Thermosetting polyurethane multiwalled carbon nanotube composites

Thermosetting polyurethane (PU) multi‐walled carbon nanotube (MWCNT) nanocomposites at loadings up to 1 wt % were prepared via an addition polymerization reaction. The morphology of the nanocomposites and degree of dispersion of the MWCNTs was studied using a combination of scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and wide angle X‐ray diffraction (WAXD), and revealed the nanotubes to be highly dispersed in the PU matrix. Addition of just 0.1 wt % MWCNTs resulted in significant enhancements in stiffness, strength and toughness. Increases in Young's modulus, % elongation at break and ultimate tensile strength of 561, 302 and 397% were measured for the nanocomposites compared to the unfilled PU. The effect of the MWCNTs on the modulus of the PU was evaluated using the Rule of Mixtures, Krenchel and Halpin‐Tsai models. Only the Halpin‐Tsai model applied to high aspect ratio nanotubes was in good agreement with the modulus values determined experimentally. Strong interfacial shear stress was found between PU chains and nanotubes, up to 439 MPa, calculated using a modified Kelly‐Tyson model. Evidence for strong interfacial interactions was obtained from the Raman spectra of both the precursor materials and nanocomposites. When the MWCNTs were added to the isophorone diisocyanate an up‐shift of 14 cm^?1 and on average 40 cm^?1 was obtained for the position of the carbon‐hydrogen (C? H) out‐of plane bending (766 cm^?1) and isocyanate symmetric stretch (1420 cm^?1) modes respectively. Moreover, an up‐shift of 24 cm^?1 was recorded for the nanotube tangential mode (G‐band) for the 1.0 wt % nanocomposite because of the compressive forces of the PU matrix acting on the MWCNTs. The dynamic mechanical (DMA) properties of the PU thermoset and the nanocomposites were measured as a function of temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanical and thermal properties of polyphenylene sulfide/multiwalled carbon nanotube composites

Polyphenylene sulfide (PPS)/multiwalled carbon nanotube (MWCNT) composites were prepared using a melt‐blending procedure combining twin‐screw extrusion with centrifugal premixing. A homogeneous dispersion of MWCNTs throughout the matrix was revealed by scanning electron microscopy for the nanocomposites with MWCNT contents ranging from 0.5 to 8.0 wt %. The mechanical properties of PPS were markedly enhanced by the incorporation of MWCNTs. Halpin‐Tsai equations, modified with an efficiency factor, were used to model the elastic properties of the nanocomposites. The calculated modulus showed good agreement with the experimental data. The presence of the MWCNTs exhibited both promotion and retardation effects on the crystallization of PPS. The competition between these two effects results in an unusual change of the degree of crystallinity with increasing MWCNT content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of carbon nanotube hydrophobicity on the mechanical properties of carbon nanotube‐reinforced thermoplastic polyurethane nanocomposites

Double walled carbon nanotubes (DWNT) were functionalized by reacting methanol, dodecylamine, or octadecylamine with a toluene 2,4‐diisocyanate linker through a two‐stage reaction procedure. TGA coupled with FTIR analysis of both the decomposition products and the DWNT samples demonstrated that the functionalization procedure was successful and proceeded as expected for all samples. A preliminary investigation of the reinforcing capabilities of the functionalized DWNT in a thermoplastic polyurethane host polymer was then conducted. Tensile testing of the resultant nanocomposites demonstrated that the octadecylamine functionality provided the greatest enhancement in tensile strength and toughness. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal stability and molecular interaction of polyurethane nanocomposites prepared by in situ polymerization with functionalized multiwalled carbon nanotubes

Polyurethane (PU) nanocomposites were prepared through conventional and in situ methods with multiwalled carbon nanotubes (MWNTs) functionalized with poly(ϵ-caprolactone). The thermal degradation and stability of PU–MWNT nanocomposites were investigated with nonisothermal thermogravimetry and were explained in terms of the interaction between MWNTs and PU molecules with Fourier transform infrared spectroscopy. The difference in thermal stability between the conventional and in situ nanocomposites was also compared. The thermal degradation of all the nanocomposite samples took place in two stages and followed a first-order reaction. The degradation temperature of the in situ nanocomposites was higher than that of the conventional nanocomposites with the same loading of MWNTs. The activation energy at 10% degradation and the half-life period were also higher in the in situ nanocomposites compared to the conventional nanocomposites. Such higher thermal stability of the in situ nanocomposites was ascribed to covalent bond formation between MWNTs and PU chains, which could result in better dispersion of MWNTs in the PU matrix for the in situ nanocomposites than for the conventional nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pseudoreinforcement effect of multiwalled carbon nanotubes in epoxy matrix composites

The carbon nanotube possesses outstanding physical properties. Theoretically, adding carbon nanotubes into a polymer matrix can remarkably improve the mechanical properties of the polymer matrix. In the present work, a series of composites was prepared by incorporating multiwalled carbon nanotubes (MWNTs) into an epoxy resin. The influences of MWNT content and curing temperature on the flexural properties of the epoxy resin were investigated. The results showed that a very low MWNT content should be used to ensure homogeneous dispersion of MWNTs in the epoxy matrix. A higher MWNT content may lead to deteriorated mechanical properties of the composites because of the aggregation of MWNTs. A decline in the flexural properties of the neat epoxy resin with increasing curing temperature was found. However, under the same curing conditions, improvement in flexural properties was observed for the composite with the low MWNT content and a mild curing temperature. The improvement was far beyond the predictions of the traditional short‐fiber composite theory. In fact, this improvement should be attributed to the retarding effect of MWNTs on the curing reaction of epoxy matrix. Therefore, the improvement in the flexural properties was only a pseudoreinforcement effect, not a nano‐reinforcement effect of the MWNTs on the epoxy resin. Perhaps, it is better for MWNTs to be used as functional fillers, such as electrical or thermal conductive fillers, than as reinforcements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3664–3672, 2006     

Polymeric carbon nanocomposites from multiwalled carbon nanotubes functionalized with segmented polyurethane

Multiwalled carbon nanotubes (MWNT) were functionalized with segmented polyurethanes (PU) by the “grafting to” approach. Raman and X‐ray photoelectron spectroscopy (XPS) spectra show that the sidewalls of MWNTs have been functionalized with acid treatment, and the amount of COOH increases with increasing acid treatment time. FTIR and X‐ray diffraction (XRD) spectra confirm that PU is covalently attached to the sidewalls of MWNTs by esterification reaction. Similar to the parent PU, the functionalized carbon nanotube samples are soluble in highly polar solvents, such as dimethyl sulfoxide (DMSO) and N,N‐dimethylformamide (DMF). The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGA). Comparative studies, based on SEM images between the PU‐functionalized and chemically defunctionalized MWNT samples, also reveal the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU‐functionalized MWNTs show enhanced mechanical properties and increased soft segment T_g. Tensile properties indicate that PU‐functionalized MWNTs are effective reinforcing fillers for the polyurethane matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

High performance polyurethane composites with isocyanate‐functionalized carbon nanotubes: Improvements in tear strength and scratch hardness

A microwave‐assisted functionalization of carbon nanotubes (CNTs) with isocyanate groups allowed a reduction of functionalization time from 24 h to 30 min with no change in the degree of functionalization or in the nanotube characteristics. Polymer nanocomposites with enhanced mechanical properties were obtained because of the tailored interface by the covalent linkage between the surface‐modified multiwalled‐carbon nanotubes (MWCNTs) and an elastomeric polyurethane (PUE) matrix. The mechanical data revealed that the composite containing 0.25 wt % of MWCNT‐NCO showed an increase of 31% in tear strength and 28% in static toughness. A good adhesion between the matrix and individually dispersed nanotubes was observed in the scanning electron microscopy and transmission electron microscopy images. Nanoindentation and nanoscratch experiments were conducted to investigate the properties on the sub‐surface. An increase by a factor of 3 in the scratch hardness was observed for the composite with 0.50 wt % of MWCNT‐NCO with respect to the neat PUE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44394.     

Thermosetting polyurethane‐multiwalled carbon nanotube composites: Thermomechanical properties and nanoindentation

In this study, composites based on a thermoset polyurethane elastomer (PU) and multiwalled carbon nanotubes (MWCNT) in the case of a PU of high elastic modulus (>200 MPa) are analyzed for the first time. As‐grown and modified nanotubes with 4 wt % of oxygenated functions (MWCNT‐ox) were employed to compare their effect on composite properties and maxima mechanical properties (elastic modulus and tensile strength) were reached at 0.5 wt % of MWCNT‐ox. Furthermore, by examining the morphology using optical and electron microscopies better dispersion and interaction of the nanotube‐matrix was observed for this material. DMTA data supports the observation of an increase in the glass transition temperature of ～20°C in the nanocomposites compared with the thermoset PU, which is an important result because it shows extended reliability in extreme environments. Finally, nanoindentation tests allowed a comparison with the conventional mechanical tests by measuring the elastic modulus and hardness at the subsurface of PU and the nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41207.     

Synthesis of s‐triazine‐based hyperbranched polyurethane for novel carbon‐nanotube‐dispersed nanocomposites

s‐Triazine‐based hyperbranched polyurethanes (HBPUs) with different hard segments were synthesized by A₂ + B₃ approach. Various kinds of multiwalled carbon nanotube (MWNT) nanocomposites with HBPU were prepared to investigate an impact of hyperbranched polymer on dispersion of MWNTs in the polymer matrix and the resulting properties of nanocomposites. Synthesized HBPUs were characterized using FTIR and NMR measurements. The highly branched structures were found very effective in enhancing the pristine MWNT dispersion in the polymer matrix. As a result, the MWNT‐reinforced HBPU nanocomposites showed a steep increase in the yield stress and modulus and enhanced shape memory effect with an increase of hard segment and MWNT loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and thermal properties of eucalyptus fiber composites bonding by blocked polyurethane adhesive

In this work, composites from eucalyptus fiber (EF) and polyurethane emulsion (PU) were prepared. Ethyl cellosolve-blocked polyisocyanate (EC-bp) was used as a novel adhesive and the mechanical and water absorption properties of the prepared composites were analyzed. The results showed that the tensile, flexural, and water resistance properties of the composites modified by such adhesive were enhanced compared with those of unmodified ones. Effects of EC-bp on the thermal degradation and the morphology of the composites were also investigated and compared. The presence of modification on the surface of EC-bp treated EF/PU composites was identified by Fourier transform infrared spectroscopy (FTIR) from the appearance of CO bands absorbance and the reducing of relative intensity of OH. Thermo-gravimetric analysis (TGA) resulted that the thermal stability of the modified composites was improved. Environmental scanning electron microscopy (ESEM) was used to observe the morphology and evaluate the interfacial adhesion of the composites. The results showed that much better homogeneity morphology of the modified composites was achieved, which indicated that the prepared EC-bp as an adhesive could improve the interfacial adhesion. These findings appeared that the occurrence of strong bonds between the composite components in the presence of EC-bp, rather than the unique existence of Van der Waals interactions among the nonpolar structures or the hydrogen bonding interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and thermal properties of polyurethane elastomers based on hydroxyl‐terminated polybutadienes and biopitch

Biopitch is a renewable source of polyol obtained from Eucalyptus tar distillation, which was studied as an active component of polyurethane (PU). The polymerization occurred in one step, with a mixture of biopitch and hydroxyl‐terminated polybutadiene polyols reacted with 4‐4′‐diphenyl methane diisocyanate in the presence of dibutyltin dilaurate. Solid‐state ¹³C‐NMR, IR spectroscopy, elemental analysis, and thermal analysis [thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)] were used to characterize the biopitch. The biopitch sample showed an aromatic and oxygenated structure with great thermal stability at high temperatures. Multiphasic PUs were synthesized and characterized by IR spectroscopy (attenuated total reflectance), elemental analysis, thermal analysis (TGA and DSC), mechanical assays (tensile strength, elongation at break, toughness, hardness, and resilience), and water absorption resistance (ASTM D 570‐81). In a comparative study of the synthesized elastomers, biopitch content increased tensile strength and hardness and decreased thermal stability, elongation at break, and water absorption. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 759–766, 2003     

Synthesis and properties of nanosilica‐reinforced polyurethane for grouting

A polyurethane/nanosilica (PU/SiO₂) hybrid for grouting was prepared in a two‐step polymerization using poly(propylene glycol) diols as the soft segment, toluene 2,4‐diisocyanate (TDI) as the diisocyanate, 3,3′‐dichloro‐4,4′‐diaminodiphenylmethane (MOCA) as the chain extender, and acetone as the solvent. The size and dispersion of nanosilica, the molecular structure, mechanical properties, rheological behavior, thermal performance, and the UV absorbance characteristic of the PU/SiO₂ hybrid were investigated by transmission electron microscopy (TEM), FTIR, mechanical tests, viscometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and UV spectroscopy. Nanosilica dispersed homogeneously in the PU matrix. The maximum values of mechanical properties such as tensile strength, elongation break, and adhesive strength showed an addition of nanosilica of about 2 wt %. Resistance to both high and low temperatures was better than with PU. And the UV absorbance of the PU/SiO₂ hybrid increased in the range of 290–330 nm with increasing nanosilica content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4333–4337, 2006     

Mechanical and surface properties of polyurethane/fluorinated multi‐walled carbon nanotubes composites

To improve the mechanical and surface properties of poly(etherurethane) (PEU), multi‐walled carbon nanotubes (MWCNTs) were surface grafted by 3,3,4,4, 5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol (TDFOL) (MWCNT‐TDFOL) and used as reinforcing agent for PEU. Fourier‐transform infrared spectroscopy revealed the successful grafting of MWCNTs. PEU filled with MWCNT‐TDFOL could be well dispersed in tetrahydrofuran solution, and tensile stress–strain results and dynamic mechanical analysis showed a remarkable increase in mechanical properties of PEU by adding a small amount of MWCNT‐TDFOL. Contact angle testing displayed a limited improvement (just 9°) in the hydrophobicity of PEU surface by solution blending with MWCNT‐TDFOL. However, a large improvement of surface hydrophobicity was observed by directly depositing MWCNT‐TDFOL powder on PEU surface, and the water contact angle was increased from 80° to 138°. Our work demonstrated a new way for the modification of carbon nanotubes and for the property improvement of PEU. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A comparative study on the properties of the different amino‐functionalized multiwall carbon nanotubes reinforced epoxy resin composites

Multiwall carbon nanotubes (MWCNTs) were amino‐functionalized by 1,2‐ethylenediamine (EDA)' triethylenetetramine (TETA), and dodecylamine (DDA), and investigated by fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). The dispersion of the DDA functionalized MWCNT in DMF is better than that of the MWCNT functionalized by the EDA and the TETA. Carbon nanotubes reinforced epoxy resin composites were prepared, and the effect of the amino‐functionalization on the properties of the composites was investigated by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and TGA. The composites reinforced by the MWCNTs demonstrate improvement in various mechanical properties. The increase of T_g of the composites with the addition of amino‐functionalized MWCNT compared to the T_g of the composites with the addition of unfunctionalized MWCNT was due to the chemical combination and the physical entanglements between amino group from modified MWNTs and epoxy group from the epoxy resin. The interfacial bonding between the epoxy and the amino group of the EDA and the TETA‐modified MWCNT is more important than the well dispersion of DDA‐modified MWCNT in the composites for the improvement of the mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical properties of carbon fiber reinforced bisphenol A dicyanate ester composites modified with multiwalled carbon nanotubes

A novel electrophoretic deposition (EPD) method was employed for grafting multiwalled carbon nanotubes (MWCNTs) on carbon fibers, which, after impregnation with bisphenol A dicyanate ester (BADCy), synergistically reinforced BADCy matrix composites (CNT‐C/BADCy). The effect of MWCNT presence on the mechanical properties of the composites was investigated. Composite tensile strength increased by 45.2% for an EPD duration of 2 min, while flexural strength exhibited a decreasing trend with EPD duration. Optical microscopy revealed that the existence of MWCNTs enhanced the fiber‐matrix interface while a large number of CNTs were observed to have pulled‐out from the matrix, a finding which explained the observed tensile strength increase in terms of energy dissipation by the specific toughening mechanism. The flexural strength decrease of the composites with CNTs as compared to specimens without nanotubes was found linked to the increased stress concentration in the BADCy matrix due to tube presence which weakens the adhesion between carbon fabrics. In a word, carbon nanotubes will enhance the micro interface and weaken the macro interface of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45100.     

Mechanical performance and flame retardancy of polypropylene composites containing zeolite and multiwalled carbon nanotubes

Intumescent‐flame‐retarded polypropylene (PP‐IFR) composites were prepared by the incorporation of methyl hydrogen siloxane treated ammonium polyphosphate and dipentaerythritol in a twin‐screw extruder. The effects of zeolite (Z), multiwalled carbon nanotubes (CNTs), and maleic anhydride grafted polypropylene on the flame retardancy, mechanical properties, and thermal stability of PP‐IFR were investigated. The addition of Z and CNT promoted the flame retardancy of PP‐IFR, and the highest limited oxygen index was 35.6%, obtained on PP‐M‐IFR‐2–Z, for which the heat‐release rate, total heat release, and smoke production rate based on cone calorimetry analyses decreased by 45.0, 51.0, and 66.3%, respectively, in comparison with those values of the PP‐IFR composites. Additionally, scanning electron microscopy analyses showed that there was a good interface interaction between the polypropylene matrix and additives. The flexural, tensile, and impact strengths of the PP‐IFR composites were improved significantly with the incorporation of CNT. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42875.     

Shape‐memory polyurethane/multiwalled carbon nanotube fibers

Shape‐memory polyurethane/multiwalled carbon nanotube (SMP–MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP–MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape‐memory behavior of the shape‐memory polymer was studied. The spinning ability of SMP–MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt‐blending, extrusion, and melt‐spinning processes for the shape‐memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The homogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Morphology,thermal expansion,and electrical conductivity of multiwalled carbon nanotube/epoxy composites

Multiwalled carbon nanotube/epoxy composites loaded with up to 0.5 wt % multiwalled carbon nanotubes were prepared and characterized. Infrared microscopy, scanning electron microscopy, thermogravimetry, differential scanning calorimetry, thermomechanical analysis, and electrical conductivity measurements of the composites were performed. Infrared microscopy and scanning electron microscopy images showed that the debundled nanotubes were well dispersed. The thermal expansion coefficients, before and after the glass transition, remained approximately constant with the addition of nanotubes, whereas the electrical conductivity at room temperature increased approximately 5 orders of magnitude. This result was attributed to the thermal expansion coefficients of the intertube gap on the carbon nanotube bundles, which were in the same range as that of the epoxy resin. Therefore, nanocomposites capable of electrostatic dissipation can be processed as neat epoxy materials with respect to the volume changes with temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of polyurethane/Mg‐Al layered double hydroxide nanocomposites

Layered double hydroxide (LDH) is a new type of nanofiller, which improves the physicochemical properties of the polymer matrix. In this study, 1, 3, 5, and 8 wt % of dodecyl sulfate‐intercalated LDH (DS‐LDH) has been used as nanofiller to prepare a series of thermoplastic polyurethane (PU) nanocomposites by solution intercalation method. PU/DS‐LDH composites so formed have been characterized by X‐ray diffraction and transmission electron microscopy analysis which show that the DS‐LDH layers are exfoliated at lower filler (1 and 3 wt %) loading followed by intercalation at higher filler (8 wt %) loading. Mechanical properties of the nanocomposite with 3 wt % of DS‐LDH content shows 67% improvement in tensile strength compared to pristine PU, which has been correlated in terms of fracture behavior of the nanocomposites using scanning electron microscope analysis. Thermogravimetric analysis shows that the thermal stability of the nanocomposite with 3 wt % DS‐LDH content is ≈ 29°C higher than neat PU. Limiting oxygen index of the nanocomposites is also improved from 19 to 23% in neat PU and PU/8 wt% DS‐LDH nanocomposites, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwalled carbon nanotubes composites

Poly(ethylene terephthalate)/multiwalled carbon nanotubes (PET/MWCNTs) with different MWCNTs loadings have been prepared by in situ polymerization of ethylene glycol (EG) containing dispersed MWCNTs and terephthalic acid (TPA). From scanning electronic microscopy images of nanocomposites, it can be clearly seen that the PET/MWCNTs composites with low‐MWCNTs contents (0.2 and 0.4 wt %) get better MWCNTs dispersion than analogous with high‐tube loadings (0.6 and 0.8 wt %). The nonisothermal crystallization kinetics was analyzed by differential scanning calorimetry using Mo kinetics equation, and the results showed that the incorporation of MWCNTs accelerates the crystallization process obviously. Mechanical testing shows that, in comparison with neat PET, the Young's modulus and the yield strength of the PET nanocomposites with incorporating 0.4 wt % MWCNTs are effectively improved by about 25% and 15%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011