Surface modification of lignosulfonates for reinforcement of styrene-butadiene rubber compounds

Recent Advances of Lignin Functionalization for High-Performance and Advanced Functional Rubber Composites

The biomass lignin is the only large-volume renewable feedstock that is composed of aromatics but has been largely underutilized and is sought for valorization as a value-added material. Recent research has highlighted lignin as a promising alternative to traditional petrol-based reinforcements and functional additives for rubber composites. This review summarized the recent advances in the functionalization of lignin for a variety of rubber composites, as well as the compounding techniques for effectively dispersing lignin within the rubber matrix. Significant progress has been achieved in the development of high-performance and advanced functional rubber/lignin composites through carefully designing the structure of lignin-based additives and the optimization of interfacial morphologies. This Review discussed the effect of lignin on composite properties, including mechanical reinforcement, dynamic properties, antiaging performance, and oil resistance, and also the advanced stimuli-responsive performance in detail. A critical analysis for the future development of rubber/lignin composites is presented as concluding remarks.

The Biomodified Lignin Platform: A Review

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat and electricity generation. Green enzyme-based modifications of technical lignin have generated a number of functional lignin-based polymers, fillers, coatings, and many other applications and materials. These bio-modified technical lignins often display similar properties in terms of their durability and elasticity as fossil-based materials while also being biodegradable. Therefore, it is possible to replace a wide range of environmentally damaging materials with lignin-based ones. By researching publications from the last 20 years focusing on the latest findings utilizing databases, a comprehensive collection on this topic was crafted. This review summarizes the recent progress made in enzymatically modifying technical lignins utilizing laccases, peroxidases, and lipases. The underlying enzymatic reaction mechanisms and processes are being elucidated and the application possibilities discussed. In addition, the environmental assessment of novel technical lignin-based products as well as the developments, opportunities, and challenges are highlighted.

Utilization of chestnut shell lignin in alginate films

BACKGROUND

Lignocellulosic structures obtained from agricultural wastes can re-design sustainable packaging materials. The present study investigated the utilization of lignocellulose (LS), alkali lignin (L) and hydroxymethylated (modified) lignin (ML), separated from chestnut shells in alginate (AL) films at 100 and 200 mg g^-1 (10% and 20%, w/w based on AL), as reinforcing agents. Lignin modification and concentration effects on the AL films were characterized by water vapor permeability (WVP), as well as morphological, mechanical, optical, thermal and active properties.

RESULTS

Fourier transform infrared spectroscopy results showed that extracted L and LS had different structures, and the modification of L resulted in a peak shift and a decrease in peak intensities between 1250 and 800 cm^-1 . The antioxidant and antimicrobial activity tests showed that films containing L had higher activity values (P < 0.05). WVP of the films containing ML was the lowest (P < 0.05) and the results revealed that 20% (w/w) concentration had an adverse effect on the WVP of films. The addition of L, LS and ML increased the tensile strength, elastic modulus and thermal properties (P < 0.05) compared to AL control films. With an increasing concentration, films containing L-based structures showed higher opacity and relatively lower L* values (P < 0.05).

CONCLUSION

These results show that the addition of lignin to biopolymers is a promising method for improving the properties of biopolymers and providing functional attributes. LS had no or little effect on the film properties; however, the modification of L had the advantage of enhancing WVP and thermal properties at the same time as showing a decrease in functional properties compared to L. © 2022 Society of Chemical Industry.

Application of Plasticizer Glycerol in Lignosulfonate-Filled Rubber Compounds Based on SBR and NBR

The work deals with the application of biopolymer fillers in rubber formulations. Calcium lignosulfonate was incorporated into styrene-butadiene rubber and acrylonitrile-butadiene rubber in a constant amount of 30 phr. Glycerol in a concentration scale ranging from 5 to 20 phr was used as a plasticizer for rubber formulations. For the cross-linking of the compounds, a sulfur-based curing system was used. The study was focused on the investigation of glycerol in the curing process; the viscosity of rubber compounds; and the cross-link density, morphology, physical-mechanical, and dynamic mechanical properties of vulcanizates. The study revealed that the application of glycerol as a plasticizer resulted in a reduction in the rubber compounds' viscosity and contributed to the better dispersion and distribution of the filler within the rubber matrices. The mutual adhesion and compatibility between the filler and the rubber matrices were improved, which resulted in the significant enhancement of tensile characteristics. The main output of the work is the knowledge that the improvement of the physical-mechanical properties of biopolymer-filled vulcanizates can be easily obtained via the simple addition of a very cheap and environmentally friendly plasticizer into rubber compounds during their processing without additional treatments or procedures. The enhancement of the physical-mechanical properties of rubber compounds filled with biopolymers might contribute to the broadening of their potential applications. Moreover, the price of the final rubber articles could be reduced, and more pronounced ecological aspects could also be emphasized.

Calcium-Lignosulfonate-Filled Rubber Compounds Based on NBR with Enhanced Physical-Mechanical Characteristics

Calcium lignosulfonate in the amount 30 phr was incorporated into rubber compounds based on pure NBR and an NBR carbon black batch, in which the content of carbon black was 25 phr. Glycerine, as a cheap and environmentally friendly plasticizer, was applied into both types of rubber formulations in a concentration scale ranging from 5 to 20 phr. For the cross-linking of rubber compounds, a sulfur-based curing system was used. The work was aimed at the investigation of glycerine content on the curing process and rheological properties of rubber compounds, cross-link density, morphology and physical-mechanical properties of vulcanizates. The results show that glycerine influences the shapes of curing isotherms and results in a significant decrease between the maximum and minimum torque. This points to the strong plasticizing effect of glycerine on rubber compounds, which was also confirmed from rheological measurements. The application of glycerine resulted in better homogeneity of the rubber compounds and in the better dispersion and distribution of lignosulfonate within the rubber matrix, which was subsequently reflected in the significant improvement of tensile characteristics of vulcanizates. A higher cross-link density as well as better physical-mechanical properties were exhibited by the vulcanizates based on the carbon black batch due to the presence of a reinforcing filler.

Turning lignin into treasure: An innovative filler comparable to commercial carbon black for the green development of the rubber industry

Driven by the global carbon neutrality action, biomass-derived functional materials have been applied in many fields to alleviate the pressure brought by the depletion of fossil energy. However, due to the complex structure, lignin faces many difficulties in its high-value utilization. The second largest biomass in the world has become the largest "natural waste". In this paper, the lignin-based biochar-silica (LB-S) hybrid nanoparticles were prepared via a combination of two-step acid precipitation and carbonization using lignin black liquor extracted from xylose residue and sodium silicate as raw materials. The effects of carbonization temperature and lignin-based biochar (LB) content on the reinforcing properties of LB-S were studied. The results show that the particle size, specific surface area, pore characteristics, and surface polarity of LB-S all affect the mechanical properties of the final vulcanizates. The reinforcement performance of the best sample (L_MB₅₀₀-S) with "high structure" characteristics can be comparable to that of commercial carbon black (CB) N550. This study shows that L_MB₅₀₀-S hybrid nanoparticles with economic benefits possess the potential to completely replace commercial CB, which can turn lignin waste into treasure and promote the green development of traditional rubber industry in the context of carbon neutrality.

A Review of Rubber Biocomposites Reinforced with Lignocellulosic Fillers

Lignocellulosic fillers have attracted considerable attention over the years as a promising alternative to conventional petroleum-based fillers (carbon black) in rubber composites due to their renewability, biodegradability, availability, high mechanical properties, low density and low cost. Based on the literature available, a comprehensive review is presented here of rubber biocomposites reinforced with plant-based fillers. The study is divided into different sections depending on the matrix (natural or synthetic rubber) and the type of lignocellulosic fillers (natural fiber, microcrystalline cellulose, lignin and nanocellulose). This review focuses on the curing characteristics, mechanical properties and dynamic mechanical properties of the resulting rubber biocomposites. In addition, the effect of hybrid filler systems, lignocellulosic filler surface modification and modification of the rubber matrix on the properties of these rubber biocomposites are presented and compared. A conclusion is finally presented with some openings for future works.

Application of Sulfur and Peroxide Curing Systems for Cross-Linking of Rubber Composites Filled with Calcium Lignosulfonate

Calcium lignosulfonate in different loadings was applied to the rubber matrix based on EPDM. A sulfur curing system, organic peroxide, and a combination of organic peroxide with two coagent types were used for cross-linking of rubber compounds. The work was focused on the investigation of filler content and curing system composition in the curing process, cross-link density, morphology, and physical–mechanical properties of composites. The achieved results demonstrated that the curing parameters of rubber compounds cured with the sulfur system were significantly different from those cured with peroxide systems. There was also an observed different influence of curing systems composition on cross link density, though in all cases, the degree of cross-linking showed a decreasing trend with increasing content of lignosulfonate. The tensile strength of the composites cured with sulfur system and organic peroxide was comparable, regardless of lignosulfonate loading. This points to the application of both curing systems in cross-linking of rubber compounds with biopolymer filler. However, the introduction of coagents in peroxide vulcanization led to the improvement of adhesion and compatibility between the rubber and the filler on the filler–rubber interface. This subsequently resulted in the improvement of the tensile characteristics of composites. The introduction of organic peroxide in combination with coagent seems to be a very simple and efficient way for the preparation of biopolymer-filled composites with applicable physical–mechanical properties.

Controllable conversion of biomass to lignin-silica hybrid nanoparticles: High-performance renewable dual-phase fillers

Due to the complex network of aromatic units, lignin is difficult to achieve high-value applications in the industrial field, becoming the largest "natural waste". In this paper, dual-phase fillers with excellent rubber reinforcement were prepared from lignin and sodium silicate through the method of controllable two-step acid precipitation without any complicated modification. During the formation of hybrid nanoparticles, silica nanoparticles were formed as templates in the first step, and then lignin was used as coating agent to bind with silica. The size and morphology of products could be easily adjusted by changing acid precipitation conditions. The L₆₀S_S hybrid nanoparticles with the best reinforcement performance showed the ability to replace carbon black (CB) in a high proportion. In addition, LS_RH-S hybrid nanoparticles made from rice husk black liquor had similar physical and chemical properties and excellent reinforcement properties to L₆₀S_S. Even if the ratio of each component of the raw material was different, the product could be flexibly controlled by the two-step acid precipitation to obtain the expected properties. The wide applicability of this method in many extraction processes based on alkaline procedures was proved, and it provided a basis for the process design of comprehensive utilization of biomass. This work will promote the application of lignin in high-value fields, and the sustainable development of the rubber industry by utilizing agricultural waste was achieved.

Hydroxymethylation-Modified Lignin and Its Effectiveness as a Filler in Rubber Composites

Kraft lignin was modified by using hydroxymethylation to enhance the compatibility between rubber based on a blend of natural rubber/polybutadiene rubber (NR/BR) and lignin. To confirm this modification, the resultant hydroxymethylated kraft lignin (HMKL) was characterized using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. It was then incorporated into rubber composites and compared with unmodified rubber. All rubber composites were investigated in terms of rheology, mechanical properties, aging, thermal properties, and morphology. The results show that the HMKL influenced the mechanical properties (tensile properties, hardness, and compression set) of NR/BR composites compared to unmodified lignin. Further evidence also revealed better dispersion and good interaction between the HMKL and the rubber matrix. Based on its performance in NR/BR composites, hydroxymethylated lignin can be used as a filler in the rubber industry.