Extraction and characterization of nanofibrillated cellulose from yacon plant (Smallanthus sonchifolius) stems

Abstract

This study aimed to evaluate the process of cellulose extraction from yacon stem using combined pulping and bleaching processes to produce nanofibrillated cellulose (NFC). First, a chemical pulping process with NaOH was applied and, subsequently, the pulp obtained was bleached. From the chemical pulp (CP) bleached, NFC was obtained by the mechanical defibrillation in a colloidal grinder. Then, chemical composition, and infrared analysis of the pulps were performed. The pulping process showed a lower amount of extractives and lignin content, as a low yield and an excessively dark pulp. The CP bleached with NaClO₂ showed the best results increased whiteness of the pulp. A suspension of NFC with fibers of 5-60 nm in diameter, high crystallinity index, and thermal stability was obtained. The results are promising and demonstrate the technical feasibility of obtaining NFC from yacon stems waste which is ideal to apply to other materials of the industry.

Keywords:
biopolymers; bleaching; nanotechnology; chemical process; lignocellulosic biomass

1. Introduction

Yacon (Smallanthus sonchifolius) is a perennial plant native to the Andes that belongs to the Asteraceae family. The plant is adaptable to different altitudes, types of climatic conditions, and soil because it is grown both at sea level (Brazil, Germany, Japan, New Zealand, Russia, and the United States) and in the Andean mountains, which reach up to 3200 m in altitude^[1,2]. Also, presents a very branched root system underground, and stems, leaves, and flowers in the aerial part plant.

The stem represents the largest fraction of the aerial part of the yacon plant, about 74%, the rest is made up of leaves and flowers. According to Kamp et al.^[3], the density of the yacon plantation can vary from 12500 to 30000 plants.ha⁻¹, as it depends on the propagation method. Also, each plant has 4 to 12 stems that can reach up to 3 m in height^[1,4]. It is composition includes 23.82% to 26.85% fiber, 9.73% to 11.37% protein, 9.60% to 10.23% ash and 1.98% to 2.26% lipids^[5]. The researches with its stem are more scarce than its leaves and roots, and its stem is actually discarded or used as animal feed^[5,6]. Nevertheless, there are reports that the young stems are used as a vegetable fresh food, in the form of celery, and dried stems used to make tea infusion along with the leaf^[7]. Therefore, the yacon stem is promising biomass to be used as a raw fiber material, as it represents a considerable fraction of its chemical composition.

The materials derived from lignocellulosic biomass have received great attention because they have a high potential as substitutes for raw material of fossil origin, due to their abundance, availability and renewability, and biodegradability^[8]. As well, it is stimulated by different aspects, as its policy, laws, and international treaties. Although the use of these materials may further advance to reduce environmental impacts, it will also require properties similar or superior to those seen in conventional materials^[9].

The nanofibrillated cellulose (NFC) obtained from non-wood biomass has gained the attention of several industry sectors, and have been applied in food packaging, biosensors, and drug delivery, because of its biocompatibility, biodegradability, renewability, availability, lower cost of raw material, lower weight, higher technical and mechanical strength^[10-12]. The NFCs are a tangled of nanofibrils with a diameter within nanoscale dimensions – i.e. up to 100 nm – and with several length micrometers^[13]. However, the choice of cellulose source and the production process has a significant impact on the quality and characteristics of NFC. To obtain NFC, the lignocellulosic biomass is submitted to pre-treatment processes such as pulping and bleaching^[14,15], followed by a refinement treatment^[16].

The chemical pulping process is the most employed in the industry, where the alkaline chemical process with sodium hydroxide (NaOH) is the most widely used and known^[17]. As advantages, alkaline treatments can efficiently remove lignin, in addition to reducing the solubilization of hemicelluloses and be applied in mild temperature conditions^[18]. After the alkaline pulping, the cellulose pulp has dark-colored, requiring the subsequent application of bleaching processes. Bleaching occurs when chemical agents oxidize the non-cellulosic compounds present in the pulp. Sodium hypochlorite (NaClO), hydrogen peroxide (H₂O₂) and sodium chlorite (NaClO₂) have been used to bleach and, at the same time, promotes the delignification of cellulose pulp^[17,19-21].

The fibers obtained in these processes are long, so additional refinement processes can be used to obtain NFC^[22]. NFC can be isolated through various processes, one of them being the defibrillation process performed in a colloidal grinder, which has been considered an appropriate method to produce NFC in a more economically viable way^[23]. To obtain smaller fibers or to produce a more uniform product, the suspension can be treated by multiple turns through the defibrillator^[20,24].

Nevertheless, the characteristics of NFCs depend mainly on the type of raw material and the processes that they were submitted, consequently the investigation of their characteristics is very important. There are recent studies with different types of lignocellulosic biomass to obtain NFC^[10,25], but there are no reports in the literature about the use of yacon's agricultural waste (stem) for this purpose and application. Therefore, the objective of this study was to investigate the feasibility of using yacon stem to produce NFC from the bleached pulp. The processes’ yields were compared, as well as the effects of pulp chemical treatments on the resulting NFC characteristics. The physical, thermal, and chemical properties of NFC obtained from the yacon stem were also evaluated.

2. Materials and Methods

2.1 Materials

The yacon plant stems were supplied by a farmer in São José dos Pinhais, Paraná, Brazil (coordinates: 25° 37’8.37” S 49° 07’15.72” W; at 882 m altitude). The reagents used in the chemical characterization of the plant and the NFC were: Absolute ethyl alcohol 99.8% (Neon©, Brazil), toluene 99.5% (Anidrol©, Brazil), sulfuric acid 98% (Sigma-Aldrich©, Brazil), sodium hydroxide 97% (Neon©, Brazil), sodium hypochlorite in 10-12% solution (Neon©, Brazil), hydrogen peroxide 35% (Neon©, Brazil), sodium chlorite 78% (Neon©, Brazil), glacial acetic acid 99.7% (Dynamics©, Brazil).

2.2 Sample preparation

The stems were washed in running water and then manually cut into pieces of approximately 5 cm in length. About 12 kg of samples with 85.96% moisture were dried in a forced-air circulation oven at 40 °C for 48 hours, to reach moisture of 6.79%. The moisture levels were determined according to the T264 method of the Technical Association of the Pulp and Paper Industry, in an oven at 105 °C for 24 hours^[26]. Subsequently, the dried yacon stems (YS) were packed in polyethylene bags, sealed, and stored in a dry and ventilated environment until the experiment was performed. The preparation of the biomass for the chemical composition analysis of the YS followed the procedures described in T257-cm02^[27].

2.3 Pulping process of cellulosic pulp

The process to obtain the chemical pulp (CP) was performed with NaOH, following the operational conditions described by Fortunati et al.^[28] with some adaptations. The YS samples were placed in containers on a dry basis proportion of 1:10 (w:v) in NaOH solution 5% and submitted to heat treatment in a laboratory autoclave (Phoenix, Brazil) at 120 °C, under pressure (98 kPa) for 1 hour, with automatic time and temperature control. Subsequently, the CP was washed and disintegrated in the disc refiner with water (1:20, w:v) at room temperature (25 °C), for 5 minutes. Finally, the CP was purified in a Brecht-Holl fiber classifier (Regmed®, model BH-6/12, Brazil) and then centrifuged (3000 rpm for 5 minutes) and stored in polyethylene bags under refrigeration (8 °C).

2.4 Bleaching processes of cellulosic pulp

The CP samples were bleached as the experimental conditions described in Table 1. The bleaching treatments were applied in a single stage with a diluted solution of the NaClO (SH), H₂O₂ (HP), and NaClO₂ (SC). A standard consistency was adopted in the proportion of 1:10 (w:v) pulp on a dry basis:solution. Briefly, the pulp was placed in a glass becker, followed by the bleaching solution and the mixture was submerged in a thermostatic bath. After treatment, the bleached pulp (CP-SH; CP-HP; CP-SC) were washed in running water, in order to eliminate possible reagent residues, then centrifuged (3000 rpm for 5 minutes) and stored in polyethylene bags under refrigeration (8 °C).

Table 1
Parameters of bleaching treatments of the chemical pulp (CP).

Parameters	NaClO [ 21 ]	H2O2 [ 22 ]	NaClO2 [ 23 ]
Treatment encoding	SH	HP	SC
Solution concentration	5%	1%	1.7%
Solution pH	11	11.5	4.5
Adjustment of solution pH	NaOH 4M	NaOH 4M	C2H4O2
Temperature	70 °C	80 °C	80 °C
Time	60 min	45 min	120 min

• Source: Adapted from Balea et al.^[19^], Berglund et al.^[20^] and Cara et al.^[21^]. A standard consistency of 1:10 (w:v) dry weight biomass:solution was set. NaClO: Sodium hypochlorite; H₂O₂: Hydrogen peroxide; NaClO₂: Sodium chlorite; NaOH: Sodium hydroxide; and C₂H₄O₂: Acetic acid.

2.5 Extraction of nanofibrillated cellulose (NFC)

The NFC extraction was performed from the bleached pulp that presented the best results in terms of yield, color, and Klason lignin content, following the defibrillation process proposed by Iwamoto et al.^[24], with some modifications. The bleached pulp was dispersed and homogenized in distilled water to a consistency of 1% in dry weight, using a food processor with 450 W of power. The pulp suspension went through the mechanical defibrillation in a colloidal grinder (Masuko Sangyo®, model MKCA6-2J, Japan) four times, at 1500 rpm, with a 0.1 mm space between the grinding stones. Subsequently, the NFC suspension was placed in polyethylene bottles and refrigerated (8 °C).

2.6 Raw fiber and pulp characterization

2.6.1 Scanning Electron Microscopy (SEM)

The morphology was visualized through a scanning electron microscope (TESCAN®, VEGA3 LMU model). The samples were fixed on metal support (stub) covered with copper conductive tape and metalized with a gold thin layer. The images were captured with an acceleration voltage of 15 kV.

2.6.2 Chemical composition

The chemical composition was performed in triplicate. The total extractives content was determined by standard method T204-om97^[29] and Klason lignin by T222-om02^[30]. The holocellulose content (HOLO), which represents the amount of cellulose and hemicellulose, was determined by difference according to the following equation:

$HOLO\left(\%\right)=100-\left(Totalextratives+Klasonlignin\right)$ (1)

2.6.3 Yield

The gravimetric yields of the pulps were calculated considering the dry weight of the recovered sample (W₂) and the dry weight of the initial sample (W₁) according to Equation 2. The yield of the NFC was determined according to by Besbes et al.^[31].

$Yield\left(\%\right)=\left(W_2/W_1\right)\times 100$ (2)

2.6.4 Fourier Transform Infrared Spectroscopy (FTIR)

The functional groups found in the samples were identified by FTIR spectrometer (Bruker, Vertex 70 model, USA), in diffuse reflectance mode (DRIFT), and, for each sample, 512 scans were performed in the 4000 to 400 cm^-1 range and with a resolution of 4 cm^-1. The spectra were manipulated in Kubelka-Munk units, correcting the baseline using the concave rubber band correction method.

2.7 Characterization of nanofibrillated cellulose (NFC)

2.7.1 Transmission Electron Microscopy (TEM)

A transmission electron microscope (JEOL©, JEM 1200EX-II model), with an accelerating voltage of 60 kV, was used to visualize the structure of the NFC. The NFC suspension was dispersed in water solution (1:1000, v:v), and a drop of this mixture was placed on a copper grid, layered with Parlodion film. The ImageJ® program determined the diameter range of cellulose fibers^[32].

2.7.2 Thermogravimetric analysis (TGA/DTG)

The TGA/DTG study was performed on a thermogravimetric analyzer (PerkinElmer©, model 4000, USA) with adapting the conditions used by Xie et al.^[33]. The assays were carried out under a dynamic nitrogen atmosphere of 20 mL.min^-1 and heat flow of 10 °C.min^-1, in a temperature range of 30 °C to 800 °C.

2.7.3 X-ray diffraction (XRD)

The crystallinity index (CrI) was obtained by XRD using a diffractometer (Bruker©, D8 Venture model). The diffraction curves were obtained by Cu-Kα radiation (λ = 1.54 Å) at 40 kV and 20 mA and with diffraction intensities in a 2θ angular range (Bragg angles) from 10° to 40°. The CrI was calculated by Equation 3, where I₂₀₀ and I_am represent the peak intensities near 2θ = 22° and the minimum near 18°, respectively^[34].

$\text{CrI}\left(\text{\%}\right)=\left[\left(I_{200}-I_{am}\right)/I_{200}\right]\times 100$ (3)

2.8 Statistical analysis

The results of the experiments were subjected to variance analysis ANOVA and the means compared with the Tukey test at 5% significance level with the support of the StatSoft®, version 13.0 (USA) Statistica software. FTIR, TGA/DTG, and XRD curves were analyzed with OriginPro 8.6 (OriginLab®, Northampton, MA, USA), using the Savitzky-Golay method at 15%-point cut, which reduces possible noises coming from the equipment.

3. Results and Discussions

3.1 Raw fiber and pulps characterization

3.1.1 Morphological analysis

Figure 1 shows the SEM micrographs of yacon stem (YS) and the fibers obtained by chemical process, as well as the bleached pulps. The structure of YS is like that of other plants in the Asteraceae family, which have vascular bundles that form a porous network analogous to honeycombs with a variety of sizes in diameter^[28]. The CP presented soft and clustered fibers with smooth connections, but trace residues of the YS remained on the fibers. The morphological characteristics of the CP reflected the chemical composition of the pulp, indicating the efficiency of the chemical process. In general, bleaching processes promoted a change in the pulp surface initially treated with NaOH, making it even smoother.

Figure 1
Image and SEM of the yacon stem (YS), chemical pulp treated with NaOH (CP) and chemical pulp bleached with NaClO (SH), H₂O₂ (HP) and NaClO₂ (SC).

3.1.2 Chemical composition, and yields

The YS (24.4% extractives, 14.0% lignin, and 61.5% holocellulose) was submitted to chemical pulping process, and the chemical composition of these materials is presented in Table 2. The lignin content found is lower than in tobacco (23%), sunflower (26%), corn (19%), and bamboo (23-28%) biomass^[25,35,36]. This is an advantage because it makes the process of fiber extraction less strict, demanding fewer chemical reagents and time. There are no reports in the literature on the composition of the yacon stem in terms of extractives, lignin, and holocellulose, highlighting the importance and innovation of this research.

Table 2
Chemical composition, yield of pulping and effect of cellulose pulp bleaching processes.

Parameters	YS	CP	CP-SH	CP-HP	CP-SC
Extractives (%)	24.4±0.7a	1.3±0.1b	0.8±0.1bc	0.1±0.0c	0.1±0.1c
Lignin (%)	14.0±0.1a	2.0±0.2b	0.9±0.1c	1.0±0.1c	0.4±0.1d
HOLO (%)	61.5±0.7d	96.8±0.4c	98.3±0.1b	98.9±0.1ab	99.5±0.1a
Yield (%)	-	33.3±1.4c	94.9±3.3a	95.0±2.5a	85.9±3.0b

• (-) not determined; (%) on dry basis; YS: yacon stem; CP: chemical pulp treated with NaOH; SH: NaClO-bleached pulp; HP: H₂O₂-bleached pulp; and SC: NaClO₂-bleached pulp; HOLO: Holocellulose. Mean ± standard deviations followed by different letters in the same line denote difference according to the Tukey test (p<0.05).

The chemical process removed a significant (p<0.05) amount of the amorphous extractives of the fibers, which affected other properties, such as yield (low) and resistance to thermal degradation, further discussed. The pulping process applied promoted a significant decrease in the extractives and lignin contents (Table 2). Alkaline pulping of the YS resulted in the removal of considerable amounts of extractives and lignin, 94.6% and 85.7% respectively, showing a pulp with 96.8% holocellulose, but with 33.29% yield. Subjecting the plant matrix to treatment with alkaline solutions at high temperatures causes a disturbance in the cell wall structure due to cleavage of the ester and ether bonds between lignin and hemicellulose, resulting in its solubilization^[37]. This explains the significant reduction of these constituents in the matrix, on the other hand, promotes an increase in the purity of cellulose fibers.

The bleaching of pulp also allows delignification, as it significantly reduced the lignin content in the pulp. The combined bleaching and hydrolysis helped with cellulose purification and isolation because of the removal of non-cellulosic components including lignin and hemicelluloses, besides facilitates mechanical defibrillation to obtain NFC^[38]. The application of more bleaching stages can be used to obtain pulps with a higher level of whiteness. The bleaching of cellulose pulp in a single stage is an advantage as it reduces costs and process time.

3.1.3 Fourier Transform Infrared Spectroscopy (FTIR)

The effects of pulping and bleaching processes on the chemical composition of YS fibers were assessed by infrared readings (Figure 2). The chemical pulping process with NaOH altered the chemical structure of the fibers as seen in the chemical characterization (Table 2). All infrared spectra of the samples have a high-intensity band around 3600 cm^-1 attributed to the vibration of hydroxyl bonds (-OH), a functional group present in cellulose, hemicellulose, and lignins^[39]. An elongation of this band is noticeable in the YS until about 3100 cm^-1, which may be related to the formation of hydrogen bonds from carboxylic and phenolic groups of the hemicellulose, lignins, and extractives structures^[40].

Figure 2
Infrared spectrum of the yacon stem fiber (YS), chemical pulp treated with NaOH (CP); and chemical pulp bleached with NaClO (CP-SH), H₂O₂ (CP-HP) and NaClO₂ (CP-SC).

In YS, the band between 2920-2850 cm^-1 represents the vibration of the C–H bond present in cellulose, hemicellulose, and lignin. The range of 1750 to 1720 cm^-1 reflects the vibration of C=O bonds, with an increase in intensity in this region (1730 cm^-1), possibly due to the acetyl groups in hemicellulose^[41,42].

The NaOH process, as well as the bleaching treatments, significantly reduced the lignin content of YS, observed in the range of 1600 to 1500 cm^-1, where there are less peaks, which are attributed to the vibration of the aromatic structure^[42]. The peak at 1250 cm^-1 disappears after alkaline treatment on YS fibers due to the vibration of hemicellulose’s C–O^[43], corroborating the chemical composition found. Moreover, the peaks at 1170 cm^-1 and 1082 cm^-1 are attributed to the vibration of the C–O–C group in the pyranose ring in polysaccharides^[41]. A considerable inversion of the spectrum signal occurs around 830 cm^-1, attributed to the presence of carbohydrates, such as hemicelluloses^[44]. Thus, among the bleached pulps and considering yields, color and residual Klason lignin content in the fibers, the NaOH-treated pulp with NaClO₂ bleaching (CP-SC) offered a more satisfactory result to proceed with the extraction of NFC.

3.2 Characterization of nanofibrillated cellulose (NFC)

3.2.1 Transmission Electron Microscopy (TEM)

Figure 3 gives an overview of the morphological characteristics of the NFC. In Figure 3a, the NFC suspension exhibited a gel-like viscous appearance where a non-phase separation has been verified during storage. Figure 3b and 3c shows how the process of obtaining NFC allowed the individualization of the fibers. Mechanical defibrillation in a colloidal grinder yields a highly branched and interwoven structure with fibers diameters ranging from 5 to 60 nm very smaller than their lengths, which characterizes a nanomaterial, and a yield of 92.7%. No reports were found in the literature about the production of NFC from the stem of the yacon plant. But, fibers of different lignocellulosic materials have a similar appearance and diameter to the fibers obtained^{[11,12,28,45]}. Therefore, it was possible to obtain NFC from the yacon stems, as wished.

Figure 3
Image (a) and TEM (b) and (c) of nanofibrillated cellulose (NFC) with magnification of 15000× and 5000×, respectively.

3.2.2 Thermogravimetric analysis (TGA/DTG)

The TGA/DTG curves of YS, CP, CP-SC, and NFC are shown in Figure 4. The constituents present in the analyzed materials exhibit three main stages of thermal degradation (Figure 4a). The first stage starts at 30 ºC and extends to 110 ºC, which is mainly caused by the loss of water mass^[13]. The second stage occurs between 150 ºC and 450 ºC, possibly due to the depolymerization of cellulosic components (cellulose and hemicellulose) and due to the traces of lignin in the samples. There are considerable mass losses between 150 °C and 300 °C for YS in the second stage, which are not explicitly seen in chemical pulps and NFC. It can be attributed to the thermal decomposition of extractive materials, such as low molecular weight polysaccharides - e.g. pectic substances^[46].

Figure 4
TGA (a) and DTG (b) of yacon stem fiber (YS), the chemical pulp (CP), NaClO₂- bleached chemical pulp (CP-SC) and nanofibrilated cellulose (NFC) as a function of weight loss.

In the third stage, there is a small mass loss at 450 ºC, where the complete degradation of residual lignin mainly occurs^[33]. The maximum thermal resistance temperature (T_max) around 360 °C is attributed to cellulose, as hemicelluloses, as well as the other components, are considered amorphous and have a low degree of polymerization^[28]. This characteristic is attractive to NFC, whose purpose is to be applied to materials in which the processing temperature is high, such as to biocomposites that may exceed 200 °C^[45]. NFC obtained of source non-wood has been used as the base or auxiliary material to produce paper and board, coatings, packaging, adhesives, sensors, filters, biomedical, among others^[47].

In Figure 4b, T_max increases as YS (335 °C) undergoes alkaline pulping (360 °C) and NaClO₂ (380 °C) bleaching treatments, but lowers to 368 °C with ultrafine fibrillation. This lower resistance to thermal degradation of NFC may be related to the defibrillation to which CP-SC was submitted, as this process may cause changes in the crystalline regions of cellulose^[48]. This effect can be noted by the XRD analysis.

3.2.3 X-ray diffraction analysis (XRD)

The processes’ effect on the crystallinity of samples can be visualized by XRD analysis (Figure 5). Similar intensity peaks were identified in all samples analyzed (YS, CP, CP-SC, and NFC) via XRD profiles, located at diffraction angles (2θ) near 17º and 22°. Another low-intensity peak is visible in the 34º angle, more evident in the pulps and the NFC. The samples have a typical diffraction curve of cellulose I, similar to other lignocellulosic materials^[32,48,49]. The crystallinity index (CrI), that relate the crystalline phase to the amorphous phase of the material, was calculated according to Equation 3, obtaining 52.21%, 65.15%, 71.28%, and 70.60% for YS, CP, CP-SC, and NFC, respectively, showing a clear increase after the bleaching treatment. The chemical pulping process and pulp bleaching increased crystallinity by 24.78% and 36.52%, respectively, in relation to the matrix (YS). Such an increase in crystallinity is related to the removal of pulp amorphous components such as extractives, hemicelluloses and lignin^[33], which corroborates the results of Table 2. In addition, a high value of crystallinity means greater rigidity of the fibers and this characteristic can be beneficial for the application as reinforcement for biocomposites^[26]. It was also noted that the CrI of the NFC had a slight decrease when compared to CP-SC, which may be related to the effect of the mechanical defibrillation in a colloidal grinder and may have affected the crystal structure^[48]. Although the process of obtaining NFC reduces the index, the crystallinity remains high (above 70%).

Figure 5
XRD of yacon stem fiber (YS), the chemical pulp treated with NaOH (CP), NaClO₂- bleached chemical pulp (CP-SC) and nanofibrillated cellulose (NFC).

4. Conclusions

This study was the first to characterize and use yacon plant stem biomass for nanofibrillated cellulose production. The best result obtained in terms of yield, color, and lignin content was the use of the alkaline pulping process with NaOH followed by bleaching with NaClO₂. The yacon NFC obtained show high crystallinity index and thermal resistance, which demonstrate the potential application in other materials, for example in biocomposites and packaging, as well as assisting in future research in this area.

5. Acknowledgements

The present study was developed with the support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Brasil (CAPES) – Grant Code 001, Projeto FINEP/CT-INFRA/3080/20112011, and Centro de Microscopia Eletrônica at the Universidade Federal do Paraná (UFPR).

• How to cite: Sousa, R. S., Andrade, A. S., & Masson, M. L. (2021). Extraction and characterization of nanofibrillated cellulose from yacon plant (Smallanthus sonchifolius) stems. Polímeros: Ciência e Tecnologia, 31(2), e2021016. https://doi.org/10.1590/0104-1428.09620

6. References

• ¹
  Food and Agriculture Organization – FAO. (2012). Yacon (Smallanthus sonchifolius [Poeppig & Endlicher] H. Robinson). Rome: FAO. Retrieved in 2020, May 12, from http://www.fao.org/tempref/codex/Meetings/CCLAC/cclac18/la18_15e.pdf
  » http://www.fao.org/tempref/codex/Meetings/CCLAC/cclac18/la18_15e.pdf
• ²
  Fernández, E. C., Viehmannová, I., Lachman, J., & Milella, L. (2006). Yacon [Smallanthus sonchifolius (Poeppig & Endlicher) H. Robinson]: a new cropin the Central Europe – Information. Plant, Soil and Environment, 52(12), 564-570. http://dx.doi.org/10.17221/3548-PSE
  » http://dx.doi.org/10.17221/3548-PSE
• ³
  Kamp, L., Hartung, J., Mast, B., & Graeff-Hönninger, S. (2019). Plant growth, tuber yield formation and costs of three different propagation methods of yacon (Smallanthus sonchifolius). Industrial Crops and Products, 132, 1-11. http://dx.doi.org/10.1016/j.indcrop.2019.02.006
  » http://dx.doi.org/10.1016/j.indcrop.2019.02.006
• ⁴
  Vilhena, S. M. C., Câmara, F. L. A., & Kakihara, S. T. (2000). The yacon cultivation in Brazil. Horticultura Brasileira, 18(1), 5-8. http://dx.doi.org/10.1590/S0102-05362000000100002
  » http://dx.doi.org/10.1590/S0102-05362000000100002
• ⁵
  Lachman, J., Fernández, E. C., & Orsák, M. (2003). Yacon [Smallanthus sonchifolia (Poepp. et Endl.) H. Robinson] chemical composition and use: a review. Plant, Soil and Environment, 49(6), 283-290. http://dx.doi.org/10.17221/4126-PSE
  » http://dx.doi.org/10.17221/4126-PSE
• ⁶
  Shin, D. Y., Hyun, K. H., Kuk, Y., Shin, D. W., & Kim, H. W. (2017). Antibiotic effect of leaf, stem, and root extracts in Smallanthus sonchifolius H. Robinson. Korean Journal of Plant Resources, 30(3), 311-317. http://dx.doi.org/10.7732/kjpr.2017.30.3.311.
  » https://doi.org/10.7732/kjpr.2017.30.3.311
• ⁷
  Valentová, K., & Ulrichová, J. (2003). Smallanthus sonchifolius and Lepidium meyenii - prospective Andean crops for the prevention of chronic diseases. Biomedical Papers, 147(2), 119-130. http://dx.doi.org/10.5507/bp.2003.017 PMid:15037892.
  » http://dx.doi.org/10.5507/bp.2003.017
• ⁸
  Xu, J. T., & Chen, X. Q. (2019). Preparation and characterization of spherical cellulose nanocrystals with high purity by the composite enzymolysis of pulp fibers. Bioresource Technology, 291, 121842. http://dx.doi.org/10.1016/j.biortech.2019.121842 PMid:31377505.
  » http://dx.doi.org/10.1016/j.biortech.2019.121842
• ⁹
  Zhu, Y., Romain, C., & Williams, C. K. (2016). Sustainable polymers from renewable resources. Nature, 540(7633), 354-362. http://dx.doi.org/10.1038/nature21001 PMid:27974763.
  » http://dx.doi.org/10.1038/nature21001
• ¹⁰
  Athinarayanan, J., Alshatwi, A. A., & Subbarayan Periasamy, V. (2020). Biocompatibility analysis of Borassus flabellifer biomass-derived nanofibrillated cellulose. Carbohydrate Polymers, 235, 115961. http://dx.doi.org/10.1016/j.carbpol.2020.115961 PMid:32122496.
  » http://dx.doi.org/10.1016/j.carbpol.2020.115961
• ¹¹
  Behzad, T., & Ahmadi, M. (2016). Nanofibers. In M. M. Rahman & A. M. Asiri (Eds.), Nanofiber research: reaching new heights crystalline (pp. 13-28). Rijeka, Croatia: InTech. http://dx.doi.org/10.5772/63704
  » http://dx.doi.org/10.5772/63704
• ¹²
  Rojas, J., Bedoya, M., & Ciro, Y. (2015). Current trends in the production of cellulose nanoparticles and nanocomposites for biomedical applications. In M. Poletto (Ed.), Cellulose: fundamental aspects and current trends (pp. 193-228). London: IntechOpen. http://dx.doi.org/10.5772/61334
  » http://dx.doi.org/10.5772/61334
• ¹³
  Lavoratti, A., Scienza, L. C., & Zattera, A. J. (2016). Dynamic-mechanical and thermomechanical properties of cellulose nanofiber/polyester resin composites. Carbohydrate Polymers, 136, 955-963. http://dx.doi.org/10.1016/j.carbpol.2015.10.008 PMid:26572434.
  » http://dx.doi.org/10.1016/j.carbpol.2015.10.008
• ¹⁴
  Abdul Khalil, H. P. S., Hossain, M. S., Rosamah, E., Nik Norulaini, N. A., Leh, C. P., Asniza, M., Davoudpour, Y., & Zaidul, I. S. M. (2014). High-pressure enzymatic hydrolysis to reveal physicochemical and thermal properties of bamboo fiber using a supercritical water fermenter. BioResources, 9(4), 7710-7720. http://dx.doi.org/10.1016/j.biortech.2007.04.029
  » http://dx.doi.org/10.1016/j.biortech.2007.04.029
• ¹⁵
  Gonzalez, R., Jameel, H., Chang, H. M., Treasure, T., Pirraglia, A., & Saloni, D. (2011). Thermo-mechanical pulping as a pretreatment for agricultural biomass for biochemical conversion. BioResources, 6(2), 1599-1614. http://dx.doi.org/10.15376/biores.6.2.1599-1614
  » http://dx.doi.org/10.15376/biores.6.2.1599-1614
• ¹⁶
  Abdul Khalil, H. P. S., Davoudpour, Y., Saurabh, C. K., Hossain, M. S., Adnan, A. S., Dungani, R., Paridah, M. T., Islam Sarker, M. Z., Fazita, M. R. N., Syakir, M. I., & Haafiz, M. K. M. (2016). A review on nanocellulosic fibres as new material for sustainable packaging: process and applications. Renewable & Sustainable Energy Reviews, 64, 823-836. http://dx.doi.org/10.1016/j.rser.2016.06.072
  » http://dx.doi.org/10.1016/j.rser.2016.06.072
• ¹⁷
  Someshwar, A. V., & Pinkerfon, J. E. (1992). Wood processing industry. In A. J. Buonicore & W. T. Davis (Eds.), Air pollution engineering manual (p. 844). New York: Van Nostrand Reinhold.
• ¹⁸
  Ferrer, A., Filpponen, I., Rodríguez, A., Laine, J., & Rojas, O. J. (2012). Valorization of residual Empty Palm Fruit Bunch Fibers (EPFBF) by microfluidization: production of nanofibrillated cellulose and EPFBF nanopaper. Bioresource Technology, 125, 249-255. http://dx.doi.org/10.1016/j.biortech.2012.08.108 PMid:23026341.
  » http://dx.doi.org/10.1016/j.biortech.2012.08.108
• ¹⁹
  Balea, A., Merayo, N., De La Fuente, E., Negro, C., & Blanco, Á. (2017). Assessing the influence of refining, bleaching and TEMPO-mediated oxidation on the production of more sustainable cellulose nanofibers and their application as paper additives. Industrial Crops and Products, 97, 374-387. http://dx.doi.org/10.1016/j.indcrop.2016.12.050
  » http://dx.doi.org/10.1016/j.indcrop.2016.12.050
• ²⁰
  Berglund, L., Noël, M., Aitomäki, Y., Öman, T., & Oksman, K. (2016). Production potential of cellulose nanofibers from industrial residues: efficiency and nanofiber characteristics. Industrial Crops and Products, 92, 84-92. http://dx.doi.org/10.1016/j.indcrop.2016.08.003
  » http://dx.doi.org/10.1016/j.indcrop.2016.08.003
• ²¹
  Cara, C., Ruiz, E., Ballesteros, I., Negro, M. J., & Castro, E. (2006). Enhanced enzymatic hydrolysis of olive tree wood by steam explosion and alkaline peroxide delignification. Process Biochemistry, 41(2), 423-429. http://dx.doi.org/10.1016/j.procbio.2005.07.007
  » http://dx.doi.org/10.1016/j.procbio.2005.07.007
• ²²
  Siró, I., & Plackett, D. (2010). Microfibrillated cellulose and new nanocomposite materials: a review. Cellulose, 17(3), 459-494. http://dx.doi.org/10.1007/s10570-010-9405-y
  » http://dx.doi.org/10.1007/s10570-010-9405-y
• ²³
  Spence, K. L., Venditti, R. A., Rojas, O. J., Habibi, Y., & Pawlak, J. J. (2011). A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods. Cellulose, 18(4), 1097-1111. http://dx.doi.org/10.1007/s10570-011-9533-z
  » http://dx.doi.org/10.1007/s10570-011-9533-z
• ²⁴
  Iwamoto, S., Abe, K., & Yano, H. (2008). The effect of hemicelluloses on wood pulp nanofibrillation and nanofiber network characteristics. Biomacromolecules, 9(3), 1022-1026. http://dx.doi.org/10.1021/bm701157n PMid:18247566.
  » http://dx.doi.org/10.1021/bm701157n
• ²⁵
  Boufi, S., & Chaker, A. (2016). Easy production of cellulose nanofibrils from corn stalk by a conventional high speed blender. Industrial Crops and Products, 93, 39-47. http://dx.doi.org/10.1016/j.indcrop.2016.05.030
  » http://dx.doi.org/10.1016/j.indcrop.2016.05.030
• ²⁶
  Technical Association of the Pulp and Paper Industry – TAPPI. (1999). T 264-om97: Preparation of wood for chemical analysis Atlanta: TAPPI.
• ²⁷
  Technical Association of the Pulp and Paper Industry – TAPPI. (2012). T 257-cm02: Sampling and preparing wood for analysis Atlanta: TAPPI.
• ²⁸
  Fortunati, E., Luzi, F., Jiménez, A., Gopakumar, D. A., Puglia, D., Thomas, S., Kenny, J. M., Chiralt, A., & Torre, L. (2016). Revalorization of sunflower stalks as novel sources of cellulose nanofibrils and nanocrystals and their effect on wheat gluten bionanocomposite properties. Carbohydrate Polymers, 149, 357-368. http://dx.doi.org/10.1016/j.carbpol.2016.04.120 PMid:27261760.
  » http://dx.doi.org/10.1016/j.carbpol.2016.04.120
• ²⁹
  Technical Association of the Pulp and Paper Industry – TAPPI. (1997). T 204-om97: solvent extractives of wood and pulp Atlanta: TAPPI.
• ³⁰
  Technical Association of the Pulp and Paper Industry – TAPPI. (1999). T 222-om02: acid-insoluble lignin in wood and pulp Atlanta: TAPPI.
• ³¹
  Besbes, I., Alila, S., & Boufi, S. (2011). Nanofibrillated cellulose from TEMPO-oxidized eucalyptus fibres: effect of the carboxyl content. Carbohydrate Polymers, 84(3), 975-983. http://dx.doi.org/10.1016/j.carbpol.2010.12.052
  » http://dx.doi.org/10.1016/j.carbpol.2010.12.052
• ³²
  Oliveira, J. P., Bruni, G. P., Lima, K. O., Halal, S. L. M. E., Rosa, G. S., Dias, A. R. G., & Zavareze, E. R. (2017). Cellulose fibers extracted from rice and oat husks and their application in hydrogel. Food Chemistry, 221, 153-160. http://dx.doi.org/10.1016/j.foodchem.2016.10.048 PMid:27979125.
  » http://dx.doi.org/10.1016/j.foodchem.2016.10.048
• ³³
  Xie, J., Hse, C. Y., De Hoop, C. F., Hu, T., Qi, J., & Shupe, T. F. (2016). Isolation and characterization of cellulose nanofibers from bamboo using microwave liquefaction combined with chemical treatment and ultrasonication. Carbohydrate Polymers, 151, 725-734. http://dx.doi.org/10.1016/j.carbpol.2016.06.011 PMid:27474619.
  » http://dx.doi.org/10.1016/j.carbpol.2016.06.011
• ³⁴
  Segal, L., Creely, J. J., Martin, A. E., Jr., & Conrad, C. M. (1959). An empirical method for estimating the degree of crystallinity of native cellulose using the X-Ray diffractometer. Textile Research Journal, 29(10), 786-794. http://dx.doi.org/10.1177/004051755902901003
  » http://dx.doi.org/10.1177/004051755902901003
• ³⁵
  Akpinar, O., Levent, O., Sabanci, S., Uysal, R. S., & Sapci, B. (2011). Optimization and comparison of dilute acid pretreatment of selected agricultural residues for recovery of xylose. BioResources, 6(4), 4103-4116. http://dx.doi.org/10.15376/biores.6.4.4103-4116
  » http://dx.doi.org/10.15376/biores.6.4.4103-4116
• ³⁶
  Yuan, Z., Kapu, N. S., Beatson, R., Chang, X. F., & Martinez, D. M. (2016). Effect of alkaline pre-extraction of hemicelluloses and silica on kraft pulping of bamboo (Neosinocalamus affinis Keng. Industrial Crops and Products, 91, 66-75. http://dx.doi.org/10.1016/j.indcrop.2016.06.019
  » http://dx.doi.org/10.1016/j.indcrop.2016.06.019
• ³⁷
  Geng, W., Narron, R., Jiang, X., Pawlak, J. J., Chang, H., Park, S., Jameel, H., & Venditti, R. A. (2019). The influence of lignin content and structure on hemicellulose alkaline extraction for non-wood and hardwood lignocellulosic biomass. Cellulose, 26(5), 3219-3230. http://dx.doi.org/10.1007/s10570-019-02261-y
  » http://dx.doi.org/10.1007/s10570-019-02261-y
• ³⁸
  Cao, Y., Jiang, Y., Song, Y., Cao, S., Miao, M., Feng, X., Fang, J., & Shi, L. (2015). Combined bleaching and hydrolysis for isolation of cellulose nanofibrils from waste sackcloth. Carbohydrate Polymers, 131, 152-158. http://dx.doi.org/10.1016/j.carbpol.2015.05.063 PMid:26256171.
  » http://dx.doi.org/10.1016/j.carbpol.2015.05.063
• ³⁹
  Peng, B., Zhang, H., & Zhang, Y. (2019). Investigation of the relationship between functional groups evolution and combustion kinetics of microcrystalline cellulose using in situ DRIFTS. Fuel, 248(1), 56-64. http://dx.doi.org/10.1016/j.fuel.2019.03.069
  » http://dx.doi.org/10.1016/j.fuel.2019.03.069
• ⁴⁰
  Pastore, T. C. M., Oliveira, C. C. K., Rubim, J. C., & Santos, K. D. O. (2008). Effect of artificial weathering on tropical woods monitored by infrared spectroscopy (DRIFT). Química Nova, 31(8), 2071-2075. http://dx.doi.org/10.1590/S0100-40422008000800030
  » http://dx.doi.org/10.1590/S0100-40422008000800030
• ⁴¹
  Fiore, V., Scalici, T., & Valenza, A. (2014). Characterization of a new natural fiber from Arundo donax L. as potential reinforcement of polymer composites. Carbohydrate Polymers, 106(1), 77-83. http://dx.doi.org/10.1016/j.carbpol.2014.02.016 PMid:24721053.
  » http://dx.doi.org/10.1016/j.carbpol.2014.02.016
• ⁴²
  Morán, J. I., Alvarez, V. A., Cyras, V. P., & Vázquez, A. (2008). Extraction of cellulose and preparation of nanocellulose from sisal fibers. Cellulose, 15(1), 149-159. http://dx.doi.org/10.1007/s10570-007-9145-9
  » http://dx.doi.org/10.1007/s10570-007-9145-9
• ⁴³
  Orue, A., Eceiza, A., & Arbelaiz, A. (2017). Pretreatments of natural fibers for polymer composite materials. In. S. Kalia (Ed.), Lignocellulosic composite materials (Springer Series on Polymer and Composite Materials, pp. 137-175). Spain: Springer. https://doi.org/10.1007/978-3-319-68696-7_3
  » https://doi.org/10.1007/978-3-319-68696-7_3
• ⁴⁴
  Mascarenhas, M., Dighton, J., & Arbuckle, G. A. (2000). Characterization of plant carbohydrates and changes in leaf carbohydrate chemistry due to chemical and enzymatic degradation measured by microscopic ATR FT-IR spectroscopy. Applied Spectroscopy, 54(5), 681-686. http://dx.doi.org/10.1366/0003702001950166
  » http://dx.doi.org/10.1366/0003702001950166
• ⁴⁵
  Alemdar, A., & Sain, M. (2008). Isolation and characterization of nanofibers from agricultural residues: wheat straw and soy hulls. Bioresource Technology, 99(6), 1664-1671. http://dx.doi.org/10.1016/j.biortech.2007.04.029 PMid:17566731.
  » http://dx.doi.org/10.1016/j.biortech.2007.04.029
• ⁴⁶
  Sarasini, F. (2018). Mechanical and thermal properties of less common natural fibres and their composites. In. S. Kalia (Ed.), Lignocellulosic composite materials (Springer Series on Polymer and Composite Materials, pp. 177-213). Spain: Springer. http://dx.doi.org/10.1007/978-3-319-68696-7_4
  » http://dx.doi.org/10.1007/978-3-319-68696-7_4
• ⁴⁷
  Dufresne, A. (2019). Nanocellulose processing properties and potential applications. Current Forestry Reports, 5(2), 76-89. http://dx.doi.org/10.1007/s40725-019-00088-1
  » http://dx.doi.org/10.1007/s40725-019-00088-1
• ⁴⁸
  Lengowski, E. C., Magalhães, W. L. E., Nisgoski, S., Muniz, G. I. B., Satyanarayana, K. G., & Lazzarotto, M. (2016). New and improved method of investigation using thermal tools for characterization of cellulose from eucalypts pulp. Thermochimica Acta, 638, 44-51. http://dx.doi.org/10.1016/j.tca.2016.06.010
  » http://dx.doi.org/10.1016/j.tca.2016.06.010
• ⁴⁹
  Khenblouche, A., Bechki, D., Gouamid, M., Charradi, K., Segni, L., Hadjadj, M., & Boughali, S. (2019). Extraction and characterization of cellulose microfibers from Retama raetam stems. Polímeros: Ciência e Tecnologia, 29(1), e2019011. http://dx.doi.org/10.1590/0104-1428.05218
  » http://dx.doi.org/10.1590/0104-1428.05218

Publication Dates

• Publication in this collection
  28 July 2021
• Date of issue
  2021

History

• Received
  28 Oct 2020
• Reviewed
  09 Feb 2021
• Accepted
  03 June 2021