Impact of fullerenes on the thermal stability of melt processed polystyrene and poly(methyl methacrylate) composites

The impact of the two fullerenes C₆₀ and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on the thermal and thermo-oxidative stability of the corresponding melt processed composites with the two polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA), was studied using both dynamic and isothermal thermogravimetric analysis (TGA). For each polymer, three different composites with C₆₀ loadings of 1.0 wt% and 3.0 wt% and PCBM loadings of 1.0 wt% were considered. The aim of this work was to compare the stabilization effect of both fullerenes on PS and PMMA. The results obtained show unequivocally that, although PCBM has lower thermal and thermo-oxidative stability than C₆₀, the PS-PCBM and PMMA-PCBM composites have higher thermal and thermo-oxidative stability than the corresponding PS-C₆₀ and PMMA-C₆₀ composites. These results corroborate our previous reports, on showing that PCBM is better than C₆₀ at improving the thermal and thermo-oxidative stability of polymers which degrade through radical degradation mechanisms.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Novel nanocomposite based on EVA/PHBV/[60]Fullerene with improved thermal properties

A novel nanocomposite was prepared from ethylene-co-vinyl acetate copolymer (EVA) and poly-3-hydroxy butyrate-co-valerate (PHBV) in combination with small amounts of [60]Fullerene (C₆₀). The thermal degradation as well as the incorporation effect of C₆₀ on the thermo-oxidative decomposition of EVA/PHBV/C₆₀ nanocomposites was investigated using thermogravimetric analysis (TGA). In order to assess the level of stabilization of nanocomposites, the oxidation induction time test was also determined. The obtained results indicated that the dispersion of C₆₀ even at low loading (0.3, 0.5 and 0.7 wt.%) exerts a significant increase on the thermal stability properties of nanocomposite. The oxidation induction time values of nanocomposites were remarkably increased with the increase of C₆₀ amounts. Surprisingly, the oxidation induction time of EVA/PHBV/C₆₀ (0.3 wt.%) is 1643 s higher than that of unfilled EVA/PHBV blend.The flammability properties investigated in pyrolysis combustion flow calorimetry (PCFC) showed that the addition of C₆₀ could prolong the time to peak of Heat Release Rate (pHRR) of around 30 °C compared to EVA/PHBV blend. It was demonstrated that C₆₀ is inhibitor of the thermal and thermo-oxidative degradation of EVA/PHBV blend.     

Low percolation conductive graphite flakes-filled poly(urethane-imide) composites with high thermal stability via imidization self-foaming structure

In the study, the conductive graphite flakes filled poly(urethane-imide) composites (PUI/GFs) with high performance were constructed by the thermal imidization self-foaming reaction. It was found that the foaming action could promote the redistribution of GFs during curing process and the formation of stable linear conductive pathways. The percolation threshold of PUI/GFs composites was lowered from 1.26 wt% (2000 mesh GFs) or 0.86 wt% (1000 mesh GFs) to 0.79 wt% (500 mesh GFs), which were relatively low percolation thresholds for polymer/GFs composites so far. When the content of 500 mesh GFs was 4.0 wt%, the electrical conductivity of the composite was as high as 3.96 × 10^?1 S/m. Also, a poly(urethane-imide) (PUI) matrix with excellent thermal stability (T_d10%: 334.97 °C) and mechanical properties (elongation at break: 324.52%, tensile strength: 15.88 MPa) was obtained by introducing the rigid aromatic heterocycle into the polyurethane (PU) hard segments. Moreover, the zero temperature coefficient of resistivity for the composites was observed at the temperature range from 30 °C to 200 °C. Consequently, PUI/GFs composites may provide the novel strategy for considerable conductive materials with high thermal stability in electrical conductivity.     

Oxidative degradation products of irradiated polyethylene

Oxidative thermal degradation products of polyethylenes at various temperatures crosslinked with electron beams have been analyzed with gas chromatography and mass spectrometry techniques. Carbon monoxide and carbon dioxide are determined at a temperature range of 200–340°C, and the activation energies of the unirradiated and the irradiated polyethylene (at 100 Mrad) are 13.5 and 11.4 Kcal/mole, respectively. C₁ to C₈ hydrocarbons produced in air and in nitrogen are determined at temperatures from 400 to 450°C for the polyethylenes. The irradiated polyethylene produces less hydrocarbons in air than the unirradiated polyethylene, contrary to the fact that the crosslinked polymer evolves more hydrocarbons than the unirradiated polymer in a nitrogen atmosphere. Aldehydes and ketones are observed in the volatile oxidative degradation products, and these carbonyl compounds increase quantitatively with increase of temperature up to about 460°C. It is concluded that irradiated polyethylene is thermally more unstable in the absence of oxygen and more easily oxidable at low degradation temperatures in air than unirradiated polyethylene. Irradiated polyethylene, however, is more heat-stable than unirradiated polyethylene from the standpoint of the ignition process.     

Radical scavenging efficiency of different fullerenes C60-C70 and fullerene soot

This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C₆₀ and C₇₀ in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C₆₀ and C₇₀ and fullerene soot. All fullerenes - C₆₀ of gold grade, C₆₀/C₇₀ (93/7, mix 1), C₆₀/C₇₀ (80 ± 5/20 ± 5, mix 2) and C₇₀ operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C₆₀ and C₇₀ the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k_(333K) = (1.9 ± 0.2) × 10⁸ (C₆₀); (2.3 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 1); (2.7 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 2); (3.0 ± 0.3) × 10⁸ (C₇₀), M⁻¹ s⁻¹. The increasing C₇₀ constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C₆₀−soot] = (2.0 ± 0.1) × 10⁻⁴ mol g⁻¹ and k_inh = (6.5 ± 1.5) × 10³ M⁻¹ s⁻¹ respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.     

Modifying transparent electrode with conjugated organic semiconductor hole transport material as interface for enhancing performance of organic solar cell

Indium tin oxide (ITO) is used as a substrate was covered with 4-[4-(4-methoxy-N-naphthalen-2-ylanilino) phenyl] benzoic acid (MNA) as a self-assembled monolayer (SAM). Poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6) C₆₁ (PCBM) were mixed and used as a donor–acceptor in organic solar cell (OSC). The MNA (SAM) layer is used as an interface instead of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) for hole injection. The HOMO-LUMO energy level of MNA-SAM molecule and the electronic charge distribution were calculated theoretically using Chemissian software. The HOMO-LUMO energy level of the MNA is calculated as E_HOMO = ?5.10 eV and E_LUMO = ?1.60 eV. The OSC modified with MNA showed an efficient performance in the absence of PEDOT: PSS as hole transport layer. The annealing of the ITO/SAM/P3HT: PCBM films at different temperatures are also investigated to study the effect of reducing defects. The interface structures of the organic semiconductor layer on ITO were characterized by Atomic Force Microcopy (AFM). In addition, Kelvin Probe Microscopy (KPM) is used to understand how the annealing changes the surface potential energy of the ITO/SAM substrate. Using the KPM method, which measures the surface potential energy of the films, the energy bands of the ITO were increased to maximum 5.09 eV. The ITO/SAM/P3HT: PCBM film's surface potential was determined to be 0.18 eV after being annealed at 80 °C. The surface potential of the modified films was discovered to be 0.33 V and 0.39 V when the annealing temperature was raised from 80 °C to 120 °C and 160 °C. The maximum device efficiency was demonstrated by the ITO/SAM/P3HT: PCBM film after an hour of annealing at 160 °C.     

Development and characterization of fully bio‐based polybenzoxazine‐silica hybrid composites for low‐k and flame‐retardant applications

In the present work, new classes of bio‐based polybenzoxazines were synthesized using eugenol as phenol source and furfurylamine and stearylamine as amine sources separately through solventless green synthetic process routes and were further reinforced with varying percentages (1, 3, 5, and 10 wt%) of silica (from rice husk) to attain hybrid composites. The molecular structure, cure behaviour, thermal stability, dielectric properties, and flame‐retardant behaviour of both benzoxazine monomers and benzoxazine composites were characterized using appropriate modern analytical techniques. The eugenol‐based benzoxazines synthesized using furfurylamine (FBz) and stearylamine (SBz) were cured at 223°C and 233°C, respectively. The differential scanning calorimetry (DSC) data reveal the glass transition temperatures (T_g) of FBz and SBz were 157°C and 132°C, respectively, and the maximum decomposition temperature (T_max) as obtained from thermogravimetric analysis (TGA), were found to be 464°C and 398°C for FBz and SBz, respectively. The dielectric constants for FBz and SBz obtained at 1 MHz were 3.28 and 3.62, respectively. Furthermore, varying weight percentages (1, 3, 5, and 10 wt%) of 3‐mercaptopropyltrimethoxysilane (3‐MPTMS) functionalized bio‐silica reinforced the composite materials as evidenced by their improved thermal stability and lower dielectric constant. Data obtained from thermal and dielectric studies suggested that these polybenzoxazines could be used in the form of adhesives, sealants, and composites for high performance inter‐layer low‐k dielectric applications in microelectronics.     

New polymer electrolyte membrane for medium-temperature fuel cell applications based on cross-linked polyimide Matrimid and hydrophobic protic ionic liquid

New hydrophobic protic ionic liquid, 2-butylaminoimidazolinium bis(trifluoromethylsulfonyl)imide (BAIM-TFSI), has been synthesized. The ionic liquid showed good thermal stability to at least 350 °C. The conductivity of BAIM-TFSI determined by electrochemical impedance method was found to be 5.6 × 10^?2 S/cm at 140 °C. Homogeneous composite films based on commercial polyimide (PI) Matrimid and BAIM-TFSI containing 30–60 wt% of ionic liquid were prepared by casting from methylene chloride solutions. Thermogravimetric analysis data indicated an excellent thermal stability of PI/BAIM-TFSI composites and thermal degradation points in the temperature range 377 °C–397 °C. The addition of ionic liquid up to 50 wt% in PI films does not lead to any significant deterioration of the tensile strength of the polymer. The dynamic mechanical analysis results indicated both an increase of storage modulus E′ of PI/BAIM-TFSI composites at room temperature and a significant E′ decrease with temperature compared with the neat polymer. The cross-linking of the PI with polyetheramine Jeffamine D-400 allowed to prepare PI/Jeffamine/BAIM-TFSI (50%) membrane with E′ value of 300 MPa at 130 °C. The ionic conductivity of this cross-linked composite membrane reached the level of 10^?2 S/cm at 130 °C, suggesting, therefore, its potential use in medium-temperature fuel cells operating in water-free conditions.     

Synthesis,characterization and kinetic computations of fullerene (C60)–CuO on the mechanism decomposition of ammonium perchlorate

CuO, C₆₀–CuO, and Al/C₆₀–CuO nanostructures were synthesized and characterized by scanning electron microscope (SEM)/energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA) measurements were performed to study the influence of these additives on ammonium percolate (AP) thermal decomposition. From the comparison of DSC and TGA plots, the catalytic effect of CuO and C₆₀–CuO has been clearly noticed in which the lower temperature decomposition of AP was decreased from 331 °C to 315 °C, 310 °C, and 303 °C (in the presence of CuO, C₆₀–CuO, and Al/C₆₀–CuO, respectively) and the HTD was dropped from 430 °C (pure AP) to 352 °C, 335 °C, and 317 °C (for the compounds AP/CuO, AP/C₆₀–CuO, and AP/Al/C₆₀–CuO, respectively). The kinetics of the samples were investigated by isoconversional models and compared with an iterative procedure. The results of pure AP indicated a complex decomposition process involving three decomposition steps with specific reaction mechanism. The nanocatalysts incorporated in the AP have clearly affected its decomposition process in which the reaction mechanism and the number of stages were changed.     

The solubility of light fullerenes in styrene over the temperature range 20–80°C

The temperature dependence (over the range 20–80°C) of the solubility of light fullerenes (C₆₀ and C₇₀) and a mixture of fullerenes (60 wt % C₆₀, 39 wt % C₇₀, and 1 wt % C_76–90) in styrene was studied. The corresponding solubility polytherms are given and characterized.     

Investigating the mechanical,thermal and melt flow index properties of HNTs – LLDPE nano composites for the applications of rotational moulding

Linear low density polyethylene (LLDPE) is the one of the most popular polymer used for rotational moulding applications such as storage tanks. But, its inferior mechanical properties and thermal stability restrict the longer service. Hence, this study experimentally demonstrates the effect of Halloysite Nanotube (HNTs) concentration on LLDPE composites for enhancing the mechanical and thermal stability. HNTs were uniformly dispersed with LLDPE matrix through ultra-sonication, followed by compression moulding used to prepare the nano composites plates. The prepared composites are shown 19.2% improved tensile strength for 2 wt% HNTs, whereas 28.9% hike in flexural strength observed for 4 wt% HNTs composite, compare to neat LLDPE. Which shows that higher concentrations of HNTs is favourable in improving the flexural strength rather than tensile properties. In addition to that, higher concentrations of HNTs are also helping in improving the storage modulus of the LLDPE composites. The increase in mechanical properties mainly attributed due to effective load carriers (HNTs) in the composite. Besides, HNTs were also contributing for improving the melting point and residual char of the composites, which is indeed for storage tanks durability. The prepared composite was thermally stable at higher temperature up to 230 °C, because of HNTs chemical structure, the inner layer of HNTs constitute with Al₂O₃ and outermost layer constitute with SiO_2, both are thermally stable. Stated enhancement proves the potential effect of HNTs reinforcement in the LLDPE composite for rotational moulding applications.     

Thermal Stability of C60-Methylnaphthalenes Solvates

The crystalline solvates containing fullerenes and (di)methylnaphthalenes were investigated by thermal analyses and X-ray diffraction methods. It was found that C₆₀ with (di)methylnaphthalenes forms two types of stable solvates: either at the molar ratio 1:2 decomposing at temperatures close to 100°C or at 1:1 molar ratio decomposing in the temperature range 120–214°C. Crystalline lattice and thermal stability of the solvates depends on the structure of the solvent molecules. The strong solute-solvent interaction is also manifested by the modification of the C₆₀ absorption spectra in solution. The results are discussed using semiempirical quantum chemistry methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

High performance of PES-GNs MMMs for gas separation and selectivity

In this study, graphene nanosheets (GNs) were incorporated into polyethersulfone (PES) by phase inversion approach for preparing PES-GNs mixed matrix membranes (MMMs). To investigate the impact of filler content on membrane surface morphology, thermal stability, chemical composition, porosity and mechanical properties, MMMs were constructed with various GNs loadings (0.01, 0.02, 0.03, and 0.04 wt%). ?The performance of prepared MMMs was tested for separation and selectivity of CO₂, N₂, H₂ and CH₄ gases at various pressures from 1 to 6 bar and temperature varying from 20 to 60 °C. It was observed that, compared to the pristine PES membrane, the prepared MMMs significantly improved the gas separation and selectivity performance with adequate mechanical stability. The permeability of CO₂, N₂, H₂ and CH₄ for the PES + 0.04 wt% GNs increases from 9 to 2246, 11 to 2235, 9 to 7151, and 3 to 4176 Barrer respectively, as compared with pure PES membrane at 1 bar and 20 °C due to improving the membrane absorption and porosity. In addition, by increasing the pressure, the permeability and selectivity of CO₂, N₂, H₂ and CH₄ are increased due to the increased driving force for the transport of gas via membranes. Furthermore, the permeability of CO₂, N₂, H₂ and CH₄ increased by increasing the temperature from 20 to 60 °C due to the plasticization in the membranes and the improvement in polymer chain movement. This result proved that the prepared membranes can be used for gas separation applications.     

Solubility of light fullerenes in oleic, linoleic, and linolenic acids at 20–80°C

Solubility of light fullerenes (C₆₀, C₇₀, and the standard fullerene mixture containing (wt %): C₆₀ 65, C₇₀ 34, C _n>70 1) in the oleic, linoleic and linolenic acids, respectively, at 20–80°C was studied and the corresponding solubility polytherms were reported.     

Solubility of light fullerenes in vegetable oils

Polythermal (in the temperature range 0−80°C) solubility of light fullerenes (C₆₀ and C₇₀), and also of fullerene mixtures (65% C₆₀, 34% C₇₀, and 1% C_76–90) in vegetable oils (of unrefined and refined sunflower, corn, olive, linen, apricot, grape, cedar, and walnut) was studied; the corresponding solubility polytherms are given and characterized.     

Catalytic pyrolysis of HDPE in continuous mode over zeolite catalysts in a conical spouted bed reactor

A study has been carried out using HZSM-5, HY and Hβ zeolite-based catalysts in the pyrolysis of high density polyethylene (HDPE) continuously fed into a conical spouted bed reactor (CSBR) at 500 °C and atmospheric pressure, with the aim being to assess the yields and composition of the main products (both light olefins and automotive fuel hydrocarbons). Product streams have been grouped into seven lumps: light olefins (C₂–C₄) and light alkanes (<C₄) in the gas fraction, the liquid fraction consisting of three lumps (non-aromatic C₅–C₁₁ compounds, single-ring aromatics and C₁₁₊ hydrocarbons), wax and coke. The results are compared with those already obtained in thermal pyrolysis in a CSBR and with those obtained in the literature using catalysts in bubbling fluidized beds. HZSM-5 zeolite-based catalyst is very selective to light olefins, ≈58 wt% once equilibrated; whereas high yields of non-aromatic C₅–C₁₁ products (around 45 wt%) are obtained with Hβ and HY zeolite-based catalysts. Wax yield increases as reactions proceed, especially with HY and Hβ zeolite-based catalysts, due to catalyst deactivation by coke formation. Product distribution with the different catalysts and their evolution throughout continuous operation by feeding HDPE is explained according to the different properties of the zeolites used.     

The hydrogenolysis of C60 and C70

Temperature-programmed reaction (TPR) of C₆₀ and C₇₀ with H₂ was carried out on nickel in order to investigate the thermal stability of the fullerenes in the catalytic hydrogenation. The TPR profiles showed two methanation peaks and the corresponding weight decrease above 420°C, indicating the hydrogenolysis to CH₄. This revised version was published online in June 2006 with corrections to the Cover Date.     

Polythermal solubility of fullerenes in higher isomeric carboxylic acids

The solubility of individual fullerenes C₆₀ and C₇₀ and a fullerene mixture enriched in higher fullerenes (C₆₀ 38.8, C₇₀ 33.0, C_76–78 5.6, C₈₄ 8.6, C₉₀ 2.6, and C₉₆ 3.3%) in higher isomeric carboxylic acids was studied within the 20–80°C temperature range; the corresponding solubility polytherms are presented.     

Size effect of silica nanoparticles on thermal decomposition of PMMA

The size effect of silica nanoparticles (SiO₂) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal degradation temperature of PMMA–SiO₂ composites depended on both fraction and size of SiO₂, the thermal degradation temperature of 23 nm (diameter) SiO₂–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO₂–PMMA (3.2 wt%) and 13 nm SiO₂–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO₂. The degree of degradation improvement was increased linearly with the surface area of SiO₂. The number of surface hydroxyl group in unit volume of SiO₂ particle increased with increasing the specific surface area of SiO₂, and the interaction between hydroxide group of SiO₂ and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA.