Thermo-oxidative Resistance Research Articles

Starch-lauric acid complex-stabilised Pickering emulsion gels enhance the thermo-oxidative resistance of flaxseed oil

Hydrophobic-modified starch complexes have the potential to form Pickering emulsions and improve the oxidative stability of flaxseed oil. Here, V-type starch–lauric acid complexes (SLACs) were fabricated via solid encapsulation within 0.5–12 h and applied in flaxseed oil Pickering emulsions. Complexing index, X-ray diffraction and differential scanning calorimetry analyses confirmed that the degree of complexation increased with the reaction time. Pickering emulsion gels stabilised by SLACs generated with reaction times of 6 h and 12 h exhibited good storage stability and high yield stress, G' values and apparent viscosity. Confocal laser scanning microscopy and cryo-scanning electron microscopy revealed a gelation mechanism involving increased interface roughness and enhanced droplet–droplet interaction. In comparison to pure flaxseed oil, higher thermo-oxidative resistance was observed at 130 °C, with a markedly longer oxidation induction for emulsions and emulsion gels stabilised by SLACs. Our findings could assist in the design of hydrophobic-modified starch and provide a new paradigm for delaying oil oxidation.

The role of non-rubber components acting as endogenous antioxidants on thermal-oxidative aging behavior of natural rubber

Natural rubber (NR) with complex compositions has more excellent thermo-oxidative resistance properties compared to synthetic high cis-1,4-polyisoprene (IR), although synthetic IR owns similar molecular chain structure to NR. Compared with synthetic IR, the existence of non-rubber components is an obvious characteristic of NR. In this study, we pay attention to the non-rubber components acting as endogenous antioxidants, causing significant impact on thermo-oxidative resistance of NR. After removal of non-rubber components, the retention of tensile strength of NR exhibits a 2.7-fold decrease (from 84.29% to 31.29%) after 24 h of aging at 100 °C. The effect of non-rubber components on improving thermo-oxidative resistance of NR can be verified and mimicked through additional acetone extract or δ-tocopherol. The results show that the retention of tensile strength of purified NR (PNR) increases from 3.06% to 64.31% and retention of elongation at break of PNR increases from 60.61% to 92.59% after 48 h of aging after adding 0.6% δ-tocopherol, which can be comparable to or even exceed some traditional antioxidants. Furthermore, the antioxidative mechanism of endogenous antioxidant is explored. This work reveals another characteristic of non-rubber components and provides a rational design for the new biomimetic rubber with unique compositions and excellent properties similar to NR.

Durability and Performance of Encapsulant Films for Bifacial Heterojunction Photovoltaic Modules.

Energy recovery from renewable sources is a very attractive, and sometimes, challenging issue. To recover solar energy, the production of photovoltaic (PV) modules becomes a prosperous industrial certainty. An important material in PV modules production and correct functioning is the encapsulant material and it must have a good performance and durability. In this work, accurate characterizations of performance and durability, in terms of photo- and thermo-oxidation resistance, of encapsulants based on PolyEthylene Vinyl Acetate (EVA) and PolyOlefin Elastomer (POE), containing appropriate additives, before (pre-) and after (post-) lamination process have been carried out. To simulate industrial lamination processing conditions, both EVApre-lam and POEpre-lam sheets have been subjected to prolonged thermal treatment upon high pressure. To carry out an accurate characterization, differential scanning calorimetry, rheological and mechanical analysis, FTIR and UV-visible spectroscopy analyses have been performed on pre- and post-laminated EVA and POE. The durability, in terms of photo- and thermo-oxidation resistance, of pre-laminated and post-laminated EVA and POE sheets has been evaluated upon UVB exposure and prolonged thermal treatment, and the progress of degradation has been monitored by spectroscopy analysis. All obtained results agree that the lamination process has a beneficial effect on 3D-structuration of both EVA and POE sheets, and after lamination, the POE shows enhanced rigidity and appropriate ductility. Finally, although both EVA and POE can be considered good candidates as encapsulants for bifacial PV modules, it seems that the POE sheets show a better resistance to oxidation than the EVA sheets.

Catalytic Polymerization of Phthalonitrile Resins by Carborane with Enhanced Thermal Oxidation Resistance: Experimental and Molecular Simulation.

Biphenyl phthalonitrile (BPh) resins with good thermal and thermo-oxidative stability demonstrate great application potential in aerospace and national defense industries. However, BPh monomer has a high melting point, poor solubility, slow curing speed and high curing temperature. It is difficult to control the polymerization process to obtain the resins with high performance. Here, a BPh prepolymer (BPh-Q) was prepared by reacting 1,7-bis(hydroxymethyl)-m-carborane (QCB) with BPh monomers. The BPh-Q exhibited much better solubility, faster curing speed and lower curing temperature compared with pure BPh and BPh modified with bisphenol A (BPh-B, a common prepolymer of BPh). Thus, the polymerization process of BPh was greatly accelerated at a low temperature, resulting in a BPh resin with enhanced thermostability and oxidation resistance. The experimental and theoretical models revealed the promotion effect of B-H bond on the curing reaction of phthalonitrile via Markovnikov addition reaction due to the special steric structure of carborane. This study provided an efficient method to obtain low-temperature curing phthalonitrile resins with high thermal and thermo-oxidative resistance, which would be potentially useful for the preparation of high-performance cyanide resin-based composites.

Effects of a novel chitosan based macromolecule antioxidant COS-GMMP on the thermo-oxidative aging of styrene-butadiene rubber/silica composites

A chitosan based macromolecule antioxidant (COS-GMMP) was prepared by using chitosan (COS), 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (antioxidant GM) and 3-mercaptopropionic acid (MPA) via Michael addition reaction and acylation reaction. The chemical structure of COS-GMMP was confirmed by 1H NMR, 13C NMR, FTIR and elemental analysis. The anti-aging behavior of styrene-butadiene rubber (SBR)/silica with COS-GMMP, as well as the low molecule antioxidant GM, was systematically investigated by the accelerated thermal aging tests, oxidation induction time (OIT), thermo-gravimetric analysis (TGA) and hot water extraction experiments. The results revealed that COS-GMMP significantly improved the thermo-oxidative aging resistance, thermal-oxidative stability and solvent extraction resistance of SBR/silica composites more effectively than the antioxidant GM. The preeminent antioxidative ability of COS-GMMP for SBR/silica composites was attributed to not only the synergistic antioxidative effect among hindered phenol, amide and thioether groups, but also its high molecular weight.

Effect of thermal exposure on carbon fiber reinforced composites used in civil infrastructure rehabilitation

In this work, characteristics related to the thermo-oxidative resistance of a wet layup ambient cured carbon-epoxy composite are investigated using dynamic scanning calorimetry, dynamic mechanical thermal analysis, and thermo-gravimetric analysis. Specimens of the unidirectional composite are exposed to temperatures between 121℃ and 232℃ for periods of time between 1 and 72 h. Initial exposure results in post-cure and enhancement of thermal characteristics whereas higher temperatures and longer periods of exposure at the higher temperatures result in deterioration. Degradation is determined through DMTA based on decreases in both peak loss modulus height and activation energy, Ea, and through TGA based on decreases in apparent decomposition activation energy, Ed, using the Coats-Redfern method. In both cases, there appears to be no deterioration within the 72 h period at the two lower temperatures of exposure, and minimal deterioration at the next two levels, whereas initiation of deterioration can be noted as early as between 8 and 16 h of exposure at the highest temperature of exposure, 232 ℃. The reaction order determined using the Kissinger method is seen to remain fairly constant except at the highest temperature level wherein drops are noted after 24 h of exposure. This provides thermal data at the materials level to guide field use within the time–temperature combinations suggesting that residual integrity can be reasonably assumed at all except the highest temperature level.

Strategy for the NR/BR blends with improved thermo-oxidative resistance

The blends based on natural rubber (NR) and cis-1, 4-polybutadiene rubber (BR) are the most popular materials in rubber industry. As is well-known, the rubber blends suffer thermo-oxidative aging during the service life. However, the problems, such as immiscibility, discrepant aging behaviors, uneven distribution of fillers in different phase, resulted in unsatisfying mechanical properties of the filled NR/BR vulcanizates, especially after thermo-oxidative aging. In this work, a novel reactive compatibilizer trans-1,4-poly (isoprene-co-butadiene) (TBIR) is introduced to resolve the above problems for improved thermo-oxidative resistance of NR/BR blends. The mechanical properties of the sulfur cured NR/BR/TBIR vulcanizates with carbon black as fillers before and after thermo-oxidative aging are analyzed. The SEM, TEM and DMA are used to characterize the phase structure, filler distribution and dynamic properties of the NR/BR/TBIR blends. The NR/BR/TBIR vulcanizates exhibit better physical mechanical properties than NR/BR vulcanizate during the thermo-oxidative aging processing. The total crosslinking density and polysulfide crosslinking density increase during the aging process for all vulcanizates. The DMA results show that the Tg of NR and BR become closer with the increasing in TBIR whenever before and after aging, indicating the TBIR improves the compatibility of NR and BR. The phase morphology observation shows the improved filler dispersion level and reduced filler aggregation before and after aging process. The performance improvement mechanism of the thermo-oxidative aging of NR/BR/TBIR blends is discussed.

The Characteristics of Natural Rubber Composites with Klason Lignin as a Green Reinforcing Filler: Thermal Stability, Mechanical and Dynamical Properties.

The objective of this work was to investigate the influences of Klason lignin as a filler on the thermal stability and properties of natural rubber composites. The modulus and tensile strength of stabilized vulcanizates were measured before and after thermo-oxidative aging. It was determined that lignin filled natural rubber had significantly enhanced thermo-oxidative aging and mechanical properties compared to those of controlled samples. The reinforcement effect of lignin increased stress with lignin loading but it decreased at 20 phr, suggesting that the reinforcement mechanism of lignin was via strain-induced crystallization. The composite samples with 10 phr filler loading had the highest mechanical properties as well as thermo-oxidative degradation resistance. Such a finding could be due to interactions between the Klason lignin filler and natural rubber matrix. Based on the findings in this work, the degradation temperature of Klason lignin occurred at 420 °C. The absorption peaks at wavenumbers 1192 and 1374 cm−1 indicated that C–O stretching vibrations of the syringyl and guaiacyl rings of hardwood lignin existed. It was also found that the Klason lignin–rubber composite containing 10 phr had the highest stress–strain, 100% modulus, and tensile strength, while lignin showed increasing aging resistance of the composite comparable with commercial antioxidant at 1.5 phr. It appears that Klason lignin from rubberwood could be used as a green antioxidant and alternative reinforcing filler and for high performance eco-friendly natural rubber biocomposites.

Enabling Superior Thermo-Oxidative Resistance Elastomers Based on a Structure Recovery Strategy.

Thermo-oxidative process leads to the structure damage of elastomers, such as the scission of main chains and destruction of crosslinks. The problem that damaged structure brings about the deterioration of mechanical properties has not been solved by the conventional anti-aging methods. Inspired by self-healing process, a structure recovery strategy for recovering the damaged structure induced by thermo-oxidative process is proposed, which endows elastomers with superior thermo-oxidative resistance. The high reactivity between 1,3-diisopropenylbenzene and free radicals realizes high recovery efficiency (from 83% to 118%); the changes in topology structure during recovery process make much more rubber chains bear external stress and improve mechanical properties significantly (from 18.5 to 29.6MPa). This work paves the way for the development of elastomers with superior thermo-oxidative resistance, meanwhile this work is helpful to push the theoretical research of self-healing to practical application.

Synthesis and Properties of Polymerization-Filled Composites Based on Polypropylene and Single-Wall Carbon Nanotubes

Composites based on polypropylene and single-wall carbon oxygen-containing nanotubes with a specific surface area of 360 and 500 m2/g are synthesized in the medium of liquid propylene using the catalytic system rac-Me2Si(2-Me-4-PhInd)2ZrCl2/МАО. Optimum polymerization conditions ensuring a fairly high rate of the process are determined, and the composites with the filler content in the range from 0.3 to 13.0 wt % are obtained. It is shown that the presence of functional groups enhances the filler agglomeration tendency during composite formation. Effects of the type of carbon nanofiller on the thermal stability, thermo-oxidative resistance, and thermal and electrophysical characteristics of the composites are studied. It is found that the filler inhibits the processes of oxidation and destruction of polypropylene crystallites.

MXene Enabling the Long-Term Superior Thermo-Oxidative Resistance for Elastomers

The ability of long-term thermo-oxidative resistance is very important for elastomers in application. However, many conventional antioxidants are difficult to realize the long-term thermo-oxidative resistance. To overcome this limitation, a design strategy is introduced by combing elastomers with MXene and natural rubber (NR) is chosen as a model material. MXene is efficient in absorbing oxygen and the generated free radicals in the NR matrix and can inhibit the diffusion of oxygen toward the interior. Moreover, MXene, like graphene and carbon black, absorbs molecular chains, inhibiting the migration of MXene toward the surface of the sample. Such characteristics of MXene endow NR/MXene with the long-term outstanding thermo-oxidative resistance. For example, after three days of the thermo-oxidative process for NR/MXene, the tensile strength is 19 MPa and the retention of tensile strength is 63%, which far exceeds the effects of conventional antioxidants. This work not only provides a good guide for the universal design of elastomers with long-term thermo-oxidative resistance but also expands the application of MXene.

Effects of a novel hindered phenol samarium complex on the thermo-oxidative aging of styrene-butadiene rubber/silica composites

A novel rare-earth complex containing hindered phenol groups (DTSm) was prepared through coordination reaction between 3,5-di-tert-butyl-4-hydroxybenzoic acid and samarium chloride hexahydrate (SmCl3·6H2O). The chemical structure of DTSm was confirmed by FTIR, XPS, ICP-OES and elemental analysis. The results of the accelerated thermo-oxidative aging tests, FTIR-ATR, TGA, methanol extraction experiments, whiteness and yellowness index revealed that DTSm significantly improved the long-term thermo-oxidative aging resistance of styrene-butadiene rubber/silica composites without discoloration, and the DTSm exhibited excellent volatility resistance and solvent extraction resistance. The outstanding antioxidative ability of DTSm for SBR/silica composites was attributed to the synergistic antioxidative effect between hindered phenols and samarium ions due to its excellent thermal stability and volatility resistance. This research is fruitful for the preparation of long-term highly aging-resistant rubber composites.

Coffee Silverskin as a Multifunctional Waste Filler for High-Density Polyethylene Green Composites

This work aims to describe the coffee silverskin effect as a lignocellulosic waste filler for high-density polyethylene (HDPE) composites development. The main task was to determine various modification effects resulting from the complex chemical composition of coffee silverskin containing compounds with potential antioxidative properties, including caffeine, polyphenols, tannins, or melanoidins. The processing, thermal, physicochemical, and thermomechanical properties of the HDPE-based composites with different filler content (1–20 wt%) were evaluated. Comprehensively realized thermomechanical analysis revealed the filler’s reinforcing effects on the HDPE matrix while defining problems with obtaining adequate adhesion in the interfacial area. At the same time, studies have shown a very beneficial effect of the silverskin addition on the thermal properties of composites, that even the smallest addition allows for a significant increase in the thermooxidative resistance of HDPE composites assessed using the oxidation induction time from 20 min for HDPE up to 140 min for the composites with 20 wt% of the filler. The obtained research results allow classifying the coffee silverskin waste filler, not only as a filler intended for the production of composites with a high degree of filling but also as an additive that significantly changes the properties of polyethylene in the case of using low concentrations. This can have a very beneficial impact on the development of novel wood polymer (WPC) and natural fiber composites (NFC).

Copolymers and interpenetrating polymer networks of thermoreactive nitrogen-containing resins. Mini review

In a short review the effective methods of optimization of structure and properties of high-performance polymers obtained from thermoreactive nitrogen-containing resins such as benzoxazines, bismaleimides, cyanate esters have been analysed. High crosslinked density copolymer thermosets are synthesized through chemical interactions between reactive functional groups, which belong to the monomers/oligomers used. The different possible processes such as copolymerization or formation of interpenetrating polymer networks are discussed. The high-performance polymers and composites from thermoreactive nitrogen-containing resins are effectively used in aerospace industry and microelectronics as materials possessing high thermal and thermooxidative stability, radiation and chemical resistance, low water absorption, low dielectric loss, high dimension stability and high adhesion to different substrate. The performance characteristics of this kind of materials can be controlled by changing their composition, temperature-time curing schedule, using catalytic systems. Keywords: copolymers, IPNs, thermoreactive resins, benzoxazine, bismaleimide, cyanate ester resins.

Natural Antioxidants as Multifunctional Additives for Polymeric Materials

The additional substances commonly used for polymeric materials mostly have a negative impact either on the natural environment or human health. Therefore, there is a need for replacing these compounds by more pro-ecological ones. In this paper, some natural antioxidants of plant origin, including xanthone, rutin hydrate, quercetin and a mixture of various polyphenols derived from green tea, were proposed as multifunctional as well as eco-friendly additional compounds for polymers. These substances were implemented by means of the impregnation process into ethylene-propylene copolymer (EPM) matrix. Some significant results of the research work are presented, including the mechanical properties and oxidation induction time (OIT) of the material tested. Moreover, ethylene-propylene copolymer (EPM) with antioxidants was investigated in terms of thermooxidative and UV ageing resistance. The impact of ageing processes on the material tested was analysed mainly by means of Fourier transform infrared spectroscopy (FT-IR) absorbance spectra and colour change assessment.

Performance evaluation of surface-organic grafting on the palygorskite nanofiber for the modification of asphalt

This paper aims to promote the application of nano-mineral materials in asphalt and improve the compatibility of modifiers with asphalt to produce high-performance and economical modified asphalt. In this paper, palygorskite (Pal) was organic grafted by γ-aminopropyltriethoxysilane (ATPES) to obtain an organomodified palygorskite (A-Pal). Then A-Pal was adopted to modify asphalt by melt blending with different contents. The microstructure and elemental distribution of the modified asphalt were characterized to confirm the interface state of different components. The rheology, water stability and aging resistance of Pal and A-Pal in the asphalt were evaluated. The organic group was successfully grafted on the surface of Pal, and A-Pal had good compatibility with asphalt. Adding A-Pal could enhance the water stability, high-temperature stability and anti-rutting capacity of asphalt binder. The thermo-oxidative aging resistance of asphalt increased after TFOT and PAV aging under the shielding effect of A-Pal fibers. Considering high- and low-temperature performances, water stability, anti-aging performances and economic benefits, the optimal amount of A-Pal in asphalt was recommended from 4 to 6%. A-Pal has been proved to be an excellent and environmental-friendly asphalt modifier for the nanofiber effect.

Vulcanization and antioxidation effects of accelerator modified antioxidant in styrene-butadiene rubber: Experimental and computational studies

In this work, a new kind of accelerator modified antioxidant denoted as BTC was synthesized successfully through a thiol-ene click reaction between accelerator 2-mercaptobenzothiazole (MBT) and antioxidant N-(4-anilino phenyl) maleic imide (MC). Then, the effects of BTC on the vulcanization and antioxidation of styrene-butadiene rubber (SBR) were comprehensively studied via experimental and computational methods. It was discovered that BTC not only reduced the negative effect of MC on the vulcanization of SBR composite but also accelerated the vulcanization reaction. Besides, the aromatic amino and thioether groups in BTC played a crucial role in improving the thermo-oxidative aging resistance of SBR composites. Moreover, as against MBT or MC, BTC with a high molecular weight, amorphous state, and low solubility parameter exhibited lower migration and better dispersion in the SBR matrix. Therefore, in contrast to MBT/SBR or MBT/MC/SBR composite, BTC/SBR composite manifested an optimal overall performance, i.e., high vulcanization efficiency, outstanding mechanical properties, and good thermo-oxidative stabilization. These results indicated that BTC could be used as a prospected multifunctional additive to fabricate the high-performance SBR composites. Furthermore, molecular simulation as a useful tool can offer valuable theoretical guidance for the molecule design of high-efficiency antioxidants.

Thermoplastic Elastomeric Composites Filled with Lignocellulose Bioadditives, Part 2: Flammability, Thermo-Oxidative Aging Resistance, Mechanical and Barrier Properties.

The work covers the characteristics of the functional properties of composites bordering thermoplastics and elastomers. The research is a continuation of considerations on blends in the form of a mixture of natural rubber (NR) with an ethylene–vinyl acetate copolymer (EVA) and the addition of a lignocellulose biofiller (wheat straw). After describing the processing and rheology as well as examining the thermal properties and morphology of composites (Part 1), the second part focuses on the characteristics of their performance. The effect of both different ratios of mixed polymers and the amount of filler on tensile strength and elongation at break, resistance to thermo-oxidative aging, hardness, tear resistance, barrier and damping properties, as well as flammability were investigated. The increased EVA content has shown a positive effect on tensile strength, elongation at break, resistance to thermo-oxidative aging, hardness, relative damping, tear strength, barrier and burning delay. On the other hand, a larger amount of natural rubber provides high flexibility and promotes the creation of a reinforcing structure by the filler used. Moreover, a significant impact of the addition of cereal straw on the barrier, damping, strength and flammability properties of composites was also noted. The great advantage of the prepared compositions in relation to commercial plastics is their environmental friendliness, primarily by replacing some petroleum derivatives of plastics with natural rubber and straw fibers.

A novel method for preparation of nanosilica from bamboo leaves and its green modification as a multi-functional additive in styrene butadiene rubber

This work reports the synthesis of nanosilica (NS) from bamboo leaves through precipitation method and its modification (MNS) with antioxidant, styrenated phenol via cost effective, mechano-chemical, green route to improve the dispersion, interfacial adhesion and thermo-oxidative resistance of Styrene Butadiene Rubber (SBR). SBR nanocomposites with 1–10 phr NS and 5 phr MNS were prepared using an internal mixer. Nanoparticles and the composites were characterized using Transmission Electron Microscopy, Field Emission Scanning Electron Microscopy, Thermogravimetric Analysis, Dynamic Light Scattering, Fourier Transform Infrared Spectroscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray diffraction analysis and BET analysis. The surface area of synthesized NS decreased from 575 m2/g to 451 m2/g on modification. Presence of 8.6 wt.% antioxidant on nanosilica improved mechanical, thermal, dynamic mechanical and aging properties of SBR 5MNS composite. Modification of nanosilica with styrenated phenol by ball milling technique not only improved the antioxidative resistance but also influenced the dispersion of nanosilica in SBR composites.

Lignin-Reinforced Nitrile Rubber/Poly(vinyl chloride) Composites via Metal Coordination Interactions

In this work, half the mass of carbon black (CB) was replaced by lignin for preparation of high-performance nitrile rubber/poly(vinyl chloride) composites via constructing interfacial Zn2+-based coordination bonds. It was demonstrated that lignin played a significant role as a natural ligand to form the Zn2+-based coordination interactions in the interphase between lignin and a rubber matrix. The tensile strength and Young’s modulus of the composites were significantly enhanced by the Zn2+-based coordination bonds owing to the dynamic fracture of coordination bonds. The thermo-oxidative aging resistance of the composites was improved by lignin and could be conveniently regulated by the content of ZnCl2 and sulfur. The high-temperature oil resistance of the composites also benefited from the partial substitution of CB by lignin and incorporation of the metal coordination bonds. This work opens a facile method for the potential application of green lignin in rubber–plastic composites through a conventional ...