Polyester-based thermoplastic elastomer/MWNT composites: Rheological, thermal, and electrical properties

Polyester-based thermoplastic elastomer (Hytrel®) was melt-compounded with multi-walled nanotubes (MWNTs) using an internal mixer and the changes in the thermal, electrical and rheological properties were investigated using a range of nanotube contents (from 0.1 to 7 wt%). Even at nanotube concentrations as low as 0.1 wt%, the crystallization temperature was remarkably elevated by 15 °C and it increased further up to 22 °C with a 5 wt% loading. On the contrary, the melting temperature increased by 2 °C with 0.1 wt% MWNTs and it was slightly decreased by further additions of MWNTs. Electrical conductivity measured by the four probe method was detected from the 1 wt% MWNTs, indicative of electrical percolation. In addition, MWNTs starting from 4 wt% and above had no significant effect on the electrical conductivity, while it rapidly increased with nanotube contents below 4 wt%. Dynamic rheological properties were measured using a strain controlled rotational rheometer. The complex viscosity increased with MWNT contents giving an abrupt increase between 0.5 and 1 wt% loadings. In addition, the storage and loss modulus increased in a different manner depending on the range of the nanotube concentration. In the Cole-Cole plot, the slope of the nanocomposites decreased from 1.63 to 0.74 with increasing nanotube contents. In the Casson plot, the addition of MWNTs up to 0.5 wt% did not show any yield behavior giving an extremely low value for the yield stress, but further additions of nanotubes increased it notably. The presence of nanotubes in the elastomer increased the relaxation time with nanotube contents and their effect became weak as the frequency increased.     

Hybrid multi-scale basalt fiber-epoxy composite laminate reinforced with Electrospun polyurethane nanofibers containing carbon nanotubes

In this study, we report the fabrication and evaluation of a hybrid multi-scale basalt fiber/epoxy composite laminate reinforced with layers of electrospun carbon nanotube/polyurethane (CNT/PU) nanofibers. Electrospun polyurethane mats containing 1, 3 and 5 wt% carbon nanotubes (CNTs) were interleaved between layers of basalt fibers laminated with epoxy through vacuum-assisted resin transfer molding (VARTM) process. The strength and stiffness of composites for each configuration were tested by tensile and flexural tests, and SEM analysis was conducted to observe the morphology of the composites. The results showed increase in tensile strength (4–13 %) and tensile modulus (6–20 %), and also increase in flexural strength (6.5–17.3 %) and stiffness of the hybrid composites with the increase of CNT content in PU nanofibers. The use of surfactant to disperse CNTs in the electrospun PU reinforcement resulted to the highest increase in both tensile and flexural properties, which is attributed to the homogeneous dispersion of CNTs in the PU nanofibers and the high surface area of the nanofibers themselves. Here, the use of multi-scale reinforcement fillers with good and homogeneous dispersion for epoxy-based laminates showed increased mechanical performance of the hybrid composite laminates.     

Enhanced mechanical and dielectric properties of poly(vinylidene fluoride)/polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotubes (MWNTs) nanocomposites with the polymer matrix composed of blends of poly(vinylidene fluoride) (PVDF) and polyurethane (PU) were prepared via functionalization of 3,4,5-triflouroaniline (TFA) on MWNTs. The MWNTs/polymer nanocomposites showed a dominantly enhanced elongation due to incorporation of PU molecules in PVDF matrix and the improved MWNTs dispersion in the polymer matrix resulting from functionalization of MWNTs with TFA. The functionalization of TFA on MWNTs was confirmed by the measurements of Raman, FT-IR spectra, SEM, and TEM images. In addition, the dielectric constant of nanocomposites increased with an increase of TFA-functionalized MWNTs in PVDF/PU/MWNTs nanocomposites. The polymer blend nanocomposites incorporating MWNTs may be available as an alternative potential route for the actuator materials.     

Electrospun nanostructures based on polyurethane/MWCNTs for strain sensing applications

Electrically conductive nanofibers were fabricated from elastic polyurethane (PU) and PU/multiwalled carbon nanotubes (MWCNTs) nanocomposite by electrospinning method. The nanocomposites were electrospun at various MWCNTs loading. Electron microscopy was used to investigate nanofibers morphology and dispersion of MWCNTs in the electrospun nanofibers. The results showed that the presence of the MWCNTs promoted the creation of fibrous structures in comparison with the PU without MWCNTs. On the other hand, increasing the MWCNTs content resulted in a slight increase in the average fiber diameter. TEM micrographs and mechanical properties of the electrospun mats indicated that the homogeneous dispersion of MWCNTs throughout PU matrix is responsible for the considerable enhancement of mechanical properties of the nanofiber mats. Electrical behavior of the conductive mats was also studied, in view of possible sensor applications. Cyclic experiments were conducted to establish whether the electrical properties were reversible, which is an important requirement for sensor materials.     

Core-sheath polyurethane-carbon nanotube nanofibers prepared by electrospinning

The core-sheath nanofibers consisting of polyurethane (PU) core and PU composites sheath with multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. At low MWNT concentration, MWNTs appeared highly aligned along the fiber axis with some curving in nanotubes, whereas in case of high concentration, some aggregation of MWNTs appeared due to difficulty in full dispersion of nanotubes. In comparison of the single component nanofiber webs, the core-sheath nanofiber webs showed much better mechanical properties of modulus and breaking stress, including an exceptional elongation-at-break. It indicates that the CNT-incorporated core-sheath structure is very effective for enhancing the mechanical properties of nanofiber webs. In addition, the core-sheath nanofibers demonstrated the fast shape recovery, compared with one component fibers of pure shape memory PU and PU/MWNTs, which provides the possibility of fabricating more sensitive intelligent materials.     

Polyvinylpyrrolidone/Carbon Nanotube/Cotton Functional Nanocomposite: Preparation and Characterization of Properties

In the last decade, preparation of multifunctional composites have attracted researchers around the World for multi-purpose application. In this regard, we produced polyvinylpyrrolidone/carbon nanotubes/cotton (PVP/CNTs/cotton) nanocomposite by coating cotton fabric via pad-dry-cure under UV irradiation. Several characterization methods were used to investigate the functionality and durability including scanning electron microscopy, thermo-gravimetric analysis, flammability test, reflectance spectroscopy, tensile strength test, water absorption and antibacterial analysis. The interactions among PVP molecular chains, CNT particles and cellulose were confirmed by Raman spectroscopy. We observed a uniform coating of PVP/CNTs on the fiber surface. An advantage of our developed method was the strong interfacial interaction among compositions, high durability along with multifunctional properties. PVP/CNT nanocomposite was able not only to improve the thermal stability of cotton, but also provided a reduced flammability and good antibacterial properties. Here, we confirm a simple and versatile method for fabrication of PVP/CNTs/cellulose nanocomposite for multi-purpose applications.     

Composites of polyvinyl alcohol and carbon nanotubes decorated with silver nanoparticles

A simple method to decorate carbon nanotubes (CNTs) with silver nanoparticles was developed to enhance the electrical conductivity of CNTs. The acid-treated CNTs were suspended in the silver acetate solution, ammonia solution was then added, and the CNTs decorated with silver nanoparticles (Ag@CNTs) were produced. The Ag@CNTs were dispersed in polyvinyl alcohol (PVA) to fabricate electrically conducting polymer composites. The electrical, thermal and mechanical properties of the composites were measured. The electrical conductivity of the composites containing 0.8 % (o.w.f.) Ag@CNTs was more than four orders of magnitude higher than those of pristine and functionalized CNTs respectively, which confirmed the effectiveness of the Ag@CNTs as conducting filler. However, the improved electrical conductivity led to somewhat decrease of mechanical properties of PVA/Ag@CNTs composites.     

Synthesis and properties of shape memory polyurethane nanocomposites reinforced with poly(ɛ-caprolactone)-grafted carbon nanotubes

Nanocomposites of polyurethane (PU) and multi-walled carbon nanotubes (MWNTs) were prepared via in-situ polymerization of poly(ɛ-caprolactone)diol (PCL)-grafted-MWNTs, 4,4′-methylene bis(phenyl isocyanate), and 1,4-butanediol. The grafting of PCL onto MWNTs was confirmed by Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The nanocomposites showed more improved mechanical properties compared to conventional nanocomposites with the same MWNT loading. The thermo-responsive shape recovery as measured in a cyclic tensile test was observed to be approximately 80 % for in-situ nanocomposites, though it showed a reduced trend as the wt% of MWNTs increased. X-ray diffraction investigation also showed that the addition of MWNTs into the polyurethane increased the crystallinity. Scanning electron microscopy and TEM measurements showed better dispersion of MWNTs in the nanocomposites synthesized using in-situ method. Consequently, the presence of PCL-g-MWNTs made an important contribution to the enhancement of the mechanical and shape memory properties of polyurethane.     

Thermal and mechanical properties of polypropylene filaments reinforced with multiwalled carbon nanotubes via melt compounding

This study examined the thermal and mechanical properties of polypropylene filaments reinforced with multi-walled carbon nanotubes (MWNTs). The MWNTs were functionalized with maleic anhydride polypropylene to increase the interfacial interactions between the CNTs and polypropylene. PP/MWNT composites with different concentrations of MWNTs were prepared by melt compounding using a twin screw extruder. The composites of the filament were then post drawn and heat treated. Tensile tests showed increased strength with the addition of only 0.1 wt% while there were only slight changes in elongation. The thermal properties were also slightly enhanced by the MWNTs.     

Improved dispersion of carbon nanotubes in chitosan

Carbon nanotubes (CNT)/chitosan films and fibers can find use in specialized applications like the artificial muscles and other intelligent switching devices. The dispersion state of the single walled carbon nanotubes (SWCNTs) in chitosan matrix plays a major role in deciding the ultimate properties of composite. A suitable chemical treatment for purification and functionalization of SWCNTs is reported. Optimal conditions to prepare water soluble and stable, dispersion of SWCNT in chitosan are presented. The dispersion behavior of purified and functionalized SWCNT was characterized by visual observations, transmission electron microscopy (TEM), and Raman spectroscopy. The dispersion obtained using functionalized SWCNT was stable, while the purified SWCNT dispersion showed limited stability. The better stability of functionalized SWCNT dispersion in chitosan was evidenced by improved interaction between chitosan and carboxyl functional groups of SWCNT.     

Effects of carbon nanotubes on morphological structure, thermal and flammability properties of electrospun composite fibers consisting of lauric acid and polyamide 6 as thermal energy storage materials

The ultrafine composite fibers consisting of lauric acid (LA) and polyamide 6 (PA6) as form-stable phase change materials (PCMs), were prepared successfully by electrospinning. The effect of carbon nanotubes (CNTs) on the structural morphology, phase change behaviors, thermal stability, flammability and thermal conductivity properties of electrospun LA/PA6 composite fibers was investigated by field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), microscale combustion calorimeter (MCC) and melting/freezing times measurements, respectively. SEM observations indicated that the LA/PA6 and LA/PA6/CNTs composite fibers possessed flat and ribbon-shaped morphologies, but the neat PA6 fibers had cylindrical shape with smooth surface; and the average fiber diameters for LA/PA6 composite fibers decreased generally with the addition of CNTs. DSC measurements indicated that the heat enthalpies of the composite fibers were lower that that of neat LA powders, while the amounts of CNTs had no appreciable effect on the phase change temperatures and heat enthalpies of the composite fibers. TGA results showed that the addition of CNTs increased the onset thermal degradation temperature, maximum weight loss temperature and charred residue at 700 °C of the composite fibers, attributed to the improved thermal stability properties. It could be found from MCC tests that there were two-step combustion processes for composite fibers, and corresponded respectively to combustion of LA and polymer chains (PA6) in composite fibers. The addition of CNTs reduced the peak of heat release rate (PHRR) of electrospun composite fibers, contributing to the decreased flammability properties. The improved thermal conductivity performances of LA/PA6/CNTs composite fibers was also confirmed by comparing the melting/freezing times of LA/PA6 composite fibers with that of neat LA powders. The results from the SEM observation showed that the composite fibers had no appreciable variations in shape and diameter after heating/cooling processes.     

Morphology and properties of polyacrylonitrile/single wall carbon nanotube composite films

Composite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in DMF subsequent to sonication. The SWNTs in the films are well dispersed as ropes with 20–30 nm thickness. Moreover, AFM surface image of the composite film displays an interwoven fibrous structure of nanotubes which may give rise to conductive passways and lead to high conductivity. The polarized Raman spectroscopy is an ideal characterization technique for identification and the orientation study of SWNT. The well-defined G-peak intensity at 1580 cm⁻¹ shows a dependency on the draw ratio under cross-Nicol. The degree of nanotube orientation in the drawn film was measurable from the sine curve obtained by rotating the drawn film on the plane of cross-Nicol of polarized Raman microscope. The threshold loading of SWNT for electrical conductivity in PAN is found to be lower than 1 wt% in the composite film. The electrical conductivity of the SWNT/PAN composite film decreased with increasing of draw ratio due to the collapse of the interwoven fibrous network of the nanotubes with uniaxial orientation.     

Scalable preparation of multiscale carbon nanotube/glass fiber reinforcements and their application in polymer composites

The introduction of carbon nanotubes (CNTs) into conventional fiber to construct a hierarchical structure in polymer composites has attracted great interest owing to their merits of performance improvement and multiple functionalities. However, there is a challenge for realizing the scalable preparation of the multi-scale CNT-glass fiber (CNTGF) reinforcements in practical application. In this work, we present a simple and continuous method of the mass production of multiscale CNT-glass fiber (CNT-GF) reinforcements. Scanning electron microscopy and thermo gravimetric analysis indicated ~1.0 wt% CNTs were highly dispersed on the whole fiber surface through a facile surfactant-assisted process. Such hybrid CNT-GF fillers were found to effectively enhance the stiffness, strength and impact resistance of polypropylene polymer. Increased storage modulus, glass transition temperature and crystallization temperature of the composites filled with the CNT-GF fillers were also observed in the differential scanning calorimetry and dynamic mechanical analysis compared with the composites containing the pristine GF fillers. Fracture surface analysis revealed enhanced interfacial quality between CNT-GF and matrix, which is likely responsible for improved performance of the hierarchical polymer composites.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

Mechanical enhancement of UHMWPE fibers by coating with carbon nanoparticles

Fiber-reinforced plastic (FRP) is composed of reinforced fibers and matrix resin, and has high specific strength and low-density materials. Because of the orientation of the fibers within them, FRPs are prone to buckling damage when under compression along the axial direction of the fiber, especially flexible organic ones. The compressive performance of FRP is largely dependent on fiber properties. the buckling load of FRP will increase with the increasing of fiber’s. In this study, we developed a way to improve the compressive and bending strength of ultra-high molecular weight polyethylene (UHMWPE) fibers. Carbon nanotubes (CNTs) and vapor-grown carbon fibers (VGCFs) were coated on the surface of UHMWPE fibers by pyrrole vapor deposition. The transverse compressive strength and bending strength of single UHMWPE fibers were determined by microcompression and single fiber bending measurements, respectively. The experiment result showed that coating UHMWPE fibers with CNTs and VGCFs increased both their transverse compressive strength and bending strength. It is excepted that the improved fiber would applied in FRP for better compressive performance.     

Study on the creep and recovery behaviors of UHMWPE/CNTs composite fiber

The creep and recovery behaviors of UHMWPE and UHMWPE/CNTs composite fibers at different temperature were studied using Dynamic Mechanical Analysis (DMA). It was found that the creep strain of the UHMWPE and the UHMWPE/CNTs fibers increased with temperature rising. And creep strain of the composite fibers was always lower than that of the neat UHMWPE fiber. Burger’s model and Weibull distribution are employed to simulate the creep and recovery behaviors of the two fibers. The results show elasticity, stiffness and the recovery property of the composite fiber were improved by adding multi walled carton nanotubes.     

Carbon nanotube/poly(vinyl alcohol) fibers with a sheath-core structure prepared by wet spinning

A method for manufacturing sheath-core structured fibers was developed using wet spinning techniques. The core portion of a fiber was prepared using a carbon nanotube (CNT) solution while the sheath used a fiber-forming polymer such as polyvinyl alcohol (PVA). Preparation methods of CNT solutions were investigated and it was found that dispersivity and concentration played an important role in the formation and spinning of fiber??s core. CNT solution prepared using a surfactant with high molecular weight such as sodium lignosulfonate (SLS) was most effective and the CNT concentration was as high as 30 g/l. Fiber processing conditions were optimized and it was determined that stretching fibers in the coagulation bath was a significant step in the formation of a solid and well structured core. Drawn fibers were so strong and flexible that they could be woven into a fabric for potential use as a pressure sensor. These results are relevant for practical applications, such as the development of large-area fabric sensors. Furthermore, the described procedure to produce sheath-core CNT fibers is scalable as wet spinning methods have been widely used in the fiber industry.     

Effect of chemically modified date palm leaf fiber on mechanical,thermal and rheological properties of polyvinylpyrrolidone

Polyvinylpyrrolidone/date palm leaf fiber (PVP/DPL) biocomposites were prepared by melt mixing fabrication technique with different weight percentage of fibers. DPL fibers were chemically modified by acrylic acid in order to have better dispersion and compatibility with PVP matrix. The interaction of DPL fibers with PVP matrix was studied by Fourier transforms infrared spectroscopy (FTIR). Field emission scanning electron microscope (FESEM) was used for the study the morphology of chemically modified DPL fibers and PVP/DPL biocomposites. Mechanical properties were improved with fiber loading due to strong interfacial adhesion between PVP and DPL fibers. The storage modulus, loss modulus and tan delta values of PVA/DPL biocomposites were measured by DMTA. The rheological properties were investigated to study the shearing storage and loss modulii along with complex viscosity of biocomposites. The thermal and conducting properties of biocomposites were measured and compared with that of virgin PVP.     

Improved interfacial properties of carbon fiber/epoxy composites through graphene oxide-assisted deposition of carbon nanotubes on carbon fiber surface

A useful reinforcement for carbon fiber (CF) composites was found by performing the assisted electrophoretic deposition (EPD) of graphene oxide (GO) for carbon nanotubes (CNTs) onto the CF surface. GO-assisted EPD of CNTs was conducted without the use any other pre-treatment or additives in order to avoid destroying the structure of the CNTs and to facilitate preparation of stable dispersion that was suitable for EPD. The presence of GO-CNTs may effectively increase both the roughness and wettability of the CF surface, resulting in an improvement to the interfacial bonding strength between the CF and the epoxy (EP). In contrast to the pristine CF/EP composite, the GO-CNTs/CF/EP composite exhibited a 64.6 % increase in interlaminar shear strength. Meanwhile, the water absorption of the composites decreased from 0.36 wt.% to 0.14 wt.%. The variable surface morphology, surface roughness, surface free energy and surface chemical composition of the CF were considered to have had an effect on the interfacial properties of the CF/EP composites; these effects could be seen using atomic force microscopes, scanning electron microscopes, X-ray photoelectron microscopes and contact angle analysis characterizations.     

Performance of PTT fabric treated with CNTs/SiO<Subscript>2</Subscript>/thiazole dye hybrid materials

A series of CNTs/SiO₂/thiazole dye hybrid materials prepared via the sol-gel process is synthesized from carbon nanotubes (CNTs) and tetraethoxysilane with heteroaryl 4-phenyl-2-amino-thiazole dyes. Heterocyclic 4-phenyl-2-aminothiazole dyes are processed with the hydrolysis-condensation reaction at a constant ratio of vinyltriethoxysilane and tetraethoxysilane condensed with modified CNTs in appropriate proportion under a catalyst. The structures of the CNTs/SiO₂/thiazole dye hybrid materials are characterized by Fourier transform infrared spectroscopy (FTIR). Polytrimethylene terephthalate (PTT) fabrics are used to evaluate the morphology structure by scanning electron microscopy (SEM). SEM images show that a uniform dyeing on the PTT fabrics to confirm the reaction of hybrid materials with PTT fabrics. The washing fastness, color evenness, water contact angle, air permeability, electric conductivity, and weatherability of PTT fabrics dyed with CNTs/SiO₂/thiazole dye hybrid materials are evaluated, with results indicating improved conductivity and water-repellent.