Effects of single‐walled carbon nanotubes on the crystallization behavior of polypropylene

Polypropylene matrix composites reinforced with single‐walled carbon nanotubes (SWNTs) were produced with different nanotube concentrations. The characterization of these new materials was performed by differential scanning calorimetry and Raman and Fourier transform infrared spectroscopy to obtain information on the matrix–nanotube interaction, on the crystallization kinetics of polypropylene, and especially on the macrostructure and organization of the nanotubes in the composite. On the one hand, the results confirmed the expected nucleant effect of nanotubes on the crystallization of polypropylene, but on the other hand, this effect was not linearly dependent on the SWNT content: there was a saturation of the nucleant effect at low nanotube concentrations. Raman spectroscopy was successfully applied to demonstrating that in the composite films, the crystallization kinetics were strongly affected by the distance between the nanotube bundles as a result of a different intercalation of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 708–713, 2003     

Effects of carbon nanotubes on glass transition and crystallization behaviors in immiscible polystyrene/polypropylene blends

Functionalized multiwalled carbon nanotubes (FMWCNTs) have been introduced into immiscible polystyrene/polypropylene (PS/PP) blends. Not only the change in glass‐transition temperatures of PS and PP but also the crystallization and melting behaviors of PP have been investigated. The results show that FMWCNTs exhibit dual effects in the blends. One is that FMWCNTs, as a plasticizer for both PS and PP, induce the change in glass‐transition behaviors in both PS and PP. The other is that FMWCNTs, as a heterogeneous nucleating agent for PP, change the crystallization behavior of PP from homogeneous/bulk crystallization process to only bulk crystallization process. Further results show that the presence of FMWCNTs also induces the morphology change of the immiscible blends to a certain degree. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Rheology,crystallization behavior,and dielectric study on molecular dynamics of polypropylene composites with multiwalled carbon nanotubes and clay

The study is focused on joint effects of two nanofillers in polypropylene (PP) reinforced with 3 wt% organo‐clay (ОC) and 0.1–5 wt% multi‐wall carbon nanotubes (MWCNTs). The composites were produced by extrusion and characterized by rheology, differential scanning calorimeter (DSC), thermally stimulated depolarization currents (TSDC), and dielectric relaxation spectroscopy (DRS). Rheological data indicates а formation of a network structure related to percolation above 1 wt% nanotubes. The flow activation energy (Ea) decreases above the percolation threshold, thus, the presence of clay improves the debundling of MWCNTs and releases the segmental motion of polymer chains. The clay does not affect the crystallization behavior of PP, but the nucleation is enhanced strongly by the MWCNTs. Dielectric measurements reveal that the presence of clay affects the molecular mobility of PP at the amorphous phase. The DSC results imply that around 80°C a cold crystallization process occur in the PP phase which has a significant impact on the dielectric segmental relaxation process and gives rise to the appearance of an additional process, the so called “interfacial” relaxation process. This new relaxation process in the three‐phase composites was attributed to an interfacial polarization process due to blocking of charge carriers at polymer/clay interfaces. POLYM. COMPOS., 37:2756–2769, 2016. © 2015 Society of Plastics Engineers     

Effects of halloysite nanotubes on kinetics and activation energy of non-isothermal crystallization of polypropylene

Halloysite nanotubes (HNTs), a kind of naturally occurring silicates possessing typical fibular structure, were introduced to fabricate polypropylene (PP)/HNTs nanocomposites. The non-isothermal crystallization behaviors were investigated by differential scanning calorimetry (DSC) method according to different treatments. The results suggest, with the inclusion of HNTs in PP matrix, the nanocomposites crystallize at higher temperature regime, which are correlated with the heterogeneous nucleating effects of HNTs during the crystallization process of PP. The kinetics studies of crystallization show that PP nanocomposites possess faster crystallization process and higher activation energy due to the nucleating effect and hindrance effect of HNTs to the motion of PP chains. The polarized light microscopy (PLM) observations further show that HNTs serve as nucleation sites and accelerate the crystallization process.     

Multiwalled carbon nanotubes‐based polypropylene composites: Influence of interfacial interaction on the crystallization behavior of polypropylene

Composites of polypropylene (PP) and multi‐walled carbon nanotubes (MWCNTs) were prepared via melt‐mixing utilizing Li‐salt of 6‐amino heaxanoic acid (Li‐AHA) modified MWCNTs in the presence of a compatibilizer (polypropylene‐g‐maleic anhydride; PP‐g‐MA). Improved interaction between the anhydride group of PP‐g‐MA and the amine functionality of Li‐AHA was confirmed via FTIR and Raman spectroscopic analysis. A higher glass transition temperature (T_g) of the PP phase has been observed in these composites as compared to pristine MWCNTs‐based composites. The crystallization temperature (T_c) of the PP phase was increased as a function of pristine MWCNTs concentration in PP/MWCNTs composites indicating hetero‐nucleating action of MWCNTs. However, T_c value was decreased in the presence of Li‐AHA modified MWCNTs indicating the adsorbed Li‐AHA on the MWCNTs surface. Moreover, T_c value was higher in the presence of Li‐AHA modified MWCNTs with PP‐g‐MA as compared to that of without PP‐g‐MA, suggesting the desorbed Li‐AHA from the MWCNTs surface due to melt‐interfacial reaction. Further, MWCNTs were extracted by hot vacuum filtration technique from PP/MWCNTs composites containing Li‐AHA and PP‐g‐MA. The isothermal crystallization kinetics showed a variation in crystallization behavior of the PP phase in the corresponding composites as compared to the “extracted MWCNTs.” POLYM. ENG. SCI., 57:183–196, 2017. © 2016 Society of Plastics Engineers     

Effects of multi-walled carbon nanotubes on the crystallization behavior of PDCs-SiBCN and their improved dielectric and EM absorbing properties

Polymer derived siliconboron carbonitride ceramics (PDCs-SiBCN) containing multi-walled carbon nanotubes (MWCNTs-SiBCN) were fabricated and heat treated at 1350 °C and 1500 °C in nitrogen atmosphere. XRD patterns show the characteristic peaks of SiC appeared in MWCNTs-SiBCN treated at 1500 °C, which is 300 °C lower than the crystallization temperature of SiC in PDCs-SiBCN. The decrease of temperature can be ascribed to the heterogeneous nucleation promoted by MWCNTs as nucleating agent. Energy change during heterogeneous nucleation is analyzed to explain the acceleration of crystallization. The dielectric and electromagnetic (EM) absorbing properties of the as-prepared MWCNTs-SiBCN are investigated, which show a better wave-absorbing ability than PDCs-SiBCN treated at the same temperature, owing to a distinctive A + B + C microstructure in MWCNTs-SiBCN. This work makes it possible to fabricate the PDCs-SiBCN with good EM absorbing property at a lower temperature, granting them potential as a matrix material candidate in ceramic matrix composite field.     

Isothermal crystallization behavior of polypropylene catalloys

The isothermal crystallization behavior of polypropylene (PP) catalloys and neat PP were studied with differential scanning calorimetry and polarized optical microscopy (POM). The crystallization kinetics of the samples were described with the well‐known Avrami equation. The crystallization rate depended remarkably on the content of the ethylene component in the PP catalloys. The crystallization half‐time increased obviously with the increase of the ethylene component in the PP catalloys. We also observed by POM that in isothermal crystallization, there were many more nuclei in the PP catalloys than that in neat PP and with an increase of the ethylene component, the average size of the spherulites decreased obviously. Even when ethylene content was as high as 27%, the crystallization rate still increased apparently, and this was quite different from common PP melting blends, in which the crystallization rate decreased when the ethylene content was relatively high because of the obstruction effect of dispersed droplets to the spherulite growth of the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 877–882, 2004     

Effects of vibration blending on the subsequent crystallization behavior of polycarbonate/polypropylene blends

The effects of blending in a novel vibration internal mixer on the subsequent multiple crystallization of 70/30 w/w polycarbonate (PC)/polypropylene (PP) were investigated by differential scanning calorimetry, wide‐angle X‐ray diffractogram, and microscopy. The vibration internal mixer was reformed from a conventional internal mixer through parallel superposition of an oscillatory shear on a steady shear. For this polypropylene‐minor phase blend, three possible crystallization peaks were observed. The crystallization behavior was sensitive to the sizes and the size distribution of the dispersed polypropylene droplets. Larger amplitude and/or higher‐frequency vibration produced more small droplets (<2 μm) and increased the number of medium droplets (2–8 μm) as a result of the spatially wider and temporally quicker variation of shear rate. The resulting subsequent low‐temperature crystallization peak became larger and shifted to lower temperature, and the intermediate‐temperature peak became obvious. On the contrary, the coalescence of small droplets, resulting from the heating treatment, weakened the low‐temperature peak but strengthened the intermediate‐temperature peak and rendered the high‐temperature peak to be wider. Mixing at the too high amplitude produced the unstable, partially cocontinuous phase morphology restricting the medium droplets and enlarging the surface area, such that the intermediate‐temperature crystallization peak did not appear. Multiple crystallization was related to phase morphology and the nucleation density as well as surface effects. Double‐fusion endotherms of the PP component were also observed, corresponding to the melting of different forms of polypropylene crystals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 92–103, 2002     

Effects of dodecyl amine functionalized graphene oxide on the crystallization behavior of isotactic polypropylene

Dodecyl amine functionalized graphene oxide (DA‐GO)/isotactic polypropylene (iPP) nanocomposites were prepared via solution mixing method. Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS) verified that the DA was successfully grafted onto the surface of graphene oxide. The crystallization behavior of iPP/DA‐GO nanocomposites was investigated by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The DSC results of both isothermal and non‐isothermal crystallization process indicated that the addition of DA‐GO can decrease the half‐time crystallization (t_1/2) and elevate crystallization peak temperature (T_p) of iPP. The results of isothermal crystallization kinetics showed that the overall crystallization rates of iPP/DA‐GO nanocomposites, especially with higher DA‐GO content, were much faster than that of neat iPP. During the non‐isothermal crystallization process, the nucleation ability (Φ) of nanocomposites containing 0.05, and 0.5 wt % DA‐GO were 0.83 and 0.69, respectively. And the crystallization activation energy of iPP decreased from 348.7 (neat iPP) to 309.2 and 283.1 kJ/m 2 by addition of 0.05 and 0.5 wt % DA‐GO, respectively. The decrease of Φ and indicated DA‐GO has strong heterogeneous nucleation effect and can promote the crystallization of iPP significantly. Additionally, POM micrographs showed the DA‐GO in iPP matrix can form more nucleation sites for the spherulite growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40000.     

Effects of nucleating agents on crystallization behavior and mechanical properties of high-fluid polypropylene

The effects of organic aluminum phosphate (NA-21) and rare earth organic coordination compounds (WBG), serving as ??, ?? nucleating agents, on crystallization and mechanical properties of high-fluid polypropylene (PP) have been investigated. As determined by differential scanning calorimetry, the isothermal crystallization temperature of PP increased from 126.5 to 137.7?°C and 133.6?°C with NA-21 and WBG, respectively. The two endothermal melting peaks of PP blending with WBG indicated the transformation of ??-crystal. The wide-angle X-ray diffraction pattern and melting behavior of PP blending with WBG testified that a high proportion of ??-crystal, which was more than 70%, was induced, while the crystal-phase of PP modified with NA-21 had little change. The mechanical properties of nucleated PP were tested by tensile testing machine and izod pendulum impact tester. A dramatic increment of impact strength, as high as 191%, was obtained for PP with the introduction of WBG, comparing to 132% by NA-21 addition. The impact fracture surfaces were observed by scanning electron microscope; the resistance of crack growth of nucleated PP was better than that of pure PP. Although flexural strength of PP improved in both scenarios, the influence of nucleators on yield strength of PP differed. Yield strength of PP increased by 8.5% when using 0.2?wt% NA-21, but decreased by 6% when using WBG at the same content. Therefore, WBG, a novel ??-nucleator, played an essential role in enhancing impact strength of PP.     

UHMWPE/CNTs复合纤维的结晶行为研究

分别用DSC、X衍射、热台偏光显微镜对超高分子质量聚乙烯（UHMWPE）和UHMWPE／CNTs（碳纳米管）复合纤维的结晶行为进行了研究。结果表明：碳纳米管的加入使得复合材料的熔点较UHMWPE有所提高,碳纳米管起到了成核剂的作用。晶片厚度较UHMWPE增加。     

Isothermal crystallization kinetics of polypropylene in melt‐mixed composites of polypropylene and multi‐walled carbon nanotubes

The isothermal crystallization behaviour of the polypropylene (PP) phase in PP/multi‐walled carbon nanotubes (MWCNTs) composites has been investigated via differential scanning calorimetric analysis, which showed the influence of the varying dispersion level of MWCNTs in the respective PP matrix. PP/MWCNTs composites were prepared via melt‐blending technique, wherein two different grades of MWCNTs of varying average “agglomerate” size and varying entanglements (N‐MWCNTs and D‐MWCNTs) were utilized. Furthermore, the influence of melt‐viscosity of the PP phase was investigated on the crystallization kinetics of the PP/MWCNTs composites. Heterogeneous nucleation ability of MWCNTs has resulted in a decrease in half time of crystallization (t _1/2) from ～14 min for pure PP to ～6 min for PP/N‐MWCNTs and ～11 min for PP/D‐MWCNTs composites at 1 wt% of MWCNTs at 132 °C. Overall rate of crystallization (k) has significantly increased to 4.9 × 10^?2 min^?1 for PP/N‐MWCNTs composite as compared with 6.2 × 10^?3 min^?1 for PP/D‐MWCNTs composite at 0.5 wt% of MWCNTs at 132 °C. Moreover, the effect of a novel organic modifier, Li‐salt of 6‐amino hexanoic acid along with a compatibilizer (PP‐g‐MA) has also been investigated on the crystallization kinetics of the PP phase in PP/MWCNTs composites. POLYM. ENG. SCI., 57:1136–1146, 2017. © 2017 Society of Plastics Engineers     

聚丙烯在溶液中的等温结晶行为

采用差示扫描量热仪（DSC）分析聚丙烯（PP）在2种不同溶剂中的等温结晶过程,并使用Avrami方程研究等温结晶动力学。 结果表明,晶体生长速率随着结晶温度的升高而降低。 同时,根据Lauritzen⁃Hoffman 二次成核理论,PP在溶液中的成核常数K_g和折叠表面自由能σ_e低于PP原料,反映了其在溶液中的结晶速率较高。     

β晶型成核剂对PP结晶行为的影响

制备了β晶型聚丙烯(β-PP),利用广角X射线衍射仪与偏光显微镜表征了球晶形态,研究了其非等温结晶行为,并用Jeziorny法、莫志深法和Kissinger法对所得数据进行处理。结果表明,添加β晶型成核剂后,PP由α晶型向β晶型转变,起始结晶温度明显提高,总结晶时间缩短,结晶活化能降低。β-PP的Avrami指数在1．69～1．89,小于PP,表明β晶型成核剂的加入改变了PP的成核机理及生长方式。     

Rheological behavior of polypropylene nanocomposites at low concentration of surface modified carbon nanotubes

This article reports the rheological behavior of nanocomposites of isotactic polypropylene with both unmodified multiwall carbon nanotubes (CNTs) and phenol and 1‐octadecanol (C18) functionalized CNT (f‐CNT) at 0.1, 0.25, 1.0, and 5.0 wt% of the nanofillers. The incorporation of CNT at low loadings of 0.1 and 0.25 wt% decreases the storage and loss modulus and complex viscosity of the system, especially for the case of using f‐CNT. Out of the two types of functionalizations, C18 functionalization registers the lowest modulus and viscosity and displays processing aid behavior at 0.1 wt% loading, which is believed to be due to the disruption of the polymer entanglements. As the nanofiller loading increases to 1 wt%, the disruption of polymer entanglements effect is balanced by the hydrodynamic effect and subsequently neat polypropylene (PP), and the filled PP systems show similar modulus and complex viscosity. As the nanofiller loading increases further to 5 wt%, the hydrodynamic effect becomes the dominating factor, and the modulus and the complex viscosity of the nanofilled system become greater than that of neat PP. Results suggest that the 0.1 wt% loading of C18 f‐CNT could be a useful processing aid additive for improving polypropylene processability. POLYM. ENG. SCI., 52:1868–1873, 2012. © 2012 Society of Plastics Engineers     

Rheological behavior of polypropylene nanocomposites with tailored polymer/multiwall carbon nanotubes interface

Maleic anhydride grafted polypropylene (MA‐g‐PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall carbon nanotube (f‐MWNT) through solution mixing. These coated f‐MWNTs and pristine MWNT (p‐MWNT) were melt microcompounded with neat PP to form PP/f‐MWNT and PP/p‐MWNT nanocomposites at 0.1–1 wt% MWNT concentration. Complex viscosity and tan δ (ratio of loss modulus to storage modulus) behavior of these systems were studied using dynamic frequency sweep test, while relaxation time, activation energy, and melt homogeneity were also calculated and compared. Among the three types of samples, PP/f‐MWNT masterbatch‐based nanocomposite demonstrated not only the presence of interphase but also good processability. As a consequence, increase of both the crystallization rate in the presence of shear and the melt elasticity during annealing were found only in the masterbatch‐based samples but not in the PP/p‐MWNT. The mechanism of such increased melt elasticity was attributed to the formation of the space‐spanning network, which is consistent with the Cole–Cole plot showing similar behavior to the branched polymers in the literature. This has implications in polymer processing due to suggested changes in the balance between melt strength and polymer flow. Nanocomposite rheological behavior has also been correlated with the mechanical properties. POLYM. ENG. SCI., 59:1763–1777, 2019. © 2019 Society of Plastics Engineers     

Morphological features and melting behavior of nanocomposites based on isotactic polypropylene and multiwalled carbon nanotubes

Nanocomposites based on low molar mass isotactic polypropylene (iPP) and a low concentrations (1–2 wt %) of multiwalled carbon nanotubes (MWCNTs) were studied using thermal analysis, optical and electronic microscopy, and X‐ray diffraction/scattering techniques. It was first determined that MWCNT decrease induction time and act as nucleating agents of the iPP crystals during nonisothermal crystallization. One of the consequences of the nucleation effect was that the original spherulitic morphology of iPP was transformed into a fibrillar‐like. The corresponding long period of the original well‐defined lamellar structure slightly increased suggesting the formation of thicker crystals in samples containing MWCNT. The nature of the α‐iPP crystalline structure was not affected by MWCNT. After nonisothermal crystallization, two melting endotherms were present during thermal scanning of the iPP/MWCNT nanocomposites their proportion changing with the heating rate. After resolving the total DSC signal in its components using MDSC, the overall evolution of such behavior could be explained in terms of the melting/recrystallization mechanism. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effects of reinforcing fibers on the crystallization of polypropylene

The effects of the incorporation of different types of fibers on the crystallization kinetics and thermodynamics of isotactic polypropylene (iPP) are investigated. The study is mainly performed by thermal analysis, both in isothermal and constant cooling rate conditions, utilizing differential scanning calorimetry (DSC). The crystallization kinetics of the studied composites is successfully described by the Avrami model. Moreover, the effects of different kind of fibers are studied comparing the values of kinetics parameters such as the Avrami exponent n, the kinetic constant of the crystallization rate, Kn and the half‐time of crystallization, T 1/2. The results of the investigation show that the fibers behave as effective nucleant agents for the crystallization of polypropylene. In fact, a dramatic decrease of the half‐time of crystallization, T1/2, as well as a sensible increase of the overall crystallization rate, Kn, are observed in the presence of all the fibers analyzed. These effects are more marked in the presence of aramid fibers. The Avrami model is successfully applied to describe the crystallization kinetics of the composites. The kinetic curves obtained under non‐isothermal conditions confirm the results obtained under isothermal conditions and demonstrate the nucleating action of the fibers on the PP crystallization. Furthermore, the spherulite growth and the transcrystallinity on the surface of the fibers are investigated by optical polarizing microscopy. It is observed that transcrystallinity takes place in all kind of fibers studied, but also in this case, aramid fibers are the most effective in promoting transcrystallinity.     

Orientation of carbon nanotubes in polypropylene melt

The correlation between shear stress and the orientation of single‐walled carbon nanotubes (SWCNTs) in an SWCNT/polypropylene composite during the melt process was investigated. Highly oriented composite fibers were produced by extruding the polypropylene melt using a capillary rheometer. The experimental range of shear rates covered those of common polymer melt‐shaping processes. The effect of functionalization of the SWCNTs on orientation was also investigated. Polarized Raman spectroscopy was used to analyze the orientation of the SWCNTs. A high degree of SWCNT orientation was observed under high shear stress, and the functionalized SWCNTs induced a higher degree of orientation than did pristine SWCNTs. The existence of a critical shear stress was observed for the orientation of the SWCNTs, and their orientation was found to occur more efficiently above this critical shear stress. The crystallization temperature and heat of fusion were characterized using a differential scanning calorimeter, and both parameters were observed to increase with the incorporation of SWCNTs. © 2012 Society of Chemical Industry     

Relating the molecular structure and crystallization behavior of polypropylene

The crystallization behavior of two polypropylene (PP) resins as used for biaxially oriented polypropylene (BOPP) and general injection mold applications, respectively, has been intensively investigated and compared by means of polarized light optical micrography (POM), differential scanning calorimetry (DSC), conventional transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). It is found that both molecular weight distribution and isotacticity of polypropylene strongly affect its crystallization characteristics, e.g., the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size and perfection of crystals in the final product, and so on. The results indicate an appropriate molecular structure is vital in producing high‐quality BOPP film. Polym. Eng. Sci. 44:1749–1754, 2004. © 2004 Society of Plastics Engineers.