Thermo-oxidative Resistance Research Articles

Synthesis and Characterization of A Novel Macromolecular Hindered Phenol Antioxidant and Its Thermo-Oxidative Aging Resistance for Natural Rubber

A novel macromolecular hindered phenol antioxidant with high antioxidative efficiency, polyhydroxylated polybutadiene (PHPB)-bound 2, 2′-thiobis (4-methyl-6-tert-butylphenol) (PHPB-b-TPH), was prepared by binding 2, 2′-thiobis (4-methyl-6-tert-butylphenol) (TPH) onto PHPB with isophorone diisocyanate (IPDI), using dibutyltin dilaurate (DBTDL) as catalyst, via a two-step nucleophilic addition reaction. The PHPB was first synthesized from hydroxyl-terminated polybutadiene (HTPB) and 2-mercaptoethanol via a thiol-ene click reaction. The PHPB-b-TPH was characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR), gel permeation chromatography (GPC), and thermal gravimetric analysis (TGA). The thermo-oxidative aging resistance of natural rubber (NR) with PHPB-b-TPH was evaluated by an accelerated thermal aging test and the oxidation induction time (OIT). The results showed that the −OH groups of PHPB first reacted with highly active secondary −NCO groups of IPDI at 35°C to form the adduct PHPB-NCO, and the PHPB-b-TPH was successfully obtained by one of the phenolic −OH in TPH reacting with the primary −NCO groups of PHPB-NCO at 70°C. The PHPB-b-TPH had better thermal stability and thermo-oxidative aging resistance for NR than TPH.

α-Tocopherol-induced radical scavenging activity in carbon nanotubes for thermo-oxidation resistant ultra-high molecular weight polyethylene-based nanocomposites

α-Tocopherol, a natural antioxidant molecule, was physically immobilized on the outer surface of multi-walled carbon nanotubes (CNTs), and the resulting functionalised particles (f-CNTs) were dispersed in ultra-high molecular weight polyethylene aiming at improving its thermo-oxidation resistance. The success of the functionalization was assessed through spectroscopic and thermal analysis, and the influence of the filler on the thermo-oxidative stability of the nanocomposites was investigated through rheological analyses and infrared spectroscopy. We found that the addition of only 1wt.% of f-CNTs brings about a surprisingly high oxidation resistance, with a five/ten-fold increase of the induction time of the degradation phenomena. Rather than to the inherent stabilizing action of the α-tocopherol, such a notable result is believed to be due to its specific chemical interactions with the CNTs, which could exhibit a considerable radical scavenging activity due to the formation of structural defects on their outer surface. The latter represent acceptor-like localized states, which radically improve the thermo-oxidative resistance of the f-CNTs-based polymer nanocomposites.

Enhanced thermo-oxidative aging resistance of EPDM at high temperature by using synergistic antioxidants

In this work, zinc dimethacrylate (ZDMA) and 2-sulfur-benzimidazole (MB)/N-4(phenyl–phenyl)-maleimide (MC) were simultaneously used as synergistic antioxidants to improve the thermo-oxidative aging resistance of peroxide vulcanized ethylene-propylene-diene monomer (EPDM) for its application at high temperature. For comparison purpose, the control sample without antioxidants, the traditional antioxidant package, the combined antioxidant MB/MC, and pure ZDMA were also investigated. The results showed that the crosslinking density of EPDM was only slightly decreased before aging by using the combined antioxidant MB/MC/ZDMA, and the increase in crosslinking density was much less than other antioxidants at the same aging time, indicating the largely improved aging resistance of EPDM. As a result, the change in mechanical properties was the lowest for EPDM with the combined antioxidant MB/MC/ZDMA at high temperature. Meanwhile, the results from structure analysis showed that the degree of oxidation of EPDM was much lower than other systems after aging at 180 °C for 216 h by using the combined antioxidant MB/MC/ZDMA. In addition, the surfaces of EPDM samples with MB/MC/ZDMA as synergistic antioxidants or the combined antioxidant MB/MC were still smooth after aging at 180 °C for 216 h, whereas severe cracks occurred for other antioxidative systems. These results suggest the good thermo-oxidative aging resistance of the synergistic antioxidant MB/MC/ZDMA. Finally, the synergistic antioxidative mechanism of MB/MC/ZDMA was carefully discussed.

Si(B)CN-doped carbon nanofibers with excellent oxidation resistance

SiBCN-doped and SiCN-doped carbon nanofibers with improved thermo-oxidative resistance were developed by thermal conversion of as-electrospun fibers from polyacrylonitrile and ceramic precursor blend solutions. Isothermal thermogravimetric analysis and muffle furnace calcining were used to evaluate the oxidation behavior. The samples after calcining were characterized by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The results revealed that the oxidation resistance of carbon nanofibers was improved by the doping of SiCN and SiBCN ceramics. Furthermore, SiCN ceramic offered only limited protection, while SiBCN ceramic gave better protection to carbon nanofibers under air at 500°C.

Simultaneous Enhancements of UV Resistance and Mechanical Properties of Polypropylene by Incorporation of Dopamine-Modified Clay

Inspired by the radical scavenging function of melanin-like materials and versatile adhesive ability of mussel-adhesion proteins, dopamine-modified clay (D-clay) was successfully incorporated into polypropylene (PP) using an amine-terminated PP oligomer as the compatibilizer. Although the PP/D-clay nanocomposites exhibit intercalated morphology, the incorporation of D-clay greatly improves the thermo-oxidative stability and UV resistance of PP owing to the strong radical scavenging ability of polydopamine (PDA) and large contact area between PP and the PDA coating on clay mineral. Moreover, the reinforcement effect brought by D-clay is fairly significant at very low clay loadings probably owing to the strong interfacial interactions between the layered silicates and the compatibilizer as well as that between the compatibilizer and the PP matrix. The work demonstrates that D-clay is a type of promising nanofiller for thermoplastics used for outdoor applications since it stabilizes and reinforces the polymers simultaneously.

Mechanical behavior, microstructure and thermooxidation properties of sequentially crosslinked ultrahigh molecular weight polyethylenes

AbstractThe aim of this study was to explore the impact of the sequential irradiation and annealing process on the microstructure, thermooxidation behavior and mechanical properties of GUR 1050 ultrahigh molecular weight polyethylene (UHMWPE) with respect to the postirradiation annealed material. For this purpose, the effects of a variety of irradiation and annealing conditions on microstructure and mechanical properties were investigated. Differential scanning calorimetry was performed to characterize melting temperature, crystalline content and crystal thickness, whereas transmission electron microscopy provided additional insights into crystal morphology. Thermogravimetric experiments in air served to assess thermooxidation resistance and changes associated to radiation‐induced crosslinking. Fatigue properties were studied from three different approaches, namely short‐term cyclic stress–strain tests, long‐term fatigue experiments and crack propagation behavior. Likewise, three experimental techniques (uniaxial tensile test, impact experiments, and load to fracture of compact tension specimens) allowed evaluation of the fracture resistance. The present findings confirm sequentially crosslinked UHMWPE exhibited improved thermooxidation resistance and thermal stability compared to post‐irradiation annealed UHMWPE. Also, the mechanical behavior, including the fatigue and fracture resistance, of these materials was generally comparable regardless of the annealing strategy. Therefore, the sequential irradiation and annealing process might provide higher oxidation resistance, but not a significant improvement in mechanical properties compared to the single radiation dose and subsequent annealing procedure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effects of poss nanoparticles on ABS‐g‐Ma thermo oxidation resistance

AbstractThermo oxidative degradation at and beyond processing temperatures has been carried out on ABS copolymer grafted with Maleic Anhydride (ABS‐g‐Ma) and three nanocomposites with the above material melt‐blended with different types of POSS, being amino‐propyl isobutyl (APOSS), glycidyl (GPOSS), and trisilanol (TPOSS). The incorporation adequacy of the nanofillers into the matrix has been assessed with scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), whereas the quantification of the thermal degradation behavior of each sample was carried out through infrared spectrography (FTIR), thermogravimetric analysis (TGA) including the degradation kinetics and color spectrophotometry (Cielab). Although the results show adequate incorporation and miscibility of the nanofillers into the matrix, the GPOSS and the TPOSS nanocomposites provided no relevant improvements in thermal stability when compared with the base ABS‐g‐Ma, and the APOSS blend exhibits a very slight decay in almost all the quantitative analysis carried out in this work. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Synthesis and Thermo-Oxidative Aging Resistance of Hydroxyl Terminated Polybutadiene Bound 2,2-Thiobis(4-methyl-6-tert-butylphenol)

A novel polymeric antioxidant HTPB-IPDI-TPH was synthesized by the reaction between 2,2-thiobis (4-methyl-6-tert-butylphenol) (TPH) and an adduct (HTPB-IPDI) from hydroxyl terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI). The effects of raw materials ratio and the reaction condition were investigated by measuring the content of the residual –NCO groups of the reactants during the reaction. The structure of HTPB-IPDI-TPH was characterized by FTIR and 1H NMR. Thermo-oxidative aging resistance of HTPB-IPDI-TPH was evaluated by oxidation induction time (OIT) from DSC of natural rubber vulcanizates. The optimal reaction conditions between IPDI and HTPB were that the amount of dibutyltin dilaurate (DBTDL) was 0.6 wt% based on IPDI, and the temperature and time were 40°C and 270 min, respectively. The reaction conditions between TPH and HTPB-IPDI were that the molar ratio of TPH to –NCO in HTPB-IPDI was 3:1, and the amount of DBTDL was 1.6 wt% based on the total of reactants, and the temperature and time were 75°C and 360 min, respectively. Thermo-oxidative aging resistance of HTPB-IPDI-TPH was obviously superior to the corresponding low molecular counterpart (TPH) for natural rubber vulcanizates.

Cotton fabrics treated with novel oxidic phases acting as effective smoke suppressants

Sol–gel processes have been applied to cotton fabrics in order to coat the fibres with a silica film, able to improve their thermo-oxidative resistance and their combustion behaviour under the irradiative heat flow of a cone calorimeter. To this aim, tetramethoxysilane, inorganic precursor of the silica phase, has been employed alone or coupled with species having either smoke suppressant features (namely, zinc oxide, zinc acetate dihydrate and zinc borate) or well known flame retardant properties (like ammonium pentaborate octahydrate, boron phosphate, ammonium polyphosphate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). In addition, the use of barium sulphate, which is a smoke suppressant and, at the same time, a flame retardant, has been investigated. Cone calorimetry turned out to be a suitable technique for assessing the flammability and smoke production of the treated fabrics (particularly when referring to total smoke release, smoke production rate and CO and CO2 yields). The composition and morphology of the deposited coatings, assessed by scanning electron microscopy, have been found to influence their combustion behaviour, as well as their thermal and thermo-oxidative stability evaluated by thermogravimetric analysis in nitrogen and air, respectively.

Structural Characterization of Hydroxyl-Terminated Polybutadiene-Bound 2, 2-Thiobis(4-methyl-6-tert-butylphenol) and Its Thermo-Oxidative Aging Resistance for Natural Rubber Vulcanizates

A novel polymeric antioxidant, hydroxyl-terminated polybutadiene-bound 2,2-thiobis(4-methyl-6-tert-butylphenol) (HTPB-IPDI-TPH), was prepared by binding 2, 2-thiobis(4-methyl-6-tert-butylphenol) (TPH) onto hydroxyl-terminated polybutadiene (HTPB) with isophorone diisocyanate (IPDI). Fourier-transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance spectroscopy (13C NMR), and gel permeation chromatography (GPC) were used to characterize the structure of HTPB-IPDI-TPH. The thermal stability of HTPB-IPDI-TPH was studied by thermogravimetry analysis (TGA). The effect of HTPB-IPDI-TPH on thermo-oxidative aging resistance of NR vulcanizates was investigated, and the mechanism of thermo-oxidative aging resistance was preliminarily discussed. The results showed that HTPB-IPDI-TPH contributed better thermal stability and thermo-oxidative aging resistance to NR vulcanizates than TPH. The thermo-oxidative aging resistance of HTPB-IPDI-TPH was more remarkable in the later stage of aging. Attenuated total-reflectance Fourier-transform infrared spectroscopy (FTIR-ATR) analysis showed that the relative content of carbonyl groups of NR vulcanizate with HTPB-IPDI-TPH was obviously lower than that with TPH after thermo-oxidative aging. It is suggested that ‒NHCOO‒ groups in HTPB-IPDI-TPH enhanced the ability of trapping alkyl peroxide radicals.

Liquid poly(silylacetylene)siloxane resin as a novel precursor of silicon carbide and silicon oxycarbide ceramics

Liquid preceramic poly(silylacetylene)siloxane resin was synthesized via a two-step protocol including organometallic condensation and hydrolysis reactions. The preceramic resin was well soluble in acetone, toluene, and tetrahydrofuran (THF), etc. By thermal cure at 180–250°C a hard monolithic solid was formed through radical polymerization of secondary ethynyl groups. The poly(silylacetylene)siloxane resin was processed easily to various nonporous shapes to silicon carbide (SiC) and silicon oxycarbide (SiCO). SiCO ceramic was obtained at a yield of >75% by pressureless pyrolysis at 900–1200°C; while SiC ceramic was obtained at 1500°C at a yield of ≈67%. The molar ratio of Si/C in the SiC was found at 1:1.1–1:3, based on ICP-MS elemental analysis. X-ray diffraction (XRD) results revealed the typical β-SiC structure in the poly(silylacetylene)siloxane derived SiC ceramics. The SiC ceramics exhibited high thermo-oxidation resistance at elevated temperatures in air atmosphere.

Enhancement of POM thermooxidation resistance through POSS nanoparticles

Thermooxidative degradation at and beyond processing temperatures has been carried out on polyoxymethylene (POM) enhanced with four different types of POSS, being Glycidyl, GlycidylIsobutyl, Aminopropylisobutyl, and Poly(ethylene glycol). The quantification of such degradation was carried out through FTIR spectrography, color spectrophotometry, and thermogravimetric analysis methods. The results showed that the presence of POSS in the blend improves dramatically the thermal stability of the POM matrix. The best performance was found with Aminopropylisobutyl, whereby the onset of degradation temperature increased by more than 50°C. Said improvement is referred to the conditions where the nanocomposite developed only 2% of carbonyl yield and 8% of yellowing of the 100% deterioration suffered by the standard POM copolymer. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Flame retardancy and thermal degradation behaviors of phosphate in combination with POSS in polylactide composites

Flame retarded polylactide with pentaerythritol phosphate (PEPA), melamine phosphate (MP) and polyhedral oligomeric silsesquioxanes (POSS) were prepared in this study. Effect of trisilanolisbutyl-POSS (TPOSS) on the thermal degradation behaviors of intumescent flame retardant polylactide (IFRPLA) composites under nitrogen or air atmosphere was investigated by thermalgravimetric analysis (TGA), thermogravimetric analysis/infrared spectrometry (TG–IR) and real time Fourier transform infrared spectra (RTFTIR). Under nitrogen atmosphere, incorporation of PEPA, MP and TPOSS could significantly reduce the release of flammable gases. Under air atmosphere, the presence of MP and PEPA can promote the formation of char layer, while TPOSS was oxidized to form silica covered on the char layer, which improved the thermo-oxidation resistance of the char. Thus, the fire retardancy of PLA was notably improved.

Synergistic effect of nanobarite and carbon black fillers in natural rubber matrix

Novel rubber nanocomposites based on natural rubber (NR), nanobarite (NB) and carbon black (CB) were prepared by mechanical compounding with the aim of determining the synergistic effect of NB and CB fillers in the NR matrix. The morphology and properties of these nanocomposites were investigated. The results indicated that the reinforcement of NB was influenced by the organic treatment method. In comparison with unmodified NB (U-NB) and NB modified by sodium stearate (SA-NB), NB modified by sodium aluminate and sodium stearate (SA-Al2O3-NB) exhibited outstanding reinforcement due to its homogenous dispersion in the NR matrix and the stronger polymer–filler interactions. In order to optimize the synergistic effect of CB and SA-Al2O3-NB in the NR matrix, thorough and systematic analyses were performed on NR/CB/SA-Al2O3-NB containing various combinations of CB and SA-Al2O3-NB, which revealed that the overall properties strongly depended on the extent of the dispersion of CB and SA-Al2O3-NB fillers. Incorporating 2wt.% SA-Al2O3-NB to the control NR containing 45wt.% CB resulted in an obvious synergistic effect, including accelerating the curing process, improving the mechanical properties and enhancing the thermo oxidative resistance and corrosion resistance.

Improvement of the thermo-oxidative stability of low-density polyethylene films by organic–inorganic hybrid coatings

LDPE films have been coated with single or bi-layer hybrid coatings formed through sol–gel reactions in order to improve their thermo-oxidative resistance. Different chemical compositions of the coating were investigated which differ either in the amount of the inorganic phase (silica deriving from tetraethoxysilane) or in the organic component (either alkoxy silane functionalized polyethylene–poly(ethylene glycol) diblock copolymers or poly(vinyl alcohol)). The thermo-oxidative stability of the coated films thus obtained has been assessed by means of isothermal differential scanning calorimetry (DSC) and isothermal thermo-gravimetric analysis (TGA) under accelerated conditions, i.e. at high temperatures in pure oxygen flow. Conventional ageing in air at lower temperature, slightly above the in-service one, has also been carried out. The obtained data show: a) a general improvement of the thermal-resistance for the coated LDPE samples; b) a particularly high thermal-resistance for LDPE coated with a bi-layer coating with pure silica in the top layer; c) the effectiveness of the accelerated techniques in qualitatively assessing the thermo-oxidative resistance of the coated polymeric systems.

Effects of aging on the properties of modified asphalt binder with flame retardants

Effects of aging on the properties of asphalt binders modified by incorporating Styrene–Butadiene–Styrene (SBS) and flame retardants (FR) were studied. Asphalt binders were artificially aged in the rolling thin film oven (RTFOT) and Pressure Aging Vessel (PAV). The flame retardancy of modified asphalt binders were characterized using limited oxygen index (LOI), and the effects of aging on the properties of asphalt binders were studied using Brookfield viscometer test and dynamic shear rheometer test. Experimental results indicated that the flame retardancy of asphalt binder was increased after aging. But the increasing amount of LOI is low when the modified asphalt binder containing more flame retardants. The variation of the LOI, softening point, penetration, ductility and viscosity of asphalt binder decreased with flame retardant content increasing, meaning the flame retardants can improve the thermo-oxidative aging resistance of asphalt binder. Furthermore, the G */sin δ, stiffness and m-value of flame retardant modified asphalt binders display smaller changes after two different aging.

Restabilization of the aging resistance of compatibilized blends of pre-aged low density polyethylene and high-impact polystyrene (LDPE/HIPS)

Blends of pre-aged low density polyethylene (LDPE) with high-impact polystyrene (HIPS) compatibilized with a 1:1 mixture of styrene–butadiene block copolymer (SBS) and ethylene-propylene-diene statistical terpolymer (EPDM) were upgraded for thermooxidative resistance with N, N’-disubstituted 1,4-phenylenediamine. The impact strength after the oven test was improved. A model experiment confirmed that the efficiency of the phenylenediamine was not lost in the system after a partial sacrificial transformation of PD into the corresponding quinone diimine. The beneficial thermal effect of the upgrading used is a consequence of cooperation between the components of the blend. The system does not protect however against photooxidative stress without a suitable fortification with photostabilizers. The material properties of the upgraded blend upon oxidative stresses were assessed by monitoring of changes in the impact strength, carbonyl index and fracture surfaces on samples aged for various time intervals. It is shown that blends fortified by proper photostabilizers (carbon black or a combination of the UV absorber with photoantioxidant HAS) have sufficient stability for outdoor application.

Amidated pectin derivatives with n-propyl-, 3-aminopropyl-, 3-propanol- or 7-aminoheptyl-substituents

Highly methylated (HM) pectin ( DM = 90%) was amidated with four amines under anhydrous conditions. The goal was to prepare modified pectins that could be useful components of composites with new properties. The yields and degree of amidation ( DA) of the products were, respectively, 67–92% and 67.3–72.0%. Maximal values were obtained for pectin propylamide ( 1) and minimal for pectin 7-aminoheptylamide ( 4). While products 1 and pectin 3-propanolamide ( 2) showed 95 g/100 g solubility in water, pectin 3-aminopropylamide ( 3) was 46 g/100 g and 4 only 3 g/100 g water-soluble. The TG/DTA data indicate that the thermal properties were not dramatically altered under inert environment and improved as far as thermooxidation resistance. From the overall prospective product 3 seems to be the most valuable component for further composite preparation.

Mechanical and thermal properties of polyimide/silica hybrids with imide‐modified silica network structures

AbstractA series of hybrid materials incorporating imide‐modified silica (IM‐silica) network structures into a polyimide (PI) matrix were produced with a sol–gel technique from solution mixtures of poly(amic acid) and tetraethoxysilane (TEOS) containing alkoxysilane‐terminated amic acids with various degrees of polymerization. The hybrid films, obtained by solvent evaporation, were heated successively to a maximum temperature of 300°C to carry out the imidization process and silica network formation in the PI matrix. The morphology and mechanical properties of these hybrids with IM‐silica networks were studied and compared with the properties of one in which reinforcement of the matrix was achieved with a pure silica network generated from TEOS. The introduction of longer imide spacer groups into the silica network led to a drastic decrease in the silica particle size. Improved tensile modulus was observed in such compatibilized hybrid systems. Comparative thermogravimetric measurements of these hybrids showed improved thermooxidative resistance. A PI hybrid with 30% IM‐silica had a thermal decomposition temperature nearly 260°C higher than that of the pure PI matrix. The high surface area of the interconnected silica domains and increased interfacial interaction were believed to restrict the segmental motion of the polymer and thus slow the diffusion of oxygen in the matrix, thereby slowing the oxidative decomposition of the polymer. The reinforcement of existing and new PIs by this method offers an opportunity for improving their thermooxidative stability without degrading their mechanical strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The Effect of Epoxidized Natural Rubber (ENR-50) or Polyethylene Acrylic Acid (PEA) as Compatibilizer on Properties of Ethylene Vinyl Acetate (EVA)/Natural Rubber (SMR L) Blends

The effect of epoxidized natural rubber (ENR) or polyethylene acrylic acid (PEA) as a compatibilizer on properties of ethylene vinyl acetate (EVA)/natural rubber (SMR L) blends was studied. 5 wt.% of compatibilizer was employed in EVA/SMR L blend and the effect of compatibilizer on tensile properties, thermal properties, swelling resistance, and morphological properties were investigated. Blends were prepared by using a laboratory scale of internal mixer at 120°C with 50 rpm of rotor speed. Tensile properties, thermal properties, thermo-oxidative aging resistance, and oil swell resistance were determined according to related ASTM standards. The compatibility of EVA/SMR L blends with 5 wt.% of compatibilizer addition or without compatibilizing agent was compared. The EVA/SMR L blend with compatibilizer shows substantially improvement in tensile properties compared to the EVA/SMR L blend without compatibilizer. Compatibilization had reduced interfacial tension and domain size of ethylene vinyl acetate (EVA)/natural rubber (SMR L) blends.