In this work, the blend films of poly(lactic acid) (PLA) and poly(ε-caprolactone) (PCL) were prepared by the solvent casting method. The influence of PCL content and compatibilizer on the structure, tensile and barrier properties was studied. The results indicated that PCL showed good dispersion in PLA matrix as tributyl citrate (TBC) was added as a compatibilizer. PCL showed a promotion effect on the crystallinity of PLA/PCL films. The compatibility of PLA and PCL was improved by TBC. The tensile modulus and the elongation at break of PLA/PCL films increased to various extents due to the input of PCL and TBC compared to pure PLA film. The improvement of oxygen and water vapor barrier properties of the blend films were provided and depended on the content of PCL and the appearance of TBC. The transparency of the blend films decreased with the increase of the PCL content.
The interlocked ⟨rod | ring⟩ structures of pseudorotaxanes and rotaxanes are usually maintained by the complex hydrogen-bonding (H-bonding) network between the rod and ring. Ab initio molecular dynamics (AIMD) using generalized energy-based fragmentation approach and polarizable force field (polar FF)-based molecular dynamics (MD) simulations were performed to investigate the conformational changes of mechanically interlocked systems and to obtain the ensemble-averaged NMR chemical shifts. Factor analysis (FA) demonstrates that the ring H-donor (2,6 pyridinedicarboxamide group) plays an important role in the ring-rod recognition. In comparison to the conventional fixed-charge force field, the polarization effect is crucial to account for the H-bonding interactions in supramolecular systems. In the hybrid scheme, the polar FF-based MD simulations are used to generate different initial states for the AIMD simulations, which are able to give better prediction of ensemble-averaged NMR signals for chemically equivalent amide protons. The magnitude of the deshielding shift of NMR signal is correlated with the length of hydrogen bond. The polar FF model with variable charges shows that the dipole-dipole interactions between the flexible diethylene glycol chain of ring and polar solvents induce the upfield shifts of NMR signals of rod H-donors and the directional distribution of the neighboring CH3CN solvents.
Aramid pulp (AP) is a highly fibrillated form of fiber， with excellent heat resistance, wear resistance, size stability, and other beneficial properties, that can be dispersed in rubber or resin matrix systems. Its fibrillation results in a large surface area. However, AP easily tangles and aggregates between fibers because of its large surface area. Consequently, it experiences difficulty in dispersing in matrices, especially when a relatively large amount of pulp is needed to be mixed. In this study, a SiO2 nanoparticle was synthesized on the surface of AP through the hydrolysis of tetraethyl orthosilicate to improve the dispersion of AP in an epoxy matrix. Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and scanning electron microscopy showed that SiO2 nanoparticles coated on the pulp could improve the thermal and mechanical properties. The optimum treatment concentration was 0.15 mol/L. Dynamic mechanical analysis tests indicated when AP modified by SiO2, the E' is higher due to the uniformly diffusion and enhanced interfacial adhesion for load transfer from the epoxy to AP. But Tg is lower as the flexibility chain SiOSi in epoxy. In comparison with the properties of the unmodified AP, the tensile strength and modulus of modified pulp/epoxy composites increased by 53.5% and 160.4%, respectively. Therefore, the dispersion and interface combination of AP modified by SiO2 in the epoxy improved because of the interaction of AP with SiO2 through the hydrogen bonding and crosslinking of SiO2 with epoxy.
The loss and fragmentation of natural space has placed tremendous pressure on green infrastructure (GI), especially in urban agglomeration areas. It is of great importance to identify key sites of GI, which are used to economically and efficiently restore urban ecological network. However, in the existing research, few scholars have explored the identification and application of GI key sites. Taking the Southern Jiangsu Urban Agglomeration as an example, based on the ecosystem service assessment and landscape connectivity analysis, we identified the multi-class key sites of GI in the study area by MSPA, InVEST model, MCR model, and Linkage mapper. The results showed that: (1) a total of 60 GI sources and 130 GI corridors were extracted. The ecological resources of the study area were densely distributed in the north and south and sparsely in the middle. (2) Three-hundred eighty GI key sites were identified, including 53 water ecological points, 251 ecological fracture points, and 76 ecological pinch points. The GI key sites we identified were large in number and widely distributed, yet were hardly included in the existing ecological protection policies. These key sites should be prioritized in GI planning and differentiated for management strategies, ensuring that limited land resources and public funds can be directed to where restoration is really needed. The present study provides land managers and urban planners with additional tools to better understand how to effectively restore and develop the ecosystems of urban agglomerations in the context of scarce land resources.
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