Functional Composite Materials最新文献

Styrene–butadiene–Rubber, SBR, is most often used in tread compounds in order to improve the Rolling Resistance (RR). The functionalized SBRs are used to increase the polymer–filler interaction in the compound to improve RR. In this study, the effect of different types of functional groups in SBR was investigated. Several types of functionalized S–SBR’s were synthesized by anionic polymerization: (i) SBR with an amine group at one end of the polymer chain, (ii) SBR with an alkoxy silane group at one end (iii) SBR with an amine group at one end and an alkoxy silane group at the other end of the polymer chain. A model reaction of silanization was conducted in a solvent to estimate how the amine functional group affects the silanization. Silica filled compounds were prepared with these SBR types. Payne effect and bound rubber measurement were done. The model silanization reaction of TESPT (Bis(triethoxysilylpropyl)tetrasulfide) with silica in the presence of amine shows that a higher amount of ethanol (EtOH) is released from TESPT compared to the amine free system. This result indicates that the silanization reaction can be accelerated by the presence of an amine functional group at the SBR polymer chain used in silica–filled compounds. The amine functionalized SBR and the alkoxy silane functionalized SBR show less Payne effect of the compounds which indicates that both functional groups can decrease the filler–filler interaction. More chemical bound rubber was obtained in branched SBRs compared to the corresponding linear SBRs. A branched polymer chain has a higher molecular weight compared to the linear type. Therefore, when one branched polymer chain reacts with silica or creates a silica–silane–polymer bond, more bound rubber can be obtained for the branched than for the linear type. The compound of the SBR with the alkoxy–silane functional group shows lower tan δ compared to the non–functionalized SBR and the amine functionalized SBR compounds. The influence of the type of functionalization of the SBR on tan δ at 70 °C was more significant in branched SBRs than in linear SBRs, due to the before–mentioned effect of the functional group on silanization and bound rubber.

The mechanical behavior of braided carbon nanotube yarns (CNTYs) on an elastomeric core to produce stretchable conductive materials were theoretically modeled and experimentally studied under tension. The elastomeric core served as the stretchable spring and the CNTYs braiding, with shape changing capabilities, as the conductive shell. A variety of samples were produced having various braiding angles on an elastomeric core and subsequently loaded in tension, and their stress–strain behavior was characterized. The model predicts the stress–strain behavior of the composite as a function of the initial braiding angle and the number of pitches. The innovative aspect was included in the model related to the friction between the braid and the core. Results indicated good agreement between the theoretical simulations and the experimental results which was not discussed in previous studies. Since the rate of the diameter decrease of the CNTYs braid was higher than that of the elastomeric core diameter, squeezing out of the core through the braid inter yarn space occurred. This limited the maximum potential extension of the braid. Thus, a critical strain was defined where the braid came into contact with the core. The addition of the friction stresses made a significant contribution to the overall stresses and the accuracy of the theoretical simulation, and its agreement with the experimental results. An apparent friction coefficient was proposed to account for the effect of the elastomer core/braid interactive restriction and squeezing out of the elastomer through the braiding, as observed in experimental results. As the CNTYs are conductive, a stretchable conductive composite was obtained having a resistivity of 9.05 × 10^–4 Ohm*cm, which remained constant throughout the tensile loading until failure and under cyclic loading.

Lack of access to potable water and abating levels of ground water level demands the reuse of unconventional water sources after remediating it in a sustainable way. In this context, purifying brackish, land and sea water seems a feasible solution to the ever-growing population.

In this work, a novel composite membrane was fabricated by 'layer-by-layer' self-assembly of poly-dopamine (PDA) and polystyrene sulfonate (PSS) supported on a highly crosslinked graphene oxide (GO) membrane to sieve ions to purify contaminated water as well as enhance the resistance towards chlorine. This GO membrane was sandwiched between layers of various nanoporous polyvinylidene difluoride (PVDF) membranes obtained by selectively etching out the PMMA component from the demixed blends. The blend membranes were designed following the melt-extrusion process and subsequent quenching to facilitate confined crystallization of PVDF and selective etching of PMMA. The membranes with different pore sizes were tuned on varying the composition in blends and a gradient in microstructure was achieved by stitching the membranes. Pure water flux, salt rejection, dye removal, and antibacterial activity were performed to study the membrane's efficiency. The GO membrane was chemically crosslinked with methylenediamine to impart dimensional stability and to enhance rejection efficiency through the nanoslits that GO offers. Besides effective rejection, the sandwiched membrane was modified with ‘layer-by-layer’ self-assembly of polyelectrolytes on the surface to improve the chlorine tolerance performance. This strategy resulted in an excellent salt (about 95% and 97% for monovalent and divalent ion, respectively) and dye rejection (100% for both cationic and anionic dye), besides facilitating excellent chlorine tolerance performance. Moreover, this modified membrane showed superior antifouling properties (flux recovery ratio is more than 90%) and excellent antibacterial performance (near about 3 log reduction).

Thus the concept of using layer-by-layer self-assembly of polycations (PDA) and polyanions (PSS) onto a hierarchical chemically modified GO sandwiched PVDF membrane proved to be a productive strategy to purify contaminated water. Thus the membrane can be a potential candidate for domestic as well as industrial application.

The interface between polymer matrices and nanofillers is critical for efficient interaction to achieve the desired final properties. In this work, block copolymers were utilized to control the interface and achieve optimum interfacial interaction. Specifically, we studied the compatibilizing effects of styrene-ethylene/butadiene-styrene (SEBS) and styrene-ethylene/propylene (SEP) block copolymers on the morphology, conductivity, and rheological properties of polypropylene-polystyrene (PP/PS) immiscible blend with 2 vol% multiwall carbon nanotube (MWCNT) at different blend compositions of PP/PS 80:20, 50:50 and 20:80.

MWCNTs induced co-continuity in PP/PS blends and did not obstruct with the copolymer migration to the interface. Copolymers at the interface led to blend morphology refinement. Adding block copolymers at a relatively low concentration of 1 vol% to compatibilize the PP/PS 80:20 blend substantially increased the electrical conductivity from 5.15*10⁻⁷S/cm for the uncompatibilized blend to 1.07*10⁻²S/cm for the system with SEP and 1.51*10⁻³S/m for the SEBS system. These values for the compatibilized blends are about 4 orders of magnitude higher due to the interconnection of the droplet domains. For the PP/PS 50:50 blend, the SEBS copolymer resulted in a huge increase in conductivity at above 3 vol% concentration (conductivity increased to 3.49*10⁻³S/cm from 5.16*10⁻⁷S/cm). Both the conductivity and the storage modulus increased as the SEBS copolymer content was increased. For the PP/PS 20:80 blend, we observed an initial decrease in conductivity at lower copolymer concentrations (1–3 vol%) and then an increase in conductivity to values higher than the uncompatibilized system, but only at a higher copolymer concentration of 10 vol%. The triblock copolymer (SEBS), which had 60 wt% PS content, shows a more significant increase in rheological properties compared to the diblock copolymer (SEP). The morphology shows that the interaction between MWCNT and PS is stronger than the interaction between MWCNT and PP, hence there is selective localization of the nanofiller in the PS phase as predicted by Young’s equation and by molecular simulation.

The exploration of a noble-metal-free and nitrogen-doped carbon (M–N/C) composite electrocatalyst for the oxygen reduction reaction (ORR) remains a great challenge. The activities of the M–N/C composite electrocatalysts are mainly affected by the metal active sites, pyridinic nitrogen, and graphitic nitrogen. In the present work, the iron-coordinated self-assembly is proposed for the preparation of iron-chelating pyridine nitrogen-rich coordinated nanosheet (IPNCN) composites as electrocatalysts. Due to the highly conjugated structure of the IPNCN precursor, the pyridine nitrogen elements at both ends of the tetrapyrido [3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine (TP) provide the multiple ligands, and the coordination interactions between the irons and the pyridine nitrogen further improve the thermodynamic stability, where the metal active sites and nitrogen elements are uniformly distributed in the whole structure. The resultant IPNCN composites exhibit excellent ORR performance with an onset potential of 0.93 V and a half potential of 0.84 V. Furthermore, the IPNCN composite electrocatalysts show the higher methanol resistance and electrochemical durability than the commercial Pt/C catalysts. It could be convinced that the as-designed IPNCN composite catalysts would be a promising alternative to the noble metal Pt-based catalysts in the practical applications.

Electrospinning is a relatively simple technique for producing continuous fibers of various sizes and morphologies. In this study, an intrinsically hydrophilic poly(3-hydroxybutarate-co-3-hydroxyvalerate) (PHBV) biopolymer strain was electrospun from a solution under optimal processing conditions to produce bilayers of beadless micro-fibers and beaded nano-fibers. The fibrous mats produced from the pure PHBV solution exhibited hydrophilicity with complete wetting. Incorporation of polydimethylsiloxane (PDMS) treated silica into the electrospinning solutions resulted in a non-wetting state with increased fiber roughness and enhanced porosity; however, the fiber mats displayed high water droplet-adhesion. The SiO₂–incorporated fibrous mats were then treated with stearic acid at an activation temperature of 80 °C. This treatment caused fiber surface plasticization, creating a tertiary hierarchical roughness owing to the interaction of PHBV chains with the polar carboxyl groups of the stearic acid. Scanning electron microscopy was used to assess the influence of the electrospinning process parameters and the incorporation of nanoparticles on surface morphology of the fibers; energy dispersive X-ray spectroscopy confirmed the presence of SiO₂ nanoparticles. Fourier transform infrared spectroscopy was performed to study the incorporation of SiO₂ and the interaction of stearic acid with PHBV at various concentrations. The chemical interaction between stearic acid and PHBV was confirmed, while SiO₂ nanoparticles were successfully incorporated into the PHBV fibers at concentrations up to 4.5% by weight. The incorporation of nanoparticles and plasticization altered the thermal properties of PHBV and a decrease in crystalline fraction was observed. The stearic acid modified bilayers produced from the micro-nano-fibrous composites showed very low water droplet sticking, a roll off angle of approximately 4° and a high static contact angle of approximately 155° were achieved.

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The focus of this research was to study the effect of combining nanofillers with different geometry and surface chemistry on the structure and properties of biopolymers as an alternative to traditional plastics. How the inclusion of 2D graphene oxide (GO) or reduced GO (rGO) combined with 1D sepiolite (SPT) or cellulose nanocrystals (CNCs) affect the structure and properties of chitosan and chitosan/carboxymethyl cellulose (CMC) materials was investigated. A 3D interconnected microstructure formed, composed of GO and SPT due to the strong interactions between these hydrophilic nanofillers. The chitosan/CMC/GO/SPT composite had the highest tensile strength (77.5 ± 1.2 MPa) and Young’s modulus (1925.9 ± 120.7 MPa). For the un-plasticised matrices, hydrophobic rGO nanosheets generally hindered the interaction of SPT or CNCs with the polysaccharides (chitosan and CMC) and consequently, composite properties were mainly determined by the rGO. However, for the chitosan matrix plasticised by 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]), rGO + CNCs or rGO + SPT disrupted polymer chain interactions more effectively than the nanofillers when added alone and resulted in the chitosan being more plasticised, as shown by increased chain mobility, ductility, and surface hydrophilicity. For the [C₂mim][OAc]-plasticised chitosan/CMC matrix, the advantages of including hybrid fillers, rGO + CNCs or rGO + SPT, were also obtained, resulting in higher thermal stability and surface hydrophobicity.

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