Taťana Vacková

Activation of cellulose by 1,4-dioxane for dissolution in N,N-dimethylacetamide/LiCl

N,N-Dimethylacetamide/lithium chloride (DMAc/LiCl) mixture is a popular solvent system used for cellulose dissolution, analysis, and derivatization. However, a pre-treatment (activation) procedure is needed for most celluloses to dissolve readily in DMAc/LiCl. Here, an optimized version of the activation protocol based on solvent exchange to 1,4-dioxane was introduced. Its universality was demonstrated by successful activation and dissolution of six different celluloses (AVICEL, Sigmacell, cotton linters, Encell, Lincell, and Whatman paper). Dissolution times varied significantly for different cellulose types and also depended on factors such as the drying method employed or the water removal step inclusion/omission. Dioxane-activated celluloses were analyzed with a variety of methods. SEC measurements indicated low destructivity of the dioxane activation method. The infrared spectroscopy analysis showed that dioxane remained adsorbed on cellulose even after rigorous drying. In addition, upon dioxane activation, stagnation or a slight increase in the total order index of celluloses was observed. This observation was in accordance with the crystallinity index changes determined by solid-state NMR. Finally, scanning electron microscopy revealed disintegration of AVICEL particles and defibrillation of fibrous celluloses upon dioxane activation; Sigmacell remained apparently unchanged.

Nucleation of Polypropylene Crystallization with Gold Nanoparticles. Part 2: Relation between Particle Morphology and Nucleation Activity

ABSTRACT The influence of gold nanoparticle morphology on nucleation of isotactic polypropylene (PP) crystallization was investigated. Previous experiments indicated certain nucleation activity of gold nanoparticles, varying with their size. In this work, eight types of gold micro/nanoparticles were used: vacuum-sputtered nanostructures (nanoparticles, nanoislands, and nanolayers), chemically prepared isometric gold nanocrystals (5, 20, and 100 nm diameters), and two types of gold microcrystals with well-developed crystal facets [with (100) and (111) facets, respectively]. To minimize the effect of particle agglomeration, we used our recently introduced sandwich method, in which the nucleating agent was deposited between thin PP films and the nucleation was evaluated by polarized light microscopy (PLM), X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The nucleation activity of Au particles in PP was lower than it might be expected from the previous studies and depended on their morphology. The nucleation activity of Au microcrystals with well-developed facets was higher than the activity of non-faceted Au nanocrystals.

Characterisation of morphological, antimicrobial and leaching properties of in situ prepared polyurethane nanofibres doped with silver behenate

Polyurethane nanofibres in situ doped with silver nanoparticles arising from three different silver precursors as well as zero-valent silver nanoparticles were prepared using free-surface electrospinning with no post-treatment. Throughout the experiment, the best results from all combinations tested were achieved for silver behenate doped nanofibres. These had homogenous nanoparticle coverage (some particles 99% as well as inhibition zones of 1.20 ± 0.12 mm for E. coli, 1.45 ± 0.08 mm for Staphylococcus aureus and 0.62 ± 0.12 mm for Pseudomonas aeruginosa at concentrations corresponding to 1 McFarland. Moreover, after 168 h, silver behenate doped nanofibres displayed the lowest silver leaching (5.8% of original silver content) of all samples prepared in this study. These nanofibres, therefore, represent a promising alternative to current silver-doped nanofibres prepared in situ.