Silicate layer dispersion in copolymer/clay nanocomposites

Factors of silicate layer dispersions in polymers have been studied with copolymers. The influence of the copolymerization ratio of copolymers and the alkyl chain lengths of organomodified reagents of organophilic clay has been examined. The dispersion of silicate layers in copolymers is dependent on the copolymerization ratios of the functional groups, that is, the polarity of the polymer matrix. The alkyl chain lengths of organomodified reagents also have an important influence on silicate layer dispersions. From a comprehensive viewpoint, the polarity matching between polymers and organophilic clay is an important factor for silicate layer dispersions in polymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1554–1557, 2005     

Assessing organo‐clay dispersion in polymer nanocomposites

Organo‐clay polymer nanocomposites offer improved material properties at very low filler loadings making them of immediate interest for application in body panels, claddings, and instrument panels. This improvement in properties requires that the organo‐clay be well dispersed if not completely exfoliated. Conventionally, the dispersion and exfoliation of the organo‐clay is evaluated using transmission electron microscopy (TEM) and X‐ray diffraction (XRD). Although both TEM and XRD data were found to correlate with flexural modulus of thermoplastic olefin nanocomposite materials, only TEM proved successful in quantifying the dispersion of the organo‐clay in all nanocomposite materials (exfoliated, tactoid, or agglomerated tactoid). XRD was found to be capable of detecting exfoliation and intercalation but is limited because of clay dilution, preferred orientation, mixed‐layering, and other peak broadening factors. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1110–1117, 2004     

硫化方法对橡胶/黏土纳米复合材料黏土片层分散状态的影响

通过熔体插层法以及常压硫化法制备了橡胶/黏土纳米复合材料,并与模压硫化法制备的复合材料进行了对比,研究了硫化方法对橡胶/黏土纳米复合材料微观分散状态的影响。结果表明:采用熔体插层法制备的橡胶/黏土混合物,其受限状态的橡胶大分子链在高温、高压条件下,在黏土片层之间处于一种热力学不稳定状态;模压处理会对橡胶/黏土混合物的分散状态产生不利影响。透射电子显微镜和X光衍射分析表明,采用模压硫化、常压硫化得到的丁基橡胶或丁苯橡胶/黏土纳米复合材料中黏土片层的微观分散状态不同;排除压力的影响,常压硫化有利于提高橡胶/黏土纳米复合材料中黏土片层的分散程度。     

Functionalized polypropylenes in the compatibilization and dispersion of clay nanocomposites

The preparation of polypropylene (PP) nanocomposites was studied using clay and three types of modified PP (m‐PP) as compatibilizers: diethyl maleate grafted PP (PP‐g‐DEM), maleic anhydride grafted PP (PP‐g‐MA), and PP grafted with carbamyl maleamic acid (PP‐g‐UMA). The clay was made organophylic by an acid treatment with octadecylamine. PP functionalization and blending were carried out in an internal mixer. Blends of PP containing 20 and 40 wt% each of the modified PP and 5 wt% of organophilic clay (IMt), in each case, were prepared. Samples were characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical microscopy, and mechanical testing. The presence of tactoid, intercalated and exfoliated structures was observed by TEM in all the samples containing clay and modified PP, which also showed improved mechanical properties with tensile modulus as much as three times that of PP. Melting temperature did not vary significantly with the addition of clay. However, because of the clay's nucleating effect, an increase in the crystallization temperature was observed, accompanied by a slight decrease in the degree of crystallinity. The best results were obtained when PP‐g‐MA was used as the compatibilizer; intermediate results were obtained with the use of PP‐g‐UMA, followed by the results obtained when PP‐g‐DEM was used. Property enhancements were obtained when a higher percentage of modified PP was employed. POLYM. COMPOS., 27:451–460, 2006. © 2006 Society of Plastics Engineers     

Effects of clay dispersion on the foam morphology of LDPE/clay nanocomposites

Intercalated and exfoliated low‐density polyethylene (LDPE)/clay nanocomposites were prepared by melt blending with and without a maleated polyethylene (PE‐g‐MAn) as the coupling agent. Their morphology was examined and confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of clay content and dispersion on the cell morphology of nanocomposite foams during extrusion foaming process were also thoroughly investigated, especially with a small amount of clay of 0.05–1.0 wt%. This research shows the optimum clay content for achieving microcellular PE/clay nanocomposite foams blown with supercritical CO₂. It is found that < 0.1 wt% of clay addition can produce the microcellular foam structure with a cell density of > 10⁹ cells/cm³ and a cell size of ～ 5 μm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2129–2134, 2007     

Investigations on clay dispersion in polypropylene/clay nanocomposites using rheological and microscopic analysis

Morphology assessment plays an important role as the ultimate properties of the processed nanocomposites mainly depend upon the morphology. This study focuses on the evaluation of polypropylene/clay nanocomposite structure using rheological and transmission electron microscopic investigation. Melt processing of nanocomposite was carried out on a co‐rotating twin screw extruder. Maleic anhydride grafted polypropylene (PP‐g‐MA) was used as a compatibilizer to facilitate better mixing of clay in polypropylene. The effect of compatibilizer to clay ratio on dispersion was analyzed through rheological data. An increase in complex viscosity and storage modulus with increase in compatibilizer content is observed at lower frequency region. Shifting of crossover frequencies to a lower value also indicate better exfoliation. Improved exfoliated morphology was also corroborated by Cole–Cole and inverse loss tangent plots. Transmission electron microscopy (TEM) micrograph based unique statistical image analysis was carried out using ImageJ software. A compatibilizer to clay content of 2 : 1 was found to be the optimum composition which was further supported by dielectric and mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4464–4473, 2013     

Effect of some compatibilizing agents on clay dispersion of polypropylene‐clay nanocomposites

Polypropylene (PP)‐clay nanocomposites were obtained and studied by using three different coupling agents, glycidyl methacrylate (GMA), acrylic acid (AA), and maleic anhydride (MA). Three different clays, natural montmorillonite (Cloisite Na+) and chemically modified clays Cloisite 20A and Cloisite 30B, have also been used. Nanocomposites were prepared by melt‐blending in a twin‐screw extruder using two mixing methods: two‐step mixing and one‐step mixing. The relative influence of each factor was observed from structural analysis by WAXD, POM, TEM, and mechanical properties. The results were analyzed in terms of the effect of each compatibilizing agent and incorporation method in the clay dispersion and mechanical properties of the nanocomposite. Experimental results showed that clay dispersion and interfacial adhesion are greatly affected by the kind of matrix modification. The polarity and reactivity of polar groups give as a result better interfacial adhesion and subsequent mechanical performance. PP‐g‐GMA and PP‐g‐MA were better compatibilizing agents than PP‐g‐AA. Better dispersion and exfoliation for the nanoclays were obtained when using two‐step mixing than one‐step mixing conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4748–4756, 2006     

Properties and morphology of nanocomposites based on styrenic polymers. Part I: Styrene-acrylonitrile copolymers

For polymer/organoclay nanocomposites formed by melt processing, interactions between the polymer, montmorillonite surface, and surfactant determine any thermodynamic driving force for dispersion of the clay in the polymer. Interactions between poly(styrene-co-acrylonitrile) (SAN) and a single organoclay were probed by varying the SAN copolymer composition. Sample preparation was accomplished by melt processing on a microcompounder followed by injection molding. The level of mechanical reinforcement was observed to increase with acrylonitrile content. Digital analyses of TEM photomicrographs of core samples suggest an optimum in the aspect ratio of the particles at ∼38 wt% acrylonitrile; montmorillonite particles are much longer and thicker for the PS-based composites indicting poor exfoliation compared to the SAN-based composites. The melt viscosity of the SAN copolymers used in this work increased with AN content; experiments showed that varying melt viscosity independent of AN content can account for some improvement in reinforcement.     

Effect of functionalized polyethylenes on clay dispersion in high density polyethylene nanocomposites

The compatibilization effects provided by maleic anhydride (MA), itaconic acid (IAc), itaconic anhydride (IA), and 2-[2-(dimethylamine)-ethoxy]ethanol (DMAE) functionalized polyethylenes for forming high density polyethylene (HDPE)-based nanocomposites were studied and compared. IAc and IA were grafted into HDPE by melt mixing to obtain functionalized polyethylenes (HDPEgIAc and HDPEgIA) and amino alcohol functionalized polyethylene was prepared by reaction of commercial HDPEgMA with DMAE in the melt to form polyethylene-grafted dimethyl-amine-ethoxy-ethanol (PEgDMAE). Nanocomposites were prepared by melt processing using a twin screw extruder by blending polyethylene and these compatibilizers with a quaternary ammonium surfactant-modified montmorillonite clay (Nanomer I28E). FTIR characterization confirmed the formation of these compatibilizers and confirmed the reaction between HDPEgMA and the amino alcohol. All the compatibilized nanocomposites had better clay exfoliation compared to the uncompatibilized HDPE nanocomposites. Barrier properties, X-ray diffraction and transmission electron microscopy results showed the following order of their performance as a compatibilizer: PEgDMAE > HDPEgAI > HDPEgAcI > HDPEgMA. This behavior was attributed to the specific interactions between the anionic surface of the clay and the functionality of the compatibilizer. Samples with higher clay content showed poorer clay dispersion or intercalation which was attributed to possible clay saturation when the van der Waals attractive interactions between the clay layers become dominant when the distance between them was small enough at a certain concentration of clay. A noticeable reduction in the degree of crystallinity with the incorporation of nanoclay was observed by thermal analysis whereas the melting temperature did not change noticeably.     

Dynamic mechanical study of clay dispersion in maleated polypropylene/organoclay nanocomposites

Morphological characteristics and the dynamic mechanical properties of maleic anhydride grafted polypropylene (PPgMA) and its clay‐filled nanocomposites with different degrees of clay exfoliation have been investigated. Fully and partially exfoliated samples were prepared through powered sonication and melt blending, respectively. Our results indicated that both mechanical α and β relaxations can be identified. The glass (β) transition of the nanocomposites shifted to slightly lower temperatures for nearly all formulations because of reduced chain cooperative motion. However, the broad α transition became more distinct with increasing clay loading for sonicated nanocomposites, and shifted to higher temperatures due to chain confinement of amorphous polymer chains in the crystalline region. The reinforcement in the glassy storage modulus E′ of PPgMA was examined by the Halpin–Tsai theory. The high aspect ratio of clay stacks in the fully exfoliated nanocomposites resulted in a significant increase in reinforcing efficiency. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Vapor barrier properties of polycaprolactone montmorillonite nanocomposites: effect of clay dispersion

Different compositions of poly(ε-caprolactone) (PCL) and (organo-modified) montmorillonite were prepared by melt blending or catalyzed ring opening polymerization of ε-caprolactone. Microphase composites were obtained by direct melt blending of PCL and sodium montmorillonite (MMT-Na⁺). Exfoliated nanocomposites were obtained by in situ ring opening polymerization of ε-caprolactone with an organo-modified montmorillonite (MMT-(OH)₂) by using dibutyltin dimethoxide as an initiator/catalyst. Intercalated nanocomposites were formed either by melt blending with organo-modified montmorillonite or in situ polymerization within sodium montmorillonite. The barrier properties were studied for water vapor and dichloromethane as an organic solvent. The sorption (S) and the zero concentration diffusion coefficient (D₀) were evaluated for both vapors. The water sorption increases with increasing the MMT content, particularly for the microcomposites containing the unmodified MMT-Na⁺. The thermodynamic diffusion parameters, D₀, were compared to the value of the parent PCL: both microcomposites and intercalated nanocomposites show diffusion parameters very near to PCL. At variance exfoliated nanocomposites show much lower values, even for small montmorillonite content. In the case of the organic vapor, the value of sorption at low relative pressure is mainly dominated by the amorphous fraction present in the samples, not showing any preferential adsorption on the inorganic component. At high relative pressure the isotherms showed an exponential increase of sorption, due to plasticization of the polyester matrix. The D₀ parameters were also compared to those of the unfilled PCL; in this case, both the exfoliated and the intercalated samples showed lower values, due to a more tortuous path for the penetrant molecules.     

Deformation and fracture behavior of polyamide nanocomposites: The effect of clay dispersion

This study describes the effect of the clay content and its dispersion on deformation and fracture behavior of polyamide nanocomposites. Two nanocomposite systems, intercalated and exfoliated nanocomposites containing layered silicate, were compared. They were prepared by melt‐compounding of polyamide with sodium montmorillonite or organophilized montmorillonite. It has been shown that while the exfoliated structure imparts to the nanocomposite higher stiffness and strength, the toughness is inferior to the intercalated nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of PEgMA/amine silane compatibilizer on clay dispersion of polyethylene-clay nanocomposites

The compatibilization effects provided by an amine silane modified polyethylene (PEgAS) versus those by a maleated polyethylene (PEgMA), for forming PE–clay based nanocomposites, were studied. PEgAS was prepared by condensation reaction between PEgMA and g-(aminopropyl) triethoxy silane (APTS). It had the triethoxy-silane functionality on one end and was solution mixed with an organomodified clay (Cloisite 20A) to promote the reaction of the silane groups with the hydroxyl groups on the surface of the clay. The obtained masterbatches were then compounded with PE to obtain PE–clay nanocomposites by melt blending in a twin screw extruder, using different compatibilizers and clay contents. FTIR, XRD, STEM, and Instron were used to characterize the structural, morphological, and mechanical properties of the nanocomposites. Results showed that the PEgAS formed more exfoliated–intercalated morphology and better mechanical properties, especially in modulus and tensile strength as compared with PEgMA composites and neat PE. The Young modulus was 35% higher, and the tensile strength was 18% higher with PEgAS composites.     

Clay dispersion effects on excimer laser ablation of polymer–clay nanocomposites

The ablation behavior of polystyrene‐organically modified montmorillonite (OMMT) nanocomposites was evaluated by measuring the weight loss induced by KrF excimer laser irradiation of the nanocomposite specimens under air atmosphere. The characteristic values of ablation, ablation threshold fluence, and effective absorption coefficient for polystyrene and its nanocomposites were calculated based on the weight loss data. The effects of morphology due to spatial variation in injection molded samples are also discussed in this article. Results demonstrate that both the dispersion state and the concentration of clay play important roles in excimer laser ablation. The sensitivity of threshold fluence and absorption coefficient to dispersion state of OMMT seem to depend on the clay concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2336–2344, 2013     

Effect of the grafted silane on the dispersion and orientation of clay in polyethylene nanocomposites

The CTAB ammonium intercalated montmorillonite clay, CMT, was modified by an alkylsilane, Dodecyltrimethoxylsilane, to improve the miscibility of organoclays with PE matrix, involving the grafting reaction between the silane and silanol groups on the edge of clay. The silane modified clays (DMT) exhibited improved thermal stability due to the replacement of the physically adsorbed ammonium by the covalently bonded silane. The clays were melt compounded with polyethylene. Compared with the composite of PE/CMT, the clay dispersion state was improved, and a unique orientation of the clay layered was observed in PE/DMT nanocomposites, which was confirmed by XRD and TEM studies. The dispersion state, orientation degree of clay and, as a result, the mechanical and thermal properties of the nanocomposites were enhanced with the increasing amount of the grafted silane, indicating that the edge grafting of silane played a crucial role in controlling the structure and properties of nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Compatibilized polyimide (R-BAPS)/BAPS-modified clay nanocomposites with improved dispersion and properties

There is a need for clay modifiers that will not thermally degrade at elevated temperatures commonly used in polymer processing operations such as extrusion and injection molding. In this context, natural montmorillonite clay (Na-MMT) was organically modified by varying concentrations of 4,4′-bis(4″-aminophenoxy)diphenylsulfone (BAPS) using different chemical dispersion methods to yield new chemically modified clays that are relatively thermally stable at elevated temperatures compared with current commercial modified clays. This paper shows that the Na-MMT chemical modification (BAPS-MMT) was confirmed by XRD that showed a shift of diffraction peak at 2Θ = 7.3° for Na-MMT towards lower 2Θ = 5.8°. Thermogravimetric analysis of the samples showed a weight loss of organically modified clay that started at a temperature of 350 °C, corresponding to the degradation temperature of the BAPS monomer. Rheological measurements in combination with XRD data showed clearly that the quality of dispersion of BAPS-MMT type particles in R-BAPS type polyimide and oligoimides strongly depends on the clay surface modification, the specific chemical modification method used, and on the polymer molecular weight. Note that the oligoimides were specifically used as model systems to confirm our expectation of improved chemical compatibility between the BAPS-MMT and the polyimide system. This study may stimulate a better understanding of the effects of rational chemical modification methods on the quality of clay dispersion in polyimide matrices, enhancing our ability to prepare useful polyimide/clay nanocomposites with improved properties for targeted high-temperature applications where current polymer nanocomposite systems are not useable.     

Effect of intercalating agents on clay dispersion and thermal properties in polyethylene/montmorillonite nanocomposites

Alkyl pyridinium, 1‐vinyl alkyl imidazolium, 1,3‐dialkyl imidazolium, and tetraalkyl phosphonium bromides were successfully used as intercalants for the preparation of highly thermally stable organophilic montmorillonites. Nanocomposites of linear low density polyethylene (LLDPE) and linear low density polyethylene grafted with maleic anhydride (LLDPE/LLDPE‐g‐MAH) were prepared from those organoclays. The micro‐ and nano‐dispersions were analyzed through X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM): intercalation and/or partial exfoliation were found to occur only for formulations based on organoclays having an initial basal distance higher than 20 Å, suggesting the existence of a critical interfoliar distance for the delamination of silicate layers in a noninteracting polymer matrix. The properties of the nanocomposites were analyzed through differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and oscillatory rheometry. The dynamic crystallization of LLDPE was not significantly affected by the presence of clay. TGA in oxidative atmosphere proved to be very sensitive to the dispersion state of the organoclay: the thermal stability was drastically enhanced for intercalated and partially exfoliated formulations. However, the inherent thermal stability of the organoclay did not appear to influence significantly the overall thermal stability of the composite in the range of temperatures investigated (160–230°C). POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Polypropylene/clay nanocomposites: Combined effects of clay treatment and compatibilizer polymers on the structure and properties

Combined effects of clay treatment and compatibilizer polymers on the structure and properties of polypropylene/clay nanocomposites were studied. Dynamic mechanical analysis was used to analyze comparatively the dynamic mechanical response of different nanocomposites prepared from polypropylene and montmorillonite‐rich bentonite, and to relate such response with the material microstructure. Two different bentonites were used: a purified Spanish natural bentonite was organophillized by means of 11‐undecyl‐ammonium ion and a commercial bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion. Three different polar copolymers were employed as compatibilizer agents in some of the formulations: maleic anhydride‐grafted polypropylene, maleic anhydride‐grafted poly(styrene‐co‐ethylenebutylene‐co‐styrene), and poly(ethylene terephthalate‐co‐isophthalate) (PET). To ascertain the microstructure characteristics in the nanocomposites, wide angle X‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry techniques were used. The nanocomposites containing both bentonite organophillized with 11‐undecyl‐ammonium ion and PET, and maleated PP as compatibilizer system, were found to have the highest storage modulus and the smallest loss factor values, which was mainly due to the better clay platelets dispersion. The dynamic mechanical response of nanocomposites prepared with bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion and maleated SEBS was strongly affected by the presence of this compatibilizer. The temperature of PP and α, β, and γ relaxations strongly depended on the interactions between the different phases in the nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1213–1223, 2006     

Migration of organic compounds from PET/clay nanocomposites: influences of clay type, content and dispersion state

Polyethylene terephthalate (PET) bottles are widely used for packaging mineral water or soft drinks. Migration of toxic residual phthalate esters from PET could potentially change the quality of the bottled contents. The main purpose of this study is to control the migration of five different phthalate esters from PET bottles into the water they contained. To achieve this goal, three different types of nanoclay particles were added to PET to slow down the migration of the toxic phthalate esters. The concentration of phthalate esters in the water in contact with PET and PET/nanoclay was measured by gas chromatography (GC-FID) combined with the directly suspended droplet microextraction method. Good precision, accuracy and reproducibility over a wide linear range were achieved by the proposed technique under optimal conditions. The experimental results reveal that adding nanoclay fillers to the PET decreases the release of the above-mentioned chemicals from PET into the water considerably due to attainment of a tortuous diffusive path. Data also indicate the significant effect of nanoclay volume fraction and exfoliated morphology on obtaining efficient barrier properties. Furthermore the effects of parameters such as storage time, temperature, and amount and type of nanoclay inclusions were studied on the migration rate, as well.     

Quantification of the layer dispersion degree in polymer layered silicate nanocomposites by transmission electron microscopy

As the performance of polymer layered silicate nanocomposites strongly depends on their interior layer dispersion, quantification of the layer dispersion degree is needed. In this work, a new methodology was developed to determine the dispersion parameter D_0.1, based on the measurement of the free-path spacing distance between the single clay sheets from the transmission electron microscopy (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites were studied. It was found that the exfoliated composites had D_0.1 over 8%, while that of intercalated composites were between 4 and 8%. In the case of intercalation, a high frequency peak appeared at a short spacing distance in the histogram, which was a characteristic of the intercalation, distinct from the exfoliation. The main utility of this TEM methodology is for the quantification of exfoliated or intercalated samples with small number of layers with stacks. The dispersion parameter D_0.1 below 4% was suggested to classify as immiscible. A unique advantage of the TEM measurement is that the dispersion degree of different fillers can be counted individually.