Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L₁₀₀ and L₀₁₀ of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003     

Preparation of thermosetting polyurethane nanocomposites by montmorillonite modified with a novel intercalation agent

A novel thermosetting polyurethane (TSPU)/organic montmorillonite (OMMT) nanocomposite has been synthesized. N‐diamino octadecyl trimethyl ammonium chloride (DODTMAC) was used as an intercalation agent to treat Na⁺‐montmorillonite (MMT) and form a novel kind of OMMT. Fourier transform infrared spectroscopy (FT‐IR), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA) data indicated that the MMT was successfully intercalated by this intercalation agent, as evidenced by the fact that the basal spacing of MMT galleries was expanded from 1.5 to 3.2 nm. This OMMT was used to prepare the TSPU nanocomposites. Both the reinforcing and compatibilizing performance of the filler were investigated. Tensile tests showed that the tensile strength of TSPU/OMMT‐4 was the highest, and was about 3.62 times higher than that of the pure TSPU, and also the elongation at break showed an enhancement. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) measurements illustrated that the glass transition temperature of the TSPU/OMMT‐4 nanocomposite was improved from 0.5 to 6.5 °C, which corresponded to the restriction of the soft segments of TSPU. The highest initial and center temperatures of TSPU/OMMT‐4 obtained from TGA were due to the highest retard effect of the TSPU molecular chains. WAXD studies showed that the formation of the nanocomposites in all the cases with the almost disappearance of the peaks corresponding to the basal spacing of MMT. SEM and TEM were used to investigate the morphologies of the TSPU/OMMT‐4 nanocomposite, and demonstrated that the nanocomposite was comprised of a well dispersion of a mixture of intercalated and exfoliated silicate layers throughout the matrix. It was proposed that the nano‐reinforcing effect caused by the well‐dispersed silicate layers might reduce the amount and size of voids and increase the length of the crack‐spreading path during tensile drawing. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 519–531, 2007.     

Crystalline structure and thermal behavior of nylon‐10,14

The structure and morphology of a novel polyamide, nylon‐10,14, and its lamellar crystals from dilute solution were examined by transmission electron microscopy and wide‐angle X‐ray diffraction (WAXD). Both the electron‐diffraction pattern and WAXD data demonstrated that nylon‐10,14 adopts the structure of a triclinic lattice similar to that of the traditional nylon‐66 but with a corresponding increase of the c parameter to 3.23 nm. In addition, the thermal behavior of melt‐crystallized nylon‐10,14 was investigated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The glass‐transition temperature of nylon‐10,14 determined by the DMA data was 46.6°C. DSC indicated that the multiple melting behavior of isothermally crystallized nylon‐10,14 probably results from the melt and recrystallization mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1422–1427, 2003     

Dispersion and distribution of organically modified montmorillonite in nylon‐66 matrix

Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 °C. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt‐compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon‐66 matrix were characterized by X‐ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon‐66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection‐molded rectangular bar of nylon‐66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection‐molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near‐surface layers and rotated themselves about the injection‐molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon‐66 was also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1234–1243, 2003     

Study of the quiescent and shear‐induced crystallization kinetics of intercalated PTT/MMT nanocomposites

An intercalated nanocomposite made of montmorillonite nanoclay, MMT, and poly(trimethylene terephthalate), PTT, was produced by twin screw extrusion and characterized by wide angle X‐ray diffraction, WAXD, and transmission electron microscopy, TEM. The quiescent isothermal and non‐isothermal and the flow‐induced crystallization of the nanocomposite were studied by differential scanning calorimetry, DSC, polarized light optical microscopy, PLOM, and rheometry. The quiescent results showed that the nanoclay acted as an efficient nucleating agent for the PTT, which result in an anticipation of the transition temperature between regimes II and III of crystallization. The fold interfacial free energy, σ_e, of the PTT in the nanocomposite during regime III was lower than in the pure state; that is, the pure PTT developed spherulites, whereas in the nanocomposite it produced a paracrystalline morphology. Under shear rate, the total times for crystallization in the nanocomposite were higher than in the pure PTT. In flow‐induced crystallization, a fibrillar nucleus must be formed as a result of chain orientation. In the nanocomposite, chain orientation only occurred after the percolated structure was broken. Therefore, the formation of a fibrillar nucleus in the nanocomposite took more time, which increased the total crystallization time. Inc. J Polym Sci Part B: Polym Phys 48: 113–127, 2010     

Water‐assisted melt compounding of nylon‐6/pristine montmorillonite nanocomposites

An exploratory pioneering study on the fabrication of nylon‐6/montmorillonite (MMT) nanocomposites with the aid of water as an intercalating/exfoliating agent via melt compounding in a twin‐screw extruder was conducted. Commercial nylon‐6 pellets and pristine MMT powder were directly fed into the hopper of the extruder. Water was then injected into the extruder downstream. After interactions with the nylon‐6 melt/pristine MMT system, water was removed from the extruder further downstream via a venting gate. As such, no third‐component residual was left within the extrudates. Transmission electron microscopy micrographs showed that pristine MMT was uniformly dispersed in the nylon‐6 matrix. The contact time between water and the nylon‐6/pristine MMT system inside the extruder was so short that nylon‐6 was subjected to very little hydrolysis, if any. The resultant nanocomposites showed higher stiffness, superior tensile strength, and improved thermal stability in comparison with their counterparts obtained without water assistance and the nylon‐6/organic MMT nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1100–1112, 2005     

Polymorphism and crystalline transitions of the novel even–odd nylons derived from undecanedioic acid

The crystal structures of nylons X 11 under different conditions (X = 2, 4, 6, 8, 10, and 12) were investigated by wide‐angle X‐ray diffraction (WAXD) and electron diffraction (ED). Both the solution‐ and melt‐crystallized samples of nylon 2 11 possess the hexagonal lattice (named γ‐form). Nylons 4 11 and 6 11 exhibit the monoclinic unit cell (termed as α‐like form) for both samples characteristic of two strong diffractions at 0.44 and 0.38 nm. For nylons 8 11, 10 11, and 12 11, the α‐like form are obtained for the solution‐crystallized samples while the β‐like ones are obtained in the case of the melt‐crystallized ones, with typical strong diffractions at 0.42 and 0.40 nm. The quenched nylon 12 11 samples annealing at different temperatures were also studied in this work to illustrate the various crystal forms obtained under different conditions. During the heating process, the α‐like forms of the solution‐crystallized samples for nylons 8 11, 10 11, and 12 11 transform into the high‐temperature hexagonal phases prior to melting, while those of nylons 4 11 and 6 11 did not show such transformations before melting. Variable‐temperature Fourier transform infrared spectroscopy was applied to investigate the crystalline transition phenomena and illustrate their essential features in the molecular level. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2048–2060, 2005     

Viscoelastic characteristics of plasticized cellulose nanocomposites

The plasticization effects of cellulose diacetate composite systems including nanoparticles (montmorillonite, MMT) and plasticizers(diethyl phthalate, DEP) were investigated by the time–temperature superposition technique and viscoelastic modeling. Exhibiting the highest modulus value in the glass state, the viscoelastic modulus of the MMT nanocomposite rapidly decreased above the glass‐transition temperature (T_g). The Arrhenius‐type activation energy of pristine cellulose acetate showed the lowest value of activation energy and both DEP‐plasticized and MMT‐reinforced systems exhibited increased values of activation energy. Although the free volume fraction at the T_g decreased with the plasticizer content, it increased with the incorporation of MMT, seemingly preventing the polymer chains from being arranged in an ordered structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 59–65, 2005     

Poly(styrene‐b‐tetrahydrofuran)/clay nanocomposites by mechanistic transformation

Synthesis of poly(styrene‐block‐tetrahydrofuran) (PSt‐b‐PTHF) block copolymer on the surfaces of intercalated and exfoliated silicate (clay) layers by mechanistic transformation was described. First, the polystyrene/montmorillonite (PSt/MMT) nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Then, the PSt‐b‐PTHF/MMT nanocomposite was prepared by mechanistic transformation from ATRP to cationic ring opening polymerization (CROP). The TGA thermogram of the PSt‐b‐PTHF/MMT nanocomposite has two decomposition stages corresponding to PTHF and PSt segments. All nanocomposites exhibit enhanced thermal stabilities compared with the virgin polymer segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2190–2197, 2009     

Morphology and structure of nylon‐2,14 single crystals from dilute solution

A perfect single crystal of nylon‐2,14 was prepared from 0.02% (w/v) 1,4‐butanediol solution by a “self‐seeding” technique and isothermal crystallization at 120 and 145 °C. The morphology and structure features were examined by transmission electron microscopy with both image and diffraction modes, atomic force microscopy, and wide‐angle X‐ray diffraction (WAXD). The nylon‐2,14 single crystal grown from 1,4‐butanediol at 145 °C inhabited a lathlike shape with a lamellar thickness of about 9 nm. Electron diffraction and WAXD data indicated that nylon‐2,14 crystallized in a triclinic system with lattice dimensions a = 0.49 nm, b = 0.51 nm, c = 2.23 nm, α = 60.4°, β = 77°, and γ = 59°. The crystal structure is different from that of nylon‐6,6 but similar to that of other members of nylon‐2Y. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1913–1918, 2002     

Grafting of polymer matrix to exfoliated montmorillonite nanoplatelets in nanocomposite film cast from soap‐free emulsion polymerized latex and its fortified mechanical properties

Poly(methyl acrylate‐co‐methyl methacrylate) [P(MA‐co‐MMA)] nanocomposite film containing 1 wt % of montmorillonite (MMT) exhibited unusual higher ductility, higher strain recovery ratio after creep, and higher modulus and strength compared to neat P(MA‐co‐MMA) as they were cast from their individual latices fabricated by soap‐free emulsion polymerization. The fortified mechanical properties were attributed to the MgO components of exfoliated MMT nanoplatelets being grafted by P(MA‐co‐MMA) chains as verified by FTIR and XPS spectroscopies, which to the best of our knowledge is the first time in the literature providing the direct evidence for the polymer chains grafting onto the exfoliated MMT. TEM investigation of the stretched nanocomposite film revealed that the microcracks in the nanocomposite film appeared mainly in the bulk region of polymer matrix, implying that the interfacial strength between P(MA‐co‐MMA) and its grafted MMT nanoplatelets was higher than the cohesion strength of P(MA‐co‐MMA). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5891–5897, 2009     

Revisit to the formation mechanism of exfoliated montmorillonite/PMMA nanocomposite latex through soap‐free emulsion polymerization

Soap‐free emulsion polymerization of methyl methacrylate (MMA) in the aqueous suspension of montmorillonite (MMT) was able to fabricate the exfoliated MMT/PMMA nanocomposite latex. Because neither MMA nor substantial quantity of potassium persulfide (KPS) initiator could be individually absorbed into the interlayer region of MMT, the polymerizing ionic radicals in water phase were considered as a major component to diffuse into the gallery of MMT. They have been observed to organize into disk‐like micelles in the interlayer regions to exfoliate MMT. The diffusion of the polymerizing ionic radicals was further supported by using sodium dodecyl sulfate (SDS) surfactant as a model compound to diffuse into the gallery of MMT. The exfoliation of MMT was almost completed before micellization stage was over. After exfoliation, the disk‐like micelles became a polymerization loci for monomers. Because the disk‐like micelles in numbers were substantially over the commonly formed spherical micelles in the typical soap‐free emulsion polymerization, the conversion rate of MMA to MMT/PMMA nanocomposite latex was faster. Based on the above experimental observation, a justified exfoliation mechanism of MMT was proposed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 459–466, 2009     

Impact fracture toughness of polyamide‐6/montmorillonite nanocomposites toughened with a maleated styrene/ethylene butylene/styrene elastomer

Polyamide‐6 (PA6)/montmorillonite (MMT) nanocomposites toughened with maleated styrene/ethylene butylene/styrene (SEBS‐g‐MA) were prepared via melt compounding. Before melt intercalation, MMT was treated with an organic surfactant agent. Tensile and impact tests revealed that the PA6/4% MMT nanocomposite fractured in a brittle mode. The effects of SEBS‐g‐MA addition on the static tensile and impact properties of PA6/4% MMT were investigated. The results showed that the SEBS‐g‐MA addition improved the tensile ductility and impact strength of the PA6/4% MMT nanocomposite at the expenses of its tensile strength and stiffness. Accordingly, elastomer toughening represents an attractive route to novel characteristics for brittle clay‐reinforced polymer nanocomposites. The essential work of fracture (EWF) approach under impact drop‐weight conditions was used to evaluate the impact fracture toughness of nanocomposites toughened with an elastomer. Impact EWF measurements indicated that the SEBS‐g‐MA addition increased the fracture toughness of the PA6/4% MMT nanocomposite. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 585–595, 2005     

Effect of MMT,SiO2, CaCO3, and PTFE nanoparticles on the morphology and crystallization of poly(vinylidene fluoride)

The crystallization and melting behaviors of poly (vinylidene fluoride) (PVDF) with small amount of nanoparticles (1 wt %), such as montmorillonite (MMT), SiO₂, CaCO₃, or polytetrafluoroethylene (PTFE), directly prepared by melt‐mixing method were investigated by scanning electron microscopy (SEM), polarizing optical microscopy, Fourier transform infrared spectroscopy, wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The nanoparticle structure and the interactions between PVDF molecule and nanoparticle surface predominated the crystallization behavior and morphology of the PVDF. Small amount addition of these four types of nanoparticles would not affect the original crystalline phase obtained in the neat PVDF sample (α phase), but accelerated the crystallization rate because of the nucleation effect. In these four blend systems, MMT or PTFE nanoparticles could be well applied for PVDF nanocomposite preparation because of stronger interactions between particle surface and PVDF molecules. The nucleation enhancement and the growth rate of the spherulites were decreased in the order SiO₂ > CaCO₃ > PTFE > MMT. The melting and recrystallization of PVDF was found in MMT addition sample, because of the special ways of ordering of the PVDF chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Suppressed molecular orientation in nylon 6/clay nanocomposite at large strain: Role of microvoiding

A micro‐FTIR measurement has been conducted to explore the molecular orientation of amorphous phase in the nylon 6/clay nanocomposite at large strain. Our results indicate that the molecular orientation in such a nanocomposite during stretching is lower than that observed for the pure nylon 6 counterpart, which is further evidenced by the true stress‐strain dependence. The relaxation of the molecular network, resulted from the destruction of γ‐crystals in part and mostly from microvoding (demonstrated by volume dilatation and 2D‐SAXS measurements), should be responsible for the suppressed molecular orientation in the nylon 6/clay nanocomposite. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 514–519, 2010     

Morphology and permeability of exfoliated PVAc‐MMT nanocomposite films cast from soap‐free emulsion‐polymerized latices

In this study, we exclusively found that the exfoliated poly(vinyl acetate)‐montmorillonite (PVAc‐MMT) nanocomposite latices could be straightforwardly fabricated by soap‐free emulsion polymerization and cast into a film. The as‐fabricated films were transparent with the exfoliated MMT nanoplatelets in flat form uniformly dispersed in the PVAc matrix. Certain bonding of PVAc matrix to the exfoliated MMT nanoplatlets refrained it from removal by acetone in Soxhlet extraction. Exfoliated MMT nanoplatlets (10 wt %) in the film was able to reduce the water vapor permeability coefficient to only 9% that of the neat PVAc. According to the generalized Nielsen's permeability model for the composites containing impermeable fillers in sheet form, the average aspect ratio of exfoliated MMT platelets was calculated as 327, similar to those directly estimated by atomic force microscopy and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5583–5589, 2007     

Synthesis of polybenzoxazine/clay nanocomposites by in situ thermal ring‐opening polymerization using intercalated monomer

A new class of polybenzoxazine/montmorillonite (PBz/MMT) nanocomposites has been prepared by the in situ polymerization of the typical fluid benzoxazine monomer, 3‐pentyl‐5‐ol‐3,4‐dihydro‐1,3‐benzoxazine, with intercalated benzoxazine MMT clay. A pyridine‐substituted benzoxazine was first synthesized and quaternized by 11‐bromo‐1‐undecanol and then used for ion exchange reaction with sodium ions in MMT to obtain intercalated benzoxazine clay. Finally, this organomodified clay was dispersed in the fluid benzoxazine monomers at different loading degrees to conduct the in situ thermal ring‐opening polymerization. Polymerization through the interlayer galleries of the clay led to the PBz/MMT nanocomposite formation. The morphologies of the nanocomposites were investigated by both X‐ray diffraction and transmission electron microscopic techniques, which suggested the partially exfoliated/intercalated structures in the PBz matrix. Results of thermogravimetric analysis confirmed that the thermal stability and char yield of PBz nanocomposites increased with the increase of clay content. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Unique photoactive nanocomposites based on rhodamine 6G/polymer/montmorillonite hybrid systems

An organo‐montmorillonite (MMT) complex [poly‐diallyldimethyl(PDDA)‐Kunipia F] with various loadings of polycation was modified with a laser dye Rhodamine 6G (R6G) to obtain a photofunctional hybrid materials for monitoring of dye‐polymer‐MMT nanocomposite interactions. The polymer‐MMTs were prepared in a colloidal state via ion‐exchange reaction. The content of polycation (PDDA) in suspensions varied from 20 mg to 1000 mg per 1 g of Kunipia F (KF) MMT. Dramatic changes was observed in the structure of PPDA‐MMT containing 200–300 mg of polymer per 1 g of KF, which was the saturation point of the polycation for this system. The PDDA molecules were able to suppress the formation of nonluminescent H‐aggregates and to enhance the overall luminescence properties. The PDDA/MMT nanocomposite systems are the novel ones that have not been studied before in order to prepare highly fluorescence hybrid systems. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2013 , 51, 1672–1679     

The influence of interlayer cations on the photo‐oxidative degradation of polyethylene/montmorillonite composites

The photo‐oxidative degradation of polyethylene/montmorillonite (PE/MMT) nanocomposite and microcomposite has been investigated. It has been found that the rate of photo‐oxidative degradation of PE/MMT nanocomposite and PE/Mⁿ⁺MMT (where Mⁿ⁺ stands for multivalent transition metal cation) microcomposites is much faster than that of pure PE. For the PE/MMT nanocomposite, the acceleration of photo‐oxidative degradation is due to the influence of MMT and ammonium ion, in which the influence of ammonium is primary. The decomposition of ammonium ion may create acidic sites on layered silicates; meanwhile, the complex crystallographic structure and habit of clay minerals could also result in some active sites. The reversible photo‐redox reaction of transition metal cations has a catalytic effect in the degradation of the polymer matrix. All these catalytic active sites can accept single electrons from donor molecules of polymer matrix and induce the formation of free radical upon UV irradiation. The generation of free radical leads to the oxidization and break of molecular chain. Thus, the materials suffer degradation and their mechanical strength decreases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3006–3012, 2004     

Morphological characterization of nylon‐6 nanocomposite following a large‐scale simple shear process

A commercial grade nylon‐6/clay nanocomposite (from Ube industries) is subjected to a large‐scale simple shear orientation process and the resulting morphology is investigated. Both the orientation and aspect ratio of nanoclays, which can be altered by the simple shear process, are studied. The incorporation of well‐dispersed nanoclays into the nylon matrix greatly reduces the nylon chain mobility as well as the percent crystallinity. Two types of lamellar orientation have been found, as revealed by small‐angle X‐ray scattering. One type of lamellae is oriented ～41° away from the clay surface, whereas the simple shear process induces another weakly preferred lamellar orientation nearly perpendicular to the clay surface. The formation of the above lamellar orientations appears to be related to both orientation of the clay in the nanocomposite and the simple shear process. The possible molecular mechanisms leading to the final morphology of the nylon‐6/clay nanocomposite is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3555–3566, 2005