From Biomass to Nanomaterials: A Green Procedure for

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From biomass to nanomaterials: A green procedure for preparation of holistic bamboo multifunctional nanocomposites based on formic acid rapid-fractionation Yongchao Zhang, Wenyang Xu, Xiaoju Wang, Shuzhen Ni, Emil Rosqvist, Jan-Henrik Smått, Jouko Peltonen, Qingxi Hou, Menghua Qin, Stefan M. Willför, and Chunlin Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05502 • Publication Date (Web): 14 Feb 2019 Downloaded from http://pubs.acs.org on February 15, 2019

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ACS Sustainable Chemistry & Engineering

From biomass to nanomaterials: A green procedure for preparation of holistic bamboo multifunctional nanocomposites based on formic acid rapid-fractionation

Yongchao Zhang,†,‡ Wenyang Xu,† Xiaoju Wang,*,† Shuzhen Ni,§ Emil Rosqvist,|| Jan-Henrik Smått,|| Jouko Peltonen,|| Qingxi Hou,‡ Menghua Qin,⊥ Stefan Willför,† and Chunlin Xu*,† †Johan

Gadolin Process Chemistry Centre, c/o Laboratory of Wood and Paper Chemistry,

Åbo Akademi University, Turku FI-20500, Finland ‡Tianjin

Key Laboratory of Pulp & Paper, Tianjin University of Science & Technology, Tianjin

300457, China §Jiangsu

Co-Innovation Center for Efficient Processing and Utilization of Forest Resources,

Nanjing Forestry University, Nanjing 210037, China ||Laboratory ⊥Organic

of Physical Chemistry, Åbo Akademi University, Turku FI-20500, Finland.

Chemistry Laboratory, Taishan University, Taian 271021, China

*Corresponding authors: E-mail: [email protected] (X. Wang); [email protected] (C. Xu)

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ABSTRACT To achieve full utilization of lignocellulosic biomass and easy integration of nanomaterials production, it is essential to develop an efficient fractionation to overcome the highly recalcitrant nature of lignocellulose and facilitate the subsequent valuable conversion. Herein, in a combined process based on the formic acid rapid-fractionation of bamboo chips, pure cellulose and lignin were firstly obtained as fractionated streams. As compared to wood Kraft pulp, the bamboo-originated cellulose was easily converted into cellulose nanocrystals (CNCs) using TEMPO oxidation in a relatively short time, which holds greater potential to meet the commercial cost target. The dissolved lignin was processed into nanoparticles (lignin-NPs), which exhibited spherical morphology and a uniform particle size distribution. Dispersions of CNCs and lignin-NPs were prepared and further filtrated to form nanocomposite membranes. The nanocomposite membranes exhibited a very smooth surface and homogeneous structure. Most impressively, at the CNCs/lignin-NPs ratio of 5, the tensile strength and Young’s modulus were improved by 44% and 47%, respectively, compared to the pure CNCs film. Owning to the presence of lignin-NPs, and the nanocomposites exhibited an effective antibacterial activity against E. coli. Keywords: bamboo, integrated treatment, cellulose nanocrystals, lignin nanoparticles, multifunctional nanocomposite

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INTRODUCTION Lignocellulosic biomass, the most abundant renewable natural resource on earth, offers an immense potential as a sustainable feedstock for the production of chemicals and materials.1,2 With the inevitable depletion of fossil fuels and the concerns related to their environmental issues, extensive research and development programs in lignocellulosic nanomaterials have been initiated to act in lieu of traditional nanomaterials that pose significant environmental hazard post-use.1,3,4 There is a wide range of applications for such environmentally biodegradable nanocomposites prepared from renewable natural nanomaterials, such as nanocellulose and lignin nanoparticles (lignin-NPs).4-6 From an industrial viewpoint, the direct conversion of raw lignocellulosic biomass is of great significance for the large-scale production of lignocellulosic nanocomposite. However, a key challenge for the commercialization strategy of lignocellulosic nanocomposite is the cost-competitiveness of the whole process relative to that of petrochemical routes, hence the efforts to integrate co-production process and to reduce the overall cost should be the research focuses. All methods that lead to different types of lignocellulosic nanomaterials (e.g., nanocellulose and lignin-NPs) depend on the treatment of raw materials. To prepare nanocellulose, the first treatment of the raw lignocellusic biomass is the delignification to remove lignin and hemicelluloses in order to overcome the recalcitrance and facilitate the subsequent processing. Sulfite, chlorite, diluted-acid, or alkaline solutions are commonly used in the delignification process, which is usually tedious and detrimental to the environment.7,8 Toward the process feasibility on an industrial scale, it is important to obtain cellulose and lignin of high purity with an effective fractionation method, which eventually facilitates the subsequent preparation of nanomaterials. Nowadays, as a new type of organosolv treatment protocol, formic acid rapid-delignification under pressure results in an efficient fractionation of lignocellulosic biomass into high purity cellulose, lignin with high chemical reactivity, and 3



hemicellulosic sugars.9,10 Equivalent delignification using common methods of ethanol pulping and alkaline pulping can only be achieved at higher temperatures with longer reaction time. To increase the techno-economic feasibility, a sustainable integrated biorefinery platform could be achieved based on the formic acid rapid-fractionation and the various fractionated components can be further converted into nanocellulose, and lignin-NPs as well as nanocomposites. Currently, numerous methods for producing cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) have been reported. Nanocelluloses are commonly produced from market wood pulp by mechanical fibrillation, chemical treatments, and enzymatic treatments; as well as a combination of two or several of the aforementioned approaches.11-13 The preparation procedures have a large impact on the intrinsic morphology and material properties of the resulted nanocelluloses. Typical preparations of CNCs involve a hydrolysis process subject to cellulosic materials in different acid solutions such as mineral acids, organic acids, and solid acids.14-18 Yet, certain issues regarding hydrolysis process or the related CNC products are existed, for example, strong corrosion, long reaction time, and less surface activity of products, etc. As a common method for producing CNFs, the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was also used to prepare CNCs.19,20 Zhou et al.20 successfully prepared CNCs from softwood bleached Kraft pulp using a 4.5 or 7 h TEMPO-mediated oxidation followed by a 3 h postreduction process with NaBH4. However, as a result of the limited reaction efficiency, relatively long reaction time or a higher chemical reagent input was also required. There is no doubt that these preparation procedures for nanocellulose substantially increase the production cost and negatively affects commercial utilization. As the most abundant aromatic polymer, the conversion of low value lignin by-products to its valorization is one of the key factors for developing an economically feasible integrated lignocellulose biorefinery.4 The preparation of lignin-nanoparticles (lignin-NPs) has been considered as the best way to build a promising versatile material platform for various 4


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downstream utilizations, especially in the emerging nanomaterial fields for enhancing UV barriers,21 antibacterial22 and antioxidant properties.23 Lignin-NPs have been fabricated by different methods, such as precipitation methods initiated with acids,24 CO2 saturation,25 solvent exchange,26 and dialysis,27 as well as by sonication28 and a water-in-oil microemulsion method.29 Among the available methods reported so far, acid precipitation is a technically and economically feasible route to achieve the green chemistry goals of benign products and processes. Furthermore, the production and application of lignin-NPs also present new market opportunities for various multifunctional nanocomposites. Among those nanomaterials, novel nanocomposite films based on lignin-containing cellulose fibers or nanocellulose have recently been developed to enhance the hydrophobicity, mechanical resistance, and oxygen-barrier properties of these materials. To achieve full utilization of lignocellulosic biomass and easy integration of nanomaterials production into current biorefinery concepts, we developed a combined method for the fabrication of novel biodegradable nanocellulose and lignin-NPs, as well as nanocomposites from lignocellulosic biomass based on formic acid rapid-fractionation. It is conceived that the formic acid rapid-fractionation will contribute to efficient fabrication of nanocellulose through TEMPO-mediated oxidation. Efficient recovery of formic acid can be accomplished by evaporation to achieve an environmentally sustainable system. The dissolved lignin and hemicellulose sugars can be easily separated by diluting the spent acid liquor. The precipitated non-sulfonated lignin can be directly used for producing lignin-NPs based on a pH change method from basic to acidic aqueous medium. The properties of the resultant nanocellulose (e.g., structure, morphology, and crystallinity) and lignin-NPs (e.g., morphology, size and Zeta potential against various pH) were comprehensively investigated. In an attempt to achieve a multifunctional nanocomposite and facilitate their application, dispersions of CNCs and ligninNPs were prepared and further filtrated to form nanocomposite membranes. The main objective 5



of the study is to demonstrate the feasibility of the combined process to integrate production of nanocomposite toward the manufacture at an industrial scale and large-scale commercial application. We envision this work reported here could open the door for building an integrated nanomaterials production platform from lignocellulosic biomass. EXPERIMENTAL SECTION Materials. Bamboo (Neosinocalamus affinis) chips (20–30 mm long, 10–20 mm wide, and 3–4 mm thick) were obtained from Sichuan Province in China and selected as the raw materials in this study. According to the NREL LAP method, the moisture content of the selected bamboo chips used in this study was 9.43%. The primary chemical compositions of the bamboo chips were detailed as follow: Klason lignin 25.56%, acid-soluble lignin 1.87%, xylan 21.96%, glucan 39.63%, ethanol-toluene extractives 2.10%, and ash 2.20%. Formic acid fractionation of bamboo chips. 100 g of dry bamboo chips was treated at a temperature of 145 ºC for 45 min using 85% (v/v) formic acid at a liquid/solid ratio of 7:1 (mL/g) in a jacketed Hastelloy alloy sealed reactor. When the reaction finished, the solid fraction (crude pulp, mainly cellulose) was filtered from the process liquor and washed with 85% formic acid and deionized water (85 °C) three times, respectively. The obtained pulp was screened with an 8-cut flat-screen to remove the rejects. The filtrate and the washing liquids were mixed together as spent liquor, and then evaporated in a rotary evaporator to recover formic acid. Then 10 volumes of distilled water were poured into the concentrated liquor to precipitate the dissolved lignin. The precipitate was centrifuged off, washed twice with distilled water, and dried. The supernatant was collected and concentrated using a rotary evaporator. The residue obtained was a hemicellulose-rich fraction. Preparation of lignocellulosic nanomaterials. Cellulose fiber obtained was bleached to 87 % ISO by a ECF (elemental chlorine free) sequence (D1EPD2P), where D stands for a

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chlorine dioxide stage, EP for an alkaline extraction with peroxide stage, and the P for a peroxide stage, according to our previous research.10 TEMPO-mediated oxidation process according to the literature method.30 Briefly, 2 g of dry bleached fibers were dispersed in 100 mL distilled water and stirred for 4.0 h at room temperature. 32 mg of TEMPO (0.1 mmol/g fiber) and 200 mg of NaBr (1.0 mmol/g fiber) were dissolved in 100 mL of distilled water, and then the solution were mixed with the dispersed fiber suspension and stirred at 300 rpm. Subsequently, the pH of the slurry was adjusted to 10.0 by dropwise adding 0.5 M NaOH. The oxidation was started by the addition of the desired amount of the 10% NaClO dropwise (10 mmol/g fiber). The total volume of the NaClO was added within the one third of the designated reaction time and the pH was maintained at 10.5 by adding drowise 0.5 M NaOH. When the desired reaction time (0.5 h–24 h) was reached, the reaction mixture was poured into 3 volumes of ethanol to precipitate the TEMPO oxidized cellulose. After the centrifugation at a speed of 3500 rpm for 10 min, the obtained cellulose gel was thoroughly washed with de-ionized water by filtration and the residual ethanol was removed by rotary evaporation. The oxidized cellulose was diluted to a consistency of 0.5%, and then fibrillated by a domestic blender (OBH Nordica 6658, Denmark) for 2 min at an output of 300 W. Finally, the obtained nanocellulose was stored at 4.0 ºC for further analysis. The carboxylate content of nanocellulose products was determined according to the literature method.30 Initially 1.0 g precipitated lignin was mixed with 150 mL milli-Q water, and the pH was increased stepwise to hit a final target pH value of 12.00 by adding 0.1 M NaOH under constant stirring (500 rpm). The sample was equilibrated for 5 min. Finally, lignin-NPs were formed by addition of 0.1 M HCl to reach the final pH value of 5.00. A particle diameter of 112.9 nm (zaverage) with a polydispersity index of 0.32 was measured. Nanocomposite films were prepared by mixing nanocelluloses and lignin-NPs suspension followed by dilution to 0.1% (w/v) during magnetic stirring (500 rpm) at room temperature for 7



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30 min. The total amount of dry substance in each film was kept constant at 300 mg. The compositional weight ratios of nanocellulose/lignin-NP in the nanocomposite films were 100, 10, 5, 2, and 1, respectively. About 300 mL of the suspension was filtrated on a nylon membrane filter with 0.1 µm pore size and 90 mm diameter (Sterlitech, USA). A nanocomposite film was obtained after drying in vacuum desiccator at 40 °C at a pressure of 88 mbar for 4.0 h. Characterization. The particle size distribution and Zeta potential of lignin nanoparticles obtained were analyzed by a Zetasizer Nano ZS instrument (Malvern Instruments Ltd., UK). All the samples suspensions with a concentration of 0.1 wt% were dispersed by ultrasonic bath (VMR, 80 W) for 10 min prior to analysis. The measurements were conducted in triplicates for each sample and runs of 10 and 13 were performed, respectively. The average data was reported after the analyses. FTIR spectra of freeze-dried nanocellulose, lignin and nanocomposite were recorded by a Thermo ScientificTM NicoletTM iSTM 50 FTIR Spectrometer (United States), respectively. Each spectra was collected with ATR mode in the absorbance mode from an accumulation of 36 scans in the range of resolution from 400 to 4000 cm-1 with a resolution of 4 cm-1. The samples for XRD measurements were prepared by pressing the freeze-dried nanocellulose into flattened sheets on a sample holder. The XRD spectroscopy (Bruker Discover D8, Germany) with a Ni-filtered Cu Kα radiation generated with an operating voltage of 45 kV and a filament current of 40 mA was used. The XRD patterns were obtained with the changing scattering angle (2 θ) from 10 to 40 ° (Scanning rate = 2 s/step, step size = 0.002 °). The crystallinity index (CrI), which was calculated using empirical Equation 1 shown as follows: CrI = (I200−Iam)*100/I200

(1)

Where I200 is the maximum peak intensity at lattice diffraction (200), Iam is the minimum intensity between planar reflections (200) and (110). 8


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The morphology of nanocelluloses, lignin-NPs and nanocomposite were evaluated using a JEM-1400 Plus TEM microscope (JEOL Ltd., Japan) with an accelerating voltage of 80 kV. The samples were dispersed by placing them in a sonicator for 5 min. 5 μL of dilute nanocellulose suspension (nanocellulose content of 0.1 mg/mL) was dropped onto a carbon supported copper grid, and then the sample was stained with 5 μL uranyl acetate solution (1 wt%) for 40 s. Afterwards, the excess liquid was carefully absorbed using filter paper, and the remaining solution formed an even layer on grid. The samples were completely air dried before imaging. The SEM images of the obtained films were taken with a LEO Gemini 1530 instrument with a Thermo Scientific UltraDry Silicon Drift Detector (SDD) (LEO, Oberkochen, Germany). The cross-sections were prepared by cryo-fracturing of the films after dipping in liquid N2. The nonconductive samples were sputter-coated with carbon prior to the measurements. Mechanical properties of composite films. The tensile strength, elongation at break, and Young’s modulus of the obtained films with ca. 5 mm width and 30 mm length were determined at a constant 5 mm/min strain rate using an Instron universal testing machine [Instron-33R4465, (Instron Corp., High Wycombe, England)] equipped with a static load cell of 100 N and a 20 mm gauge length. The mechanical testing was conducted at 23 ºC and 50 % RH in a climate room. The pre-run was first conducted on a rate of 2 mm/min until 0.1 N load was reached before the main run at 5 mm/min, so as to eliminate the error which is caused by loosely attached samples. The thickness and width of the specimen were measured using a micrometer (Lorentzen & Wettre, Kista, Sweden, precision 1 µm) and a digital caliper (Mahr GmbH 16ER, Germany, precision10 µm), respectively. Each sample was tested in at least ten specimen from three replicate films. Thermal Analysis. The thermal stability of the nanocomposites was investigated by a Thermal Gravimetric Analyser (Q600, TA instruments). The test samples of 4–6 mg, which 9



were vacuum dried at 40 ºC for 48 h in prior to the measurements, were heated in an aluminum crucible from ambient temperature up to 600 ºC at a heating rate of 10 ºC/min, while using a constant nitrogen flow as an inert atmosphere during the experiment. Antibacterial activity analysis. The antibacterial activity of the nanocomposites obtained was examined against E. coli ATCC 11229 (provided by Canadian Research Institute for Food Safety (CRIFS) at the University of Guelph). The ring-diffusion method was a qualitative approach to confirm the nonleaching effect of the film sample. The specific procedures are detailed as follow: 0.2 mL bacterial culture (106 CFU/mL) of Gram-negative bacterium Escherichia coli (E. coli) was spread on the LB agar plates, and then round pieces of nanocomposite samples were plated on the surface. After 12 h of cultivation in the incubator at 37 °C, the non-leaching effect was evaluated by examining whether there was any inhibition zone (ring) around the film sample. RESULTS AND DISCUSSION Formic acid treatment and preparation of lignocellulosic nanoparticles. Based on the integrated biorefinery concept, each component from lignocellulosic biomass should be significantly fractionated and this process should also facilitate the subsequent valorization of all the fractions obtained. As described in Figure 1, one-step rapid-fractionation using formic acid efficiently separates bamboo into three major components, namely cellulose pulp, lignin, and a hemicellulose-rich fraction. In such a fractionation process, 42.2 g cellulose pulp, 31.5 g crude lignin and 8.5 g hemicellulosic sugars could be obtained from 100.0 g of oven-dried bamboo chips, and only 0.50 g hydroxymethylfurfural (HMF) was detected, demonstrating that the rapid-fractionation using formic acid exhibited a good selectivity towards cellulose. To achieve valorization of main compositions and easy integration production into a modern biorefinery concept, the one-step rapid treatment strategy followed by TEMPO oxidation and

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acid precipitation for cellulose and lignin, respectively, was employed to produce nanocellulose and lignin-NPs. Furthermore, a nanocomposite film can be facilely prepared using the suspension of nanocellulose and lignin-NPs obtained from the integrated process. The characterization and property of the nanomaterials obtained will be discussed in the following text. Characterization of nanocellulose. Cellulose fibers were isolated by a formic acid rapidfractionation process combined with bleaching treatment prior to nanofibrillation. In the present study a commercial bleached Kraft pulp (KP) was evaluated as a reference for the preparation of nanocellulose. The nanocellulose samples prepared from reference KP and bleached formic acid pulp (FP) through different reaction time (5 h or 24 h) with TEMPO-mediated oxidation process were coded as (KP-CNFs, 24 h), (FP-CNCs, 5 h), and (FP-CNCs, 24 h). The nanocelluloses obtained via TEMPO-mediated oxidation were diluted and further characterized by TEM. The sample of (KP-CNFs, 24 h) displayed a spaghetti-like nanofibrous structure, consisting of CNFs with lengths below 1 µm and widths between 5–9 nm, as shown in Figure 2a. Meanwhile, the nanocellulose samples of (FP-CNCs, 5 h) and (FP-CNCs, 24 h) showed a morphology more similar to individual rods rather than fibrils, as seen in the Figure 2b and Figure 2c, respectively. Both nanocelluloses presented a length in the range of 80–300 nm and widths of 5–9 nm, which are similar to the dimensions of CNCs commonly obtained by sulfuric acid hydrolysis or TEMPO-mediated oxidation.19,31 The CNCs samples (FP-CNFs, 5 h; FPCNCs, 24 h) from FP could be well dispersed in water due to their high surface charge density and no fiber bundles were observed, indicating high efficiency for the nanofibrillation by combining formic acid rapid-fractionation and TEMPO-mediated oxidation. It also suggested that almost all individual particles had been peeled off from original formic acid fiber bundles with a 5 h TEMPO-mediated oxidation. It is feasible on an industrial scale to meet the technoeconomic requirements. 11



Figure 3a shows the FTIR spectra of three nanocellulose samples along with that of the original fibers, the characteristic peaks are identified as listed in Table S1. Most importantly, a strong band at 1604 cm−1 appeared in the spectra of all three nanocelluloses, which corresponded to the antisymmetric stretching of COO- in carboxylate salts, while this band was very weak in the spectra of both original Kraft pulp (KP) and formic acid pulp (FP). This suggests that the carboxyl groups were introduced on the nanocellulose after modification of KP and FP by TEMPO-mediated oxidation, which is in agreement with a previous report.16 The amount of carboxyl groups in the nanocellulose was quantified with respect to the reaction time in TEMPO-mediated oxidation. As displayed in Figure 3b, the carboxyl group content was originally 0.27 mmol/g in FP fiber and 0.16 mmol/g in KP fiber. The carboxylate content in both KP fiber and FP fiber showed a rapid rise within the initial reaction period of 5 h, followed by a slight increase up to 24 h and then leveled off. Under the same reaction conditions, the carboxylate content of the nanocellulose obtained from FP could reach 1.63 mmol/g with a 5 h reaction time, while that of the KP-CNF could only reach 1.58 mmol/g with a 24 h reaction time. The lower carboxylate content of KP-CNF is probably due to the higher hemicellulose content of the original fiber.30 As shown in Table S2, the hemicellulose content in the KP (16.3%) was higher than that in the FP (7.5%). It is suggested that most of the hemicelluloses have been sufficiently extracted by formic acid rapid-fractionation which gives in a relatively pure cellulose. Furthermore, the higher carboxylate content of nanocellulose is a crucial factor determining the dispersibility of the resultant nanocellulose in the suspension,16 which was in good agreement with the TEM analysis shown in Figure 2. The relative degrees of cellulose crystallinity in the nanocellulose samples and original fiber were evaluated by XRD analysis, as displayed in Figure 3c. All the diffractograms showed characteristic peaks around 2 θ = 16.5 ° and 22.5 °, which correspond to the typical cellulose I structure.32 The results indicate that the crystallinity index (CrI) of nanocellulose samples decreased compared to that in the original

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fibers. This may be due to oxidizing reagents possibly penetrating into the crystallites during TEMPO-mediated oxidation.33 In addition, the variation of CrI at the oxidation time 5 h and 24 h was minimal. Properties of lignin nanoparticles. The dissolved lignin and hemicelluloses in the spent liquor can be separated simply through precipitation by diluting the spent liquor with distilled water. The precipitated lignin was further used for producing lignin-NPs based on a solubility change under pH values from basic to acidic aqueous medium. The obtained lignin-NPs suspensions were analyzed for particle size, Zeta potential, and morphology. The variation of the ζ-potentials and hydrodynamic diameter of the lignin-NPs with increasing pH are shown in Figure 4a and Figure 4b, respectively. The lignin-NPs dispersions were stable in a broad pH range from 5.0 to 8.0, with a diameter of about 100 nm and ζ-potentials of around -25 mV. At pH < 5.0, the magnitude of the electrical double layer repulsion decreased significantly, due to the protonation of charged functional groups, which resulted in the aggregation of lignin-NPs. When the pH > 9, the particle size decreased to about 50 nm. The decrease in particle size can be attributed to the onset of the disassembly of the particle toward dissolution, where the complete dissolution occurred at pH > 12.0. Figure 5 shows TEM micrographs of lignin-NPs and it is clear that uniform particles in the range of 60–80 nm were formed under neutral conditions in water. The lignin-NPs presented clear boundaries and exhibited a spherical morphology. Meanwhile, the hydrodynamic diameter of the lignin-NPs suggested by DLS analysis were found to be larger than the particle size indicated in the TEM analysis, which was due to the formation of a hydration sphere around the lignin-NPs in water. Thus, the uniform particle size, spherical morphology and high stability of the lignin-NPs indicated that they might be promising candidates for producing holistic bamboo nanocomposites with nanocellulose obtained above.

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Preparation and characterization of functional nanocomposite films. In consideration of the techno-economic feasibility of the bamboo-based biorefinery, a full value chain of the lignocellulosic streams obtained from formic acid rapid-fractionation with integration of nanomaterials production was also explored. Nanocomposites based on cellulose nanocrystals (FP-CNCs, 5 h) and lignin-NPs with defined compositions were prepared from their aqueous dispersions by filtration. The direct preparation of all-bamboo-based nanocomposite membranes enables the full utilization of the fractionated streams. The nanocomposite membranes, in varied compositional ratios of CNCs and lignin-NP, were elaborately characterized with SEM, FTIR, and TGA, as well as their antibacterial activity and mechanical properties were investigated. SEM images (Figure 6) of the cross-sections of selected nanocomposite showed a multilayer network with numerous layers of CNCs surrounded by lignin-NPs compared to the pure CNCs film. This architecture indirectly suggested the lignin-NPs were homogeneously dispersed in the CNCs matrix without any visible aggregations. The top-view SEM images revealed a rather rough topography for the surface of pure CNCs film, while a very smooth and homogenous surface was formed with the interspaces in the CNCs network filled by the ligninNPs. Possibly, the strong interactions between CNCs and lignin-NPs, mainly arising from the hydrogen bonds formed among the abundant hydroxyl groups in both lignin and cellulose molecules contribute to the homogenous dispersity of lignin-NPs in the CNCs network.21,34 The results of FTIR (Figure S1), which was conducted on selected nanocomposites and starting materials, confirmed this hypothesis. It was shown that the –OH stretching band for the pure CNCs film and lignin-NPs shifted from a higher wavenumber to a lower wavenumber in the spectra of nanocomposite, indicating that hydrogen bonds were formed between the CNCs and the lignin-NPs.4

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Mechanical properties are essential for the utilization of these nanocomposite films to meet the requirements of various applications. The tensile strength, the elongation at break, the Young’s modulus, and thickness for the nanocomposite films of CNC/lignin-NPs at various compositional ratio are reported in Table 1. The incorporation of lignin-NPs tended to increase the tensile strength and Young’s modulus of the nanocomposite films. The CNCs/lignin-NPs film with a compositional ratio of 5, gave the highest values of tensile strength, Young’s modulus and elongation at break at 91.84 MPa, 7.24 GPa and 2.86%, which were much higher than those for the pure CNCs film at 63.15 MPa, 4.94 GPa and 2.52%. The lignin-NPs reinforced the CNC films owing to the strong hydrogen bonds which allow good interfacial adhesion between CNCs and lignin-NPs.21,34 It is acknowledged that thermal properties of the nanocomposites also play an important role in determining the downstream processability and usability of the composites. Thus, thermogravimetric analysis (TGA) was subsequently conducted on selected sample films. As shown in Figure 7a, TGA results show that the thermal stability of the nanocomposite films was significantly improved with increasing the incorporated lignin-NPs content, as compared to those of the pure CNCs film. The nanocomposite samples are observed to have similar decomposition profiles and the degradation of the nanocomposites takes place in two stages, as indicated in the derivative TG curves (Figure 7b). The first decomposition temperature (T1) is around 260 °C and the second decomposition temperature (T2) is around 315 °C, which corresponds to the degradation of the polymer backbone. The nanocomposite with the CNCs/lignin-NPs compositional ratio at 2 revealed higher T1 and T2 when compared to the film with the CNCs/lignin-NPs compositional ratio at 5. The enhanced thermal stability of these nanocomposites as the increased content of lignin-NPs can be attributed to molecular interactions formed between CNC and lignin-NPs.35

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The inhibition zone tests on the nanocomposites against E. coli are visually displayed in Figure 8. As presented, the nanocomposite film with varied CNCs/lignin-NPs ratio at 10, 5, 2 and 1 all formed inhibitive holes with the diameters ranged in 9–16 mm. Whereas, the pure CNCs film showed no inhibitive zone. Clearly, the incorporation of lignin-NPs significantly imposed the nanocomposites with antibacterial activity against E. coil. Generally, the biocidal activity by the antibacterial agent is expressed on its attacking on the bacterial cell membrane and thus induces the formation of pores with consequent release of cell content that causes the final lysis of bacterial cells. Indeed, while lignin could be used as an innovative antimicrobial natural material, its antibacterial properties comes from its original source; Phenolic compounds and the presence of certain functional groups with oxygen in its structure has been ascribed to its antibacterial performance.36 Therefore, all-bamboo-based nanocomposite films with high mechanical performance, high thermal stability, and efficient antibacterial activity could be prepared from CNCs and lignin-NPs by such a fast and economically-feasible approach, offering an excellent potential to substitute petrol-based chemicals in a broad spectrum of applications, such as packaging. CONCLUSION To increase the technical and economic feasibility, using a combined process based on formic acid rapid-fractionation, a full utilization of lignocellulosic biomass and easy integration of nanomaterials production to convert raw lignocellulose into nanomaterials can be achieved using a combined process based on formic acid rapid-fractionation. Pure cellulose, lignin, and hemicelluloses were firstly fractionated. It is indicated that formic acid rapid-fractionation contributed to efficient fabrication of nanocellulose through TEMPO-mediated oxidation in a relatively short time in comparison to wood Kraft pulp. The precipitated non-sulfonated lignin was directly used for producing lignin-NPs which exhibited spherical morphology and a uniform particle size distribution. The all-bamboo-originated nanocomposite membranes based 16


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on the CNCs and lignin-NPs possessed a very smooth and homogenous surface, and also showed superior tensile strength, thermal stability, and effective antibacterial activity as compared to pure CNCs-based membranes. The full transformation of lignocellulose with this combined process is of great significance for the building of a promising versatile material platform in the emerging nanocomposite fields to meet the green chemistry principles and the commercial cost target. ACKNOWLEDGEMENT The authors would like to acknowledge financial support from the China Scholarship Council, the Graduate School of Chemical Engineering, Fortum Foundation, the Independent Innovation

and

Achievements

Transformation

Project

of

Shandong

Province

(2014CGZH0302), and the Yellow River Mouth Scholar Program (DYRC20120105). This work is also part of the activities within Johan Gadolin Process Chemistry Centre, the Center of Excellence appointed by Åbo Akademi University during 2015-2018. ASSOCIATED CONTENT Supporting Information Supplementary data associated with this article can be found, in the online version. REFERENCES 1. Nascimento, D. M.; Nunes, Y. L.; Figueirêdo, M. C.; de Azeredo, H. M.; Aouada, F. A.; Feitosa, J. P.; Rosa, M. F.; Dufresne, A. Nanocellulose nanocomposite hydrogels: technological and

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Figure captions Figure 1. A schematic process flow diagram illustrating the preparation of nanocellulose and lignin nanoparticles based on formic acid rapid-fractionation for producing multifunctional nanocomposite films. Figure 2. TEM images of nanocellulose prepared from different types of original fiber though TEMPO-mediated oxidation. (a) (KP-CNFs, 24 h); (b) (FP-CNCs, 5 h); (c) (FP-CNCs, 24 h). Figure 3. (a) FTIR, (b) carboxylate contents and (c) XRD spectra of nanocelluloses compared with that of the original fiber. Figure 4. Surface charge related properties of lignin nanoparticles: (a) ζ-potentials of the lignin nanoparticles as a function of pH. (b) Effect of pH on average hydrodynamic diameter of lignin nanoparticles. Figure 5. TEM images of lignin nanoparticles with different magnifications. Figure 6. SEM images of nanocomposite film: surface (top row) and cross section (bottom row). Figure 7. Thermal stability of different nanocomposites produced under the various CNCs/lignin-NPs ratio: (a) TGA weight loss; (b) TGA temperature derivative weight loss. Figure 8. Inhibition halos measured and spot diffusion assay of nanocomposites tested toward E. coli.

23



Page 24 of 42

Table 1. Young’s modulus, tensile strength, elongation at break, and thickness of composite films with different ratio of CNCs/lignin-NPs. CNC/lignin

tensile strenth

elongation at break

Young’s modulus

thickness

-NPs

(MPa)

(%)

(GPa)

(µm)

100

63.15±4.2

2.52±0.2

4.94±0.01

95.9±2.1

10

82.70±0.3

2.62±0.2

6.53±0.02

70.6±1.9

5

91.84±0.3

2.86±0.3

7.24±0.01

70.2±1.2

2

69.70±4.3

1.39±0.3

6.23±0.1

69.6±1.1

1

66.03±3.7

1.62±0.1

5.62±0.02

67.1±1.4

24


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Figure 1.

25



Figure 2.

26


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Figure 3.

27



Figure 4.

28


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Figure 5.

29



Figure 6.

30


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Figure 7.

31



Figure 8.

32


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Abstract Graphic:

An integrated borefinery process based on formic acid rapid-fractionation offers an extended route for valorizing feedstock in a form of multifunctional all-bamboo-nanocomposites.

33


ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Biomass

Page 34 of 42

Biodegradation 200 nm

Nanocomposite film

200 nm

Cellulose Base

Formic acid treatment

Solvent Recycling

Nanocellulose

Mixing

Acid

Dispersion 200 nm

Lignin

Lignin nanoparticles


Page 35 of 42


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a

500 nm

b

200 nm

c

200 nm



Figure 3


Page 36 of 42

Page 37 of 42

20

a

Lignin NPs

Zeta potential (mV)

10 0

-10 -20 -30 -40 -50

1000

b

2

4

6

8

10

12

Lignin NPs

150 125

Average diameter (nm)

1200

Average diameter (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

800 600

75 50 25 0

400

4

5

6

7

8 9 pH

10

11

12

200 0

2

4

6

pH


8

10

12


Page 38 of 42

a

200 nm

b

100 nm


Page 39 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) CNC film

(b) CNC/lignin-NPs (5:1)


(c) CNC/lignin-NPs (2:1)


a

100

Weight residue (%)

90 80 70 60 50 40 30

CNC film CNC/Lignin-NPs (5:1) CNC/Lignin-NPs (2:1)

-1

dm/dt (mg*min-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 42

-2 -3 -4 -5 -6

b 50 100 150 200 250 300 350 400 450 500 550 Temperature (°C)


Page 41 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) CNC film


(b) CNC/lignin-NPs (c) CNC/lignin-NPs (d) CNC/lignin-NPs (e) CNC/lignin-NPs (2:1) (10:1) (5:1) (1:1)



TOC 405x281mm (150 x 150 DPI)


Page 42 of 42

From Biomass to Nanomaterials: A Green Procedure for

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