Properties of matrix-grafted multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposites synthesized by in situ reversible addition-fragmentation chain transfer polymerization

Multi-walled carbon nanotubes (MWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by the in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in the presence of MWCNTs, at which the bulk polymer was grafted onto the surface of nanotubes through the ??grafting through?? strategy. For this purpose, MWCNTs were formerly functionalized with polymerizable MMA groups. MMA and PMMA-grafted MWCNTs were characterized by Fourier-transform infrared spectroscopy, Raman, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Dissolution of nanotubes was examined in chloroform solvent and studied by UV?Cvis spectroscopy. Thermogravimetric and degradation behavior of prepared nanocomposites was investigated by TGA. MWCNTs had a noticeable boosting effect on the thermal stability of nanocomposites. TGA thermograms showed a two-step weight loss pattern for the degradation of MWCNT-PMMA/PMMA nanocomposites which is contrast with neat PMMA. Introduction of MWCNTs also improved the dynamic mechanical behavior and electrical conductivity of nanocomposites. TEM micrograph of nanocomposite revealed that the applied methods for functionalization of nanotubes and in situ synthesis of nanocomposites were comparatively successful in dispersing the MWCNTs in PMMA matrix.     

Decoration of Fe3O4 nanoparticles on the surface of poly(acrylic acid) functionalized multi‐walled carbon nanotubes by covalent bonding

Fe₃O₄ nanoparticles were indirectly implanted onto functionalized multi‐walled carbon nanotubes (MWCNTs) leading to a nanocomposite with stronger magnetic performance. Poly(acrylic acid) (PAA) oligomer was first reacted with hydroxyl‐functionalized MWCNTs (MWCNTs‐OH) forming PAA‐grafted MWCNTs (PAA‐g‐MWCNTs). Subsequently, Fe₃O₄ nanoparticles were attached onto the surface of PAA‐g‐MWCNTs through an amidation reaction between the amino groups on the surface of Fe₃O₄ nanoparticles and the carboxyl groups of PAA. Fourier transform infrared spectra confirmed that the Fe₃O₄ nanoparticles and PAA‐g‐MWCNTs were indeed chemically linked. The morphology of the nanocomposites was characterized using transmission electron microscope (TEM). The surface and bulk structure of the nanocomposites were examined using X‐ray diffraction, X‐ray photoelectron spectrometer (XPS), and thermogravimetric analysis (TGA). The magnetic performance was characterized by vibrating sample magnetometer (VSM) and the magnetic saturation value of the magnetic nanocomposites was 47 emu g^?1. The resulting products could be separated from deionized water under an external magnetic field within about 15 s. Finally, the magnetorheological (MR) performances of the synthesized magnetic nanocomposites and pure Fe₃O₄ nanoparticles were examined using a rotational rheometer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Effect of acid treated multi-walled carbon nanotubes on the mechanical, permeability, thermal properties and thermo-oxidative stability of isotactic polypropylene

The effect of acid treatment of multi-walled carbon nanotubes (MWCNTs) on the mechanical, thermal and mainly thermo-oxidative stability of isotactic polypropylene (iPP) was evaluated. From the acid treatment surface carboxylic groups were mainly formed, while the nanotubes' length was gradually reduced by increasing the treatment time. Young's modulus, tensile strength and storage modulus of the iPP/MWCNT nanocomposites were increased by increasing the treatment time of the MWCNTs, due to finer dispersion inside the polymer matrix, as revealed by TEM and micro-Raman spectroscopy. Furthermore, the nanotubes acted as nucleating agents, an effect more pronounced with finer filler dispersion. Thermal stability in an inert atmosphere also increased. Thermo-oxidative stability tests in air and O₂ revealed that oxidative degradation took place in two stages. In the first stage, corresponding to temperatures up to 230 °C, the MWCNTs accelerated the oxidation of iPP, while at higher than 300 °C temperatures the trend was reversed. Incubation studies proved that, at the first stages, oxidation was due to random chain scission of iPP and oxygen uptake. This behaviour was accelerated by the MWCNTs' surface carboxylic groups and, as found by O₂ permeability studies, was mainly a surface process. In the second stage, due to the shielding effect of MWCNTs, the removal of the gases produced during decomposition was hindered. At this stage the presence of MWCNTs resulted in more thermo-oxidatively stable nanocomposites.     

Thermal curing behavior of MWCNT modified vinyl ester‐polyester resin suspensions prepared with 3‐roll milling technique

This study aims to investigate the curing behavior of a vinyl ester‐polyester resin suspensions containing 0.3 wt % of multiwalled carbon nanotubes with and without amine functional groups (MWCNTs and MWCNT‐NH₂). For this purpose, various analytical techniques, including Differential Scanning Calorimetry (DSC), Fourier infrared spectroscopy (FTIR), Raman Spectroscopy, and Thermo Gravimetric Analyzer (TGA) were conducted. The resin suspensions with carbon nanotubes (CNTs) were prepared via 3‐roll milling technique. DSC measurements showed that resin suspensions containing CNTs exhibited higher heat of cure (Q), besides lower activation energy (E_a) when compared with neat resin. For the sake of simplicity of interpretation, FTIR investigations were performed on neat vinyl ester resin suspensions containing the same amount of CNTs as resin. As a result, the individual fractional conversion rates of styrene and vinyl ester were interestingly found to be altered dependent on MWCNTs and MWCNT‐NH₂. The findings obtained from RS measurements of the cured samples are highly proportional to those obtained from FTIR measurements. TGA measurements revealed that CNT modified nanocomposites have higher activation energy of degradation (E_d) compared with the cured polymer. The findings obtained revealed that CNTs with and without amine functional groups alter overall thermal curing response of the surrounding matrix resin, which may probably impart distinctive characteristics to mechanical behavior of the corresponding nanocomposites achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1511–1522, 2009     

Thermal degradation kinetics of in situ prepared PET nanocomposites with acid-treated multi-walled carbon nanotubes

A series of PET/acid-treated multi-walled carbon nanotubes (MWCNTs) nanocomposites of varying nanoparticles’ concentration were prepared, using the in situ polymerization technique. TEM micrographs verified that the dispersion of the MWCNTs into the PET matrix was homogeneous, while some relatively small aggregates co-existed at higher filler contents. Intrinsic viscosity of the prepared nanocomposites was increased at low MWCNTs contents (up to 0.25 wt%), while at higher contents a gradual reduction was observed. The surface carboxylic groups of acid-treated MWCNTs probably reacted with the hydroxyl end groups of PET, acting as chain extenders at smaller concentrations, while at higher concentrations, on the other hand, led to the formation of branched and cross-linked macromolecules, with reduced apparent molecular weights. From the thermogravimetric curves, it was concluded that the prepared samples exhibited good thermostability, since no remarkable mass loss occurred up to 320 °C (<0.5%). The activation energy (E) of degradation of the studied materials was estimated using the Ozawa, Flynn, and Wall (OFW), Friedman and Kissinger’s methods. Pure PET had an E = 223.5 kJ/mol, while in the PET/MWCNTs nanocomposites containing up to 1 wt% the E gradually increased, indicating that MWCNTs had a stabilizing effect upon the decomposition of the matrix. Only the sample containing 2 wt% of MWCNTs exhibited a lower E due to the existence of the aforementioned cross-linked macromolecules. The form of the conversion function for all the studied samples obtained by fitting was the mechanism of nth-order auto-catalysis.     

Thermal degradation behavior of multi-walled carbon nanotubes/polyamide 6 composites

This paper focuses on the thermal degradation behavior of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites under air and nitrogen atmosphere using thermogravimetric analysis (TGA). The results show that the dispersion of amino-functionalized MWNTs (f-MWNTs) in PA6 is more homogeneous than purified MWNTs (p-MWNTs). The presence of MWNTs improves the thermal stability of PA6 under air obviously, but has little effect on the thermal degradation behavior of PA6 under nitrogen atmosphere. The activation energies for degradation under air, E_a, estimated by Kissinger method, are 153, 165 and 169 kJ/mol for neat PA6, p-MWNTs/PA6 and f-MWNTs/PA6 composites, respectively. The p-MWNTs/PA6 composites show two-step degradation not only under air but also under nitrogen atmosphere, however, neat PA6 and the f-MWNTs/PA6 composites exhibit two-step degradation only under air.     

Bismaleimides and bisnadimides derived from 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene and their polymerization to heat-resistant matrix resins

Six new structurally different bismaleimides or bisnadimides based on 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene (BADT) were synthesized and characterized by infrared (IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Chain-extension of several bismaleimides was accomplished by incorporating various imide, amide, and urea groups. The bismaleimide and bisnadimide prepared by reacting BADT with maleic or nadic anhydride, respectively, were soluble in various organic solvents. The monomers were thermally polymerized or by a Michael reaction with certain aromatic diamines. Curing behavior was investigated by differential thermal analysis (DTA). The thermal and thermo-oxidative stability of polymers was evaluated by dynamic thermogravimetric analysis (TGA) and isothermal gravimetric analysis (IGA). The polymers derived from bismaleimide of BADT as well as from the bismaleimides chain-extended by imide groups were stable up to 355–392°C in N₂ or air and afforded anaerobic char yield 66–74% at 800°C. The polymers obtained by curing the bismaleimide-diamine adducts showed a relatively lower thermal stability.     

Multi‐walled carbon nanotubes encapsulated with polyurethane and its nanocomposites

Poly(acryloyl chloride) (PACl) was employed to enhance the surface of multi‐walled carbon nanotubes (MWCNTs). MWCNTs were first acid treated to generate hydroxyl groups on the surface, which was reacted with PACl to obtain an encapsulation. The numerous acryloyl chloride groups on the out layer were esterified with a proper amount of ethylene glycol (EG). Subsequently, 4,4′‐methylenebis (phenylisocyanate) (MDI) and 1,4‐butanediol (BDO) were introduced into the system, and a polyurethane (PU) layer was formed in situ. The formation of PU layers on MWCNTs was confirmed by Fourier transform infrared spectrometer (FTIR) and X‐ray photoelectron spectroscope (XPS). The morphology of encapsulated MWCNTs was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). Thermo gravimetric analysis (TGA) showed the grafted polymer fraction was up to 90%. On introducing the modified MWCNTs into a PU matrix, an increase in tensile strength by 60.6% and improvement in modulus by 6.3% over neat PU was observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4857–4865, 2008     

Thermal degradation characteristics of a novel flame retardant coating using TG-IR technique

A novel phosphate acrylate monomer (TGMAP) has been synthesized by allowing phosphoric acid to react with glycidyl methacrylate. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The char yield was 36.3% at 600 °C. TG data indicate that the material undergoes degradation in three characteristic temperature stages, which can be attributed to the decomposition of the phosphate, thermal pyrolysis of aliphatic chains, and degradation of an unstable structure in char, respectively. The volatilized products formed on thermal degradation of TGMAP indicated that the volatilized products are CO, CO₂, carboxylic acid, acid anhydride, water, alkane, and aromatic compounds according to the temperature of onset formation.     

Viscoelasticity and thermal stability of polylactide composites with various functionalized carbon nanotubes

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T_5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (T_max). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.     

Thermal degradation and combustion of a novel UV curable coating containing phosphorus

A novel phosphorus monomer (BDEEP) has been synthesized by allowing phosphorus oxychloride to react with 2-hydroxyethyl acrylate (HEA) and 1,4-Butane diol. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The UV-curing behavior was investigated by FTIR. The combustibility was examined by microscale combustion colorimeter (MCC). The heat release rate (HRR) and heat release capacity (HRC) are 42.1 w/g and 44.0 J/g K, respectively. The thermal degradation was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The curve of TGA indicates that there are three characteristic degradation temperature stages for the cured film, which was further characterized by real time Fourier transform infrared (RTFTIR) measurement. It is proposed that the flame retardant action results from decomposition of phosphate to form poly(phosphoric acid), which catalyses the breakage of bonds adjacent to carbonyl groups to form the char, preventing the sample from burning further. The volatilized products formed on thermal degradation of BDEEP indicated that the volatilized products are CO, CO₂, water, alkane, carbonyl, phosphorus compounds and aromatic compounds according to the temperature of onset formation.     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

Superhydrophobic surface fabricated by modifying silica coated multiwalled carbon nanotubes composites

A superhydrophobic surface with maximum static water contact angle of 156° and sliding angle of 3.5° was fabricated by modifying the silica coated multiwalled carbon nanotube composites (SiO₂/MWCNTs) using a silane coupling agent vinyltriethoxysilane. The structures of SiO₂/MWCNTs and superhydrophobic surface were investigated by infrared spectrometer and transmission electron microscopy. The results indicated that silica had been successfully grafted onto MWCNTs and the SiO₂/MWCNTs had been chemical modified by vinyl triethoxy successfully. The morphology of our prepared superhydrophobic surface, investigated by scanning electron microscopy, showed a characteristic rough structure. The effects of pH value and exposure time on the stability of the superhydrophobic surface were also investigated. The superhydrophobic film shows reliable acid and alkali resistance and aging resistance, indicating that it will have a wide range of applications.     

Comparisons of MWCNTs and acidified process by HNO<Subscript>3</Subscript> on thermal stability by DSC and TG-FTIR

Multi-walled carbon nanotubes (MWCNTs) have remarkable properties. However, their thermal stability characteristics, which may represent potential hazards during the production or utilization stage, concern unsafe or unknown properties researches. Our aim was to analyze the thermokinetic parameters of different heating rates by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG), and then to compare thermal decomposition energy parameters under various conditions by well-known kinetic equations. MWCNTs were acidified via nitric acid (HNO₃) in various concentrations from 3 to 15 N and were characterized by means of Fourier transform infrared (FTIR) spectrometry. For original and modified MWCNTs, we further identified the thermal degradation characteristics of the functional group by TG-FTIR. Finally, we established an effective and prompt procedure for receiving information on thermal decomposition characteristics and reaction hazard of MWCNTs that could be applied as an inherently safer design during normal or upset operation.     

Effect of a triazine ring‐containing charring agent on fire retardancy and thermal degradation of intumescent flame retardant epoxy resins

A triazine ring‐containing charring agent (PEPATA) was synthesized via the reaction between 2,6,7‐trioxa‐l‐phosphabicyclo‐[2.2.2]octane‐4‐methanol (PEPA) and cyanuric chloride. It was applied into intumescent flame retardant epoxy resins (IFR‐EP) as a charring agent. The effect of PEPATA on fire retardancy and thermal degradation behavior of IFR‐EP system was investigated by limited oxygen index (LOI), UL‐94 test, microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA) and thermogravimetric analysis/infrared spectrometry (TG‐IR). The glass transition temperatures (T_g) of IFR‐EP systems were studied by dynamic mechanical analysis (DMA). The LOI values increased from 21.5 for neat epoxy resins (EPs) to 34.0 for IFR‐EP, demonstrating improved flame retardancy. The TGA curves showed that the amount of residue of IFR‐EP system was largely increased compared to that of neat EP at 700 °C. The new IFR‐EP system could apparently reduce the amount of decomposing products at higher temperatures and promotes the formation of carbonaceous charred layers that slowed down the degradation. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Understanding of thermal/thermo-oxidative degradation kinetics of polythiophene nanoparticles

The polythiophene nanoparticles (nano-PT) were prepared with average diameter of 20–35 nm. The nanostructurals of polythiophene were confirmed by TEM and SEM analyzes. The kinetics of the thermal degradation and thermal oxidative degradation of nano-PT were investigated by thermogravimetric analysis. Kissinger method, Flynn–Wall–Ozawa method, and advanced isoconversional method have been used to determine the activation energies of nano-PT degradation. The results showed that the thermal stability of nano-PT in pure N₂ is higher than that in air atmosphere. The analyzes of the solid-state processes mechanism of nano-PT by Criado et al. method showed: the thermal degradation process of nano-PT goes to a mechanism involving second-order (F ₂ mechanism); otherwise, the thermo-oxidative degradation process of nano-PT is corresponding to a phase boundary controlled reaction mechanism (R ₂ mechanism).     

Crystallization and melting behavior of PP/CaCO3 nanocomposites during thermo-oxidative degradation

The crystallization and melting behavior of PP/CaCO₃ nanocomposites during thermo-oxidative degradation process were studied using differential scanning calorimetry and X-ray diffraction. The results indicated that addition of nano-CaCO₃ and compatibilizer significantly reduced the thermo-oxidative stability of PP. Before degradation, thermal aging resulted in an increase in the melting temperature and crystallinity of PP due to the annealing crystallization. Thermo-oxidative degradation decreased the melting temperature and increased melting range, and caused an increase in crystallinity of PP due to the chemi-crystallization. The investigation also indicated that the influence of degradation on the small crystals were much more significant than that on the large ones.     

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.     

Effect of MWCNTs Doping on the Morphology,Structure and Properties of Chitosan Beads

A series of chitosan (CS)/multi-walled carbon nanotubes (MWCNTs) composite hydrogel beads with different MWCNTs contents are prepared via a solution blending method. The effects of MWCNTs on the morphology, structure and properties of chitosan beads have been investigated. Digital pictures show that the composite beads obtained are of good morphological characteristics, and the SEM micrographs indicate that the addition of MWCNTs into CS beads made the surface of the CS/MWCNTs hydrogel beads contain much larger wrinkles. Fourier transform infrared spectra (FTIR) show that the main chain of CS bead is not changed, but there are some electrostatic interactions between CS and MWCNTs, which lead to very significant changes in the crystallization behavior of CS and MWCNTs. The thermal stability of CS/MWCNTs composites at high temperatures is increased with the existence of MWCNTs, indicating a possible electrostatic interaction between MWCNTs and CS lattices to limit the motivation of CS. The adsorption capacity of CS beads doped with a lower percentage of MWCNTs (0.02 wt%) for acid fuchsin is 112.76 mg/g, higher than that of pure CS beads (35.62 mg/g).