Molecular motion,morphology, and thermal properties of multiwall carbon nanotube/polysilsesquioxane composite

Diglycidyl ether of bisphenol A (DGEBA)‐bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with 3‐aminopropyltriethoxysilane. Acid‐modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A‐bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A‐bridged polysilsesquioxane (MWCNT/DGEBA‐PSSQ) composites. The molecular motion of MWCNT/DGEBA‐PSSQ nanocomposites was studied by high‐resolution solid‐state ¹³C NMR. Acid‐modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA‐PSSQ decreased with acid‐modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA‐PSSQ was increased. SEM and TEM microphotographs confirm that acid‐modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA‐PSSQ. The dynamic mechanical properties of acid‐modified MWCNT/DGBEA‐PSSQ composites are more favorable than those of unmodified MWCNT. T_g of the DGEBA‐PSSQ decreased from 174.0 °C (neat DGEBA‐PSSQ) to 159.0 °C (1 wt % unmodified MWCNT) and 156.0 °C (1 wt % acid‐modified MWCNT). The storage modulus (at 30 °C) of the DGEBA‐PSSQ increased from 1.23 × 10⁹ Pa (neat DGEBA‐PSSQ) to 1.65 × 10⁹ Pa (1 wt % acid‐modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA‐PSSQ decreased to 6.88 × 10⁸ Pa (1 wt % unmodified MWCNT). At high temperature, above 150 °C, storage modulus of nanocomposites was higher than that of neat polymer system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 472–482, 2008     

Synthesis and self‐assembly of polystyrene‐grafted multiwalled carbon nanotubes with a hairy‐rod nanostructure

Polystyrene‐grafted multiwalled carbon nanotubes (PS‐g‐MWNTs) with a hairy‐rod nanostructure were synthesized by the in situ free‐radical polymerization of styrene in the presence of multiwalled carbon nanotubes (MWNTs) terminated with vinyl groups. To quantitatively study the molecular weight and composition of polystyrene (PS) chains in PS‐g‐MWNTs, PS‐g‐MWNTs were fully defunctionalized by hydrolysis. The results showed that 1 of every 100 carbon atoms in MWNTs was functionalized at the tips and outer walls of the carbon nanotubes and grafted by PS with a weight‐average molecular weight of 9800 g/mol; therefore, a uniform thin layer (ca. 8–10 nm) of a PS shell was formed on the outer wall of MWNTs. PS‐g‐MWNTs were soluble in dimethylformamide and tetrahydrofuran. The thermal stability and glass‐transition temperature of PS in PS‐g‐MWNTs were obviously increased. Nanopins were formed on the glass substrates by the self‐assembly of PS‐g‐MWNTs, and the dewetting effect between the glass substrate and PS chains covered MWNTs during the evaporation of the solution. Both the length and diameter of the nanopins increased with the solution concentration. When PS‐g‐MWNTs were compression‐molded, MWNTs were dispersed uniformly in the PS matrix and formed good networks, such as circlelike and starlike structures, because of the entanglements of hairy PS chains on MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3869–3881, 2006     

Melt‐crystallization mechanism of poly(ethylene terephthalate)/multi‐walled carbon nanotubes prepared by in situ polymerization

A series of poly(ethylene terephthalate)/multi‐walled carbon nanotubes (PET/MWCNTs) nanocomposites were prepared by in situ polymerization using different amounts of multi‐walled carbon nanotubes (MWCNTs). The polymerization of poly(ethylene terephthalate) (PET) was carried out by the two‐stage melt polycondensation method. The intrinsic viscosity (IV) of the composites is ranged between 0.31 and 0.63 dL/g depending on the concentration of the MWCNTs. A decrease of IV was found by increasing MWCNTs content. This is due to the reactions taking place between the two components leading to branched and crosslinked macromolecules. These reactions are, mainly, responsible for thermal behavior of nanocomposites. The melting point of the nanocomposites was shifted to slightly higher temperatures by the addition till 0.55 wt % of MWCNTs while for higher concentration was reduced. The degree of crystallinity in all nanocomposites was, also, reduced by increasing MWCNTs amount. However, from crystallization temperature, it was found that MWCNTs till 1 wt % can enhance the crystallization rate of PET, whereas at higher content (2 wt %), the trend is the opposite due to the formation of crosslinked macromolecules. From the extended crystallization analysis, it was proved that MWCNTs act as nucleating agents for PET crystallization. Additionally, the crystallization mechanism due to the existence of MWCNT becomes more complicated because two mechanisms with different activation energies are taking place in the different degrees of crystallization, depending on the percentage of MWCNT. The effect of molecular weight also plays an important role. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1452–1466, 2009     

Preparation and morphological,electrical, and mechanical properties of polyimide‐grafted MWCNT/polyimide composite

Precursor of polyimide, polyamic acid has been prepared sucessfully. Acid‐modified carbon nanotube (MWCNT) was grafted with soluble polyimide then was added to the polyamic acid and heated to 300 °C to form polyimide/carbon nanotube composite via imidation. Morphology, mechanical properties and electrical resistivity of the MWCNT/polyimide composites have been studied. Transmission electron microscope microphotographs show that the diameter of soluble polyimide‐grafted MWCNT was increased from 30–60 nm to 200 nm, that is a thickness of 70–85 nm of the soluble polyimide was grafted on the MWCNT surface. PI‐g‐MWCNT was well dispersed in the polymer matrix. Percolation threshold of MWCNT/polyimide composites has been investigated. PI‐g‐MWCNT/PI composites exhibit lower electrical resistivity than that of the acid‐modified MWCNT/PI composites. The surface resistivity of 5.0 phr MWCNT/polyimide composites was 2.82 × 10⁸ Ω/cm² (PI‐g‐MWCNT) and 2.53 × 10⁹ Ω/cm² (acid‐modified MWCNT). The volume resistivity of 5.0 phr MWCNT/polyimide composites was 8.77 × 10⁶ Ω cm (PI‐g‐MWCNT) and 1.33 × 10¹³ Ω cm (acid‐modified MWCNT).Tensile strength and Young's modulus increased significantly with the increase of MWCNT content. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3349–3358, 2007     

Structure–property relationships in polyamide 6/multi‐walled carbon nanotubes nanocomposites

Polyamide 6 (PA6)/multi‐walled carbon nanotubes (MWCNT) nanocomposites were produced by diluting a masterbach containing 20 wt % nanotubes using melt mixing. The influence of the addition of well dispersed MWCNT (as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)) on the thermal transitions, and crystallization behavior of the PA6 matrix is investigated. Differential scanning calorimetry (DSC) results show a reduction in heat capacity jump at the glass transition which is interpreted by an immobilized interfacial layer near the nanotubes. Furthermore, both DSC and X‐ray diffraction (XRD) measurements indicate that nanotubes favor the formation of the α crystalline form of PA6. These findings are correlated with the observed improvement of the storage modulus as revealed by dynamic mechanical thermal analysis (DMTA). Additionally, a new crystallization peak appears when MWCNT are added, and is attributed to the formation of a different morphology of the same type crystallite around the nanotubes walls (trans‐crystallinity). Finally, water sorption measurements show an increase of water content, normalized to the amorphous polymer fraction, in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 764–774, 2009     

PTMG-Modified MWCNT/PTMG-based polyurethane nanocomposites: Strong interaction and homogeneous dispersion

Soft and flexible chains of poly(tetramethylene glycol) (PTMG) were covalently grafted with multi-walled carbon nanotubes (MWCNT). FE-SEM images showed that the polyether PTMG formed a surrounding shell around the nanotubes with about 5 nm in thickness. The modified nanotubes (MWCNT-PTMG) were then loaded into an in situ prepared polyurethane elastomer (PUE) with different loading contents below 1 wt %. In addition to the modifier of MWCNT, polyether PTMG was also used for preparing the polyurethane matrix. Thermal analyses (TG/DTG and DTA) showed two endothermic phase transitions in associated with the two main thermo-degradations of the resulting PUE nanocomposites. Moreover, DMA technique exhibited an appreciable increase in the T _g values due to a strong interaction between PTMG-modified MWCNT and PTMG-based PUE matrix.     

Nanocomposite prepared from in situ grafting of polypyrrole to aminobenzoyl‐functionalized multiwalled carbon nanotube and its electrochemical properties

We reported the functionalization of multiwalled carbon nanotube (MWCNT) with 4‐aminobenzoic acid by a “direct” Friedel–Crafts acylation reaction in a mild polyphosphoric acid (PPA)/phosphorous pentoxide (P₂O₅) medium. The resulting 4‐aminobenzoyl‐functionalized MWCNT (AF‐MWCNT) was used as a platform for the grafting of polypyrrole (PPy) in ammonium persulfate (APS)/aqueous hydrochloric acid solution to produce PPy‐grafted MWCNT (PPy‐g‐MWCNT) composite. After dedoping with alkaline treatment, PPy‐g‐MWCNT displayed 20 times higher electrical conductivity than that of PPy. The current density and cycle stability of PPy‐g‐MWCNT composite were also remarkably improved compared with those of PPy homopolymer, suggesting that an efficient electron transfer between PPy and MWCNT was possible through covalent links. In addition, PPy‐g‐MWCNT displayed high electrocatalytic activity for oxygen reduction reaction (ORR). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Precision Polyolefin Nanoalloy Polypropylene/Poly(ε‐caprolactone)

This communication reports the first example of precision polyolefin nanoalloys where an exotic immiscible polymer is nanometrically dispersed with stability in a polyolefin matrix in a highly controlled mode. Following the preparation of polypropylene/multiwalled carbon nanotubes nanocomposites (PP/MWCNTs) by in situ Ziegler‐Natta polymerization, the hydroxyl groups on the surfaces of individual MWCNTs are used to initiate ring‐opening polymerization of ε‐caprolactone, resulting in PP/poly(ε‐caprolactone) (PCL) alloy with PCL grafted on MWCNTs. Upon phase formation, the PP/MWCNTs‐g‐PCL alloys exhibit a unique PCL dispersion morphology, which is stable and solely governed by PCL molecular weight.

     

Poly(N‐vinyl imidazole) grafted silica nanofillers: Synthesis by RAFT polymerization and nanocomposites with polybenzimidazole

In this report, we synthesized poly(N‐vinyl imidazole) (PNVI) grafted silica nanoparticles (SiNP) by using RAFT polymerization through grafting‐from approach to demonstrate that the self‐assembled structure of SiNP is the key diving force in improving physical properties of SiNP based nanocomposites. In a multistep synthetic process, well‐defined PNVI chains with tunable molecular weights and surface chain densities were grown from the RAFT agent anchored SiNP surface using N‐vinyl imidazole (NVI) as a monomer. Spectroscopic and thermal analysis confirmed surface grafting of PNVI on SiNP surface and the amount of grafted PNVI chins were also quantified. The mean diameter of the PNVI grafted SiNP (PNVI‐g‐SiNP) particles altered between 50 and 100 nm with the variation of PNVI chain lengths. The present approach is metal‐catalyst free, straight forward, and provides PNVI functionalized SiNP in a simple manner in comparison to the reported methods. Further, these PNVI‐g‐SiNP particles were used as a nanofiller to prepare nanocomposites with Poly(4,4′‐diphenylether‐5,5′‐bibenzimidazole) (OPBI). These nanocomposites displayed significantly higher mechanical, proton conductivity and less acid leaching properties than the pristine OPBI. The anisotropic self‐assembled ordered structure formation of nanofillers in the nanocomposites believed to be the driving force for the enhanced physical properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 365–375     

Preparation and characterization of PP/clay nanocomposites based on modified polypropylene and clay

X‐ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)‐modified maleic‐anhydride‐grafted polypropylene/clay (PP‐g‐MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP‐g‐MA (designated as PP‐g‐HMA) and then mixing the PP‐g‐HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X‐ray diffraction data and transmission electron microscopy images of PP‐g‐HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP‐g‐HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP‐g‐HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three‐dimensional crystal growth to a two‐dimensional spherulitic growth. Mechanical properties of PP‐g‐HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP‐g‐HMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3242–3254, 2005     

Nucleation,Crystallization, and Thermal Fractionation of Poly (ε‐Caprolactone)‐Grafted‐Lignin: Effects of Grafted Chains Length and Lignin Content

Poly(ε‐caprolactone)‐grafted‐lignin (PCL‐g‐lignin) copolymers with 2 to 37 wt % lignin are employed to study the effect of lignin on the morphology, nucleation, and crystallization kinetics of PCL. Lignin displays a nucleating action on PCL chains originating an intersecting lamellar morphology. Lignin is an excellent nucleating agent for PCL at low contents (2–5 wt %) with nucleation efficiency values that are close to or >100%. This nucleating effect increases the crystallization and melting temperature of PCL under nonisothermal conditions and accelerates the overall isothermal crystallization rate of PCL. At lignin contents >18 wt %, antinucleation effects appear, that decrease crystallization and melting temperatures, reduce crystallinity degree, hinder annealing during thermal fractionation and significantly retard isothermal crystallization kinetics. The results can be explained by a competition between nucleating effects and intermolecular interactions caused by hydrogen bonding between PCL and lignin building blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1736–1750     

Thermal curing behavior of MWCNT modified vinyl ester‐polyester resin suspensions prepared with 3‐roll milling technique

This study aims to investigate the curing behavior of a vinyl ester‐polyester resin suspensions containing 0.3 wt % of multiwalled carbon nanotubes with and without amine functional groups (MWCNTs and MWCNT‐NH₂). For this purpose, various analytical techniques, including Differential Scanning Calorimetry (DSC), Fourier infrared spectroscopy (FTIR), Raman Spectroscopy, and Thermo Gravimetric Analyzer (TGA) were conducted. The resin suspensions with carbon nanotubes (CNTs) were prepared via 3‐roll milling technique. DSC measurements showed that resin suspensions containing CNTs exhibited higher heat of cure (Q), besides lower activation energy (E_a) when compared with neat resin. For the sake of simplicity of interpretation, FTIR investigations were performed on neat vinyl ester resin suspensions containing the same amount of CNTs as resin. As a result, the individual fractional conversion rates of styrene and vinyl ester were interestingly found to be altered dependent on MWCNTs and MWCNT‐NH₂. The findings obtained from RS measurements of the cured samples are highly proportional to those obtained from FTIR measurements. TGA measurements revealed that CNT modified nanocomposites have higher activation energy of degradation (E_d) compared with the cured polymer. The findings obtained revealed that CNTs with and without amine functional groups alter overall thermal curing response of the surrounding matrix resin, which may probably impart distinctive characteristics to mechanical behavior of the corresponding nanocomposites achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1511–1522, 2009     

Preparation,structure, and property of polyoxymethylene/carbon nanotubes thermal conducive composites

Polyoxymethylene (POM)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in POM, MWNTs were chemically functionalized with PEG‐substituted amine (MWNT‐g‐PEG), which exhibited strong affinity with POM due to their similar molecular structure. The thermal conductivity and the mechanical properties of the composites were investigated, which showed that the thermal conductive properties of POM were improved remarkably in the presence of MWNTs, whereas reduced by using MWNT‐g‐PEG due to the heat transport barrier of the grafted‐PEG‐substituted amine chain. A nonlinear increase of the thermal conductivity was observed with increasing MWNTs content, and the Maxwell‐Eucken model and the Agari model were used for theoretical evaluation. The relatively high effective length factor of the composite predicted with mixture equation indicated that there were few entangles of MWNTs for the samples of MWNT‐g‐PEG in the composites. The mechanical strength of the composites can be improved remarkably by using suitable content of such functionalized MWNTs, and with the increase of the aliphatic chain length of PEG‐substituted amine, the toughness of the composites can be enhanced. Transmission electron microscope result indicated that MWNT‐g‐PEG exhibited strong affinity with POM and a good dispersion of MWNTs was achieved in POM matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 905–912, 2010     

Influence of multiwall carbon nanotube on physical properties of poly(ethylene 2,6‐naphthalate) nanocomposites

Polymer nanocomposites consisting of multiwall carbon nanotube (MWCNT) and poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending process in a twin‐screw extruder. The storage modulus (G′) and loss modulus (G″) of the PEN/MWCNT nanocomposites increased with increasing frequency, and this increment being more significant at low frequency. The terminal zone slope of G′ for the PEN/MWCNT nanocomposites decreased with increasing MWCNT content, and the nonterminal behavior of those was related to the dominant nanotube–nanotube interactions at higher MWCNT content, leading to the formation of the interconnected or network‐like structures of MWCNT in the polymer nanocomposites. The decrease in the slope of the plot of log G′ versus log G″ for the PEN/MWCNT nanocomposites with increasing MWCNT content suggested the changes in the microstructures of the polymer nanocomposites by incorporating MWCNT. The incorporation of very small quantity of MWCNT significantly improved the mechanical properties of the PEN/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1062–1071, 2006     

The influence of grafted cellulose nanofibers and postextrusion annealing treatment on selected properties of poly(lactic acid) filaments for 3D printing

l ‐lactide monomers were grafted onto cellulose nanofibers (CNFs) via ring‐opening polymerization, forming poly(lactic acid) grafted cellulose nanofibers (PLA‐g‐CNFs). PLA‐g‐CNFs and pristine PLA were then blended in chloroform and dried to prepare a master batch. PLA‐g‐CNFs/PLA composite filaments targeted for 3D printing were produced by compounding the master batch in PLA matrix and melt extrusion. The as‐extruded composite filaments were subsequently thermal annealed in a conventional oven, and their morphological, thermal, and mechanical properties were evaluated. PLA was successfully grafted on the surface of CNFs as demonstrated by elemental analysis, and the concentration of grafted PLA was estimated to be 33 wt %. The grafted PLA were highly crystallized, contributing to the growth of crystalline regions of PLA matrix. The incorporation of PLA‐g‐CNFs improved storage modulus of the composite filaments in both low temperature glassy state and high temperature rubbery state. Postextrusion annealing treatment led to 28 and 63% increases for tensile modulus and strength of the filaments, respectively. Simulated Young's moduli from the Halpin‐Tsai and Krenchel models were found comparable with the experimental values. The formed composite filaments are suitable for use in 3D printing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 847–855     

Polypeptide/Multiwalled carbon nanotube hybrid complexes stabilized through noncovalent bonding interactions

In this study, we used click chemistry to synthesize new linear polypeptide‐g‐pyrene polymers from a mono‐azido‐functionalized pyrene derivative (N₃‐Py) and several poly(γ‐propargyl‐l ‐glutamate) (PPLG) oligomers. Incorporating the pyrene units as side chains enhanced the α‐helical conformations of these PPLG oligomers in the solid state, as determined using Fourier transform infrared (FTIR) spectroscopy; it also increased the temperature stability of the α‐helical secondary structures of the grafted PPLG oligomers, relative to those of the pure PPLG species, as revealed through temperature‐dependent FTIR spectroscopic analyses. In addition, the thermal properties of the PPLG‐g‐Py polypeptides (e.g., glass transition temperatures increased by ca. 100 °C) were superior to those of pure PPLG oligomers. Mixing the PPLG‐g‐Py oligomers with multiwalled carbon nanotubes (MWCNTs) in dimethylformamide led to the formation of highly dispersible PPLG‐g‐Py/MWCNT organic/inorganic hybrid complex materials. Fluorescence emission spectra revealed significant π–π stacking between the PPLG‐g‐Py oligomers and the MWCNTs in these complexes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 321–329     

Nanocomposites derived from in situ grafting of linear and hyperbranched poly(ether‐ketone)s containing flexible oxyethylene spacers onto the surface of multiwalled carbon nanotubes

Linear and hyperbranched poly(ether‐ketone)s (PEKs) containing flexible oxyethylene spacers grafted multiwalled carbon nanotube (PEK‐g‐MWNT) nanocomposites were prepared by direct Friedel‐Crafts acylation as the polymer forming and grafting reaction. To achieve the composites, in situ polycondensations of AB monomers 3‐(2‐phenoxyethoxy)benzoic acid (3‐PEBA) and 4‐(2‐phenoxyethoxy)benzoic acid (4‐PEBA), and AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid (3,5‐BPEBA) were carried out in the presence of multiwalled carbon nanotubes (MWNTs). The reaction conditions, polyphosphoric acid (PPA) with additional phosphorous phentoxide (P₂O₅) in the temperature range of 110–120 °C, were previously optimized. The conditions were used as the polymerization and grafting medium that were indeed benign not to damage MWNTs but strong enough to promote the covalent attachment of PEKs onto the surface of the electron‐deficient MWNTs. From scanning electron microscopy (SEM) and transmission electron microscopy studies, the polymers were uniformly grafted onto the MWNTs. The resultant nanocomposites are soluble in most strong acids such as trifluoroacetic acid, methanesulfonic acid, and sulfuric acid. Both isothermal and dynamic TGA studies in air showed that nanocomposites displayed improved thermo‐oxidative stability when compared with those of corresponding PEK homopolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3471–3481, 2008     

Effects of carbon nanotubes on crystallization and melting behavior of poly(L‐lactide) via DSC and TMDSC studies

In this work, multiwalled carbon nanotubes (MWNTs) were surface‐modified and grafted with poly(L ‐lactide) to obtain poly(L ‐lactide)‐grafted MWNTs (i.e. MWNTs‐g‐PLLA). Films of the PLLA/MWNTs‐g‐PLLA nanocomposites were then prepared by a solution casting method to investigate the effects of the MWNTs‐g‐PLLA on nonisothermal and isothermal melt‐crystallizations of the PLLA matrix using DSC and TMDSC. DSC data found that MWNTs significantly enhanced the nonisothermal melt‐crystallization from the melt and the cold‐crystallization rates of PLLA on the subsequent heating. Temperature‐modulated differential scanning calorimetry (TMDSC) analysis on the quenched PLLA nanocomposites found that, in addition to an exothermic cold‐crystallization peak in the range of 80–120 °C, an exothermic peak in the range of 150–165 °C, attributed to recrystallization, appeared before the main melting peak in the total and nonreversing heat flow curves. The presence of the recrystallization peak signified the ongoing process of crystal perfection and, if any, the formation of secondary crystals during the heating scan. Double melting endotherms appeared for the isothermally melt‐crystallized PLLA samples at 110 °C. TMDSC analysis found that the double lamellar thickness model, other than the melting‐recrystallization model, was responsible for the double melting peaks in PLLA nanocomposites. Polarized optical microscopy images found that the nucleation rate of PLLA was enhanced by MWNTs. TMDSC analysis found that the incorporation of MWNTs caused PLLA to decrease the heat‐capacity increase (namely, ΔC_p) and the C_p at glass transition temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1870–1881, 2007     

Preparation and properties of isobutylene–isoprene rubber–clay nanocomposites

Isobutylene isoprene rubber (IIR)‐clay nanocomposites have been prepared successfully by melt intercalation with maleic anhydride‐grafted IIR (Ma‐g‐IIR) and organophilic clay. In IIR‐clay nanocomposites, the silicate layers of the clay were exfoliated and dispersed into the monolayer. The nanocomposites exhibited greater gas barrier properties compared with those of Ma‐g‐IIR. When 15 phr clay was added, gas barrier properties were 2.5 times greater than those of Ma‐g‐IIR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1182–1188, 2006     

Semiconductive bionanocomposites of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and MWCNTs for neural growth applications

Bionanocomposites of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (P3HB3HHx) (13 % by mol of HHx) with multiwalled carbon nanotubes (MWCNTs) were prepared to obtain semiconductive nanocomposites for potential applications as scaffolds for nerve repair. The effect of the polymer/nanotube interface on the composite properties was studied using oxidized (oxi‐MWCNTs) and surface modified MWCNTs with low‐molecular weight P3HB3HHx (pol‐MWCNTs), in a ratio from 0.3 to 1.2 wt % for each type of MWCNTs employed. Morphology and conductive properties of the composites indicated a good interaction between pol‐MWCNTs and the polymer matrix. Composites with improved conductivity were obtained with only 0.3 wt % of pol‐MWCNTs added. However, agglomeration and lower conductivity was observed for samples with oxi‐MWCNTs. Cell viability studies carried out with neurospheres showed that samples with 1.2 wt % of pol‐MWCNTs are not cytotoxic and, in addition favors the neurospheres growth on the composite surface. Considering the electrical properties and biological behavior, nanocomposites of P3HB3HHx and pol‐MWCNTs are promising substrates for the regeneration of nerve tissue. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 349–360