Crystallization and thermal stability of polypropylene/multi-wall carbon nanotube nanocomposites (original) (raw)
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Macromolecular Chemistry and Physics, 2013
Nanocomposites of isotactic polypropylene (iPP) containing modifi ed multi-walled carbon nanotubes (MWCNTs) are prepared by melt mixing. MWCNTs with alkyl groups (alkyl-MWCNTs) and with methyl-PEG (mPEG-MWCNTs) are used, as well as unmodifi ed MWCNTs, to prepare the three series of nanocomposites. The surface treatment and the content of MWCNTs affect the mechanical properties of the iPP. In all cases, theoretical models are used to estimate the effect of surface treatment. The crystallization rates of nanocomposites in both isothermal and non-isothermal crystallization conditions are measured. The nanocomposites containing unmodifi ed MWCNTs crystallize faster than those with modifi ed MWCNTs.
Crystallization and melting behavior of isotactic polypropylene and carbon nanotube nanocomposites
2009
Polymer nanocomposites (PNCs) are the most recent development in the field of polymer science and technology. Geared toward creating novel polymer based materials, PNCs are the largest commercial application for nanotubes. Spherulitic polymer crystal growth was changed by inducing new fibrillar crystals on the surface of carbon nanotubes. Upon isothermal melt crystallization at 135^oC, CNTs lead to monoclinic crystal growth perpendicularly to the long axis of the nanotubes, explained by the multiple nucleation centers formed at the interface of the carbon nanotube and the polymer chains. Using Microscopic Transmission Ellipsometry (MTE), the sign of the alpha crystallographic phase was determined as positive. Using Differential Scanning Calorimetry (DSC), a decrease in the Avrami exponent was measured with increase of concentration of nanotubes.
Effect of carbon nanotubes content on crystallization kinetics and morphology of polypropylene
2009
Thermoplastic nanocomposites were prepared in a laboratory mixer using polypropylene (PP) and different amounts of single-walled carbon nanotubes (SWNT) in the range 0.25-2 wt%. The effect of SWNT content on the thermal and mechanical properties and also morphology of the PP/SWNT nanocomposites were studied. The results obtained from nonisothermal crystallization of PP and the nanocomposites, which were carried out using the differential scanning calorimetry technique, showed that not only the overall rate of crystallization of PP increased when SWNT was added to the polymer but also the rate of nucleation was higher and the crystallite size distribution was more uniform for the nanocomposites than for PP. From the optical microscopy studies, it was found that the PP spherulites decreased in size when SWNT was introduced into the polymer and also the mature spherical shaped crystals of PP changed in part to the immature kidney-or beanshaped crystal forms in the nanocomposites. In addition, the crystallization kinetics was also studied by using isothermal spherulitic growth rate, and the values of nucleation constant, K g , and end surface free energy, s e , were calculated for PP and the nanocomposites according to Lauritzen-Hoffman theory. The reductions of these two parameters were in agreement with the fact that the rate of crystallization of PP in nanocomposites was higher than that of the pristine polymer.
Journal of Applied Polymer Science, 2013
Modulated differential scanning calorimetry (MDSC) was used to measure the complex specific heat of the crystallization and melting transitions of nanocomposites of isotactic polypropylene (iPP) and carbon nanotubes (CNT) as function of CNT weight percent and temperature scan rate. In the last few years, great attention has been paid to the preparation of iPP/CNT nanocomposites due to their unique thermal and structural properties and potential applications. As the CNT content increases from 0 to 1 wt %, heterogeneous crystal nucleation scales with the CNT surface area. Above 1 wt %, nucleation appears to saturate with the crystallization temperature, reaching 8Kabovethatoftheneatpolymer.Heatingscansrevealacomplex,two−step,meltingprocesswithasmallspecificheatpeak,firstobserved8 K above that of the neat polymer. Heating scans reveal a complex, two-step, melting process with a small specific heat peak, first observed 8Kabovethatoftheneatpolymer.Heatingscansrevealacomplex,two−step,meltingprocesswithasmallspecificheatpeak,firstobserved8 K below a much larger peak for the neat iPP. For iPP/CNT samples, these two features rapidly shift to higher temperatures with increasing / w and then plateau at $3 K above that in neat iPP for / w ! 1 wt %. Scan rates affect dramatically differently the neat iPP and its nanocomposites. Transition temperatures shift nonlinearly, while the total transition enthalpy diverges between cooling and heating cycles with decreasing scan rates. These results are interpreted as the CNTs acting as nucleation sites for iPP crystal formation, randomly pinning a crystal structure different than in the neat iPP and indicating complex transition dynamics.
Polymer Engineering & Science, 2011
Carbon nanotubes (CNTs) have been added to polypropylene (PP) matrix to improve the overall performance of composites. The mixing process has been carried out by melt compounding using a twin screw co‐rotating extruder with different CNTs amounts in the 0.5–10 wt% from a concentrated PP‐CNTs masterbatch (20 wt% CNTs). Results show a remarkable increase in tensile strength and elastic modulus while a decrease in elongation at break is detected. With regard to thermal behavior, a remarkable increase in thermal stability at high temperatures (decomposition process studied by thermogravimetric analysis) is obtained as the CNTs amount increases. In addition to this improvement, a noticeable increase in thermal stability at medium temperatures (degradation onset determined by differential scanning calorimetry, DSC) is also observed. In a similar way, other property related to thermal and mechanical performance, such as Vicat softening temperature (VST) is improved with CNTs content. The o...
Journal of Materials Research and Technology, 2019
In this study, multi-walled carbon nanotube (MWCNT) filled polypropylene (PP) nanocomposites prepared by melt processing methods by employing extruder and injection molding techniques were examined with various characterization methods and test procedures, in detail. Aim and novelty of the work were to merely investigate the effects of amount and dispersion of MWCNTs on mechanical, thermal and rheological properties of PP including no compatibilizer and thus chemical interaction and/or interfacial adhesion effect. The mechanical test results showed that the incorporation of MWCNTs increased the tensile strength (18.4%), flexural strength (35.2%) and modulus of elasticity (45%) while it decreased the impact strength (18%) and elongation at break (690%) values of PP/MWCNT nanocomposites. Thermal analysis data revealed that the MWCNT addition slightly increased the crystallization peak onset and peak maximum temperatures of PP under non-isothermal conditions. Frequency-dependent melt rheological behaviors of nanocomposites in linear viscoelastic regime pointed out that the storage modulus (G'), loss modulus (G"), complex viscosity (Á*), and relaxation time of PP increased with the increasing amount of MWCNT. Non-linear rheological tests such as creep and stress relaxation also depicted that nanocomposites exhibited lower creep strain and relaxation rate than PP. Based on the thermal and mechanical test results, 0.3 wt% of MWCNT could be considered as the critical filler amount also called as "percolation threshold" for improving the solid-state physical properties of PP/MWCNT nanocomposites under the circumstances of no compatibilizer.
Polymer International, 2013
In this study, polypropylene/carbon nanotube nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler − Natta catalytic system. In this system, magnesium ethoxide and multiwall carbon nanotubes (MWCNTs) are jointly used as catalyst supports. SEM images reveal the distribution and quite good dispersion of MWCNTs throughout the polypropylene (PP) matrix. The thermal properties of the samples were examined using DSC and TGA tests. The results show that the crystallization temperature of the nanocomposites significantly increases while the melting point is not markedly affected. In addition, the thermal stability is improved. The melt rheological properties of PP/MWCNT nanocomposites in the linear and nonlinear viscoelastic response regions were studied. An increment of the complex viscosity (η *), storage modulus (G) and loss modulus (G) and a decrement of the loss factor (tan δ) compared with neat PP are observed. Steady shear flow experiments show an increase in shear viscosity with increasing the MWCNT content.
Polymer International, 2014
In this study, polypropylene/carbon nanotube nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler − Natta catalytic system. In this system, magnesium ethoxide and multiwall carbon nanotubes (MWCNTs) are jointly used as catalyst supports. SEM images reveal the distribution and quite good dispersion of MWCNTs throughout the polypropylene (PP) matrix. The thermal properties of the samples were examined using DSC and TGA tests. The results show that the crystallization temperature of the nanocomposites significantly increases while the melting point is not markedly affected. In addition, the thermal stability is improved. The melt rheological properties of PP/MWCNT nanocomposites in the linear and nonlinear viscoelastic response regions were studied. An increment of the complex viscosity (η *), storage modulus (G) and loss modulus (G) and a decrement of the loss factor (tan δ) compared with neat PP are observed. Steady shear flow experiments show an increase in shear viscosity with increasing the MWCNT content.
Thermal properties of polypropylene nanocomposites: Effects of carbon nanomaterials and processing
Polymer Engineering & Science, 2011
Design of experiments was used to elucidate the complex interactions that determine nanocomposite properties and enable predictive models for optimization. The thermal properties of nanocomposites containing polypropylene, single-walled carbon nanotubes (SWNTs), dodecyl-functionalized SWNTs, and vaporgrown carbon fibers were investigated as a function of extrusion temperature, screw speed, and time. The effects of extruder processing conditions on thermal properties was dependent on the fraction of polymer chains stabilized in the interphase, the extent of polymer degradation, and the type of nanomaterial incorporated. Melting and crystallization temperatures were primarily affected by nanomaterial type. However, thermal decomposition temperature was affected significantly by processing conditions and the response was dependent on the type of nanomaterial incorporated. POLYM. ENG.
In this research, the significance effects of MWCNTs at lower percentage addition in affecting the thermomechanical behavior of the fabricated PP/MWCNTs nanocomposites were studied. PP/MWCNTs nanocomposites were compounded by using the internal mixer, through the simple melt blending technique. The improvement effects of MWCNTs addition were well justified by the transmission electron microscopy (TEM) surface morphological observation. The interrelationships between the TEM surface observations with the thermomechanical results were established by manipulating the three major plots of dynamic mechanical analysis of storage modulus, loss modulus and damping modulus (tanδ). From this work, it was found that the improvement of dynamic thermomechanical properties is directly related to the amount of MWCNTs added and the quality of MWCNTs dispersion within the PP matrix.