Modified polysaccharide-based particles for strengthening paper

[摘要] ENGLISH ABSTRACT: The ongoing trend in papermaking industries is to lower production costs by increasingthe low cost filler content in the sheets. However, the disruption of inter-fibre bonding isaccompanied by a deterioration of paper stiffness and mechanical properties if filler contentexceeds 18 wt%. Polysaccharide solutions, such as starch, are often used as a low costbiodegradable additive to improve internal sheet strength when added to the wet-end ofproduction. The amount of starch that can be added is however limited as only a small percentagewill be retained in the paper web.A dual additive multifunctional polysaccharide system was developed to allow higherfiller loading levels without detrimental deterioration in paper properties. In order to achieve alarger surface area for fibre/filler interaction and to reduce drainage losses, at least one of theseadditives was in particulate form. Anionic, cationic, and unsaturated derivatives were preparedusing sodium monochloroacetate, 3-chloro-2-hydroxypropyltrimethylammonium chloride, andallyl bromide, respectively. The degree of substitution was determined by 1H-NMR spectroscopyand back titration methods and the interaction of the ionic modified derivatives with papercomponents was determined using fluorescence microscopy.Anionic modified polysaccharide particles were prepared using techniques such asmacrogel ultrasonification, water-in-water emulsification, and in-situ cross-linking andcarboxymethylation of granular starch. A process of adding sequential layers of oppositelycharged polyelectrolyte layers onto the filler particles was also investigated. A novel approach ofpreparing modified particles with tailored size and distribution using microfluidics was studiedand modelled using response surface methodology.Hand sheets were prepared using the dual additive system and improvements in stiffness,tear resistance, breaking length, and folding endurance were observed. The modified granularmaize starch particles had a pre-eminent effect on improving stiffness at higher filler loadings(14% improvement at 30 wt% filler loading), while bulky particles prepared using microfluidicsshowed a more consistent improvement (between 6% and 10%) across the loading range.Overall improvements gained by the introduction of multi-layered soluble polymers ontofillers suggest that the introduction of nanotechnology to the papermaking process should be ofpotential benefit to the industry. Furthermore, the dual additive system developed during thecourse of this study should also be tested on a continuous pilot plant papermaking process.

[发布机构] Stellenbosch University