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Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob
Materials Today: Proceedings xxx (xxxx) xxx
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Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob H.K. Singh a, T. Patil a, S.K. Vineeth a, S. Das b, A. Pramanik b, S.T. Mhaske a,⇑ a b
Department of Polymer and Surface Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India Strategic Science Group, Unilever R & D Bangalore, 64, Main Road, Bangalore 560066, India
a r t i c l e
i n f o
Article history: Received 17 August 2019 Received in revised form 5 December 2019 Accepted 8 December 2019 Available online xxxx Keywords: Corn stover Corn cover Corn cob Acid hydrolysis Optimization parameters Microcrystalline cellulose
a b s t r a c t This study investigates the isolation of microcrystalline cellulose (MCC) from corn stover biomass by acid hydrolysis method with aiming towards its constituents viz; corn cover and corn cob. The process comprises chemical treatments with varying concentrations to optimize the concentrations of chemical reactants. The cellulose crystals produced with optimized concentrations of 2% w/v NaOH, 2% w/v acidified NaClO2 and 10% v/v H2SO4 gives the yield of 25.90%, 29.60% and 39.32% of cellulose from corn cover, corn cob and corn stover respectively. The isolated needle-shaped MCC from corn stover showed the particle dimension in the range of 1.3–2.5 mm solely with a narrow distribution. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
1. Introduction In the last decade, the increasing concern towards environmental degradation has attracted considerable interest in the development of new types of green bio-based, green and degradable materials from various natural sources. This is purposely to find out an alternative of non-renewable and non-biodegradable materials due to their harmful effects on the environment [1,2]. In consequence to this, cellulose has been found as one of the most abundant biopolymers having applications in various fields because of its outstanding properties such as biodegradability, biocompatibility and availability [3,4]. This is long-chain, high molecular weight polysaccharide composed of repeated units of dimers or disaccharides of the anhydro-D-glucopyranose unit (AGU), known as cellobiose. Each anhydro-D-glucopyranose unit is connected by b-1,4 glycosidic linkage and every other monomer is rotated 180° concerning its neighboring unit [5,6]. The properties of isolated cellulose are affected by the source of cellulose and their isolation method. This, in turn, gives rise to two main class of cellulose viz; micro and nano cellulose. Isolated cellulosic materials with one dimension in the nanometer range are referred to generically as nanocellulose [7]. The recent studies for
⇑ Corresponding author.
the isolation of cellulose from various biomasses with novel forms such as crystallites, nanocrystals, whiskers, nanofibrils and nanofibers are generating much activity for its potential applications in various fields viz; building materials, cosmetics, medicines, food packaging, ultrafiltration membranes, food stabilizer, functional food ingredient, bio-medical, reinforcing agent for making nanocomposites, emulsion, dispersion, paper and paperboard, etc [8–10]. There are several studies reported for isolation of cellulose material by chemical pretreatment steps from various bio sources e.g.; the isolation of nanocellulose particles and rods by acid hydrolysis with 60% H2SO4 utilizing sugarcane bagasse, raw cotton linter and mengkuang leaves has been reported [11–14]. Furthermore, cellulose material with nanocrystalline morphology from forestry residues has been obtained by Moriana et al. [15] via acid hydrolysis with 65% H2SO4 and pretreatment steps including 4.5% NaOH and 1.7% aqueous chlorite solution. Maiti et al. [16] prepared nanocellulose by employing China Cotton, South Africa cotton and Waste tissue paper by means of acid hydrolysis with 47% H2SO4. Additionally, whisker and rod shaped cellulose nanocrystals has also been prepared from rice husk, grape skins, oil palm trunk, Ushar seed fiber and tomato peels by utilizing 64% H2SO4 [17– 21]. Apart from the utilization of varying concentration of strong acid the studies are frequently reported for using the varying concentration of alkali and bleaching agents also for removal of non-
E-mail address: [email protected] (S.T. Mhaske). https://doi.org/10.1016/j.matpr.2019.12.065 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx
cellulosic components [22]. Even though all these studies report the successful isolation of cellulose material of different morphologies but its large-scale production will always demand the better optimization of reaction conditions viz; reactant concentrations, reaction time, temperature and product yield. Among the various biomasses, corn stover is one of the major agricultural raw materials with its composition comprising about 40–45% cellulose, 25–35% hemicellulose and 7–10% total lignin of its dry weight along with other non-structural components like moisture, ash and extractives [23,24]. The significant abundance of corn stover material is found in India, where it is obtained from the third most important crop maize after wheat and rice [25]. Although, a considerable amount of literature has been published on the extraction of cellulose from corn stover, but information regarding cellulose extraction from its components remains lacking. With this point of view, the novelty of current works lies in determining individual cellulose contents of corn cover and corn cob followed by extraction and characterization of micro cellulose from its mixed composition also i.e.; corn stover by acid hydrolysis method taking consideration of minimum chemical concentration utilization for the removal of non-cellulosic components and isolation of cellulose.
(4000 rpm, 20 min). All the experiments were performed thrice to check the repeatability of the reactions. The determination of the chemical composition of raw corn stover constituents viz; corn cover and corn cob was done as per the standards (TAPPI 2000), (TAPPI 222 88-m) and (TAPPI T19 m54). The FTIR spectra of all the samples were recorded using Bruker Alpha FTIR, USA spectrophotometer with 24 scans at a resolution of 4 cm1 and wavenumber range of 4000–500 cm1, using the KBR pellet method at room temperature. The crystalline nature of the samples was determined by XRD (Rigaku, Miniflex, Japan) by placing the samples on a glass slide and spectra were recorded using Cu Ka radiation at 30 kV and 15 mA with scanning in the 2h range of 2–80°. The scan speed was 2.00°/min with a resolution of 0.02°. The particle size distribution measurements were carried out by Nanoplus zeta/nanoparticle analyzer (Particulate system, USA) instrument using water as a dispersant media. An optical microscope (Olympus, BX41, Japan) was used to observe the samples and the morphology of the fibers was captured by digital imaging software. The Thermogravimetric Analysis was performed using Pyris 1 instrument of Perkin Elmer. The tests were carried out with samples weight of around 5–10 mg at the temperature range of 30–600 °C with a heating rate of 10 °C/min under nitrogen atmosphere.
2. Experimental details 3. Results and discussions 2.1. Materials 3.1. The chemical composition of corn stover Corn stover used was obtained from the local market in Mumbai, India. Sodium hydroxide (Analytical Grade, 98.00%), sodium chlorite (Analytical Grade, 80.00%), acetic acid (Analytical Grade, 99.50%), sulphuric acid (Analytical Grade, 98.00%) were procured from S.D. Fine chemicals Ltd. Mumbai. 2.2. Isolation of microcellulose (MCC) from corn stover Prior to isolation of micro cellulose, corn cover and corn cob were separated, washed with hot water several times to remove the aqueous soluble extractives, impurities, waxy substances and oily layers, dried at 100 °C and used for the further treatment. Micro cellulose was isolated from corn cob and corn cover separately and in a mixture (corn stover) also. The dried biomass was subjected to alkali treatment through proper optimization using the varying concentration of NaOH i.e.; 0.5%, 1.0%, 2.0% and 5.0% w/v to remove the hemicellulose and other impurities. The mixture of fiber to liquor ratio of 1:40 for each concentration of NaOH was mechanically stirred at 200– 300 rpm at 60 °C for 5 h. Finally, the biomass was washed with distilled water until it got free from alkali and dried at 70 °C to constant weight. The optimized alkali-treated fibers were subjected to bleaching to remove the lignin by use of sodium chlorite at acidic pH. The biomass was treated with two different concentrations of sodium chlorite i.e.; 1% and 2% w/v for proper optimization at acidic pH 4.0–4.5 maintained by buffer solution of sodium acetate/acetic acid (1:3). The reaction was stirred at 200– 300 rpm at 80 °C for 4 h with maintaining the fiber to liquor ratio of 1:40. The bleached biomass was further subjected to acid hydrolysis to get the suspension of micro cellulose crystals. The hydrolysis was performed by using 10% v/v concentration of H2SO4 keeping fiber to solution ratio of 1:100 for 6 h at 80 °C with mechanical stirring at 600–700 rpm. After completion of hydrolysis, the reaction was stopped by adding five-fold of ice-cold water and mixture was neutralized by a concentrated sodium hydroxide solution. The resulting cellulose crystals were washed repeatedly to remove the salt formed and separated through centrifugation
The yields of non-cellulosic chemical constituents during the cellulose extraction depend upon the source of biomass and methodology of isolation. The chemical composition of the noncellulosic and cellulosic constituent was achieved separately for corn cover and corn cob based on the study from TAPPI standards and presented in Table 1. 3.2. Extraction yields of non-cellulose and micro cellulose from corn cover, corn cob and corn stover During the cellulose production from raw biomass, the optimization of chemical treatment becomes mandatory since the use of higher concentration could affect the strength of cellulose. For optimum removal of hemicellulose and lignin, 2% w/v NaOH and 2% w/v NaClO2 was found to be optimal concentrations respectively. This can be justified based on yields comparison obtained on the basis of TAPPI standard treatments (Table 1) and optimized concentration treatments (Table 2). In order to get the cellulose crystals, the bleached biomass was further hydrolyzed by the minimum concentration of acid (10% v/v H2SO4). The so obtained yields of non-cellulosic and cellulosic components as per optimized chemical concentrations are depicted in Table 2, which gives good repeatability and further clears that optimized concentrations are well in agreement with the studies reported in the literature. It further justifies that corn cover and corn cob individually comprises 25.90% and 29.60% of cellulose respectively, which was further obtained as 39.32% cellulose during isolation from corn stover. Fig. 1 shows the images of utilized corn stover biomass and so
Table 1 Chemical composition of corn cover and corn cob after TAPPI standard treatments. Components
Corn Cover (wt%)
Corn Cob (wt%)
Hemicellulose Lignin Cellulose
51.44% 12.86% 24.87%
48.88% 14.40% 32.60%
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 2 Chemical composition of corn cover, corn cob and corn stover after optimized chemicals treatments. Components
Corn Cover (wt%)
Corn Cob (wt%)
Corn Stover (wt%)
Hemicellulose Lignin Cellulose
55.87% 15.85% 25.90%
47.55% 11.40% 29.60%
41.52% 7. 59% 39.32%
obtained cellulose material. Literature studies report varying reaction conditions for cellulose isolation viz; concentration of chemicals, reaction time and temperature. But this study focuses on utilizing minimum chemical concentration so that aspects of green chemistry to make a greener chemical process with least waste and avoiding the post-treatment of unutilized reactants and solvents can succeed. 3.3. FTIR analysis Fig. 2 depict the FTIR spectra of raw corn cover, corn cob, alkalitreated form, bleached form and acid hydrolyzed cellulose. The band at 3340–3420 cm1 is related to the stretching of H-bonded OH groups and the peaks near 2920 cm1 to CAH stretching. For raw biomass, the peak intensity of AOH group was found with less intensity due to the presence of other non-cellulosic components like waxes, hemicellulose and lignin which inhibits its exposure. A very weak shoulder at nearly 1730 cm1 in raw biomass is indicative of acetyl and uronic ester group of the trace amounts of hemicellulose which is seen in the untreated sample and completely disappeared due to its removal after alkali treatment [26]. This indicates that optimized 2% w/v concentration of NaOH is optimum for the removal of hemicellulose. The band at nearly 1640 cm1 is due to the OH-bending of absorbed water and indicates exposure of the OH group. The peak at 1430 cm1 is due to ACH2- bending and is a crystalline peak of cellulose. In addition, the vibration peak at 1372 cm1 is related to bending of CH and CO bonds in polysaccharide aromatic rings [27]. The peak obtained at 1254 cm1 presents the CO out-of-plane stretching of aryl groups in lignin [15]. The 899 cm1 bands in all samples represent the glycosidic CH deformation and OH bending, which are known characteristics of b-glycosidic linkages between anhydroglucose units between cellulose units [26].
crystalline and amorphous regions shows the change in crystallinity on removing the noncellulosic components through chemical treatment. It can be noted from the diffractograms that there is an increase in peak intensity, which could be assigned to the dissolution of noncellulosic polysaccharides. The gradual removal of non-crystalline materials transformed the nature of biomass to more crystalline one [26]. All the diffractograms show welldefined peaks around 2h = 16.1° with a sharp peak at 2h = 22.5°, which are characteristic peaks of cellulose [11]. From the X-ray diffraction patterns, the crystallinity index of the samples was calculated using the following formula:
Crystallinity IndexðIcÞ ¼
Icrystalline Iamorphous 100 Icrystalline
where Icrystalline is the height of the peak at 2h = 22.5° and Iamorphous is the peak height at 2h = 18°. The so obtained values of crystallinity index of corn stover biomass treated at various steps of chemical treatment are as; raw biomass-58.88%, alkali-treated biomass-80.22%, bleached biomass-84.36% and acid hydrolyzed cellulose-91.26%. In the pretreatment steps, the alkali and bleach treatment with optimized concentration leads to removal of cementing materials like lignin, hemicellulose and pectin, which increases the percent crystallinity. These results indicate that isolation of cellulose from corn stover biomass with the optimized concentrations in the pretreatment steps leads to optimal removal of non-cellulosic components with the maximum crystallinity of isolated cellulose. 3.5. Particle size distribution analysis The isolated microcrystalline cellulose was subjected to evaluate its particle size employing DLS technique. The particle size distribution of the cellulose mainly depends upon its source and method of isolation viz; type of acid, acid concentration, reaction time, temperature, the process of hydrolysis and mechanical treatment. Fig. 4 shows the particle size distribution of the isolated cellulose with the acid concentration of 10% v/v. The distribution depicts that after chemical treatment, the obtained size of cellulose ranges from 1.3 to 2.5 mm. On the basis of the histogram, it can be concluded that almost 100% of the cellulose under study falls under micro range justifying the presence of microcellulose.
3.4. XRD analysis
3.6. Morphology analysis
Fig. 3 shows the X-ray diffraction analysis of the corn stover biomass at different stages of chemical treatment and modification. The raw biomass which is mainly constituted of
Optical microscopy (OM) analysis has been carried out to observe the morphology of the isolated microcellulose, which is depicted in Fig. 5. The OM images for isolated cellulose showed
Fig. 1. Images of the raw corn stover biomass and isolated microcrystalline cellulose.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 2. FTIR spectra of raw corn cover, corn cob, its alkali-treated form, bleached form and acid hydrolyzed cellulose.
needle-shaped crystals. The surface was found to be rough, which could be assigned to the removal of structural components. The image reveals the existence of larger size cellulose crystals with the diameter in the range of micrometers. The so obtained results are well supported by particle size measurement which depicts that almost 100% of total particles are present in the range of 1.3–2.5 mm. 3.7. Thermal analysis
Fig. 3. XRD patterns of raw corn stover, alkali-treated form, bleached form and acid hydrolyzed cellulose.
The comparative thermal decomposition parameters of raw corn stover, alkali-treated corn stover, bleached corn stover and acid hydrolyzed corn stover were investigated by TGA and DTG curves which are shown in Fig. 6. The initial weight loss of 5– 18 wt% in the range of 30–125 °C could be assigned to the removal of moisture for all the samples. The peak obtained near 150 °C could be due to the evaporation of low molecular weight compounds which are remaining from isolation steps. The other main degradation observed between 250 and 400 °C is related to the thermal degradation of the samples [28]. Almost similar thermal behavior has been seen in all the samples except acid hydrolyzed corn stover during the cellulose isolation steps. It is clear that second decomposition started at 203.3 °C for raw corn stover, 209.2 °C for alkali-treated corn stover, 224.9 °C for bleached corn stover and 236.1 °C for hydrolyzed corn stover. The increment in the thermal
Fig. 4. Particle size distribution of isolated MCC from corn stover.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Fig. 5. Morphology of isolated MCC from corn stover.
Fig. 6. TGA and DTG curves of raw corn stover, alkali-treated, bleached and acid hydrolyzed cellulose.
stability of 5.9 °C for alkali-treated corn stover, 21.6 °C for bleached corn stover and 32.8 °C for hydrolyzed corn stover with respect to raw corn stover could be assigned to the decomposition and removal of hemicellulose, lignin and increase in crystallinity which results in high thermal stability [29]. This is in agreement with the XRD analysis which showed the increase in the crystallinity of the chemically treated corn stover and isolated cellulose as compared to the raw corn stover. Similar results were reported by Rambabu et al. [30], where they reported the isolation of cellulose from the raw pinecone. Alemdar et al. [31] has published similar studies for the wheat straw and soya hull also. The parallel thermal profile was observed in DTG curves also accept the absence of a peak at nearly 275–300 °C for isolated cellulose which reflects that profile of cellulose shifts to a higher temperature range indicating its high thermal stability with the absence of any residuals.
4. Conclusion In this study, corn stover which is one of the readily available biomass with good cellulose content has been utilized for the isolation of cellulose microcrystals using acid hydrolysis method. The main aim of the performed work was to study the cellulose content of its constituents viz; corn cover and corn cob with optimized chemical concentrations. Corn cover and corn cob gave 25.90% and 29.60% yields of cellulose respectively whereas, corn stover gave the yield of 39.32%. The morphological observation showed the needle-shaped crystals with a crystallinity index of 91.26% and particle size in the range of 1.3–2.5 mm. The so isolated MCC can be well utilized for its applications in various fields.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement We would like to thank Unilever Industries Pvt. Ltd., Bangalore, for providing financial support in the form of our joint project.
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Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob H.K. Singh a, T. Patil a, S.K. Vineeth a, S. Das b, A. Pramanik b, S.T. Mhaske a,⇑ a b
Department of Polymer and Surface Engineering, Institute of Chemical Technology, Matunga, Mumbai 400019, India Strategic Science Group, Unilever R & D Bangalore, 64, Main Road, Bangalore 560066, India
a r t i c l e
i n f o
Article history: Received 17 August 2019 Received in revised form 5 December 2019 Accepted 8 December 2019 Available online xxxx Keywords: Corn stover Corn cover Corn cob Acid hydrolysis Optimization parameters Microcrystalline cellulose
a b s t r a c t This study investigates the isolation of microcrystalline cellulose (MCC) from corn stover biomass by acid hydrolysis method with aiming towards its constituents viz; corn cover and corn cob. The process comprises chemical treatments with varying concentrations to optimize the concentrations of chemical reactants. The cellulose crystals produced with optimized concentrations of 2% w/v NaOH, 2% w/v acidified NaClO2 and 10% v/v H2SO4 gives the yield of 25.90%, 29.60% and 39.32% of cellulose from corn cover, corn cob and corn stover respectively. The isolated needle-shaped MCC from corn stover showed the particle dimension in the range of 1.3–2.5 mm solely with a narrow distribution. Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
1. Introduction In the last decade, the increasing concern towards environmental degradation has attracted considerable interest in the development of new types of green bio-based, green and degradable materials from various natural sources. This is purposely to find out an alternative of non-renewable and non-biodegradable materials due to their harmful effects on the environment [1,2]. In consequence to this, cellulose has been found as one of the most abundant biopolymers having applications in various fields because of its outstanding properties such as biodegradability, biocompatibility and availability [3,4]. This is long-chain, high molecular weight polysaccharide composed of repeated units of dimers or disaccharides of the anhydro-D-glucopyranose unit (AGU), known as cellobiose. Each anhydro-D-glucopyranose unit is connected by b-1,4 glycosidic linkage and every other monomer is rotated 180° concerning its neighboring unit [5,6]. The properties of isolated cellulose are affected by the source of cellulose and their isolation method. This, in turn, gives rise to two main class of cellulose viz; micro and nano cellulose. Isolated cellulosic materials with one dimension in the nanometer range are referred to generically as nanocellulose [7]. The recent studies for
⇑ Corresponding author.
the isolation of cellulose from various biomasses with novel forms such as crystallites, nanocrystals, whiskers, nanofibrils and nanofibers are generating much activity for its potential applications in various fields viz; building materials, cosmetics, medicines, food packaging, ultrafiltration membranes, food stabilizer, functional food ingredient, bio-medical, reinforcing agent for making nanocomposites, emulsion, dispersion, paper and paperboard, etc [8–10]. There are several studies reported for isolation of cellulose material by chemical pretreatment steps from various bio sources e.g.; the isolation of nanocellulose particles and rods by acid hydrolysis with 60% H2SO4 utilizing sugarcane bagasse, raw cotton linter and mengkuang leaves has been reported [11–14]. Furthermore, cellulose material with nanocrystalline morphology from forestry residues has been obtained by Moriana et al. [15] via acid hydrolysis with 65% H2SO4 and pretreatment steps including 4.5% NaOH and 1.7% aqueous chlorite solution. Maiti et al. [16] prepared nanocellulose by employing China Cotton, South Africa cotton and Waste tissue paper by means of acid hydrolysis with 47% H2SO4. Additionally, whisker and rod shaped cellulose nanocrystals has also been prepared from rice husk, grape skins, oil palm trunk, Ushar seed fiber and tomato peels by utilizing 64% H2SO4 [17– 21]. Apart from the utilization of varying concentration of strong acid the studies are frequently reported for using the varying concentration of alkali and bleaching agents also for removal of non-
E-mail address: [email protected] (S.T. Mhaske). https://doi.org/10.1016/j.matpr.2019.12.065 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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cellulosic components [22]. Even though all these studies report the successful isolation of cellulose material of different morphologies but its large-scale production will always demand the better optimization of reaction conditions viz; reactant concentrations, reaction time, temperature and product yield. Among the various biomasses, corn stover is one of the major agricultural raw materials with its composition comprising about 40–45% cellulose, 25–35% hemicellulose and 7–10% total lignin of its dry weight along with other non-structural components like moisture, ash and extractives [23,24]. The significant abundance of corn stover material is found in India, where it is obtained from the third most important crop maize after wheat and rice [25]. Although, a considerable amount of literature has been published on the extraction of cellulose from corn stover, but information regarding cellulose extraction from its components remains lacking. With this point of view, the novelty of current works lies in determining individual cellulose contents of corn cover and corn cob followed by extraction and characterization of micro cellulose from its mixed composition also i.e.; corn stover by acid hydrolysis method taking consideration of minimum chemical concentration utilization for the removal of non-cellulosic components and isolation of cellulose.
(4000 rpm, 20 min). All the experiments were performed thrice to check the repeatability of the reactions. The determination of the chemical composition of raw corn stover constituents viz; corn cover and corn cob was done as per the standards (TAPPI 2000), (TAPPI 222 88-m) and (TAPPI T19 m54). The FTIR spectra of all the samples were recorded using Bruker Alpha FTIR, USA spectrophotometer with 24 scans at a resolution of 4 cm1 and wavenumber range of 4000–500 cm1, using the KBR pellet method at room temperature. The crystalline nature of the samples was determined by XRD (Rigaku, Miniflex, Japan) by placing the samples on a glass slide and spectra were recorded using Cu Ka radiation at 30 kV and 15 mA with scanning in the 2h range of 2–80°. The scan speed was 2.00°/min with a resolution of 0.02°. The particle size distribution measurements were carried out by Nanoplus zeta/nanoparticle analyzer (Particulate system, USA) instrument using water as a dispersant media. An optical microscope (Olympus, BX41, Japan) was used to observe the samples and the morphology of the fibers was captured by digital imaging software. The Thermogravimetric Analysis was performed using Pyris 1 instrument of Perkin Elmer. The tests were carried out with samples weight of around 5–10 mg at the temperature range of 30–600 °C with a heating rate of 10 °C/min under nitrogen atmosphere.
2. Experimental details 3. Results and discussions 2.1. Materials 3.1. The chemical composition of corn stover Corn stover used was obtained from the local market in Mumbai, India. Sodium hydroxide (Analytical Grade, 98.00%), sodium chlorite (Analytical Grade, 80.00%), acetic acid (Analytical Grade, 99.50%), sulphuric acid (Analytical Grade, 98.00%) were procured from S.D. Fine chemicals Ltd. Mumbai. 2.2. Isolation of microcellulose (MCC) from corn stover Prior to isolation of micro cellulose, corn cover and corn cob were separated, washed with hot water several times to remove the aqueous soluble extractives, impurities, waxy substances and oily layers, dried at 100 °C and used for the further treatment. Micro cellulose was isolated from corn cob and corn cover separately and in a mixture (corn stover) also. The dried biomass was subjected to alkali treatment through proper optimization using the varying concentration of NaOH i.e.; 0.5%, 1.0%, 2.0% and 5.0% w/v to remove the hemicellulose and other impurities. The mixture of fiber to liquor ratio of 1:40 for each concentration of NaOH was mechanically stirred at 200– 300 rpm at 60 °C for 5 h. Finally, the biomass was washed with distilled water until it got free from alkali and dried at 70 °C to constant weight. The optimized alkali-treated fibers were subjected to bleaching to remove the lignin by use of sodium chlorite at acidic pH. The biomass was treated with two different concentrations of sodium chlorite i.e.; 1% and 2% w/v for proper optimization at acidic pH 4.0–4.5 maintained by buffer solution of sodium acetate/acetic acid (1:3). The reaction was stirred at 200– 300 rpm at 80 °C for 4 h with maintaining the fiber to liquor ratio of 1:40. The bleached biomass was further subjected to acid hydrolysis to get the suspension of micro cellulose crystals. The hydrolysis was performed by using 10% v/v concentration of H2SO4 keeping fiber to solution ratio of 1:100 for 6 h at 80 °C with mechanical stirring at 600–700 rpm. After completion of hydrolysis, the reaction was stopped by adding five-fold of ice-cold water and mixture was neutralized by a concentrated sodium hydroxide solution. The resulting cellulose crystals were washed repeatedly to remove the salt formed and separated through centrifugation
The yields of non-cellulosic chemical constituents during the cellulose extraction depend upon the source of biomass and methodology of isolation. The chemical composition of the noncellulosic and cellulosic constituent was achieved separately for corn cover and corn cob based on the study from TAPPI standards and presented in Table 1. 3.2. Extraction yields of non-cellulose and micro cellulose from corn cover, corn cob and corn stover During the cellulose production from raw biomass, the optimization of chemical treatment becomes mandatory since the use of higher concentration could affect the strength of cellulose. For optimum removal of hemicellulose and lignin, 2% w/v NaOH and 2% w/v NaClO2 was found to be optimal concentrations respectively. This can be justified based on yields comparison obtained on the basis of TAPPI standard treatments (Table 1) and optimized concentration treatments (Table 2). In order to get the cellulose crystals, the bleached biomass was further hydrolyzed by the minimum concentration of acid (10% v/v H2SO4). The so obtained yields of non-cellulosic and cellulosic components as per optimized chemical concentrations are depicted in Table 2, which gives good repeatability and further clears that optimized concentrations are well in agreement with the studies reported in the literature. It further justifies that corn cover and corn cob individually comprises 25.90% and 29.60% of cellulose respectively, which was further obtained as 39.32% cellulose during isolation from corn stover. Fig. 1 shows the images of utilized corn stover biomass and so
Table 1 Chemical composition of corn cover and corn cob after TAPPI standard treatments. Components
Corn Cover (wt%)
Corn Cob (wt%)
Hemicellulose Lignin Cellulose
51.44% 12.86% 24.87%
48.88% 14.40% 32.60%
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 2 Chemical composition of corn cover, corn cob and corn stover after optimized chemicals treatments. Components
Corn Cover (wt%)
Corn Cob (wt%)
Corn Stover (wt%)
Hemicellulose Lignin Cellulose
55.87% 15.85% 25.90%
47.55% 11.40% 29.60%
41.52% 7. 59% 39.32%
obtained cellulose material. Literature studies report varying reaction conditions for cellulose isolation viz; concentration of chemicals, reaction time and temperature. But this study focuses on utilizing minimum chemical concentration so that aspects of green chemistry to make a greener chemical process with least waste and avoiding the post-treatment of unutilized reactants and solvents can succeed. 3.3. FTIR analysis Fig. 2 depict the FTIR spectra of raw corn cover, corn cob, alkalitreated form, bleached form and acid hydrolyzed cellulose. The band at 3340–3420 cm1 is related to the stretching of H-bonded OH groups and the peaks near 2920 cm1 to CAH stretching. For raw biomass, the peak intensity of AOH group was found with less intensity due to the presence of other non-cellulosic components like waxes, hemicellulose and lignin which inhibits its exposure. A very weak shoulder at nearly 1730 cm1 in raw biomass is indicative of acetyl and uronic ester group of the trace amounts of hemicellulose which is seen in the untreated sample and completely disappeared due to its removal after alkali treatment [26]. This indicates that optimized 2% w/v concentration of NaOH is optimum for the removal of hemicellulose. The band at nearly 1640 cm1 is due to the OH-bending of absorbed water and indicates exposure of the OH group. The peak at 1430 cm1 is due to ACH2- bending and is a crystalline peak of cellulose. In addition, the vibration peak at 1372 cm1 is related to bending of CH and CO bonds in polysaccharide aromatic rings [27]. The peak obtained at 1254 cm1 presents the CO out-of-plane stretching of aryl groups in lignin [15]. The 899 cm1 bands in all samples represent the glycosidic CH deformation and OH bending, which are known characteristics of b-glycosidic linkages between anhydroglucose units between cellulose units [26].
crystalline and amorphous regions shows the change in crystallinity on removing the noncellulosic components through chemical treatment. It can be noted from the diffractograms that there is an increase in peak intensity, which could be assigned to the dissolution of noncellulosic polysaccharides. The gradual removal of non-crystalline materials transformed the nature of biomass to more crystalline one [26]. All the diffractograms show welldefined peaks around 2h = 16.1° with a sharp peak at 2h = 22.5°, which are characteristic peaks of cellulose [11]. From the X-ray diffraction patterns, the crystallinity index of the samples was calculated using the following formula:
Crystallinity IndexðIcÞ ¼
Icrystalline Iamorphous 100 Icrystalline
where Icrystalline is the height of the peak at 2h = 22.5° and Iamorphous is the peak height at 2h = 18°. The so obtained values of crystallinity index of corn stover biomass treated at various steps of chemical treatment are as; raw biomass-58.88%, alkali-treated biomass-80.22%, bleached biomass-84.36% and acid hydrolyzed cellulose-91.26%. In the pretreatment steps, the alkali and bleach treatment with optimized concentration leads to removal of cementing materials like lignin, hemicellulose and pectin, which increases the percent crystallinity. These results indicate that isolation of cellulose from corn stover biomass with the optimized concentrations in the pretreatment steps leads to optimal removal of non-cellulosic components with the maximum crystallinity of isolated cellulose. 3.5. Particle size distribution analysis The isolated microcrystalline cellulose was subjected to evaluate its particle size employing DLS technique. The particle size distribution of the cellulose mainly depends upon its source and method of isolation viz; type of acid, acid concentration, reaction time, temperature, the process of hydrolysis and mechanical treatment. Fig. 4 shows the particle size distribution of the isolated cellulose with the acid concentration of 10% v/v. The distribution depicts that after chemical treatment, the obtained size of cellulose ranges from 1.3 to 2.5 mm. On the basis of the histogram, it can be concluded that almost 100% of the cellulose under study falls under micro range justifying the presence of microcellulose.
3.4. XRD analysis
3.6. Morphology analysis
Fig. 3 shows the X-ray diffraction analysis of the corn stover biomass at different stages of chemical treatment and modification. The raw biomass which is mainly constituted of
Optical microscopy (OM) analysis has been carried out to observe the morphology of the isolated microcellulose, which is depicted in Fig. 5. The OM images for isolated cellulose showed
Fig. 1. Images of the raw corn stover biomass and isolated microcrystalline cellulose.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
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H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 2. FTIR spectra of raw corn cover, corn cob, its alkali-treated form, bleached form and acid hydrolyzed cellulose.
needle-shaped crystals. The surface was found to be rough, which could be assigned to the removal of structural components. The image reveals the existence of larger size cellulose crystals with the diameter in the range of micrometers. The so obtained results are well supported by particle size measurement which depicts that almost 100% of total particles are present in the range of 1.3–2.5 mm. 3.7. Thermal analysis
Fig. 3. XRD patterns of raw corn stover, alkali-treated form, bleached form and acid hydrolyzed cellulose.
The comparative thermal decomposition parameters of raw corn stover, alkali-treated corn stover, bleached corn stover and acid hydrolyzed corn stover were investigated by TGA and DTG curves which are shown in Fig. 6. The initial weight loss of 5– 18 wt% in the range of 30–125 °C could be assigned to the removal of moisture for all the samples. The peak obtained near 150 °C could be due to the evaporation of low molecular weight compounds which are remaining from isolation steps. The other main degradation observed between 250 and 400 °C is related to the thermal degradation of the samples [28]. Almost similar thermal behavior has been seen in all the samples except acid hydrolyzed corn stover during the cellulose isolation steps. It is clear that second decomposition started at 203.3 °C for raw corn stover, 209.2 °C for alkali-treated corn stover, 224.9 °C for bleached corn stover and 236.1 °C for hydrolyzed corn stover. The increment in the thermal
Fig. 4. Particle size distribution of isolated MCC from corn stover.
Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065
H.K. Singh et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Fig. 5. Morphology of isolated MCC from corn stover.
Fig. 6. TGA and DTG curves of raw corn stover, alkali-treated, bleached and acid hydrolyzed cellulose.
stability of 5.9 °C for alkali-treated corn stover, 21.6 °C for bleached corn stover and 32.8 °C for hydrolyzed corn stover with respect to raw corn stover could be assigned to the decomposition and removal of hemicellulose, lignin and increase in crystallinity which results in high thermal stability [29]. This is in agreement with the XRD analysis which showed the increase in the crystallinity of the chemically treated corn stover and isolated cellulose as compared to the raw corn stover. Similar results were reported by Rambabu et al. [30], where they reported the isolation of cellulose from the raw pinecone. Alemdar et al. [31] has published similar studies for the wheat straw and soya hull also. The parallel thermal profile was observed in DTG curves also accept the absence of a peak at nearly 275–300 °C for isolated cellulose which reflects that profile of cellulose shifts to a higher temperature range indicating its high thermal stability with the absence of any residuals.
4. Conclusion In this study, corn stover which is one of the readily available biomass with good cellulose content has been utilized for the isolation of cellulose microcrystals using acid hydrolysis method. The main aim of the performed work was to study the cellulose content of its constituents viz; corn cover and corn cob with optimized chemical concentrations. Corn cover and corn cob gave 25.90% and 29.60% yields of cellulose respectively whereas, corn stover gave the yield of 39.32%. The morphological observation showed the needle-shaped crystals with a crystallinity index of 91.26% and particle size in the range of 1.3–2.5 mm. The so isolated MCC can be well utilized for its applications in various fields.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement We would like to thank Unilever Industries Pvt. Ltd., Bangalore, for providing financial support in the form of our joint project.
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Please cite this article as: H. K. Singh, T. Patil, S. K. Vineeth et al., Isolation of microcrystalline cellulose from corn stover with emphasis on its constituents: Corn cover and corn cob, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.065