Thermal degradation kinetics of PET/SWCNTs nanocomposites prepared by the in situ polymerization

The decomposition and thermal behavior of poly(ethylene terephthalate) (PET)/carbon nanotubes (CNTs) nanocomposites were studied using thermogravimetric (TG) analysis in air atmosphere. A series of PET/single-walled CNTs (SWCNTs) materials of varying nanoparticles concentration were prepared using the in situ polymerization technique. Transmission electron microscopy and scanning electron microscopy micrographs verified that the dispersion of the SWCNTs in the PET matrix was homogeneous, while some relatively small aggregates co-existed at higher filler concentration. Two-stage decomposition was observed in the experiments. During first stage, strong chemical bonds are broken, i.e., aliphatic bonds and benzyl ring containing molecules decompose into small molecules in the gaseous phase. During second stage, when temperature is higher, the remaining nanotubes along with the residues of the first stage are burned. Kissinger and Coats–Redfern (5, 10, 20, 50 K min^?1) methods were applied to TG data to obtain kinetic parameters (activation energy, Arrhenius constant at 600 K and A factor) and Criado method to kinetics model analysis. In this kinetic model, energy activation is increasing with the increase of nanotubes concentration.     

Effect of acid-treated multi-walled carbon nanotubes on thermo-oxidative stability and degradation behavior of silicone rubber

The effect of acid-treated multi-walled carbon nanotubes (MWCNTs) on thermo-oxidative stability and degradation behavior of silicone rubber (SR) was evaluated. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric (TG) analysis were performed to characterize the surface states of MWCNTs samples. The results demonstrated that after acid treatment the nanodefects and surface oxygen-containing groups (mainly hydroxyl and carboxyl groups) were formed and the number of them was gradually increased by increasing the treatment time. Then these MWCNTs were embedded into SR matrix. Furthermore, the thermo-oxidative stability and degradation behavior of MWCNTs/SR composites were studied using thermogravimetric/infrared spectrometry (TG-IR). Thermo-oxidative stability test in air revealed that the degradation of SR, at relatively low temperature, was mainly due to the oxidation of Si-CH₃ side groups and the generation of free radicals. This behavior was hindered by the MWCNTs’ surface nanodefects and hydroxyl groups, as proved by TG-IR study which revealed that the amount of carbonyl compounds was reduced more than 60%, compared with that of neat SR. Therefore, acid treatment led a better thermo-oxidative stability of MWCNTs/SR. For 4hAT-MWCNTs/SR, with maximum hydroxyl groups on MWCNTs surface, the T_i (defined as the temperature for 5% mass loss) of it is increased by 34.8 °C compared to that of neat SR, and even increased by 18.5 °C compared with that of raw-MWCNTs/SR.     

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.     

Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.     

Isothermal crystallization kinetics and melting behaviour of PET/ATO nanocomposites prepared by in situ polymerization

Neat poly(ethylene terephthalate) (PET) and PET/antimony doped tin oxide (ATO) nanocomposites were prepared by in situ polymerization. The study of the isothermal crystallization behaviors of neat PET and PET/ATO nanocomposites was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For neat PET and PET/ATO nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing ATO content. These suggested that the crystallization types related to the values of n in the Avrami theory could not be suitable for the crystallization of PET and its nanocomposites. The change of the n values indicated that the addition of ATO resulted in the increase of the crystallizing growth points. That is a heterogeneous nucleating effect of ATO on crystallization of PET. In the DSC scan after isothermal crystallization process, multiple melting behavior was found. And the multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae produced during different crystallization processes. The equilibrium melting temperature of PET in the nanocomposites increased with increasing the ATO content. Surface free energy of PET chain folding for crystallization of PET/ATO nanocomposites was lower than that of neat PET, confirming the heterogeneous nucleation effect of ATO.     

Synthesis and physicochemical properties of calcium hydroxylapatite/multi-walled carbon nanotubes nanocomposites

Calcium hydroxylapatite/carbon nanotubes (HA/CNT) composites with various CNT contents have been synthesized by coprecipitation from aqueous solutions in the CaCl₂-(NH₄)₂HPO₄-NH₃-CNT-H₂O system (25°C) under conditions modeling the interaction between HA (Ca₁₀(PO₄)₆(OH)₂), which is an inorganic component of osseous tissue, and multi-walled CNTs. The empirical formula of the composites is Ca₁₀(PO₄)₆(OH)₂ · nCNT · 6H₂O, where n = 0.2?C5.0. The synthesis products have been identified by the solubility (Tananaev??s residual concentration) method, pH measurements, chemical analysis, X-ray diffraction, IR spectroscopy, electron spectroscopy for chemical analysis, and scanning and transmission electron microscopy. The effect of the CNT concentration in aqueous solution on the composition of the HA/CNT composites and on the crystallographic and morphological characteristics of HA nanocrystals in HA/CNT has been investigated.     

A comprehensive assessment on degradation of multi-walled carbon nanotube-reinforced EMA nanocomposites

Thermal degradation kinetics of MWNT-reinforced EMA-based nanocomposites having different methyl acrylate (MA) contents (by % mass) ranging from 9 to 30% have been monitored. Kissinger and Flynn?CWall?COzawa methods for evaluating non-isothermal degradation of polymers have been examined. Overall, the thermal stabilities of the nanocomposites are the function of amount of MWNTs loading and their state of dispersion that depends on the MA content of respective EMAs. Composite samples exhibit higher activation energy (E _a) than the neat EMAs but the E _as of the composites diminish with increased MA contents of the matrices. TG-Mass spectrometry has been used to identify the volatile products resulting from thermal degradation of composites, and a promising mechanism has been proposed over different range of temperatures of degradation. It is proposed that the side-group scission of methoxycarbonyl group initiates thermal decomposition following combination of chain end and random chain scission reactions, ensuing pseudo second-order kinetics.     

Thermal oxidative degradation kinetics of flame-retarded polypropylene with intumescent flame-retardant master batches in situ prepared in twin-screw extruder

The thermal oxidative degradation kinetics of pure PP and the flame-retarded (FR) PP materials with intumescent flame-retardant (IFR) master batches in situ prepared in twin-screw extruder were investigated using Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern method. The results showed that the activation energy order of PP and FR PP samples with different blowing agent/char former ratios obtained by Kissinger method agrees well with that obtained by Coats-Redfern one, which well illustrates the relationship between the composition of IFRs and their flame-retardancy, i.e. FR material with richer carbonization agent has higher activation energy for thermal oxidative degradation, hence leading to a better flame-retardancy. For Flynn-Wall-Ozawa method, due to its adoption of Doyle approximation, the obtained activation energy and its order of samples are very different from those of both Kissinger and Coats-Redfern methods. Criado method was finally used to determine the degradation reaction mechanism of various samples.     

Thermal degradation of organophosphorus flame-retardant poly(methyl methacrylate) nanocomposites containing nanoclay and carbon nanotubes

Filler nanoparticles pave the way for the development of novel halogen-free flame-retardant polymers. The aim of this study was to investigate the thermal degradability, and in particular, the thermal degradation mechanism of organophosphorus flame-retardant poly(methyl methacrylate) (PMMA) nanocomposites containing nanoclay (NC) and multi-walled carbon nanotubes (CNT). For this purpose, thermogravimetry and direct pyrolysis mass spectrometry analysis were utilized. The onset of degradation was delayed through increased maximum degradation temperature and suppressed mass loss corresponding to initial degradation stage with carbon nanotubes and nanoclays, respectively. Possibility of reactions of melamine and/or melamine derivatives and interactions between carbonyl groups of PMMA and phosphinic acid leading to thermally more stable products was increased owing to the barrier effect of filler nanoparticles. In the presence of NC better flame retarding characteristics was detected as anhydride formation, leading to charring being more effective.     

Effect of multi-walled carbon nanotubes on non-isothermal crystallization kinetics of polyamide 6

The non-isothermal crystallization behaviors of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites were investigated by differential scanning calorimetry (DSC). Three methods, namely, Avrami, Ozawa and Mo, were carried out to analyze the non-isothermal crystallization data. The results showed that the MWNTs in PA6 acted as effective nucleation agents. However the crystallization rate of composites obtained was lower than that of the neat PA6. It is indicated that the presence of MWNTs influenced the mechanism of nucleation and the growth of PA6 crystallites.     

Characterization of electrodes modified with nanocomposites of cobalt tetraaminophenoxyphthalocyanine,reduced graphene and multi-walled carbon nanotubes

Abstract

Glassy carbon electrodes or plates were modified with nanocomposites consisting of cobalt tetraaminophenoxyphthalocyanine (CoTAPhPc), reduced graphene oxide nanosheets (rGONs) and multi-walled carbon nanotubes (MWCNTs). The modified electrodes were characterized using cyclic voltammetry, scanning electrochemical microscopy (SECM) and time-of-flight-secondary ion mass spectrometer (TOF-SIMS). The electrocatalytic activity of the modified electrode was tested for detection of L-cysteine. The presence of CoTAPhPc on sequential layers of MWCNT and rGONs resulted in improved detection currents compared to CoTAPhPc alone or when MWCNT/rGONs are mixed in CoTAPhPc–MWCNT/rGONs (mix)–glassy carbon electrode (GCE). CoTAPhPc–MWCNT–GCE (without rGONS) showed higher sensitivity toward l-cysteine as compared to the probes incorporating rGONs with a catalytic rate constant of 4.62?×?10⁴ M^?1s^?1 and a detection limit of 30?nM. The presence of rGONs improved the stability of the electrode.     

Influence of amine-grafted multi-walled carbon nanotubes on physical and rheological properties of PMMA-based nanocomposites

In this work, poly(methyl methacrylate) (PMMA) was grafted onto amine treated multi-walled carbon nanotubes (NH-MWNTs) and the physical and rheological properties of the NH-MWNTs–g-PMMA nanocomposites were investigated. The graft reaction of NH-MWNTs and the PMMA matrix was confirmed from the change of the N_1S peaks, including those of amine oxygen and amide oxygen, by X-ray photoelectron spectroscopy (XPS). The thermal and mechanical properties of the NH-MWNT–g-PMMA nanocomposites were enhanced by the graft reaction between NH-MWNTs and PMMA matrix. In addition, the viscosity of the nanocomposites was increased with the addition of NH-MWNTs. Storage (G′) and loss modulus (G″) were significantly increased by increase in the NH-MWNT content compared to acid-treated MWNTs/PMMA nanocomposites. This increase was attributed to the strong interaction by the grafting reaction between NH-MWNTs and the PMMA matrix.     

A facile approach to synthesize poly(4-vinylpyridine)/multi-walled carbon nanotubes nanocomposites: highly water-dispersible carbon nanotubes decorated with gold nanoparticles

A facile approach to attach high-density and uniform gold nanoparticles on individual multi-walled carbon nanotubes (MWNTs) is achieved. By simple grinding, water-soluble linear polymers poly(4-vinylpyridine) (PVP)-wrapped around nanotubes and thus rendered them reversibly soluble in water, ethanol, and DMF. Individual tubes are clearly observed after PVP-wrapped nanotubes were spin-coated onto a silicon wafer. Subsequently, Au nanoparticles were densely decorated on the individual MWNTs by in situ reduction of HAuCl₄ in the homogeneous aqueous solution of MWNTs–PVP to form stable water-dispersible Au/PVP/MWNTs hybrid. Morphology of Au nanoparticles was determined by scanning electron microscope and atomic force microscope. The diameter of the Au nanoparticles is controlled in the range of 3.5 to 13.5 nm. The presence of gold nanoparticles with decreased particle size was also detected by UV–Vis spectroscopy.     

Asymmetric end-functionalization of multi-walled carbon nanotubes

Asymmetric end-functionalization of carbon nanotubes was achieved by sequentially floating a substrate-free aligned carbon nanotube film on two different photoreactive solutions with only one side of the nanotube film being contacted with the photoreactive solution and exposed to UV light each time. The resultant nanotubes with different chemical reagents attached onto their opposite tube-ends should be very useful for site-selective self-assembling of carbon nanotubes into many novel functional structures for various potential applications.     

Thermokinetics simulation for multi-walled carbon nanotubes with sodium alginate by advanced kinetics and technology solutions

To accomplish an effective analysis of adsorption, the strong acid dye from aqueous solution of sodium alginate (SA) and multi-walled carbon nanotubes (MWCNTs) composite gel beads were used as important parameters. Differential scanning calorimetry (DSC) was used to measure the heat of breakdown reaction. The experimental conditions were set at 0.5, 1, 2, 4, and 8 °C min^?1, and the temperature range was 30–300 °C. The heating rates and the temperature range were set as follows: Four kinds of proportion in this experiment contained 2 SA % w/v (SA), 0.03, 0.09, 0.18, 0.36 % w/v (MWCNTs), and 10 % w/v calcium chloride, respectively. Four samples, 5, 6, 7, 8, and 9 mg, were used to detect the experimental data. It contributed to understanding the reaction for the distinctive MWCNTs. With the thermokinetic data by isoconversional approach obtained from advanced kinetics and technology solutions (AKTS), the related thermal safety information can be obtained from the thermal reaction of MWCNTs. Valuable parameters, such as activation energy (E _a) and heat of decomposition, can be applied in operation, including adsorption and desorption processes. After DSC tests, and under the four compositions of SA/MWCNTs, at different heating rates of 0.5, 1, 2, 4, and 8 °C min^?1, primarily we found that when the heating rate was increased, exothermic onset temperature would increase gradually. After analyzing E _a value by isoconversional kinetics, we learned that in four different adsorption compositions, SA/MWCNTs_0.03 (161.20 kJ mol^?1) was the minimum. Among them, the highest value was SA/MWCNTs_0.18 (220.48 kJ mol^?1). However, in this study, for SA/MWCNTs compositions we found that E _a value will drop in the final material SA/MWCNTs_0.36. Accordingly, if the ratio of SA and calcium chloride was fixed, then different compositions of the MWCNTs would affect adsorption efficiency of SA/MWCNTs and E _a variation.     

Thermal decomposition kinetics of multiwalled carbon nanotube/polypropylene nanocomposites

In this study, non-isothermal crystallization of neat high density polyethylene (HDPE) and HDPE/titanium dioxide (TiO₂) composite was studied using differential scanning calorimetry. Non-isothermal kinetic parameters were determined by Jeziorny approach and Mo’s method. Polarized optical microscopy and wide angle X-ray diffraction were applied to observe the crystal morphology and investigate the crystal structure, respectively. It was found TiO₂ particles could act as nucleating agent during the crystallization process and accelerate the crystallization rate. The Avrami index indicated nucleating type and growth of spherulite of HDPE was relatively simple. The result of activation energy indicated it was more and more difficult for the polymer chains to crystallize into the crystal lattice as the crystallization progressed. HDPE/TiO₂ composites exhibited lower ΔE values, suggesting TiO₂ particle could make the crystallization of HDPE easier. HDPE/TiO₂ composites had much smaller spherulite size than that of neat HDPE. HDPE formed more perfect crystal when TiO₂ particles were added into its matrix without changing the original crystal structure of HDPE.     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Covalent decoration of multi-walled carbon nanotubes with silica nanoparticles

We describe a novel tunable approach for the synthesis of carbon nanotube-silica nanobead composites. The control of nanotube morphology and bead size coupled with the versatility of silica chemistry makes these structures an excellent platform for the development of biosensors, or for optical, magnetic and catalytic applications.     

Impact behaviour of polypropylene filled with multi-walled carbon nanotubes

Multi-walled carbon nanotubes/polypropylene composites were compounded using a twin-screw extruder. Here, nanotubes with different lengths, i.e. 1-2 μm and 5-15 μm, respectively, were applied at a constant volume content of 1%. Notched Charpy impact tests showed that toughening effects of nanotubes depended highly on testing temperatures. The impact resistance was notably enhanced at a temperature above the glass transition temperature of matrix. Longer nanotubes performed more effective in toughening compared to the shorter ones. The increment of impact resistance of nanotube-filled polypropylene was considered due to enhanced load-carrying capability and much-increased deformation of matrix. SEM fractography further revealed the toughening mechanisms in a micro-scale. The impact energy was improved via nanotube breakage and pullout, which likely led to a series of energy consuming actions. In addition, the smaller spherulite size induced by nanotubes would be favourable to the impact resistance partially.