The role of non-covalent interactions and matrix viscosity on the dispersion and properties of LLDPE/MWCNT nanocomposites

Linear low density polyethylene (LLDPE)/multi-walled carbon nanotube (MWCNT) composites were prepared by melt compounding, following two different compatibilization strategies that involved non-covalent interactions between the matrix and the filler. The first approach involved grafting pyridine aromatic moieties on the maleated polyolefin backbone, which are able to interact by π–π stacking with the surface of the nanotubes. The second method implemented non-covalent/non-specific surface functionalization of the MWCNTs with a hyperbranched polyethylene (HBPE). The enhanced interfacial interactions established in the composites containing LLDPE functionalized with pyridine grafts improved the dispersion of the nanotubes within the polymer matrix. Dispersion was also favoured by higher matrix viscosity. Composites containing finely dispersed MWCNTs exhibited an increase in the rheological and electrical percolation thresholds, and a significant improvement in mechanical properties. On the contrary the composites based on the low viscosity matrix contained large amounts of aggregates, which promoted lower percolation thresholds. Manipulation of matrix viscosity and compatibilization resulted in composites with good mechanical properties, and low percolation thresholds.     

Expanding the Genetic Code in Xenopus laevis Oocytes

Heterologous expression of ligand‐gated ion channels (LGICs) in Xenopus laevis oocytes combined with site‐directed mutagenesis has been demonstrated to be a powerful approach to study structure–function relationships. In particular, introducing unnatural amino acids (UAAs) has enabled modifications that are not found in natural proteins. However, the current strategy relies on the technically demanding in vitro synthesis of aminoacylated suppressor tRNA. We report here a general method that circumvents this limitation by utilizing orthogonal aminoacyl‐tRNA synthetase (aaRS)/suppressor tRNA_CUA pairs to genetically encode UAAs in Xenopus oocytes. We show that UAAs inserted in the N‐terminal domain of N‐methyl‐D ‐aspartate receptors (NMDARs) serve as photo‐crosslinkers that lock the receptor in a discrete conformational state in response to UV photo treatment. Our method should be generally applicable to studies of other LGICs in Xenopus oocytes.     

Preparation of a C6 quaternary ammonium chitosan derivative through a chitosan schiff base with click chemistry

In this study, we explored a new method for preparing C₆ quaternary ammonium chitosan (CTS) derivatives. The C₂? NH₂ of CTS was first protected by benzaldehyde. The C₆? OH of CTS was then transformed into a sulfonyl ester, which was then reacted with NaN₃ through nucleophilic substitution to introduce the ? N₃ group at the CTS C₆ position. This intermediate was reacted in a click chemistry reaction with a terminal alkynyl quaternary ammonium salt; this was followed by the deprotection of C₂? NH₂ with acid to furnish the C₆ quaternary ammonium CTS derivative. The structures and properties of synthesized products in the reactions were characterized by Fourier transform infrared spectroscopy, NMR, X‐ray diffraction, and thermogravimetric analysis, respectively. The effects of the reaction conditions on the degree of Schiff‐base CTS quaternization were evaluated by elemental analysis. The largest inhibition zone test and the minimum inhibitory concentration test showed that compared with CTS, the prepared CTS derivative had significantly improved antibacterial activity toward Staphylococcus aureus and Escherichia coli. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and crystalline properties of monomer casting Nylon‐6/Sio2 composites prepared via in situ polymerization

A series of monomer casting (MC) nylon‐6/SiO₂ composites were prepared via in situ polymerization. It was found that the tensile strength, storage modulus, and notched charpy impact strength of the composites were improved and reached maximum at 3–5 wt% loading of SiO₂. The α relaxation peak corresponding to the glass transition temperature (T_g) shifted to high temperature with increasing SiO₂ content. Addition of SiO₂ led to an increase of the melting and crystallization temperatures, and crystallinity. It also reduced the induction time of crystallization, advance the crystallization process of MC nylon‐6, and improve the crystal growth rate. The self‐nucleation crystallization analysis indicated that SiO₂ particles played the role of facilitating the crystallization of the matrix mainly via accelerating the generation of crystal nucleus. By addition of SiO₂ particles, the fracture surface of MC nylon‐6 changed to distant striations with many yield folds accompanied by a large number of stress whitening, displaying much obvious character of tough fracture. SiO₂ particles can be pulled‐out under stress by being covered with MC nylon‐6 resin due to strong interfacial interaction and presented a skin–core structure. © 2012 Society of Plastics Engineers.     

Hydrophilic modification of poly(vinylidene fluoride) membrane with poly(vinyl pyrrolidone) via a cross‐linking reaction

A highly hydrophilic hollow fiber poly(vinylidene fluoride) (PVDF) membrane [PVDF‐cl‐poly(vinyl pyrrolidone) (PVP) membrane] was prepared by a cross‐linking reaction with the hydrophilic PVP, which was immobilized firmly on the outer surface and cross‐section of the PVDF hollow fiber membrane via a simple immersion process. The cross‐linking between PVDF and PVP was firstly verified via nuclear magnetic resonance measurement on PVP solution after cross‐linking. The hydrophilic stability of the modified PVDF membrane was evaluated by measuring the pure water flux after different times of immersion and drying. The anti‐fouling properties were estimated by cyclic filtration of protein solution. When the cross‐linking time was as long as 6 hr and the PVP content reached 5 wt %, the pure water flux (J_v) was constant as ～ 600 L m^?2 hr^?1. The hydrophilicity of the PVDF‐cl‐PVP membrane was significantly enhanced and exhibited a good stability. The PVDF‐cl‐PVP membrane showed an excellent anti‐protein‐fouling performance during the cyclic filtration of bovine serum albumin solution. Therefore, a highly hydrophilic and anti‐protein‐fouling PVDF hollow fiber membrane with a long‐term stability can be prepared by a simple and economical cross‐linking process with PVP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

应用型人才培养与物理化学实验教学改革

为了适应郴州有色金属行业发展的应用型人才培养需求,提高学生为当地经济和社会发展服务的能力,课题组对应用化学专业的物理化学实验进行了实践教学改革。以"会做人、会思考、有技能、有创新"为人才培养目标,倡导专业精神,厚实理论基础,转变基础示范,强化专业技术,并着力探索了分阶段的实践教学考核机制。实践教学改革显著提高了学生的积极性,并取得了良好的成效。     

高阻隔液态牛奶包装膜

介绍新型的高阻隔材料——丙烯酸酯共聚物。将其配制成高阻隔涂布液,再用涂布设备将高阻隔涂布液涂布于三层共挤聚乙烯底膜上,干燥后在高阻隔层上复合一层聚乙烯薄膜,得到高阻隔高保香性的液态牛奶包装膜。该产品在阻隔效果、投资成本、包装成本和卫生环保等诸多方面,都要比市场上的其他阻隔材料优秀很多。     

软模板法合成多级孔沸石分子筛及其催化性能研究进展

详细介绍了软模板法合成多级孔沸石分子筛及其催化性能。合成多级孔沸石分子筛的软模板主要包括两种类型,一种是含多季铵基团的烷基季铵盐;另一种是双亲有机硅表面活性剂。对采用这两种表面活性剂合成多级孔沸石分子筛的方法以及得到的材料结构特性进行了综述。进一步讨论了这两种方法得到的分子筛的催化性能。关于这些材料的催化性能研究主要有三方面内容:有机大分子化合物合成的活性和选择性,生物质催化热解特性和大分子化合物合成中抗积炭失活性能。     

Novel polyarylates containing aryl ether units: synthesis,characterization and properties

To improve the processability of the poly(p‐hydroxybenzoic acid), copolyarylates containing m‐aryl ether units were synthesized using p‐acetoxybenzoic acid, 1,4‐diacetoxybenzene and 1,3‐bis(4'‐carboxyphenoxy)benzene by melt transesterification reaction. The structure and properties of these polyarylates were characterized using infrared spectra, differential scanning calorimetry, thermogravimetric analyses, wide‐angle X‐ray diffraction and polarized optical microscopy etc. The results showed that all polyarylates were semicrystalline materials and could form a thermotropic liquid crystalline intermediate state. As the content of aryl ether units increased, the crystallization and melting temperatures of the polyarylate decreased; meanwhile, the crystalline ability became lower. The introduction of the aryl ether could restrain the formation of a liquid crystalline structure and reduce the thermal stability to some extent. After solid state polymerization (SSP), the intrinsic viscosity, melting temperature, crystallinity and thermal stability of the polyarylate increased while the melting range narrowed. However, the SSP reaction might be accompanied by degradation and crosslinking.