This review reports on recent advances in the design of biodegradable polymers built from petroleum and renewable resources using reactive extrusion processing. Reactive extrusion represents a unique tool to manufacture biodegradable polymers upon different types of reactive modification in a cost‐effective way. Partially based on our ongoing research, ring‐opening polymerization of biodegradable polyesters will be approached as well as the chemical modification of biodegradable polymers, particularly natural polymers. The development of environmentally friendly polymer blends as well as (nano)composites from natural polymers, including natural fibers and nanoclays, through reactive extrusion, as an efficient way to improve the interfacial adhesion between these components, will be also discussed.
The effect of ZrC on the mechanical response of ZrB2 ceramics has been evaluated from room temperature to 2000 °C. Zirconium diboride ceramics containing 10 vol% ZrC had higher strengths at all temperatures compared to previous reports for nominally pure ZrB2. The addition of ZrC also increased fracture toughness from for nominally pure ZrB2 to due to residual thermal stresses. The toughness was comparable with ZrB2 up to 1600 °C, but increased to at 1800 °C and 2000 °C. The increased toughness above 1600 °C was attributed to plasticity in the ZrC at elevated temperatures. Electron back-scattered diffraction analysis showed strong orientation of the ZrC grains along the [001] direction in the tensile region of specimens tested at 2000 °C, a phenomenon that has not been observed previously for fast fracture (crosshead displacement rate = 4.0 mm min?1) in four point bending. It is believed that microstructural changes and plasticity at elevated temperature were the mechanisms behind the ultrafast reorientation of ZrC. 相似文献
Metallic doping can stabilize cubic phase Li7La3Zr2O12 (LLZO) solid electrolyte for high conductivity, due to the enhanced vacancies and disordered Li-site. However, the understanding of metallic doping in the crystal lattice during the high-temperature sintering process is still not clear. In present study, a gradient series of Fe doped LLZO are formulated via solid-phase reaction, and then investigated through crystal analysis and morphological characterization. Pair distribution function essay implies that doped Fe3+ promotes random distribution of Li+ over the available sites in the located crystal. Additionally, the ceramic morphology confirms that the particles sizes in LLZO pellets suddenly grow above 1000 ℃, and Fe doping can obviously suppress Li loss above 600 ℃. As a result, the LLZF0.15 exhibits the relatively high ionic conductivity of 1.99 × 10–5 S cm–1 at 45 ℃. 相似文献
通过水热处理、柠檬酸处理及其复合处理对Beta分子筛进行后改性,并以改性后的载体制得铂/Beta催化剂。采用X射线衍射(XRD)、X射线荧光光谱仪(XRF)、程序升温脱附(NH3-TPD)、红外吡啶吸附(Py-IR)、骨架铝核磁共振技术(27Al MAS NMR)及骨架硅核磁共振技术(29Si MAS NMR)等表征了改性前后Beta分子筛的物化性质,并考察了改性前后铂/Beta的多环芳烃选择性开环性能。结果表明,Beta分子筛在柠檬酸处理过程中可同时发生络合脱铝与骨架补铝,实现骨架铝的再分布;Beta分子筛在水热处理过程中优先脱除稳定性相对较低的Si(2 Al)处骨架铝,产生骨架缺陷的同时生成一定比例的二次介孔结构;水热-柠檬酸复合处理影响Beta分子筛骨架补铝及骨架铝再分布的效果,水热处理后Beta分子筛中存在更多的骨架缺陷,促进活性Al(OH)2+物种的骨架补铝作用。当Beta分子筛采用水热-柠檬酸复合处理顺序时,骨架补铝及骨架铝再分布效果显著,样品以中强酸为主,且具有较高的B酸量与L酸量的比值,所制备催化剂的多环芳烃选择性开环活性及稳定性最优。 相似文献