Michaela Džuganová

Pilot-scale kraft lignin, unmodified (UKL) or tall-oil/rosin-modified (MKL), was assessed as a sustainable alternative to carbon black in nitrile–butadiene rubber (NBR). NBR composites with 30–50 phr UKL or MKL were compounded and vulcanized, and their mechanical, thermal, and viscoelastic properties were evaluated. Lignin produced a strong reinforcing effect: tensile strength more than doubled to ~14 MPa at 30–50 phr with MKL, comparable to conventional carbon-black-filled NBR, while elongation at break increased alongside modulus and hardness. MKL also improved thermal stability, shifting the oxidative decomposition onset to ~365°C (versus ~290°C for UKL), and caused a slight upward shift in T _g . Contact-angle analysis showed higher surface free energy for MKL (≈62.4 versus ≈55.3 mJ/m ² ), consistent with modified interfacial behavior, reduced lignin self-association, and improved dispersion/interfacial contact. Thus, simple chemical modification turns kraft lignin into an application-ready, bioderived filler for demanding NBR applications. Impact statement: This work shows that industrial kraft lignin, a byproduct of pulp mills, can move from the boiler to the product and act as a viable, tunable alternative to carbon black in nitrile rubber. By combining pilot-scale LignoBoost™ lignin with a simple tall-oil/rosin modification, we demonstrate that lignin can deliver carbon-black-level reinforcement in nitrile–butadiene rubber while simultaneously improving thermal robustness and maintaining elasticity. Scientifically, the study links lignin structure, glass transition, surface free energy and interfacial energetics to filler dispersion and composite performance, offering a design framework that is transferrable to other polar elastomers and polymer blends. Practically, the use of pilot-scale lignin and standard sulfur vulcanization shows that integration into existing rubber compounding lines is realistic without radical process changes. At the policy and societal level, replacing a portion of fossil-derived carbon black with bioderived lignin supports the circular bioeconomy, opens higher-value product streams for pulp mills, and reduces the CO ₂ footprint of seals, hoses, gaskets, and other industrial rubber components. The results point to lignin-based fillers as an immediately relevant lever for decarbonizing rubber technology. Graphic Schematic overview of kraft lignin valorization into nitrile–butadiene rubber (NBR) composites: lignin isolated from hardwood black liquor is used either unmodified (UKL) or after tall-oil/rosin modification (MKL), compounded into NBR, and evaluated for interfacial compatibility and composite performance (thermal stability and mechanical reinforcement, benchmarked against carbon black).

Glycolysate and glycerolysate—organic substances recovered from the chemical recycling of polyurethane waste—were investigated as sustainable plasticizers for acrylonitrile-butadiene rubber composites filled with 30 phr of calcium lignosulfonate or kraft lignin. The study evaluated the impact of these recycled plasticizers (added at 10 and 15 phr) on the curing process, morphology, rheology, mechanical and dynamic mechanical performances. Rheological analysis confirmed that both plasticizers significantly reduced the complex viscosity of the rubber compounds, with the effect being most pronounced at the 15 phr loading. While the incorporation of glycolysate and glycerolysate slightly extended the optimum cure time and decelerated the curing process, the cross-link density remained consistently within the range of 3.5–4 × 10⁻⁴ mol·cm⁻³. Morphological studies revealed that the plasticizers facilitated better dispersion of both lignin types and improved interfacial adhesion. However, the mechanical response differed significantly depending on the filler type. A consistent increase in elongation at break was observed only for composites filled with kraft lignin, where values rose from 341% for the reference up to 571% for the sample with 15 phr of glycolysate. In contrast, the application of plasticizers to calcium lignosulfonate-filled composites led to an initial decrease in both tensile strength and elongation at break. Notably, kraft lignin-filled composites exhibited superior overall mechanical performance, with glycolysate effectively maintaining tensile strength levels comparable to the reference. While both recovered substances performed effectively as processing aids, they had a negligible effect on the glass transition temperature. The results demonstrated that these recovered polyurethane derivatives are highly effective, sustainable alternatives to conventional plasticizers, showing a clear synergistic effect particularly with kraft lignin.

Lignin, a major component of lignocellulosic biomass, is gaining attention as a renewable alternative to fossil-based materials in polymer composites. Its complex polyphenolic structure imparts antioxidant, antimicrobial, UV-resistant, and biodegradable properties, enabling its integration into thermoplastics, thermosets, and elastomers, often without extensive modification. Technical lignins from industrial processes such as Kraft, sulfite, and organosolv methods offer scalable feedstocks for sustainable materials. In plastics, lignin enhances mechanical, thermal, and aging resistance while supporting biodegradability; in rubber composites, it serves as both a reinforcing agent and a stabilizer against oxidation and UV degradation. Performance can be further improved through plasticization and compatibilization. This article also surveys patents, reflecting the growing industrial interest and commercial potential of lignin valorization. Graphical abstract

Magnetic soft manganese–zinc ferrite in a concentration scale ranging from 100 to 500 phr was incorporated into acrylonitrile-butadiene rubber. The work was focused on the investigation of manganese–zinc ferrite content on electromagnetic interference shielding effectiveness and mechanical properties of composites. The rubber-based products used in industrial practice should not only provide good utility and functional properties but should also exhibit good stability towards degradation factors, like oxygen and ozone. Therefore, the samples were exposed to the thermo-oxidative and ozone ageing conditions, and the influence of both factors on the composites’ properties was evaluated. The results demonstrated that the incorporation of ferrite into the rubber matrix resulted in the fabrication of composites with absorption-shielding performance. It was demonstrated that the higher the ferrite content, the lower the absorption-shielding ability. Electrical and thermal conductivity showed an increasing trend with increasing content of ferrite. On the other hand, the study of mechanical properties implied that ferrite acts as a non-reinforcing filler, leading to a decrease in tensile characteristics. Thermo-oxidative ageing tests revealed that ferrite, mainly in high amounts, could accelerate the degradation processes in composites. Though the absorption-shielding performance of composites after ageing corresponded to that of their equivalents before ageing, it can also be concluded that the higher the amount of ferrite in the rubber matrix, the lower the composites’ stability against ozone ageing.

This study investigates the characterization and processing of rubber crumb (RC) obtained as a waste from tread part of truck tyres with a focus on its devulcanization and stabilization using kraft lignin. Thermogravimetric analysis was employed to assess the composition of RC, revealing a three-step degradation pattern. Soxhlet extraction demonstrated the influence of processing temperature on sol fraction and together with rheological testing indicated that mechanical shearing at 65 °C (RC65) maximizes polysulphidic chain scission. Fourier transform infrared spectroscopy (FTIR) confirmed changes in alkane and sulphur-related bands, supporting partial devulcanization of RC samples. FTIR analysis further revealed that lignin (RCL) reduces the main chain scission in devulcanized RC, suggesting a stabilizing effect during devulcanization. The incorporation of devulcanized RC samples in virgin SBR compound resulted in improved cross-linking behaviour and mechanical properties, particularly for SBR/RC65 and SBR/RCL samples. Scanning electron microscopy further confirmed good compatibility of RCL with the SBR matrix. These findings underline the potential of lignin-stabilized devulcanized rubber as a sustainable additive in new rubber composites, advancing waste tyre recycling technologies. Graphical abstract

Calcium lignosulfonate was incorporated into rubber compounds based on styrene–butadiene rubber (SBR) and acrylonitrile–butadiene rubber (NBR) in amounts ranging from 10 to 60 phr. A sulfur-based curing system and a peroxide curing system consisting of dicumyl peroxide in combination with methacrylic acid zinc salt were used for cross-linking of the compounds. The aim of the work was to investigate the influence of lignosulfonate and curing system composition of the cross-linking process, morphology, physical–mechanical and dynamic–mechanical characteristics of the composites. The achieved results showed that peroxide cured composites demonstrated higher cross-link density, which was found not to be influenced by the content of lignosulfonate. The cross-link density of sulfur-cured composites was lower and showed a decreasing tendency with increasing amounts of the biopolymer. A lower cross-linking degree was reflected in a higher elongation at break and higher increase in the elongation at break of the corresponding composites. On the other hand, peroxide-cured composites exhibited a higher modulus M100 and higher hardness. The microscopic analysis revealed that co-agent in peroxide vulcanization contributed to the improvement of adhesion between the biopolymer and the rubber resulting in higher tensile strength of the equivalent composites. The higher cross-link density of peroxide-cured composites caused higher restriction of the chain segments’ mobility, due to which these composites exhibited a higher glass transition temperature.

Calcium lignosulfonate as a biopolymer component was incorporated into acrylonitrile butadiene rubber in the amount—50 phr. Four low-molecular organic molecules—1,4-butanediol, ethylene glycol, and two glycerols with different purity—were used as plasticizers. They were applied in rubber compounds in the amount ranging from 5 to 30 phr. The influence of the plasticizers on the curing process, cross-link density, morphology, and physical–mechanical properties was investigated. The blooming of plasticizers was also under observation. The results revealed that the application of plasticizers resulted in the deceleration of the curing kinetics and reduction in torque increments, pointing to the decrease in the rubber compounds’ viscosity. This was subsequently confirmed by the rheological measurements. The plasticizers softened the rubber matrix as well as the biopolymer filler. The higher the polarity of the plasticizer, the higher the plasticizing effect on lignosulfonate. The plasticizing effect increased in the following order: 1,4-butanediol < ethylene glycol < glycerols. Softened lignosulfonate formed small, soft filler-like domains well distributed within the rubber matrix. Good compatibility and adhesion between the rubber and the biopolymer on their interface was observed, leading to the enhancement in the tensile characteristics of the vulcanizates plasticized with ethylene glycol and glycerols.

Rubber blends based on styrene–butadiene rubber, ethylene–propylene–diene monomer rubber and a combination of both rubbers were cured with different sulfur and peroxide curing systems. In sulfur curing systems, two type of accelerators, namely tetramethylthiuram disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and combinations of both accelerators were used. In peroxide curing systems, dicumyl peroxide, and a combination of dicumyl peroxide with zinc diacrylate or zinc dimethacrylate, respectively, were applied. The work was aimed at investigating the effect of curing systems composition as well as the type of rubber or rubber combinations on the curing process, cross-link density and physical–mechanical properties of vulcanizates. The dynamic mechanical properties of the selected vulcanizates were examined too. The results revealed a correlation between the cross-link density and physical–mechanical properties. Similarly, there was a certain correlation between the cross-linking degree and glass transition temperature. The tensile strength of vulcanizates based on rubber combinations was higher when compared to that based on pure rubbers, which points out the fact that in rubber combinations, not only are the features of both elastomers combined, but improvement in the tensile characteristics can also be achieved. When compared to vulcanizates cured with dicumyl peroxide, materials cured with a sulfur system exhibited higher tensile strength. With the application of co-agents in peroxide vulcanization, the tensile strength overcame the tensile behavior of sulfur-cured vulcanizates.

Three types of composites were tested for electromagnetic interference (EMI) absorption shielding effectiveness, the curing process, and their physical–mechanical properties. For the first type of composites, nickel–zinc ferrite, manganese–zinc ferrite, and both fillers in their mutual combinations were incorporated into acrylonitrile–butadiene rubber. The overall content of the filler, or fillers, was kept at 200 phr. Then, carbon black or carbon fibers were incorporated into each rubber formulation at a constant loading of—25 phr, while the content of magnetic fillers was unchanged, at —200 phr. This work focused on the understanding of correlations between the electromagnetic shielding parameters and electrical conductivity of composites in relation to their EMI absorption shielding effectiveness. The absorption shielding abilities of materials were evaluated within a frequency bandwidth from 1 MHz to 6 GHz. This study revealed good correlation among permittivity, conductivity, and EMI absorption effectiveness. Although the absorption shielding efficiency of composites filled only with ferrites seems to be the highest, the absorption maxima of those composites reached over 6 GHz. The application of carbon-based fillers resulted in the higher electrical conductivity and higher permittivity of composites, which was reflected in their lower absorption shielding performance. However, the composites filled with ferrites and carbon-based fillers absorbed electromagnetic radiation within the desired frequency range. The presence of carbon-based fillers caused improvement in the tensile behavior of composites. This study also demonstrated that the higher the ratio of nickel–zinc ferrite in combined magnetic fillers, the better the absorption shielding efficiency.

The sulfur curing system, peroxide curing system and their combinations were applied for the cross-linking of unfilled and carbon black-filled rubber formulations based on ethylene-propylenediene-monomer rubber. The results demonstrated that the type of curing system influenced the course and shape of curing isotherms. This resulted in the change of curing kinetics of rubber compounds. The cross-link density of materials cured with combined vulcanization systems was lower than that for vulcanizates cured with the peroxide or sulfur system. Good correlation between the cross-link density as well as the structure of the formed cross-links and physical–mechanical characteristics of the cured materials was established. Both filled and unfilled vulcanizates cured with combined vulcanization systems exhibited a higher tensile strength and elongation at break when compared to their equivalents vulcanized in the presence of the peroxide or sulfur curing system. It can be stated that by proper combination of vulcanization systems, it is possible to modify the tensile behavior of vulcanizates in a targeted manner. On the other side, dynamical–mechanical properties were found not be significantly influenced by the curing system composition.