Self-assembled lignin-silica hybrid material derived from rice husks as the sustainable reinforcing fillers for natural rubber

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.

Study on lignin amination for lignin/SiO2 nano-hybrids towards sustainable natural rubber composites

Lignin-based hybrid fillers are of increasing importance with regards to the valorization of low-value biomass and the requirement of sustainability in rubber industry, however, a facile lignin modification approach tuning the supramolecular interactions to favor the assembly of the hybrids is in demand. This study aimed to design a lignin/SiO₂ nano-hybrid via an in-situ assembly of diethylamine grafted lignin (DL) and SiO₂, and investigate its reinforcing effect on natural rubber (NR). DL was prepared through Mannich modification of lignin, and the grafted diethylamine can be clearly identified by FTIR, NMR and elemental analysis. The resultant hybrid (DLSi) displays as homogeneous nanospheres with well integrated DL and SiO₂ components as shown in the TEM images, and the hybrid (DLSi1) prepared with weight ratio of DL/SiO₂ = 1/2 shows a minimum particle size of 101.8 nm and significantly reduced polarity. Compared to the reference composite filled only with carbon black (CB), NR composites filled with DLSi/CB of 10/40 phr shows comparable mechanical properties and reduced rolling resistance, which is due to the low particle size, homogenous dispersion and strong rubber-filler interfacial affinity. Such remarkable performance suggests that the DLSi hybrid can be a promising versatile biobased filler for the application in gasoline-saving "green" tires.

A review of the extraction methods and advanced applications of lignin-silica hybrids derived from natural sources

The global trend of increasing energy demand along the large volume of wastewater generated annually from the paper pulping and cellulose production industries are considered as serious dilemma that may need to be solved within these current decades. Within this discipline, lignin, silica or lignin-silica hybrids attained from biomass material have been considered as prospective candidates for the synthesis of advanced materials. In this study, the roles and linking mechanism between lignin and silica in plants were studied and evaluated. The effects of the extraction method on the quality of the obtained material were summarized to show that depending on the biomass feedstocks, different retrieval processes should be considered. The combination of alkaline treatment and acidic pH adjustment is proposed as an effective method to recover lignin-silica with high applicability for various types of raw materials. From considerations of the advanced applications of lignin and silica materials in environmental remediation, electronic devices and rubber fillers future valorizations hold potential in conductive materials and electrochemistry. Along with further studies, this research could not only contribute to the development of zero-waste manufacturing processes but also propose a solution for the fully exploiting of by-products from agricultural production.

Highly Strong and Damage-Resistant Natural Rubber Membrane via Self-Assembly and Construction of Double Network

Natural rubber latex (NRL) is commonly employed to manufacture medical protective appliances. However, the characteristics of weakness and fragility of NRL membranes limit their further application. To achieve excellent strength and damage-resistance of the rubber membrane, this work reported a facile core-shell structure construction strategy via self-assembly with modified sodium lignosulfonate (MSLS) and NRL to create a tough membrane. The double network can be formed after introducing polyamide epichlorohydrin resin (PAE) into the NRL membrane. Specifically, the first robust MSLS-PAE network can break in advance to dissipate applied energy, thereby achieving high fracture energy and tensile strength of ~111.51 kJ m^-2 and ~37 MPa, respectively, which overtakes numerous soft materials. This work facilitates more studies on latex/lignin-based products with high performance and good stability for the functional application of biopolymer.

From residue to resource: new insights into the synthesis of functionalized lignin micro/nanospheres by self-assembly technology for waste resource utilization

Among the most abundant biopolymers in the biosphere, lignin is a renewable aromatic compound that represents an untapped opportunity to create new biological products. However, the complex interlacing structures of cellulose, hemicellulose and lignin, as well as the unique properties of lignin, limit the utilization of value-added lignin. Lignin-based nanomaterials open the door for lignin applications in environmental pollutant remediation, biofuel production, biomedicine, and other fields. Herein, we present various factors influencing the formation of micro-nanospheres by self-assembly techniques through a review of previous literature, and emphasize the simple and green synthesis of lignin micro/nanospheres (LMNPs) under non-modified conditions. More importantly, we discuss the mechanism of the formation of nanospheres. Considering the heterogeneity of lignin and the polarity of different solvents, we propose that self-assembly techniques should focus more on the influence brought by lignin itself or the solvent, so that the external conditions can be controlled to prepare LMNPs, which can be used in specific fields. A brief overview of the contribution of lignin-based nanomaterials in various fields is also presented. This review could provide insight for the development of lignin-based nanomaterials.

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 Silica–Lignin Hybrid Filler in a Natural Rubber Foam Composite as a Green Oil Spill Absorbent

Oil spills in the marine environment are a rising concern due to their adverse impacts on living creatures and the environment. Hence, remediation methods have been used to remove the oil from the contaminated water. A sorbent material is considered the best method for oil spill absorption. However, commonly used commercial sorbents are made from nonrenewable and nonenvironmentally friendly materials. In this research, natural rubber foam (NRF) was used as a sorbent material with the addition of a filler, i.e., silica and a silica–lignin hybrid, to increase its oil sorption capacity and reusability. The silica and silica–lignin hybrid were extracted from rice husk waste by means of the precipitation method. The silica–lignin hybrid-filled NRF exhibited excellent hydrophobicity, with a water contact angle of 133°, and had more stable reusability compared to unfilled NRF and silica-filled NRF. In addition, the optimum oil absorption capacity of silica–lignin hybrid-filled NRF was 1.36 g g⁻¹. Overall, the results showed that silica–lignin hybrid-filled NRF has the potential to be developed as a green oil absorbent material and is promising in terms of economic and environmental aspects.

Utilizing Pyrolytic Biomass Products for Rubber Reinforcement: Effect of the Silica Content in Biomass Feed Stocks

Biochar has been exploited as a substitution of carbon black in the rubber industry and various biochars exhibit diverse reinforcing abilities due to the different compositions. This work aims at studying the effect of silica on the modification process and reinforcing performance through the comparison of three biochars with different contents of silica, pyrolytic rice husks (PRH, 34 wt%), pyrolytic bamboos (PB, 7 wt%) and pyrolytic corn cobs (PC, 0.4 wt%). The results reveal that PRH requires higher rotational speed (300 min–1) than PB (200 min–1) and PC (200 min–1) to achieve similar particle sizes during the ball milling process because of the aggregations of higher silica content. Meanwhile, silica-rich pyrolytic biomass exhibits enhanced reinforcement on mechanical properties and thermal stability of rubber, and the elongation at break of vulcanizates continues to improve with increasing silica contents. Combined with the energy consumption and reinforcement, biochar containing a little amount of silica is more suitable to be widely used as bio-filler in rubber industry. This work should serve as a valuable reference to select appropriate biochar for the production of bio-fillers with high reinforcement.

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.

Performance and multi-scale investigation on the phase miscibility of poly(lactic acid)/amided silica nanocomposites

In this work, amino-functionalized nano-SiO₂ (m@g-SiO₂) was synthesized through coupling reaction on the surface of nano-SiO₂. Moreover, the optimum preparation conditions of m@g-SiO₂ were selected via orthogonal experiments as follows: reaction temperature of 80 °C, reaction time of 8 h, the mass ratio of stearic acid, N,N'‑carbonyldiimidazole, imidazole hydrochloride and g-SiO₂ of 0.5:0.7:0.7:1. Fourier transform infrared spectroscopy, static angle measurement and X-ray photoelectron spectroscopy unanimously confirmed the formation of m@g-SiO₂. Furthermore, poly(lactic acid)(PLA)/m@g-SiO₂ nanocomposites was prepared with m@g-SiO₂ as fillers to improve the comprehensive performance of PLA. Then, the mechanical properties and crystallization behavior of PLA/m@g-SiO₂ nanocomposites were studied, which showed that the impact strength and elongation-at-break of PLA/m@g-SiO₂ (0.3 wt%) nanocomposites were increased by 78.05% and 1148%, respectively, and its crystallinity was increased by 26.46%. Simultaneously, thermal gravimetric analysis indicated that the thermal stability of PLA/m@g-SiO₂ nanocomposites was improved. Eventually, the multi-scale investigation on the phase miscibility of PLA/m@g-SiO₂ nanocomposites was probed by rheological behaviors analysis and the molecular dynamics simulations, which confirmed that surface modification of SiO₂ greatly enhanced the interaction energy and miscibility between the filler and PLA bulk.