The Effect of Clay Loading on the Morphology and Properties of Poly(styrene‐co‐butyl acrylate)/Clay Nanocomposites

This paper investigates the effect of both the clay loading and the monomer feed rate on the morphology and properties of poly(styrene‐co‐butyl acrylate)‐clay nanocomposites prepared in emulsion polymerization. Analysis by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) of the nanocomposites prepared by batch polymerization showed that the polymer clay nanocomposites (PCNs) with 1–3 wt.‐% clay loading resulted in intercalated structures, while exfoliated structures were obtained at 10 wt.‐% clay loading. The polymerization was also carried out with semi‐batch polymerization. The morphology, thermal stability, and mechanical properties of nanocomposites obtained were found to be more strongly dependent on the clay/polymer ratio than the monomer feed rate.

     

Effect of the Addition of Toluene on the Structure and Properties of Styrene‐Isoprene‐Butadiene Rubber/Montmorillonite Nanocomposites

Summary: Styrene‐isoprene‐butadiene rubber/montmorillonite nanocomposites were synthesized by the addition of toluene into clay and living anionic polymerization. These silicate layers (B‐M) were exfoliated within 30 min after polymerization initiation, whereas the layers in the nanocomposites prepared without using toluene (A‐M) were only partially exfoliated and not well‐dispersed in the matrix. The results of TEM and X‐ray diffraction revealed disperse silicates and a strong interaction between the terpolymer matrix and clay in the B‐M nanocomposites. The B‐M‐exfoliated nanocomposites exhibited higher decomposition and glass transition temperatures, storage moduli, tensile strengths and elongations at the break than those of the pure terpolymer and A‐M. With an organophilic montmorillonite (OMMT) content of 3 wt.‐%, the exfoliated nanocomposite exhibited the best thermal stability and mechanical properties. In addition, GPC and ¹H NMR results showed that the introduction of OMMT caused a slight increase in the of terpolymer, but hardly affected the microstructure of the terpolymer independent of the preparation method. Thus, the addition of toluene plays an important role in enhancing the dispersion of OMMT, which leads to the improvement of the structure and properties of the B‐M nanocomposites.

TEM image of the SIBR/MMT nanocomposite.     

Nanocomposite Formation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite as a Function of the Intercalant Type

Summary: Hydrogenated acrylonitrile butadiene rubber (HNBR) was melt compounded with montmorillonite (MMT) and organophilic modified MMTs prior to sulfur curing. In contrast to the micro‐composite formation resulting from the compounding of the HNBR and pristine MMT, the modified MMTs (i.e., octadecylamine: MMT‐ODA, octadecyltrimethylamine: MMT‐ODTMA, methyltallow‐bis(2‐hydroxyethyl) quaternary ammonium: MMT‐MTH intercalants) produced nanocomposites. It was found that the organoclay with primary amine intercalant (cf. MMT‐ODA) gave confined structures along with the exfoliated/intercalated structures. This was traced to its reactivity with the curatives. By contrast, the organoclays containing less reactive quaternary ammonium compounds (cf. MMT‐ODTMA, MMT‐MTH) were exfoliated and intercalated based on X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results. The hydroxyl functional groups of the MMT‐MTH supported the clay dispersion. The better adhesion between MMT‐MTH and HNBR was explained by hydrogen bonding between the hydroxyl groups of the intercalant and the acrylonitrile group of the HNBR matrix. This HNBR/MMT‐MTH nanocomposite showed the best mechanical properties as verified by tensile mechanical tests and dynamic mechanical thermal analysis (DMTA). The high tensile strength along with the high elongation at break for the rubber nanocomposites were attributed to the ability of the ‘clay network’ to dissipate the input energy upon uniaxial loading.

Scheme of failure development in rubber/organoclay mixes with poor (a) and good (b) dispersion of the clay layers.     

Extrusion Foaming of Poly(styrene‐co‐acrylonitrile)/Clay Nanocomposites Using Supercritical CO2

Supercritical CO₂ has been used as a blowing agent to foam poly(styrene‐co‐acrylonitrile)‐based materials in a single screw extruder specially adapted to allow fluid injection. The cellular morphology depends on foaming temperature, more regular cells being obtained with decreasing extrusion temperature. In a second step, a natural and an organomodified nanoclay have been added for the purpose of imparting some flame resistance to the foamed material. The filler efficiency in reducing sample combustion rate appeared to be dependent on its delamination level inside the matrix and better results were obtained when the organomodified clay was first delaminated in the polymer in an efficient twin screw extruder using water assistance, prior to foaming in the single screw extruder.

     

Preparation of Polystyrene/Clay Nanocomposites by Free‐Radical Polymerization in Dispersion

Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.

     

The Effect of γ‐Irradiation on the Structure and Properties of Poly(propylene)/Clay Nanocomposites

The oxidative degradation of PP/OMMT nanocomposites under γ‐irradiation was studied. Changes in structure and properties resulting from γ‐exposure in the range 0–100 kGy were investigated. The results were analyzed by comparing the influence of PP‐g‐MA and pristine OMMT on the oxidation kinetics of neat PP. γ‐Irradiation in the presence of air strongly degraded the properties of PP materials, particularly for radiation doses above 20 kGy. The rate of oxidative degradation of PP/OMMT/PP‐g‐MA nanocomposites was much faster than that of neat PP. This suggests that PP‐g‐MA and pristine OMMT components behave as oxidation catalysts, leading to the formation of free radicals in the polymer matrix.

     

Applying the Traditional Solution Melt Polymerization for the in situ Intercalation of Polyamide 6.6‐Clay Nanocomposites

The traditional PA 6.6 production route, i.e. solution melt polymerization followed by extrusion, is applied to the in situ intercalation of PA 6.6/clay nanocomposites. Organoclays of different types are tested and the derived nanocomposites are thoroughly characterized in terms of molecular weight, thermal properties and morphology. Reaction acceleration is found in the presence of fully exchanged organoclays, which is attributed to a chain extension mechanism based on clay SiOH groups. Analysis of the nanocomposites' nanostructure indicates that the applied solution melt polymerization process results in some flocculation of the tested organoclays, which is improved in some cases after extrusion and leads to partially exfoliated nanocomposites.

     

Studies on the poly(styrene‐b‐butadiene‐b‐styrene)/clay nanocomposites prepared by melt intercalation

Two types of SBS/OMMT composites are prepared by melt blending using a twin‐screw extruder. An X‐ray diffractometer indicates that polymer chains have intercalated into the gallery of the clay. It is shown in TEM photos that the thickness of the layer aggregate in the SBS1301 matrix is approximately 200 Å, but in the SBS4402 matrix the size of the filler particle is in micrometers. When SBS1301 is intermingled into SBS4402/OMMT, the particle size is reduced obviously. The tensile strength and elongation at break of the nanocomposite, SBS1301/OMMT, increase with the addition of OMMT; and when addition is 5phr, they achieve maximum. A small content of OMMT (less than 5phr) can prevent the deterioration of the mechanical properties of the SBS1301/MMT. In addition, a small content of SBS4402 (less than 20 wt %) can improve the mechanical properties of the SBS1301/OMMT composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 146–152, 2005     

Preparation and Properties of Vinylester Resin/Clay Nanocomposites

Summary: Vinylester resin matrix composites were fabricated with 1, 3, 5 and 10 wt.‐% loadings of organoclay. The composite samples were subjected to various characterization techniques like X‐ray diffraction, flexural testing, dynamic mechanical analysis, thermogravimetric analysis, and scanning electron microscopy. The clay samples as well as the clay–resin composites were investigated by X‐ray diffraction. From the shift in the peak positions and the change in d‐spacing values, it was evident that there was intercalation in the 10 wt.‐% composites, whereas exfoliation occurred in the 1, 3, and 5 wt.‐% composites. The flexural strength and the breaking energy of all the composites were decreased compared with the unfilled resin, but there was an increase in flexural modulus value by 13%. From the dynamic mechanical analysis of the 3 and the 5 wt.‐% composites, it was observed that the loss modulus value was higher in the 3 wt.‐% composites, but the glass transition temperature was slightly higher in the 5 wt.‐% composites. Thermal degradation behavior was also improved in the 5 wt.‐% composites compared with the 3 wt.‐% composites.

Fracture surface of 3 wt.‐% clay filled vinylester resin matrix composite in different magnifications.     

Effects of Characteristics of Rubber,Mixing and Vulcanization on the Structure and Properties of Rubber/Clay Nanocomposites by Melt Blending

Summary: Three rubber‐based nanocomposites, natural rubber (NR), styrene‐butadiene rubber (SBR), and ethylene‐propylene‐diene rubber (EPDM) matrixes, were prepared with octadecylamine modified fluorohectorite (OC) by melt blending. X‐ray diffraction (XRD) revealed that the SBR/OC and EPDM/OC nanocomposites exhibited a well‐ordered intercalated structure and a disordered intercalated structure, respectively. In the case of the NR/OC nanocomposite, it exhibited an intermediate intercalated and even exfoliated structure. These results were in good agreement with transmission electron microscopy (TEM) observations. Furthermore, in the NR/OC and SBR/OC systems, the mixing process played a predominant role in the formation of nanometer‐scale dispersion structure, whereas the intercalated structure of EPDM/OC formed mainly during the vulcanization process. The tensile strength of SBR/OC and EPDM/OC nanocomposites loading 10 phr OC was 4–5 times higher than the value obtained for the corresponding pure rubber vulcanizate, which could be ascribed to the slippage of the rubber molecules and the orientation of the intercalated OC. For the strain‐induced crystallization NR, the exfoliated OC efficiently improved the modulus of the NR/OC nanocomposite relative to the pure NR. However, its hindrance on NR crystallization during the tensile process may be the main reason for the decrease in tensile strength of NR/OC.

XRD diffraction patterns of three nanocomposites containing 10 phr organoclay.     

Poly(4‐methyl‐1‐pentene)/clay nanocomposites: effect of organically modified layered silicates

The preparation and properties of poly(4‐methyl‐1‐pentene) (PMP)/clay nanocomposites are reported. Melt intercalation of PMP is carried out with organoclays of different cation/charge exchange capacities and modifiers to facilitate intercalation of the polymer into the silicate layers. The effect of modifiers on the structure and properties of PMP/clay nanocomposites is explored. XRD patterns confirm the intercalation of polymer in the layered silicates as evidenced by the increase in the inter‐layer spacing which is dependent on the type of modifier used. Dynamic mechanical analysis shows increments in the storage modulus over the temperature range studied for all of the three clays, but the extent depends on the type of clay modifier used. The coefficient of thermal expansion is lower for all of the nanocomposites, as compared to the pristine polymer, indicating improved dimensional stability Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of poly(propylene)/montmorillonite nanocomposites by simultaneous grafting‐intercalation

A novel process for the preparation of poly(propylene)/montmorillonite (PP/MMT) nanocomposites was developed via simultaneous solution grafting‐intercalation in the presence of a reactive ammonium cation that can be grafted onto poly(propylene). Partially introducing this reactive cation into long alkyl ammonium modified MMT interlayers can transfer a conventional microcomposite into intercalated/exfoliated nanocomposites, which was evidenced by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The PP chains were tethered onto the clay surface through the bridge of the reactive ammonium cations, which can be characterized by FTIR. The bridged chemical bonding also results in a good interface adhesion between PP and MMT, as confirmed by SEM investigation. The enhanced thermal properties of PP/MMT nanocomposites were characterized by thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1018–1023, 2004     

Preparation of Poly(ethylene‐octene) Elastomer/Clay/Wood Flour Nanocomposites by a Melting Method

Summary: The new nanocomposites consisting of metallocene poly(ethylene‐octene) (POE), silicate clay and wood flour (WF) were prepared by means of a melt blending method. In addition, maleic anhydride grafted poly(ethylene‐octene) (POE‐g‐MAH) was studied as an alternative to POE. The samples were characterized by XRD, FT‐IR spectroscopy, DSC, TGA, SEM, and mechanical testing. Based on the consideration of thermal and mechanical properties, it was found that the clay content of 11 wt.‐% was optimal for the preparation of POE‐g‐MAH/clay nanocomposites. The POE‐g‐MAH/clay/WF hybrid could obviously improve the mechanical properties of POE‐g‐MAH/WF hybrid since the former had the smaller WF phase size (being always less than 1.5 µm), the Si? O? C bond and the nanoscale dispersion of silicate layers in the polymer matrix. The biodegradation studies showed that the mass of hybrids reduced by about the content of WF. The new POE‐g‐MAH/clay/WF nanocomposites produced from our laboratory can provide a plateau tensile strength at break when the WF content was up to 50 wt.‐%.

     

Effect of Clay Type on Structure and Properties of Poly(methyl methacrylate)/Clay Nanocomposites

Summary: PMMA nanocomposites using natural Cloisite 6A and synthetic Lucentite SPN clays were produced via melt blending. The degree of intercalation or exfoliation was measured for both composites using transmission electron microscopy (TEM) and the results were confirmed with small angle X‐ray scattering (SAXS). The smaller dimensions of the synthetic SPN, as well as the complete absence of Fe ion impurities allowed for the production of a composite which was optically clear and completely colorless. TEM and SAXS measurements were performed on samples heated to high temperatures. The data showed that in both cases large ribbons composed of the individual platelets were formed. We postulated that these ribbons formed a barrier against spreading of the flame and hence the smaller clays, which are more mobile, had a higher efficiency.

TEM image of a high degree of exfoliation of synthetic clay SPN in the PMMA matrix.     

Polymer‐Clay Nanocomposites Based on Blends of Polyamide‐6 and Polyethylene

The preparation of polyamide‐6/clay, high‐density polyethylene/clay, and high‐density polyethylene/ polyamide‐6/clay nanocomposites is considered. X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier Transform Infrared (FTIR) measurements show that the clay enhances the crystallization of the γ‐form of polyamide‐6. The clay also acts as a nucleation agent and causes a reduction of spherulitte size. Scanning electron microscopy (SEM) analysis of fracture surfaces shows that the clay reduces the PA‐6 particle size in the HDPE/PA‐6/clay nanocomposites and changes the morphology. Mechanical properties and the effect of maleated polyethylene are also reported.     

Improvement of Flex‐Fatigue Life of Carbon‐Black‐Filled Styrene‐Butadiene Rubber by Addition of Nanodispersed Clay

Summary: The flex‐fatigue life of carbon‐black‐filled SBR was dramatically improved by incorporation of 4–5 phr nanodispersed clay. Addition of clay did not decrease the degree of crosslinking of the composite but improved the hysteresis and tearing energy. ESEM observation of the flexing‐fracture morphology indicated that nanodispersed clay layers had the advantage over carbon black in that they could blunt the crack.

Effect of the clay amount on the flex fatigue life of the composites.     

Preparation and Characterization of 4,4′‐Bis(4‐aminophenoxy)diphenyl Sulfone Based Fluoropoly(ether‐imide)/Organo‐Modified Clay Nanocomposites

A series of fluoropoly(ether‐imide) (6F‐PEI), and [6F‐PEI/montmorillonite (MMT) clay) nanocomposites films were made by thermal curing of respective formulations containing fluoropoly(ether‐amic acid) (6F‐PEAA), synthesized from 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 4,4′‐bis(4‐aminophenoxy)diphenyl sulfone (p‐SED), and increasing concentration of p‐SED treated montmorillonite clay (modified MMT clay) at temperature from RT to 350 °C. These films showed excellent solvent resistance as well as very good thermal stability, and increased glass transition (T_g) values with increasing % clay. In addition, these trifluoromethyl groups‐containing nanocomposites films showed sharp lowering of coefficient of thermal expansion (CTE) by 22%. Furthermore, they exhibited increased long‐term thermo‐oxidative stability (TOS), with % weight retention in the range of 86 to 92% in isothermal heating at 300 °C for 300 h in air, reduced water absorption at 100 RH at 50 °C in the range of 0.5 to 1.15%. These data are still much lower than those of neat ULTEM® 1000 and Kapton® H film. The modulus of elasticity is on an average 38% higher for the nanocomposite films relative to neat fluoropoly(ether‐imide) (6FDA + p‐SED), and above non‐fluorinated polyimide films. The surface energy measurement by One‐Liquid and Two‐Liquid method showed a comparable trend of decreasing contact angle. For the nanocomposite films having 15% hydrophobic clay, the contact angle decreased by 21 and 20% for DI‐water and formamide, respectively. The surface energy increase was in the range of 8.21–8.54 mJ/m².

     

Synthesis and characterization of poly(glycidyl methacrylate)/Na‐montmorillonite nanocomposites

Poly(glycidyl methacrylate)/Na–montmorillonite nanocomposites were synthesized by free‐radical polymerization of glycidyl methacrylate containing dispersed montmorillonite. By changing the concentration of glycidyl methacrylate several polymer–clay nanocomposites were prepared and the resulting nanocomposites were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The results indicated that the properties of the composite were significantly improved. The thermogravimetric analysis results revealed that the degradation temperatures of nanocomposites were higher than that of pure polymer and the thermal degradation rates decreased. Examination of these materials by scanning electron microscopy showed that the clay layers are dispersed homogenously in the polymer matrix and the formation of intercalation nanostructure. Furthermore, adsorptive, moisture regain, and water uptake properties of nanocomposites were also investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1532–1538, 2004     

Isothermal crystallization of poly(ethylene‐co‐glycidyl methacrylate)/clay nanocomposites

Poly(ethylene‐co‐glycidyl methacrylate) (PEGMA)/clay nanocomposites with clay concentrations of 1, 3, or 5 wt % were prepared via y melt blending in a twin‐screw extruder. Wide‐angle X‐ray diffraction showed that the clay layers were intercalated by PEGMA. Differential scanning calorimetry was used to analyze the isothermal crystallization, and the equilibrium melting temperature was determined with the Hoffman–Weeks method. The Avrami, Tobin, Malkin, and Urbanovici–Segal models were applied to describe the kinetics of crystallization from the melt state under isothermal conditions. The crystallization kinetics showed that the addition of clay facilitated the crystallization of PEGMA, with the clay functioning as a heterophase nucleating agent; at higher concentrations, however, the physical hindrance of the clay layers to the motion of PEGMA chains retarded the crystallization process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1051–1064, 2005     

Impact,Thermal, and Morphological Properties of Poly(Lactic Acid)/Poly(Methyl Methacrylate)/Halloysite Nanotube Nanocomposites

Poly(lactic acid)/poly(methyl methacrylate) blends containing halloysite nanotube (2 and 5 phr) and epoxidized natural rubber (5–15 phr) were prepared by melt mixing. The impact strength of poly(lactic acid)/poly(methyl methacrylate) blend was slightly improved by the addition of halloysite nanotube. Adding epoxidized natural rubber further increased the impact strength of poly(lactic acid)/poly(methyl methacrylate)/halloysite nanotube nanocomposite. Single T_g of poly(lactic acid)/poly(methyl methacrylate) is observed and this indicates that poly(lactic acid)/poly(methyl methacrylate) blend is miscible. The addition of halloysite nanotube into poly(lactic acid)/poly(methyl methacrylate) slightly increased the T_g of the blends. The epoxidized natural rubber could encapsulate some of the halloysite nanotube and prevent the halloysite nanotube from breaking into shorter length tube during the melt shearing process.