Roberto Aguado

Cationic cellulosic derivatives as flocculants in papermaking

Water-soluble cationic cellulose derivatives were synthesized by three different procedures, cationizing bleached hardwood kraft pulp with (3-chloro-2-hydroxypropyl) trimethylammonium chloride. The first procedure involved a previous depolymerization step with orthophosphoric acid. The second one consisted on dissolving cellulose in NaOH/urea before cationization. For the third procedure, the reaction medium was heterogeneous since it was carried out with a part of cellulose with high degree of polymerization. Oppositely to the common methods, cationization occurred under mild conditions. Differences among the three derivatives are illustrated by X-ray diffraction patterns of pretreated samples, infrared spectra, and determinations of the degree of substitution, the zeta potential, the charge density and the molecular weight. The performance of these polyelectrolytes for the flocculation of mineral fillers used in papermaking was tested by laser diffraction spectrometry. The flocculant with the highest degree of polymerization and charge originated the best results, particularly when the filler used was kaolin, proving that water-soluble cationic cellulose derivatives can aid in the flocculation of fillers used in papermaking. On the contrary, the shortest-chained derivative was not effective. The results were interpreted in terms of the characteristics of the cellulose derivatives flocculants and of the fillers, and neutralization and patching were proposed as the dominant mechanisms.

Cationization of Alpha-Cellulose to Develop New Sustainable Products

Papermaking has been using high quantities of retention agents, mainly cationic substances and organic compounds such as polyamines. The addition of these agents is related to economic and environmental issues, increasing contamination of the effluents. The aim of this work is to develop a cationic polymer for papermaking purposes based on the utilization of alpha-cellulose. The cationization of mercerized alpha-cellulose with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) is governed by a pseudo-second-order reaction. The initial amorphous fraction of cellulose is reacted with CHPTAC until the equilibrium value of nitrogen substitution is reached. Nitrogen is incorporated as a quaternary ammonium group in the polymer. Also, the kinetic constant increased with decreasing crystallinity index, showing the importance of the previous alkalization stage. The use of modified natural polysaccharides is a sustainable alternative to synthetic, nonbiodegradable polyelectrolytes and thus is desirable with a view to developing new products and new processes.

Alkalization and Cationization of Cellulose: Effects on intrinsic viscosity

Researchers have studied the cationization of polysaccharides to replace conventional cationic polyelectrolytes, linked to environmental issues. However, cationic celluloses have not achieved the success of cationic starches. The knowledge of the cellulose cationization proccess needs to be improved. In this work, we pretreat (alkalize) and cationize cotton linters and α-cellulose powder, using 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in an aqueous-alcoholic alkaline solution. The pretreatment took place under different conditions, whereas the cationization itself was always performed at 70 ºC, for a CHPTAC/AGU (anhydro glucose units) mole ratio of 4, and for a total time of 5 h for cotton linters or 100 min for α-cellulose powder. The degree of substitution, the crystallinity index and the temporal evolution of intrinsic viscosity are provided for the 18 experiments performed. The background was uncertain about the effect of cationization on intrinsic viscosity. Here, we report increasing viscosity with increasing degree of substitution and cationization time. Furthermore, intrinsic viscosity increased with increasing cationization time, even when the degree of substitution had leveled off. Seemingly, the incorporation of positive charges into cellulose changed the polymer distribution and the interactions between the polymer and the solvent.

Cationized fibers from pine kraft pulp: advantages of refining before functionalization

Abstract A partial cationization of cellulosic pulps has been suggested to enhance the retention of fillers and fines in the paper and board manufacturing industry. The challenge is the highly crystalline structure of cellulose and the mass transfer limitations of softwood fibers, which are long and resistant to and hinder the chemical reactions. In the present paper, it was demonstrated that refining (leading to decrystallization) and alkaline treatments facilitate the subsequent cationization process with quaternary ammonium groups. Cationization was performed with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) at 120°C for 2 h, and degrees of substitution above 0.3 were achieved. Beating to 4000 or 4500 PFI revolutions was found to be an optimum to achieve these high degrees of substitution. Mixing a small percentage (4%) of cationized pulp (with a charge density of approximately 0.8 meq g−1) with the untreated pulp could compensate for the negative surface charge of the original fibers. In this way, the highest charge density and opacity of the paper and the best retention of fines were achieved. If cationization was implemented in a paper mill, it should follow, not precede, the refining stage.

NIRS Characterization of Paper Pulps to Predict Kappa Number

Rice is one of the most abundant food crops in the world and its straw stands as an important source of fibres both from an economic and an environmental point of view. Pulp characterization is of special relevance in works involving alternative raw materials, since pulp properties are closely linked to the quality of the final product. One of the analytical techniques that can be used in pulp characterization is near-infrared spectroscopy (NIRS). The use of NIRS has economic and technical advantages over conventional techniques. This paper aims to discuss the convenience of using NIRS to predict Kappa number in rice straw pulps produced under different conditions. We found that the resulting Kappa number can be acceptably estimated by NIRS, as the errors obtained with that method are similar to those found for other techniques.