Styrene-butadiene-styrene copolymer compatibilized carbon black/polypropylene/polystyrene composites with tunable morphology, electrical conduction and rheological stabilities

Thermochemical compatibilization of reclaimed tire rubber/ poly(ethylene-co-vinyl acetate) blend using electron beam irradiation and amine-based chemical

Waste tire rubber is commonly recycled by blending with other polymers. However, the mechanical properties of these blends were poor due to lack of adhesion between the matrix and the waste tire rubber. In this research, the use of electron beam irradiation and (3-Aminopropyl)triethoxy silane (APTES) on enhancing the performance of 50 wt% reclaimed tire rubber (RTR) blend with 50 wt% poly(ethylene-co-vinyl acetate) (EVA) was investigated. Preparation of RTR/EVA blends were carried out in the internal mixer. The blends were then exposed to electron beam (EB) irradiation at doses ranging from 50 to 200 kGy. APTES loading was varied between 1 to 10 wt%. The processing, morphological, mechanical, and calorimetric properties of the blends were investigated. The stabilization torque and total mixing energy was higher in compatibilized blends. Mechanical properties of RTR/EVA blends were improved due to efficiency of APTES in further reclaiming the RTR and compatibilizing the blends. APTES improved the dispersion of embedded smaller RTR particles in EVA matrix and crosslinking efficiency of the blends. Calorimetric studies showed increased crystallinity in compatibilized blends which corresponds to improved mechanical properties. However, the ductility of the blend was decreased due to increased interaction between EVA and APTES. Presence of APTES increased the efficiency of electron beam irradiation induced crosslinking which was shown through gel content analysis and Charlesby-Pinner equation.

Dielectric properties of solution-processed BaTiO3–styrene butadiene styrene nanocomposite films

Polymer–ceramic nanocomposite films comprising ceramic nanoparticles dispersed in a polymer matrix (0–3 composites) have garnered increasing interest due to their superior performance characteristics, and can be used in flexible modern electronics and energy storage systems.

Effect of phase coarsening under melt annealing on the electrical performance of polymer composites with a double percolation structure

The effect of phase coarsening on the evolution of the carbon black (CB) nanoparticle network under quiescent melt annealing and the electrical performance of polypropylene/polystyrene/carbon black (PP/PS/CB) composites with a double percolation structure was investigated. The results showed that when the CB content is low, the coarsening process of PP/PS/CB blends can be divided into two stages. In the first stage, the coarsening rate is fast before the formation of the CB nanoparticle network, and after annealing for a certain time, the evolution of the co-continuous morphology can drive the CB nanoparticles to self-assemble into a complete nanoparticle network. In the second stage, the coarsening rate is slow after the formation of the CB nanoparticle network. When the CB content is high, the CB nanoparticle network can be maintained throughout the whole annealing process, so that the conductivity and morphology of the PP/PS/CB composites are stable. Moreover, the electrical conductivity of the PP/PS/CB composites greatly increases after annealing for a certain time, and a percolation threshold as low as 0.07 vol% can be obtained. These results reveal the relationship between the evolution of the morphology and the conductivity in the conductive polymer composites with a double percolation structure, and provide a more in-depth and comprehensive understanding of the double percolation structure.

Kinetic Control of Graphene Localization in Co-continuous Polymer Blends via Melt Compounding

Selective localization of graphene in co-continuous polymer blends is an attractive method for preparing conductive polymer composites. Localization of graphene at the interface between the two polymer phases produces good conductivity at ultra-low concentrations. Although graphene localization is ultimately dependent on thermodynamic factors such as the surface energy of graphene and the two polymer components, kinetics also strongly affects the migration and localization of graphene in polymer blends during melt compounding. However, few studies have systemically investigated the important role of kinetics on graphene localization. Here, we introduced graphene nanoplatelets (GNPs) in polylactic acid (PLA)/polystyrene (PS) co-continuous polymer blends. Although GNPs in thermal equilibrium prefer the PS phase, we were able to kinetically trap GNPs at the interface of polymer blends via control of melt-compounding sequences, mixing times and shear rates. Utilizing morphological, rheological, and electrical measurements, we verified graphene localization and the suppression of coarsening in co-continuous polymer blends during annealing. When GNPs were premixed with the thermodynamically less-favorable PLA phase before mixing with the PS phase, GNPs can be kinetically trapped at the interface during melt compounding. Moreover, we show that a shorter melt-compounding time gives rise to a higher GNP interfacial coverage and a more effective morphology stabilization effect. Blends with as low as 0.5 wt % GNPs with only 30 s of melt compounding have a room-temperature conductivity of ∼10^-6 S/cm, which is larger than blends with longer melt-compounding times and potentially useful for antistatic materials. The in-depth study on the kinetics of graphene localization in our work provides a general guideline for the kinetic control of the localization of platelike nanofillers in polymer blends. Our study also demonstrates a facile method for manufacturing conductive polymer blends with low percolation thresholds.

Tunable Electrical Conductivity of Carbon-Black-Filled Ternary Polymer Blends by Constructing a Hierarchical Structure

A type of hierarchical structured composite composed of a minor thermoplastic polyurethane (TPU) phase spreading at the interface of two major phases polyoxymethylene/polyamide copolymer (POM/COPA) and carbon black (CB) particles selectively localized at the TPU/COPA interface of the tri-continuous blends was fabricated by melt compounding. The hierarchical structure was designed according to predictions and verified by a combination of electron microscopy and solvent extraction technique. The hierarchical structured composites show the dramatically decreased percolation threshold, a reduction of 60% compared to those without TPU where CB is selectively distributed in the COPA phase. The effects of CB contents and TPU on the phase morphology of POM/COPA were investigated, showing the occurrence of the POM/COPA phase inversion from a sea-island to a co-continuous structure beyond the percolation threshold of CB in the presence of TPU. The mechanism for the formation of conductive network is construction of CB network at the TPU/COPA interface of tri-continuous POM/COPA/TPU blends and double percolation effect.

Improved electrical conductivity of TPU/carbon black composites by addition of COPA and selective localization of carbon black at the interface of sea-island structured polymer blends

The electrical percolation threshold of carbon black (CB) in thermoplastic polyurethane (TPU) decreases by 46% with the incorporation of 20 wt% polyamide copolymer (COPA) through selective localization of CB particles at the interface of sea-island structured TPU/COPA blends. Composites with a composition of TPU/20 wt% COPA/9 wt% CB were prepared by four different mixing sequences and their morphologies were investigated by FESEM and TEM. The majority of CB particles were observed at the interface of sea-island structured blends irrespective of the compounding sequence used, although the percentage of CB particles at the interface is considerably less in the composite prepared by adding COPA to premixed TPU/CB. The driving force for the interfacial localization of most CB particles is the hydrogen bonding of CB with both TPU and COPA, which is confirmed by FTIR and DMA investigations. CB particles act like Janus particle-type compatibilizers with bonded TPU molecules toward the TPU phase and bonded COPA chains toward the COPA phase. Highly efficient conductive paths are formed through the CB-covered domains and a short inter-domain distance.

Conductivity and phase morphology of carbon black-filled immiscible polymer blends under creep: an experimental and theoretical study

The simultaneous evolution of conductivity and phase morphology of blend composites was investigated under shear and in the quiescent state.

Effect of multi-walled carbon nanotubes on the morphology evolution, conductivity and rheological behaviors of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends during isothermal annealing

MWNTs migrate and aggregate in SAN-rich phase to form the double percolated structure with thermal-induced phase separation of blend matrix.

Compatibilization of Immiscible Polymer Blends Using in Situ Formed Janus Nanomicelles by Reactive Blending

Block or graft copolymers located at polymer-polymer interfaces have been considered as ideal compatibilizers for immiscible polymer blends. Herein, we report a novel compatibilization mechanism using Janus nanomicelles (JNMs) formed in situ at the polymer-polymer interface in immiscible polyvinylidene fluoride (PVDF)/polylactic acid (PLLA) blends. A small amount of a reactive graft copolymer, poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (P((S-co-GMA)-g-MMA)), is incorporated into the PLLA/PVDF blends by simple melt mixing. The in situ grafting of PLLA chains onto P((S-co-GMA)-g-MMA) during melt mixing leads to the formation of numerous JNMs with a shell structure consisting of PLLA and PMMA hemispheres. These JNMs are located at the PLLA/PVDF interface, where they behave as effective compatibilizers for the immiscible PLLA/PVDF blends. This interfacial micelle compatibilization (IMC) mechanism opens new opportunities to exploit interfacial emulsification using JNMs and should be of great significance in the compatibilization of polymer alloys.

Role of block copolymer morphology on particle percolation of polymer nanocomposites

In this study, the effects of nanoparticle volume fraction, block stiffness, and diblock composition on the microstructure and electrical properties of composites are investigated using molecular dynamics simulation. It is shown that selective localization of conductive nanoparticles in a continuous block of diblock copolymer can dramatically reduce the percolation threshold. In the flexible-flexible copolymer systems with a relatively low particle loading, as the ratio of two blocks varies, one sees four kinds of phase structure: signal continuous, lamellar, co-continuous, and dispersed, corresponding to the order-disorder and continuity-dispersion transitions. In consideration of particle connectivity, the best electrical performance can be achieved with a special tri-continuous microstructure. While in the semi-flexible systems, the existence of rigid blocks can destroy the lamellar structure. If particles are located in the flexible block, a moderate stiffness of the rigid block can extensively enlarge the tri-continuous region, and high conductivity can be realized over a wide range of diblock compositions. If particles are located in the rigid block, however, high conductivity only emerges in a narrow composition range. In addition, the block should be prevented from becoming overstiff because this will cause direct particle aggregation.