Yihu Song

Grafting of copolymers onto graphene by miniemulsion polymerization for conductive polymer composites: improved electrical conductivity and compatibility induced by interfacial distribution of graphene

A facile and general method to covalently functionalize graphene oxide (GO) with copolymers, using poly(styrene-co-methylmethacrylate) (P(St-co-MMA)) as an example, via miniemulsion polymerization is described in this study. After in situ reduction, insulating GO is converted to conductive reduced-graphene oxide (RGO). P(St-co-MMA) grafted RGO as conducting filler was incorporated into immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend to prepare conductive polymer composites (CPCs). The lowest percolation threshold (0.02 vol%) among all the reported values for graphene-filled CPCs was achieved due to the controllable preferential distribution of the modified RGO at the interfacial region between PS and PMMA phases, attributed to P(St-co-MMA) grafted on the surface of RGO behaving as compatibilizers to improve interfacial interactions with both the two phases. Moreover, P(St-co-MMA) grafting modified RGO could obviously enhance the compatibility reflected by a significant reduction of the size of dispersed phase, for an example, by nearly one order of magnitude for PS/PMMA (4/1 in volume) blends.

Environmentally friendly reduced graphene oxide as a broad-spectrum adsorbent for anionic and cationic dyes via π–π interactions

π–π interactions between graphene and organic dyes with a conjugate aromatic structure play a key role in the field of high-efficiency, broad-spectrum adsorbents for the removal of water contaminants. L-Cysteine reduced graphene oxide (RGO-Cys) has a good conjugate structure and dispersity in aqueous solution, endowing it with great adsorption efficiency towards anionic, nonionic and cationic dyes with a conjugate aromatic structure mainly via π–π interactions, as proved by the Raman spectrum and special adsorption experiments. The maximum adsorption capability for anionic indigo carmine (IC) and cationic neutral red (NR) is as high as 1005.7 mg g−1 and 1301.8 mg g−1, respectively, the former being the highest among those reported for adsorbents known to date. The total adsorption amount in mixed dye solutions is even higher (>3500 mg g−1), the highest total capability for simultaneous adsorption of anionic and cationic dyes in their solution mixtures. The π–π stacking adsorption mechanism ensures RGO-Cys to be used as a broad-spectrum adsorbent with high efficiency for many kinds of dye contaminants in water while the remnant carboxyl groups on graphene nanosheets facilitate effective adsorption towards Cu2+ with a capability as high as 139.2 mg g−1, opening up many possibilities for the use of graphene in water cleaning including disinfection, decontamination, and desalination.

Influence of annealing on linear viscoelasticity of carbon black filled polystyrene and low-density polyethylene

Influence of annealing on linear dynamic rheology of carbon black filled polystyrene and low-density polyethylene before and after annealing was investigated in relation to a recently proposed two phase model. Annealing-induced improvements in dynamic complex modulus of filled polymers in the linearity region are related to increases in amplification factor and characteristic moduli and to retardation in dynamics of the filler phase. It is suggested the characteristic modulus and dynamics of the filler phase are interrelated to each other, and their relationship is independent of thermal history. Moreover, annealing-induced variations in global viscoelasticity of filled polymers are ascribed to the geometric changes of the filler phase consisting of filler clusters with a constant fractal dimension.

The electric self-heating behavior of graphite-filled high-density polyethylene composites

The electric self-heating behavior of graphite-powder-filled high-density polyethylene is studied. Two equations are proposed to describe the electric-field dependence of the self-heating temperature and resistance dependence of the critical field. Based on Ohmic and non-Ohmic approximations and the heat-dissipation model, the self-heating equations are also derived theoretically. The equations show that self-heating is determined by the initial resistance and true positive temperature coefficient (PTC) effect under fields. Design and application principles for polymer PTC heaters are suggested on the basis of the experimental results and proposed equations.

On time-temperature-concentration superposition principle for dynamic rheology of carbon black filled polymers

Time-temperature-concentration superposition principle is disclosed to linear dynamic rheology of carbon black (CB) filled high-density polyethylene (HDPE) with a wide range of CB volume fraction. The time-concentration superposition (TCS) principle is also validated in CB filled ethylene-tetrafluoroethylene (ETFE) alternating copolymer at 260 °C. The frequency-dependent viscoelastic functions can be superposed onto universal master curves with the reference of the unfilled HDPE and ETFE. The filler network and strain amplification concepts are used for accounting for the TCS principle.

Influence of annealing on rheological and conductive behaviors of high-density polyethylene/carbon black composites

A simultaneous measurement on dynamic viscoelastic and conductive behaviors was carried out to investigate the effect of high temperature annealing on the properties of carbon black (CB) filled high-density polyethylene composites. The results showed that dynamic storage and loss moduli of the composites increased significantly with increasing annealing time, and there existed a liquid- to solid-like transition at a critical time (tc) which is dependent on temperature and CB content. Accompanying with the variation in dynamic moduli, electrical resistance (R) decreased sharply with time. What’s more, the increase of R could be observed in the long time region. The activation energy determined from tc as a function of reciprocal temperature was found to be irrespective of CB content. The evolutions of moduli and R induced by thermal treatment were discussed on the base of the concept of filler flocculation in the melt.

Improved tensile strength of glycerol-plasticized gluten bioplastic containing hydrophobic liquids

The aim of the present work has been to study the influence of hydrophobic liquids on the morphology and the properties of thermo-molded plastics based on glycerol-plasticized wheat gluten (WG). While the total amount of castor oil and glycerol was remained constant at 30 wt%, castor oil with various proportions with respect to glycerol was incorporated with WG by mixing at room temperature and the resultant mixtures were thermo-molded at 120 degrees C to prepare sheet samples. Moisture absorption, morphology, dynamic mechanical properties, and tensile properties (Youngs modulus, tensile strength and elongation at break) of the plastics were evaluated. Experimental results showed that the physical properties of WG plastic were closely related to glycerol to castor oil ratio. Increasing in castor oil content reduces the moisture absorption markedly, which is accompanied with a significant improvement in tensile strength and Youngs modulus. These observations were further confirmed in 24 wt% glycerol-plasticized WG plastics containing 6 wt% silicone oil or polydimethylsiloxane (PDMS) liquid rubber.

Mechanical and thermal properties of nanosized titanium dioxide filled rigid poly(vinyl chloride)

Nano-sized rod-like titanium dioxide (TiO2) filled rigid poly(vinyl chloride) (PVC) nanocomposites were prepared by using injection-molding method. Vicat, Charpy impact and tensile tests as well as thermogravimetric and dynamic mechanical analyses were used to characterize the structure and properties of the nanocomposites. The results showed that nano-TiO2 could improve Vicat softening temperature and also improve thermal stability of PVC during the stages of dehydrochlorination and formation of carbonaceous conjugated polyene sequences, which can be ascribed to restriction of the nanoparticles on the segmental relaxation as being evidenced by raises in glass transition and β-relaxation temperatures of PVC upon filling TiO2. Addition of TiO2 nanoparticles less than 40 phr (parts per hundreds of resin) could significantly improve impact strength of the composites while the TiO2 agglomeration at high contents leads to a reduction in impact toughness.

Annealing-induced rheological and electric resistance variations in carbon black-filled polymer melts

Annealing-induced viscoelastic and electric conduction variations were traced by simultaneous measurement of resistance and dynamic modulus to carbon black (CB)-filled high-density polyethylene, polystyrene, and polypropylene at elevated temperatures. The resistance decay during annealing the melts is closely related to terminal relaxation of polymer chains and the temperature-mediated interfacial tension between CB and the matrix. On the other hand, a time–temperature–concentration superposition principle was disclosed to evolution of dynamic modulus for the filled melts at different temperatures and CB volume fractions. Annealing the filled melts causes a liquid-to-solid-like transition and the differences in kinetic constant for evolution of dynamic modulus among the three systems at the same condition are involved in interfacial tension.

Rheological behaviors of doughs reconstituted from wheat gluten and starch

Hydrated starch-gluten reconstituted doughs were prepared and dynamic rheological tests of the reconstituted doughs were performed using dynamic strain and dynamic frequency sweep modes. Influence of starch/gluten ratio on rheological behaviors of the reconstituted doughs was investigated. The results showed that the reconstituted doughs exhibited nonlinear rheological behavior with increasing strain. The mechanical spectra revealed predominantly elastic characteristics in frequency range from 10−1 rad s−1 to 102 rad s−1. Cole-Cole functions were applied to fit the mechanical spectra to reveal the influence of starch/gluten ratio on Plateau modulus and longest relaxation time of the dough network. The time-temperature superposition principle was applicable to a narrow temperature range of 25°C ~40°C while it failed at 50°C due to swelling and gelatinization of the starch.