Exfoliated Structure Research Articles

A polymeric flame retardant and surfactant‐free montmorillonite nanocomposites: Preparation and exfoliation mechanism discussion

A polymeric flame retardant (PDEPD) and various amounts of sodium montmorillonite (Na‐MMT) nanocomposites with exfoliation structure were prepared via one‐step polycondensation, attempting to prepare flame‐retardant nanocomposites. The nanocomposites exhibited high thermal stability at high temperature. Based on several comparative studies, we investigated and proposed the possible exfoliation mechanism of Na‐MMT in PDEPD substrate. The microscale combustion calorimeter and cone calorimeter results showed the PDEPD/Na‐MMT nanocomposites could significantly improve the flame retardancy of polystyrene and polyurethane elastomer (TPU), especially the TPU matrix. This study provides new viewpoint for preparing flame‐retardant nanocomposites without surfactants. POLYM. COMPOS., 35:167–173, 2014. © 2013 Society of Plastics Engineers

Nanoclay Gel for Poly(lactic Acid)/Clay Nanocomposite

Nanoclay gel was prepared using organoclay swollen and dispersed in agar which is the hydrocolloid. Bentonite clay was used for preparation of organoclay with quaternary ammonium salt by cationic exchange method. The organoclays loadings in nanoclay gel were 10, 20, 30, 40 and 50 wt%. Results on X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed exfoliation structure and well dispersing developed. Moreover, the application of nanoclay gel as reinforcing filler in polylactic acid (PLA) prepared with melt extrusion process at 1, 3, 5, 7 and 10 wt%, respectively. The tensile properties and morphologies were observed. The tensile strength and the elongation at break increased with increasing the clay content up to 3 wt% and then slightly decreased at higher clay content. The modulus increased with increasing clay loading. The high degree of dispersion PLA/clay nanocomposites were observed with SEM micrographs.

Effects of dihydrogen phosphate intercalated layered double hydroxides on the crystal behaviors and flammability of polypropylene

ABSTRACTMg‐Al‐H2PO4– layered double hydroxides (LDHs) was prepared by anion exchange method, and polypropylene (PP)‐LDH composites were prepared by melt compounding. The dispersion of LDH in PP matrix was characterized by Transmission electron microscope and X‐ray diffraction (XRD), and the results showed that both exfoliation structures and aggregation structures can be found in the composites. The effects of LDH on the crystal behaviors of PP was investigated by XRD and Differential scanning calorimetry (DSC), and it indicated that LDH can induce the formation of β crystal and serve as a heterogeneous nucleating agent in PP. The significant decrease of both the crystallization and the melting enthalpy (ΔHc and ΔHm) was observed in PP composite at the presence of LDH platelets. Both the peak heat release rate and total heat release (THR) were significantly decreased after the addition of treated LDH. The possible chemical structural change in the condensed phase of PP composite during heating was studied by Fourier transform infrared spectroscopy (FT‐IR). The mechanism of modified LDH in improving the fire performance of PP and the possible relationship between flame retardancy and crystal behavior have been proposed and discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3645–3651, 2013

UV curable transparent urethane-acrylate/clay nanocomposite coating materials with thermal barrier property

The incorporation of organically modified montmorillonite (MMT) as thermal barriers into an UV curable urethane-acrylate based resin system was attempted to prepare nanocomposite coating materials with improved thermal barrier property using a two-step solution mixing process. The prepared nanocomposite sols were deposited on glass substrates using a bar coating method, and cured under radiation. We explored the correlation between the mixing time in association with shear stress imposed on clay agglomerates, and the resulting nanostructured morphology including the degree of exfoliation and dispersion state of the clay in the prepared nanocomposites. The effects of the nanoclay loading level on the properties and morphology of the nanocomposites were also investigated. As a result, it was revealed that with an appropriate level of clay loading at 5wt.% and shear stress, high degree of intercalation and exfoliation structure with homogeneous clay dispersion in the matrix could be achieved, and for the nanocomposite-coated glass, the thermal barrier performance was noticeably enhanced by 72% over that of non-coated glass, while exhibiting fairly good optical transparency with light transmittance over 80%. In addition, the thermal stability and dynamic mechanical properties of the nanocomposites were also improved. It can be anticipated that a novel method for preparing the UV curable nanocomposite coatings on glass, which is presented in this study, will be utilized to fabricate the thermally insulated transparent window system.

Bio‐based polymer nanocomposites based on layered silicates having a reactive and renewable intercalant

ABSTRACTSoybean oil‐based polymer nanocomposites were synthesized from acrylated epoxidized soybean oil (AESO) combined with styrene monomer and montmorillonite (MMT) clay by using in situ free radical polymerization reaction. Special attention was paid to the modification of MMT clay, which was carried out by methacryl‐functionalized and quaternized derivative of methyl oleate intercalant. It was synthesized from olive oil triglyceride, as a renewable intercalant. The resultant nanocomposites were characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of increased nanofiller loading in thermal and mechanical properties of the nanocomposites was investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The nanocomposites exhibited improved thermal and dynamic mechanical properties compared with neat acrylated epoxidized soybean oil based polymer matrix. The desired exfoliated nanocomposite structure was achieved when the OrgMMT loading was 1 and 2 wt % whereas partially exfoliated nanocomposite was obtained in 3 wt % loading. It was found that about 400 and 500% increments in storage modulus at glass transition and rubbery regions, respectively were achieved at 2 wt % clay loading compared to neat polymer matrix while the lowest thermal degradation rate was gained by introducing 3 wt % clay loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2031–2041, 2013

Synthesis of polymer–clay nanocomposites of some vinyl monomers by surface-initiated atom transfer radical polymerization

The surface of Cloisite 30 B clay was treated with bromopropionyl bromide to form the clay Br-ended initiator needed for surface-initiated atom transfer radical polymerization (SI-ATRP). Several homo- and co-(SI-ATRP) polymerizations were conducted on the cured surface of the Cloisite 30 B clay using vinyl monomers, such as methyl methacrylate, styrene (St), and 2-(dimethylaminoethyl) methacrylate, along with the ligands 2,2′-bipyridine (bpy) and 1,1,4,7,10,10-hexamethyltriethylene tetraamine, and CuBr, as a catalyst. These grafted polymer–clay nanocomposites were characterized by X-ray diffraction, Thermal gravimetric analysis, differential scanning calorimetry, and Transmission electron microscopy. Most of the prepared nanocomposites displayed semi-exfoliated to exfoliated structures.

Study on novel exfoliated polyampholyte nanocomposite hydrogels based on acrylic monomers and Mg–Al–Cl layered double hydroxide: Synthesis and characterization

Novel exfoliated polyampholyte nanocomposite hydrogels (NH-LDHs) based on acrylic acid (AA), 2-(diethylamino) ethyl methacrylate (2-DEAEMA), N,N-methylenebisacrylamide (NMBA) and layered double hydroxide (Mg–Al–Cl LDH) were synthesized using an in situ free radical addition polymerization method in aqueous media. First, Mg–Al–Cl LDH with a highly crystalline structure was prepared and characterized using FTIR, XRD, TGA and SEM analyses. The formation of NH-LDHs was confirmed by FTIR and XRD analyses. The morphological structure and select properties, such as the thermal, swelling and mechanical properties, of the NH-LDHs were also investigated. NH-LDHs have an exfoliated structure and smooth and nonporous surface morphologies. They can also be used as thermally stable nanocomposite hydrogels. The results revealed that adding a small amount of exfoliated Mg–Al–Cl LDH could effectively increase the compressive modulus of the polyampholyte gels. When the Mg–Al–Cl LDH was incorporated into the polyampholyte hydrogel matrix, two synergic effects, additional co-crosslinking and additional hydrophilicity, occur in the swelling behaviors of the gels. All NH-LDHs are sensitive to pH, and they have zwitterion characteristics at pH 5.5. It was concluded that the NH-LDHs synthesized in this study might be used as alternative water absorbents in solutions with different pH. The diffusion of water into the NH-LDHs gel systems in deionized water at room temperature is assumed to be a non-Fickian behavior.

Removal of methylene blue from aqueous solution by sorption on lignocellulose-g-poly(acrylic acid)/montmorillonite three-dimensional cross-linked polymeric network hydrogels

Batch lignocellulose-g-poly(acrylic acid)/montmorillonite (LNC-g-PAA/MMT) hydrogel nanocomposites were applied as adsorbents. The nanocomposites were characterized by FTIR, XRD, SEM, and TEM. The results showed that montmorillonite (MMT) could react with the monomers and change the structure of polymeric network of the traditional superabsorbent materials, an exfoliated structure was formed in the nanocomposites. The effect of process parameters such as MMT content (wt%), contact time (t), initial concentration of dye solution (C0), adsorption temperature (T), and pH value (pH) of the dye solution for the removal of methylene blue (MB) from aqueous solution were also studied. The results showed that the adsorption capacity for MB increased with increasing contact time, initial dye concentration, and pH value, but decreased with increasing MMT content and temperature. The adsorption kinetics were better described by the pseudo-second-order equation, and their adsorption isotherms were better fitted for the langmuir equation. By introducing 20 wt% MMT into LNC-g-PAA polymeric network, the obtaining hydrogel composite showed the high adsorption capacity 1994.38 mg/g and economic advantage for MB. The desorption studies revealed that the composite provided the potential for regeneration and reuse after MB dye adsorption, which implied that the composite could be regarded as a potential adsorbent for cationic dye MB removal in a wastewater treatment process.

Preparation and Properties of Clay-Reinforced Epoxy Nanocomposites

The clay-reinforced epoxy nanocomposite was prepared by the polymerization method. The effect of clay addition on the mechanical properties of epoxy/clay nanocomposites was studied through tensile, flexural, impact strength, and fracture toughness tests. The morphology and tribology behavior of epoxy/clay nanocomposites were determined by X-ray diffraction (XRD) and wear test, respectively. The wear test was performed to determine the specific abrasion of the nanocomposites. In addition, the water absorption characteristic of the nanocomposites was also investigated in this study. XRD analysis indicated that the exfoliation structure was observed in the epoxy nanocomposites with 3 wt% of clay, while the intercalated structure was shown at 6 wt% of clay. It was found that the addition of clay up to 3 wt% increased the tensile strength, flexural strength, impact strength, and the fracture toughness. On the contrary, the presence of above 3 wt% of clay produced a reverse effect. It could be concluded that the best properties in mechanical, wear resistance, and water resistance were obtained for the epoxy nanocomposites containing 3 wt% of clay.

Nanoparticle size and water diffusivity in nanocomposite agro-polymer based films

Nanocomposite films were prepared by a thermo-mechanical process from wheat gluten (WG) and unmodified montmorillonite (MMT). The present work aims at predicting the relationships between the decrease in relative diffusivity of liquid water and the structure of the nanocomposite films, from in situ evaluation of the MMT size aspect ratio and volume fraction, and by using a simple tortuous path mathematical model. The modelling approach first allowed predicting and validating the tortuosity effect of MMT particles on liquid water transport properties of WG-based films. In spite of a well-exfoliated nanocomposite structure, the liquid water diffusivity in WG-based films can at best be decreased by a factor of 2 with this type of clay nanoparticle, which was in agreement with the Bharadwaj model predictions. This study underlines the necessity to achieve a totally exfoliated nanocomposite structure, and above all, to select layered silicates displaying higher size aspect ratio values in order to efficiently improve water barrier properties of WG-based nanocomposite films. Furthermore, the extremely complex structure of nanocomposite materials makes detailed morphological studies often difficult, time and cost consuming.

Morphology control of nanofillers in poly (phenylene sulfide): A novel method to realize the exfoliation of nanoclay by SiO2 via melt shear flow

We for the first time report a novel method to achieve the morphology control of two kinds of dimensional different nanofillers, the platelike nanoclay and globelike SiO2, by using their “filler to filler” interaction in poly (phenylene sulfide) (PPS). The strong interaction between layered nanoclay and rigid SiO2 is obtained by their different response to shear flow in PPS melt processing. As a result, the exfoliation structure of nanoclay and well-dispersed nano-SiO2 are realized simultaneously. With this successful morphology control, the reinforcement effect of nanofillers in PPS is improved with very little addition. Moreover, with the restriction of exfoliated clay and nano-SiO2 particles, the mobility of PPS molecular chains is confined, leading to the significant change in crystalline behaviors of PPS.

Organophilic bentonites based on Argentinean and Brazilian bentonites: part 2: potential evaluation to obtain nanocomposites

This work describes the preparation of composites of polypropylene and organophilic bentonites based on Brazilian and Argentinean bentonites. During the processing of the samples in a twin screw microextruder, torque and pressures of the extruder were accompanied and the viscosity values were calculated. No significant changes in the torque, pressure and viscosity were found for composites prepared with different bentonites. The samples were characterized by XRD and TEM to evaluate the structure and dispersion of the organophilic bentonites. Composites with exfoliated, partially exfoliated and intercalated structures were obtained and correlations between the intrinsic properties of the sodium clays and organophilic bentonites and their influence on the composites were studied. The cation exchange capacity of the sodium bentonites and the swelling capacity of the organophilic bentonites were the most important properties to obtain exfoliated structures in composites. All bentonites showed the potential to obtain polymer nanocomposites, but the ones from Argentina displayed the best results.

Properties of Thermal Conductivity on Polyimide/Clay Nanocomposite Foams

We synthesized polyimide (based on ODA-PMDA) and polyimide foam and polyimide/clay foam that pore size was uniform about 1㎛. We identified that the clay layers are well dispersed in polyimide matrix and achieved exfoliation structure by X-ray diffraction. And we compared thermal conductivity of PI, PI foam, PI/clay foam. Thermal conductivity decreased up to maximum 28 % by introducing both pores and clay layers. Exfoliated structure of clay leads to decrease of thermal conductivity by thermal barrier effect. Also, the presence of clay could considerably reinforce the poor mechanical properties of polyimide by foam because of interfacial interaction between clay layers and polymer matrix. Through the this results, it has shown that this study may provide an effective method to prepare polymer/clay nanocomposite foams having exfoliation structure, and can be used as insulating material having low thermal conductivity.

Study on Organic Montmorillonite Modified Recycled Optical-Grade Polycarbonate Nanocomposite

Optical–grade polycarbonate (PC) was separated from optical disks by a chemical approach and used to prepare nanocomposite to make full use of the wasted polymers. A quaternary ammonium-modified montmorillonite (organic montmorillonite, OMMT) was chosen as a modifier and an auxiliary functional resin (CBT160) was utilized to exfoliate the layers of montmorillonite. The characterization results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) for PC/ OMMT (5wt %) revealed that an exfoliation structure of the nanocomposite was obtained. The mechanical measurements show a great increase in tensile strength and Izod impact strength of PC/ OMMT nanocomposite compared with the recycled optical–grade PC.

Thermogravimetric Analysis of OMMT Filled HDPE/EPDM Treated EB Irradiation

In the current study, high density polyethylene (HDPE)/ ethylene propylene diene monomer (EPDM) blend and organophilic montmorillonite (OMMT) filled HDPE/EPDM was develop aiming at enhancing the thermal properties. Maleic anhydride polyethylene (MAPE) agent and electron beam (EB) irradiation technique were applied as HDPE/EPDM blend and OMMT filled HDPE/EPDM treatments. HDPE/EPDM blend and OMMT filled HDPE/EPDM were first prepared via melt intercalation technique at 4 vol% OMMT loading. For EB irradiation technique, the absorbed dose was set at 100 kGy. The effectiveness of these surface modification treatments were compared with control one (no surface modification) and analyzed based on the thermal test as well as transmission electron microscope (TEM). It was found that the thermal properties of both HDPE/EPDM blend and OMMT filled HDPE/EPDM were significantly enhanced by EB irradiation technique as compared to the control and MAPE systems. Transmission electron microscope (TEM) illustrated the mixed intercalated and partial exfoliated structures of OMMT filled HDPE/EPDM with EB irradiation technique.

A surface analysis of polypropylene/clay nanocomposites exposed to electron irradiation

AbstractThe effects of electron irradiation in air at various doses on surface chemical composition of nanofilled polypropylene were explored by X‐ray photoelectron spectroscopy. An organically modified nanoclay ingredient along with a functional compatibilizer was employed for this purpose. The nanocomposite formation was confirmed by means of transmission electron microscopy, where in presence of compatibilizer, an exfoliated structure was brought about. Medium irradiation dose was established to be considerably effective in raising surface oxygen content, while at very high electron beam fluence, the ablation (etching) predominated. The optimal electron beam intensity was also found with respect to the extent of the functionalization. Various moieties of ether, ester, and alcohol characteristics were produced after exposure which could act as functional, active precursors being suitable for subsequent functionalization reactions. Furthermore, it could be understood that the electron irradiation spur organoclay migration toward surface layers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation of poly(butylene terephthalate)/modified organoclay nanocomposite via in-situ polymerization

Nanocomposites of poly(butylene terephthalate) (PBT)/modified montmorillonite organoclay were prepared via in-situ polymerization of terephthalic acid and butanediol in the presence of different clay content. Cloisite 30B, a commercially available amino modified montmorillonite, was modified with 3-aminopropytriethoxysilane (APS) through a silylation reaction. Morphology and properties of all samples were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1HNMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The extent of clay layers in samples was confirmed by XRD. Results of XRD and TEM showed that an exfoliation structure was produced in nanocomposites. Studies of crystallization showed that the presence of nanoclay leads to an increase in the crystallization rate and enhances the thermal stability of nanocomposites. Crystallization kinetics were described by the Avrami equation. Crystal growth was spherulitic. According to dynamic mechanical analysis (DMA), storage modulus of nanocomposites was remarkably improved compared with homo PBT. Moreover, a shrinkage test was carried out. Results showed a reduction in shrinkages along and across the flow direction that means a decrease in free volume. Flammability based on the UL-94 test was applied to study the flame retardancy effect of nanoclay on the samples.

Solid‐state graft polymerization of styrene in spherical polypropylene particles in the presence of montmorillonite

AbstractIn this work, cetyltrimethyl ammonium bromide and methacryloyloxyethyhrimethyl ammonium chloride were used to prepare organophilic montmorillonite (O‐MMT). Then, polypropylene (PP)–clay nanocomposites were prepared by the in situ grafting polymerization of styrene (St)‐containing O‐MMT onto PP with tert‐butyl perbenzoate as an initiator in the solid state. Fourier transform infrared spectroscopy, gel permeation chromatography, transmission electron microscopy, and X‐ray diffraction were applied to study the structure of the layered silicate and modified PP. The surfaces of the composites and, thus, the distribution of the clay in the PP matrix were characterized by scanning electron microscopy. The rheology and mechanical properties were studied and are discussed. According to the characterization results, OMMT and St were already grafted onto the PP main chain. Also, the intercalated structure of montmorillonite could be stabilized, and a stable exfoliated structure could be attained. Namely, intercalated PP/OMMT nanocomposites were obtained. The rheological results clearly show that these PP/OMMT nanocomposites had long‐chain‐branched structures. The peroxide modification of PP had minor effects on the tensile and bending strengths of the modified PP; however, this modification resulted in a significant reduction in the impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Performance evaluation of linear and nonlinear nanocomposite modified asphalts

Polymeric nanocomposites have been widely acknowledged recently. In this study, the effects of nanoclay on two grades of styrene–butadiene–styrene (SBS) modified asphalts, linear and branch, have been investigated. The physical, mechanical and rheological properties of original binder, polymer modified asphalts and nanocomposite modified asphalts have been studied and compared. The results have shown that nanoclay can improve the physical properties, rheological behaviors and the storage stability of the polymeric asphalts. Linear SBS-nanocomposite modified asphalt may form an exfoliated structure, whereas the Branch SBS-nanocomposite modified asphalt may form an intercalated structure, based on the X-ray diffraction (XRD) results.

Study of the Mechanical and Dynamic Mechanical Properties of Polypropylene/Talc/Nanoclay Ternary Nanocomposites

Inorganic micro and nano fillers such as talc and nanoclay are used to improve various properties of polypropylene (PP). In general, the use of inorganic fillers affects the mechanical, rheological and service temperature of the matrix. In recent years, the simultaneous use of nano and micro fillers and investigation of the effect of these hybrid systems on various properties of the composite has gained the attention of many scientists. In this work, ternary nanocomposites, PP/talc/nanoclay, were prepared via melt compounding of the ingredients in a twin-screw extruder. The dispersion status of the fillers was followed by XRD and TEM techniques. The mechanical and dynamic mechanical properties of the composites were investigated in comparison to the binary composites (PP/talc and PP/nanoclay). The results showed that in ternary nanocomposites, the nanoclay was better exfoliated than that of PP/nanoclay composite. This could be due to higher matrix viscosity as the result of the presence of talc, which provides a balance between shear stress and molecular diffusion. As a result of this better exfoliated structure, a substantial increase in modulus, yield stress and other mechanical and dynamic mechanical properties was achieved in PP/talc/nanoclay nanocomposites.