Preparation and characterization of cationic nanofibrillated cellulose from etherification and high-shear disintegration processes

Oat straw cellulose pulp was cationized in an etherification reaction with chlorocholine chloride. The cationized cellulose pulp was then mechanically disintegrated in two process steps to obtain trimethylammonium-modified nanofibrillated cellulose (TMA-NFC). The materials thus obtained were analyzed by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and other techniques. A higher nitrogen content of TMA-NFC samples was found by XPS analysis than by elemental analysis, which indicates that the modification occurred mainly on the surface of cellulose fibrils. XPS also confirmed the existence of ammonium groups in the samples. SEM provided images of very fine network structures of TMA-NFC, which affirmed the positive effect of ionic charge on mechanical disintegration process. According to XRD and SEM results, no severe degradation of the cellulose occurred, even at high reaction temperatures. Because of the different properties of the cationic NFC compared to negatively charged native cellulose fibers, TMA-NFC may find broad applications in technical areas, for instance in combination with anionic species, such as fillers or dyes. Indeed, TMA-NFC seems to improve the distribution of clay fillers in NFC matri

High refractive index films of polymer nanocomposites

Solutions of PbS particles and gelatin were used for the preparation of nanocomposites by a spin-coating process. This allows for the preparation of nanocomposite films with controlled thickness, e.g., between 40 nm and 2 μm for a film containing 45 wt.% PbS. Surface roughness and film thickness were investigated by surface profilometry and scanning electron microscopy (SEM). The refractive index at 632.8 nm can be expressed by a linear function of the volume fraction of PbS in the range of 0 to 55 vol. % PbS. In this range, the refractive index increases from 1.5 to 2.5 with increasing PbS ratio and belongs, therefore, to the highest refractive indices known for polymeric composite material

A simple method for the determination of refractive indices of (rough) transparent solids

Simple methods for the determination of refractive indices of transparent polymers and inorganic and organic solids of irregular geometry or with scratched or corrugated surfaces are rare. A classical procedure is based on the invisibility of a body immersed in a liquid with the same refractive index as that of the body. In order to avoid the laborious procedure connected with the search for a liquid with matching refractive index and to find an approach which is independent of the observation by eye, we describe here a modified immersion method which allows the ready determination of the refractive index of solids. The present method is based on the interpolation of the maximum transmission (nTmax) of a solid immersed in liquids with different, typically non-matching, refractive indices. Illustrations with quartz glass, crown glass and poly(vinylidene fluoride) (PVDF) films showed that nTmax can be determined with a reproducibility of ± 0.003. By comparison with refractive indices determined by ellipsometry, it was concluded that the refractive index of a solid can be determined with the modified immersion method within an accuracy better than ± 0.01 when systematic errors resulting from the fit method are also taken into consideratio

Processing and characterization of nanofibrillated cellulose/layered silicate systems

Recently, nanofibrillated cellulose with cationic functional groups was synthesized. This trimethylammonium-modified nanofibrillated cellulose (TMA-NFC) was applied in this study for the preparation of composites with various layered silicates. These belonged to the groups of montmorillonite, kaolin, talc, vermiculite, and mica. The respective composites were prepared by high-shear homogenization followed by filtration and hot-pressing. Data on crystal structures, chemical compositions, cation exchange capacity, specific surface area, density, and morphology of all clays and micas themselves as well as structure information of the corresponding composites have been collected. Possible microstructural features responsible for the composite appearances were tentatively identified. Principally, the interactions between TMA-NFC and the layered silicates were pronounced, due to electrostatic attraction of cationic cellulose fibrils and anionic silicate layers. This mutual interaction between TMA-NFC and layered silicate, however, was influenced not only by layered silicate properties but also by the composite preparation method, as discussed in this stud

Preliminary study of the mechanical and hygrothermal performance of concrete reinforced with fibrillated cellulose

Cement, being the most widely used building material, is the responsible for a large share of greenhouse gas emissions. To reduce the environmental impact of its production, natural fibres can be used as eco-friendly additives. Moreover, their potential use in traditional lime-based mortars makes them an ideal choice for green buildings as well as for the retrofit of historical buildings. An innovative cementitious composite reinforced with fibrillated cellulose (hereafter called «green concrete») was tested to assess its mechanical and physical properties. Samples were casted using Portland cement and natural hydraulic lime and varying the ratios among the constituents. Viscosity and setting time of the fresh pastes were determined with a viscosimeter and a Vicat apparatus, while their hydration was studied by thermal analysis. The influence of the fibres on the flexural strength of the final composite was determined through mechanical tests. The expected hygrothermal performance of the «green concrete» was explored through dynamic hygrothermal simulation to investigate its potential use as a retrofit material. A sensitivity analysis (SA), based on the hygrothermal properties of natural-based building materials similar to the «green concrete», was conducted to identify the parameters influencing more the simulation of annual internal temperature and moisture variations. The preliminary assessment of the mechanical properties of the «green concrete» showed that at higher percentages the cellulose fibres can negatively affect the workability/setting time of the fresh pastes and the flexural strength. The most promising samples were identified and will undergo further investigation. The SA results outlined that the «green concrete» might not be effective for thermal insulation, although it might be used as a moisture-buffering layer by adjusting the values of the free water saturation moisture content, the equilibrium moisture content at RH=80% and the dry vapour diffusion resistance factor of the final composite

High Refractive Index Materials of Iron Sulfides and Poly(ethylene oxide)

High refractive index composites of iron sulfides and poly(ethylene oxide) (PEO) have been prepared by co-precipitation from aqueous solution. Several reaction parameters were varied: inorganic reactants, reactant ratios, reaction temperatures, and reaction times. Selected samples were characterized with organic microelemental analysis, x-ray fluorescence spectroscopy, x-ray diffraction, DSC, and TEM. The nanocomposites with the highest refractive indices have been prepared using PEO, Mohr's salt, and H2S or NaHS. The analyses indicate that the iron sulfides in these materials consist of finely dispersed mackinawite and greigite ("amorphous” FeS) and, partially, also pyrite. The refractive indexes of the resulting composites are clearly above 2 at 632.8 and 1295 nm and can assume values between 2.5 and 2.

Poly(phenylene methylene)-based coatings for corrosion protection : replacement of additives by use of copolymers

Poly(phenylene methylene) (PPM) is a thermally stable, hydrophobic, fluorescent hydrocarbon polymer. Recently, blended PPM has been proposed as a valuable anti-corrosion coating material, and, in particular, rheological additives such as external plasticizers resulted crucial to prevent crack formation. Accordingly, to avoid common problems related to the use of external plasticizers, the development of PPM-related copolymer-based coatings containing n-octyloxy side chains and their anti-corrosion behavior were explored in this study. The aluminum alloy AA2024, widely employed for corrosion studies, was selected as a substrate, covered with a thin layer of a polybenzylsiloxane in order to improve adhesion between the underlying hydrophilic substrate and the top hydrophobic coating. Gratifyingly, coatings with those copolymers were free of bubbles and cracks. The n-octyloxy side-chains may be regarded to adopt the role of a bound plasticizer, as the glass transition temperature of the copolymers decreases with increasing content of alkoxy side-chains. Electrochemical corrosion tests on PPM-substituted coatings exhibited good corrosion protection of the metal surface towards a naturally aerated near-neutrally 3.5% wt.% NaCl neutral solution, providing comparable results to blended PPM formulations, previously reported. Hence, the application of rheological additives can be avoided by use of proper design copolymers

Coordinatively Saturated Tris(oxazolinyl)borato Zinc Hydride-Catalyzed Cross Dehydrocoupling of Silanes and Alcohols

The four-coordinate zinc compound ToMZnH (1, ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) catalyzes selective alcoholysis of substituted hydrosilanes. The catalytic reaction of PhMeSiH2 and aliphatic alcohols favors the monodehydrocoupled product PhMeHSi–OR. With the aryl alcohol 3,5-C6H3Me2OH, the selectivity for mono(aryloxy)hydrosilane PhMeHSiOC6H3Me2 and bis(aryloxy)silane PhMeSi(OC6H3Me2)2 is controlled by relative reagent concentrations. Reactions of secondary organosilanes and diols provide cyclic bis(oxo)silacycloalkanes in high yield. The empirical rate law for the ToMZnH-catalyzed reaction of 3,5-dimethylphenol and PhMeSiH2 is −d[PhMeSiH2]/dt = k′obs[ToMZnH]1[3,5-C6H3Me2OH]0[PhMeSiH2]1 (determined at 96 °C) which indicates that Si–O bond formation is turnover-limiting in the presence of excess phenol

Shaping gold nanocomposites with tunable optical properties

We report the synthesis of morphological uniform composites using miniemulsions of poly(tert-butyl acrylate) or poly(styrene) containing organically capped gold nanocrystals (NCs). The optical features of such hybrid structures are dominated by plasmonic effects and depend critically on the morphology of the resulting nanocomposite. In particular, we demonstrate the ability to tune the overall optical response in the visible spectral region by varying the Au NCs arrangement within the polymer matrix, and therefore the interparticle plasmon coupling, using Au NCs resulting from the same batch of synthesis. This is a consequence of two well-known effects on the optical properties of Au particles: the variation of the surrounding dielectric refractive index and interparticle plasmonic coupling. The research reported here shows a general strategy to produce optical responsive nanocomposites via control of the morphology of submicrometric polymer particles containing metal nanocrystals and thus is an alternative to the more common strategy of size tuning metal nanoparticles used as nanofillers