Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs

Abstract

Broader use of bio-based fibres in packaging becomes possible when the mechanical properties of fibre materials exceed those of conventional paperboard. Hot-pressing provides an efficient method to improve both the wet and dry strength of lignin-containing paper webs. Here we study varied pressing conditions for webs formed with thermomechanical pulp (TMP). The results are compared against similar data for a wide range of other fibre types. In addition to standard strength and structural measurements, we characterise the induced structural changes with X-ray microtomography and scanning electron microscopy. The wet strength generally increases monotonously up to a very high pressing temperature of 270 °C. The stronger bonding of wet fibres can be explained by the inter-diffusion of lignin macromolecules with an activation energy around 26 kJ mol−1 after lignin softening. The associated exponential acceleration of diffusion with temperature dominates over other factors such as process dynamics or final material density in setting wet strength. The optimum pressing temperature for dry strength is generally lower, around 200 °C, beyond which hemicellulose degradation begins. By varying the solids content prior to hot-pressing for the TMP sheets, the highest wet strength is achieved for the completely dry web, while no strong correlation was observed for the dry strength.

Utilizing and Valorizing Oat and Barley Straw as an Alternative Source of Lignocellulosic Fibers

“…This observation was contrary to the earlier results for mechanical wood fibers [ 16 ]. The time needed for major lignin interdiffusion [ 37 , 38 ] may be longer for the straw raw materials, whose surface properties and dimensions differ from those of wood fibers. In addition to cellulose, the IR spectra ( Figure 7 ) showed a weak band of the aromatic ring, characteristic of lignin [ 54 ], only in the sample made from refined oat fibers (Oat, 80 °C, 60 min, NaOH 12).…”

“…Moreover, dry strength dropped from the level obtained with shorter pressing. This suggests that significant amounts of hemicelluloses degrade with extended heat treatment [ 37 ].…”

“…Hot pressing [ 31 , 32 , 33 ] has been shown to lead to high dry and wet tensile strength for lignin-containing wood pulps. In that case, the strength increase is caused by the interdiffusion mechanism [ 37 , 38 ] that occurs at temperatures exceeding the softening temperature of lignin (c.a. 150 °C).…”

Emerging 3D printed thermal insulating materials for sustainable approach: A review and a way forward

“…16 Thermal insulating materials have been extensively explored for a long time and are utilized in constructing buildings and infrastructures that need insulation from heat. 17 As there is an increase in the construction of residential and commercial sectors, thermal insulation has become an important aspect due to the parallel rise in global warming. 18 Elevation in the construction directly corresponds to the elevation in the consumption of energy and thus increases the production of greenhouse gases such as CO 2 , NO, and so on, and are responsible for rising global temperature.…”

State-of-the-art luminescent materials based on wood veneer with superior strength, transparency, and water resistance

“…The observations indicate that hydrogen bonds between cellulose molecular chains were reduced by the addition of alkyl groups (hydrophobic chains). Nevertheless, when density is taken into account, the specific strength and modulus of FA-FTW films were much higher than those of most metallic alloys (steel, aluminum alloys, magnesium alloys, titanium alloys) [34][35][36], engineering plastics (polycarbonate (PC), polyamide (nylon), polyphenylene sulfide (PPS)) [37], pressed paper [38] or nanocellulose films [39][40][41]. The results highlight the potential to replace petroleum-based polymers or engineered materials in applications, such as those relevant to packaging and automotive materials.…”