海洋储碳机制及区域碳氮硫循环耦合对全球变化的响应

海洋作为地球表面最大的活跃碳库,其碳收支在很大程度上决定了全球气候变化的走向.然而,海洋碳循环是一个多时空尺度的过程,相关的碳收支估算存在很大的; 不确定性,其控制过程与机理更是一个颇具挑战性的难题(胡敦欣等, 2015),特别是海洋储碳机制,是研究全球变化及应对的核心内容之一.国家重点研发计划专项全球变化及应对项

Solid State Foaming of Poly(lactic acid) Blown with Compressed CO2:Influences of Long Chain Branching and Induced Crystallization on Foam Expansion and Cell Morphology

In this study, poly(lactic acid) (PLA) resins with linear (L-PLA) and branched structure (B-PLA) were selected, and the solid state foaming technology was applied to prepare PLA foams. B-PLA foams exhibited a high expansion ratio of about 40 and cell density of 105-6 cells/cm3, whereas L-PLA foams only had the highest expansion ratio of 29.8 and cell density of 103？6 cells/cm3. When PLA resins were induced crystallization during CO2 saturation, however, the prepared L-PLA foams presented the highest expansion ratio of 37.4 and cell density of 106？7 cells/cm3. The cell structure evolution of PLA foams with the foaming time suggested that the in situ formed crystal domains supplied nucleating sites to enhance cell nucleation and acted as physical cross-linking points to stabilize cell structure. These interesting results demonstrated that the induced crystallization might be more attractive than the chain modification to improve the foaming behavior using solid state foaming technolog

Tensile properties of microcellular poly(lacticacid) foams blown by compressed CO2

In this study, microcellular poly(lactic acid) foams with various crystallinities, cell morphologies, and densities were prepared using CO2 as the physical blowing agent. The evolution of crystallinity developments of four types of poly(lactic acid) samples during the saturation, foaming, and annealing processes was investigated. Crystallization of about 20% was reached in poly(lactic acid) samples after CO2 saturation, a high crystallinity of about 38.2% could be achieved for the foamed poly(lactic acid) that has the highest crystallization ability. Poly(lactic acid) samples had low elongation at break of 3.6–15.1%. After foaming, however, poly(lactic acid) foam presented a significant increase in the elongation at break up to 15.1 times compared with that of the unfoamed counterpart. On the other hand, microcellular foaming endowed poly(lactic acid) foams with a maximum increase in specific tensile strength of 53.1%. The influences of crystallinity, foam density, and cell morphology on the tensile properties of poly(lactic acid) foams were investigated

Lightweight, Multifunctional Polyetherimide/Graphene@Fe3O4 Composite Foams for Shielding of Electromagnetic Pollution

Novel high-performance polyetherimide (PEI)/graphene@Fe3O4 (G@Fe3O4) composite foams with flexible character and low density of about 0.28？0.4 g/cm3 have been developed by using a phase separation method. The obtained PEI/G@Fe3O4 foam with G@Fe3O4 loading of 10 wt % exhibited excellent specific EMI shielding effectiveness (EMI SE) of～41.5 dB/(g/cm3)at8？12 GHz. Moreover, most the applied microwave was verified to be absorbed rather than being reflected back, resulting from the improved impedance matching, electromagnetic wave attenuation, as well as multiple reflections. Meanwhile, the resulting foams also possessed a superparamagnetic behavior and low thermal conductivity of 0.042？0.071 W/(m K). This technique is fast, highly reproducible, and scalable, which may facilitate the commercialization of such composite foams and generalize the use of them as EMI shielding materials in thefields of spacecraft and aircraft

Enhanced interfacial interaction between polycarbonate and thermally reduced graphene induced by melt blending

Melt blending is the most economically choice to disperse graphene into polymer matrix because of its high efficiency, easy to scale up, and no solvent is involved. Therefore, it is meaningful to generate an enhanced interfacial interaction directly through melt blending of graphene and polymers. In this study, the effect of melt blending on the interfacial interaction between thermally reduced graphene oxide (TRG) and polycarbonate (PC) had been investigated. Ultracentrifugation of the melt-mixed PC/TRG composite solutions led to dark-colored supernatants, indicating the improved dispersion of TRG in some solvents, suggesting the existence of enhanced interfacial interaction between TRG and PC. The shift of C=O stretching vibration of PC (interacted with TRG) in the FT-IR spectra as well as the shift of absorption peak of phenyl groups in the UV–vis spectra suggested the formation of chemical bonding between the carbonate groups in PC chains and the carboxyl groups on TRG through transesterification and the formation of noncovalentp–pstacking interaction between PC and TRG during melt blending. Furthermore, the effect of melt blending on mechanical reinforcement of the PC/TRG composites was also evaluated

Chemical functionalization of graphene oxide toward the tailoring of the interface in polymer composites

In this work, we demonstrated that the composites with strong interfacial interactions between graphene–matrix could achieve excellent mechanical properties even the dispersion of graphene is poor. In terms of the above reason, an epoxy resin was coupled onto graphene oxide (GO) sheets via the ‘‘grafting to’’ method. Since each epoxy chain bears two terminated epoxide groups, it is inevitable that one epoxy chain connects two GO sheets together, causing the crosslinking of GO layers via the epoxy chain. When blending these resultant GO (GO–epoxy) with polycarbonate (PC), the dispersion was less-than-ideal due to these crosslinking. However, the residue active sites in the grafted epoxy chains, such as the unreacted epoxide groups as well as hydroxyl groups, could further react with PC carbonate to form chemical bonds,leading to strong interfacial interactions between the matrix and GO sheets. Owing to these strong interfacial interactions, the enhancement of the mechanical properties of PC/GO–epoxy composites was significantly higher than that of PC/(GO/epoxy) samples, as well as those shown in other similar works on thermally reduced graphene oxide (TRG)/PC composites with better dispersio