Yanda Lei

Hydrolysable tannin as environmentally friendly reducer and stabilizer for graphene oxide

An environmentally friendly method for preparing reduced graphene oxide (rGO) was established based on the typical hydrolysable tannin, tannic acid (TA). TA is fully competent in reducing GO and stabilizing rGO simultaneously.

Biobased Poly(propylene sebacate) as Shape Memory Polymer with Tunable Switching Temperature for Potential Biomedical Applications

From the point of better biocompatibility and sustainability, biobased shape memory polymers (SMPs) are highly desired. We used 1,3-propanediol, sebacic acid, and itaconic acid, which have been industrially produced via fermentation or extraction with large quantities as the main raw materials for the synthesis of biobased poly(propylene sebacate). Diethylene glycol was used to tailor the flexibility of the polyester. The resulted polyesters were found to be promising SMPs with excellent shape recovery and fixity (near 100% and independent of thermomechanical cycles). The switching temperature and recovery speed of the SMPs are tunable by controlling the composition of the polyesters and their curing extent. The continuously changed switching temperature ranging from 12 to 54 °C was realized. Such temperature range is typical for biomedical applications in the human body. The molecular and crystalline structures were explored to correlate to the shape memory behavior. The combination of potential biocompatibility and biodegradability of the biobased SMPs makes them suitable for fabricating biomedical devices.

Adsorption of Ionic Liquid onto Halloysite Nanotubes: Mechanism and Reinforcement of the Modified Clay to Rubber

An ionic liquid (IL), 1-butyl-3-methyl-imiazolium hexafluorophosphate [BMIm]PF6, was coated onto halloysite nanotubes (HNTs) in tetrahydrofuran–water mixture. The IL layers on the HNTs were confirmed by thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, determination of contact angle, and porosity analysis. The interaction between IL and HNTs, proposed to be hydrogen bonding, was verified by various spectral results such as Raman spectroscopy, nuclear magnetic resonance and X-ray photoelectron spectroscopy. Because of their interaction, the crystallization behavior of IL in the presence of HNTs was found to be changed, as indicated by the results of differential scanning calorimetry. The IL-coated HNTs (m-HNTs) were used as reinforcement for styrene–butadiene rubber. Compared with the compounds with uncoated HNTs, the uncured compounds with m-HNTs showed faster curing, and the resulting vulcanizates showed substantially higher tensile strength and much lower hardness. The unique changes in the compounds are correlated to the changes in filler dispersion and interaction between IL and HNTs.

Fluorescent whitening agent stabilized graphene and its composites with chitosan

Individually dispersed graphene colloid is prepared using common and industrially available fluorescent whitening agents (FWAs) as stabilizers. Characterizations by UV-vis, fluorescence and Raman spectra demonstrate that FWAs are successfully anchored onto graphene sheets by π–π interaction. The results from AFM indicate the individual dispersion of graphene sheets in water. FWAs are demonstrated as highly efficient in suspending graphene with high concentration(6.2 mg ml−1). Subsequently, the obtained graphene sheet is incorporated into a chitosan (CS) matrix by solution casting to fabricate CS/graphene composites. Morphological observations substantiate the homogeneous dispersion of graphene in the CS matrix and the strong interfacial adhesion between them. The significant improvements in tensile strength and toughness of the composite films are concurrently observed.

Curing behaviour of epoxy resin/graphite composites containing ionic liquid

By adopting the isoconversional method, subtle changes in the curing activation energy (E?) among epoxy resin/graphite composites by the inclusion of expanded graphite (EG), ionic liquid of 1-butyl-3-methyl-imidazolium hexafluorophosphate ([BMIm]PF6) or their combination are shown in the whole conversion range. At lower concentrations (1?phr) of EG, compared with the E? of the neat epoxy resin, the composite with EG has a lower E? before the gelation, and a higher E? after the gelation. At higher concentrations of EG, however, in the whole conversion range, the composite with EG shows a higher E? compared with the neat epoxy resin. As the curing proceeded, a peculiar increase in E? is found in systems containing [BMIm]PF6. Due to the formation of hydrogen bonding between [BMIm]PF6 and the hardener (Jeffamine), the reactivity of Jeffamine is considerably decreased, leading to a much higher E? in [BMIm]PF6-containing systems, especially at higher conversion. In systems containing a combination of [BMIm]PF6 and EG, due to the interactions between EG and [BMIm]PF6, the shielding effect provided by the well-dispersed EG sheets constrains the formation of the hydrogen bonding between [BMIm]PF6 and Jeffamine, leading to lowered E? compared with that for the system containing [BMIm]PF6 only.

Tubular Clay Composites with High Strength and Transparency

Optically transparent composites containing nanotubular clay up to 65 wt%, prepared by a facile “one-pot” process, exhibited high mechanical strength and heat resistance. The attractive characteristics of the composites, in addition to their transparency, include use of low-cost and nontoxic raw materials, easy scaling-up, and possible petroleum independence. The properties of the composites were ascribed to the strong interfacial interactions and the excellent dispersion of nanotubular clay.

Reinforced Rubber with Ionic Liquid Modified Carbon Black

The ionic liquid, 1-butyl-3-methylimidazole hexafluorophosphate (BmimPF6), was utilized to modify carbon black (CB) via microwave (MW) irradiation. The conditions for the preparation of the modified CB (m-CB) were optimized. The reinforceability of the m-CB in styrene-butadiene rubber (SBR), butadiene rubber (BR) and nitrile rubber (NBR) composites were evaluated. The curing behaviour, morphology and tensile properties of the rubber/m-CB composites were studied and compared with those of composites filled with unmodified CB. Rubber/m-CB compounds showed a significant increase in the curing rate for a generated zinc complex with the alkylimidazoles. Compared with CB, m-CB exhibited a significantly improved reinforceability of the rubbers at lower filler loading, although the mechanical properties were changed slightly at higher filler loading. A possible mechanism was proposed, based on the molecular slippage theory in which the interfacial bonding, the filler loading and the chain flexibility of the rubber molecules were all considered.

High perfermance light-colored rubber nanocomposites

High performance light-colored rubber-inorganics nanocomposites were fabricated by the direct incorporation of sorbic acid (SA) in the filled rubber compounds. The mechanisms of largely improved performance were studied in details. The strong interfacial bonding between rubber matrix and the filler and significantly improved dispersion of the filler were resulted through SA intermediated linkages. Effect of SA on the vulcanization behavior, morphology and mechanical properties were studied. Formation of zinc disorbate (ZDS) and its reinforcing effect on rubber was investigated. High content of ZDS leaded to high ionic crosslink density and had a more signficantly effect on enhancing the performance of rubber. The composites with high nanotubular clay content were found to be highly ionic crosslinked, optical transparent and exhibited high mechanical strength and heat resistance. The properties of the composites were ascribed to the strong interfacial interactions and the excellent dispersion of nanotubular clay.