Cellulose nanofibrils as filler for adhesives: effect on specific fracture energy of solid wood-adhesive bonds

Abstract

Cellulose nanofibrils were prepared by mechanical fibrillation of never-dried beech pulp and bacterial cellulose. To facilitate the separation of individual fibrils, one part of the wood pulp was surface-carboxylated by a catalytic oxidation using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as a catalyst. After fibrillation by a high pressure homogenizer, the obtained aqueous fibril dispersions were directly mixed with different urea–formaldehyde-(UF)-adhesives. To investigate the effect of added cellulose filler on the fracture mechanical properties of wood adhesive bonds, double cantilever beam specimens were prepared from spruce wood. While the highest fracture energy values were observed for UF-bonds filled with untreated nanofibrils prepared from wood pulp, bonds filled with TEMPO-oxidized fibrils showed less satisfying performance. It is proposed that UF-adhesive bonds can be significantly toughened by the addition of only small amounts of cellulose nanofibrils. Thereby, the optimum filler content is largely depending on the adhesive and type of cellulose filler used.

Effect of Cellulose Nanofibrils on the Bond Strength of Polyvinyl Acetate and Starch Adhesives for Wood

“…On the other hand, the amounts of CNF addition were limited, as it caused an increasing viscosity of the adhesives that exhibited the wood penetrating ability. Veigel et al (2011) also claimed that cellulose addition increased the viscosity of adhesives, which restricted the amount of nanofibrils that could be added. In this study, the highest amount of CNF in suspensions (1.28%) led to over-viscous systems that were less applicable to the wood surface as an even film and may have required a longer curing time, although the potential benefits of CNF dose and press time were not investigated nor optimized here.…”

Toughening mechanisms in poly(lactic) acid reinforced with TEMPO-oxidized cellulose

“…For almost three decades, since the first appearance of a paper by Turbak et al [2], there has been interest in the potential of cellulose, from a variety of sources, as a polymer modifier or composite reinforcement. For instance, it has been shown that the toughness of urea-formaldehyde wood adhesive can be increased by 45 % upon the addition of up to 2 % by weight of high pressure homogenised beech pulp [3]. It has also been shown that the inter-laminar initiation fracture toughness of plain woven carbon fibre (CF)-reinforced epoxy could be increased by 80 % upon the modification of the epoxy matrix with 2 % weight fraction of micro-fibrillated cellulose (MFC) [4].…”

Inovativna raba bukovine slabše kakovosti in ostankov

“…CNC so kratki in togi delci, medtem ko imajo NFC dolgo nitasto obliko s kristaliničnim in amorfnim delom. Če dodamo NFC delce k različnim vlakninskim in polimernim materialom, s tem povečamo njihovo jakost, vezivnost, fleksibilnost in številne druge lastnosti, kar je zlasti pomembno pri razvoju lahkih, močnih, funkcionalnih in biorazgradljivih kompozitov (Veigel et al, 2011(Veigel et al, , Žepič et al, 2014(Veigel et al, , Žepič et al, 2015.…”