Room temperature processing of epoxy-clay nanocomposites

Polymer/Clay nanocomposites consisting of an epoxy matrix filled with nanolayered silicate clay particles have been investigated. Recent and ongoing research has shown that dramatic enhancements can be achieved in mechanical and thermal properties by adding a small volume percent of clays. In the present work nanocomposites are processed by mechanical mixing of epoxy with organoclays and unmodified clays using a high speed electric shear mixer at room temperature. The addition of different organoclay wt% [1–3, 5 and 10] indicates good enhancement in hardness, dynamic mechanical properties, and also the molecular mobility of the polymer is reduced by the presence of the silicate layers, which in turn causes large stiffness improvements. X-ray diffraction (XRD) results show the intercalation/exfoliation of clays in the epoxy matrix. The influence of organoclay restricts the weight loss at varying temperatures. Experiments show improved elastic modulus for both modified and unmodified clays.     

Thermal, mechanical and vibration characteristics of epoxy-clay nanocomposites

Diglycidyl ether of bisphenol-A (DGEBA) epoxy resin system filled individually with organoclay (OC) and unmodified clay (UC) were synthesized by mechanical shear mixing with the addition of diamino-diphenylmethane (DDM) hardener. The unmodified clay used was Na⁺-Montmorillonite (MMT) and the organoclay was alkyl ammonium treated MMT clay. The reinforcement effect of OC and UC in the epoxy polymer on thermal, mechanical and vibration properties were studied. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) were used to study the structure and morphology of nanocomposites. Curing study shows that the addition of OC in epoxy resin aids the polymerization by catalytic effect, and UC addition does not show any effect in the curing behavior of epoxy polymer. Thermogravimetry analysis (TGA) shows enhanced thermal stability for epoxy with OC fillers than that of epoxy with UC fillers. The epoxy with OC fillers shows considerable improvement on tensile and impact properties over pure epoxy polymer and epoxy with UC fillers. The improvement in tensile and impact properties of nanocomposites is supported with the fracture surface studies. Epoxy with OC fillers shows enhanced vibration characteristics than that of the pure epoxy polymer and epoxy with UC fillers.     

Mill processing and properties of rubber–clay nanocomposites

The dispersion of nanoscale composites in elastomers, which generally have higher molecular weight and viscosity as compared to plastics, is a challenge. Several techniques have been proposed for improvement of the dispersion of nanofillers in the polymers [1]. For example, the interaction of natural layered silicates can be improved by ion-exchange of hydrated cation with organic cations such as introducing bulky alkylammoniums to obtain larger interlayer spacing and provide the galleries for the polymer chain diffusion. The resultant swollen nanoclay was dried and dispersed in the polymer matrix by means of high shear mixers [2–3]. In this paper we describe the results from a new method of incorporating nanofillers into solid rubber by use of a conventional two-roll mill, which we call the modified mill method. The properties of the resultant material are compared with that of the material prepared by a latex method. We also test processability parameters, tensile behavior and crosslink density of carbon black composites prepared by the same two methods to provide a comparison between the nanocomposites. The rubber–clay nanocomposites prepared by the mill method are shown to have a fine dispersed phase structure and good reinforcement properties.     

Structure and mechanical properties of polycarbonate modified clay nanocomposites

Polycarbonate (PC)/modified clay nanocomposites were prepared, in the absence and presence of different amounts of maleic anhydride grafted polypropylene (PP-g-MA), by direct melt blending. Their structures, as well as mechanical, morphological and thermal properties, were characterized by X-ray diffractometry (XRD), tensile testing, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD results of the PC/clay nanocomposites showed that they had intercalated structures, although some exfoliation was visible at low clay contents, that the gallery heights of the PC/clay nanocomposites were almost the same, and that some of the clay layers collapsed as a result of modifier decomposition at the high processing temperature. The XRD patterns of the PC/PP-g-MA/clay nanocomposites clearly show less intercalation and more exfoliation with increasing PP-g-MA content. These results were supported by TEM observations. Both the tensile strength and modulus show substantial improvements with both increasing clay and PP-g-MA contents, while the elongation at break substantially decreases, although the presence of PP-g-MA somewhat improves these values. All the nanocomposites have lower thermal stability than pure PC, but the presence of PP-g-MA seems to improve the thermal stability of these samples.     

Effect of metal volume fraction on the mechanical properties of alumina/aluminum composites

The influence of metal volume fraction on the mechanical properties of Al₂O₃/Al composites with constant diameter of metal ligaments was studied. Alumina/aluminum composites with interpenetrating networks and metal content between 12 and 34 vol.% were fabricated by gas-pressure infiltration technique. The fabricated composites exhibited good mechanical properties, e.g. the bending strength of 740 MPa for samples containing 12 vol.% of Al. The bending strength of the composites decreased with increasing volume fraction of metal phase. High strength of the fabricated composites was explained by strong interfacial bonding between alumina and aluminum. The fracture toughness of the composites increased, however, with increasing volume fraction of aluminum. The highest fracture toughness values of 6 MPa m were measured for the composites containing 25 vol.% of Al. Fractographic analysis of fractured surfaces showed deformed metal ligaments which demonstrated that crack bridging by plastic deformation of the metal phase is the main toughening mechanism in Al₂O₃/Al composites.     

Factors controlling mechanical properties of clay mineral/polypropylene nanocomposites

Effects of two factors on the mechanical properties of clay mineral/polypropylene nanocomposites were examined. The first factor is the presence of a small amount of poly(diacetone acrylamide) formed between clay mineral layers. This material was expected to separate effectively the stacked layer structure of the clay mineral on mixing with polypropylene. The stacked layer structure, however, was not separated sufficiently in spite of expansion of the interlayer distance of clay mineral, leading to poor improvement of the mechanical properties of the nanocomposite. Another factor is the kind of clay mineral. Montmorillonite and mica resulted in less favorable separation of the stacked structure than hectorite, but the resulting nanocomposites gave outstanding improvement of the properties. The stiffness of clay mineral layer was considered to influence the properties of the nanocomposite strongly.     

Effect of processing parameters on the microstructure and mechanical properties of Al–steel composite foam

Al–steel composite foams comprise of steel hollow spheres embedded in an aluminum matrix and are processed using a gravity casting technique. The effect of processing parameters such as casting temperature and cooling rate on the microstructure and mechanical behavior was studied to establish structure–property relationships. Results show that the amount and composition of intermetallic phases present in the foam microstructure is directly related to casting temperature and cooling rate. Highest strength and energy absorption were obtained from Al–steel foams with fast solidification rates that minimize the growth of intermetallic phases.     

Preparation,microstructure and thermal mechanical properties of epoxy/crude clay nanocomposites

To improve the performance/cost ratio of epoxy/clay nanocomposites, epoxy resin was reinforced with crude clay with the help of a silane modifier. The epoxy/crude clay nanocomposites were produced through a recently developed “slurry compounding” approach. The microstructure of the nanocomposites was characterized with X-ray diffraction (XRD), optical microscopy and transmission electron microscopy (TEM). The thermal mechanical properties were studied with dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). It has been shown that only 5 wt% of silane modifier is required to facilitate the dispersion and exfoliation of crude clay in epoxy matrix. The storage moduli and thermal stability were improved with the addition of crude clay.     

尼龙6/橡胶/天然粘土纳米复合材料的制备及其力学性能

采用一种新型的超细全硫化粉末橡胶/蒙脱土复合粉末(UFPRM),可以制备出剥离型的尼龙6/橡胶/天然粘土(尼龙6/UFPRM)纳米复合材料,所用的橡胶是一种具有特殊结构的超细全硫化粉末橡胶(UFPR).微观分析表明,橡胶粒子在尼龙6基体中分散良好,同时天然粘土在橡胶粒子之间的基体中剥离.在一定份数下,复合粉末可以同时提高尼龙6的韧性、刚性及耐热性;随着复合粉末含量的增加,材料的冲击强度进一步增加.而且,复合粉末对高分子量尼龙6的增强、增韧效果好于低分子量尼龙6.进一步研究发现,在适当的剪切速率下,尼龙6/橡胶/天然粘土纳米复合材料可以获得较好的综合力学性能.     

Effect of carbon nanotube orientation on the mechanical properties of nanocomposites

Carbon nanotubes (CNTs) have been regarded as ideal reinforcements of high-performance composites with enormous applications. In this paper, nano-structure is modeled as a linearly elastic composite medium, which consists of a homogeneous matrix having hexagonal representative volume elements (RVEs) and homogeneous cylindrical nanotubes with various inclination angles. Effects of inclined carbon nanotubes on mechanical properties are investigated for nano-composites using 3-D hexagonal representative volume element (RVE) with short and straight CNTs. The CNT is modeled as a continuum hollow cylindrical shape elastic material with different angles. The effect of the inclination of the CNT and its parameters is studied. Numerical equations are used to extract the effective material properties for the hexagonal RVE under axial as well as lateral loading conditions. The computational results indicated that elastic modulus of nano-composite is remarkably dependent on the orientation of the dispersed SWNTs. It is observed that the inclination significantly reduces the effective Young’s modulus of elasticity under an axial stretch. When compared with lateral loading case, effective reinforcement is found better in axial loading case. The effective moduli are very sensitive to the inclination and this sensitivity decreases with the increase of the waviness. In the case of short CNTs, increasing trend is observed up to a specific value of waviness index. It is also found from the simulation results that geometry of RVE does not have much significance on stiffness of nano-structures. The results obtained for straight CNTs are consistent with ERM results for hexagonal RVEs, which validate the proposed model results.     

Epoxy based nanocomposites with fully exfoliated unmodified clay: mechanical and thermal properties

The unmodified clay has been fully exfoliated in epoxy resin with the aid of a novel ultrafine full-vulcanized powdered rubber. Epoxy/rubber/clay nanocomposites with exfoliated morphology have been successfully prepared. The microstructures of the nanocomposites were characterized by means of X-ray diffraction and transmission electron microscopy. It was found that the unmodified clay was fully exfoliated and uniformly dispersed in the resulting nanocomposite. Characterizations of mechanical properties revealed that the impact strength of this special epoxy/rubber/clay nanocomposite increased up 107% over the neat epoxy resin. Thermal analyses showed that thermal stability of the nanocomposite was much better than that of epoxy nanocomposite based on organically modified clay.     

Experimental and theoretical analyses of mechanical properties of PP/PLA/clay nanocomposites

Compatibilized and non-compatibilized blends of polypropylene (PP) and poly(lactic acid) (PLA) with various compositions containing nanoclay particles were prepared by one step melt compounding in a twin screw extruder. Two nanocomposite systems with different matrices i.e. PP-rich (75/25 composition) containing Cloisite 15A and PLA-rich (25/75 composition) containing Cloisite 30B were selected for investigation of effect of nanoclays and n-butyl acrylate glycidyl methacrylate ethylene terpolymers (PTW) as compatibilizer on mechanical properties of PP/PLA/clay nanocomposites. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. Tensile modulus and strength of the blends were increased while elongation at break decreased by increasing PLA content. There was an irregular relationship between impact strength of the blends and PLA content. Several proposed models for blends and nanocomposites were used for prediction of tensile modulus of the samples. Most of the proposed models for blends could predict the tensile modulus of the blends successfully at low content of PLA. Another notable point was that most of the micromechanical models for nanocomposites fitted well to experimental values at low content of the clays and showed deviations at high clay loadings.     

Pultruded fibre reinforced polyurethane composites II. Effect of processing parameters on mechanical and thermal properties

This paper presents a novel process for the fabrication of pultruded polyurethane (PU) composites. The effects of the processing parameters on the mechanical properties (flexural strength and flexural modulus, etc.) and thermal properties (HDT) of the fibre reinforced PU composites by pultrusion have been studied. The processing parameters investigated include pulling rate (in-line speed), die temperature, filler type and content, and post-cure time and temperature. Results show that the composites possessed various optimum pulling rates at different die temperatures. On the basis of the DSC diagram, the swelling ratio, the mechanical properties and the thermal properties of composites, the optimum die temperature can be determined. It is found that the mechanical and thermal properties increase with filler content for various types of filler. The mechanical and thermal properties increase at a suitable post-cure temperature and time. Furthermore, the properties which decreased due to the degradation of composite materials for a long post-cure time will be discussed.     

Improving the mechanical properties of thermoplastic starch/poly(vinyl alcohol)/clay nanocomposites

Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites, exhibiting the intercalated and exfoliated structures, were prepared via melt extrusion method. The effects of clay cation, water, PVOH and clay contents on clay intercalation and mechanical properties of nanocomposites were investigated. The experiments were carried out according to the Taguchi experimental design method. Montmorillonite (MMT) with three types of cation or modifier (Na⁺, alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties in comparison with pristine MMT. It was also observed that increases in tensile strength and modulus would be attained for nanocomposite samples with 10%, 5% and 4% (by weight) of water, PVOH and clay loading, respectively. The clay intercalation was examined by X-ray diffraction (XRD) patterns. The chemical structure and morphology of the optimum sample was also probed by FTIR spectroscopy and transmission electron microscopy (TEM).     

Influence of clay incorporation on the physical properties of polyethylene/Brazilian clay nanocomposites

High density polyethylene/Brazilian clay nanocomposites were prepared by the melt intercalation technique. A montmorillonite sample from Boa Vista/PB, Northeast of Brazil, was organically modified with esthearildimethylammonium chloride (Praepagen WB) quaternary ammonium salt. The unmodified and modified clays with the quaternary ammonium salt were introduced in 1, 2, 3 and 5 wt% in a PE polymer matrix. The dispersion analysis and the interlayer distance of the clay particles were obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of tensile and the flammability of the nanocomposites were studied. In general, the mechanical properties of the systems presented superior values compared to the matrix. The systems showed a reduction on the burning rate, indicating that the flammability resistance of nanocomposites was improved.     

The effect of processing parameters on the mechanical properties of auxetic polymeric fibers

Auxetic polymeric fibers have been produced using a melt-spinning technique. The effect of the processing parameters on the fibers has been examined. It was found that the auxetic effect occurs over a very tight temperature window with screw speed, take-off speed and die geometry affecting homogeneity and auxeticity. This is an important finding as it provides a method of producing more homogeneous auxetic fibers with tailored values of Poisson’s ratio.     

Investigation on the competing effects of clay dispersion and matrix plasticisation for polypropylene/clay nanocomposites. Part I: morphology and mechanical properties

The key compatibiliser role of maleated polypropylene (MAPP) to improve the clay dispersability has been explicitly addressed in the fabrication process and material characterisation of polypropylene (PP)/clay nanocomposites. However, its matrix plasticiser role, which has been rarely mentioned, could adversely influence the excellent mechanical properties of such nanocomposites, resulting from the homogeneous clay dispersion. PP/clay nanocomposites in the presence of MAPP were prepared by twin screw extrusion and subsequently injection moulded with three typical material formulations in fixed parametric settings: (1) weight ratio (WR) of clay and MAPP, WR = 1:2; (2) MAPP content of 6 wt% and (3) clay content of 5 wt%. The morphological structures and mechanical properties of PP/clay nanocomposites were examined by using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and universal mechanical testing. The further improvement of mechanical properties was evidently hindered with very inconsiderable alteration of morphological structures in terms of the clay dispersion level. This observation could be ascribed to the change of MAPP role from a compatibiliser to a plasticiser because of its excessive amount used above a certain saturation level, which was found in the range of 3–6 wt% in MAPP contents for the enhancements of tensile and flexural properties of PP/clay nanocomposites.     

无压浸渗制备SiC_p/Al复合材料的微观组织及弯曲性能

利用无压浸渗法制备高体积分数的SiCp/Al复合材料。采用X射线衍射(XRD)和扫描电镜(SEM)对复合材料的相组成、微观组织及断口形貌进行分析,研究了基体合金成分对复合材料抗弯性能的影响。结果表明,以Al-10%Si-8%Mg合金为基体制备的复合材料组织均匀,致密度好,无明显气孔缺陷,界面反应产物为Mg2Si、MgAl2O4和Fe,且抗弯强度高于以Al-10%Si合金为基体制备的复合材料;复合材料整体上表现出脆性断裂的特征。