Polypropylene Clay Research Articles

Essential work of fracture and failure mechanisms of polypropylene–clay nanocomposites

The fracture behavior of polymer nanocomposites (PNCs) based on a polypropylene with organo-modified clays (2 wt.%) and different coupling agents was studied by means of essential work of fracture (EWF). The PNC microstructure was characterized by clay particle dispersion at the micron scale (>1 μm) and sub-micron scale (200 nm to 1 μm), with good intercalation and partial exfoliation (<100 nm). Tensile testing showed significant improvements (+25–50%) corresponding to nanoparticle reinforcement effects. Fracture surfaces revealed that fracture occurred by void initiation at larger clay particles, followed by void growth and coalescence as the surrounding matrix stretched into ligaments. EWF improvements (+20%) were noted for PNCs that had fewer micron scale particles and showed higher tensile improvements. Toughness improvements were attributed to higher voiding stresses and improved matrix resistance attributed to finer, more oriented clay nanoparticles.

Additional evidence for the migration of clay upon heating of clay–polypropylene nanocomposites from X-ray photoelectron spectroscopy (XPS)

The explanation for reduction in the peak heat release rate of polymer–clay nanocomposites which is normally accepted is that clay accumulates at the surface, forming a thermal shield which is also a barrier to mass transport. The process by which this clay arrives at the surface has never been described in print but the common assumption is that pyrolysis is required for clay accumulation to occur. In this work, X-ray photoelectron spectroscopy, a tool much more sensitive in surface analysis than conventional techniques, is used to probe the surface of polypropylene–clay nanocomposites that have been annealed at relatively low temperatures, well below that required for pyrolysis. The composition of the surface changes with time and temperature of annealing, which provide a strong indication that the clay at the surface undergoes chemical change at fairly low temperatures.

Nonisothermal crystallization behavior of polypropylene–clay nanocomposites

The influence of two concentrations of clay nanoparticles on the nonisothermal crystallization behavior of the intercalated polypropylene–clay nanocomposites is investigated here. It is observed that the crystallization peak temperature ( T p) of PP–clay nanocomposites is marginally higher than neat PP at various cooling rates. Furthermore, the half-time for crystallization ( t 0.5) decreased with increase in clay content, implying the nucleating role of clay nanoparticles. The nonisothermal crystallization data is analyzed using Avrami, Ozawa and Mo and coworkers methods. The validity of kinetic models on the nonisothermal crystallization process of PP–clay nanocomposites is discussed. The approach developed by Mo and coworkers successfully describes the nonisothermal crystallization behavior of PP and PP–clay nanocomposites. The activation energy for nonisothermal crystallization of pure PP and PP–clay nanocomposites based on Kissinger method is evaluated.

Impact fracture behavior of clay–reinforced polypropylene nanocomposites

The micromechanism of plastic deformation during impact loading of polypropylene–clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70 °C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle–matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite.

Near surface deformation associated with the scratch in polypropylene–clay nanocomposite: A microscopic study

The near surface deformation during scratching of neat polypropylene (PP) and polymer nanocomposites (PP–clay) at loads of 0.2–6 kgf is described in terms of characteristics of scratch morphology and scratch deformation parameters. In neat PP, the application of higher loads introduces severe ironing deformation, disrupting the periodic parabolic nature of scratch tracks such that the material plastically flows along the ironing zone. Under identical test conditions, the severity of surface deformation in PP–clay nanocomposites, which leads to stress whitening is significantly reduced. At lower loads, the periodic nature of tracks is retained together with ironing, while at higher loads, ploughing occurred. The resistance to scratch deformation is discussed in terms of modulus, elastic recovery, and scratch hardness.

Polypropylene–clay blends compatibilized with MAH‐g‐POE

AbstractA series of new Polypropylene (PP)–clay blends, containing 5 wt % clay, were prepared by melt compounding with maleic anhydride grafted poly(ethylene‐co‐octene) (MAH‐g‐POE) as the compatibilizer by varying its content from 0 to 20 wt %. The effect of MAH‐g‐POE on the PP–clay miscibility was examined by X‐ray diffraction (XRD), scanning electronic microscope (SEM) observation, differential scanning calorimeter (DSC) analysis, dynamic mechanical thermal analysis (DMTA), and rheological testing in sequence. The results showed that the addition of MAH‐g‐POE could improve the dispersion of clay layers in PP matrix and promoted the interaction between PP molecules and clay layers. At 10 wt % MAH‐g‐POE, the PP–clay blend exhibited a highest value of Tc,onset and Tg as well as a biggest melt storage modulus (G′), indicating the greatest PP–clay interaction. On the other hand, improved toughness and stiffness coexisted in blends with 5–10 wt % loading of MAH‐g‐POE. In view of SEM and DMTA observations, MAH‐g‐POE was well miscible with the PP matrix, even with the concentration up to 20 wt %. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2558–2564, 2006

Chlorosulfonated polypropylene: preparation and its application as a coupling agent in polypropylene–clay nanocomposites

Polypropylene nanocomposites containing organophilic layered silicate were prepared by melt mixing. In order to increase polypropylene polarity, Cl and SO 2Cl groups were introduced by reaction with sulfuryl chloride under UV irradiation. Chlorosulfonated polypropylene was subsequently melt-compounded with organophilized montmorillonite clay to produce a masterbatch. The masterbatch was then blended with commercial isotactic polypropylene. An organophilized silicate (Cloisite 15A) and three chlorosulfonated polypropylenes with different degrees of functionalization were used in this study. The effect of various processing procedures was examined as well. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved. The observed morphologies affected the resulting tensile mechanical behaviour: both stiffness and strength significantly increased.

Photo-oxidative degradation of polypropylene/montmorillonite nanocomposites

The photo-oxidative behavior of the polypropylene (PP)/montmorillonite (MMT) nanocomposites and microcomposites has been investigated upon ultraviolet exposure using the technique of infrared spectroscopy. The rate of photo-oxidative degradation of PP/MMT nanocomposites is much faster than that of pure PP. The influence of pristine MMT, alkylammonium and compatibilizer were investigated, respectively. All these components can catalyze the photo-oxidation of PP matrix, in which the influence of compatibilizer and pristine MMT is primary. Moreover, the dispersion state of the clay particles in the polymer matrices has a little influence on the photo-oxidative degradation of polymer matrix. Consequently, an integrated catalysis mechanism of the photo-oxidative degradation of PP clay nanocomposite is proposed. It would provide benefit direction for the preparation and usage of polymer layered silicate nanocomposites (PLSN).

Properties of polypropylene clay nanocomposites modified with difunctional compounds

Three commercially available adhesion promoters based on silanes were used to modify montmorillonite. The short and highly reactive 3-aminopropyltrimethoxysilane (APS) is not able to expand the silicate layers. 3-(2-aminoethyl)aminopropyltrimethoxysilane (AEAPS) and 3-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) can be used for a cation exchange reaction in montmorillonite, but the layer distance in the modified clay material is rather low, especially for AHAPS. So mixtures with surfactants were used to modify montmorillonite. With dimethyldistearylammonium chloride as comodifier three ways of preparation of silanized organoclay were tested. Two of them lead only to a rather low content of silane adhesion promoter according to elemental analysis. After compounding with PP-g-MA a reaction of the primary amino group of the silane with PP-g-MA can be shown by IR-spectroscopy. Some samples were made in an amount sufficient for preparing composites on a Berstorff extruder and specimens were made by injection moulding. These were tested according to CAMPUS conditions showing increased mechanical properties in comparison to not silanized montmorillonite nanocomposites, although TEM pictures prove a worse distribution of clay.

Polypropylene–clay nanocomposites prepared by in situ grafting-intercalating in melt

Polypropylene–clay nanocomposites (PPCN) were prepared by in situ grafting-intercalating in melt. The organoclay was first modified with maleic anhydride (MA) in solution with a small quantity of a co-swelling agent and an initiator. It was then blended with PP in melt to obtain PP/clay grafting-intercalating composites (GIC). Finally, the GIC were blended with PP in melt to obtain PPCN. The nanostructure materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The XRD patterns show that the basal distance in the MA-modified organoclay was 30 nm, which was larger than that of the original organoclay (19.6 nm). The XRD and TEM results for GIC and PPCN demonstrate that the layers of clay were partially exfoliated in the GIC and fully exfoliated in the PPCN. PPCN showed good thermal stability in the TGA analysis. The increased storage modulus indicates that the clay has a reinforcing effect in the PP matrix. The increased T g of the PP/clay nanocomposites in dynamic mechanical analysis (DMA) implies that the PP macromolecules are intercalated or exfoliated between the interlayers of the silicate.

Thermal and mechanical properties of a polypropylene nanocomposite

AbstractAn experimental polypropylene (PP) nanocomposite, containing approximately 4 wt % of an organophilic montmorillonite clay, was prepared and characterized, and its properties were compared with those of talc‐filled (20–40 wt %) compositions. Weight reduction, with maintained or even improved flexural and tensile moduli, especially at temperatures up to 70°C, was a major driving force behind this work. By a comparison with the analytical data from a nylon 6 (PA‐6) nanocomposite, it was found that the PP nanocomposite contained well‐dispersed, intercalated clay particles; however, X‐ray diffraction, transmission electron microscopy, dynamic mechanical analysis, and permeability measurements confirmed that exfoliation of the clay in PP was largely absent. The increased glass‐transition temperature (Tg) of a PA‐6 nanocomposite, which possessed fully exfoliated particles, indicated the molecular character of the matrix–particle interaction, whereas the PP nanocomposite exhibited simple matrix–filler interactions with no increase in Tg. The PP nanocomposite exhibited a weight reduction of approximately 12% in comparison with the 20% talc‐filled PP, while maintaining comparable stiffness. Undoubtedly, considerable advantages may be available if a fully exfoliated PP nanocomposite is fabricated; however, with the materials available, a combination of talc, or alternative reinforcements, and nanocomposite filler particles may provide optimum performance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1639–1647, 2003

Early Stage Quiescent and Flow-Induced Crystallization of Intercalated Polypropylene Nanocomposites by Time-Resolved Light Scattering

Time-resolved light scattering demonstrates that the early-stage quiescent and flow-induced crystallization kinetics of an intercalated polypropylene clay nanocomposite differs significantly from t...

In-situ reactive blending to prepare polystyrene–clay and polypropylene–clay nanocomposites

Nanocomposites of polystyrene and polypropylene with organically-modified clay may be prepared by melt blending in a Brabender mixer the clay and the polymer. The presence of maleic anhydride increases the likelihood of nanocomposite formation for polystyrene but is less important for polypropylene. The materials that result are immiscible materials, in that the clay is not uniformly distributed throughout the polymer matrix, but there is polymer inserted between the clay layers. The results from cone calorimetry suggest that nanocomposite formation has occurred, since there is a significant reduction in the peak heat release rate.

Photodegradation of polypropylene nanocomposites

The photochemical behaviour of polypropylene–clay nanocomposites was studied. The samples were prepared by blending in the molten state isotactic polypropylene, organo-modified montmorillonite, i.e. layered silicate or clay modified with alkyl ammonium cations, and maleic anhydride-grafted polyprolylene as compatibilizer. The montmorillonite dispersion state within the iPP matrix was analyzed by Transmission Electron Microscopy. Accelerated photoageing of nanocomposites carried out at λ>300 nm and 60 °C was analysed by infrared spectroscopy. The oxidation products formed have been identified and the contribution of each component of the nanocomposite evaluated by studying different formulations. The presence of stabilisers in the formulation has also been analysed from the comparison of the rates of oxidation of several stabilised and non-stabilised nanocomposites.

Polypropylene–clay nanocomposites: effect of compatibilizing agents on clay dispersion

In this work, polypropylene–clay nanocomposites are obtained and studied by using two different coupling agents, diethyl maleate and maleic anhydride. Two different clays, a commercial montmorillonite (Nanomer I30.TC) and a sodium bentonite purified and modified with octadecylammonium ions have also been used. The relative influence of each factor, matrix and clay modification, can be observed from structural analysis (SAXS, TEM) and mechanical properties. An explanation of the results is proposed according to the microstructure and chemical nature of the systems and the thermodynamic interactions operating during nanocomposite preparation.

Plastic deformation behaviour of thermoplastic/clay nanocomposites

Polymer/clay nanocomposites are materials that display rather unique properties, even at low clay content, by comparison to more conventional mineral-filled polymers. Two systems are considered in the present study: the first one consists of nylon 6/clay hybrids in which in situ polymerisation is aimed at obtaining a nylon matrix strongly bonded to the delaminated clay platelets. The second one is prepared by melt dispersion of organophilic clay in polypropylene, which should in principle result in a reduced degree of polymer–clay interaction. Dynamic viscoelastic analysis is indeed indicative of a noticeable difference when referring to the molecular dynamics of the glass transition. Plasticity results, in which volume strain is recorded by video-extensometry, show extensive cavitational behaviour while retaining a fairly large strain at break, as long as deformation is performed above the glass transition temperature of the matrix. In the particular case of PA6, it is clear that the usual shear banding plastic deformation mode is altered at least in its initiation step. Localised interfacial damage promotes extensive polymer matrix fibrillation and fracture occurs predominantly in areas where delamination of the clay platelets was not fully achieved.

Polymeric Nanocomposites for Automotive Applications

New nanocomposites are currently being developed that have real industrial potential—loading a polymer with a small (ca. 5 %) amount of inorganic nanoparticles (the Figure shows a polypropylene–clay hybrid composite) is expected to give rise to significant improvement to the materials properties with only a minor increase in cost. Recent developments in this area are summarized here.

Preparation and mechanical properties of polypropylene-clay hybrids based on modified polypropylene and organophilic clay

Polypropylene–clay hybrids (PPCHs) were prepared by melt blending maleic anhydride modified PP and organophilic clay. In these PPCHs the silicate layers of the clay were exfoliated and dispersed to the monolayers. The hybridization of the clay in PP was achieved with modified PP with a small amount of maleic anhydride groups. The tensile modulus of the PPCH with 5 wt % clay was 1.9 times higher than that of the matrix resin at 25°C. The dynamic storage moduli (E′) of the PPCHs were also higher than those of the modified PP. The E′ was 2.5 times higher than that of the matrix resin at 60°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1918–1922, 2000