Zhenxiang Xin

Fabrication of superhydrophobic surface by a laminating exfoliation method

We report a novel and facile approach to achieve a self-cleaning, flexible, transparent, template free, cheap and non-toxic polymeric film. The superhydrophobic surface will become active only by peeling off the laminated polymer film; this kind of “instant superhydrophobic surface” can be delivered to customers as “peel and use”.

Prediction and Optimization of Mechanical Properties of Polypropylene/Waste Tire Powder Blends using a Hybrid Artificial Neural Network-Genetic Algorithm (GA-ANN)

Blends of Polypropylene (PP) and waste ground rubber tire powder are studied with respect to the effect of ethylene—propylene—diene monomer (EPDM) and polypropylene grafted maleic anhydride (PP-g-MA) compatibilizer content by using the Design of Experiments methodology, whereby the effect of the four polymers content on the final mechanical properties are predicted. Uniform design method is especially adopted for its advantages. Optimization is done using hybrid Artificial Neural Network-Genetic Algorithm technique. A rubber formulary with respect to the four ingredients are optimized having maximum tensile strength and then compared with a blend predicted to have maximum elongation at break. It is concluded that the blends show fairly good properties provided that it has a relatively higher concentration of PP-g-MA and EPDM content. SEM investigations also corroborates with the observed mechanical properties. A quantitative relationship is then shown between the material concentration and the mechanical properties as a set of contour plots, which are then tested and confirmed experimentally to conform to the optimum blend ratio.

TEMPO-mediated oxidation of microcrystalline cellulose: Influence of temperature and oxidation procedure on yields of water-soluble products and crystal structures of water-insoluble residues

A series of microcrystalline cellulose samples were reacted with catalytic amounts of 2, 2, 6, 6-tetramethyl-1-piperidine oxoammonium salt (TEMPO), sodium hypochlorite and sodium bromide in Na2CO3/NaHCO3 buffer solution at different temperature (15 °C, 20 °C, 30 °C, 35 °C, 40 °C, 50 °C). The oxidation procedures included first and second oxidation. The first oxidation was a classical process for activating cellulose for the second oxidation. A substantial increase in the reactivity of the second oxidation cellulose samples was observed in comparison to those in the first oxidation and a relationship between oxidation procedures and accessibility of cellulose primary hydroxyl groups was directly established. For the characterization, we have used several methods, mainly XRD, FTIR. In all samples, the partial primary alcohol groups were selectively oxidized into carboxyl groups. The reaction during the first oxidation procedure mainly occurs in disordered regions of MCC and crystal surface. But the second oxidation procedure took place not only in disordered regions and crystal surface but inside crystalline region of cellulose I.

Mechanically stable superhydrophobic polymer films by a simple hot press lamination and peeling process

Mechanically stable superhydrophobic polymer films were prepared from a blend of polypropylene (PP) and ultrahigh molecular weight polyethylene (UHMWPE) polymers using a simple hot-press lamination and peeling method. The films surface morphology, wetting characteristics and resistance against wear abrasion were studied for varying PP/UHMWPE blend ratios. At a minute scale, the superhydrophobic surface was extensively covered with small fibrous protrusions having sizes in the micron to sub-micron range while at larger scales some bigger sized protrusions were also present on the films surface. The number of bigger protrusions was found to increase with increasing UHMWPE content of the PP/UHMWPE blend films, simultaneously enhancing the wear abrasion resistance and friction characteristics of the films. The bigger sized protrusions on the surface acted as sacrificial protrusions during the wear abrasion of the surface leaving the finer fibrous structures unaffected. The work demonstrated the possibility of producing polymer films with a mechanically stable superhydrophobic surface by a simple hot-press lamination and peeling method which is facile, environmentally friendly and adaptable for mass-production.

Synergistic effect of graphene and silicon dioxide hybrids through hydrogen bonding self-assembly in elastomer composites

A novel graphene–silicon dioxide hybrid (HGS) was prepared by plant polyphenol-tannic acid (TA) functionalized pristine graphene (G-TA) and primary amine-containing silane coupling agent modified SiO2 (Si–NH2). Through strong hydrogen-bonding interaction between the phenolic hydroxyl groups on G-TA and primary amine groups on Si–NH2, SiO2 was uniformly loaded to the surface of graphene. Due to the synergistic dispersion effect of graphene and SiO2, which prevents restacking and re-aggregating of both graphene and SiO2, HGS hybrids were distributed evenly in the natural rubber (NR) matrix (HGS@NR). Simultaneously, the surface roughness of graphene after loading SiO2 and the interfacial interaction between the HGS hybrid and NR matrix were substantially improved. Due to the good dispersion and strong interface, the overall properties of HGS@NR nanocomposites are drastically enhanced compared with those of GS@NR nanocomposites prepared by dispersing the blend of unmodified graphene and SiO2 (GS) in NR. The HGS@NR nanocomposites possess the highest tensile strength up to 27.8 MPa at 0.5 wt% and tear strength of 60.2 MPa at 0.5 wt%. Thermal conductivities of the HGS@NR nanocomposites were found to be 1.5-fold better than that of the GS@NR nanocomposites. Also, the HGS@NR nanocomposites exhibit excellent abrasive resistant capacity that is nearly 2-fold better than that of the GS@NR nanocomposites. These results suggest that HGS has great potential in high-performance nanocomposites and a new strategy of constructing the efficient graphene–SiO2 hybrid fillers has been established.

Covalent hybrid of graphene and silicon dioxide and reinforcing effect in rubber composites

AbstractFor developing high performance graphene and silicon dioxide (SiO2)-based green rubber nanocomposites, dispersal of graphene nanosheets and SiO2 particles in rubber hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia of graphene and the poor interaction with the organic matrix of SiO2. Here we report an efficient method to hybrid graphene nanosheets and SiO2 paticles. The SiO2 molecules were covalently bonded to the graphene surface via functionalized graphene, using plant polyphenol tannic acid (TA) as stabilizer and functional reagent, followed by further covalent derivatization through the Michael addition reaction between phenolic hydroxyl group on TA and primary amine on silane coupling agents modified SiO2. Through covalent hybridization, the SiO2 particles are uniformly decorated on the surface of graphene. The improved dispersion state of hybrid filler was attested by XRD, TEM and FTIR. SEM, DMA, mechanical analysis, thermal conductivity measurements and applied to characterize the hybrid nanocomposites. The results imply that the strategy of using hybrid fillers with covalent interactions has been established to be an efficient way to achieve high-performance rubber nanocomposites. The prominent confinement effect arising from nanosheets resulted in nearly 7.0% increase in the thermal conductivity of the highly synergistic hybridization graphene-SiO2 nanocomposites than that of the composite of graphene and SiO2 mixtures. The former possesses 45.4% increase in tensile strength and 32.6% in tear strength and 35.4% in compression set. The covalent hybridization nanocomposites exhibit excellent abrasive resistant capacity with nearly 36.6% increase than that of the composite of graphene and SiO2 mixtures. These results suggest that SiO2 and graphene covalent hybrid fillers have a high potential to be used in engineering composits. Graphical abstractThe synergistic hybridization graphene-SiO2 and reinforcing effect in rubber