Nanocomposite Melts Research Articles

The effect of polymer-induced attraction on dynamical arrests of polymer composites with bimodal particle size distributions

We explore the flow properties of nanocomposite melts where the particles have bimodal size distributions and experience a weak attraction produced by suspending silica particles in polyethylene glycol melts with a molecular weight of 2000 (PEG2000). The polymer is unentangled and adsorbs to the particle surface. The volume fraction ratio of large particles to total particle volume fraction, R, is systematically varied to study the effects of this polymer-induced attraction on suspension rheology. The maximum volume fraction, ϕm, of the particles varies in a nonmonotonic manner of R as demonstrated in studies of the same mixtures when suspended in polyethylene glycol with a molecular weight of 400 (PEG400), where the particles experience excluded volume interactions. The dynamical arrest volume fraction ϕx, of nanocomposite melts in PEG2000 monotonically increases with R. In frequency sweep experiments, the plateau elastic modulus is dominated by attractive interactions and increases with the total partic...

Online ultrasonic film casting of LLDPE and LLDPE/clay nanocomposites

AbstractTransparent cast films of linear low density polyethylene (LLDPE) with nanoclay up to 10 wt % were prepared in one step process using an ultrasonically assisted compounding extruder operating at various ultrasonic amplitudes combined with film casting machine operating at various take up speeds. Thermal, rheological, morphological, and mechanical properties and gas permeability of these films were studied. Ultrasonic treatment introduced an increase in the complex viscosity and storage modulus and a reduction in the tangent loss of LLDPE/clay nanocomposite melts. Cast films prepared by ultrasonic treatment at an amplitude of 7.5 μm showed the highest mechanical properties in both the machine and transverse directions and the lowest oxygen permeability. X‐ray diffraction patterns along with the SEM and TEM images revealed the presence of the exfoliated structure due to the ultrasonic treatment for cast films containing up to 7.5 wt % of clay loading. NMR studies of LLDPE cast films showed an increase of branching due to the ultrasound treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

HMSPP nanocomposite and Brazilian bentonite properties after gamma radiation exposure

This work concerns the study of the mechanical and thermal behavior of the nanocomposite high melt strength polypropylene (HMSPP) (obtained at a dose of 12.5kGy) and a bentonite clay Brazilian Paraiba (PB), which is known as “chocolate” and is used in concentrations of 5% and 10% by weight, in comparison to the American Cloisite 20A clay nanocomposites. An agent compatibilizer polypropylene-graft (PP-g-AM) was added at a 3% concentration, and the clay was dispersed using the melt intercalation technique using a twin-screw extruder. The specimens were prepared by the injection process. The mechanical behavior was evaluated by strength, flexural strength and impact tests. The thermal behavior was evaluated by the techniques of differential scanning calorimetry (DSC) and thermogravimetry (TGA). The morphology of the nanocomposites was studied with scanning electron microscopy (SEM), while the organophilic bentonite and nanocomposites were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).

The orientation of carbon nanotubes in poly(ethylene‐co‐octene) microcellular foaming and its suppression effect on cell coalescence

AbstractPoly(ethylene‐co‐octene)/multiwall carbon nanotube (PEOc/MWNT) nanocomposites were prepared by a melt blending process. The MWNT's solubility and the transmission electron microscopy (TEM) observation indicated that the MWNT bonded well with a PEOc matrix. This facilitated the orientation of the MWNT when shear and extensional forces were applied to the nanocomposite melts. Microcellular PEOc/MWNT nanocomposite foams were prepared by a rising temperature process using supercritical CO2 as the blowing agent. Various foaming times were selected to reveal the cell‐structure evolution during the cell growth stage. The obvious cell opening, resulting from cell coalescence, was observed in the cell wall in the neat PEOc foams. When the MWNT was introduced, however, the MWNT tended to orient in the cell wall. Here, as a result of the strain hardening, it acted as a self‐reinforcing element, protecting the cells from destruction during cell growth. Consequently, a dramatic decrease in the open cell content and a still high cell density at long foaming times were obtained in the PEOc/MWNT nanocomposite foams. The present study provides experimental evidence of the vital effects of nanoparticle orientation on cell coalescence. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

The role of cellulose nanofibres in supercritical foaming of polylactic acid and their effect on the foam morphology

In this paper, we investigate the role of cellulose nanofibres (CNFs) in the supercritical foaming process of polylactic acid (PLA). The supercritical foaming process of nanocomposites is determined by the nucleating efficiency of the nanoparticle and rheological properties of the polymer melt. Here, the nucleating efficiency of surface acetylated CNFs was compared with that of native CNFs and different CNF loadings were introduced into the PLA matrix forming more or less stiff networks. We characterized the tensile and shear properties of the nanocomposite melts and studied the surface tension at the nucleating site. It was observed that the introduction of CNFs significantly improved the morphology of PLA foams. Both the amount of CNFs and surface acetylation contributed to the reduction in cell size and increase in cell density. The nucleating effect of the CNF surface was clearly evidenced and revealed to be enhanced by surface acetylation. Improved morphology in nanocomposite foams was therefore explained by the interplay of the nucleating and rheological effects of CNFs during the foaming process. Finally, the potential of CNFs to generate nanoporous structures via supercritical foaming was discussed.

PPDO-PU/Montmorillonite Nanocomposites Prepared by Chain-Extending Reaction: Thermal Stability, Mechanical Performance and Rheological Behavior

A two-step approach was employed to prepare Poly(p-dioxanone)-PU/organic montmorillonite (PPDO-PU/OMMT) nanocomposites. In the first step, PPDO diol prepolymers with different molecular weights were synthesized by ring-opening polymerization of p-dioxanone; in the second step, PPDO-PU/OMMT nanocomposites were prepared by coupling PPDO diol melt swollen with organo-modified MMT (OMMT), using 1,6-hexamethylene diisocyanate (HDI) as the chain-extender. The intercalated-exfoliated coexistence morphology of nanocomposites was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TG), high-pressure capillary rheometer, and mechanical test were performed to investigate the properties of the nanocomposites. The results showed that the thermal stability and mechanical performance of nanocomposites were greatly improved compared to that of pure PPDO. The enhancement of shear viscosity and low temperature sensitivity of the nanocomposite melts enabled it to produce thin films by blowing process successfully.

Study on Structure and Rheological Properties of PET/PTT/MMT Nanocomposites

Poly(ethylene terephthalate)(PET)/poly(trimethylene terephthalate)(PTT) /Montemorillonite(MMT) nanocomposites were prepared by melt blending through a co-rotating twin screw extruder. The wide angle X-ray diffraction(WAXD) patterns proved the nanocomposites formed exfoliated or intercalated structures. The rheological properties of PET/PTT/MMT were studied by RH2000 capillary rheometer. The results show that PET/PTT and PET/PTT/MMT melts are all pseudo-plastic fluids, and the addition of one to five part MMT can obviously improve the flow property of PET/PTT melt. The apparent viscosity (ηa) of the nanocomposite melts is lower than that of PET/PTT melt, and their flow behavior is better than that of PET/PTT melt, so the nanocomposites can be processed at lower temperature. The viscous flow activation energy(ΔEη) of the nanocomposite melts is higher than that of PET/PTT melt, and it is more proper for the nanocomposite melts to improve their flow properties by increasing temperature.

Poly(propylene)/Carbon Nanofiber Nanocomposites: Ex Situ Solvent‐Assisted Preparation and Analysis of Electrical and Electronic Properties

AbstractCNF‐reinforced PP nanocomposites were fabricated from CNFs dispersed in a boiling PP/xylene solution. Their thermal properties were characterized by TGA and DSC and shown to exhibit improved thermal stability and higher crystallinity. They were further processed into thin films by compression molding. The electrical conductivity and dielectric property of the PP/CNF nanocomposite thin films were studied. Both electric conductivity and real permittivity increased with increasing fiber loading. Electrical conductivity percolation is observed between 3.0 and 5.0 wt.‐% fiber loading. The rheological behavior of the nanocomposite melts were also investigated. It was found that a small fiber concentration affects the modulus and viscosity of PP melt significantly. magnified image

Dependence of microstructures and melt behaviour of polypropylene/fullerene C60 nanocomposites on in situ interfacial reaction

Polypropylene (PP)/fullerene C60 nanocomposites, in which the interfacial reaction between two components was in situ mediated by peroxide, were prepared by a melt mixing method. Structural characterization showed that the interfacial reaction strongly affected the microstructures of PP/C60 nanocomposites at different scales, such as improving the dispersion state of C60 nanoparticles and forming long chain branched structures in which C60 acts as a branching point. This was ascribed to the ability of C60 (as a reactive nanoparticle) for preferentially trapping carbon-centred macroradicals of PP to in situ form long chain branched structures of PP on the surface of C60 during melt mixing. As a result, the shear-responsive sensitivity of the nanocomposite melts in low shear frequency regions was dramatically enhanced compared to parent PP and the nanocomposites without interfacial reaction. The nanocomposites also showed high melt strength. In addition, the transition from the melt state to solid state (crystallization process) occurred at higher temperature after the interfacial reaction between PP and C60 took place.

Effect of the structure and shape of filler nanoparticles on the physical properties of polyimide composites

Model nanocomposites on the basis of specially synthesized amorphous and semicrystalline polyimide matrices, silicate (natural and synthetic) and carbon nanoparticles with different morphology (tubes, platelets, discs, and spheres) have been developed. The influence of nanoparticle morphology on the rheological behavior of nanocomposite melts at the stage of their processing has been investigated.

Anomalous chain diffusion in polymer nanocomposites for varying polymer-filler interaction strengths

Anomalous diffusion of polymer chains in a polymer nanocomposite melt is investigated for different polymer-nanoparticle interaction strengths using stochastic molecular dynamics simulations. For spherical nanoparticles dispersed in a polymer matrix the results indicate that the chain motion exhibits three distinct regions of diffusion, the Rouse-like motion, an intermediate subdiffusive regime followed by a normal Fickian diffusion. The motion of the chain end monomers shows a scaling that can be attributed to the formation of strong "networklike" structures, which have been seen in a variety of polymer nanocomposite systems. Irrespective of the polymer-particle interaction strengths, these three regimes seem to be present with small deviations. Further investigation on dynamic structure factor shows that the deviations simply exist due to the presence of strong enthalpic interactions between the monomers with the nanoparticles, albeit preserving the anomaly in the chain diffusion. The time-temperature superposition principle is also tested for this system and shows a striking resemblance with systems near glass transition and biological systems with molecular crowding. The universality class of the problem can be enormously important in understanding materials with strong affinity to form either a glass, a gel or networklike structures.

“Gel-like” Mechanical Reinforcement in Polymer Nanocomposite Melts

We critically explore the role of particle dispersion on the melt state mechanical properties of nanocomposites formed by mixing polystyrene homopolymers with polystyrene grafted silica nanoparticl...

Nonlinear time-dependent response of polypropylene/nanoclay melts: Experiments and modeling

Abstract Observations are reported on polypropylene/compatibilizer/nanoclay hybrid melts with a fixed clay/compatibilizer proportion 1:2 and various concentrations of filler (from 0 to 5 wt.%) in start-up shear tests with a constant strain rate and relaxation tests at various strains (in the interval of shears between 1 and 20). It is shown that growth of nanoclay content leads to formation of stress overshoot in start-up tests and slowing down of the relaxation process (which is strongly affected by strain). A constitutive model is derived for the time-dependent response of nanocomposite melts under three-dimensional deformations with finite strains, and its adjustable parameters are found by fitting the experimental data. It is demonstrated that some critical concentration of nanoclay exists (about 1 wt.%), at which the mean activation energy for rearrangement of chains and its standard deviation are minimal. The presence of a threshold concentration of filler is confirmed by observations in uniaxial tensile tests on solid nanocomposites.

The chaos-to-order transition in critical modes of shearing for polymer and nanocomposite melts

Two unusual experimental phenomena that were found for polymer melts or solutions containing the dispersed phases of Na-montmorillonite or detonation synthesis nanodiamond have been studied. These phenomena consist in the reduction of viscosity upon addition of specified amount of particles and in the formation of regular morphology by these particles in strong flows looking as a system of concentric rings. In other words, under certain conditions, there is transition to stratified shear stream and the viscosity of such a regular heterogeneous system canbe lower than that for the polymer matrix itself. Hence, both phenomena are mutually related; and the main problem here is the analysis of driving forces leading to the regular texture formation taking place in intense flows for unfilled viscoelastic polymers as well. As a preliminary explanation, the conception of the special kind of the elastic instability is discussed. This instability appears either in the regular helix-like structure formation or in the irregular elastic turbulence. The particles of the filler play a role of tracers that revealed the relief of texture.

Rheology and Microstructure of Entangled Polymer Nanocomposite Melts

The rheology and microstructure of 44 nm diameter silica particles suspended in entangled poly(ethylene oxide) (PEO) melts are studied through measurement of filled melt viscosity and X-ray scattering measurement of interparticle structure factors, S(q,ϕc), where q is the scattering vector and ϕc is the silica volume fraction. The particles have a similar refractive index to PEO which minimizes van der Waals attractions acting between particles. The introduction of particles causes an elevation in the viscosity of the nanocomposite melt more than would be expected of particles merely interacting with hard core repulsions. Further addition of particles causes a rise in the elastic and viscous moduli. The rheological characterization of these nanocomposite melts is discussed in terms of several critical particle volume fractions that result from confinement of polymer, adsorption of polymer segments to the particle surface, and overlap and entanglement of adsorbed polymer as the particle volume fraction is ...

Preparation of extruded melt‐mixed polypropylene/montmorillonite nanocomposites with inline monitoring

AbstractThis article advances the use of an inline optical detector to monitor the disaggregation of the montmorillonite (MMT) clay tactoids during the preparation of polypropylene (PP)/MMT nanocomposites via polymer melt compounding. During the exfoliation of the tactoids their size are reduced below the minimum particle size to produce light extinction and so, the signal of the inline detector reduces as the nanosize composite is formed. The measurement is done at the transient state with the MMT clay added as a pulse with constant weight into the PP extrusion melt flow and followed by the optical detector. The data comes out as the common residence time distribution curves having its maximum intensity related to the tactoids average particle size, keeping all other variables constants. The light extinction was measured for composites with different clays (Cloisite® 15A, 30B, Na+, and Sintered 20A) using the same PP grafted with maleic anhydride compatibilizer. The dissaglomeration/exfoliation efficiency increases as: ‘‘Sintered 20A’’ < ‘‘Na+ clay’’ < ‘‘organo‐modified clay’’ < ‘‘organo‐modified clay + compatibilizer’’. The best result is obtained using Cloisite® 15A and Cloisite® 20A following the expected reduction of the particle size obtained during a nanocomposite melt processing. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Dynamic Rheological Behavior of Isotactic Polypropylene Filled With Nano-Calcium Carbonate Modified by Stearic Acid Coating

2 wt% and 6 wt% stearic acid (SA)-coated calcium carbonate (CaCO3) nanoparticles were compounded with isotactic polypropylene (iPP). Small-amplitude oscillatory shear tests were used to study the linear viscoelastic properties of the nanocomposite melts. The filler loading at which the composites exhibited the terminal modulus plateau was found to be much lower in the 6 wt% SA-coated particle composites than in the 2 wt% counterpart, and at the same filler content, apparently higher dynamic moduli and complex viscosities at low frequencies were shown in the former. The characteristics of pseudo-solid-like behavior almost disappeared in the 2 wt% SA-coated particle composites as the gap distance increased but were still observed in the 6 wt% counterpart. The results indicate that the dispersion of nanoparticles played a critical role in the motion of the macromolecular chains. At the same filler loading, the mobility of the iPP melts was more severely restricted by properly coated and well-dispersed nanoparticles than by aggregates due to insufficient coating.

Rheology and Microstructure of an Unentangled Polymer Nanocomposite Melt

The rheology and microstructure of 44 nm diameter silica particles suspended in unentangled polyethylene oxide (PEO) melts are studied through measurement of filled melt viscosity and X-ray scattering measurement of interparticle structure factors, S(q,ϕc), where q is the scattering vector and ϕc is the silica volume fraction. The neat polymer melts are Newtonian over the probed shear range. Filled melts have a constant viscosity at low particle concentrations and shear thin at high concentrations. At the same particle volume fraction, filled melt viscosities increase with polymer molecular weight. By defining an effective particle volume, assuming polymer adsorption adds 2.9Rg to the particle diameter, suspension viscosities of both molecular weights at all volume fractions resemble that of hard sphere suspensions. The particle osmotic compressibility and position and coherence of the first nearest neighbor shell suggest that the particles have radii larger than the core size due to polymer structuring n...

Viscoelasticity of polyethylene/montmorillonite nanocomposite melts

Observations are reported on low-density polyethylene melts reinforced with montmorillonite nanoclay at concentrations of filler ranging from 0 to 10wt.% in small-amplitude shear oscillatory tests, start-up tests with a constant strain rate, and relaxation tests. Constitutive equations are derived for the time-dependent response of a nanocomposite melt at three-dimensional deformations with finite strains. The model accounts for (i) inhomogeneity in the distribution of nanoparticles, (ii) non-affinity of an equivalent polymer network with sliding junctions, and (iii) evolution of energies of inter-chain interaction driven by orientation of clay platelets. It is demonstrated that the stress–strain relations correctly describe the experimental data and adjustable parameters change consistently with nanoclay content.

Thermo-viscoelastic response of nanocomposite melts

Observations are reported in shear oscillatory tests with small strains (the frequency-sweep mode) on a hybrid nanocomposite melt [thermoplastic elastomer (ethylene–octene copolymer) reinforced with various concentrations of montmorillonite nanoclay] at temperatures ranging from 150 to 210 °C. A constitutive model is developed for the viscoelastic behavior of a nanocomposite melt at arbitrary three-dimensional deformations with small strains. The melt is treated as an inhomogeneous, permanent polymer network with sliding junctions (entanglements and physical cross-links at the surfaces of nanofiller). It is assumed that macro-deformation induces sliding (plastic flow) of junctions between strands with respect to their reference positions, and the strain energy of the network depends on strain tensors for elastic and plastic deformations. Stress–strain relations are derived by using the laws of thermodynamics. These equations involve four adjustable parameters that are found by fitting the observations. It is demonstrated that (i) the governing equations correctly reproduce the experimental data and (ii) the material parameters change consistently with temperature and concentration of filler.