Comparison of covalent and noncovalent interactions of carbon nanotubes on the crystallization behavior and thermal properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

In this study, multiwalled carbon nanotubes (MWCNTs) were dispersed into a poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, in which PHBV was either covalently attached to the nanotubes through an esterification reaction between the carboxylic groups of functionalized MWCNTs and the hydroxyl groups of PHBV with toluene diisocyanate as a coupling agent or physically mixed to result in only noncovalent interactions. The structure, crystallization behavior, and thermal properties of the resulting nanocomposites were studied. We found that the crystallization of PHBV grafted onto the MWCNTs (PHBV‐g‐MWCNTs) was markedly hindered and exhibited an exothermic peak caused by cold crystallization, whereas the nonisothermal crystallization of PHBV was enhanced because a heterogeneous nucleation effect appeared in the PHBV/MWCNTs. Moreover, the maximum decomposition temperature of the PHBV‐g‐MWCNTs was improved by about 14.4°C compared with that of the PHBV/MWCNTs and by about 23.7°C compared with that of the original PHBV. Furthermore, the PHBV‐g‐MWCNTs exhibited the wider melt‐processing window than the PHBV/MWCNTs and original PHBV. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4299–4307, 2013     

Crystallization and melting behavior of multi‐walled carbon nanotube‐reinforced nylon‐6 composites

The crystallization and melting behavior of neat nylon‐6 (PA6) and multi‐walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt‐compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T_{CC, 1} and T_{CC, 2}) for PA6/MWNTs composites instead of a single exotherm (T_{CC, 1}) for the neat matrix. The formation of the higher‐temperature exotherm T_{CC, 2} is closely related to the addition of MWNTs. X‐ray diffraction (XRD) results indicate that only the α‐phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α‐phase to γ‐phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one‐dimensional MWNTs and two‐dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α‐phase crystals of PA6. The dominant α‐phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry     

Effects of fumed silica on the crystallization behavior and thermal properties of poly(hydroxybutyrate‐co‐hydroxyvalerate)

The effects of fumed silica on the crystallization behavior and thermal properties of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) were investigated. The PHBV/silica composites were prepared by a melt‐blending method. The nonisothermal crystallization, melting process, and isothermal crystallization kinetics of PHBV and PHBV/silica composites were characterized with differential scanning calorimetry. The spherulite development and morphology were observed by polarized optical microscopy. In addition, the thermal degradation properties were determined via thermogravimetric analysis. The results indicated that the melting and crystallization kinetics of PHBV were greatly affected by fumed silica, and this was due to the effective nucleation function of silica, which enhanced the crystallization process. The thermal onset degradation temperature of PHBV increased with the addition of fumed silica. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and electrical multifunctional poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)—multiwall carbon nanotube nanocomposites

In this work, nanocomposites of poly(hydroxybutyrate‐co‐hydroxyvalerate) PHBV and multiwalled carbon nanotubes (MWNT) were prepared by melt blending. Mechanical, thermal, morphological, and electrical properties of the prepared PHBV/MWNT nanocomposites were investigated. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) results showed MWNT effectively enhanced the crystallization and nucleation of PHBV. Dynamic thermo‐mechanical and static uniaxial mechanical tensile and compressive properties were increased by the addition of MWNT. MWNT observed in the nanocomposites using transmission electron microscopy (TEM) showed dimensions similar to separated nanotubes inferring a good dispersion. The presence of nanotubes in close vicinity with each other formed an interconnecting network that led to the formation of electrically conductive nanocomposites. The electrical resistance of the nanocomposites was reduced with the addition of MWNT. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Electrical conductivity and thermal properties of acrylonitrile‐butadiene‐styrene filled with multiwall carbon nanotubes

Composites of Acrylonitrile‐butadiene‐styrene (ABS) and multiwall carbon nanotubes (MWNTs) have been prepared via solution‐blending. The electrical conductivity of these composites is analyzed. The MWNT‐filled ABS shows percolation point of the electrical conductivity at low filler loadings (1–2 wt%). The micro‐structure of the composites is also analyzed by scanning electron microscopy showing that the nanotubes are dispersed quite homogeneously in the polymer‐matrix. The thermogravimetric analysis is used to study the thermal degradation of ABS/MWNTs composites in nitrogen. MWNTs tend to destabilize the ABS matrix in the 220–450°C degradation regions but improve the thermal stability in the 425–850°C regions. With further addition of MWNTs, the features of the destabilization in the 220–450°C degradation region did not change much but in the 425–850°C degradation process, the MWNTs reinforced stabilization and the quality of the char residue of amorphous carbon deposition was improved. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Preparation and characterization of polydiphenylamine/multi‐walled carbon nanotube composites

We describe the synthesis of methane sulfonic acid (MeSA)‐doped poly(diphenylamine) (PDPA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Diphenylamine monomers were adsorbed on to the surface of c‐MWNTs and polymerized to form PDPA/c‐MWNT composites. SEM and TEM images indicated two different types of materials: the thinner fibrous phase and the larger globular phase. The individual fibrous phase had a diameter around 100–130 nm, which should be the carbon nanotubes (diameter 20–30 nm) coated with a PDPA layer. The structure of PDPA/c‐MWNT composites was characterized by FTIR, UV‐visible spectroscopy and X‐ray diffraction patterns. The electrical conductivities of PDPA/c‐MWNT composites were much higher than that of PDPA without c‐MWNTs. Copyright © 2006 Society of Chemical Industry     

Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites

Composites with multi‐walled carbon nanotubes (MWNTs) involved in polyamide 11 (PA11) were prepared via a conventional melt blending method. The structure, morphology, crystallization behavior, electrical, and dielectric properties of composites were investigated. The results demonstrated that the dispersed uniformly MWNTs favored the formation of α crystal of PA11 when the composites were quenched from melt. The dielectric constant of composites was dependent on the electric field frequency and MWNTs content, and the highest value of dielectric constant was as high as 350 for the composite with 1.21 vol % MWNTs at 10³ Hz, accompanied by a low dielectric loss. The enhanced dielectric properties could be interpreted by the formation of abundant nanocapacitors within the composites and the interfacial polarization effect resulting from accumulation of charge carriers at the internal interfaces between MWNTs and PA11. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42642.     

High thermal conductive m‐xylylenediamine functionalized multiwall carbon nanotubes/epoxy resin composites

In this study, multiwall carbon nanotubes (MWNTs) functionalized by m‐xylylenediamine is used as thermal conductive fillers to improve their dispersibility in epoxy resin and the thermal conductivity of the MWNTs/bisphenol‐A glycidol ether epoxy resin composites. Functionalization with amine groups of MWNTs is achieved after such steps as carboxylation, acylation and amidation. The thermal conductivity, impact strength, flexural strength, and fracture surfaces of MWNTs/epoxy composites are investigated with different MWNTs. The results show that m‐xylylenediamine is successfully grafted onto the surface of the MWNTs and the mass fraction of the organic molecules grafted onto MWNTs is about 20 wt %. The thermal conductivity of MWNTs/epoxy composites is further enhanced to 1.236 W/mK with 2 wt % m‐MWNTs. When the content of m‐MWNTs is 1.5 wt %, the impact strength and flexural strength of the composites are 25.85 KJ/m², 128.1 MPa, respectively. Scanning electron microscope (SEM) results show that the fracture pattern of composites is changed from brittle fracture to ductile fracture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41255.     

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     

Multiwalled carbon nantoubes‐reinforced poly(hydroxyaminoether) prepared by one pot graft‐from method

Multiwalled carbon nanotubes (MWNTs)‐reinforced poly(hydroxyaminoether) (PHAE) was fabricated via one pot graft‐from method. The modification of MWNTs and in situ polymerization of PHAE were combined in one reaction pot without interruption for the purification of modified carbon nanotubes. Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and Raman spectra clearly indicated that PHAE was successfully attached to the surface of MWNTs via esterification reaction between epoxy and carboxylic acid from MWNTs. Tensile tests showed that the tensile strength and modulus of PHAE/MWNTs composites were improved compared with that of pristine PHAE. Moreover, the reinforcing effect of one pot graft‐from method was found to be better than that of graft‐to method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of homogeneously dispersed polyamide 6/MWNTs nanocomposites via simultaneous in situ anionic ring‐opening polymerization and compatibilization

Toluene 2, 4‐diisocyanate (TDI) functionalized multiwalled carbon nanotubes (MWNTs‐NCO) were used to prepare monomer casting polyamide 6 (MCPA6)/MWNTs nanocomposites via in situ anionic ring‐opening polymerization (AROP). Isocyanate groups of MWNTs‐NCO could serve as AROP activators of ?‐caprolactam (CL) in the in situ polymerization. Fourier transform infrared (FTIR) showed that a graft copolymer of PA6 and MWNTs was formed in the in situ polymerization. MWNTs‐PA6 covalent bonds of the graft copolymer constituted a strong type of interfacial interaction in the nanocomposites and increased the compatibility of MWNTs and MCPA6 matrix. The nanocomposites were characterized for the morphology, mechanical, crystallization, and thermal properties through field emission transmission electron microscopy (FETEM), tensile testing, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). FETEM analysis showed that MWNTs were homogeneously dispersed in MCPA6 matrix. The initial tensile strengths and tensile modulus of the nanocomposite with 1.5 wt % loading of MWNTs were enhanced by about 16 and 13%, respectively, compared with the corresponding values for neat MCPA6. DSC analysis indicated that the crystallization temperature of the nanocomposites was increased by 8°C by adding 1.5 wt % MWNTs compared with pure MCPA6. Besides, it was found that the thermal stability of MCPA6 was improved by the addition of the MWNTs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A Kinetic Study on the Thermal Degradation of Multi‐Walled Carbon Nanotubes‐Reinforced Poly(propylene) Composites

Summary: The influence of the multi‐walled carbon nanotubes (MWNTs) content on the thermal degradation behavior of MWNTs‐reinforced poly(propylene) (PP) composites was investigated by using non‐isothermal thermogravimetric analysis (TGA). Kinetic parameters of degradation were evaluated by using the Flynn‐Wall‐Ozawa iso‐conversional method and the pseudo first‐order method. As a result, compared with pristine PP, MWNTs‐PP nanocomposites have lower peak temperatures of degradation, narrower degradation temperature ranges and a higher amount of residual weight at the end of the degradation, which is likely to be a result of specific interactions between complimentary functional groups. The values of the reaction order of MWNTs‐PP nanocomposites determined by the Kissinger method are close to 1 in the non‐isothermal degradation process. There is a good correlation between the E_a in region II and the peak temperature of degradation for the composites.

Activation energies for degradation of different contents of MWNTs‐filled PP nanocomposites as a function of conversion.     

Fabrication of hybrid ladderlike polysilsesquioxane‐grafted multiwalled carbon nanotubes

Ladderlike polysilsesquioxanes (LPSs) containing chloromethylphenyl groups were synthesized from (p‐chloromethyl)phenyltrimethoxysilane under basic conditions. Functionalized multiwalled carbon nanotubes (MWNT–COOH) were prepared by the acid treatment of pristine multiwalled carbon nanotubes (MWNTs). MWNT–COOH was reacted with LPS to prepare LPS‐grafted MWNTs via ester linkages. The functionalization of MWNTs with LPS significantly altered the surface roughness of the MWNTs; there was a significant increase in the diameter of the MWNTs. The LPS‐grafted MWNTs had a 10–20 nm thickness along the outer walls according to the functionalization of the MWNTs with LPS. An advantage of the hybrid LPS‐grafted MWNTs was shown as improved thermal behavior. The composition, thermal properties, and surface morphology of the LPS‐grafted MWNTs were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, energy‐dispersive spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nickel‐multiwalled carbon nanotubes/polyvinylidene fluoride composites with high dielectric permittivity

Composites with nickel particles coated multiwalled carbon nanotubes (Ni‐MWNTs) embedded into polyvinylidene fluoride (PVDF) were prepared by solution blending and hot‐press processing. The morphology, structure, crystallization behavior, and dielectric properties of composites were studied. The results showed that the crystallization of PVDF was affected by Ni‐MWNTs. With the increment of Ni‐MWNTs, the content of β‐phase in PVDF increased. The dielectric permittivity was as high as 290 at 10³ Hz when the weight fraction of Ni‐MWNTs was 10%. The results can be explained by the space charge polarization at the interfaces between the insulator and the conductor, and the formation of microcapacitance structure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3746–3752, 2013     

Poly (N‐methylaniline)/multi‐walled carbon nanotube composites—Synthesis,characterization, and electrical properties

This study described the synthesis of hydrochloric acid (HCl)‐doped poly (N‐methylaniline) (PNMA) with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) via in situ polymerization. Based on the π–π electron interaction between c‐MWNTs and the N‐methylaniline monomer and the hydrogen bond interaction between the carboxyl groups of c‐MWNTs and imine groups of N‐methylaniline monomers, N‐methylaniline molecules were adsorbed on the surface of c‐MWNTs and polymerized to form PNMA/c‐MWNT composites. Scanning electron microscopy images showed that both the thinner fibrous phase and the larger block phase could be observed. The individual fibrous phases had diameters from several tens to hundreds of nanometers, depending on the PNMA content. Transmission electron microscopy proved that PNMA/c‐MWNTs composite fibrous phases were core (c‐MWNT)‐shell (PNMA) tubular structures. The structure of PNMA/c‐MWNT composites was characterized by FTIR, UV–vis spectra, and X‐ray diffraction patterns. The electrical conductivities of PNMA/c‐MWNT composites were much higher than that of PNMA without c‐MWNTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2356–2361, 2006     

Effect of multi‐walled carbon nanotubes on crystallization,thermal, and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWNTs). Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) results showed that the crystalline structure of PVDF was changed by the addition of MWNTs and a MWNTs‐induced crystal transformation from α‐phase to β‐phase of PVDF was confirmed. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMA) techniques, thermal and mechanical properties of the composite films were examined. As the DSC results showed, addition of MWNTs would lead to the increased cooling crystallization temperature (T_c), implying that MWNTs nanoparticles could act as nucleating agents, which is further proved with the help of polarized optical microphotographs. On the other hand, the decreasing of D_d (degree of crystallinity) implied that the MWNTs networks can confine the crystallization of PVDF. Through the curve analysis of the dynamic mechanical measurements, it was found that the storage modulus (E′) is significantly enhanced, revealing that a strong interaction should exist between PVDF and MWNTs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Isothermal crystallization kinetics and melting behavior of multiwalled carbon nanotubes/polyamide‐6 composites

Pristine and functionalized multiwalled carbon nanotubes (MWNTs) were used to fabricate polyamide 6 (PA6) composites through melt blending. The functionalized MWNTs were obtained by grafting 1,6‐hexamethylenediamine (HMD) onto the pristine MWNTs to improve their compatibility with PA6 matrix. The effect of MWNTs on the isothermal crystallization and melting behavior of PA6 was investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). The Avrami and Lauritzen–Hoffmann equations are used to describe the isothermal crystallization kinetics. The values of the Avrami exponent found for neat PA6, the pristine MWNTs/PA6 and functionalized MWNTs/PA6 composite samples are about 4.0, 1.7, and 2.3, respectively. The activation energies are determined by the Arrhenius method, which is lower for the composites, ?320.52 KJ/mol for pristine MWNTs/PA6 and ?293.83 KJ/mol for functionalized MWNTs/PA6, than that for the neat PA6 (?284.71 KJ/mol). The following melting behavior reveals that all the isothermally crystallized samples exhibit triple melting endotherms at lower crystallization temperature and double melting endotherms at higher crystallization temperature. The multiple melting endotherms are mainly caused by the recrystallization of PA6 during heating. The resulting equilibrium melting temperature is lower for the composites than for neat PA6. In addition, polarizing microscopy (PLM) and small angle light scanning (SALS) were used to study the spherulite morphology. The results show that the MWNTs reduce the spherulite radius of PA6. This reduction is more significant for pristine MWNTs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Crystallization and mechanical behavior of covalent functionalized carbon nanotube/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) nanocomposites

To improve the dispersity of multi‐walled carbon nanotubes (MWCNTs) in poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, MWCNTs functionalized with carboxyl groups, hydroxyl groups, and atactic poly (3‐hydroxybutyrate) (ataPHB) through acid oxidation, esterification reaction, and “grafting from” method, respectively, were used to fabricate nanofiller/PHBV nanocomposites. The crystallization behavior, dispersion of MWCNTs before and after functionalization in PHBV matrices, and mechanical properties of a series of nanocomposites were investigated. The differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscope results suggested that the four types of MWCNTs acted as effective heterogeneous nucleation agents, inducing an increase in the crystallization rate, crystallinity, and crystallite size. Scanning electron microscope observations demonstrated that functionalized MWCNTs showed improved dispersion comparing with MWCNTs, suggesting an enhanced interfacial interaction between PHBV and functionalized MWCNTs. Consequently, the mechanical properties of the functionalized MWCNTs/PHBV nanocomposites have been improved as evident from dynamic mechanical and static tensile tests. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42136.     

Effect of graft modification with poly(N‐vinylpyrrolidone) on thermal and mechanical properties of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. The effect of graft modification with PVP on the thermal and mechanical properties of PHBV was investigated. The thermal stability of grafted PHBV was remarkably improved while the melting temperature (T_m) was almost not affected by graft modification. The isothermal crystallization behavior of samples was observed by polarized optical microscopy and the results showed that the spherulitic radial growth rates (G) of grafted PHBV at the same crystallization temperature (T_c) decreased with increasing graft yield (graft%) of samples. Analysis of isothermal crystallization kinetics showed that both the surface free energy (σ_e) and the work of chain‐folding per molecular fold (q) of grafted PHBV increased with increasing graft%, implying that the chains of grafted PHBV are less flexible than ungrafted PHBV. This conclusion was in agreement with the mechanical testing results. The Young's modulus of grafted PHBV increased while the elongation decreased with increasing graft%. The hydrophilicity of polymer films was also investigated by the water contact angle measurement and the results revealed that the hydrophilicity of grafted PHBV was enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nucleation effect of hydroxyl‐purified multiwalled carbon nanotubes in poly(p‐phenylene sulfide) composites

To investigate the nucleation effect of hydroxyl‐purified multiwalled carbon nanotubes (MWNTs‐OH) in poly(p‐phenylenesulfide) (PPS), a series of composites were prepared by blending PPS with MWNTs‐OH at 1, 2, and 3 wt %, respectively. Under SEM observation MWNTs‐OH were found homogeneously dispersed in the PPS matrix. DSC thermograms revealed that the enthalpy (ΔH_c) of the composites increased with increasing MWNT‐OH content, whereas the crystallization temperature (T_c) decreased progressively. The decrease in T_c was in accordance with the smaller crystallite size determined with WXRD characterization, and the increase in ΔH_c was evidenced by FTIR and XPS analyses. The higher ΔH_c shows that MWNTs‐OH serves as a nucleating agent, providing sufficiently multiplied sites for crystal growth. The lowering of T_c was attributed not only to MWNTs‐OH network hindrance to PPS chain fusing rearrangement, but also to a poorer affinity between MWNTs‐OH and PPS; both effects coordinately govern T_c of PPS/MWNTs‐OH composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013