Organosolv Lignin as a Green Sizing Agent for Thermoformed Pulp Products

Abstract

The purpose of this study was to investigate the use of organosolv lignin as a sizing agent for thermoformed pulp products as a sustainable material with improved water resistance. For this purpose, an in-house-produced organosolv lignin from softwood (Norway Spruce) was mixed with bleached and unbleached chemi-thermomechanical pulp fibers. In addition, the isolated organosolv lignin was characterized by ATR–FTIR spectroscopy, size-exclusion chromatography, and thermogravimetric analysis. The analysis showed that organosolv lignin was of a high purity and practically ash-free, exhibiting low molecular weight, a glass transition temperature below the thermoforming temperature, and a high content of phenolic OH groups. The mechanical properties and water resistance of the organosolv lignin-sized thermoformed pulp materials were measured. A small decrease in strength and an increase in stiffness and density were observed for the lignin-sized thermoformed materials compared to the reference, that is, unsized materials. The addition of organosolv lignin decreased the wettability and swelling of the thermoformed product. These results are due to the distribution of organosolv lignin on the surface, filling in the pores and cavities, and providing a tighter fit within the thermoformed materials. In conclusion, the results from our study encourage the use of organosolv lignin as a sizing additive to thermoformed products, which can improve the water resistance to use it in sustainable packaging applications.

Functional surfaces, films, and coatings with lignin – a critical review

“…High densities of up to 1200 kg m −3 were reported, where the uptake of water is hindered not only by limiting mass-transport, but also by confining the swelling of cellulose fibers. 88 …”

“…Application of the lignin can be done via an aqueous dispersion or alternatively by impregnation after dissolution in a solvent. 35,88 A similar approach was used to treat beech wood with lignin nanoparticle via dip-coating, which improved the weathering resistance of the wood. 89 Such dip-coating may preserve breathability of the substrate due to the porous structure.…”

“…The discussed effects could also be induced by the lignin acting as a binder, hence filling gaps and providing an overall tighter network. 36,88 Riviere et al combined lignin-nanoparticles and cationic lignin with CNF, however, the oxygen barrier and mechanical strength were lower than the CNF without added lignin. 108 This effect was likely due to a disruption of the binding between CNF networks.…”

“…Three recent studies have found that incorporating lignin into a molded pulp materials can reduce the wettability of the material, as witnessed by an increase in contact angle or a decrease in water-uptake. 8,36,88 The advantage of such implementation is that high temperature and pressure will promote densification, as the lignin can flow into cavities. High densities of up to 1200 kg m −3 were reported, where the uptake of water is hindered not only by limiting mass-transport, but also by confining the swelling of cellulose fibers.…”

Sustainable Materials from Organosolv Fibers and Lignin, Kraft Fibers, and Their Blends

“…Lignin, the second-most abundant biopolymer from lignocellulosic biomass, is considered a byproduct from various biorefinery processes, which is still underutilized as of today. Hence, because of its abundance and chemical structure, lignin has a significant potential to be used in many applications such as biopolymeric materials [10], reinforced filler materials [11], bioactive components [10], and internal sizing agents [12]. As such, the application of lignin in thermoformed fiber materials is a promising alternative, which can improve the properties of fiber-based materials, while additionally creating added-value applications for lignin in fully biobased products.…”