Determination of physical emulsion stabilization mechanisms of wood hemicelluloses via rheological and interfacial characterization

Abstract

Materials manufacturing industries seek efficient, economic, and sustainable compounds for stabilizing dispersed systems such as emulsions. In this study, novel, abundant biobased hydrocolloids spruce galactoglucomannans (GGM) and birch glucuronoxylans (GX) were obtained from a forestry biorefining process and characterized as versatile stabilizers of rapeseed oil-in-water emulsions. For the first time, GGM and GX isolated by pressurized hot water extraction (PHWE) of spruce and birch saw meal, respectively, were studied in emulsions. The PHWE wood hemicelluloses-polysaccharides with relatively low molar mass-facilitated the formation of emulsions with small average droplet size and efficiently prevented droplet coalescence. GGM and GX lowered the surface tension of emulsions' oil-water interface and increased the viscosity of the continuous phase. However, viscosity of the wood hemicellulose-based systems was low compared to that of commercial polymeric stabilizers. GGM-stabilized emulsions with varying oil volume fractions were characterized in terms of their rheological properties, including large amplitude oscillation shear (LAOS) measurements, and compared to emulsions prepared with a classical small-molecular surfactant, Tween20. The physical emulsion stabilization mechanisms of GGM and GX are suggested as steric repulsion assisted by Pickering-type stabilization. Wood hemicelluloses have potential as highly promising future bioproducts for versatile industrial applications involving colloidal systems and soft materials.

Strategies for structuring diverse emulsion systems by using wood lignocellulose-derived stabilizers

“…58) and that from PHWE is about 10 000 g mol −1 . 12 However, the composition of isolated GX and GGM extracts is more complex than that described above, as the extracts often contain co-components, such as lignin fragments or other wood-derived extractives. [59][60][61] Pressurized hot waterextracted hemicelluloses are characterized by up to 70 mg gallic acid equivalent per g hemicelluloses, 14 indicating presence of lignin.…”

“…34 The molar mass of pressurized hot water extracted (PHWE) birch GX is about 6500 g mol −1 . 12 The backbones of GGM and glucomannan consist of alternating β-D-glucopyranosyl and β-D-mannopyranosyl units attached with (1 → 4)-bonds. Softwood GGM contains α-D-galactopyranosyl units (1 → 6)-linked to the backbone mannosyl units.…”

“…Due to their intermediate molar mass, the viscosity of aqueous GX and GGM solutions is low, even at high concentrations. 12…”

“…Various methods are used to convert wood or pulp into efficient stabilizers. For example, optimized aqueous extraction of hemicelluloses yields native functional emulsifiers; [12][13][14][15] cellulose may be disintegrated into nanoparticles 16,17 or modified to become a water-soluble derivative; 18 and lignin may be transformed into amphiphilic molecules via grafting with other building blocks. 19,20 Subsequently, emulsion stability is achieved through interfacial activity of the amphiphilic surfactants, Pickering stabilization with insoluble particles, or an increase in the viscosity of the continuous phase.…”

The structure of galactoglucomannan impacts the degradation under alkaline conditions

“…Moreover, many fiber-based products would benefit from retaining the hemicellulose fraction, resulting in an increased yield and improved properties in mainly cellulose based products (Tavast et al 2015;Salmén and Lindström 2015). Hemicelluloses have also shown good properties as oxygen barriers (Mikkonen et al 2011;Kisonen et al 2014), in hydrogels (Edlund and Albertsson 2008) and as emulsifiers (Mikkonen et al 2016), gaining great attention of the pulping industry in the context of an integrated biorefinery. However, the number of hemicellulose-based products is still limited.…”