Synthesis and characterization of cellulose nanomaterials from

: Recycling plant-based materials for various applications not only reduces the harm to the


Introduction:
Since about 150 years ago, cellulose, the most prevalent renewable and naturally oc-34 curring polymer, has been utilized either directly as raw fibres or after being processed 35 [1]. Waste newspapers (WNPs) are being used more effectively as raw materials for a va-36 riety of applications because of the depletion of non-renewable resources. Standard waste 37 newspapers (WNPs), which contain inexpensive cellulosic material and make up a good 38 amount of municipal solid waste, are made of biomass resources. All over the world, mil-39 lions of tons of WNPs are produced and utilized, producing a sizeable amount of waste-40 paper. As a result of the cellulose content, WNPs, high-value cellulose-based materials 41 made from WNPs can offer an alternate form of recycling. history of use in a wide range of products, including paper, clothing, adhesives, textiles, 1 food, cosmetics, and pharmaceuticals [3]. The separation of nanocellulose from diverse 2 renewable sources and its use in technical applications have drawn more interest in the 3 development of nanotechnology [4,5]. The creation of cellulose nanocrystals (CNC) using 4 WNPs has recently attracted more attention for research studies. Recent years have seen 5 the publication of several studies utilizing nanocellulose as a reinforcing phase in bio-6 composite materials [6]. Only a few researchers have used old newspapers or newsprint 7 paper to create nanocellulose; as a result, more understanding in this field is desirable. In 8 this regard, on-site nanocellulose synthesis offers a highly interesting alternative. 9 Since Ranby initially isolated CNC in 1951 using cellulose fibres and sulfuric acid 10 hydrolysis, CNC has gained prominence [7]. In comparison to cellulose fibres, these CNC 11 have several benefits, including high strength, high surface area, special optical character-12 istics, lightweight, stiffness, etc. Its intrinsic renewability and sustainability have also re-13 ceived significant interest, in addition to its qualities and potential for wide application 14 [8]. 15 One of the promising preparation methods that have been thoroughly researched in 16 the literature is strong sulfuric acid hydrolysis. Acid hydrolysis preferentially targets the 17 disordered cellulose, leaving the crystalline cellulose as the ultimate CNC product. The 18 final CNC result was crystalline cellulose [9]. CNC has certain qualities that make it very 19 desirable for applications that add value, including a high elastic modulus, a profusion of 20 hydroxyl (-OH) groups [10], and chemical reactivity [11]. In numerous possible uses, in-21 cluding those in food, medicine, cosmetics, pulp, paper, reinforcing, and other special 22 function additives, cellulose nanocrystals (CNC) are emerging as a new material [12]. 23 The WNPs were deinked using a chemical pre-treatment in the current work that 24 included sodium hydroxide and hydrogen peroxide. The chemical makeup, fibre shape, 25 and brightness of the WNP were examined to improve the technological conditions for 26 deinking. The CNC was prepared using carefully controlled sulfuric acid hydrolysis. The 27 processed CNC is then characterized using techniques which include scanning electron 28 microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction 29 (XRD), Zeta potentials measurements and UV-Visible spectroscopy for further studies. Waste Newspapers (WNPs) from households were taken as raw material. Sodium 33 hydroxide (NaOH), hydrogen peroxide (H2O2), sulfuric acid (H2SO4), and sodium silicate 34 (Na2SiO3) were purchased from Merck (India). All other chemicals used in the study are 35 of analytical grade and purchased from standard agencies. 36   As represented in Figure 2, CNC was prepared by the chemical hydrolysis method. 3 The obtained dried WNPs were added into 100mL of 1 M sulfuric acid at 50ºC, with con-4 stant stirring. Then stir for 4hrs (say T2) and 6hrs (say T3) at 500 rpm and 50ºC. DI water 5 was added in plenty to terminate the reaction of sulfuric acid with WNP pulp, followed 6 by centrifugation of the suspension to remove the sulfuric acid. Further, filtered and 7 washed with DI water till neutralized. The obtained CNC was then dried and placed un-8 der vacuum conditions. 9 Figure 2. The process design represents acid hydrolysis of WNP pulp for 4hrs and 6hrs. 1g of the obtained dried WNPs was mechanically ground by ball milling for 4hrs (say 12 T4) and 6hrs (say T5) with 80g of 0.5 mm porcelain balls to obtain the CNC.  To determine the chemical makeup of the lignocellulosic components present in the 21 samples, FTIR analysis was used. Frontier 94942 technology was used (PerkinElmer, 22 USA). This instrument has a resolution of 2 cm -1 . 64 scans were performed using the at-23 tenuated total reflectance accessory to record the spectra between 400 and 4000 cm -1 . 24 2.2.3.3. X-ray diffraction (XRD): 25 Graphite monochromators and an auto-divergent slit on a Philips X'Pert MPD X-Ray 26 diffractometer with Cu-Kα radiation operating at 45 kV and 40 mA were used to obtain 27 X-ray diffraction (XRD) spectra. At a scanning rate of 1.5 o /min, XRD patterns were cap-28 tured from 10 to 80 o . The estimated crystal size of the nanocellulose distributed in water was determined 31 as the hydrodynamic radius. A dynamic light scattering system (ALV-CGS3) with a fixed 32 90 o scattering angle was used to gather the data. The laser used was a 22 mW HeNe po-33 larized laser with a 633 nm wavelength. 34 Using a ZetaPALS apparatus based on electrophoretic light scatting, the zeta poten-35 tials of CNC suspensions were measured. Three measurements were used to average the 36 data, which was done at a constant 25 °C.

UV-Visible Spectroscopic:
1 Spectroscopy in the UV-visible range was used to characterize the CNC. After dilut-2 ing the sample with ethanol, the UV-visible spectra of the solutions were measured to 3 determine the number of WNPs decreased chemically. A UV-vis spectrophotometer was 4 used to monitor the spectra of the CNC solution in the 200-700 nm wavelength range. To 5 change the baseline, ethanol was utilized as a placeholder. 6  14 the sample showed precipitation. It might be a sign that the resulting nanostructures 15 are unstable and that the precipitation happens because of aggregates being deposited. 16 The introduction of sulfuric acid in the CNC-chemical samples caused the amorphous 17 region to disintegrate and led to the grafting of negatively charged sulfate groups onto 18 the CNC surface. The colloidal suspension is stabilized by repulsive interparticle force 19 thanks to these findings [14,15]. Taking the stability of the nanostructures into considera-20 tion, the CNC-chemical is providing a better result. 21

X-ray diffraction (XRD):
22 Figure 4a shows the XRD spectra of the hydrolyzed samples T2 and T3. T2, hydro-23 lyzed for 4hrs had major diffraction peaks at 2θ = 23.15 against the lattice plane (002). The 24 T2 also showed some smaller peaks. In addition, the sample T3, hydrolyzed for 6hrs had 25 major diffraction peaks around 2θ = 23.31 for hkl-lattice at (002), together are some small 26 peaks present [16]. The presence of characteristic peaks in XRD for samples T2 and T3 27 confirms the formation of cellulose supporting the FTIR analysis. 28

Fourier transform infrared spectroscopy (FTIR)
The FTIR spectra of the samples T2 and T3 are displayed in Figure 4b. It illustrates 1 how the chemical makeup of the fibre changes over time. The modifications in the hy-2 droxyl and carboxyl sections are used to track variations related to the transition from 3 macro-to nanomaterials. The hydroxyl group and aliphatic saturated C-H stretching vi-4 brations of cellulose were responsible for the peaks at around 3336 and 2899 cm -1 , which 5 were found in all the samples [17]. The samples' spectra clearly showed the peak at about 6 1640 cm -1 connected to the O-H bending vibration of absorbed water. Regarding the po-7 tential effects of extractions on transmittance bands, smoothed peaks were seen between 8 1100 and 1500 cm -1 , an area where it is impossible to attach signatures for specific vibra-9 tions because complicated overlap effects may take place. The hemicelluloses and proteins 10 found in the cellulose fibre walls may also be the cause of these tiny peaks [18]. Each sam-11 ple has cellulose-typical spectra. Spectra of nanocellulose (CNC-chemical (T2, T3)) show 12 peaks at around 1040 and 910 cm -1 , which, according to the literature, indicate the purity 13 of the crystalline band of cellulose and have characteristics of C-O stretching vibration 14 and elongation of cellulose typical pulp -glycoside bonds, respectively [19]. It is significant 15 to notice that the recovered nanocellulose exhibits transmittance signals at around 1428, 16 1158, and 910 cm -1 , indicating that the majority of the nanocellulose produced was in the 17 form of the cellulose I structure, which is the form of native cellulose [20]. Thus, the FTIR 18 analysis confirms the formation of cellulose I in both samples T2 and T3.

Dynamic light scattering (DLS) and Zeta potentials measurements:
21 DLS is a useful tool for approximating the distribution of particle sizes in nano-sized 22 materials. In this approach, the CNC is modelled as spheres in Brownian motion. meas-23 uring the particles' hydrodynamic radius (RH) 21, which is equivalent to the translational 24 diffusion coefficient of the particles. The particle-size distribution of the CNC-chemical 25 and CNC-mechanical samples is depicted. 26 Although the potential is low i.e., -3.95 mV for T2 and -8.25 mV for T3 as in Table 1, 27 it is evident from the visuals in Figure 5, that there are charges surrounding the droplets. 28 The potential values have a negative sign because of the presence of a negative charge on 29 CNC-chemical because of the grafting as discussed earlier in SEM. Zeta potential meas-30 urements gave a conductivity for T2 and T3 of 0.388 mS/cm and 0.586 mS/cm respectively. 31 Higher zeta potential, as well as conductivity, is found for sample T3 as compared to T2.  Table 1. Zeta potential (mV) and conductivity for CNC-chemical, samples T2 and T3. 2

UV-Vis spectroscopic analysis:
3 Studies using UV-Vis ( Figure 6) can easily distinguish between the samples T2 and 4 T3. Substantial progress was made. Due to the -* and n-* excitations of conjugated phe-5 nolic groups, T2 exhibits two separate UV peaks (without any shoulders). While T3 has a 6 total of three peaks visible suggesting, having superiority. NaOH has a hypochromic ef-7 fect, which causes the primary absorption, which is typically around 280 nm, to shift to 8 200-220 nm [13]. In this study, CNC was isolated from waste newspapers. First, the newspaper is 3 deinked, followed by chemical and mechanical methods, for 4hrs and 6hrs to study the 4 effect of the time on the as-synthesized material. Observations done by SEM analysis of 5 CNC-chemical and CNC-mechanical suggested that both processes give different mor-6 phologies and tend to agglomerate. Formation of cellulose I can be confirmed by FTIR 7 analysis and XRD analysis for T2 and T3. Zeta potential measurements and UV-vis give a 8 better result for T3 as compared to T2. Where T3 has approximately double values for 9 potential and conductivity as compared to that of T2. Additionally, more peaks are pre-10 sent for T3 in UV-vis as compared to T2. Analyzing the samples with the help of the above-11 mentioned characterizations, although CNC-chemical sample T3 seems to be better than 12 other samples, further studies are required to establish this observation. The data presented in this study are available on request from the 22 corresponding author. The data are not publicly available because it is part of the study which will 23 be published in a full-length paper later.