Novel cross-linked chitosan-based films were prepared using the solution casting technique. A naturally occurring and nontoxic cross-linking agent, genipin, was used to form the chitosan and chitosan/poly(ethylene oxide) (PEO) blend networks, where two types of PEO were used, one with a molecular weight of 20 000 g/mol (HPEO) and the other of 600 g/mol (LPEO). Genipin is used in traditional Chinese medicine and extracted from gardenia fruit. Importantly, it overcomes the problem of physiological toxicity inherent in the use of some common synthetic chemicals as cross-linking agents. The mechanical properties and the stability in water of cross-linked and un-crosslinked chitosan and chitosan/PEO blend films were investigated. It was shown that, compared to the transparent yellow, un-cross-linked chitosan/PEO blend films, the genipin-cross-linked chitosan-based film, blue in color, was more elastic, was more stable, and had better mechanical properties. Genipin-cross-linking produced chitosan networks that were insoluble in acidic and alkaline solutions but were able to swell in these aqueous media. The swelling characteristics of the films exhibit sensitivity to the environmental pH and temperature. The surface properties of the films were also examined by contact angle measurements using water and mixtures of water/ethanol. The results showed that, with the one exception of cross-linked pure chitosan in 100% water, the cross-linked chitosan and chitosan/PEO blends were more hydrophobic than un-crosslinked ones.

A covalently bonded polyethylene grafted graphene oxide hybrid material was fabricated successfully. Gamma-aminopropyltriethoxysilane (APTES) was firstly coated onto the graphene oxide sheets, and then maleic anhydride grafted polyethylene (MA-g-PE) was grafted onto the APTES coated graphene oxide sheets, which were confirmed by means of Fourier transform infrared, X-ray photoelectron and differential scanning calorimetry techniques. Functionalization resulted in 96 wt% polymer grafting efficiency, and a 10 C increase in the crystallisation temperature, compared with that of the pure MAg-PE. An encapsulating structure of the functionalised graphene oxide sheets was observed by means of TEM. For the potential application of the functionalised graphene oxide, PE/functionalised graphene oxide nanocomposites as an example was assessed in this paper. Initial results showed that Young's modulus, yielding strength and tensile strength of PE can be improved by incorporation of the PEgraft-graphene oxide at very low loadings. This protocol could broad the potential application of graphene in the development of non-polar polymer/graphene nanocomposites.

The three different sized chemical functionalized graphene (GO) sheets, namely GO-1 (D 50 = 10.79 μm), GO-2 (D 50 =1.72 μm) and GO-3 (D 50 = 0.70 μm), were used to fabricate a series of epoxy/GO nanocomposites. Fracture toughness of these materials was assessed. The results indicate that GO sheets were dramatically effective for improving the fracture toughness of the epoxy at a very significant low loading. The enhancement of the epoxy toughness was strongly dependent on the size of GO sheets incorporated. GO-3 with smaller sheet size gave the maximum reinforcement effect compared with GO-1 and GO-2. The incorporation of only 0.1 wt% GO-3 was observed to increase the fracture toughness of pristine epoxy by ~75 %. The toughening mechanism was well understood by fractography analysis of the tested samples. Massive cracks in the fracture surfaces of the epoxy/GO nanocomposites were observed. The GO sheets effectively disturbed and deflected the crack propagation due to its two dimensional structure. GO-3 sheets with smaller size were * Corresponding author: Tel: +44 1509223160. E-mail address: m.song@lboro.ac.uk (M. Song) 2 / 30 highly effective in resisting crack propagation, and a large area of whitening zone was observed. The incorporation of GO also enhanced the stiffness and thermal stability of the epoxy. IntroductionToughening of thermosets has been a challenging issue that limits their applications in high performance areas such as automotive, aerospace and defence.[1] A high crosslinked density is always necessary for a thermoset material to achieve excellent mechanical properties. However, high crosslinked density could result in lower propagation by producing large amount of plastic deformation. Palmeri et al. [14] pointed that the presence of the coiled structure of graphene sheets could absorb significant amount of energy. Zhao et al. [21] studied the influence of the particle size of 2D nanofiller on improvement of epoxy toughness by computer simulation. The simulation results revealed that the stress concentration factor reduced as the particle size decreased, and when particle size was smaller than 1μm the stress concentration factor was unchanged. Very recently, Chatterjee et al. [22] reported that the bigger size of graphene sheets resulted in the greater reinforcement of fracture toughness for epoxy resin, which experimental result conflicts with Zhao's simulation result. So far,although many studies on graphene toughening of epoxy resin have been made, some questions such as the one above mentioned still remain.In our research, a series of epoxy/graphene oxide (GO) nanocomposites were successfully fabricated by addition of three different sizes of GO sheets. In this communication we attempt to evaluate whether the size of graphene sheet influences fracture toughness and also to develop an understanding of the toughening mechanism for the epoxy resin. Experimental MaterialsDiglycidyl ether of bisphenol-A (DGEBA) epoxy (D.E.R*331) (epoxide equivalent weight is 182-192 g•eq -1 ) was provi...

Knowledge of the mineral effects of biochars on their sorption of hydrophobic organic contaminants (HOCs) is limited. Sorption of phenanthrene (PHE) by plant-residue derived biochars (PLABs) and animal waste-derived biochars (ANIBs) obtained at two heating treatment temperatures (HTTs) (450 and 600 °C) and their corresponding deashed biochars was investigated. The decreased surface polarity and increased bulk polarity of biochars after deashing treatment indicated that abundant minerals of biochars benefit external exposure of polar groups associated organic matter (OM). Organic carbon (OC)-normalized distribution coefficients (K(oc)) of PHE by biochars generally increased after deashing, likely due to enhancement of favorable and hydrophobic sorption sites caused by mineral removal. Positive correlation between PHE log K(oc) by PLABs and bulk polarity combined with negative correlation between PHE log K(oc) values by ANIBs and surface polarity suggested PLABs and ANIBs have different sorption mechanisms, probably attributed to their large variation of ash content because minerals influenced OM spatial arrangement within biochars. Results of this work could help us better understand the impact of minerals, bulk/surface polarity, and sorption domain arrangement of biochars on their HOCs sorption and predict the fate of HOCs in soils after biochar application.

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