Possibilities for the Physical Modification of Cellulose Shapes Using Ionic Liquids

Summary: Functional cellulose shapes offer valuable properties for innovative application potentials in textile and medical products. Thereby excellent textile physiological properties of cellulose are allowed to be connected with novel application characteristics like bioactivity, electrical conductivity, heat storage or ability to adsorb liquids or gases. A very advantageous way to modify the properties of fibres, films or textile structures is to introduce particular additives via the Lyocell process. Regard to technical applications, functional additives will be able to incorporate themselves in the shape matrix and, in the case of using N-methylmorpholine-N-oxide monohydrate (NMMO) as solvent, implicate massive technological difficulties and deterioration of properties of the spinning dope. Beside a couple of limiting moments, ionic liquids (ILs) offer as direct solvents an excellent chance for physical modification of cellulose shapes. In contrast to NMMO, they exhibit a significantly higher thermal stability as well as a higher chemical resistance. ILs exhibit most widely a better dissolving capability for a number of different polymers. First results of the development of adsorber materials as well as novel bioactive fibres will be discussed and fibre characteristics will be given.     

Studies on the Stabilization of Modified Lyocell Solutions

Additives with functional properties makes the Lyocell process a versatile tool for the creation of new innovative materials beyond the textile sector. Occupying functional groups or active surfaces the additives emphasize the suitability of Lyocell fibers, but simultaneously enhance the complexity of chemical reactions in cellulose/N-methylmorpholine-N-oxide (NMMO) solutions, respectively. Concerning to the concentration acidic ion exchange resins, activated charcoals, carbon black etc. shift the start of decomposition to lower temperatures, decrease the viscosity, enhance the formation of amines as the main degradation products or cause autocatalytic reactions. New routes in stabilization of modified Lyocell solutions applying a polymeric stabilizer system are described. Using calorimetric, UV/VIS, ESR and HPLC analysis the degradation processes and thermal stability of modified Lyocell solutions compared to the unstabilized were studied. Moreover, as kinetic investigations show a distinguished behavior for modified solutions autocatalytic reactions can be suppressed by the stabilizing system. ESR kinetic study of radicals reveals that formation and recombination rates of radical reactions depend on cellulose concentration in Lyocell solutions and additional ingredients.     

Block sampling under strong dependence

The paper considers the block sampling method for long-range dependent processes. Our theory generalizes earlier ones by Hall et al. (1998) [11] on functionals of Gaussian processes and Nordman and Lahiri (2005) [16] on linear processes. In particular, we allow nonlinear transforms of linear processes. Under suitable conditions on physical dependence measures, we prove the validity of the block sampling method. Its finite-sample performance is illustrated by a simulation study.     

Dithienylethene-Based Single Molecular Photothermal Linear Actuator

By employing a mechanically controllable break junction technique, we have realized an ideal single molecular linear actuator based on dithienylethene (DTE) based molecular architecture, which undergoes reversible photothermal isomerization when subjected to UV irradiation under ambient conditions. As a result, open form (compressed, UV OFF) and closed form (elongated, UV ON) of dithienylethene-based molecular junctions are achieved. Interestingly, the mechanical actuation is achieved without changing the conductance of the molecular junction around the Fermi level over several cycles, which is an essential property required for an ideal single molecular actuator. Our study demonstrates a unique example of achieving a perfect balance between tunneling width and barrier height change upon photothermal isomerization, resulting in no change in conductance but a change in the molecular length, which results in mechanical actuation at the single molecular level.     

Collection and storage of CO2 for 13C analysis: An application to separate soil CO2 efflux into root- and soil-derived components

Soil surface CO2 efflux is comprised of CO2 from (i) root respiration and rhizosphere microbes and (ii) heterotrophic respiration from the breakdown of soil organic matter (SOM). This efflux may be partitioned between these sources using delta13C measurements. To achieve this, continuous flow isotope ratio mass spectrometry can be used and, in conjunction with 10 mL septum-capped vials, large numbers of samples may be analysed using a Finnigan MAT Delta(plus)XP interfaced to a Gas Bench II. Here we describe a number of advances to facilitate such work, including: (i) a technique for monitoring mass spectrometer performance, (ii) improvements to sample storage, and (iii) a gas-handling system for incubating and sampling the CO2 derived from roots and soils. Mass spectrometer performance was monitored using an automated refillable vial. Compressed air analysed with this system had mean delta13C of -9.61 +/- 0.16 per thousand (+/- 1sigma, n = 28) collected over four runs. Heating the butyl rubber septa used to seal the vials at 105 degrees C for 12 h improved the sample storage. After air transportation over 12 days, the isotope composition of the CO2 at ambient concentrations was unchanged (before: -35.2 +/- 0.10 per thousand, n = 4; after: -35.3 +/- 0.10 per thousand, n = 15); without heat treatment of the septa the CO2 became slightly enriched (-35.0 +/- 0.14 per thousand, n = 15). The linearity of the Gas Bench II was found to decline above 8000 micromol CO2 mol(-1). To stay within a linear range and to allow the incubation of soil and root material we describe a gas-handling system based around a peristaltic pump. Finally, we demonstrate these methods by growing a C-4 grass (Guinea grass, Panicum maximum Jacq.) in a C-3 soil. Root respiration was found to contribute between 5 and 22% to the soil surface CO2 efflux. These methodologies will facilitate experiments aimed at measuring the isotopic composition of soil-derived CO2 across a range of ecological applications.     

Literatur

Ohne Zusammenfassung     

Controlled radical polymerization of 4-vinylpyridine

2,2,6,6-Tetramethylpiperidine-N-oxyl (TEMPO)-mediated free radical polymerization of 4-vinylpyridine is found to proceed in a “controlled” manner. A linear increase of molecular weight along with an increase in conversion occurs at varying temperatures. Polymerization of styrene with a poly(4-vinylpyridine) block as macromer results in block copolymers with narrow polydispersity. The polymers are characterized by different size exclusion chromatography methods and converted to cationic polyelectrolytes as well as to polysulfo- and polycarbobetaines.