Direct Melt Mixing Research Articles

Processing dependency of percolation threshold of MWCNTs in a thermoplastic elastomeric block copolymer

We prepared carbon nanotube thermoplastic elastomeric block copolymer nanocomposites using a commercial styrene–ethylenebutylene–styrene (SEBS) block copolymer and multiwall carbon nanotubes (MWCNTs) at different filler concentrations. Hereto we applied two different processing strategies, namely direct melt mixing and solution-precipitation. We observe that the mechanical and electrical properties such as storage module and electrical percolation threshold are clearly affected by the processing approach. We studied these effects in detail by means of dielectric spectroscopy, which provided important information about the dispersion state of the MWCNT filler network. It revealed a fractal filler behaviour of the samples independent of the processing method. However, in samples prepared by melt mixing an additional dielectric response related to nanoscopic gap junctions of 1.5nm was identified. This response was not present in solution-mixed samples, which are characterized by improved polymer wetting. We discuss how the interactions between CNTs and the two phases of the block copolymer matrix are affected by the processing conditions resulting in the important differences in the filler network structure, which directly influence the final electrical and mechanical properties of the composite.

Investigation of Thermoplasticity of Zein and Kafirin Proteins: Mixing Process and Mechanical Properties

Conventional direct melt mixing technology was investigated on zein and kafirin, two vegetable proteins extracted, respectively, from maize and sorghum. A lab scale internal mixer has been used to thoroughly study the thermo-plasticization process of the proteins with several plasticizers. Different compositions were investigated under different processing conditions. In particular, the lengthy procedures of forming the protein/solvent/plasticizer solution followed by drying or the protein/plasticizer emulsion followed by the precipitation of the extrudable resin, reported in the literature for these systems, were avoided and the protein and plasticizer were directly fed into the mixer to obtain a plastic-like material. The effect of plasticizer type and content and mixing process variables on the mechanical properties was analyzed. Compression molded slabs were transparent, strong and flexible, with properties similar to the cast films reported in the literature, prepared with the same type of plasticizers. However, lower plasticizer content was sufficient to produce equally flexible films, proving an enhanced plasticization efficiency of the mixing process, as compared to casting.

Exfoliation of clay layers in polypropylene matrix using potassium succinate-g-polypropylene as compatibilizer

The efficiency of potassium succinate-g-polypropylene (KPPSA) as compatibilizer for the dispersion of clay in a high molecular weight polypropylene during melt mixing for the preparation of nanocomposites was evaluated and compared with maleic anhydride-g-polypropylene (PPMA). Nanocomposites were prepared by direct melt mixing and by masterbatch methods and the structure obtained was characterized by WAXD and TEM. The exfoliation and better dispersion of the organoclay was observed with KPPSA than PPMA. The dispersion of clay was found to be dependent on the method of preparation, type and the amount of compatibilizer used. The dispersion was better when the nanocomposites were prepared by two step masterbatch route than the single step direct mixing method. Flexural moduli and crystallization behavior were studied and correlated with the dispersion of organoclay in the PP matrix.

Thermoplastic Elastomer Nanocomposites Based on PA6/NBR

Abstract Thermoplastic elastomer nanocomposites (TPE nanocomposites) based on PA6/ NBR/Cloisite 30B were prepared through a direct melt mixing process in an internal mixer. The effects of NBR content (10, 30 and 50 wt.%) and nanoclay loading (3, 5 and 7 wt.%) on morphology and mechanical properties of the nanocomposites have been studied and compared with unfilled PA6/NBR blends as well. The TPE nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and mechanical properties. XRD results suggested that the nanoclay is exfoliated into the TPE nanocomposite matrix. TEM image of the PA6/NBR/nanoclay composite showed partial exfoliated structure of silicate layers dispersed through the both NBR and PA6 phases. The SEM photomicrograph of PA6/NBR nanocomposite showed an increasing of the rubber particles size in comparison with unfilled PA6/NBR TPE. By presence of nanoclay, improved modulus of the prepared TPE nanocomposites was achieved. DSC studies showed that loading of the nanoclay reduced the degree of crystallinity of the nanocomposite samples.

The Role of Polyhedral Oligomeric Silsesquioxane on the Thermo-Mechanical Properties of Polyoxymethylene Copolymer Based Nanocomposites

Hybrid nanocomposites formed with polyoxymethylene copolymer (POM) and different types of polyhedral oligomeric silsesquioxane (POSS) nanoparticles have been investigated. Four types of POSS have been studied in contents of 2.5% and 5% wt. The POSS were incorporated by direct melt-mixing. Traditionally copolymerization has been the preferred approach used to form polymer-POSS nanocomposites because the possibility of immiscibility with the polymer matrix is reduced. However, melt-blended POSS nanoparticles can also improve the thermo-mechanical properties of some polymers. Different morphologies were obtained depending on the type of POSS used. GI-POSS and O-POSS exhibit sub-micron or micron-sized inclusions which size increased with increasing percentages of POSS added. On the other hand, both G-POSS and T-POSS appeared to be uniformly dispersed in the POM matrix probably at a molecular level. This is a clear indication of miscibility between these systems and also that POSS solubility in POM is higher than 5 wt%. G-POSS improved the thermal stability of the systems. However, the melting temperature and the modulus of elasticity were found to slightly decrease. On the other hand, the O-POSS produced the opposite effect in the matrix. Finally T-POSS filled systems do not yield important variations in regard to polymethylene oxide properties although interaction between T-POSS and the matrix was detected.

Optical properties of particle‐filled polycarbonate, polystyrene, and poly(methyl methacrylate) composites

AbstractTransparency is a key material property of polycarbonate (PC), polystyrene (PS), and poly(methyl methacrylate) (PMMA). To study the optical properties of particle‐filled PC, PS, and PMMA, composites containing inorganic particles in different sizes and concentrations were produced by direct melt mixing in this work. The optical properties characterized by total light transmittance, haze, and clarity were studied. The results show that the optical properties of polymer composites are strongly affected by particle content, particle size, and especially by difference in refractive indices between polymer matrix and particles. It is also revealed that the light transmittance and haze of composites are mainly affected by difference in refractive indices, whereas the clarity is more affected by particle size. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Polypropylene‐organoclay nanocomposite: Preparation, microstructure, and mechanical properties

AbstractA series of polypropylene (PP) nanocomposites containing 2, 4, and 6 wt % of an organophilic montmorillonite clay was prepared via direct melt mixing in the presence of maleic anhydride grafted polypropylene (PP‐g‐MAH) as compatibilizing agent. Microstructure characterization was performed by X‐ray diffraction analysis. Nanocomposites exhibited a 15 and 22% enhancement in tensile modulus and impact strength, respectively. The heat deflection temperature of PP nanocomposites was 36°C greater than for pure PP. Thermal and mechanical properties of nanocomposites were compared to properties of traditional PP‐talc and PP‐glass fiber composites. The results showed that the properties of nanocomposites improved compared to ordinary polypropylene composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Structure-stress relaxation relationship in polystyrene/fluorohectorite micro-and nanocomposites

Sodium fluorohectorite (FH) was incorporated into polystyrene (PS) in amounts of 4.5 and 7 wt.% by melt mixing, with and without latex precompounding. The latex precompounding was used for the latex-mediated predispersion of FH particles. The related masterbatch was produced by mixing PS latex with the water-swellable FH, followed by drying. The dispersion of FH in PS was studied by transmission-, scanning electron-, and atomic force microscopy techniques (TEM, SEM, and AFM, respectively). The stress relaxation in the PS composites was determined in short-term isothermal tests. The latter were performed at various temperatures between 25 and 75°C. The direct melt mixing of FH with PS resulted in microcomposites, whereas the masterbatch technique gave rise to nanocomposites. The master curves (relaxation modulus vs. time), constructed by applying the time-temperature superposition principle (TTSP), showed that the Williams-Landel-Ferry (WLF) equation, the Maxwell model, and the Findley power law were fairly applicable to the experimental results obtained.

Poly(caprolactone)/clay masterbatches prepared in supercritical CO2 as efficient clay delamination promoters in poly(styrene-co-acrylonitrile)

Poly(styrene-co-acrylonitrile) (SAN)/clay nanocomposites with a high degree of clay exfoliation were prepared upon melt blending of pre-exfoliated poly(e-caprolactone) (PCL)/organoclay masterbatches in a Brabender-type internal mixer. These highly filled masterbatches were synthesized by a one-pot process using supercritical carbon dioxide as a polymerization medium. During their dispersion into SAN, PCL is expected to act as a compatibilizer at the polymer–clay interface as it is miscible with the host matrix under these conditions. Reference nanocomposites based on direct melt mixing of the commercial organoclay were also prepared for the sake of comparison. The superiority of the masterbatch route in term of clay delamination efficiency has been evidenced by XRD analysis, visual and TEM observations. The effect of the nanocomposite morphology on the polymer properties was then investigated. A substantial improvement of the fire behaviour and a decrease in gas permeability have been observed for the nanocomposite containing the highest level of clay exfoliation, accompanied with a higher brittleness as evidenced by traction and impact tests.

Fabrication and characterization of poly(butylene succinate)-grafted carbon fiber/poly(L-lactide) nanocomposites

A new poly(butylene succinate) (PBS)-grafted vapor grown carbon fiber (VGCF)/poly(L-lactide) (PLLA) nanocomposites were successfully prepared by an in situ condensation reaction between PBS (Mw = 6,000) and surface oxidized VGCF, followed by direct melt mixing technique, and their mechanical and thermal properties were evaluated. Fourier transform infrared spectroscopy and scanning electron microscopy studies indicate a chemical interaction between the PBS and the surface of VGCF. It was found that the maximum tensile strength and modulus of PBS-grafted VGCF/PLLA nanocomposites were 135 MPa (27% increase relative to neat PLLA) and 4,400 MPa (29% increase relative to neat PLLA), respectively. The results indicate that significant improvement in the mechanical properties can be accomplished by optimizing the surface modification conditions for VGCF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4433–4441, 2008

Thermally stable exfoliated poly(ethylene terephthalate) (PET) nanocomposites as prepared by selective removal of organic modifiers of layered silicate

Exfoliated poly(ethylene terephthalate) (PET) nanocomposite excluding organic modifier (M-P etLSN eom) was successfully prepared by the melt processing via solution method with solvent–nonsolvent system. PET nanocomposites including organic modifier (M-P etLSN iom and D-P etLSN) as counterpart of M-P etLSN eom were prepared by using the melt processing via solution method without solvent–nonsolvent system and the only conventional direct melt mixing process, respectively. From elemental analysis (EA) and thermogravimetric analysis (TGA), organic modifier in M-P etLSN eom was confirmed to be well removed by solution method with solvent–nonsolvent system. Then, it was found that M-P etLSN eom and M-P etLSN iom had exfoliated structure by wide angle X-ray diffraction (WAXD) and high-resolution transmission electron microscopy (HR-TEM), whereas no expansion of gallery height was observed for D-P etLSN. To elucidate the effect of organic modifier on the physical properties of PET nanocomposites, the crystallization behavior, optical transparency, thermal stability, and mechanical properties of M-P etLSN eom, M-P etLSN iom, D-P etLSN, and neat PET were evaluated by differential scanning calorimetry (DSC), UV–visible (UV–vis) spectroscopy, TGA, and universal testing machine (UTM). All of the PET nanocomposites exhibited faster crystallization kinetics and better thermal and mechanical properties compared to neat PET due to the presence of silicate layer in PET. However, M-P etLSN iom and D-P etLSN including organic modifier showed lower crystallization constant rates, longer crystallization half times, and poorer optical, thermal, and mechanical properties than M-P etLSN eom. These results were ascribed to the thermal decomposition of the organic modifiers presented in M-P etLSN iom and D-P etLSN during the melt processing.

Alumina‐filled polystyrene micro‐ and nanocomposites prepared by melt mixing with and without latex precompounding: Structure and properties

AbstractAlumina fillers were incorporated in polystyrene (PS) in 4.5 wt % by melt blending with and without latex precompounding. Latex precompounding was used for the latex‐mediated predispersion of the alumina particles. The related masterbatch was produced by mixing PS latex with water dispersible boehmite alumina in various particle sizes followed by drying. The dispersion of the alumina in the PS was studied by transmission and scanning electron microscopy (TEM and SEM, respectively). The mechanical and thermomechanical properties of the PS composites were determined in uniaxial tensile, dynamic‐mechanical thermal analysis (DMTA), and short‐time creep tests performed at various temperatures. In addition, the melt flow of the composites was characterized in a plate/plate rheometer. It was found that direct melt mixing of the alumina with PS resulted in micro‐, whereas the masterbatch technique in nanocomposites. The stiffness and resistance to creep (summarized in master curves) of the nanocomposites were improved compared to those of the microcomposites. The properties of the composites were upgraded by decreasing nominal size of the water dispersible alumina. The preparation technique and the size of the alumina particles affected the tensile strength, melt viscosity, and heat distortion temperature in lesser extent than the stiffness and thus compliance data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Preparation and characterization of polyethylene‐g‐maleic anhydride–styrene/montmorillonite nanocomposites

AbstractIt is difficult to prepare polyethylene/montmorillonite by direct melt mixing because of the difference in character between polyethylene and montmorillonite. Therefore, it is necessary to modify polyethylene with polar groups, which can increase the hydrophilicity of polyethylene. At the same time, the inorganic montmorillonite should be modified with long‐chain alkyl ammonium to increase the basing space between the interlayers. Thus, through the grafting of the polar monomer onto the main chain of polyethylene by reactive extrusion, polyethylene/montmorillonite nanocomposites can be prepared by the melt mixing of the grafter and organic montmorillonite. Fourier transform infrared has been used to prove that the monomers are grafted onto polyethylene. X‐ray diffraction and transmission electron microscopy have been employed to characterize the nanocomposites. Furthermore, thermogravimetric analysis measurements show that the thermal stability of the nanocomposites is improved in comparison with that of the virgin materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 805–809, 2006

Novel Copolymers as Dispersants/Intercalants/Exfoliants for Polypropylene‐Clay Nanocomposites

AbstractThe use of various copolymers as dispersants/intercalants/exfoliants in polypropylene (PP)‐clay nanocomposites based on unmodified montmorillonite clays (NaMMT) has been explored. The primary objective of this research has been to find dispersants that allow PP nanocomposites to be formed by direct melt mixing, that are effective with unmodified clays and that comprise only a minor component of the overall composition both with respect to both clay and PP. Two classes of dispersants were investigated: PEO‐based nonionic surfactants and amphiphilic copolymers based on a long chain (meth)acrylate (e.g. octadecyl acrylate) and a more polar comonomer (e.g. maleic anhydride, N‐vinylpyrrolidone, methyl methacrylate). The state of dispersion achieved and the properties of the derived nanocomposites were found to depend strongly on both on the level of dispersant and its overall composition but interestingly properties are not particularly dependent on the dispersant architecture (i.e. whether statistical, gradient or block copolymer). The nanocomposites possess a tensile modulus up to 40% greater that the precursor PP while elongation at break and impact strength are significantly improved over “clay alone” composites and reference organoclay‐based nanocomposites. Also notable are significantly better thermal and thermo‐oxidative stability as compared to both PP and “clay alone” composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20–50 wt‐%) of the composition with respect to clay.

Non‐Ionic, Poly(ethylene oxide)‐Based Surfactants as Intercalants/Dispersants/Exfoliants for Poly(propylene)‐Clay Nanocomposites

AbstractSummary: Poly(propylene) (PP)‐clay nanocomposites were prepared from unmodified montmorillonite clays (NaMMT), with poly(ethylene oxide)‐based nonionic surfactants as dispersants/intercalants/exfoliants. The primary objective of this research was to find dispersants that (a) allow PP nanocomposites to be formed by direct melt mixing; (b) are effective with unmodified clays and (c) comprise of only a minor component with respect to both the clay and the overall composition. Linear, branched, gemini and sugar‐based surfactants and structures containing poly(dimethyl siloxane) and poly(methyl methacrylate) blocks were examined. These additives were found to be effective in breaking down the clay agglomerates to tactoids, giving some expansion of the clay structure and partial exfoliation and providing substantially improved clay dispersion. The properties of the derived nanocomposites depend on the level of additive and its structure. Tensile and impact properties show significant improvement over the precursor PP. Also notable are the significantly better thermal and thermo‐oxidative stabilities, as compared to both PP and “clay alone” composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20–50%) of the composition, with respect to the clay. A preferred surfactant is linear PE‐block‐PEO, with a short PEO block and an alkyl chain with approximately 30 carbon atoms (C30). magnified image

Structure and Properties of BR Nanocomposites Reinforced with Organoclay

Butadiene rubber (BR)/organoclay nanocomposites were prepared by direct melt mixing of BR and clay modified with different primary and quaternary ammonium salts. BR/pristine clay composite and BR/organoclay nanocomposites were analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The vulcanization characteristics and the mechanical properties of the BR/pristine clay and BR/organoclay composites were investigated. The results showed that the interlayer distance of the organoclays was expanded, which indicated that intercalated BR/organoclay nanocomposites had been prepared. Organoclay effectively accelerated the vulcanization of BR, which was attributed to the intercalatant used to modify the clay. The tensile strength, elongation at break and tear strength of BR/organoclay nanocomposites are much higher than those of gum BR vulcanizate and BR/pristine clay composites. The organoclay modified with dimethyl dihydrogenated tallow ammonium chloride (DDAC) gave the best reinforcement effect in BR of all the organoclays.

Polyethylene/grafted polyethylene/graphite nanocomposites: Preparation, structure, and electrical properties

AbstractPolyethylene (PE)/maleic anhydride grafted PE (g‐PE)/expanded graphite (EG) electrically conductive nanocomposites were successfully prepared by solution intercalation (SI) and masterbatch melt mixing (MMM). Electrical conductivity (σ) measurements; transmission electron, scanning electron, and optical miscroscopy observations; and differential scanning calorimetry analyses were employed to examine the influences of the preparation methods, EG volume or weight fractions (ϕ or fw), and g‐PE weight contents (Cg) on the structure and σ of the nanocomposites, as compared to PE/g‐PE/EG composites and PE/EG control produced by direct melt mixing (DMM). The percolation thresholds (ϕc) of the SI, MMM, and DMM composites (Cg/fw = 1.5) and the DMM control were measured and found to be 2.19, 3.81, 4.68, and 5.35%, respectively. As the Cg/fw increases from 1 to 4, the σ of the MMM and DMM composites with fw = 9% rises from the order of 10−16 to 10−4 and 10−8 S/cm, respectively. These were closely associated with the morphology and microstructure of the composites varying with the preparation methods (ϕ and Cg/fw) and could also be interpreted in terms of percolation theory. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 51–59, 2005