Mechanical and Structural Characterization of Pineapple Leaf Fiber

Evidence-based research had shown that elevated alkali treatment of pineapple leaf fiber (PALF) compromised the mechanical properties of the fiber. In this work, PALF was subjected to differential alkali concentrations: 1, 3, 6, and 9% wt/wt to study the influence on the mechanical and crystal properties of the fiber. The crystalline and mechanical properties of untreated and alkali-treated PALF samples were investigated by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and tensile testing analysis. The XRD results indicated that crystal properties of the fibers were modified with 6% wt/wt alkali-treated PALF recording the highest crystallinity and crystallite size of 76% and 24 nm, respectively. The FTIR spectra suggested that all alkali-treated PALF samples underwent lignin and hemicellulose removal to varying degrees. An increase in the crystalline properties improved the mechanical properties of the PALF treated with alkali at 6% wt/wt, which has the highest tensile strength (1620 MPa). Although the elevated alkali treatment resulted in decreased mechanical properties of PALF, crystallinity generally increased. The findings revealed that the mechanical properties of PALF not only improve with increasing crystallinity and crystallite size, but are also dependent on the intermediate bond between adjacent cellulose chains.

Compression of Spin-Adapted Multi-Configurational Wave Functions in Exchange-Coupled Polynuclear Spin Systems

We present a protocol based on unitary transformations of molecular orbitals to reduce the number of non-vanishing coefficients of spin-adapted configuration interaction expansions. Methods that exploit the sparsity of the Hamiltonian matrix and compactness of its eigensolutions, such as the FCIQMC algorithm in its spin-adapted implementation, are well suited to this protocol. The wave function compression resulting from this approach is particularly attractive for anti-ferromagnetically coupled polynuclear spin systems, such as transition metal cubanes in bio-catalysis and, Mott and charge-transfer insulators in solid state physics. Active space configuration interaction calculations on the stretched N2 and square N4 compounds, the chromium dimer, and a [Fe2S2] model system are presented as a proof-of-concept. For the Cr2 case large and intermediate bond distances are discussed, showing that the approach is effective in cases where static and dynamic correlation are equally important. The [Fe2S2] case shows the general applicability of the method.

Compression of Spin-Adapted Multi-Configurational Wave Functions in Exchange-Coupled Polynuclear Spin Systems

We present a protocol based on unitary transformations of molecular orbitals to reduce the number of non-vanishing coefficients of spin-adapted configuration interaction expansions. Methods that exploit the sparsity of the Hamiltonian matrix and compactness of its eigensolutions, such as the FCIQMC algorithm in its spin-adapted implementation, are well suited to this protocol. The wave function compression resulting from this approach is particularly attractive for anti-ferromagnetically coupled polynuclear spin systems, such as transition metal cubanes in bio-catalysis and, Mott and charge-transfer insulators in solid state physics. Active space configuration interaction calculations on the stretched N2 and square N4 compounds, the chromium dimer, and a [Fe2S2] model system are presented as a proof-of-concept. For the Cr2 case large and intermediate bond distances are discussed, showing that the approach is effective in cases where static and dynamic correlation are equally important. The [Fe2S2] case shows the general applicability of the method.

Through-Space Transmission of 19F-13C Coupling Via an Intermediate Bond. An Experimental and Theoretical Study

In order to obtain a deeper insight into the title effect, several compounds with an F atom very close to a C-H of a nearby functional group were synthesized and the relevant couplings measured. The most conspicuous case was that of 8-fluoro-2-hydroxynaphthalene-1-carbaldehyde where a close proximity between the F and H atoms is the result of fluorine-oxygen repulsion and the formation of an intramolecular hydrogen bond between the hydroxyl and carbonyl groups. The experimental four-bond J(F,CHO) coupling is 26.2 Hz. A compound very similar to this one, but without the OH group, was chosen on which to perform a polarization propagator analysis of the through-space (TS) coupling pathways, at the RPA-INDO level. The expression for the TS coupling in terms of the projected polarization propagator and perturbators was numerically analysed. It is found that this coupling is completely dominated by a TS component of the Fermi contact (FC) term, the main features of which are: ( i ) It decays exponentially with the F-H distance; (ii) Its main contribution comes from an electron excitation involving the F lone-pair, the C-H bond of the CHO moiety and its corresponding antibonding orbital;(iii) The π-type lone-pair does not contribute to the TS coupling pathway of the FC term.

The Reactivity-Hydrolysis Relationship in Chemical Finishing of Cotton

The reactivity-hydrolysis relationship in chemical finishing of cotton with N-methyloltype reactants under acidic conditions has been discussed. Theoretical and practical justifications for the relationship have been presented to demonstrate that the ease of formation of links is related directly to the ease of hydrolysis of links, and relative rates in both directions are predictable, based on steric and electronic effects on the resonance-stabilized intermediate. Bond cleavage during hydrolysis has been shown to occur first at the carbon-oxygen bond of the methylol groups, whether or not the link was formed from a substituted urea-formaldehyde adduct or a substituted urea-glyoxal adduct. Limitations for the relationship are also discussed.