Co-continuous Phase Research Articles

Morphology development and compatibilization effect in nanoclay filled rubber blends

The present work introduces a new method for the characterization of morphology development and kinetics of nanoclay distribution in hydrogenated acrylonitrile butadiene rubber (HNBR)/natural rubber (NR) blends based on the measurement of electrical conductance during the mixing process. It was found that the online measurable electrical conductance of rubber–clay mixtures, which is originated from the release of the ionic surfactant from the nanoclay galleries during the mixing process depends on two factors: the phase specific localization of nanoclay and the change of the blend morphology. The former is due to the favorable interaction of nanoclay with one of the blend phases whereas the latter is caused by the compatibilization effect of nanoclay. It became obvious that the presence of clay influences the morphology of the blends drastically; a significant change from the co-continuous phase morphology into an island–matrix morphology was observed in HNBR/NR/clay nanocomposites. Thus, the method of the online conductance promises to be a powerful tool to study the nanoclay dispersion processes and to monitor the quality of rubber–nanoclay composites.

Dynamic Vulcanization of HDPE/EVA Blend Using Silane

Dynamic vulcanization of high-density polyethylene and ethylene vinyl acetate (HDPE/EVA) blends (50/50 wt%) in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the HDPE phase by transesterification reaction between ester groups of the EVA and alkoxysilane groups of tetrapropoxysilane, catalyzed by dibutyl tin oxide. Torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during dynamic vulcanization. The degree of cross-linking of EVA in the HDPE/EVA materials was estimated by the gel content (insoluble EVA fraction). The changes in the HDPE/EVA phase morphology caused by different degrees of EVA cross-linking were investigated by scanning electron microscopy. Melt-state linear viscoelastic properties of the materials were investigated by small amplitude oscillatory shear rheometry. For the composition and processing conditions adopted in this study, the HDPE/EVA showed a coarse co-continuous phase morphology, with large EVA domains interconnected with HDPE domains. Following the dynamic vulcanization, this changed to a more refined co-continuous morphology. The linear viscoelastic relaxation behavior of dynamically vulcanized HDPE/EVA materials suggests the existence of a percolated network structure of high viscous and elastic EVA domains interconnected with thermoplastic HDPE domains.

Carbon black self-networking induced co-continuity of immiscible polymer blends

This work aims to clarify the mechanism of nanoparticle-induced co-continuity in immiscible polymer blends. An industrially relevant system, carbon black (CB)-filled acrylonitrile-butadiene-styrene (ABS)/polyamide 6 (PA6) blends, is investigated via scanning electron microscopy, selective extraction tests, dynamic mechanical analysis, and electrical conductivity measurements. The CB particles are found to be preferentially localized in the PA6 phase, and with an increase in CB loading (ΦCB), the critical volume fraction of PA6 (ΦPA6) that is essential for building the co-continuous structure decreases. The product of ΦPA6 and ΦCB, n, remains constant for the given system, suggesting that there exists an intrinsic cooperative effect between the CB and the CB-localized polymer phase. A further decrease in ΦPA6 is achieved either by loading CB with a higher self-networking capability or by isothermal post-treatments for sufficient self-agglomeration of the CB clusters. It is demonstrated that, under the direction of CB self-networking, the CB-localized polymer domains tend to fuse together into co-continuous organization with little phase coarsening. Therefore, CB self-assembly not only plays a key role in extending phase co-continuity over a much larger composition range but also acts on stabilizing the co-continuous polymer domains during the melt processing.

Significant Ultra-low Percolation Threshold, Enhanced Positive Temperature Coefficient Effect and Dielectric Permittivity in Polymer-based Composites with Immiscible Polymers

AbstractSignificant conductive polymer-based composites consisting of immiscible semi-crystalline polymers PP and PVDF, at different volume ratios loaded with a certain concentration of CB were prepared by blending and sequent hot-pressing technology. The distributing status of CB in the polymers was evaluated through the micrographs of the composite. The percolation threshold of this kind of composite is much lower than those of the individual polymers. Even more, the composite at 1/1 volume ratio of PP and PVDF displays the best conductivity among different ratios at a certain concentration of CB, and it displays an outstanding PTC effect more than five orders of magnitude, and synchronously an enhanced dielectric permittivity about 24.9 at 100 Hz. These inimitable properties may owe to the formation of PP/PVDF co-continuous phases and a double-percolation effect in the composite. The novel polymer-based composite with ultra-low percolation threshold, enhanced PTC effect, as well as the significant dielectric permittivity is promising a potential application.

Mesoscale simulation of polymer electrolyte membranes based on sulfonated poly(ether ether ketone) and Nafion

We present a statistical mechanical approach for predicting the self-assembled morphologies of amphiphilic copolymers—sulfonated poly (ether ether ketone) (sPEEK) and Nafion—which combine, in one macromolecule, both hydrophobic and hydrophilic segments, giving rise to a constrained hydrophobic/hydrophilic nano-separation. We have developed a coarse-grained model of sPEEK that constitutes an important class of the promising membrane materials for fuel cell applications. Using a mesoscale dynamic density functional theory (DDFT) framework, we explore the phase behavior of sPEEK and Nafion in the presence of physisorbed water. To determine the impact of polymer chemistry on the morphology of sPEEK membranes, multiblock copolymers with a variation in both molecular architecture (block size) and chemical composition (degree of sulfonation) are studied in a large window of water contents. At sufficiently high hydration levels, the simulations predict a tricontinuous morphology, where all the microphase-separated subphases—hydrophilic and hydrophobic blocks and water—percolate, resulting in the formation of three co-continuous phases. Above the percolation threshold, the distribution of water in the sPEEK membrane can be represented as a topologically complex sponge-like network consisting of narrow channels, while the main structural motif of Nafion is characterized by the presence of long but randomly packed water-filled tubes, in agreement with the fibrillar model recently proposed by Schmidt-Rohr and Chen. Although the polymer matrix of sPEEK tends to confine water to narrower channels compared to those in Nafion, the average cross-sectional area of the channels is comparable for the two systems with the same hydration level.

Compatibilization of NR/EVA blends by natural rubber grafted poly(dimethyl(methacryloyloxymethyl)phosphonate) compatibilizer

AbstractGraft copolymer of natural rubber (NR) and poly(dimethyl (methacryloyloxymethyl) phosphonate (PDMMMP) (i.e., NR-g-PDMMMP) was prepared and used as a blend compatibilizer in 50/50 NR/EVA simple blends. Influence of various loading levels of NR-g-PDMMMP (i.e., 0, 1, 3, 5, 7, 9, 12 and 15 wt% of NR) on rheological, dynamic, mechanical and morphological properties was investigated. The results showed that the best compatibilization effect was observed in the blend with a loading level of NR-g-PDMMMP at 7 wt%. That is, the highest complex viscosity, tensile strength, elongation at break as well as the lowest values of tension set and tan δ value (i.e., damping factor) were observed. This indicates the highest mechanical strength and the supreme elastic response of the material. Morphological properties of 50/50 NR/EVA blends with any loading levels of NR-g-PDMMMP compatibilizer showed co-continuous phase system. However, in the NR/EVA blend with NR-g-PDMMMP at a loading level of 7 wt%, the finest phase morphology was observed. The 50/50 NR/EVA blend with lower and higher loading amounts of NR-g-PDMMMP compatibilizer exhibited inferior dynamic, mechanical properties as well as larger phase morphologies.

Dynamic rheology–morphology relationship of PP/EPDM blends prepared by melt mixing under Sc-CO2

It was demonstrated that the high mixing efficiency of twin screw extruder (TSE) helped to disperse the ethylene–propylene–diene terpolymer (EPDM) domains in polypropylene (PP) matrix, but could not lead to the uniform distribution of EPDM phase with small sizes because of the thermodynamical immiscibility between PP and EPDM. So supercritical carbon dioxide (Sc-CO2) was environmentally and economically introduced to the twin screw extrusion to assist the melt mixing of PP and EPDM. The scanning electron microscopy photographs showed that co-continuous phase morphology was formed to some extent for the PP/EPDM 60/40 blend prepared with Sc-CO2, especially with 2.5 wt% Sc-CO2. This was the one important reason for that the complex viscosity and storage modulus of PP/EPDM 60/40 blend increased with the increase of Sc-CO2 concentration.

Morphology of poly(ethylene terephthalate) blends: An analysis under real processing conditions by rheology and microscopy

AbstractThe present work describes the formation of co‐continuous phase morphologies in uncompatibilized and compatibilized poly(ethylene terephthalate) (PET)–poly(m‐xylene adipamide) (MXD6) and PET– poly(ethylene‐co‐vinyl alcohol) (EVOH) melt‐extruded blends. Phase continuity has been determined by using the Jordhamo relationship. Viscosity values, which are essential for the calculation of the phase continuity, have been obtained by capillary rheometry. Thermal behavior of the blends has been analyzed by employing differential scanning calorimetry and phase continuity has been investigated for the noncompatibilized and the compatibilized blends by scanning electron microscopy. PET–MXD6 blends [92.35:7.65 (v/v) and 84.5:15.5 (v/v)] and PET–EVOH blends [73.63:26.37 (v/v)] exhibit droplet‐in‐matrix phase morphology, whereas uncompatibilized PET–MXD6 [75.8:24.2 (v/v)] blend has a combination of rod‐like, droplet–matrix structure, and quasi‐interpenetrating network structure. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:173–184, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20156

Ethylene–acrylic acid copolymer induced electrical conductivity improvements and dynamic rheological behavior changes of polypropylene/carbon black composites

AbstractThe experimental data reveal that the addition of ethylene–acrylic acid copolymer (EAA) into carbon black (CB)/polypropylene (PP) composites can improve the electrical conductivity of CB/PP composites by two to six orders of magnitude at a comparatively low CB content (φ), and when φ = 2.5 vol %, 60/40 of PP/EAA is an optimum for electrical conductivity improvement. The dynamic rheological data show that with increasing φ there are apparent rheological percolations for CB/PP composites. A modified Kerner–Nielson equation can be used to describe the correlation between electrical percolation and dynamic viscoelastic percolation. The addition of EAA into CB/PP composites leads to apparent changes in dynamic rheological behaviors. When φ = 2.5 vol %, a rheological percolation appears in CB/PP/EAA (CPE) composites with increasing EAA content. The similar rheological behaviors correspond to the similar morphological structures for CPE composites with φ = 5.0 vol %. The appearance of bumps in the van‐Gurp–Palmen plots corresponds to the formation of network structure in CB/PP and CPE composites, and the more perfect the networks, the higher the amplitude of the bumps. All data indicate that the van‐Gurp–Palmen plot is sensitive to the formation of filler particle networks or cocontinuous phase which spans the whole composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1762–1771, 2009

Nanoscale Phase Separation of Sulfonated Poly(arylene ether sulfone)/Poly(ether sulfone) Semi-IPNs for DMFC Membrane Applications

Unprecedented improvement in the selectivity (the ratio of proton conductivity to methanol permeability) of DMFC (direct methanol fuel cell) membranes has been demonstrated with a value roughly 16 times higher than that of Nafion117 having been achieved. The novel morphology of semi-interpenetrating polymer network (semi-IPN) membranes characterized by nanometer-sized domains as well as well-developed phase cocontinuity is a key factor in enabling such notable progress, which has not been seen in conventional microscale phase separation. The semi-IPN membranes (sIPN-100) consisted of a hydrophilic component acting as a proton conductor, that is, acrylate-terminated fully sulfonated poly(arylene ether sulfone) oligomers (acSPAES-100, degree of sulfonation = 100%), and a hydrophobic component functioning as a methanol barrier, that is, poly(ether sulfone) copolymers (RH-2000). We determined the nanoscale phase separation of sIPN-100 by deliberately controlling the kinetics (the change of solvent-evaporation...

Morphology and electrical properties of polyamide 6/polypropylene/multi-walled carbon nanotubes composites

Morphology, electrical properties and conductive mechanisms of polyamide 6/polypropylene/muti-walled carbon nanotubes (PA6/PP/MWNTs) composites with varied compositions and different blending sequences were investigated. The MWNTs were found to be located preferentially in the PA6 phase in the composites, whatever the PA6 was continuous or dispersed phase. While the incorporation of MWNTs changed the dispersed PA6 phase from spherical to elongated or irregular shape. The PA6/PP/MWNTs (20/80/4) composite with a dispersed PA6 phase exhibited a higher electrical conductivity in comparison with the PA6/PP/MWNTs (50/50/4) composite which has a co-continuous phase and exhibits double percolation. This was due to the formation of a conductive MWNTs networks in the PA6/PP/MWNTs (20/80/4) composite as proved by means of field emission scanning electron microscopy and rheological measurements. The morphology and electrical properties of the PA6/PP/MWNTs (20/80/4) composites were significantly influenced by blending sequences. When blending 3.9 phr MWNTs with a pre-mixed PA6/PP/MWNTs (20/80/0.1) composite, the dispersed PA6 phase formed an elongated structure, which was beneficial to the electrical properties.

Mechanical properties and flammability of polycarbonate alloys containing nanosize additives

AbstractDifferent organic–inorganic composite particles [montmorillonite/poly(butyl acrylate) (PBA)/poly(methyl methacrylate) (PMMA), SiO2/PBA/PMMA, and CaCO3/PBA/PMMA] were synthesized by emulsion polymerization. Furthermore, polycarbonate (PC) alloys were prepared via the doping of these composite particles into PC with a twin‐screw extruder. The structure, mechanical properties, and flammability of the PC alloys were studied in detail. Although the tensile modulus of PC decreased a little, the flexibility and impact resistance were improved by the addition of these composite particles. This result was attributed to the fact that the composite particles were well dispersed in the PC matrix, with a cocontinuous phase formed between the particles and PC. In addition, the combustion behavior of the PC alloys, compared with that of the pure PC, resulted from a ceramic‐like char that formed on the surface of the PC alloys during burning. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mieszaniny uwodornionego i karboksylowanego kauczuku butadienowo-akrylonitrylowego - sieciowanie i wybrane wlasciwosci

Hydrogenated and carboxylated acrylonitrile-butadiene rubbers (HNBR and XNBR, respectively) were blended in various ratios by reactive mixing and then the compositions were subjected to selective dynamic curing with use of MgO and subsequent static curing of the whole system with dicumyl peroxide (DCP). The effects of XNBR content in the blend, curing agents added and dispergation time on the properties of vulcanizates obtained were investigated. It was found that during the dynamic curing of XNBR in the blend with HNBR the change in morphology occurred: with two co-continuous phases to mixed partially lamellar, rod-like and droplet ones (Fig. 1). Curing degree of the composition, calculated on the basis of equilibrium swelling (V r ) measurements and elasticity constants 2C 1 , increase with increasing XNBR content in the system (Fig. 2, 3). Tensile strength (TS b ) and elongation at break (Eb) depend on the components' dispergation time and process conditions (Fig. 5-10).

Controllable Growth of Gradient Porous Structures

Cocontinuous phase structures of immiscible polymers can be developed under appropriate melt-blending conditions. Because of the presence of interfacial tension, such cocontinuous structures start to coarsen when heated to a temperature higher than the melting/softening temperature of both phases. In this study, a method for controllable growth of gradient porous structures utilizing variable coarsening rates in a gradient temperature field was investigated. The phase structure coarsens at a higher rate in higher temperature regions but at a slower rate in lower temperature regions, resulting in the generation of a gradient phase morphology. Subsequent dissolution of one phase in the binary blend yields a gradient porous structure made of the remaining polymer component. A polystyrene/poly(lactic acid) (PLA) blend was used as a model system. By designing proper thermal boundary conditions and introducing different thermal gradients during annealing, different types of gradient porous structures of PLA were created.

Optimum Blend of Chitosan and Poly-(ε-caprolactone) for Fabrication of Films for Food Packaging Applications

The present work deals with the preparation and characterization of the chitosan and poly-e-caprolactone (PCL) solution-casted blended films in various proportions (chitosan–PCL ratio 90:10, 80:20, and 70:30). The films were casted and dried at 55 °C, which were characterized based on the mechanical, barrier, thermal, and microscopic properties. The film prepared from chitosan to PCL ratio 80:20 resulted in increase percentage elongation by 20.56% as compared to pure chitosan film. Fourier transform infrared spectrum indicated a shift in peak of absorption from 1743.9 to 1724.8 cm−1 due to carbonyl group of PCL indicating the miscibility and interaction between the PCL and chitosan. Scanning electron microscopy revealed that PCL appeared as a co-continuous phase with chitosan for ratio 80:20, confirmed the interaction between chitosan and PCL. The above study indicated that the properties of chitosan films can be modified with the addition of PCL and may find its versatile use in food packaging.

Polypropylene/natural rubber thermoplastic elastomer: Effect of phenolic resin as a vulcanizing agent on mechanical properties and morphology

AbstractThe aim of this study is to characterize thermoplastic elastomers (TPEs) from polypropylene and natural rubber with and without phenolic resin as a vulcanizing agent. The blends containing 40–60 wt % of polypropylene were mixed in an internal mixer and pressed with a compression molding machine. TPEs without rubber vulcanization, named as unvulcanized thermoplastic natural rubber (uTPNR) were compared to TPEs containing dynamic vulcanized rubber, referred as vulcanized thermoplastic natural rubber (vTPNR). The uTPNRs illustrated cocontinuous phase morphology, whereas the vTPNRs displayed dispersed phase of vulcanized natural rubber. Tensile properties, tear strength, thermal ageing resistance, ozone resistance, tension set, hardness and swelling test in toluene, IRM 903 oil and engine oil were carried out according to ASTM. It was found that tensile and tear strength, hardness and tension set of the uTPNRs increased with increasing polypropylene content. Dynamic vulcanization improved tensile strength, elongation at break, tension set and degree of swelling of the TPEs, whereas hardness and tear strength did not show significant change after dynamic vulcanization. The vTPNRs exhibited higher ozone resistance and swelling resistance than the uTPNRs. Reprocessability of the vTPNRs was investigated and showed that tensile strength decreased at 20 and 30% and elongation at break decreased at 13 and 27% for the first and the third reprocessing respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Structure and properties of new thermoforming bionanocomposites based on chitin whisker‐graft‐polycaprolactone

AbstractThermoformable bionanocomposites of chitin whisker‐graft‐polycaprolactone (CHW‐g‐PCL) were synthesized by initiating the ring‐opening polymerization of caprolactone monomer onto the CHW surface under microwave radiation. In this case, the “graft from” strategy contributed to long and dense “plasticizing” PCL tails onto the CHW surface as the key of thermoforming, and, therefore, such bionanocomposites were injection‐molded as the sheets with a structure of cocontinuous phase mediated with the entanglement of grafted PCL chains. The structure and properties of the molded CHW‐g‐PCL sheets were investigated by FTIR, XRD, SEM, DSC, DMTA, contact angle measurement, and tensile test. With an increase of the PCL content in CHW‐g‐PCL, the strength and elongation as well as the hydrophobicity of the nanocomposites increased at one time. This is the first report on the thermoformable polymer‐grafted nanocrystal derived from natural polysaccharide. Moreover, such new bionanocomposites with good mechanical performances could have great potential applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Morphology and mechanical properties of polyamide 12 (PA12)/poly(vinylidene fluoride) (PVDF) blends

Morphology and mechanical properties of polyamide 12 (PA12)/poly(vinylidene fluoride) (PVDF) blends The morphology, thermal and mechanical properties of polyamide 12 (PA12)/poly(vinylidene fluoride) (PVDF) blends were investigated. These polymers are engineering, semi-crystalline polymers which are reciprocally immiscible. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) were used to characterize the polymeric materials. Mechanical properties were examined by static tensile test. The investigations demonstrate that blends with higher amount of PVDF, with the morphology of two co-continuous semicristalline phases, exhibit better mechanical properties. The blends with small content of PVDF and prepared by extrusion show the morphology of small separated domains of PVDF and full continuous PA phase. The morphology of these blends is different than the blends prepared by internal mixer and have better mechanical properties too. Thus they can be used in particular applications without a compatibilizing agent.

One-pot polymerization, surface grafting, and processing of waterborne polyurethane-cellulose nanocrystal nanocomposites

A series of new waterborne polyurethane (WPU)/cellulose nanocrystal (CN) composites have been successfully synthesized viain situpolymerization. The conditions were optimized to induce the grafting of part of the pre-synthesized WPU chains on the surface of cellulose nanocrystals (CNs) and the corresponding nanocomposites were processed by casting and evaporation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by scanning electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and tensile tests. The success of the grafting was substantiated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and differential scanning calorimetry. Thus, it was demonstrated that the grafted WPU chains formed crystalline domains on the surface of CNs which expedited the crystallization of the polycaprolactone (PCL) soft segment domains in the WPU/CN nanocomposites. This co-crystallization phenomenon induced the formation of a co-continuous phase between the matrix and filler which significantly enhanced the interfacial adhesion and consequently contributed to an improvement in the thermal stability and mechanical strength of the nanocomposites. Although the ductility of the final nanocomposites was slightly reduced, in the CN content range from 0 to 10 wt-%, the Young's modulus and strength were significantly improved as shown by the change from 1.7 to 107.4 MPa and 4.4 to 9.7 MPa, respectively.

Controlling Nanoparticle Location via Confined Assembly in Electrospun Block Copolymer Nanofibers

Coaxial nanofibers with poly(styrene-block-isoprene) (PS-b-PI)/magnetite nanoparticles as core and silica as shell are fabricated using electrospinning.1-4 Thermally stable silica helps to anneal the fibers above the glass transition temperature of PS-b-PI and form ordered nanocomposite morphologies. Monodisperse magnetite nanoparticles (NPs; 4 nm) are synthesized and surface coated with oleic acid to provide marginal selectivity towards an isoprene domain. When 4 wt% nanoparticles are added to symmetric PS-b-PI, transmission electron microscopy (TEM) images of microtomed electrospun fibers reveal that NPs are uniformly dispersed only in the PI domain, and that the confined lamellar assembly in the form of alternate concentric rings of PS and PI is preserved. For 10 wt% NPs, a morphology transition is seen from concentric rings to a co-continuous phase with NPs again uniformly dispersed in the PI domains. No aggregates or loss of PI selectivity is found in spite of interparticle attraction. Magnetic properties are measured using a superconducting quantum interference device (SQUID) magnetometer and all nanocomposite fiber samples exhibit superparamagnetic behavior.