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Cellulose wet adhesives are applied to enhance the wet strength of paper products by binding individual paper fibers together. However, the recycling of the wet strength paper is a challenge as the fibers are hard to re-disperse in water. This project demonstrates new strategies for developing cellulose wet adhesives with controllable degradability, facilitating the recycling of wet strength papers. In this project, regenerated cellulose membranes were used to simulate paper fibers. In adhesion measurements, two wet cellulose membranes were laminated with a thin layer of adhesive (1–30 mg/m2), and the 90-degree wet-peel was used as a measure of cellulose wet adhesion. It was shown that the wet-peel was a simple and reliable method to evaluate the wet adhesives for paper products. Cellulose wet adhesives, in the form of microgels or linear polymers, were synthesized by incorporation of hydrazide, amine or azetidinium functional groups that can form covalent bonds to cellulose surfaces. Two strategies to design degradable adhesives were demonstrated in this project. 1) Reductant-responsive microgel adhesives were created by introducing cleavable disulfide linkages, either in the polymer chains tethering adhesive groups or as the microgel crosslinks. More than 70% reduction in wet adhesion was achieved after exposure to a reductant. 2) Degradable polymer cohesive bonds were used to “switch off” the cellulose wet adhesion. This adhesive was created by introducing labile boronate-dextran complexes to the PVAm adhesive layer between cellulose surfaces. The introduction of this new interaction between PVAm chains enhanced the cellulose wet adhesion. In response to subtle pH changes or the presence of monosaccharides, the wet adhesion decreased by 60%. / Thesis / Doctor of Philosophy (PhD) / Wet strength is important for paper products such as paper towels and paper packaging. In paper manufacturing, cellulose wet adhesives are applied to enhance the strength of wet papers by “gluing” together individual cellulose fibers. However, the recycling of wet strength papers is a challenge because the current adhesives prevent the easy disintegration of waste paper back to a suspension of discrete cellulose fibers. As an important part of the bio-based economy, the next generation of paper products are required to be both strong in water and easy to recycle. This thesis explores new designs for wet-strength adhesives that will facilitate recycling. Both nanoparticles and linear polymers were synthesized in this study as cellulose wet adhesives. Many important properties of wet adhesives were probed, including the size of nanoparticles, the pre-treatment of cellulose surfaces, the dosage of adhesives and the choice of adhesive chemistries. A few types of novel cellulose wet adhesives with controllable degradability were synthesized and evaluated. I demonstrated that the cellulose wet adhesion can be “switched off” in response to subtle pH changes, reducing agents or sugars, showing a promising start for the recycling of wet strength papers.

In response to the demands of 21st century teacher preparation practices, this developmental study was instigated by the need to employ appropriate strategies in the teaching of English as second language (L2) in Malawi. Using situated cognition theoretical construct as a basis, a framework for teaching L2 English as a situated practice was created. The development process was guided by views and practices of English methodology faculty members in Malawi's five secondary school teacher training institutions. The study was conducted in three phases, (i) analysis, where eight English methodology faculty members from Malawi's five institutions of higher learning were interviewed on the strategies they use to train pre-service secondary school teachers of English, (ii) development, where the framework was created based on results from the analysis phase, and (iii) evaluation and revision where the framework was reviewed and validated by a situated cognition expert and three of the faculty members interviewed in Malawi before it was revised. / Ph. D.