A simple, easily accessible solvent‐free method for the dispersion of MWCNTs into PET is proposed, based on the preparation of a microparticulate polymer/nanotube masterbatch via cryogenic impact‐milling and its subsequent melt blending with the bulk polymer. Thermal and mechanical properties of nanocomposites prepared using this method were evaluated as a function of nanotube concentration. Thermal stability was improved, and superior crystallization behavior of PET in the nanocomposites was observed. Significant improvements of around 25% in tensile strength and tensile modulus of the nanocomposites was achieved using this strategy, with only 0.25 wt.‐% MWCNT, compared to previous literature data where 1 wt.‐% MWCNT was employed.
The thermal conductivity of a rubber compound is studied as a function of its state of curing. The device is presented and the calculations in order to obtain samples with controlled and homogeneous vulcanization rates are performed. The hot disk technique is used to measure the thermal conductivity of the rubber. This transient, plane‐source and non‐destructive method allows rapid and accurate measurement of the thermal conductivity based on the measurement of the electrical resistance of a plane sensor placed between two identical samples. The obtained results show that the thermal conductivity may vary significantly as a function of vulcanization rate. The effect of this variation on the prediction of the reaction progress is discussed.
UHMWPE/MWCNT and UHMWPE/GNS composites with a segregated network are prepared. TEM and SEM images indicate that the conducting fillers are distributed on the UHMWPE surface and form a segregated conducting network. The percolation threshold of UHMWPE/GNS composites is ≈0.25 wt% and that of UHMWPE/MWCNT composites is 0.20 wt%. The electrical conductivity of UHMWPE/GNS composites is almost four orders of magnitude lower than that of the UHMWPE/MWCNT composites. For equivalent concentrations of GNS and MWCNT, the composites with hybrid fillers exhibit a lower percolation threshold and a higher conductivity than that with GNS or MWCNT alone. Due to the high strength of the fillers and the segregated network structure, the mechanical properties of the composites first increase and then decrease with increasing filler content.
We report a ternary system of poly(styrene‐co‐acrylonitrile) (SAN), poly(vinyl chloride) (PVC), and multi‐walled carbon nanotube (MWCNT) composites prepared by both a solution blending method and the SOAM. The MWCNT content in the composites was optimized by both TGA and mechanical characterization of binary mixtures of SAN/MWCNT and PVC/MWCNT composites. The dispersion of MWCNTs in the miscible SAN/PVC blends was characterized by FT‐Raman spectroscopy, FE‐SEM, and FE‐TEM. The distribution of MWCNTs in the SAN/PVC blends was examined in terms of their wetting coefficients and minimization of the interfacial energy. Composites prepared using the SOAM method showed superior physical properties to the SAN/PVC blends and SAN/PVC/MWCNT composites prepared using the solution blending method.
1, 2, 3, 5, and 7.5 wt% MWCNTs are incorporated into PS in a twin‐screw extruder at varying speeds, throughputs and extruder barrel temperatures. Increased SME at enhanced processing speeds seems to have the single largest effect in enhancing dispersion. A relative evaluation of PS/MWCNT interactions indicate an interfacial layer growth of 24% for 2 wt% MWCNT at 1100 rpm compared to 18% growth at 500 rpm. Raman analysis does not show an MWCNT peak shift but a constant increase in FWHM is observed irrespective of the MWCNT content. A significant enhancement of thermal stability occurs up to 2 wt% MWCNT loading while 1–2 wt% shows the rheological threshold. The volume resistivity decreases dramatically in a 2 wt% sample processed at 1100 rpm compared to those processed at 500 rpm.
The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS‐modified PET/LCP blends were prepared by melt‐extrusion using twin‐screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase‐separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS‐modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re‐crystallisation. Finally, non‐isothermal crystal‐growth kinetics of pure and OMLS‐modified blends were investigated.
An in situ lubrication dispersion method is developed to achieve electrical conductivity in PP containing a small amount of MWCNTs. Good dispersion of the MWCNTs in PP is observed even after a short mixing time because the interactions between the entangled nanotubes are reduced. By in situ lubrication dispersion, the electrical percolation threshold of the PP nanocomposite can be as low as 0.5–0.7 wt% MWCNT. Rheological data also support percolation at 0.5 wt% MWCNT. With 0.5 wt% MWCNT, the slope of G′ at low frequency approaches unity and shows non‐terminal behavior. The proposed dispersion method enhances the wetting of MWCNTs and improves MWCNT dispersion compared to both direct mixing of MWCNT powder with a polymer melt and conventional master batch dilution.
PPy was synthesised by oxidative chemical polymerisation using xylan, CMC and NFC as additives. Conducting nanocomposite films were cast from aqueous slurries using doped PPy particles, CMC and NFC as the conducting and reinforcing phase, respectively. NFC‐based composites had higher conductivity and lower mechanical properties than CMC‐based homologues. SEM analysis showed that in PPy/NFC composites, PPy and NFC were arranged in two entangled networks, whereas, in PPy/NFC composites, CMC formed a continuous matrix around PPy particles, thus limiting conductivity. Mechanical properties of nanocomposite films were interpreted as reflecting the presence of different structures when using NFC or CMC as reinforcing phase.
Novel nanocomposites prepared by melt mixing of MWCNTs in a hot‐melt adhesive PCL‐based polyurethane are investigated. The nucleating effect of MWCNTs and the confinement they cause to polymer chains are considered. The broadening of the glass transition is indicative of a growth of the immobilized amorphous fraction adhered to MWCNTs. In the molten state the formation of a combined polymer/MWCNT network is observed. Practical requisites of hot melt adhesives, such as adequate melting temperature, crystallization degree, and viscosity are preserved when MWCNTs are added. Improvement of strength at room temperature and welding rate during cooling, are observed.
Unfilled and MWCNT‐filled PA fibers are prepared and the effect of the extensional flow on their mechanical performance and morphological variations is investigated. Morphological analyses using SEM, TEM, and SAXS suggest a stronger orientation of the MWCNTs along the fiber direction with increasing extensional flow. A particular MWCNT bundle formation in the PA drawn nanocomposite fibers is observed for the first time, and a pull‐out of the central nanotube in some bundles is noted. The maintenance of the “shish‐kebab” structure upon extensional flow is responsible for the mechanical improvements and dimensional stability in MWCNT‐filled PA fibers.
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
p‐tert‐Butylcalix[6]arene was acylated with different carboxylic acid anhydrides to improve their solubility in dimethacrylate cross‐linkers. An esterification of p‐tert‐butylcalix[6]arene 1 with octanoic anhydride followed by methacrylation of the residual hydroxy groups with methacrylic anhydride resulted mainly in the formation of a pentaoctanoatemonomethacrylate 2a . In the radical polymerization of methyl methacrylate the inhibition effect of residual hydroxy groups in 2a was evaluated. Dimethacrylate containing composites based on a monomer matrix of cross‐linking dimethacrylates and 0–30 wt.% of 2a were prepared. The addition of 2a resulted in a significant decrease of the polymerization shrinkage, whereas the modulus of elasticity of the visible light cured composites was not affected.
Natural biomaterials were used to improve the biocompatibility of synthetic biopolymers. PCL was electrospun with natural biopolymers, silk fibroin, and small intestine submucosa. Due to increased electrical conductivity, the diameter of the composite fibers highly depended on the amount of SIS in the polymer solution. PCL/SF/SIS electrospun composites exhibited various synergistic effects, including enhanced mechanical properties and incredibly improved hydrophilicity compared to those of pure PCL and PCL/SF fibers. An initial cell attachment test demonstrated that the interactions between PC‐12 nerve cells and the PCL/SF/SIS composites were more favorable than those between PC‐12 cells and a PCL/SF composite.
Novel polyurethane (PU) composites were prepared, based on hybrid inorganic/organic phosphazene‐containing microspheres. The FT‐IR spectra have shown that the microspheres have been linked with PU matrix. The microstructure of the composites is investigated by SEM. In comparison with PU, the glass transition temperatures and thermal stability of the composites are increased. The results from tensile testing of the composites have indicated that tensile strength is improved and elongation at break is almost invariable. The investigation on the surface properties of the composites showed that the water contact angles are obviously increased by adding 2 and 4 wt.‐% microspheres to the matrix.
A 1‐D through‐the‐thickness transient heat transfer model is built to simulate the curing process of thick‐walled glass‐fibre‐reinforced anionic polyamide‐6 (APA‐6) composites. The temperature and the degree of polymerisation through the thickness of the composite are calculated and compared to the experimentally obtained results. The kinetic models describing the polymerisation behaviour of APA‐6 are implemented in the model. The kinetic model not taking into account the convection in the polymerisation process shows the best results. It is found that the predicted temperature profiles agree well with the experimental data.
Three types of acrylonitrile‐butadiene‐styrene rubbers with different rubber contents were used in the preparation of PC/ABS/MWCNT composites. It was found that localization of MWCNTs changes from PC to ABS phase when rubber content of ABS varies from 5 to 60%. This is discussed by a combination of thermodynamics and kinetics. Melting sequence and high viscosity of ABS are used to explain the localization of MWCNTs in the high viscosity ABS phase. The relationship between the localization of MWCNTs and the electrical resistivity of the composite is also investigated.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
MWCNT‐based composites have been successfully synthesized via layer‐by‐layer self‐assembly of crosslinked polyphosphazene nanoparticles on the surface of MWCNTs. The amino‐terminated CNTs were characterized by XPS, FT‐IR spectroscopy, EDS, XRD and TEM. The degree of functionalization could be controlled by simply changing the mass of hexachlorocyclotriphosphazene with 4,4′‐diaminodiphenyl ether. The activity of the surface amino groups was confirmed by the reaction of these groups with HAuCl4. In addition, the effects of the mass of HCCP and ODA ratios on the content of the surface amino groups was also investigated.
Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.
Biofibers such as soy hull, switchgrass, miscanthus, and their hybrids are used as reinforcements to engineer green composites in poly(3‐hydroxybutyrate‐co‐valerate) and polylactide blends through melt mixing. The physico‐mechanical performance of the composites is evaluated by means of mechanical testing, DSC and SEM. The combination of agricultural residues as hybrids is shown to reduce supply chain concerns for injection‐molded green composites. The use of inexpensive biofibers and their hybrids proves an alternate way of getting cheap sustainable materials with better performance.
