Effects of clay on phase morphology and mechanical properties in polyamide 6/EPDM-g-MA/organoclay ternary nanocomposites

In this study, both organoclay and EPDM-g-MA rubber were used to simultaneously improve the toughness and stiffness of polyamide 6 (PA6). We first prepared PA6/EPDM-g-MA/organoclay ternary nanocomposites using melt blending. Then the composites were subjected to traditional injection molding and so-called dynamic packing injection molding. The dispersion of clay, phase morphology, crystallinity and orientation of PA6 as well the mechanical properties were characterized by WAXD, SEM, DSC, 2D-WAXS and mechanical testing, respectively. The effects of clay on phase morphology and mechanical properties of PA6/EPDM-g-MA blends could be summarized as follows: (1) weakening interphase adhesion between PA6 and EPDM-g-MA rubber particles, resulted in increasing of rubber particle size, as the clay and rubber contents are low; (2) preventing coalescence of rubber domains, arisen in decreasing of rubber particle size, as the clay and rubber contents are high; (3) the blocking effect on the overlap of stress volume around rubber particles caused broadening of the brittle-ductile transition region and decrease of toughness, and (4) the effective stress transfer leading a better reinforcement when the interparticle distance is smaller than the critical value.     

The effect of organoclay on the mechanical properties and morphology of injection‐molded polyamide 6/polypropylene nanocomposites

Nanocomposites containing a thermoplastic blend and organophilic layered clay (organoclay) were produced by melt compounding. The blend composition was kept constant [polyamide 6 (PA6) 70 wt % + polypropylene (PP) 30 wt %], whereas the organoclay content was varied between 0 and 10 wt %. The mechanical properties of the nanocomposites were determined on injection‐molded specimens in both tensile and flexural loading. Highest strength values were observed at an organoclay content of 4 wt % for the blends. The flexural strength was superior to the tensile one, which was traced to the effect of the molding‐induced skin‐core structure. Increasing organoclay amount resulted in severe material embrittlement reflected in a drop of both strength and strain values. The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersion X‐ray analysis (EDX), and X‐ray diffraction (XRD). It was established that the organoclay is well dispersed (exfoliated) and preferentially embedded in the PA6 phase. Further, the exfoliation degree of the organoclay decreased with increasing organoclay content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 175–189, 2004     

Investigation on the polyamide 6/organoclay nanocomposites with or without a maleated polyolefin elastomer as a toughener

Polyamide 6 (PA 6)-based nanocomposites were prepared using a melt-mixing technique in this study. One commercial organoclay (denoted 30B) and one maleated polyolefin elastomer (denoted POEMA) served as the reinforcing filler and toughener, respectively. The X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS) and transmission electron microscopy (TEM) results confirmed the nano-scaled dispersion of 30B in the composites. Different mixing sequences presented similar phase morphology for the same formulated nanocomposites. XRD results also revealed that both 30B and POEMA would induce the formation of γ form PA 6 crystal, with 30B exhibiting a higher efficiency. Differential scanning calorimetry (DSC) results indicated that the addition of 30B altered the crystallization kinetics of PA 6, which was mainly attributed to the prevailing formation of γ form crystal. Complex melting behaviors were observed for neat PA 6 and the nanocomposites. These complex behaviors are associated with different polymorphs and the ‘melting-recrystallization-remelting’ phenomenon. Moderate thermal stability enhancement of PA 6 after adding 30B and/or POEMA was confirmed using thermogravimetric analysis (TGA). The storage modulus, Young's modulus and tensile strength of PA 6 were increased after adding 30B. However, these properties declined after further incorporation of POEMA. The different-processed PA 6/30B/POEMA nanocomposites displayed balanced tensile properties and toughness between those of neat PA 6 and PA 6/30B nanocomposite.     

Morphology and mechanical properties of polypropylene/organoclay nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin‐screw extruder. The effect of molecular weight of PP‐MA (maleic anhydride‐ modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP‐MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X‐ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP‐ MA330k/clay, a well‐dispersed two‐component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP‐MA330k/clay, an intercalated three‐component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002     

Influence of organo-montomorillonite on mechanical and rheological properties of polyamide nanocomposites

The effect of organically modified montmorillonite (OMMT) on polyamide nanocomposites was studied. OMMT/polyamide nanocomposites were prepared through direct melt compounding on a conventional twin screw extruder. With increasing the loading of OMMT, the Young modulus, elongation at break and tensile strength increased. 1 mass% loading of OMMT/polyamide resulted in 11% increase of the elongation at break compared to virgin polymer, while 4% loading showed 13%. Rheological data like torque, fusion time, viscosity and shear rate were also recorded on Brabender Plasticorder and were correlated with M = CS^a and τ = K(γ)ⁿ. The value n < 1 indicated pseudo-plastic nature of the polyamide/OMMT. The torque decreased with increased loading due to soft nature of OMMT, which acts as a lubricating agent. This improvement in mechanical properties with increase in amount of OMMT loading was also indicated by the reduction in shear viscosity and torque.     

Microstructures and mechanical properties of polypropylene/polyamide 6/polyethelene-octene elastomer blends

A series of polymer blends were designed and manufactured. They are composed of three phases: polypropylene (PP), polyamide-6 (PA6) and polyethylene-octene elastomer (POE) grafted with maleic anhydride. The weight fraction of PA6 was adjusted from 0 to 40% by increments of 10%, and the weight fraction of POE was systematically half that of PA6. The morphology, essentially made of PA6 particles dispersed in the PP matrix, was characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the extruded plates prepared with the blends, the shape of the dispersed PA6 particles showed an elongated ellipsoidal shape, whose aspect ratio increased somehow with alloying content. The POE modifier was observed both as a thin interlayer (less than 100 nm thickness) at the PP/PA6 interface, and as a few isolated particles. The elastic modulus and yield stress in tension are nearly constant for PP and blends. By contrast, the notched Izod impact strength increases very much with alloying content. This remarkable effect is interpreted in terms of POE interphase cavitation, enhanced plastic shear deformation and resistance of PA6 particles to crack propagation.     

Morphology and mechanical properties of PA6/organoclay nanocomposites toughened by bulk rubber and core-shell rubber

Reactive bulk rubber (EOR-g-MA) and reactive core-shell rubber (ABS-g-MA) are selected as toughening agents to toughen PA6 nanocomposites. The two blends are designed with 20?wt-% rubber phase and 3?wt-% organoclay. X-ray diffraction, transmission electron microscopy and scanning electron microscopy were used to evaluate the degree of exfoliation of organoclays and morphology of the nanocomposites. The organoclay platelets are well exfoliated in the nanocomposites. At the same time, the size of the elastomer particles and interfacial adhesion between polyamide 6 and elastomers are dramatically affected by the existence of organoclay. ABS-g-MA is found to promote the toughness efficiency of PA6 than does EOR-g-MA, which reveals higher impact strength and elongation at break. However, tensile strength and Young's modulus of PA6 blends based on EOR-g-MA elastomer are higher than those based on ABS-g-MA elastomer.     

Microstructure and mechanical properties of microcellular injection molded polyamide-6 nanocomposites

The microstructure and mechanical properties of microcellular injection molded polyamide-6 (PA6) nanocomposites were studied. Cell wall structure and smoothness were determined by the size of the crystalline structure, which, in turn, were based on the material system and molding conditions. The correlation between cell density and cell size of the materials studied followed an exponential relationship. Supercritical fluid (SCF) facilitated the intercalation and exfoliation of nanoclays in the microcellular injection molding process. The orientation of nanoclays near the surface of microcells and between microcells was examined and a preferential orientation around the microcells was observed. Nanoclays in the microcellular injection molding process promoted the γ-form and suppressed the α-form crystalline structure of PA6. Both nanoclays and SCF lowered the crystallinity of the parts. Microcells improved the normalized toughness of the nanocomposites. Both microcells and nanoclay had a significant influence on the mechanical properties of parts depending on the molding conditions.     

Preparation and characterization of polyimide/organoclay nanocomposites

Organically modified montmorrillonite clay, containing a long chain aliphatic quarternary ammonium cation, was used to prepare polyimide/organoclay hybrids. Several approaches were examined in an attempt to achieve fully exfoliated nanocomposites. These included simple mixing of the clay in a pre-made high molecular weight poly(amide acid) solution; simple mixing followed by sonication of the organoclay/poly(amide acid) solutions; and the preparation of high molecular weight poly(amide acid)s in the presence of the organoclay dispersed in N-methyl-2-pyrrolidinone (NMP). The best results were obtained using the in-situ polymerization approach. The resulting nanocomposite films (both amide acid and imide), containing 3-8% by weight of organoclay, were characterized by differential scanning calorimetry (DSC), dynamic thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thin film tensile properties. A significant degree of dispersion was observed in the nanocomposite films of the amide acid and the imide. After thermal treatment of amide acid films to effect imidization, in both air and nitrogen, the films were visually darker than control films without clay and the level of clay dispersion appeared to have decreased. In the latter case, the separation between the layers of the clay decreased to a spacing less than that present in the original organoclay. These observations suggest that thermal degradation of the aliphatic quarternary ammonium cation occurred likely during thermal treatment to effect imidization and solvent removal. These thermal degradation effects were less pronounced when thermal treatment was performed under nitrogen. The polyimide/organoclay hybrid films exhibited higher room temperature tensile moduli and lower strength and elongation to break than the control films.     

The effect of clay on the thermal degradation of polyamide 6 in polyamide 6/clay nanocomposites

The degradation pathway of polyamide 6/clay nanocomposites was studied as a function of clay content. Well-dispersed polymer-clay nanocomposites can be easily obtained by simple melt blending between organically-modified clays and polyamide 6. Polyamide 6-clay nanocomposites exhibit a large reduction in the peak heat release rate, 60%, measured by cone calorimetry. There are no significant differences in the evolved products during thermal degradation of polyamide 6 and polyamide 6/clay nanocomposites in terms of composition and functionality. The main degradation pathway of polyamide 6 is aminolysis and/or acidolysis, primarily through an intra-chain reaction, producing ε-carprolactam, which is the monomer of polyamide 6. As the clay loading is increased, the relative quantity of ε-carprolactam in the evolved products decreases and the viscosity of the soluble solid residues increases. It is thought that inter-chain reactions become significant in the presence of clay because the degrading polymer chains are trapped in the gallery space of the clay during thermal degradation.     

Effects of organoclay Soxhlet extraction on mechanical properties, flammability properties and organoclay dispersion of polypropylene nanocomposites

The organic treatment on a layered silicate used in nanocomposite synthesis is the interface between the hydrophilic layered silicate (clay) and hydrophobic polymer in the case of polypropylene. However, the typical synthesis of an organoclay can result in excess organic treatment which can hinder mechanical and flammability benefits. This excess organic treatment may result in plasticization of the polymer matrix, possibly removing some of the mechanical and flammability property benefits provided by the nanocomposite. In this paper, the effects of using Soxhlet Extraction on the Organoclays after synthesis was investigated. Soxhlet extraction times on organoclays were found to have an effect on the mechanical and flammability properties of the resulting polypropylene nanocomposite. The removal of excess organic treatment by Soxhlet extraction resulted in improvements in flex modulus, improved clay dispersion, delayed time to ignition, and lowered heat release rate during burning.     

Crystallization behavior of polypropylene/polyamide 6/montmorillonite nanocomposites

Polymer blended materials such as polyamide 6 (PA6)/polypropylene (PP) blends have received considerable attention in recent years. To improve the compatibility of PA6 and PP, compatibilizers like maleic anhydride‐g‐polypropylene (MPP) are often added. In addition, organically modified montmorillonite (MMT) is also used to improve the properties of various materials. In this work, the crystallization behavior of PP/PA6/MMT nanocomposites with MPP compatibilizer was investigated systematically. The annealing process effectively improved the crystallization of α‐PP. The crystallization temperature (T_c) of PA6 was increased by ca 2–3 °C on introducing MPP or MMT alone to the PP/PA6 system, whereas T_c of PP underwent no obvious change. However, when MPP and MMT were added simultaneously, T_c of PP and PA6 increased by 6.6 and 4.2 °C, respectively, and a new crystallization peak corresponding to PP‐g‐PA6 copolymer phase was observed at 162.5 °C. The combined effect of MPP and MMT led to better compatibility of PP with PA6. Moreover, the results of a non‐isothermal crystallization kinetics experiment revealed that the simultaneous introduction of MPP and MMT markedly shortened the crystallization time. Copyright © 2010 Society of Chemical Industry     

Investigation on the Polyamide 6/SEBS-g-MA/Organoclay Nanocomposites with Glycidyl Methacrylate as a Compatibilizer

Polyamide 6 (PA6)/maleated styrene-ethylene/butadiene-styrene copolymers (SEBS-g-MA)/organoclay (DK5) composites with glycidyl methacrylate (GMA) as a compatibilizer were prepared by melt compounding. The influences of maleating, DK5 and GMA on interfacial adhesion and mechanical properties of PA6 composites were investigated in terms of SEM observations, mechanical testing, Molau tests, IR analyses, and rheological behavior. Satisfactorily balanced mechanical properties of the composite could be achieved in the presence of GMA. Both DK5 and GMA retarded the crystallization of PA6. The storage modulus, loss modulus, and complex viscosity of the composites were obviously affected by the addition of DK5 and GMA.     

Effect of organoclay structure on morphology and properties of nanocomposites based on an amorphous polyamide

An amorphous polyamide (a-PA) and three organoclays, M₃(HT)₁, M₂(HT)₂ and (HE)₂M₁T₁, were melt processed to explore the effect of the organoclay structure on the extent of exfoliation and properties of these nanocomposites. Wide angle X-ray scattering, transmission electron microscopy, and stress-strain behavior were used to determine the degree of exfoliation of the nanocomposites. For quantitative assessment of the structure of the nanocomposites, a detailed particle analysis was made to provide various averages of the clay dimensions and aspect ratio. The results evaluated from different methods were generally consistent with each other. Nanocomposites based on the organoclays with one alkyl tail and hydroxyl ethyl groups gave well-exfoliated structures and high matrix reinforcement while nanocomposites from two-tailed organoclay contain a considerable concentration of intercalated stacks. Nanocomposites from the organoclays with one alkyl tail showed slightly better exfoliation and matrix reinforcement than those from the organoclays with hydroxyl ethyl groups. The organoclay structure trends for a-PA are analogous to what has been observed for nylon 6; this suggests that a-PA, like nylon 6, has good affinity for the pristine silicate surface of the clay leading to better exfoliation and enhanced mechanical properties with one-tailed organoclay than multiple-tailed organoclay. Furthermore, heat distortion temperatures were predicted from the dynamic mechanical properties of nanocomposites.     

The morphology and mechanical properties of dynamic packing injection molded PP/PS blends

As a part of long-term project aimed at super polyolefin blends, in this work, we report the mechanical reinforcement and phase morphology of the immiscible blends of polypropylene (PP) and polystyrene (PS) achieved by dynamic packing injection molding (DPIM). The shear stress (achieved by DPIM) and interfacial interaction (obtained by using styrene-butadiene-styrene (SBS) as a compatibilizer) have a great effect on phase morphology thus mechanical properties. The shear-induced morphology with core in the center and oriented zone surrounding the core was observed in the cross-section areas of the samples. The phase inversion was also found to shift towards lower PS content under shear stress, at 70 wt% in the core and 30 wt% in the oriented zone, compared with 80 wt% for static samples (without shear). The tensile strength, tensile modules and impact strength were found largely increase by means of either shear stress or compatibilizer. The PS particle size is greatly reduced with adding of SBS, and the reduced particle size results in greater resistance to deformation, which causes the co-continuous structure at oriented zone change into droplet morphology. The morphology resulting from blending and processing was discussed based on effect of interfacial tension, shear rate, phase viscosity ratio and composition. The observed change of mechanical properties was explained based on the combined effect of phase morphology (droplet-matrix or co-continuous phase) and molecular orientation under shear stress.     

Water absorption and hygrothermal aging study on organomontmorillonite reinforced polyamide 6/polypropylene nanocomposites

The water absorption and hygrothermal aging behavior of organomontmorillonite (OMMT) reinforced polyamide 6/polypropylene (PA6/PP ratio = 70/30), with and without maleated PP (MAH‐g‐PP), was studied at three different temperatures (30, 60, and 90°C). The water absorption and hygrothermal aging response of the composites was studied and analyzed by tensile tests and morphology assessment (scanning electron microscopy and transmission electron microscopy), indicating the effect of the immersion temperature, OMMT, and MAH‐g‐PP compatibilizer. The mathematical treatment used in analyzing the data was the single free phase model of diffusion, which assumed Fickian diffusion and utilized Fick's second law of diffusion. The kinetics of water absorption of the PA6/PP nanocomposites conformed to Fickian law behavior, whereby the initial moisture absorption follows a linear relationship between the percentage gain at any time t and t^1/2 (the square root of time), followed by saturation. It was found that the equilibrium moisture content and the diffusion coefficient are dependent on the OMMT loading, MAH‐g‐PP concentration, and immersion temperatures. Both the tensile modulus and strength of the PA6/PP nanocomposites deteriorated after being exposed to hygrothermal aging. MAH‐g‐PP acted as a good compatibilizer for PA6/PP/OMMT nanocomposites, which was attributed to its higher retention ability in modulus and strength (in the wet and redried states), lower equilibrium moisture content, and reduced water diffusivity of the nanocomposites. Morphological sketches for both uncompatibilized and MAH‐g‐PP compatibilized PA6/PP/OMMT nanocomposites, toward water uptake are proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 780–790, 2005     

Oxygen permeation through films of compatibilized polypropylene/polyamide 6 blends

Polypropylene/polyamide 6 blends were prepared by melt mixing, without or with the addition of a suitable commercial product, a polypropylene grafted with 1% maleic anhydride, used as an interfacial modifier. The oxygen permeation through their films was studied as a function of temperature and the effect of the presence of the compatibilizer on the barrier properties of the material was examined. In addition, the diffusion coefficients were measured. The relationships between transport parameters and blend morphology were investigated by microscopic observations, together with chemical etchings, and a simple model was applied for interpreting the experimental permeation data. Differential scanning calorimetry was used in the determination of the degree of crystallinity of the blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1941–1949, 1999     

Cocontinuous phase morphology for an asymmetric composition of polypropylene/polyamide 6 blend by melt mixing of polypropylene with premelted polyamide 6/organoclay masterbatch

Cocontinuous morphology was obtained for an asymmetric composition of polypropylene/polyamide 6 (70/30 w/w) blend by controlling melt compounding sequence of PP, PA6, and organoclay. Three different compounding sequences were tested: direct melt mixing of all the components, melt mixing of PP with PA6/organoclay masterbatch, and melt mixing of PP with premelted PA6/organoclay masterbatch. Only the third method promotes cocontinuous morphology. In all three cases, organoclay locates preferentially in the PA6 phase and at the interface, although the level of organoclay dispersion is poorer in the case of direct mixing than in the two‐masterbatch approaches. The morphology evolution processes of the three different compounding sequences were investigated and revealed that the main reason for the formation of cocontinuous morphology in the third method is the inhibiting effect of organoclay preincluded in the premelted PA6 phase on phase inversion. The viscosity of PA6 phase and the barrier effect of organoclay were confirmed to be two key factors in promoting cocontinuous structure. Dynamic mechanical analysis shows that the blend having cocontinuous morphology displays higher storage modulus than those having matrix‐dispersed morphology at the same organoclay loading. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Twin‐screw extrusion compounding of polypropylene/organoclay nanocomposites modified by maleated polypropylenes

Polypropylene/organoclay nanocomposites modified with different maleic anhydride grafted polypropylene (PPgMA) compatibilizers were compounded on a twin‐screw extruder. The effectiveness of the feeding sequence and compatibilizer type toward the dispersion of organoclay into PP matrix was critically studied. The composites prepared with side feed appeared to provide better dispersion and modulus improvement over that with hopper feed. The effect of PPgMA compatibilizers, including PB3150, PB3200, PB3000, and E43, with a wide range of maleic anhydride (MA) content and molecular weight was also examined. The structure was investigated with X‐ray diffraction and transmission electron microscopy. 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 were determined by dynamical mechanical analysis and tensile and impact tests. Maleated polypropylene with low‐melt flow index and moderate MA content enhanced clay dispersion and resulted in significant improvement in tensile modulus of the nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 100–112, 2004     

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