Research Articles

A study was made of the hygroscopicity of two samples of cork with the same characteristics, taken from trees of the same age but with a 38-year gap between debarking. This was achieved by plotting the 35ºC sorption-desorption isotherms and fitting them using the GAB model. Infrared spectra were used to determine any chemical changes in the cell wall. Extended exposure to controlled relative humidity and temperature did not cause hygroscopic changes to the cork. The equilibrium moisture content values were not significantly different in the two samples, but the monolayer saturation moisture content values were significantly lower in the older cork. This may be due to partial saturation of the moisture sorptive sites in the cell wall over time.

Electrochemical generation of oxidants was studied to find new solutions to control microbial contamination at paper mills. Laboratory and semi-pilot trials using a Wet End Simulator indicated that the combination of an electrochemically produced halogen-containing oxidant together with sodium percarbonate was an efficient new biocide concept, especially in fine papermaking. Addition of sodium percarbonate considerably reduced the need for halogen-containing biocides, thus lessening risk of corrosion. The trials with samples from fine paper machines indicated that the new concept required halogenated biocides to be dosed first, and the time delay between additions of biocide needed to be sufficient to ensure that no residual halogen was left when sodium percarbonate was added. Electrochemical generation enables on-site biocide production, which decreases transportation cost, risk associated with storage of hazardous chemicals, and biocide lost due to degradation. Thus, on-site generation of biocides together with potential reduction in amount of halogen containing oxidants make this dual concept economically attractive and environmentally positive.

In this research, the cell morphology and physico-mechanical properties of HDPE/EVA/Rice hull hybrid foamed composites were investigated. For this aim, composites were prepared via melt mixing and then foamed using a compression molding method. Mechanical properties such as tensile strength, tensile and flexural modulus, and density were measured. Morphology of the samples was also evaluated by scanning electron microscopy (SEM). Results indicated that the tensile strength, tensile and flexural modulus, and density increased with the increase of rice hull content. However, with addition of blowing agent content and EVA content, mechanical properties and density of foamed composites decreased. Rice hull fibers acted as nucleating agents that substantially reduced cell size and increased cell density. In addition, EVA played an important role in foaming process by increasing the melt viscosity of the polymer matrix, in a way that samples with higher content of EVA have the highest cell density and the lowest cell size.

Dynamic mechanical and thermal analysis of oil palm empty fruit bunches (EFB)/jute fiber reinforced epoxy hybrid composites were carried out. The effect of layering pattern on dynamic mechanical properties (storage modulus (E’), loss modulus (E”), and tan δ) was investigated as a function of temperature. The storage modulus (E’) was found to be decreased with temperature in all cases, and hybrid composites had almost the same values of E’ at glass transition temperature (Tg). The tan δ peak height was minimum for jute composites and maximum for epoxy matrix. Layering pattern affected the dynamic mechanical properties of hybrid composites. Cole-Cole analysis was carried out to understand the phase behaviour of the composite samples. Thermogravimetric analysis (TGA) results indicated an increase in thermal stability of pure EFB composite with the incorporation of jute fibers. The overall results showed that hybridization with jute fibers enhanced the dynamic mechanical and thermal properties.

The hydrolysis and condensation (aging) dynamics of aqueous solutions of (3-glycidyloxypropyl)trimethoxysilane (GPS), vinyltrimethoxysilane (VTS), and (3-aminopropyl)trimethoxysilane (APS) and their penetrability into the cell walls of European spruce (Picea abies) wood were studied to investigate the feasibility of using silanes as a cell wall modifying agent for wood and other lignocellulosic materials. The size distribution of silane particles in aqueous solution was determined using a dynamic light scattering apparatus and increased with the aging time, but at different rates depending on the silane monomer. With increasing aging time, the treated wood exhibited decreased cell wall bulking (swelling), and the water vapour sorption behaviour was less affected by treatments when compared with unmodified wood; SEM-EDX analysis revealed that there was a reduced amount of silane in the cell walls with increased aging time. These findings demonstrate the reduced accessibility of silane to cell walls following aging.

Papermaking pulps are a mixture of fibres, fibre fragments, and small cells (parenchyma or ray cells), usually called pulp fines. The interactions between pulp fines and a cationic copolymer of acrylamide and acryloxyethyltrimethyl ammonium chloride were investigated based on solid-liquid isotherms prepared under different turbulence, and subsequent advanced surface characterization using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface charge and surface area of pulp fine substrates were measured by methylene blue sorption-XPS analysis and nitrogen adsorption combined with mercury porosimetry, respectively. The driving force behind polyelectrolyte adsorption was the amount of the surface anionic charge, whereas surface area appeared to be of less importance. Based on a comparison of solid-liquid and XPS sorption isotherms, different polyelectrolyte conformations were suggested, depending on the types of fines: A flatter conformation and partial cell-wall penetration of polyelectrolytes on kraft fines from freshly prepared pulp, and a more free conformation with extended loops and tails on lignocellulosic fines from recycled pulp. Additionally, ToF-SIMS imaging proved that recycled pulp fines contained residual de-inking chemicals (primarily palmitic acid salts) that possibly hinder the electrostatic interactions with polyelectrolytes.

Copper sulfide-containing lignocellulose nanocomposites with improved electroconductivity were obtained. Two methods for preparing the copper sulfide lignocellulose nanocomposites were developed. An optimization of the parameters for obtaining of the nanocomposites with respect to obtaining improved electroconductivity, economy, and lower quantities and concentration of copper and sulfur ions in waste waters was conducted. The mechanisms and schemes of delaying and subsequent connection of copper sulfides in the lignocellulosic matrix were investigated. The modification with a system of 2 components: cupric sulfate pentahydrate (CuSO4. 5H2O) and sodium thiosulfate pentahydrate (Na2S2O3.5H2O) for wood fibers is preferred. Optimal parameters were established for the process: 40 % of the reduction system; hydromodule M=1:6; and ratio of cupric sulfate pentahydrate:sodium thiosulfate pentahydrate = 1:2. The coordinative connection of copper ions with oxygen atoms of cellulose OH groups and aromatic nucleus in lignin macromolecule was observed.

Kinetic modeling of lignin removal under conditions of high-boiling solvent (HBS, i.e. 1,4-butanediol) auto-catalyzed pulping of bagasse has been studied. The experimental data were collected based on the absorption of dissolved lignin in black liquor at a wavelength of 320 nm, which can eliminate the interferences arising from furfural (F) and 5-hydroxymethyl furfural (HMF) generated during pulping. The results indicated that the delignification process consists of two distinct phases. The initial phase, involving a very fast reaction, is followed by a rather slow second phase. The delignification equation was determined as: D=87.71×C0.8982× (1-e-1.757t) ×100%, which is valid within an HBS concentration range of 50% to 80% and can be used for predict the lignin removal from bagasse by HBS pulping.

It has been generally accepted that some ionic liquids are good media for homogeneous functionalization of cellulose. However, phthalylated cellulosic derivatives prepared in ionic liquids without any catalyst have lower DS as compared to the acetylated ones. In order to prepare the phthalylated cellulosic derivatives with higher DS, chemical modification of sugarcane bagasse cellulose with phthalic anhydride using ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl) as a solvent and 4-dimethylaminopyridine (DMAP) as a catalyst has been examined. The results indicated that DMAP could enhance the reaction efficiency. The native cellulose and cellulose phthalates were characterized by FT-IR, solid-state CP/MAS 13C NMR, and thermogravimetric analysis. The results from FT-IR and solid-state CP/MAS 13C NMR analyses indicated that the phthalylation between cellulose and phthalic anhydride was successfully achieved. In addition, it was found that the thermal stability of the cellulose phthalates decreased upon chemical modification.

Dissolved cellulose was contacted with dissolved linear or slightly branched lignophenol polymers in alkaline solution, and films were formed through precipitation. Lignophenol is a polymeric lignin derivative isolated from wood meal, and due to its size and chemical structure, it is expected to a better model for natural lignin compared to the previously exploited small lignin model molecules. Smooth and even of cellulose-lignophenol films were achieved, and the interactions between cellulose and lignophenol were tentatively detected. The formed film structures had the crystalline form of cellulose II, and they did not contain any fibril-like material. Although the amount of hemicelluloses was negligible, it seems that the lignin modelling lignophenol tended to positively interact with cellulose.