High‐Performance Carbon Nanotube‐Reinforced Bioplastic

The inherent properties of poly(lactide), a biocompatible and biodegradable polymer, are concurrently improved by the incorporation of a small amount of surface functionalized carbon nanotubes. A new method has been used to functionalize the CNTs' outer surface with hexadecylamine. A composite of PLA with functionalized CNTs has been prepared by melt‐extrusion. FT‐IR spectroscopy, Raman spectroscopy, DSC, and optical microscopy are used to investigate the thermal and mechanical property improvement mechanism in f‐CNTs containing PLA composite.

     

Thermal and Mechanical Behavior of Carbon‐Nanotube‐Filled Latex

Summary: Composite films were prepared from a mixture of poly(vinyl acetate) latex and SWNTs. SEM images reveal a segregated SWNT network that grows heavier with increasing concentration. Nanotube segregation is the result of excluded volume created by the much larger polymer particles in the latex. Thermal conductivity exhibits a sharp rise with increasing quantity of nanotubes, although the maximum value is only 10% greater than that of the polymer matrix due to large thermal interface resistance. Storage modulus exhibits a peak and subsequent drop due to pore formation. In the absence of porosity, the Halpin‐Tsai model accurately predicts the composite modulus at 25 °C. The segregated network improves the composite modulus above T_g by nearly an order of magnitude with only 2 wt.‐% SWNT.

Schematic illustration of a segregated network of carbon nanotubes.     

Performance of MWCNT/HDPE Nanocomposites at High Strain Rates

Performance of HDPE/MWCNT composite at high strain rate up to 10⁴ s^?1 was investigated in a split Hopkinson pressure bar. The results revealed that the incorporation of MWCNTs into HDPE can enhance the impact strength of HDPE. High strain rate impact has a significant influence on morphology, density, crystallinity and melting temperature of the composite. With increase in strain rate, the densities of both HDPE and HDPE/MWCNT composite decreased. The drop of the density of HDPE/MWCNT composite was quicker than that of HDPE density. This could be the reason that much more cracks were formed in the HDPE/MWCNT composite, which could result in high energy dissipation, during SHPB test. The corporation of MWCNTs did lead to the decrease in yield stress.

     

Elaboration of Ultra‐High Molecular Weight Polyethylene/Carbon Nanotubes Electrospun Composite Fibers

Micron‐sized fibers of UHMWPE reinforced with CNT were fabricated by the electrospinning process. Conditions for a metastable mutual solution of UHMWPE and CNTs were found at elevated temperature. These solutions were used for electrospining using a device having controlled temperature and gaseous environment around the electrospun liquid jet. The fabricated micron‐sized fibers exhibited the reinforcing CNTs as self‐organized nano‐ropes embedded within them. A post‐spinning drawing process enhanced the mechanical properties of the composite fibers to the level of 6.6 GPa strength and elongation at break of 6%. The CNT nano‐ropes form spontaneously in the liquid jet during electrospinning, and provide the reinforcement framework which is amenable for post‐drawing of the fibers for subsequent utilization as composite nanofibers. The experimental results exhibit the highest strength value reported to date for electrospun fibers.

     

Solid Ceramic Fibers via Impregnation of Activated Carbon Fibers

A process has been developed which allows the preparation of some solid ceramic fibers. In this process, activated carbon fibers which are porous throughout their entire diameter are impregnated with metal-containing solutions such as silicon tetrachloride. Calcination and sintering result in the formation of solid SiO₂ fibers. Use of woven mats or nonwoven felts of activated carbon fibers results in the formation of woven mats or nonwoven felts of silica fibers.     

Fluid‐Induced Alignment of Carbon Nanofibers in Polymer Fibers

Carbon nanofiber/polycaprolactone (CNF/PCL) composite fibers are fabricated using a microfluidic approach. The fibers are made with different content levels of CNFs and flow rate ratios between the core and sheath fluids. The electrical conductivity and tensile properties of these fibers are then investigated. It is found that at a CNF concentration of 3 wt%, the electrical conductivity of the composite fiber significantly increases to 1.11 S m⁻¹. The yield strength, Young's modulus, and ultimate strength of the 3 wt% CNF increase relative to the pure PCL by factors of 1.72, 2.88, and 1.23, respectively. Additionally, the results show that a microfluidic approach can be considered as an effective method to align CNFs along the fibers in the longitudinal direction.

     

Highly Stretchable and Compressible Carbon Nanofiber–Polymer Hydrogel Strain Sensor for Human Motion Detection

With the development of technology and the improvement of living standards, wearable electronic devices have attracted more attention. Here, both stretchable and compressible hydrogel strain sensors based on carbon nanofiber powder (CFP) and polyvinyl alcohol (PVA) are prepared by freezing–thawing cycles. The PVA/CFP hydrogel exhibits excellent stretchable (366%) and compressible strains (70%). During 1000 loading–unloading cycles, the PVA/CFP hydrogel has a low plastic deformation (<10%, for both stretching and compressing), small energy loss efficiency (5.62% under stretching and 12.13% under compressing), and stable mechanical strength and excellent sensitivity, at conditions whether it is stretched to 100% or compressed to 50% strains. The stretchable and compressible PVA/CFP hydrogel can not only accurately detect multiple stretching behaviors of human activity, such as bending of joints, swallowing or breathing, but also detect the changes of pressure during walking. Besides, the PVA/CFP hydrogel can operate electronic screens due to its internal ions, with more potential application in soft robotics and electronic skin.     

Modification of epoxy resins via m‐chloroperbenzoic acid‐epoxidized carbon nanotubes

In this article, epoxidized carbon nanotubes (CNTs) are used to modify current epoxy resins. The produced epoxy groups on the nanotube surface significantly enriched nanotube chemistry and made them soluble in the organic solvents. Atomic force microscopy characterization indicated that epoxidized nanotubes were well dispersed in the organic solvent and most of them were isolated. Fracture surface of modified epoxy resins suggested that fracture toughness of the modified resins was significantly improved, demonstrating fracture characteristic of typical ductile materials. Epoxidized CNTs‐modified epoxy resins demonstrated a 50% increase in the Young's modulus, 32% improvement in the tensile strength with 1 wt % loading. This study provides an effective way to synthesize novel epoxy resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Lignin‐based polyurethane doped with carbon nanotubes for sensor applications

Modified eucalyptus kraft lignin doped with multiwall carbon nanotubes (MWCNTs) was used as a macromonomer in step‐growth polymerization with tolylene 2,4‐diisocyanate terminated poly(propylene glycol) with the aim of producing a conductive copolymer for all‐solid‐state potentiometric chemical sensor applications. The crosslinked elastomeric polyurethane obtained was characterized by Fourier transform infrared attenuated total reflection spectroscopy, scanning electron microscopy, tunnelling electron microscopy and atomic force microscopy. Doping of lignin‐based polyurethane with MWCNTs produced a significant enhancement of its electrical conductivity without deterioration of thermal and viscoelastic properties. The polymer composite displayed a low percolation threshold at an MWCNT concentration of 0.18% (w/w), which was explained by the oriented distribution of MWCNTs along lignin clusters. All lignin‐based polyurethanes doped with MWCNTs at concentrations above the percolation threshold are suitable for sensor applications. Copyright © 2012 Society of Chemical Industry     

Flexible strain sensors with high sensitivity and large working range prepared from biaxially stretched carbon nanotubes/polyolefin elastomer nanocomposites

Flexible strain sensors are a new generation of flexible and stretchable electronic devices that attracted increasing attention due to their practical applications in many fields. However, maintaining a wide detectable strain range while improving the sensitivity of flexible strain sensors remains challenging. In this study, flexible strain sensors with a large working range based on biaxially stretched carbon nanotubes (CNTs)/polyolefin elastomer (POE) nanocomposites were fabricated. Biaxial stretching was demonstrated to enhance the uniform dispersion and orientation of CNTs, thereby improving the performance of sensors. The optimal stretching ratios (SRs) of nanocomposites were investigated and the data revealed an increment in the sensitivity of sensors with SRs, while the working range first increased after biaxial stretching and decreased at higher SRs. Compared to the 9 wt% CNT/POE-1.0 sensor with a gauge factor (GF) value of 2.37 and a detectable range of 0.5%–230%, the CNT/POE-2.0 sensor exhibited an enhanced sensitivity (GF = 3935.12) coupled with a wider detectable range (0.5%–710%) and better stability. Besides, CNT/POE-2.0 sensor also achieved the monitoring of head movements, mouth opening, facial expression, and physiological signals, showing a potential for use in wearable electronic products.     

Polymer nanocomposites reinforced with multi‐walled carbon nanotubes for semiconducting layers of high‐voltage power cables

Polymer nanocomposites reinforced with multi‐walled carbon nanotubes (MWCNTs) have been newly introduced for semiconducting layers of high‐voltage electrical power cables. Homogeneity of the MWCNT‐reinforced polymer nanocomposites was achieved by solution mixing, and their mechanical, thermal and electrical properties were investigated depending on the type of polymer. By changing the polymer matrix, the volume resistance of the MWCNT‐reinforced polymer nanocomposites could be varied by more than four orders of magnitude. Through systematic experiments and analysis, two possible factors affecting the volume resistance were found. One is the degree of crystallinity of the polymer used and the other is the change of MWCNT morphology under strain. By increasing the degree of crystallinity above a certain level, the volume resistance linearly increased. The MWCNTs embedded in the nanocomposites gradually protruded through the surface on stretching the sample and reversibly returned back to the original positions at a relatively small strain (below 20%). Based on the criteria of tensile properties and volume resistance, a poly[ethylene‐co‐(ethyl acrylate)]/MWCNT nanocomposite was selected as the best candidate for the semiconducting layers of high‐voltage electrical power cables. Copyright © 2009 Society of Chemical Industry     

Pyridine‐Modified Polymer as a Non‐Covalent Compatibilizer for Multi‐Walled CNT/Poly[ethylene‐co‐(methacrylic acid)] Composites Fabricated by Direct Melt Mixing

Multi‐wall CNT/poly[ethylene‐co‐(methacrylic acid)] composites were prepared by melt mixing. To improve dispersion and promote polymer/nanotube interactions, a novel non‐covalent compatibilizer is synthesized by reacting the polymer with 4‐(aminomethyl)pyridine. The composite based on the pristine polymer shows electrical and rheological percolation thresholds at nanotube loadings of 1.85 and 1.4 wt%, respectively. When 5 wt% of the pyridine‐modified compatibilizer is added, the corresponding values are reduced to 1.44 and 0.8 wt%, respectively. The electrical resistivity decreases even further as 10 wt% of the novel dispersing agent is used. Microscopy and Raman spectroscopy confirm the improved dispersion and π‐interactions established during melt mixing.

     

Chemically Enhanced Wet‐Spinning Process to Accelerate Thermal Stabilization of Polyacrylonitrile Fibers

In this study, a fast and inexpensive approach is introduced to assist stabilization of polyacrylonitrile (PAN) fibers by adding ammonium iron(II) sulfate in coagulation bath. Effects of chemical treatment on stabilization process and structural evolution of fibers are studied using calorimetric, infrared, and X‐ray techniques. A stepwise infrared study confirms the assisted cyclization reaction, and an X‐ray analysis reveals a significant improvement in crystallinity and orientation of polymer chains which lead to an increase in tensile strength and modulus of PAN fibers. Differential scanning calorimetry results show 13 °C reductions in peak temperature of the stabilization reaction which means a sign of chemical activation at lower temperature by adding sulfate ions. Quantification of IR spectra shows a 7% increase in extent of reaction of chemically treated fibers and higher degree of conjugation compared with untreated and post‐treated fibers. Finally, mechanical properties of chemically treated fibers are improved due to an increase in size and orientation of polymer chains after chemical treatment in the coagulation bath. Compared to control and post‐treated PAN fibers, thermochemical properties of presented fibers are improved due to chemically assisted stabilization, and as a consequence, energy consumption of the stabilization step will be reduced by a simple and facile treatment.     

Clustering of Coated Droplets in Clay‐Filled Polymer Blends

The selective positioning of clay platelets at the polymer/polymer interface in a blend with drop/matrix morphology has a contrasting effect: on the one hand, it promotes a refinement of the morphology during the intense flows which occur during melt compounding; on the other hand, it induces coarsening in the course of prolonged slow flows experienced during rheological analysis. Rather than to a usual coalescence process, the increase of the average sizes of the dispersed phase is primarily due to a clustering mechanism of clay‐coated droplets, which keep their individuality inside the clusters because of the elastic connotation of the layered interface.

     

Cellulose‐Derived Carbon Fibers with Improved Carbon Yield and Mechanical Properties

The manufacture of high mechanical strength cellulose‐based carbon fibers (CFs) is accomplished in a continuous process at comparably low temperatures and with high carbon yields. Applying a sulfur‐based carbonization agent, i.e., ammonium tosylate (ATS), carbon yields of 37% (83% of theory), and maximum tensile strengths and Young's moduli up to 2.0 and 84 GPa are obtained already at 1400 °C. For comparison, the use of the well‐known carbonization aid ammonium dihydrogenphosphate ((NH₄)H₂PO₄), ADHP, is also investigated. Both the precursor and the CFs are characterized via elemental analysis, wide‐angle X‐ray scattering, Raman spectroscopy, scanning electron microscopy, and tensile testing. Thermogravimetric analysis coupled with mass spectrometry/infrared spectroscopy discloses differences in structure formation between ATS and ADHP‐derived CFs during pyrolysis.     

Fabrication of High Performance PET/TLCP Fibers through the Synergistic Interfacial Enhancement and Compatibilization of Functional 1D and 2D Carbon Nanomaterials

The maleic anhydride functionalized graphene oxide (GO-MA) is fabricated by an efficient and solvent-free Diels–Alder reaction. Polyethylene terephthalate (PET)/thermotropic liquid crystal polyester (TLCP), PET/TLCP/GO-MA, PET/TLCP/aminated multi-walled carbon nanotubes (MWCNTs-NH₂), and PET/TLCP/GO-MA/MWCNTs-NH₂ composite fibers are systematically melt-spun. The structure and compatibilizing effects of GO-MA and MWCNTs-NH₂ on the mechanical, thermal, and crystallization properties of the composite fibers are indicated. The non-isothermal crystallization kinetics and X-ray diffraction (XRD) data show that TLCP and nanofillers can change the crystalline morphology of PET. The mechanical properties of the fibers rise with increasing TLCP content. The tensile strength 929 MPa and modulus 17.5 GPa of the fibers with 7 wt% TLCP and 0.25 wt% nanofillers (0.1 wt% GO-MA and 0.15 wt% MWCNTs-NH₂) are significantly higher than those with 7 wt% TLCP (tensile strength 622 MPa and modulus 16.1 GPa) and even higher than those with 15% TLCP (tensile strength 836 MPa, and modulus 18.0 GPa). When the GO-MA and MWCNTs-NH₂ co-exist, the anti-dripping phenomenon is improved. Therefore, the TLCP, GO, and MWCNTs synergistically strengthens the mechanical properties. This is promising for the industrial fabrication of high-strength fibers.