: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Nitrogen-doped species (NDs) are theoretically accepted as a determinant of the catalytic activity of metal-free N-doped carbon (NC) catalysts for oxygen reduction reaction (ORR). However, direct relationships between ND type and ORR activity have been difficult to extract because the complexity of carbon matrix impairs efforts to expose specific NDs. Herein, we demonstrate the fabrication of a 3D hierarchically porous NC catalyst with micro-, meso-, and macroporosity in one structure, in which sufficient exposure and availability of inner-pore catalytic sites can be achieved due to its super-high surface area (2191 cm(2) g(-1)) and interconnected pore system. More importantly, in-situ formation of graphitic-N species (GNs) on the surface of NC stimulated by KOH activation enables us to experimentally reveal the catalytic nature of GNs for ORR, which is of great significance for the design and development of advanced metal-free NC electrocatalysts.

High-Rate Oxygen Electroreduction over Graphitic-N Species Exposed on 3D Hierarchically Porous Nitrogen-Doped Carbons

The rapid rise in the applications of carbon fibre reinforced polymer matrix composites (CFRPs) is creating a waste recycling challenge. The use of high-performance thermoset polymers as the matrix makes the recovery of the fibres and the resins extremely difficult. Implementation of a circular economy that can eliminate waste and re-use resources warrants the use of efficient processes to recycle end-of-life CFRP components and manufacturing wastes. To this end, herein we present a critical review of the current technologies for recovering carbon fibres and/or the polymers and re-manufacturing CFRPs. New research opportunities in developing new biodegradable thermosets and thermoplastic matrices are also outlined together with more radical recycling strategies for the future.

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Current status of carbon fibre and carbon fibre composites recycling

Metal matrix composites consist of a metal or an alloy as the continuous matrix and a reinforcement that can be particle, short fiber or whisker, or continuous fiber. In this chapter, we first describe important techniques to process metal matrix composites, then we describe the interface region and its characteristics, properties of different metal matrix composites, and finally, we summarize different applications of metal matrix composites.

Metal Matrix Composites

The thermal stability and pyrolysis mechanism of boron-containing phenolic resins: The effect of phenyl borates on the char formation

High char yield of aryl boron-containing phenolic resins: The effect of phenylboronic acid on the thermal stability and carbonization of phenolic resins

Boron-containing polymers have many applications resulting from their prominent properties. Organoboron species with reversible B–O bonds have been successfully employed for the fabrication of vari...

Boronic Ester Based Vitrimers with Enhanced Stability via Internal Boron–Nitrogen Coordination

The cross-linked structures of traditional thermosetting resins not only endow carbon fibre-reinforced polymer (CFRP) composites with excellent performance, but also make their efficient recovery a real challenge. The goal of this paper is to create reversible thermosets using dynamic boronic ester bonds as cross-links in replacement of traditional irreversible covalent bonds. Specifically, we used phenylboronic acid (PBA) to crosslink traditional novolac resin (NR), namely PBNR. By combining the reprocessability of thermoplastics with the desirable chemical and thermal stability of conventional thermosets, controlled degradation and full recycling of cross-linked resins and CFRP composites under ambient conditions were realized through a gentle alcoholysis process. The PBNR/CFRP composites fabricated by hot-pressing showed excellent mechanical properties. The multiple recycling experiments revealed near-total recovery of the clean fibre cloth and binder materials, which could be reprocessed into composites with similar mechanical properties to fresh materials. Dynamic boronate bonds have been demonstrated to open up a new pathway for full recycling of thermosetting resins and CFRP composites, which has a great impact in aeronautical, astronautics, adhesive, coating, or electronic packaging fields.

Room-temperature fully recyclable carbon fibre reinforced phenolic composites through dynamic covalent boronic ester bonds

Using TEM, Auger spectroscopy, EDX, and convergent beam electron diffraction, a thorough characterization of the interphase region between SCS6 fibers and Ti–6Al–4V matrix in a metal matrix composite has been performed. The interphase region is shown to be very complex, consisting of numerous layers of varying compositions and thicknesses. The chemical interaction of the fiber and matrix results in a 0.5–1.5 μm thick TiC layer. Evidence for the existence of a Tix Siy (C) layer is also presented. The SCS6 overlayer on the fibers has inhibited any chemical interaction between the matrix and the SiC filament itself, 60% of the interphase region originating from the SCS6 protective coating. In situ fracture experiments (in an Auger spectrometer) reveal that fracture takes place between the TiC and an amorphous carbon layer.

Shujuan Wang

Papers

The thermal stability and pyrolysis mechanism of boron-containing phenolic resins: The effect of phenyl borates on the char formation

High char yield of aryl boron-containing phenolic resins: The effect of phenylboronic acid on the thermal stability and carbonization of phenolic resins

Boronic Ester Based Vitrimers with Enhanced Stability via Internal Boron–Nitrogen Coordination

Room-temperature fully recyclable carbon fibre reinforced phenolic composites through dynamic covalent boronic ester bonds

The characterization of an SCS6/Ti–6Al–4V MMC interphase