Morphology and rheology of cellulose nanofibrils derived from mixtures of pulp fibres and papermaking fines

The rheological behaviour of homogenised fibres originally having different lengths was evaluated. For this purpose, mixtures of pulp fibres and fines were fibrillated mechanically without pre-treatment and characterised with regard to morphology and viscosity. It was found that, for all samples, a similar number of homogenisation passes was needed to reach a viscosity plateau. However, the value of the final viscosity differed significantly: homogenised suspensions derived from fines achieved only about 60 % of the viscosity of suspensions derived from pulp. Already after a few homogenisation cycles, no differences between the samples could be measured using optical devices, indicating that fibrillation on the nanometre scale was responsible for the distinct rheological behaviours. Atomic force microscopy measurements indicated significantly reduced fibril lengths for the suspensions derived from fines, which explains their reduced viscosity.     

Solvent nucleophilicities of hexafluoroisopropanol/water mixtures

First‐order rate constants k₁ for the trapping of various donor‐ and acceptor‐substituted benzhydrylium ions in mixtures of 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) and water ranging from 50 to 99% HFIP (w/w) were determined by laser flash photolytic generation of benzhydrylium ions from benzhydryl triarylphosphonium salts in these solvents. From these rate constants, we derived the solvent‐specific reactivity parameters N₁ and s_N for HFIP/water mixtures as defined by the linear free energy relationship lg k₁(20 °C) = s_N(N₁ + E). Copyright © 2012 John Wiley & Sons, Ltd.     

Ethenesulfonyl Fluoride: The Most Perfect Michael Acceptor Ever Found?

The kinetics of the reactions of ethenesulfonyl fluoride (ESF) with sulfonium and pyridinium ylides were measured photometrically to determine the electrophilicity parameter of ESF according to the correlation lg k_{20 °C}=s_N(N+E). With E=?12.09, ESF is among the strongest Michael acceptors in our comprehensive electrophilicity scale, which explains its excellent performance in reactions with many nucleophiles. Its predicted usability as a reagent in electrophilic aromatic substitutions with electron‐rich arenes was confirmed by uncatalyzed reactions with alkyl‐substituted pyrroles.     

The Nucleophilicity of Persistent α‐Monofluoromethide Anions

α‐Fluorocarbanions are key intermediates in nucleophilic fluoroalkylation reactions. Although frequently discussed, the origin of the fluorine effect on the reactivity of α‐fluorinated CH acids has remained largely unexplored. We have now investigated the kinetics of a series of reactions of α‐substituted carbanions with reference electrophiles to elucidate the effects of α‐F, α‐Cl, and α‐OMe substituents on the nucleophilic reactivities of carbanions.     

Stereoselective Synthesis and Reactions of Secondary Alkyllithium Reagents Functionalized at the 3‐Position

Secondary alkyllithium reagents bearing an OTBS group (TBS=tert‐butyldimethylsilyl) at the 3‐position can be prepared stereoconvergently through an I/Li exchange from a diastereomeric mixture of the corresponding secondary alkyl iodides. These lithium reagents react with a range of electrophiles, including carbon electrophiles, with retention of configuration to yield various 1,3‐difunctionalized derivatives with good diastereoselectivities. Kinetic studies show that the 3‐siloxy group strongly accelerates the epimerization at the lithium‐substituted carbon atom. This method offers a new way to construct chiral open‐chain molecules with excellent stereoselectivity.     

Approximate method for obtaining source quantities for calculation of structure-borne sound transmission into lightweight buildings

An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.