Compatibilizing effect of acrylic acid modified polypropylene on the morphology and permeability properties of polypropylene/organoclay nanocomposites

This work dealt with the morphology and permeability properties of polypropylene/organoclay nanocomposites prepared using an acrylic acid grafted polypropylene (PP-g-AA) as compatibilizing agent. Two PP-g-AA containing the same acrylic acid content (6 wt.%) and having different molar masses were tested. The o-MMT content was 0, 1 or 5 wt.% and the PP-g-AA/o–MMT mass ratio was 0/1, 1/1, 2/1 or 5/1. Results of wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) showed that without the PP-g-AA, the o-MMT was dispersed in the PP/o-MMT in a micrometer scale, similar to a conventional microcomposite. With the PP-g-AA, the o-MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. CO₂ permeability values decreased for all samples with the incorporation of the organoclay. The compatibilized samples showed a more significant reduction in CO₂ permeability, up to 50% when compared to the neat PP. In general, the PP-g-AA acted satisfactorily in compatibilizing PP/organoclay nanocomposites. Moreover, samples prepared with the compatibilizer/organoclay ratio of 5/1 had better barrier properties.     

Structure and properties of EVOH/organoclay nanocomposites

The nanocomposites of poly(ethylene-co-vinyl alcohol) (EVOH) with organoclay were prepared by a solution-precipitation method. The structures of nanocomposites were examined by X-ray diffraction. The exfoliation of organoclay was more evident in the nanocomposites of the EVOH containing 18 mol% vinyl alcohol (EVOH18), compared to the EVOH containing 5 mol% vinyl alcohol (EVOH5). Some of the bilayer alkylammonium structures at the clay gallery changed to monolayer structures in the nanocomposites. The thermal properties measured by differential scanning calorimetry showed the organoclay enhanced the crystallization of EVOH, however, it retarded crystallization when there was too much. The modulus of EVOH18 showed about a 2-fold increase of pristine polymer when using 7% of reinforcing organoclay.     

Effects of maleination and heat treatment on morphology and dynamic mechanical thermal behavior of polypropylene/organoclay nanocomposites

Effects of maleinated compatibilizer and heat treatment on the internal structure and physical properties of PP/organoclay nanocomposites were investigated by using various measurements, e.g., SAXS, TEM, DSC and DMTA, and rotational rheometer. Experimental results showed that maleination and heat treatment affected the internal structure and dynamic mechanical properties of PP/organoclay nanocomposites. Storage modulus and loss tangent of PP/organoclay nanocomposites were strongly related to the compatibilizer loadings and heat treatment conditions because the interfacial structure between PP molecular chains and organoclay particles had been changed by the addition of compatibilizer to PP/organoclay nanocomposites. DSC and DMTA results of the compatibilized nanocomposites and effects of heat treatment on crystallization and dynamic mechanical thermal properties demonstrated that there is a small change in the glass transition temperature because the chain mobility and free volume in the amorphous region are increased by heat treatment. It was found that heat treatment imposed influence on both amorphous and crystalline regions of PP/organoclay nanocomposites.     

Dispersion and rheology of polypropylene/organoclay nanocomposites: effect of cation exchange capacity and number of alkyl tails

Nanocomposites of montmorillonite organoclays and polypropylene (PP) were prepared via direct melt intercalation using maleic anhydride functionalized polypropylene (PP-g-MA) as a compatibilizer. Two montmorillonite clays (MMT) with different cation exchange capacities (CEC) were exchanged with alkyl ammonium ions, in which one or two octadecyl chains are attached to the nitrogen atom. The role of alkyl chain numbers and CEC value on the dispersion of clay and rheology of PP nanocomposites under shear and extensional flow was evaluated by X-ray diffraction, scanning electron microscopy, and rheologic techniques. It was found that the low-CEC organoclay with one alkyl chain could only form a conventional composite. However, the low-CEC organoclay with two alkyl chains or high-CEC organoclay with one alkyl chain can disperse finely in the matrix. Nanocomposites containing these two organoclays showed typical shear rheologic properties of intercalated nanocomposites, but only the former showed a mild strain-hardening behavior in uniaxial extensional flow. When using an intercalant with two tails, the high-CEC clay would lead the organoclay to form mixed structures which further resulted in an inferior dispersion quality. It was proposed that the dispersion quality and rheologic properties of nanocomposites were related to the arrangement of modifier molecules in the clay galleries, which was determined by the CEC of clay and the structure of alkyl ammonium ions.     

Mechanical reinforcement in natural rubber/organoclay nanocomposites

Aim of this work is to get an insight into the mechanisms by which nanofillers produce mechanical reinforcement in polymers above their glass transition temperature. To this purpose, the mechanical behaviour of natural rubber/organo-modified montmorillonite vulcanisates produced by melt mixing with various filler contents was investigated. Data of the initial modulus, evaluated from stress–elongation curves obtained in tensile tests carried out at room temperature and a fixed cross-head rate, were analysed as a function of the organoclay content by applying mechanical models proposed in the literature. Such analysis provided an evaluation of the filler percolation threshold. Further, tests performed with varying temperature and rate pointed out appreciable rate and temperature dependence only for samples containing amounts of organoclay higher than the percolation limit, that is in presence of filler networking. Such a typical viscoelastic behaviour associated to the presence of the filler network contributes to support the hypothesis that in filled rubbers the mechanisms of filler networking is based on the formation of confined regions of immobilised polymer that join the filler particles of the network, as recently proposed.     

Microstructures and toughening mechanisms of organoclay/polyethersulphone/epoxy hybrid nanocomposites

Hybrid nanocomposites (HNCs) with high fracture toughness were successfully prepared by incorporating polyethersulphone (PES) and organoclay into epoxy resin. Their microstructures were studied. They were composed of homogeneous PES/epoxy matrices and micron-scale organoclay agglomerates. These agglomerates consisted of smaller tactoid-like regions which were comprised of ordered exfoliated nanolayers. The toughening mechanisms of the two tougheners were also studied and then related to their microstructures. For one thing, the PES which was dissolved in the epoxy resin homogeneously improved the ductility of the epoxy resin and made it easier to deform. For another, the organoclay agglomerates induced crack front bowing, crack bridging, crack deflection, crack bifurcation and plastic deformation of the matrices on the micron-scale, respectively. These toughening processes were achieved by the ordered exfoliated nanolayers with various orientations, which debonded from the matrices, bridged the cracks and induced the plastic deformation of the matrices on the nanoscale.     

Study of rheological properties of polypropylene/organoclay hybrid materials

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.     

Intercalation behavior of polyimide/organoclay nanocomposites during thermal imidization

To understand the intercalation behavior of polyimide (PI)/clay nanocomposites during thermal imidization, two different types of poly(amic acid) (PAA) were synthesized, and the corresponding hybrids with organically treated clays (O-MMT) were also prepared. The changes in molecular structure of the polymer matrix, interlayer spacing, and fracture morphology with a series of thermal imidization steps were investigated. The PAA/clay nanocomposites initially showed two X-ray diffraction peaks, indicating two levels of intercalation. As the temperature at which the thermal imidization step was performed increased, the peak intensity of the higher angle peak increased, and it remained as a unique peak at 2θ=6.70 (d-spacing of 13.2 Å) for both PI(1), based on pyromellitic dianhydride (PMDA)+4,4′-oxydianiline (ODA), and PI(2), based on PMDA+4,4′-(9-fluorenylidene)-dianiline (9FDA). However, the lower angle peak became smaller and broader, and the angle became higher. This peak finally disappeared after thermal treatment at 300 °C for PI(1), but did not disappear completely for PI(2), although the peak showed a marked decrease in intensity and became broader.     

Morphology development in layered silicate thermoset nanocomposites

The role of processing temperature on the morphology development of organically modified montmorillonite-epoxy nanocomposites was examined to determine the sensitivity of exfoliation to processing and the potential to achieve desired morphologies through processing routes. In situ small-angle X-ray scattering studies were performed to relate the initiation and levels of exfoliated morphologies with time and temperature. Scattering data was correlated with key stages in morphology development to provide insight into the process-morphology relationship. Absolute temperature as well as heating rate was shown to directly affect the development of exfoliated nanocomposite morphology.     

Fracture behavior of polypropylene/clay nanocomposites

Polypropylene (PP)/clay nanocomposites have been prepared via a reactive compounding approach with an epoxy based masterbatch. Compared with PP and common PP/organoclay nanocomposites, the PP/clay nanocomposites based on epoxy/clay masterbatch have higher impact strength. The phenomenon can be attributed to the epoxy phase dispersed uniformly in the PP matrix, which may act as impact energy absorber and helps to form a large damage zone, thus a higher impact strength value is achieved.     

Phase separation of polystyrene/poly(vinylmethylether)/organoclay nanocomposites

The effect of addition of organically modified montmorillonite (OMMT) on the phase separation of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was examined. Using two types of OMMT modified with two different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing on three major aspects: phase transition, morphological study, and melt rheological behavior both below and above the critical transition temperature. X-ray diffraction (XRD) patterns revealed the formation of intercalated nanocomposites and transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in blend matrix is well matched with the XRD patterns. The addition of clay was found to affect both the mechanism of phase separation and the final morphology. Such effects resulted in uncommon rheological behavior of the blend both below and above the critical transition temperature. Surface phase separation of thin films for virgin blend and nanocomposites was also examined by atomic force microscopy (AFM). Morphology resulting after phase separation was found to be dependent on the nature and the amount of OMMT added to the polymer blend.     

Millable polyurethane/organoclay nanocomposites: preparation, characterization, and properties

Novel millable polyurethane (PU)/organoclay nanocomposites have been successfully prepared by conventional transformation techniques. One natural (C6A) and two organically modified (C15A and C30B) montmorillonites have been used as clays for preparing PU nanocomposites. The optimum dispersion of nanofiller at a nanometer scale in PU matrix was confirmed by X-ray diffraction patterns and transmission electron microscopy. A substantial improvement of the PU properties by addition of only a small amount of organoclay was observed. It is worthy to note that the organoclays show a different interfacial interaction with the PU matrix, which was reflected in different macroscopic properties. Thus, C30B organoclay seems to react with PU chains to form covalent bonds, while C15A only interacts physically with PU chains. Mechanical and barrier properties are analyzed.     

聚丙烯/纳米蒙脱土复合材料的超声研究

文章对用溶体插层方法制备的聚丙烯／蒙脱土纳米复合材料进行了超声实验研究。对一组采用不同蒙脱土掺杂比及不同方法掺杂的样品用超声脉冲回波法和声显微法测量了在不同频率下的纵波、横波声速,计算了这组样品的剪切模量、杨氏模量、泊松比和声品质因数,并据此分析了材料的特点。     

Influences of clay and manufacturing on fire resistance of organoclay/thermoset nanocomposites

The organoclay GFRP nanocomposites are prepared using the vacuum assisted resin transfer moulding method. Two grades of organophilic clay with three content levels, three types of thermosetting resins (polyester, vinyl ester and epoxy), and three nanoclay dispersion techniques are investigated. To understand the effects of these factors on the fire performance, Taguchi design of experiments (DoE) method is employed and preferred combinations of factors are determined using a one-step and a proposed two-step GLM ANOVA. The one-step ANOVA is applied directly on the experimental results, while the two-step ANOVA is conducted on the signal-to-noise ratios obtained from the Taguchi analysis. The combination of mechanical and ultrasonic dispersing procedure has been found to have considerable influence on the of nanoclay distribution. While both approaches provide insights into the influences of each fabrication factor, the two-step gives a better prediction of the favourable response combination for the nanocomposites when validated with experiments.     

纳米蒙脱土/聚丙烯复合材料热氧老化动力学

对熔融插层法所制备的纳米蒙脱土/聚丙烯（OMMT1/PP）复合材料, 分别在100℃、 110℃、 120℃进行0～12d的热氧老化, 考察其热性能、 热稳定性、 拉伸强度的衰减及其动力学。TG、 DSC、 FTIR分析结果表明: 纳米OMMT1/PP复合材料比PP的热分解温度升高37℃, 结晶度由51%提高到71%, 而且有机化的纳米MMT片层与PP之间存在较强的作用, 因此热氧作用的C O吸收峰明显弱化, 表面轻微开裂。100～120℃老化后OMMT1/PP的强度保持率大大优于纯聚丙烯材料（8~22倍）, OMMT1/PP 110℃老化12d后拉伸强度仍然达54％。建立了以拉伸强度?问腛MMT1/PP热氧老化的一级反应动力学方程, 其热氧老化反应的活化能为52.3kJ/mol, 为PP的1.7倍。分析认为: OMMT1/PP较高的活化能值以及优良的抗热氧老化能力来自其剥离型纳米化MMT片层对PP的力学?ぷ饔谩?物理阻隔效应以及OMMT1与PP之间化学交互作用的综合结果。      

Melt processing of polypropylene/clay nanocomposites modified with maleated polypropylene compatibilizers

Maleic anhydride-grafted polypropylene (PPgMA) and organically modified clay composites were prepared in a plasticorder. PPgMAs, including PB3150, PB3200, PB3000, and E43, with a wide range of MA content and molecular weight were used. The structure was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). PPgMA compatibilizers gave rise to similar degree of dispersion beyond the weight ratio of 3 to 1 with the exception of E43, which had the highest MA content and the lowest molecular weight. It was found that thermal instability and high melt index were responsible for ineffective modification by E43. Furthermore, PPgMA with low melting point and high melt index was compounded at low equilibrium temperature in order to maintain a certain level of torque. We then modified polypropylene/organoclay nanocomposites with different levels of PPgMA compatibilizers on a twin-screw extruder. The PP/E43/clay system, as shown through XRD patterns and TEM observation, yielded the poorest clay dispersion among the compatibilizers under investigation. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by dynamical mechanical analysis and thermogravimetric analysis, respectively. Though PPgMA with lower molecular weight and higher MA content could lead to good clay dispersion in PP/clay composites, it caused the deterioration in both mechanical and thermal properties of PP/PPgMA/clay composites.     

Properties of silane grafted polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites were prepared by melt compounding using organosilane modified polypropylene (PP-g-VTES) as compatibilizing agent. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), tensile modulus, and Izod impact strength. Addition of PP-g-VTES improved clay dispersion, as shown by the distribution of platelets per particle, and improve the interaction between clay and polymer matrix. Crystallization peak temperature (T_p) was increased in 10 °C using PP-g-VTES as compatibilizing agent. However the crystallization process and its rate were unmodified. The tensile modulus of compatibilized nanocomposite is 1.5 times higher compared to pure PP.     

Mechanically improved and optically transparent polycarbonate/clay nanocomposites using phosphonium modified organoclay

The present study deals with the properties of polycarbonate (PC)/clay nanocomposites prepared through melt and solution blending at two different clay loadings (0.5 phr and 1 phr) with preserved optical transparency of PC. The organoclay was prepared by exchanging the Na⁺ ions presented in the clay galleries of Na-MMT with butyltriphenylphosphonium (BuTPP⁺) ions, and denoted as BuTPP-MMT. The outstanding thermal stability of the BuTPP-MMT (∼1.44 wt% loss at 280 °C, after 20 min), concomitant with the increase in gallery height from 1.24 nm to 1.83 nm, proved its potentiality as nanofiller for melt-blending with PC. The X-ray diffraction analysis (XRD) revealed the destruction of the ordered geometry of aluminosilicate layers in the nanocomposites. However, from direct visualization through transmission electron microscopy, a discernible amount of clay was found to be localised in PC matrix in the 1 phr clay loaded nanocomposites (TEM). The differential scanning calorimetric (DSC) study revealed a nominal increase in glass transition temperature (T_g) of the PC in the nanocomposites. The thermal stability of the nanocomposites was increased with increase in clay loading. The nanocomposites possessed improved tensile strength and modulus than that of the virgin PC and the properties were related to the amount of clay loading and degree of clay dispersion. The dynamic mechanical analysis (DMA) revealed that the storage modulus increased in both the glassy and rubbery region with increase in clay loadings in the nanocomposites. Moreover, the optical transparency of the PC was retained in the PC/clay nanocomposites without development of any colour in the nanocomposites.