Abstract
The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were fibrillated and compared to sugar beet pulp as a representative non-wood cellulose resource, and conventional microfibrillated cellulose produced from bleached pulp. An alkali pre-treatment of woody and sugar beet raw materials enhanced the degree of fibrillation achieved, same as TEMPO-mediated oxidation of microfibrillated cellulose. Nanopapers produced from fibrillated material showed highly variable density and mechanical performance, demonstrating that properties may be tuned by the choice of raw material. While nanopaper strength was highest for TEMPO-oxidated microfibrillated cellulose, fibrillated untreated sugar beet pulp showed the best adhesive performance. Different microscopic methods (AFM, SEM, light microscopy) examined the interface between wood and fibrillated material, showing particular distinctions to commercial adhesives. It is proposed that fibrillated material suspensions, which achieve bond strength up to 60% of commercial urea-formaldehyde adhesive, may provide a viable solution to bio-based adhesives in certain applications where wet-strength is not an issue.
Highlights
Adhesive bonding is a key processing step in the production of modern engineered materials.Recently, there is a growing interest in bio-based solutions for adhesive bonding as an alternative to well-established high-performance fossil-based adhesives
One approach consists of the synthesis and use of partially or fully bio-based adhesives [1]
Lignin is a widely available resource in this context and intense efforts are being undertaken towards the partial replacement of phenol in the synthesis of phenol-formaldehyde based resins [2]
Summary
Adhesive bonding is a key processing step in the production of modern engineered materials. There is a growing interest in bio-based solutions for adhesive bonding as an alternative to well-established high-performance fossil-based adhesives. One approach consists of the synthesis and use of partially or fully bio-based adhesives [1]. Lignin is a widely available resource in this context and intense efforts are being undertaken towards the partial replacement of phenol in the synthesis of phenol-formaldehyde based resins [2]. The most important hindrance with regard to broad lignin utilization in adhesive synthesis is still its lack of reactivity compared to phenol [1]. Tannins as a bio-based adhesive component extracted from the bark or xylem of trees are polyhydroxyphenols which start auto condensation when hexamine is added.
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