polycondensation. Additionally, to grant elastic properties of polyesters, systems containing 50 wt.% of bio-based polyTHF®1000 (pTHF) with a molecular mass of 1000 g/mol, have been prepared. The composition and chemical structure have been determined by 1H nuclear magnetic resonance (NMR) and Fourier transformed infrared spectroscopy (FTIR) analyses. The temperatures corresponding to phase transition changes were characterized by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) analyses. The crystalline structure was examined by X-ray diffraction (XRD) analysis. Additionally, the influence of pTHF–rich segment on the tensile properties, water absorption, as well as thermal and thermo-oxidative stability, has been analyzed. It was found that incorporation of soft phase allows creation of thermoplastic elastomers with tensile characteristics comparable to the commercially available ones, by means of elongation at break higher than 500%, low values of tensile modulus, without exhibiting yield point.

Thermo-oxidative aging and thermal cycling of PETI-340M composites

Polyimide composites (PETI-340M) were fabricated and subjected to high-temperature aging and thermal cycling to evaluate resistance to degradation. Mechanical-degradation mechanisms and kinetics depended on aging temperature. Aging at 232°C resulted in strength loss due to polymer degradation, while intra-tow cracking was the dominant mechanism during aging at 288°C. Composite panels subjected to thermal-cycling fatigue (−54°C to 232°C) retained mechanical properties without microcracking. However, in regions containing pre-existing fabrication-induced defects (primarily voids), intra-tow microcracks were observed after thermal cycling. Unlike some polyimide composites (PMR-15), oxidative aging effects during thermal cycling were negligible. The thermo-oxidative stability and the retention of mechanical performance after thermal cycling indicates potential for long-term, high-temperature structural applications.

Effect of Sunflower, Almond, and Rapeseed Oils as Additives on Thermal Properties of a Machinery Oil

Vegetable oils are considered to be eco-friendly and to offer good lubricant properties; however, their low thermo-oxidative stability makes their use as a lubricant base challenging. In this research, sunflower, almond, and rapeseed vegetable oils were added in volumes of 5, 10, 15, and 20% to a machinery oil, and the thermal properties of the resulting fluids were studied. Sunflower, almond, and rapeseed oils were chosen considering their fatty acid composition and the tocopherol content. During this investigation, thermal diffusivity was measured by using the thermal wave resonance cavity technique, while thermal effusivity was determined by the inverse photopyroelectric method, and the obtained values ranged from 4.63 to 5.75 Ws1/2m−2K−1 × 102. The thermal conductivity was calculated by obtaining a complete thermal characterization. The results showed a linear relationship between the percentage of vegetable oil and the thermal diffusivity. It was also noted that the thermal properties of diffusivity and effusivity could be tuned when using almond, sunflower, and rapeseed oils in the appropriate percentages. Hence, the influence of vegetable oils on the thermal properties of lubricating oil were closely related to the number of fatty acids.

Accelerated oxidation method and simple kinetic model for predicting thermooxidative stability of edible oils under storage conditions

A kinetic model for predicting thermooxidative stability of fats under storage conditions is developed and parametrized using induction periods (IPs) measured at different temperatures and oxygen pressures using the Oxitest method. The model does not rely on a degradation mechanism, nor it requires determination of degradation products. Berthelot–Hood function was chosen for modeling the temperature dependence as it provides more realistic estimates compared to the Arrhenius equation. The geometry of the sample is taken into account via surface-to-volume ratio. For a commercially available sunflower oil, the estimated temperature coefficient of the Berthelot–Hood function was 0.0915 K−1 and the apparent reaction order with respect to oxygen was 0.155. Using these values, the estimated IP at 25 °C in air and surface-to-volume ratio 35 m−1 is 521 days with an uncertainty of 180 days. This is comparable to 460–490 days measured by Martín-Polvillo, et al. (2004) for an oil with similar composition using a long-term storage experiment. Despite only requiring a fraction of time, the model yields induction periods close to those from experiments at ambient conditions.

Chemical, Thermal and Antioxidant Properties of Lignins Solubilized during Soda/AQ Pulping of Orange and Olive Tree Pruning Residues.

Some agroforestry residues such as orange and olive tree pruning have been extensively evaluated for their valorization due to its high carbohydrates content. However, lignin-enriched residues generated during carbohydrates valorization are normally incinerated to produce energy. In order to find alternative high added-value applications for these lignins, a depth characterization of them is required. In this study, lignins isolated from the black liquors produced during soda/anthraquinone (soda/AQ) pulping of orange and olive tree pruning residues were analyzed by analytical standard methods and Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (solid state 13C NMR and 2D NMR) and size exclusion chromatography (SEC). Thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and antioxidant capacity (Trolox equivalent antioxidant capacity) were also evaluated. Both lignins showed a high OH phenolic content as consequence of a wide breakdown of β-aryl ether linkages. This extensive degradation yielded lignins with low molecular weights and polydispersity values. Moreover, both lignins exhibited an enrichment of syringyl units together with different native as well as soda/AQ lignin derived units. Based on these chemical properties, orange and olive lignins showed relatively high thermal stability and good antioxidant activities. These results make them potential additives to enhance the thermo-oxidation stability of synthetic polymers.

New sustainable flame retardant DOPO-NH-functionalized polyamide 6 and filament yarn

This work presents a unique approach for the preparation of a flame retardant (FR) polyamide 6 (PA6) polymer with chemically bonded 9,10-dihydro-9,10-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as a pendant group bridged to the polymer via an –NH- group. A novel phosphonamidate co-monomer (DOPO-A-CLM) was synthesized from DOPO and α-amino-ε-caprolactam (A-CLM). This co-monomer was subsequently used in the hydrolytic polymerization with ε-caprolactam (CLM) in different weight ratios to prepare DOPO-NH-functionalized PA6 (PA6-xDC, x = 7, 10, and 15 wt% DOPO-A-CLM). Chemical incorporation of DOPO-A-CLM into the PA6 backbone decreased the molecular weight of the polymer from 15387 for neat PA6 to 12375, 10516 and 9316 for PA6-7DC, PA6-10DC and PA6-15DC, respectively. The DOPO-NH– pendant group accelerated start of the PA6 thermal decomposition and increased the char residues at 500 °C from 1% for PA6 to 4.6, 4.9, and 5.0% for the PA6-7DC, PA6-10DC, and PA6-15DC samples, respectively, indicating crosslinking reactions in the condensed phase. The evolved phosphorus-active species in the gas phase inhibited the PA6 depolymerization, resulting in increased thermo-oxidative stability and about a fourfold higher residue at 500 °C in the case of PA6-15DC compared to PA6. The intrinsically flame retardant PA6 filament yarns with chemically bound FR pendant group were successfully melt spun from PA6-10DC, drawn and wound on bobbin. The DOPO-NH– pendant group decreased filament flammability and inhibited flame propagation, resulting in immediate self-extinguishment after flame removal. Incorporation of DOPO-A-CLM decreased the filament tensile properties compared to the neat PA6, which correlates with the decreased polymer molecular weight.

Microwave Hydrophobized Lignin with Antioxidant Activity for Fused Filament Fabrication

The poor compatibility and aggregation propensity of lignin in nonpolar polymer matrices greatly limits its application in polymer blends and composites. We demonstrate an efficient, solvent-free, and catalyst-free microwave-assisted approach for hydrophobization of alkali lignin to enhance its compatibility with polylactide. Effective modification with up to 98% substitution of lignin’s hydroxyl groups was achieved under mild and catalyst-free reaction conditions. The modified acetylated and hexanoated lignins exhibited enhanced thermal stability and thermoplasticity, which were reflected by the good melt-extrusion and 3D printing properties of the corresponding polylactide/lignin blends. The tensile properties varied somewhat depending on the degree and type of substitution and the amount of hydrophobized lignin but in general the tensile properties were in the same range as those of polylactide. Blends consisting of up to 50 weight-% acetylated lignin were successfully extruded to filaments and 3D printed, demonstrating good processability and tensile properties regardless of the high lignin content, while it was not possible to extrude continuous filaments of polylactide and nonmodified alkali lignin even at low concentration (10 weight %). Additionally, the polylactide/acetylated lignin blends exhibited antioxidant activity as revealed by radical scavenging ability and improved thermo-oxidative stability with up to 40 °C increase in oxidation induction temperature compared to neat polylactide. The sustainable compatibilization strategy proposed herein paves the way for value-added utilization of lignin in fully biobased 3D printing filaments with improved oxidative stability.

A halogen-free, flame retardant, waterborne polyurethane coating based on the synergistic effect of phosphorus and silicon

In this study, p-hydroxybenzaldehyde, 3-aminopropanol and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were used as raw materials, and a novel flame retardant with dihydroxy groups, namely 4-DOPO-((3-hydroxypropyl) imino) methyl) phenol (PHID), was synthesized. Then, a flame retardant, water-based polyurethane with phosphorus (P) and silicon (Si) units (FR/Si-WPU) was successfully prepared. Limited oxygen index (LOI), vertical burning tests, and cone calorimetry were employed to investigate the flammability characterizations of the WPU. In contrast to pure WPU, the LOI value of FR/Si-WPU was found to be increased from 18.2% to 28.6%, the UL 94 rating was upgraded to V-0. The peak heat release rate (pk-HRR) and peak smoke production rate (pk-SPR) were found to be decreased by 80.5% and 70.5%, respectively. In addition, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis-infrared spectrometry (TG-IR), laser Raman spectroscopy (LRS), and X-ray photoelectron spectroscopy (XPS) were employed to evaluate the synergistic mechanisms of P and Si. The results demonstrated that the synergistic effect of PHID with hydroxyl silicone oil (HO-Si) can generate a more compact char to protect the underlying polyurethane, the decomposition of PHID can produce PO· radicals that combine with H· and OH· radicals to interrupt the combustion reaction, and HO-Si can produce a special insulating SiO layer to improve the thermo oxidative stability. The synergistic effects of these factors contribute to the designable flammability of the WPU coating. Further investigation revealed that Si units can efficiently balance the other properties of the WPU, and the cold resistance and mechanical properties of FR/Si-WPU were found to increase instead of decrease. In this work, a flame retardant WPU coating with good comprehensive performance was fabricated via a simple and efficient method.

Silica-encapsulated red phosphorus for flame retardant treatment on textile

Red phosphorus (RP) particles are commercially available as a flame-retardant additive for polymers. Conventionally, RP is encapsulated with a protective organic coating. In the present work, we propose an alternative approach for the encapsulation of RP with an inorganic SiO2 shell (SiO2@RP), to be employed in textiles. The silica shell was obtained by two steps sol-gel of tetraethyl orthosilicate (TEOS) precursor in RP aqueous dispersion. A homogenous silica shell was consistently achieved. The chemical structure and morphology of the as-obtained powder were characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of the silica coating on the thermal stability of RP was investigated through thermogravimetric coupled-differential thermal analysis (DT-TGA) that revealed improved thermo-oxidative stability. The application of the prepared coated and uncoated RP as flame retardant additives for fabric back-coating is then investigated. Only the fabrics treated with SiO2@RP successfully self-extinguished the flame during flammability test, based on BS-5852 normative, achieving the no-ignition classification required for a practical application. The proposed fully inorganic encapsulation strategy opens up to new and efficient flame retardant solutions based on RP that can potentially be exploited in several application fields.

Low-melting phthalonitrile monomers containing maleimide group: Synthesis, dual-curing behavior, thermal and mechanical properties

Novel dual-functional phthalonitrile monomers containing a maleimide group were synthesized and characterized. Ortho, meta, and para isomers were obtained and only the meta-isomer can be considered as a low melting phthalonitrile monomer with a melting point of 107.4°С. Analysis of the dual-curing behavior of monomers showed radical homopolymerization of maleimides followed by phthalonitrile polymerization with the formation of isoindoline, triazine, and phthalocyanine ring structures. Two alternative copolymerization processes of maleimide groups via ene reaction and ring-opening amidation were investigated. The approach of dual-curing maleimide and phthalonitrile fragments in a single molecule allowed combining the excellent inherent mechanical properties of bismaleimide resins and the outstanding thermo-oxidative stability of phthalonitriles. After curing of both functional groups impact strength was as high as 11.81 kJ m−2, flexural strength was 108 MPa, Young's modulus was 4.38 GPa. On the contrary, Tg of this polymeric system was above 370°С and T5% was higher than 450°С in air.