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

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

Beichen Xue, Xiaofeng Wang, Liyun Yu, Bing Di, Zhixiao Chen, Yanchao Zhu, Xiaoyang Liu PII:

S0141-8130(19)35386-3

DOI:

https://doi.org/10.1016/j.ijbiomac.2019.12.182

Reference:

BIOMAC 14210

To appear in:

International Journal of Biological Macromolecules

Received date:

12 July 2019

Revised date:

20 December 2019

Accepted date:

20 December 2019

Please cite this article as: B. Xue, X. Wang, L. Yu, et al., Self-assembled lignin-silica hybrid material derived from rice husks as the sustainable reinforcing fillers for natural rubber, International Journal of Biological Macromolecules(2019), https://doi.org/ 10.1016/j.ijbiomac.2019.12.182

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© 2019 Published by Elsevier.

Journal Pre-proof

Self-assembled lignin-silica hybrid material derived from rice husks as the sustainable reinforcing fillers for natural rubber Beichen Xue, Xiaofeng Wang*, Liyun Yu, Bing Di, Zhixiao Chen, Yanchao Zhu and Xiaoyang Liu** State Key Laboratory of Inorganic Synthesis & Preparative Chemistry, College of Chemistry，Jilin University, Changchun 130012, PR China. *Corresponding author, Fax: +86 431 85168601, E-mail address: [email protected]

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**Corresponding author, Fax: +86 431 85168316, E-mail address: [email protected]

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Abstract

Biomass derived fillers have been developed as sustainable substitution of

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carbon black (CB) used in rubber industry to reduce the dependence on fossil fuels.

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Lignin is the abundant component of biomass, but has poor reinforcing performance due to its huge particle size. In this work, we prepared a lignin/silica (LS) hybrid

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material from rice husks via a facile self-assembly method. The formation of LS cut lignin macromolecules into fragments and resulted in a small average particle size of

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320 nm. When LS was filled into the natural rubber to substitute 10 phr CB, both filler-filler interaction and filler-rubber interaction were enhanced compared with the

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single use of CB. In consequence, the obtained 10LS/40CB/NR vulcanizates showed overall improvement in tensile strength, tear strength and abrasion resistance compared with the 50CB/NR vulcanizates. For the sustainable development of rubber industry, the natural LS hybrid material with low production cost is a promising reinforcing filler for the partial replacement of CB.

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1. Introduction Elastomers are one of the most important products that influence the modern technological development and they are widely applied in many industrial fields, such as automobile, aerospace and seals, etc. [1-3] To satisfy the diverse applications, the mechanical properties of elastomers need to be reinforced by fillers. In the rubber industry, carbon black (CB) is the most commonly used filler owing to its high reinforcing performance [4, 5]. However, due to the high energy consumption and

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environmental issues, CB is often in short supply and at high price [6]. Commercial

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silica has been used to partially substitute CB [7], but the entire production process is still non-renewable and high energy consuming [8]. Recently, the use of

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biomass-based materials has aroused increasing interests of researchers, because they

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are expected to further reduce the dependence on fossil fuel and promote the

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sustainable development of rubber industry [9].

Biomass fillers are recognized as low-cost, abundant, and environment friendly

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candidate substitutes for CB and commercial silica [10-17]. Nevertheless, owing to the large particle size and hydrophilic surface, most bio-fillers form severe

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aggregations in the rubber matrix and show poor reinforcement of rubber mechanical properties [8]. It is well known that the filler particle size plays a crucial role in the reinforcing performance. The smaller particle size allows the larger contact area between fillers and rubber chains, which leads to the formation of more active sites to transport the loading stress. Hence, the preparation of nanoscale material is imperative to improve the reinforcing performance of bio-based fillers. To date, the control of bio-based filler particle size was mainly dependent on procedures such as pulverization technology [8, 18] and co-precipitation of fillers with rubber latex [19, 20]. However, it is still difficult to prepare nanoscale particles. With the rapid advancement of nanotechnology, various nanostructures have been fabricated from the bulk biomass resources, which might offer a feasible strategy for the preparation of bio-based fillers. Lignin, the second most abundant natural macromolecules behind cellulose, has

Journal Pre-proof attracted global attention for a high-value utilization. According to previous studies, lignin is a potential filler which could impart rubber several desirable properties, such as antioxidant, antifungal and UV-resistance capabilities [21-25]. However, the addition of lignin resulted in detrimental rubber mechanical properties, due to the large particle size. For instance, Bahl et al. found that adding lignin into CB fillers lowered the viscoelastic loss of rubber composites, but lowered the tensile strength simultaneously [26]. Yu et al. reported the partial replacement of precipitated silica by lignin improved the processability, anti-flex cracking and anti-aging resistance of

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rubber composites, while decreased the tensile strength and hardness with the

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increased lignin loading [27]. As a result, nano-lignin is required for the potential application in rubber industry. Recently, researchers have reported the preparation of

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lignin/silica (LS) nanostructures from rice husk (RH) biomass [28-30]. The formation

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of hybrid material led to the lignin-silica interaction instead of the lignin-lignin or

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silica-silica self-aggregation, which benefited to reducing the particle size of lignin. Furthermore, hybrid fillers tend to develop synergistic effect and improve the filler

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dispersion in rubber matrix [31, 32], thus the formation of LS is expected to promote the utilization of lignin in rubber reinforcement.

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In this study, RH-derived LS nanostructures were prepared to substitute CB for rubber reinforcement. The particle size of lignin could be controlled in nanoscale by the formation of hybrid material. When 10 phr CB usage was substituted by LS nanostructures, the resultant vulcanized natural rubber (NR) exhibited comprehensive improvements in tensile strength, tear strength and abrasion resistance, compared with the vulcanized NR filled with CB only. The LS nanostructures showed a promising applications in green rubber industry and offered a strategy to convert biomass waste to high-value products.

2. Experimental 2.1 Materials RHs were collected from the rice field around Changchun City, China. They were washed with deionized water to remove the dust and then crushed into powders.

Journal Pre-proof Sodium hydroxide (NaOH), sulfuric acid (H2SO4) and hydrofluoric acid (HF) were purchased from Beijing Chemical Reagent Co. Polyethylene glycol-2000 (PEG-2000) was purchased from Guangfu Chemical Reagent Co. The chemical reagents were of analytical grade. CB N550 was purchased from Blackcat Carbon Black Inc., Ltd. (Jiangxi, China). Rubber additives, such as zinc oxide, stearic acid, paraffin, aromatic oil, anti-aging agent

N,

N’-diphenyl-p-phenylenediamine

(antioxidant

H)

and

poly(1,2-dihydro-2,2,4-ttimethyl-quinoline) (antioxidant RD), N-isopropyl-N’-phenyl

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phenylene diamine (4010NA), sulfur and N-(oxidiethylene)-2-benzothiazolyl

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sulfonamide (NOBS) of industrial grade were purchased commercially.

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2.2 Preparation of LS hybrid material

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Firstly, the hemicellulose of RHs was hydrolyzed by diluted H2SO4 solution to

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prepare D-xylose, which was widely used in the fields of food and pharmaceutical industry. The detailed experimental conditions were reported in our earlier study [33].

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Secondly, 50 g acid-treated RHs were mixed with 350 mL 8 wt% NaOH solution, followed by boiling for 4 h. The extraction solution was separated from the residues

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by vacuum-assisted filtration, followed by mixing with deionized water and ethanol at the volume ratio of 2:1:1 (extraction solution : deionized water : ethanol). Under magnetic stirring at room temperature, 1M H2SO4 was added drop-wise into the solution until silica started to precipitate (pH=9). Afterwards, 5 g PEG-2000 was added into the solution and mixed by ultra-sonication for 3 min, followed by continuous addition of 1M H2SO4 until pH=3. The solution was left statically for 30 min to form the assembly of lignin and silica. Finally, the LS product was collected by vacuum-assisted filtration, washed with deionized water to neutral and dried at 80 ℃ overnight. To compare the morphology, two controlled samples, pure lignin (Sample L) and pure silica (Sample S) were further prepared. Sample L was prepared from the silica-free RHs, in which we washed RHs using 40 wt% HF solution to remove silica and then repeated the synthesis procedure of LS nanostructures. Sample S was prepared by burning LS at 700 ℃ in air.

Journal Pre-proof Additionally, the major component in the alkali treated filtration residues should be cellulose, which could be utilized for paper manufacturing and the production of various cellulose derivatives such as cellulosic ethanol and cellulosic nanofibers.

2.3 Preparation of natural rubber vulcanizates The vulcanizates were prepared in two steps. In the first step, NR, fillers and other rubber additives were directly mixed in a laboratory internal mixer (model KY-3220 C). Total combined filler (CB+LS) loading was 50 phr, with the LS filler

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concentrations of 0, 10, 20, 30 phr. The detailed compounding formulation is shown

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in Table 1. In the second step, the compounds obtained in Step 1 was hot pressed at 140 °C under 25 MPa for 15 min. Finally, the vulcanizates were produced and their

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properties were tested after 24 h.

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2.4 Characterizations

The quantitative analysis of lignin and silica in the acid-treated RHs was based

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on the method to produce Klason lignin [34]. The detailed experiments were shown in Supporting Information and the resultant product, which was comprised of lignin and

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silica as well, was collected and labeled as K-LS. The yield of LS nanostructures was calculated as follows:

Yield =

𝑚𝑝 𝑚𝑅 ∙ 𝜂

× 100%

(1)

where mp is the mass of product, mR (50 g) is the mass of acid-treated RHs and η (51.8 wt%) is the mass percentage of lignin and silica in acid-treated RHs. The morphology and structure of LS were observed under a scanning electron microscope (SEM, HITACHI SU8020). The thermal stability was assessed by thermogravimetry analysis (TGA, TA Q500) in nitrogen atmosphere. The particle size was measured by a laser scattering particle size analyzer (Malvern Nano ZS90). The chemical groups were characterized by Fourier transform infrared spectroscopy (FTIR, Bruker Optics VERTEX 80V). The chemical structure of lignin was analyzed by solid state 13C NMR spectroscopy (Bruker AVANCE III 400 WB).

Journal Pre-proof The tensile strength and tear strength of NR vulcanizates were measured according to GB/T 528-2009 and GB/T 529-2008, respectively. The abrasion resistance was investigated by the use of Akron instrument in accordance with GB/T 1689-1998. The crosslinking density of vulcanizates was determined on the basis of solvent-swelling measurement. The vulcanizates were cut into 20 mm × 20 mm × 10 mm specimens. Subsequently, the specimens were immersed in toluene at room temperature for 7 days. The swelling ratio was calculated as follows: Wt - W0 W0

×100%

(2)

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Swelling ratio=

where the W0 and Wt are the weights of specimens before and after immersion,

1 V1

[

ln(1− 𝑉𝑟 )+ 𝑉𝑟 +𝑥1 𝑉𝑟2 1/3

Vr − Vr /2

]

(3)

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v= −

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respectively. Crosslinking density (v) was calculated using the Flory-Rehner equation:

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where V1 is the molar volume of toluene (106.2 cm3 g-1 mol-1) and x1 is the rubber-toluene interaction parameter (0.393). Vr is the volume fraction of rubber in a

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swollen network, which is calculated as follows: Wr /ρr

Wr /𝜌𝑟 + 𝑊𝑠 /𝜌𝑠

(4)

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Vr =

Where the Wr and Ws are the weights of dried rubber and the absorbed toluene,

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respectively. The ρr and ρs are the density of rubber and toluene, respectively. The dynamic thermal properties were investigated on an advanced dynamic mechanical analyzer (DMA, TA Instrument Q800) in a tension mode. The testing temperature ranged from -80 ℃ to 80 ℃ with the heating rate of 3 ℃ min-1, and the frequency was 10 Hz.

3. Results and discussion 3.1 Characterizations of LS hybrid material In order to understand the synthetic mechanism, pictures of synthesis process are shown in Fig. S1. Lignin and silica were firstly extracted from RHs by hot NaOH solution. In the brown alkali solution (Fig. S1a), silica was dissolved in the form of SiO32-. The long lignin macromolecules were hydrolyzed to shorter fragments through the cleavage of α- and β-aryl ether [35], which facilitated the rearrangement of lignin.

Journal Pre-proof As the H2SO4 was added drop-wise to pH=9, the color of solution turned to light brown and some precipitates appeared (Fig. S1b). Silica precipitated first at about pH=9 [29] and acted as a framework which significantly influenced the size and shape of the final particles. The water-ethanol mixture and PEG-2000 was used to facilitate the formation of spherical silica with uniform size distribution [36]. Subsequently, lignin started to precipitate at pH≈6 and the solution color became dark yellow (Fig. S1c). As the pH value dropped to 3 (Fig. S1d), lignin entirely precipitated on the silica surface and they assembled together via hydrogen bonds (as shown in Scheme 1). The

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resultant LS product was a yellow powder, a hybrid of brown lignin and white silica.

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LS contained 58 wt% lignin and 42 wt% silica measured by TG in air at 800 ℃. In addition, particle size analysis showed that LS had an average particle size of 320 nm,

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which demonstrated the LS nanostructure was successfully fabricated from the bulky

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RH biomass. The product yield was 69.5%.

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The morphology of LS was examined by SEM images. As shown in Fig. 1a and 1b, LS contained sphere-like particles with the size of ~300 nm, which is consistent

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with the results of particle size analysis. LS exhibited similar morphology as that of pure silica (Sample S, Fig. 1c), because silica acted as the framework of the hybrid

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material. Compared with pure silica, LS showed slightly rougher surface and more irregular shape. The rougher surface was attributed to the lignin coated on the surface, which confirmed the assembly of silica and lignin. Different from the LS and silica, the pure lignin (Sample L) has extremely irregular shape and a large particle size of above 5 μm (Fig. 1d), indicating lignin formed strong complexes without the silica framework. It is noteworthy that no bulky lignin particles were observed in the LS images, because the lignin was hydrolyzed into smaller fragments by NaOH solution and uniformly distributed on the silica spheres. This phenomenon implied that during the co-precipitation process, lignin preferred to interacting with silica than forming aggregates itself [37]. Besides that, the morphology of K-LS

(the lignin/silica

composites obtained by concentrated H2SO4 treatment of RHs) was shown in Fig. S2, which was much different from that of LS. The shape of K-LS was polygonal and the particle size was of several micrometers. These results indicated the fabrication of LS

Journal Pre-proof hybrid material was efficient to inhibit the aggregation and reduce the particle size. Chemical groups of LS was characterized by FTIR in the wavelength range of 4000 to 400 cm-1. In the FTIR spectrum (Fig. 2a), a strong absorption peak at 1087 cm-1 is assigned to the stretching vibrations of Si-O-Si. The peaks at 801 and 586 cm-1 are assigned to the stretching and bending vibrations of Si-O, respectively. The peak at 948 cm-1 is attributed to the presence of Si-OH. These peaks revealed the existence of silica, in accordance with the results of previous literatures [28, 38]. Additionally, the structures of lignin were also detected in the FTIR spectrum. A series of individual

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peaks between 1800 and 1300 cm-1 are presented in the inset image of Fig. 2a. The

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peak around 1710 cm-1 is assigned to the C=O groups. The peaks at 1600 and 1512 cm-1 are related to the aromatic skeletal vibration of lignin, while the peaks at 1462

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and 1423 cm-1 reflect the deformation vibration of C-H in aromatic rings [1]. Another

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group found at 1352 cm-1 is attributed to the C-O stretching. Moreover, two peaks at

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2931 and 2881 cm-1 indicate the C-H stretching of methyl and methylene groups. According to the FTIR spectrum, these absorption peaks indicated the co-existence of

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lignin and silica in LS hybrid materials. Furthermore, a broad peak at 3390 cm-1 is attributed to the presence of hydroxyl groups, which are necessary to bridge lignin

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and silica via hydrogen bonds.

Fig. 2b shows the 13C NMR spectra of LS nanostructures. The peaks in the range of 20 to 50 ppm are assigned to methyl and methylene groups. The intense peaks at 55 and 70 ppm are assigned to –OCH3 and –OCH2 groups, respectively [26]. The peaks at 115, 128 and 133 ppm are corresponding to guaiacyl units, p-hydroxyphenyl units and p-hydroxybenzoate substructures, respectively [39]. The peaks from 147 to 180 ppm are attributed to unsaturated CO groups including aldehyde and ketone groups. The TG and DTG curves are presented in Fig. 3 to show the thermal stability of LS and lignin. A small weight loss occurred below 150 ℃ due to the removal of absorbed water. The broad DTG peak in the range of 200-600 ℃ was mainly caused by the decomposition of lignin [40]. The methyl-aryl ether bonds were degraded in the temperature of 200-350 ℃, while the aromatic rings and side chains of lignin were degraded at around 450 ℃. Different from the pure lignin, LS exhibited an extra peak

Journal Pre-proof at 510 ℃, which was likely the result of lignin binding with silica [28]. The silica bound lignin showed increased thermal stability, leading to lignin decomposition at a higher temperature. DTG analysis indicated there was strong binding between lignin and silica.

3.2 Mechanical properties of NR vulcanizates The mechanical properties of NR vulcanizates filled with CB and LS fillers are listed in Table 2. The tensile strength, tear strength and abrasion loss of 50CB/NR

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were 19.9 MPa, 54.2 MPa and 0.463 cm3 respectively. When the LS hybrid fillers

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were introduced, 10LS/40CB/NR exhibited the best performance with the highest tensile strength of 23.3 MPa, the highest tear strength of 54.6 MPa and the lowest

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abrasion loss of 0.251 cm3 among all obtained vulcanizates. These superior properties

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compared with 50CB/NR indicated the introduction of LS enhanced the reinforcing

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effects of the blending fillers. As previously reported, both filler-filler network and filler-rubber interaction significantly contributed to the rubber reinforcement [6]. In

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this work, the enhanced rubber mechanical properties could be attributed to the following two factors. Firstly, it was easier for LS to form filler-filler interactions than

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CB via hydrogen bonds and dispersive forces, thus generating stronger filler network to complement the reinforcing effect of CB. Secondly, LS with 10 phr loading improved the filler-rubber interactions as well. Crosslinking density is an important parameter to evaluate the degree of filler-rubber interactions in vulcanizates. Fig. 4 shows 10LS/40CB/NR had a maximal crosslinking density, indicating the stronger filler-rubber interactions than other vulcanizates. The enhanced filler-rubber interactions were due to the nano-sized LS could be homogenously dispersed in the rubber matrix, which formed large contact area to interact with rubber chains. In addition, aromatic rings of lignin might provide - interaction with alkene of rubber molecules [41], leading to additional reinforcement. In consequence, both filler network and filler-rubber interaction were enhanced in 10LS/40CB/NR. When 10 phr CB was substituted by LS, the blending fillers exhibited the strongest synergistic effect in rubber matrix for much improved mechanical properties.

Journal Pre-proof When continuously increasing the LS loading, 20LS/30CB/NR showed a slight improvement in tensile strength and abrasion resistance, while 30LS/20CB/NR showed an overall decline in mechanical properties compared with 50CB/NR. The declined properties compared with 10LS/40CB/NR might result from the aggravated aggregation of LS. Fig. 5 shows the tensile fracture surfaces of vulcanizates filled with CB and LS in different ratios. It can be seen that there was no obvious difference in surface morphology between 10LS/40CB/NR and 50CB/NR, indicating 10 phr LS was well blended with CB and dispersed in the rubber matrix. However, on the

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surface of 20LS/30CB/NR and 30LS/20CB/NR, LS aggregated into particles of

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several micrometers in size. These large aggregates were pulled out of the rubber matrix, suggesting the fillers had poor absorption on the rubber chains. The filler

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aggregates would severely reduce the contact area with rubber chains, owing to the

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large particle size. Therefore, the 20LS/30CB/NR and 30LS/20CB/NR showed

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decreased crosslinking density, indicative of the weaker filler-rubber interactions. Fig. 4 shows the swelling ratio of the vulcanizates after immersed in toluene for 7 days.

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The increased swelling ratios of 20LS/30CB/NR and 30LS/20CB/NR reflected the large void spaces at the interfaces between filler and rubber matrix, which might

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cause poor filler-rubber interactions and act as flaws to initiate the rubber chain breakage. Moreover, the reduced CB proportion was the crucial cause of the decreased filler-rubber interactions. CB is a strong reinforcing filler with non-polar surface that could interact with rubber matrix to contribute an additional crosslinking network [42]. The high-proportion substitution of CB would decrease filler-rubber interactions, even though LS could enhance the filler network as a complement. On the other hand, the fillers containing hydroxyl groups would absorb the rubber additives and delay the vulcanization [27]. The higher loading of LS introduced the more hydroxyl groups, which caused the decreased crosslinking density. As a result, the optimal amount of LS was 10 phr, which balanced the reinforcement by increased filler network and filler-rubber interaction. The dynamic mechanical properties of various vulcanizates were investigated by DMA test. Fig. 6 shows the temperature dependence of loss factor tan δ from -80 ℃ to

Journal Pre-proof 80 ℃. At the glass transition region, the peak value of tan δ increased with the LS loading in the vulcanizates. The increased peak value of tan δ demonstrated the mobility of rubber chains was enhanced, which was resulted from the reduced interfacial interactions between rubber chains and fillers [43]. CB has a great capacity of winding rubber molecules by its branched structure [44], leading to stronger restriction of chain mobility compared with LS. Hence, the partial substitution of CB would release more rubber chains to participate in chain segment relaxation. Fig. 6b and 6c show the magnified tan δ curves near 0 ℃ and 60 ℃ respectively. For the tread

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rubber composites, the tan δ value at 0 ℃ reflects the wet skid resistance and the value

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at 60 ℃ reflects the rolling resistance [31]. The 10LS/40CB/NR exhibited a higher tan

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resistance but increased rolling resistance.

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δ value than 50CB/NR at both 0 ℃ and 60 ℃, indicating the improved wet skid

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4. Conclusion

In this study, a self-assembled LS hybrid material was prepared and used as the

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reinforcing filler. Lignin and silica extracted from RHs assembled into nanostructures by hydrogen bonds with an average size of 320 nm. The formation of LS

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nanostructures significantly reduced the particle size of lignin and promoted the potential application in rubber reinforcement. As the LS was filled into NR to substitute 10 phr CB, both the filler-filler interactions and filler-rubber interactions were enhanced. As a result, an increased reinforcement effect of the blending filler was observed. However, a greater LS substitution resulted in weaker reinforcement effect, due to the formation of filler aggregates and the decreased filler-rubber interactions. Hence, the 10LS/40CB/NR showed the best mechanical properties among the vulcanizates filled with LS and CB. LS was shown to be a promising bio-based filler to partially substitute CB, with the advantages of high reinforcing effect and low production cost.

Conflicts of interest The authors declared no conflicts of interest

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Acknowledgements This work was supported by the National Key Research and Development Program of China under Grant No.2016YFF0201204, and the Foundation of Jilin Kaiyu Biomass New Materials Co. Ltd.

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[41] C. Jiang, H. He, H. Jiang, L. Ma, D.M. Jia, Express Polymer Letters, 7 (2013) 480-493. [42] J.M. Chenal, C. Gauthier, L. Chazeau, L. Guy, Y. Bomal, Polymer, 48 (2007) 6893-6901. [43] Y. Li, B. Han, S. Wen, Y. Lu, H. Yang, L. Zhang, L. Liu, Composites Part A: Applied Science and

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Manufacturing, 62 (2014) 52-59.

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[44] Q.S. Fu, J. Chen, Z.X. Yu, R.S. Yang, Applied Mechanics and Materials, 496-500 (2014) 106-109.

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Figures

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Scheme 1 The preparation procedure of LS and the application in NR.

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Sample L.

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Fig. 1. SEM images of morphology of (a, b) LS hybrid material, (c) Sample S and (d)

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Fig. 2. (a) FTIR spectra and (b) 13C NMR spectra of LS.

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Fig. 3 TG and DTG curves of LS and Sample L.

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Fig. 4 Crosslinking density and swelling ratio of the vulcanizates filled with various

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LS substitution.

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Fig. 5. SEM images of the tensile fracture surfaces of (a) 50CB/NR, (b)

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10LS/40CB/NR, (c) 20LS/30CB/NR and (d) 30LS/20CB/NR vulcanizates.

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Fig. 6 Temperature dependence of loss factor tan δ of different vulcanizates.

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Tables Table 1 Compounding formulation of the NR vulcanizates. Materials

Compound (phr) 100

CB

50

40

30

20

LS

0

10

20

30

Stearic acid

2.5

Zinc oxide

5

Paraffin

1

Aromatic oil

6

4010NA

1.8

Antioxidant RD

1

Antioxidant H

0.3

NOBS

0.7

Sulfur

2.3

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NR

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Elongation (%)

Abrasion loss (cm3)

Tear strength (N/mm)

50CB/NR

19.9

942

0.463

54.2

10LS/40CB/NR

23.3

1257

0.251

54.6

20LS/30CB/NR

22.5

1471

0.436

42.0

30LS/20CB/NR

19.5

1567

0.523

36.2

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Samples

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Author Statement Manuscript title: Self-assembled lignin-silica hybrid material derived from rice husks as the sustainable reinforcing fillers for natural rubber Beichen Xue: Conceptualization, Methodology, Investigation & Writing - Original Draft Xiaofeng Wang: Conceptualization, Project administration, Supervision, Writing - Review & Editing Liyun Yu: Investigation

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Bing Di: Investigation

Yanchao Zhu: Resources & Investigation

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Xiaoyang Liu: Supervision, Writing - Review & Editing

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Zhixiao Chen: Investigation

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Highlights •The bulky rice husks (RHs) biomass was converted to lignin-silica nanostructures. •Lignin and silica were self-assembled via hydrogen bonds. •Silica acted as a framework to form spherical particles with the size of 320 nm.

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•Lignin-silica partially substituted carbon black with a better reinforcing property.