Polymer/layered silicate nanocomposites: a review from preparation to processing

To progress from the laboratory to commercial applications, it will be necessary to develop industrially scalable methods to produce large quantities of defect-free graphene. Here we show that high-shear mixing of graphite in suitable stabilizing liquids results in large-scale exfoliation to give dispersions of graphene nanosheets. X-ray photoelectron spectroscopy and Raman spectroscopy show the exfoliated flakes to be unoxidized and free of basal-plane defects. We have developed a simple model that shows exfoliation to occur once the local shear rate exceeds 10(4) s(-1). By fully characterizing the scaling behaviour of the graphene production rate, we show that exfoliation can be achieved in liquid volumes from hundreds of millilitres up to hundreds of litres and beyond. The graphene produced by this method performs well in applications from composites to conductive coatings. This method can be applied to exfoliate BN, MoS2 and a range of other layered crystals.

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Scalable production of large quantities of defect-free few-layer graphene by shear exfoliation in liquids

Infrared thermography for condition monitoring – A review

https://cyberleninka.org/article/n/397502.pdf

Melt rheology of organoclay and fumed silica nanocomposites

This paper is a review of polymer nanocomposites used for flame retardancy applications, including commercial materials and open literature examples. Where possible, details on how the nanocomposite and flame retardant work together will be discussed. The key lesson from this review is that while the polymer nanocomposite can be considered to be flame retarded (or a flame retardant) by definition, these materials by themselves are unable to pass regulatory fire safety tests such as UL-94 V. Therefore, additional flame retardants are needed in combination with the polymer nanocomposite to pass these tests. In multiple examples, the nanocomposite works with other flame retardants in a synergistic or cooperative manner to lower the polymer flammability (heat release rate). Finally, a discussion on research needs and outlook for polymer nanocomposite flammability research is included. Copyright © 2006 John Wiley & Sons, Ltd.

Flame retarded polymer layered silicate nanocomposites: a review of commercial and open literature systems†

Nanocomposites of polystyrene (PS) with up to 20 wt% organoclay were prepared by melt compounding in a co-rotating, intermeshing twin-screw extruder. Three grades of PS with different molecular weights were used. In this paper we discuss preparation and characterization of the mixtures. Residence time and its distribution were measured by ultrasonics (US). They were found to be independent of the PS grade, but the US attenuation and sound velocity varied with the organoclay loading. According to the XRD diffraction data, the organoclay was dispersed into two types of platelet stacks evidenced by the diffraction peaks at about 2θ = 2.1 and 5.5°, i.e., with the interlayer spacings of d 001 = 4.20 and 1.6 nm, respectively. Since neat organoclay has d 001 = 1.93 nm, the first peak indicates intercalation by PS and the other a collapse of the interlamellar gallery during compounding. The XRD spectra depended on the organoclay content, but not on PS grade. According to TEM analysis, the degree of intercalation of organoclay in the polymer matrix is highest for the low-molecular-weight polystyrene. TEM results also confirm the collapse of interlamellar spacing in parts of the samples. FT-IR spectroscopy showed that there was some thermal degradation of the onium compound present in the nanoclay.

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Melt compounding of different grades of polystyrene with organoclay. Part 1: Compounding and characterization

During the molding of industrial parts using injection molding, the molten polymer flows through converging and diverging sections as well as in areas presenting thickness and flow direction changes. A good understanding of the flow behavior and thermal history is important in order to optimize the part design and molding conditions. This is particularly true in the case of automotive and electronic applications where the coupled phenomena of fluid flow and heat transfer determine to a large extent the final properties of the part. This paper presents a 3D finite element model capable of predicting the velocity, pressure, and temperature fields, as well as the position of the flow fronts. The velocity and pressure fields are governed by the generalized Stokes equations. The fluid behavior is predicted through the Carreau Law and Arrhenius constitutive models. These equations are solved using a Galerkin formulation. A mixed formulation is used to satisfy the continuity equation. The tracking of the flow front is modeled by using a pseudo-concentration method and the model equations are solved using a Petrov-Galerkin formulation. The validity of the method has been tested through the analysis of the flow in simple geometries. Its practical relevance has been proven through the analysis of an industrial part.

3D finite element method for the simulation of the filling stage in injection molding

Polyethylene terephthalate (PET) was mixed by extrusion with clay (montmorillonite) to produce nanocomposites. Additives (pentaerythrytol and maleic anhydride) were added to induce compatibility between the particles and the matrix. Thermal, mechanical and rheological properties of the nanocomposites were evaluated. The nanocomposites with additives presented improved mechanical strength. In shear, the viscoelastic properties decrease with rising particle concentration and additives content. The resulting new materiales present processing advantages and potential improvements in performance.

Production of nanocomposites of PET‐montmorillonite clay by an extrusion process

Polystyrene-based nanocomposites (PNC) were prepared using three grades of polystyrene (different molecular weights). The resin was melt-compounded with 0 to 10 wt% of commercial organoclay in a co-rotating twin-screw extruder. Owing to thermo-oxidative degradation the degree of dispersion was poor. The rheological properties of PNC were determined under dynamic and steady state shear as well as under extensional flow conditions. At the higher clay content, dynamic strain sweep demonstrated that the storage and loss moduli decrease continuously with an increase of strain. To characterize this nonlinear viscoelastic behavior, the Fourier-transform rheology was applied. The low strain frequency sweep showed that the storage and loss moduli increase with organoclay content. The extracted zero-shear viscosity data were used to calculate the intrinsic viscosity and then the aspect ratio of dispersions. In spite of nonlinear viscoelastic behavior, the time-temperature superposition was observed in the full range of concentration. The horizontal and vertical shift factors were found to be almost independent of organoclay content and molecular weight of PS. For comparison, PNC was also prepared by the solution method. A high degree of dispersion was obtained, reflected in the aspect ratio: p = 269, to be compared with p = 16 calculated for the melt-compounded PNC.

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Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

We discuss the effects of the melt compounding variables, matrix molecular weight and organoclay content on the X-ray diffraction (XRD) and mechanical properties of polystyrene (PS)/organoclay nanocomposites (PNC) prepared in a twin-screw extruder. An increase of residence time reduced the height of the first XRD peak and increased that of the second peak. Barrel temperature and screw configuration had a little influence on the tensile properties and impact strength. Young's modulus increased with organoclay content and it was almost independent of matrix PS molecular weight. The stress-at-break and impact strength decreased with organoclay content and increased with PS molecular weight. Young's modulus and impact strength decreased with residence time. Since the slopes of these dependencies for PNC were similar to that of the neat PS, the matrix degradation seems to play the major role. The relationship between impact strength and elongation at break of PNC showed high dependency on matrix grade. However, better empirical correlation was observed between the impact and tensile strengths. According to theoretical model of Ji et al. [32], the Young's modulus vs. clay concentration dependence indicated the presence of low interphase thickness. POLYM. ENG. SCI. 45:827–837, 2005. © 2005 Society of Plastics Engineers

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A. Garcia-Rejon

Papers

Melt compounding of different grades of polystyrene with organoclay. Part 1: Compounding and characterization

3D finite element method for the simulation of the filling stage in injection molding

Production of nanocomposites of PET‐montmorillonite clay by an extrusion process

Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

Melt compounding of different grades polystyrene with organoclay. Part 3: Mechanical properties