TEOS as an improved alternative for chitosan beads cross‐linking: A comparative adsorption study

In this work the use of tetraethoxysilane (TEOS) for cross‐linking of chitosan hydrogel beads was studied at the level of 1 mmol TEOS per gram of chitosan. They were compared with glutaraldehyde and epichlorohydrin cross‐linked beads. The hydrogels were characterized by FTIR, SEM, water content, nitrogen content, and their point of zero charge. The performance of the anionic dye Remazol Black (RB) and the cationic Cd(II) adsorptions was assessed in order to characterize the sorbate–sorbent interaction. Adsorption experimental data were analyzed using two‐ and three‐parameter isotherm models along with the evaluation of mean adsorption energy and standard free energy. The adsorption was observed to be pH dependent. The uptake rate of RB and Cd(II) showed that the three type of beads followed a similar kinetic behavior. For both sorbates the TEOS cross‐linked beads showed the higher maximum adsorption capacity, followed by epichlorohydrin and glutaraldehyde cross‐linked beads. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41005.     

Miscanthus sinensis fractionation by different reagents

Miscanthus sinensis L. was fractionated by different reagents (ethanol, soda and soda–ethanol) in order to obtain cellulose, hemicelluloses and lignin. Characterization of original M. sinensis fibres (66.6% holocellulose, 36.1% α-cellulose, and 15.5% lignin) was done and compared with other biomass species chemical composition (alternative raw materials, agriculture residues, coniferous and leafy plants). Obtained solid fractions were chemically characterized and compared with solid fractions from other biomass products (palm oil empty fruit bunches (EFB) and rice straw) generated by similar fractionation processes (soda and organosolv). Soda process produced the solid fraction with the highest content in α-cellulose and lowest content in lignin revealing a strong fractionation effect. On the contrary, soda–ethanol process was found to present low fractionation capability. Obtained cellulose samples were characterized by FTIR to complete the chemical structure analysis. Lignin samples isolated from the liquid fractions were submitted to FTIR, ¹H NMR, GPC, DSC and TGA in order to suggest suitable applications for the products based on their properties.     

Novel Antibacterial and Bioactive Silicate Glass Nanoparticles for Biomedical Applications

In this work, the authors propose a new quick sol–gel procedure for bioglass nanoparticles production containing 10% mol of silver (AgBGs). These new AgBGs are characterized by Zeta potential analysis, scanning electron microscopy with X‐ray microanalysis (SEM/EDS), X‐ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and microbiological tests to confirm their bioactive and antibacterial properties. SEM shows that the average particle size is less than 200 nm and EDS confirms the successful incorporation of Ag₂O in the bioglass matrix. XRD confirms the amorphous nature of the AgBGs and, after SBF immersion, reveals their bioactive behavior with the presence of crystalline phase of calcium silicate and phosphorus oxide, which are also detected by FTIR analysis. FTIR also confirms the formation of typical siloxane bonds resulting from the condensation of silicate glass. Lastly, it is found that the developed AgBGs has an antibacterial effect against two different types of bacteria, thus demonstrating their ability to reduce the bacterial infection within 16 h.

     

Calibrated quantitative thermogravimetric analysis for the determination of portlandite and calcite content in hydrated cementitious systems

Portlandite and calcite are compounds of interest regarding different processes related to microstructural and durability issues of cementitious materials, such as carbonation, pozzolanic action, and hydration degree. The quantification of their contents in cementitious systems is thus frequently required. Thermogravimetry (TG) measures the change in mass of a material (as a function of time) over a temperature range using a predetermined heating rate. The TG method can be applied with certain success to estimate portlandite and calcite contents in the hydrated cement system, considering the temperature range at which each compound decomposes and releases water or carbon dioxide, respectively. However, a mature hydrated cement paste contains hydrated calcium silicate, portlandite and calcite phases. The quantification procedure is therefore complicated because of the concurrent interference among them. The tangential method over the TG signal or the integral method over the derivative TG curve is usually used to discount water loss from hydrated calcium silicates over the temperature range at which portlandite and calcite decompose. However, by the use of TG consistent underestimation of portlandite content in hydrated cementitious systems is still described in the literature. Potential causes for this underestimation are analysed in this paper, and a calibration procedure by means of an internal standard is proposed. Cement paste and aggregate samples are analysed. Differences between TG quantifications of these pure samples and those diluted with low contents of internal standards are compared with the added amounts of internal standard. In that way, a calibration method of the device is applied for correction of the actual portlandite and calcite contents in the samples. For this purpose, both analytic quality calcite and freshly prepared portlandite were used as internal standards. The results show that improved quantifications can be achieved with this calibration. Also, calcite seems to be more suitable as internal standard than portlandite as the best outcome was obtained for the first case.     

Hemicelluloses obtaining from rapeseed cake residue generated in the biodiesel production process

The processing of rapeseed oil seeds for biodiesel production generates huge amounts of lignocellulosic cake residue mainly composed by cellulose, hemicelluloses and lignin. In this work, the valorisation of these components, especifically the majoritary fraction, hemicelluloses, was studied. Hemicelluloses were extracted, purified and characterized by different techniques (FTIR, ¹H NMR, ¹³C NMR, and GPC). Autohydrolysis and acid hydrolysis processes were applied to obtain sugar monomers and oligomers. Glucose and xylose were the main simple sugars in the obtained hydrolysates, representing 22.7% and 40.2% of total sugars content in the autohydrolysis hydrolysates and 27.7% and 36.6% in the acid hydrolysates respectively. Arabinose, galactose and mannose were present in relatively minor quantities.     

Lignins as macromonomers for polyurethane synthesis: A comparative study on hydroxyl group determination

The hydroxyl group contents of four technical lignins [Indulin AT (Meadwestvaco), Alcell (Repap), Curan 27‐11P (Borregaard LignoTech), and Sarkanda (Granit SA)] were investigated in view of their valorization as polyols in polyurethane synthesis. The different hydroxyl group contents were determined by the following methods: titration and ¹H‐NMR, ¹³C‐NMR, and ³¹P‐NMR spectroscopy. The titration method chosen was on the basis of a standard method commonly used to characterize commercial polyols for polyurethanes synthesis. The values of the total and phenolic hydroxyl contents determined by the different techniques were found to be in good agreement. For the total hydroxyl contents, coefficients of variation of 5.6% (Alcell), 3.2% (Indulin AT), 2.3% (Sarkanda), and 6.2% (Curan 27‐11P) were established. For the phenolic hydroxyl contents, a good correlation was observed between data obtained from ³¹P‐NMR and ¹³C‐NMR for all lignin samples, except for the Sarkanda lignin, for which a relatively high coefficient of variation (12.6%) was found. For softwood lignins (Indulin AT and Curan 27‐11P), the phenolic hydroxyl content determined by ¹H‐NMR was always lower than that deduced from ³¹P‐NMR and ¹³C‐NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008