Biljana M. Bujanovic

Reducing the consumption of single-use plastics is becoming reality in today’s society. More than 300 million tons of plastic waste are generated annually globally, with a significant portion coming from disposable food packaging. The development of sustainable paper-based packaging coated with biopolymers has gained prominence in the packaging sector due to its biodegradability, non-toxicity and biocompatibility properties. These materials offer additional advantages, such as resistance to moisture and oxidation, which increases the durability of packaged food products. Improving the knowledge and their applications are essential to ensure the sustainability of production processes and meet growing environmental and economic demands. However, ongoing research is needed to overcome challenges such as production scalability and the high cost of some biopolymers in order to ensure their viability on a large scale. Additionally, it has the potential to stimulate innovation in the packaging industry, offering solutions that align sustainability and competitiveness in the market.

Food packaging is the largest segment of the global plastics market, yet its low degradability and limited performance in preserving perishable goods highlight the need for more sustainable alternatives. This study investigates the use of industrial softwood kraft lignin, a renewable polyol, and γ-valerolactone (GVL), an excellent green lignin solvent, to synthesize bio-based polyurethane (PU) coatings for recycled linerboard. PU was synthesized with hexamethylene diisocyanate (HDI), GVL, and 1,4-diazabicyclo[2.2.2]octane (DABCO) as a catalyst and applied to recycled linerboard (166.6 g/m²) at three coating weights: 13.5, 16.5, and 23.5 g/m². The coating enhanced water resistance, as shown by the reduced water vapor transmission rate (WVTR) and Cobb₁₈₀₀ values. Oil resistance was also significantly improved, reaching a Kit rating of 11 at the highest coating weight. Mechanical performance was maintained or enhanced, with increases in ring crush strength (RCT) and tensile index. These findings confirm the effectiveness of lignin-based PU in improving both the barrier and mechanical properties of packaging paper. Additionally, this approach presents an environmentally responsible alternative to petroleum-based coatings, adding value to lignin as a byproduct of the pulp and paper industry and supporting the transition toward more circular and sustainable packaging materials.

This work demonstrates the use of kraft lignin as an effective raw material for flexible non-isocyanate polyurethane (NIPU) foams, reaching densities below 100 kg m⁻³ while displaying flexible compression properties.

Pelletizing enhances competitiveness of lignocellulosic biomass (LCB) as a fuel by increasing its bulk and energy density. However, LCB pellets are prone to degradation from moisture, have high ash, and pose safety risks due to carbon monoxide (CO) emissions during storage. Hot water extraction (HWE), a mild hydrothermal treatment particularly effective for angiosperms, removes most hemicelluloses (xylans), reduces ash, and increases lignin content in remaining HWE-LCB. Based on the current understanding of CO formation, these changes suggested that HWE could reduce CO emissions. In this study, we evaluated the effects of HWE on pellets made from shrub willow, miscanthus, and wheat straw. A statistical analysis was conducted on ash, energy content, bulk density, durability, pellet length and density, moisture absorption, and CO emissions. All HWE-LCB pellets demonstrated significant increases in energy content (up to 3.54%) and reductions in moisture absorption (up to 23.84%). Although not all effects reached statistical significance, HWE generally had positive effects on ash content, bulk density, durability, and average pellet length and density. Contrary to expectations, HWE-LCB pellets emitted significantly more CO under both ambient and isothermal temperature conditions (up to 4.25 times overall increase), although still less than commercial hardwood/softwood blend pellets (300 ppm).

This study aimed to investigate the intrinsic efficiency of renewable alcohols, applied under autocatalytic conditions, for removing lignin from aspen and hot-water-extracted aspen while substantially preserving the lignin structure so as to facilitate various valorization strategies. Ethylene glycol (EG), propylene glycol (PG), 1,4-butanediol (BDO), ethanol (EtOH), and tetrahydrofurfuryl alcohol (THFA) were evaluated based on their lignin solubilization ability, expressed as the relative energy difference (RED) following the principles of the Hansen solubility theory. The findings indicate that alcohols with a higher lignin solubilization potential lead to increased delignification, almost 90%, and produce a lignin with a higher content of β-O-4 bonds, up to 68% of those found in aspen milled wood lignin, thereby indicating their potential for valorization through depolymerization. However, these alcohols also produce lignin with a higher content of β-β and β-5 bonds, resulting in a higher molecular weight and polydispersity, due to readily occurring homolytic reactions. Hot-water extraction (HWE) conducted prior to alcohol treatment reduced the delignification efficiency and resulted in a lignin with a lower β-O-4 bond content. The lignins produced in these experiments exhibited a superior UV-A absorption capacity compared with synthetic benzophenone, as well as a greater radical quenching ability than synthetic butylated hydroxytoluene, indicating their potential for use in the protection of polymers against degradation.

Lignin-poly(ethylene)glycol diglycidyl ether hydrogels were synthesized from lignin fractions readily extracted during the hot-water treatment of angiosperms: hardwoods, sugar maple and energy-crop willow, monocotyledons, grasses, miscanthus and agriculture residues, and wheat straw. These lignins represent a broad range of chemical structures and properties as a comparative analysis of their suitability to produce the hydrogels as a novel carrier of chaga–silver nanoparticles. The formation of hydrogels was assessed via attenuated total reflectance Fourier-transformed infrared spectroscopy. Then, the hydrogels were observed via scanning electron microscopy and evaluated for their free-absorbency capacity and moduli of compression. Furthermore, a hydrogel produced from kraft lignin and two commercial hydrogels was evaluated to benchmark the effectiveness of our hydrogels. Chaga extracts were prepared via the hot-water extraction of chaga mushroom, a method selected for its relatively higher yields and preserved antioxidizing activities. Hydrogels synthesized with lignins of monocotyledons, wheat straw, and miscanthus were found to be suitable carriers for chaga–silver nanoparticles due to their favorable absorption and release behaviors.

Shrub willow (Salix spp.) is an emerging lignocellulosic biomass utilized in fuel pellets as an energy source. However, improvements are needed to increase the efficacy of pellets in areas such as the energy content, durability, and hazardous carbon monoxide emissions. This study examined the effect of utilizing lignin as an additive on willow pellet properties. Two types of lignin were used in individual treatments: lignin recovered from the hot water extraction of willow (RecL) and commercial softwood kraft lignin (ComL). A statistical analysis of the ash content, energy content, bulk density, durability, pellet length, moisture absorption, and carbon monoxide emissions for the pellets with and without the addition of RecL or ComL lignin was conducted. The observed significant reduction in carbon monoxide emissions from RecL pellets was an important effect of the lignin addition. There were also significant increases in the energy content, bulk density, and durability of lignin-added pellets. While the production of carbon monoxide via pellets continues to be explored, lignin can be utilized as an additive to reduce carbon monoxide emissions and simultaneously improve other pellet properties.

A blend of commercial willow cultivars (Salix spp.) was subjected to hydrothermal pretreatment: hot‐water extraction in a pilot plant 65‐ft³ digester. Lignin recovered from the autohydrolyzate (willow lignin, WL) was used to produce hydrogels and thermoplastic blends. Lignin‐kaolin‐acrylamide (WL 10.7 % w/w) and lignin‐poly(ethylene)glycol diglycidyl ether (WL 66.7 % w/w) hydrogels exhibited favorable adsorption and absorption properties, respectively. Dye adsorption kinetics, swelling capacities, fragrance emanation, and compression moduli were measured for the hydrogels, along with SEM characterization. Additionally, WL was esterified by acetylation (C₂, WAc) and acylation with lauroyl chloride (C₁₂, WFAE and WFAE_H). The crude and esterified lignin samples were blended (1–12 % w/w) with polylactic acid (PLA) via lab‐scale melt extrusion to produce thermoplastic blends. The physicochemical properties of the blends were evaluated. They exhibited an increase in degradation temperature and UV absorbance with potential to hinder photodegradation of PLA and may be leveraged in packaging applications.

We investigated miscanthus (MS) and willow (W) lignin-furfural based resins as potential reinforcement agents on softwood and hardwood kraft paper. These resins might be sustainable alternatives to the commercial phenol-formaldehyde (PF) resins. Phenol is a petrochemical product and formaldehyde has been classified as a carcinogen by the U.S. Environmental Protection Agency. The lignin used in this study was derived from hot water extraction (160ºC, 2 h) of MS and W biomass, and may be considered sulfur-free. These biorefinery lignins were characterized for their chemical composition and inherent properties via wet chemistry and instrumental techniques. The resin blends (MS-resin and W-resin) were characterized for their molecular weight, thermal behavior, and mechanical properties. Mechanical properties were measured by the resin’s ability to reinforce softwood and hardwood kraft papers. The effect of adding hexamethylenetetramine (HMTA), a curing agent, to the resin was also examined. Mixtures of PF and lignin-based resins were investigated to further explore ways to reduce use of nonrenewables, phenol, and carcinogenic formaldehyde. The results show that lignin-based resins have the potential to replace PF resins in kraft paper applications. For softwood paper, the highest strength was achieved using W-resin, without HMTA (2.5 times greater than PF with HMTA). For hardwood paper, MS-resin with HMTA gave the highest strength (2.3 times higher than PF with HMTA). The lignin-based resins, without HMTA, also yielded mechanical properties comparable to PF with HMTA.

Miscanthus (Miscanthus sp. Family: Poaceae) was hot-water extracted (two h, at 160 °C) at three scales: laboratory (Parr reactor, 300 cm³), intermediate (M/K digester, 4000 cm³), and pilot (65 ft³-digester, 1.841 × 10⁶ cm³). Hot-water extracted miscanthus, hydrolyzate, and lignin recovered from hydrolyzate were characterized and evaluated for potential uses aiming at complete utilization of miscanthus. Effects of scale-up on digester yield, removal of hemicelluloses, deashing, delignification degree, lignin recovery and purity, and cellulose retention were studied. The scale-dependent results demonstrated that before implementation, hot-water extraction (HWE) should be evaluated on a scale larger than a laboratory scale. The production of energy-enriched fuel pellets from hot-water extracted miscanthus, especially in combination with recovered lignin is recommended, as energy of combustion increased gradually from native to hot-water extracted miscanthus to recovered lignin. The native and pilot-scale hot-water extracted miscanthus samples were also subjected to enzymatic hydrolysis using a cellulase-hemicellulase cocktail, to produce fermentable sugars. Hot-water extracted biomass released higher amount of glucose and xylose verifying benefits of HWE as an effective pretreatment for xylan-rich lignocellulosics. The recovered lignin was used to prepare a formaldehyde-free alternative to phenol-formaldehyde resins and as an antioxidant. Promising results were obtained for these lignin valorization pathways.