Cellulose interaction with cationic polyelectrolyte : engineering paper strength, structure and surface

Paper engineering of strength, structure and surface using interactions between cellulose and cationic polyelectrolytes are investigated with the aim of improving paper-based bio-analytical devices (PADs). Advances are described based on fundamental knowledge and engineering aspects in this field that have enable the development of lighter weight papers that have high wet strengths, controlled porosities and multi-functional properties that can be fine tuned. The influence of reactive cationic polyelectrolyte, polyamideamine-epichlorohydrin (PAE) on paper strength behaviour was studied using hardwood fibers, both with and without inorganic electrolyte. Ion type and concentration in the papermaking process water was found to influence the strength development in different ways. The relationship between repulpability of PAE- strengthened paper and wet strength is described. The effect of blending microfibrillated cellulose (MFC) with hardwood fibers is compared with the refining of hardwood fibers on paper composite properties, with and without PAE addition. Papers incorporating tethered MFC, produced by refining of hardwood fibres, are found to provide equivalent strength properties to papers incorporating untethered MFC with significant drainage benefits and formation uniformity. Air permeability of the composites decreases with untethered and tethered MFC addition. MFC achieved by ball milling and cellulose micro-particles (CMPs) developed by cryogenic milling softwood fiber are compared with commercial MFC produced by homogenization. The effect of blending two MFCs and CMPs with hardwood fibers on the paper composites properties is investigated in terms of nano/micro cellulose dimensions. CMPs act as mechanical debonding agents and decrease substrate density and strength whereas MFC have higher aspect ratios and smaller size distributions that significantly improve strength and density of composite sheets while decreasing porosities. The addition of MFC combined with PAE can increase both dry and wet strength. The different stress-strain curves under wet conditions are described and these suggest two different mechanisms of strength development: MFC-fiber entanglement and fiber-fiber contact reinforcement. The role of paper macroscale properties and structure are described in PADs used to type human red blood cells (RBCs). A series of commercial and laboratory-generated papers varying in fibre composition, basis weight, density and porosity are studied and their abilities to separate antibody agglutinated (specific) from non-agglutinated (non-specific) RBCs are reported. Image analysis is used to measure the intensities of blood spots produced by sequentially absorbing solutions of antibodies and blood samples on paper then eluting with a saline solution. The performance of these papers in blood typing is found to decrease linearly with paper density and thickness and it is inversely proportional to paper pore size. The type of fibres plays a minor role. Porous cellulose webs modified with cationic polyelectrolyte further optimize blood typing analysis. Cellulose model surfaces, in the form of quasi molecularly smooth thin cellulose films, are investigated to examine the interactions between cellulose, cationic polyelectrolytes and biomolecules. Thin smooth cellulose films are prepared by spin coating either a nanocellulose crystal suspension, or a cellulose acetate solution onto silicon surfaces with subsequent hydrolysis. Film smoothness is greatly improved by controlling the concentration of cellulose acetate and the hydrolysis time in methanolic sodium methoxide. High molecular weight polyacrylamides (CPAM) are used as model polyelectrolytes, and the nanoscale conformation of adsorbed CPAM at the cellulose/water interface is characterized in situ by specular neutron reflectometry. The effect of CPAM charge density and added NaCl (10-3 M) is described. At constant molecular weight, the thickness of the CPAM layer adsorbed on cellulose increases with polymer charge density. Addition of NaCl decreases the thickness of a CPAM layer already adsorbed on cellulose. However the thickness of the adsorption layer on cellulose of a CPAM solution pre-equilibrated in NaCl is much higher, because the re-shrunk polymer coils do not relax as much upon adsorption. Deuterated cellulose film having better contrast for neutron reflectometry is investigated. Incorporation of deuterium into bacterial cellulose is achieved by growing Gluconacetobacter xylinus - strain ATCC 53524 in a mixture of deuterated glucose and deuterated glycerol. Two strategies are compared for synthesizing deuterated cellulose derivatives that are soluble in volatile solvents (acetone and toluene) suitable for spin coating: one involves acetylation in acetic anhydride, the other trimethylsilylation in ionic liquid (1-butyl-3-methylimidazolium chloride). The trimethylsilylation of deuterated cellulose results in a much higher yield of product, and is used to prepare toluene solutions for spin-coating onto smooth flat silicon substrates. The resulting thin film is hydrolysed back to deuterated cellulose using hydrogen chloride vapour. The data generated is used to prepare improved substrate papers for use in PADs with high wet strength, controlled structure and fine-tuned surface properties