Good Dispersion State Research Articles

High Mechanical and Thermal Properties of Epoxy Composites with Liquid Crystalline Polyurethane Modified Graphene.

Graphene nanosheets (GNs) often result in incompatibility with the hydrophobic polymer matrix, and the tendency to form aggregates during processing. Herein, liquid crystalline polyurethane modified GNs (GPLP) were obtained by π–π stacking interactions between GNs and perylene bisimide derivatives, and then in-situ polymerization of liquid-crystalline polyurethane. Spectroscopic studies, elemental analysis, and thermal properties confirmed the successful π–π stacking and the integrated structure of GPLP. The good dispersion state of GPLP in the epoxy matrix (EP), and the strong interactions between GPLP and EP, lead to the significant improvement of the thermal and mechanical performance of the GPLP/EP composites. The impact strength, Young’s modulus, tensile strength, and toughness of the GPLP/EP composites with 1.47 wt % GNs reached the highest values of 54.31 kJ/m2, 530.8 MPa, 112.33 MPa and 863 J/m3, which significantly increased by 210%, 57%, 143%, and 122% compared to that of neat epoxy, respectively. As well, the glass transition temperature increased by a notable 33 °C. It is hoped that this work can be used to exploit more efficient methods to overcome the poor adhesion between GNs and polymers.

Dual modification of graphene by polymeric flame retardant and Ni(OH)2 nanosheets for improving flame retardancy of polypropylene

To improve its dispersion and flame retardant efficiency, graphene oxide (GO) is dually modified with polymeric flame retardant and the nanomaterial with catalytic carbonation ability. Via the reactions between oxygen functional groups in GO and PCl groups in hexachlorocyclotriphosphazene, phosphazene-based flame retardant is grafted to GO. Due to the strong affinity of Ni2+ with NH2 groups in this phosphazene flame retardant, the decoration of Ni(OH)2 nanosheets on the graphene is facilitated. Transmission electron microscopy images confirm good dispersion and exfoliation state of graphene in polypropylene (PP) matrix. The incorporation of functionalized graphene oxide (FGO) results in the reduction of peak heat release rate, total heat release and smoke release of PP during the combustion. Flame mechanism of FGO is concluded according to the results of thermal decomposition and char analysis. This work provides a novel modification strategy for enhancing the dispersion and flame retardant efficiency of graphene.

The effect of ultraviolet radiation on the mild photo-responsive surface functionalization of carbon nanotubes

ABSTRACTThe effect of ultraviolet radiation on the mild photo-responsive surface functionalization of carbon nanotubes (MWCNTs) was investigated. Functional MWCNTs were prepared via standard physisorption, followed by nitrene addition using azido compounds upon ultraviolet activation. The results imply that the organic molecules involved adsorption onto the side wall of MWCNTs, then MWCNTs reacted with azido groups in organic molecules. After immersed in ethanol for 50 days, the as-obtained MWCNTs with 700 seconds ultraviolet activation remain in the good dispersion state, which can bear comparison with that of MWCNTs oxidized with mixture acids. Therefore, this approach is a more attractive than oxidation method to functionalize MWCNTs and can be used as an effective and replaceable first step for the following functionalization.

Preparation of polypropylene nanocomposites by melt‐mixing: Comparison between three organoclays

ABSTRACTPolypropylene (PP)‐based nanocomposites reinforced with three different organoclays (Dellite© 67 G, Cloisite© 20, and Cloisite© 30B) were prepared via melt‐mixing in an internal mixer. The three organoclays differ essentially via their organic modifier and interlamellar distance. The nanocomposites microstructure was characterized at different scales through scanning electron microscopy (SEM) observations, X‐ray diffractometry, and rheological measurements. The influence of processing parameters such as rotor speed and mixing time was quantified. The results show that Dellite© 67 G and Cloisite© 20 present a good dispersion state, with an intercalation of the tactoids by the polymer chains and a good level of exfoliation. In contrast, whatever the processing conditions, Cloisite© 30B was not dispersed correctly in the matrix, showing neither intercalation nor exfoliation, even in the presence of compatibilizer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45053.

Halloysite Nanotubes Noncovalently Functionalised with SDS Anionic Surfactant and PS-b-P4VP Block Copolymer for Their Effective Dispersion in Polystyrene as UV-Blocking Nanocomposite Films

A simple and versatile method is reported for the noncovalent functionalisation of natural and “green” halloysite nanotubes (HNTs) allowing their effective dispersion in a polystyrene (PS) thermoplastic matrix via solvent mixing. Initially, HNTs (pristine HNTs) were modified with physically adsorbed surfactant molecules of sodium dodecyl sulphate (SDS) and PS-b-P4VP [P4VP: poly(4-vinylpyridine)] block copolymer (BCP). Hereafter, SDS and BCP modified HNTs will be indicated as SDS-m-HNT and BCP-m-HNT. Nanocomposite films with 1, 2, and 5 wt.% HNT loadings were prepared, abbreviated as PS-SDS-m-HNT1, PS-SDS-m-HNT2, and PS-SDS-m-HNT5 and PS-BCP-m-HNT1, PS-BCP-m-HNT2, and PS-BCP-m-HNT5 (where 1, 2, and 5 correspond to the wt.% of HNTs). All nanocomposites depicted improved thermal degradation compared to the neat PS as revealed by thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) confirmed the good dispersion state of HNTs and the importance of modification by SDS and BCP. X-ray diffraction (XRD) studies showed the characteristic interlayer spacing between the two silicate layers of pristine and modified HNTs. The PS/HNT nanocomposite films exhibited excellent ultraviolent-visible (UV-vis) absorbance properties and their potential application as UV-filters could be envisaged.

Synthesis and characterization of the nano alumina-filled tetraglycidyl-4, 4′-diaminodiphenylmethane epoxy resin

In this study, the in situ incorporation of the inorganic alumina nanoparticles into the reactants of tetraglycidyl-4, 4′-diaminodiphenylmethane (TGDDM) epoxy resin represented an efficient way for the preparation of alumina/TGDDM nanocomposite. The surface modification of the alumina nanoparticles was carried out using two individual silane coupling agents, namely, aminopropyltriethoxysilane (APS) and glycidoxypropyltrimethoxysilane (GPS). The degree of silane grafting was evaluated for both coupling agents using FTIR spectroscopy and thermogravimetric analysis. The epoxy equivalent weight (EEW) of the epoxy resin in addition to the weight percentage of the lost nanoparticles during TGDDM polymerization was used as measurements of the polymerization yield. The neat nano alumina has more adverse effect on the epoxy EEW value (171 g/mol) than both silane-modified nano alumina (143–157 g/mol, depending on the reaction conditions). The degree of nano alumina dispersion in the epoxy matrix was investigated using SEM micrographs. The longer and more deflected crack pathways on the fractured surface of the alumina/TGDDM nanocomposites may be attributed to a relatively good degree of dispersion of the silane-modified alumina nanoparticles in the epoxy matrix. Compared to neat alumina, the better dispersion of the silane-modified alumina nanoparticles may be related to the improved interfacial interactions between the oxiran or amine groups available on the silane-modified alumina nanoparticles and the TGDDM epoxy functional groups. Besides, the higher exothermic heat of cure (i.e., 30–53 %) as evidenced in differential scanning calorimetry may be due to a rather good state of dispersion of silane-modified alumina nanoparticles.

Conductive PVDF-HFP/CNT composites for strain sensing

A strain sensor based on the composites of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) filled by multi-walled carbon nanotube (MWNT) was prepared using a proposed fabrication process. Three kinds of MWNT loadings, i.e., 1.0[Formula: see text]wt.%, 2.0[Formula: see text]wt.% and 3.0[Formula: see text]wt.% were employed. Due to good dispersion state of MWNT in PVDF-HFP matrix, which was characterized by scanning electron microscope (SEM), this sensor was found to be of high sensitivity and stable performance. The sensor’s piezoresistivity varied in a weak nonlinear pattern, which was probably caused by the tunneling effect among neighboring MWNTs. The gauge factor of the sensor of 1.0[Formula: see text]wt.% MWNT loading was identified to be the highest, i.e., 33. This sensor gauge factor decreased gradually with the increase of addition amount of MWNT, which was 5 for the sensor of 3.0[Formula: see text]wt.% MWNT loading. This gauge factor was still higher than that of conventional metal-foil strain sensors. The electrical conductivity of PVDF-HFP/MWNT composites was also studied. It was found that with the increase of the addition amount of MWNT, the electrical conductivity of the PVDF-HFP/MWNT composites varied in a perfect percolation pattern with a very low percolation threshold, i.e., 0.77 vol.%, further indicating the very good dispersion of MWNT in the PVDF-HFP matrix.

Dispersion Characteristics of Multi-Walled Carbon Nanotubes with Gallic Acid.

Dispersions of multi-walled carbon nanotubes (MW-CNTs) assisted by non-covalent surface modification and covalent surface modification were prepared using different concentration of gallic acid aqueous solution. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the dispersion states and effect of MWNTs. FTIR results demonstrate that concentration of gallic acid has great effect on the surface modification of multi-walled carbon nanotubes. With the content of gallic acid increasing, modification effect were firstly increased and then decreased in that the optimal concentration is about 10 μg/ml as it is its solubility in water. SEM and TEM results also show that gallic acid not only can ensure the integrity of the MW-CNTs, but also can purify it. These results confirmed achievement of a good dispersion state and effect of MW-CNTs with gallic acid. The dispersion mechanism of non-covalent surface modification and covalent surface modification was analyzed.

Effect of synthesis catalyst on structure of nitrogen-doped carbon nanotubes and electrical conductivity and electromagnetic interference shielding of their polymeric nanocomposites

Different catalysts including Co, Fe, and Ni were used to synthesize nitrogen-doped carbon nanotubes (N-CNTs) by chemical vapor deposition technique. Synthesized N-CNTs were melt mixed with a polyvinylidene fluoride (PVDF) matrix using a small scale mixer at different concentrations ranging from 0.3 to 3.5 wt%, and then compression molded. The characterization techniques revealed significant differences in the synthesis yield and the morphological and electrical properties of both N-CNTs and nanocomposites depending on the catalyst type. Whereas Co and Fe resulted in yields comparable to industrial multiwalled CNTs, Ni was much less effective. The N-CNT aspect ratio was the highest for Co catalyst, followed by Ni and Fe, whereas nitrogen content was the highest for Ni. Raman spectroscopy revealed lowest defect number and highest N-CNT crystallinity for Fe catalyst. Characterization of N-CNT/PVDF nanocomposites showed better dispersion for N-CNTs based on Co and Fe as compared to Ni, and the following order of electrical conductivity and electromagnetic interference shielding (from high to low): Co > Fe > Ni. The superior electrical properties of (N-CNT)Co nanocomposites were ascribed to a combination of high synthesis yield, high aspect ratio, low nitrogen content and high crystallinity of N-CNTs combined with a good state of N-CNT dispersion.

Influence and mechanism of mechanical grinding on disaggregation of silica white particles in aqueous medium

The method of mechanical grinding in aquatic medium is applied in this paper to find out the influence of mechanical treatment on the disaggregation and dispersion of silica white. The results show that the size of silica white aggregates can be greatly reduced, and the particles also can keep a good dispersion state when dispersant is added. The median diameter (D50) of the silica white particles reduce to 3·80 μm, and D90 reduced to 7·50 μm. The results of SEM observation are consistent with the particle-size analysis results. The calculations show that the strip effect energy work on silica white particles from mill balls is 1·78 × 10–9 J. This number is greater than the effect energy needed in disaggregation which is calculated to be 2·33 × 10−10 J. The stripping of grinding ball could be an important mechanism on the disaggregation of silica white particles.

Wettability Investigation of UV/O3 and Acid Functionalized MWCNT and MWCNT/PMMA Nanocomposites by Contact Angle Measurement

The dispersion state of individual MWCNT in the polymer matrix influences the mechanical, thermal, and electrical properties of the resulting composite. One method of obtaining a good dispersion state of MWCNT in a polymer matrix is to functionalize the surface of MWCNT using various treatments to enhance the surface energy and increase the dispersibility of MWCNT. In this study, wettability and surface energy of UV/O3 and acid‐treated multiwall carbon nanotubes (MWCNTs) and its polymethyl methacrylate (PMMA) polymer nanocomposites were measured using contact angle analysis in various solvent media. Contact angle analysis was based on ethylene glycol‐water‐glycerol probe liquid set and data was further fitted into geometric mean (Fowkes), van Oss‐Chaudhury‐Good (GvOC), and Chang‐Qing‐Chen (CQC) models to determine both nonpolar and acid base surface energy components. Analysis was conducted on MWCNT thin films subjected to different levels of UV/O3 and acid treatments as well as their resulting MWCNT/PMMA nanocomposites. Contact angle analysis of thin films and nanocomposites revealed that the total surface energy of all samples was well fitted with each other. In addition, CQC model was able to determine the surface nature and polarity of MWCNT and its nanocomposites. Results indicated that the wettability changes in the thin film and its nanocomposites are due to the change in surface chemistry. Finally, electrical properties of nanocomposites were measured to investigate the effect of surface functionality (acid or basic) on the MWCNT surfaces.

손상감지용 CNT 나노복합재료의 손상 감지능 및 보강효과 연구

ABSTRACT: Nancomposites manufacture has been developed rapidly, because of reinforcing effects of CNT in termsof mechanical, electrical and thermal properties. In this study, 10 wt% CNT paste was fabricated with good dispersionstate and easy processability. Damage sensing and reinforcing effect of CNT paste were investigated in nanocomposites.10 wt% CNT paste exhibited better tensile and flexural properties than those of general 1 wt% CNT nanocomposites.To observe the healing effect of CNT paste, a crack was made artificially with 30wt% CF30wt%/PP composites, andthe CNT paste was filled inside the crack. The damage sensing of CNT paste in CF30wt%/PP composites wasinvestigated by electrical resistance measurement and mechanical tests. CNT paste exhibited good reinforcing effect inmechanical properties of CF30wt%/PP composites, and this reinforcing effect was getting better with larger cracks.The reason was because CNT paste had good interfacial adhesion with CF30wt%/PP composites to resist crackpropagation. In electrical resistance measurement, there was a jump in electrical resistance signal at the adhesioninterface. The jumping signal could be used to predict fracture of CF/PP composites. CNT nanocomposites fordamage sensing had crack reducing effect and dama ge detection using electrical resistance method. 초록

Combination of Plasma Functionalization and Phase Inversion Process Techniques for Efficient Dispersion of MWCNTs in Polyamide 6: Assessment through Morphological, Electrical, Rheological and Thermal Properties

Different contents of multiwalled carbon nanotube (MWCNTs) functionalized by He-dielectric barrier discharge (DBD) plasma followed by an exposure to NH3 were incorporated into PA6 matrix via a phase inversion based solution method. Optical and electron microscopic results were indicative of the excellent dispersion state of the MWCNTs. The differential scanning calorimetry and thermogravimetric analysis measurements revealed that even addition of a slight amount of the MWCNTs significantly increased the thermal stability and crystallization temperature. Moreover, the low electrical percolation threshold of the PA 6/functionalized MWCNTs nanocomposites was another confirmation for achieving a good dispersion state of MWCNTs using this approach.

Tuning the interface of graphene platelets/epoxy composites by the covalent grafting of polybenzimidazole

This paper reported a facile one-pot strategy for covalent functionalization of graphene platelets (GnPs) by polybenzimidazole, and the fabrication of their composites with epoxy resin. The functionalized GnPs (fGnPs) was prepared by subsequently acylation reaction between dicarboxylic acid and GnPs, and in-situ polymerization of polybenzimidazole. Spectroscopic studies and elemental analysis confirmed the successful grafting of polymer chains and the highly integrated structure of fGnPs, while TEM images demonstrated the well exfoliated state of fGnPs in organic solvent. As a consequence of the good dispersion state of fGnPs in matrix, and the covalent interactions between fGnPs and epoxy, the fGnPs/Epoxy composites showed significantly improved Young's modulus, tensile strength and fracture toughness as compared to neat epoxy or unmodified GnPs reinforced epoxy. The improved dynamic mechanical properties and thermal stabilities of composites filled with fGnPs were also demonstrated.

The effect of tungsten disulfide nanotubes on the properties of silicone adhesives

The effects of tungsten disulfide inorganic nanotubes (INT-WS2) on the bulk and adhesion properties of silicone nanocomposites were investigated. The nanocomposites were prepared using solvent mixing which enhanced the distribution and dispersion of the nanotubes in the high viscosity silicone matrix. The quality of dispersion was evaluated using scanning electron microscopy (SEM) which indicated good dispersion state. It was found that the optimal concentration of INT-WS2 in the nanocomposites was 2wt%, exhibiting 33% higher storage modulus, 6% improvement in tensile strength, 17% reduction in the coefficient of linear thermal expansion and 13% improvement in shear strength, compared to the neat polymer. Above this threshold value the nanocomposites adhesion properties were reduced.

The effect of multiwall carbon nanotubes on the properties of room temperature-vulcanized silicone adhesives

The effects of surface-functionalized and pristine multiwall carbon nanotubes (MWCNT) on the bulk and adhesion properties of silicone nanocomposites were investigated. The MWCNTs surface functionalization was carried out by silanization of methacryloxy or vinyl-based silanes. The nanocomposites were prepared using solvent mixing which enhanced distribution and dispersion of the MWCNTs in the high-viscosity silicone matrix. The quality of dispersion was evaluated using scanning electron microscopy (SEM) indicating good dispersion state. It was found that the optimal concentration of both treated and untreated MWCNTs in the nanocomposites was 1 wt.%. Above this threshold value, the nanocomposites properties were reduced. Furthermore, the silane treatment of the MWCNTs was proven to be an effective process that resulted in a significant increase in the nanocomposites properties compared to the neat polymer, leading to higher storage modulus simultaneously with up to 27% improvement in the tensile strength and elongation, 20–30% reduction in the thermal expansion coefficient, 220–300% enhancement in crystallinity (enthalpy of fusion), and up to 56% improvement in the lap shear strength. SEM analysis indicated that significant changes in the fracture morphologies occurred due to higher energy absorption in the case of silane-treated MWCNTs. It was concluded that incorporation of silane-treated MWCNTs is an effective route to reinforce and increase the toughness of silicone-based adhesives.

Preparation of polypropylene/graphite nanocomposite with the aids of rotating solid‐state mixing and dynamic packing injection molding

In this work, to achieve good dispersion state of graphite in the nonpolar intractable polymer, polypropylene (PP), two specific compounding/molding techniques, rotating solid‐state mixing (RSSM), and dynamic packing injection molding (DPIM), were used during the preparation of PP/graphite nanocomposite. The enhanced dispersion/exfoliation of graphite substance in PP matrix induced by RSSM and/or DPIM treatment was well identified by a combination of polarized optical microscopy, wide‐angle X‐ray diffraction, and scanning electronic microscopy. A comparative analysis indicated that RSSM mainly pulverizes graphite pristine‐particles into tactoids with significantly decreased diameter‐size, while DPIM offers strong melt shear force for exfoliating graphite tactoids into nanosheets whose thicknesses are about tens nanometers and length of 1 micron. Uniform dispersion of graphite nanosheets leaded to substantial increase in heterogeneous crystallization rate and mechanical properties. Our present study proposes a facile effective approach for large‐scale preparation of polymer/graphite nanocomposite with high‐performances. POLYM. COMPOS., 35:1943–1951, 2014. © 2014 Society of Plastics Engineers

Mechanical properties of multi-walled carbon nanotube/polyester nanocomposites

Carbon nanotubes (CNTs), due to their superlative mechanical and physical properties, have shown a high potential to improve properties of polymeric composites. Adding CNTs into polymers at very low weight fractions can improve mechanical properties of the resulting nanocomposites. In the present paper, multi-walled carbon nanotubes (MWCNTs) at different weight ratios (0.05, 0.1, and 0.5 wt.%) were added to polyester. Mechanical stirring and sonication technique were used to achieve good dispersion state of MWCNTs in the polymeric matrix. The results of mechanical tests (tensile and flexural) exhibit improvements of tensile and flexural strengths by 6% and 20%, respectively, at only 0.05 wt.% MWCNT. Improvements in Young's modulus and flexural modulus were also observed. Scanning electron microscopy was employed to determine the dispersion state of nanotubes in the matrix as well as the fracture surface properties.

On the dispersion of CNTs in polyamide 6 matrix via solution methods: assessment through electrical, rheological, thermal and morphological analyses

In this study, polyamide 6 (PA 6)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by different solution methods based on phase inversion, drop-casting and simple evaporation processes. Optical microscopy and field emission scanning electron microscopy techniques were used to investigate the dispersion states of the nanotubes in PA 6 matrix. The results indicated that the dispersion state of MWCNTs in the nanocomposites prepared by the phase inversion-based method was better than those in the nanocomposites prepared by the other two methods. Electrical, rheological, differential scanning calorimetry and thermo-gravimetric analysis measurements showed that the PA 6/MWCNTs nanocomposites prepared by the phase inversion-based method had higher electrical conductivity, storage modulus, crystallization temperature and thermal stability in comparison with those prepared by the other two methods, attributed to the better dispersion state of MWCNTs. These results confirmed achievement of a good dispersion state of MWCNTs within PA 6 matrix by the phase inversion-based efficient approach.

Improvement of solid-state symmetric cell performance with lithium vanadium phosphate

We constructed a Li3V2(PO4)3/Li1.5Al0.5Ge1.5(PO4)3/Li3V2(PO4)3 symmetric all solid-state Li-ion battery. Since the rechargeable capacity of Li3+xV2(PO4)3 anode is lower than that of Li3−xV2(PO4)3 cathode, the symmetric cell capacity is restricted by the anode capacity. So, the improvement of Li3+xV2(PO4)3 anode properties was tried using mechanical milling to uniformly mix Li3V2(PO4)3 and carbon. The charge and discharge capacity of Li3V2(PO4)3/C using mechanical milling was greatly increased compared to Li3V2(PO4)3/C using hand milling. The structure change with the insertion and extraction of lithium confirmed using ex-situ XRD measurements. The Li extraction/insertion of Li3V2(PO4)3 with a NASICON structure can proceed to the reversible expansion/contraction of the lattice due to the structural strength and flexibility of NASICON framework with the corner-sharing matrix. The discharge capacity of the all solid-state battery per Li3V2(PO4)3 in cathode weight achieved 92 mAh g−1 by good dispersion state of Li3V2(PO4)3 and carbon using mechanical milling.