Abstract
The outer surface of corn stalk (CS) plays a key role in the interfacial compatibility of non-wood-based panel products. To improve the bonding performance of the stalk surface, changes to the outer surface before and after four pretreatments (oxalic acid, oxalic acid + ultrasound, NaOH, NaOH + ultrasound) were investigated. Changes in the chemical composition, surface elements, aggregation structure, and microstructure of CS before and after pretreatment were analyzed. The results revealed that the wax layer, benzene–alcohol extract, and ash content of the outer surface of CS were decreased under different pretreatment conditions. The degree of reduction decreased in the order of NaOH + ultrasound > oxalic acid + ultrasound > NaOH > oxalic acid. The crystallinity of CS was obvious after pretreatment, and it increased in the order of oxalic acid + ultrasound > oxalic acid > NaOH + ultrasound > NaOH. Considering the properties of CS after pretreatment and the lignin activation modification of the CS surface, the optimal pretreatment conditions of CS were determined as oxalic acid + ultrasound, i.e., 5% oxalic acid and ultrasonication at 50 °C for 1 h.
Download PDF
Full Article
Comparative Effects of Pretreatment on Composition and Structure of Corn Stalk for Biocomposites
Yuejing Bin,a,b Sidan Li,a,b Feng Jiao,c Shan Zhong,a,b and Yuan Yuan a,b,*
The outer surface of corn stalk (CS) plays a key role in the interfacial compatibility of non-wood-based panel products. To improve the bonding performance of the stalk surface, changes to the outer surface before and after four pretreatments (oxalic acid, oxalic acid + ultrasound, NaOH, NaOH + ultrasound) were investigated. Changes in the chemical composition, surface elements, aggregation structure, and microstructure of CS before and after pretreatment were analyzed. The results revealed that the wax layer, benzene–alcohol extract, and ash content of the outer surface of CS were decreased under different pretreatment conditions. The degree of reduction decreased in the order of NaOH + ultrasound > oxalic acid + ultrasound > NaOH > oxalic acid. The crystallinity of CS was obvious after pretreatment, and it increased in the order of oxalic acid + ultrasound > oxalic acid > NaOH + ultrasound > NaOH. Considering the properties of CS after pretreatment and the lignin activation modification of the CS surface, the optimal pretreatment conditions of CS were determined as oxalic acid + ultrasound, i.e., 5% oxalic acid and ultrasonication at 50 °C for 1 h.
DOI: 10.15376/biores.17.3.4395-4409
Keywords: Corn stalk; Pretreatment; Oxalic acid; Crystallinity; Surface element; Microstructure
Contact information: a: College of Mechanical and Resource Engineering, Wuzhoul University, Wuzhou 543000, China; b: Wuzhou Engineering Research Center of Resource Recycling, Wuzhou 543000, China; c: College of Agronomy, Heilongjiang Bayi Agricultural University, Daqing 163319, China;
* Corresponding author: yuan__yuan2014@sina.com
INTRODUCTION
Crop straws are the fourth largest source of energy, with an annual production averaging 2.9 billion tons worldwide, led by corn stalk (CS). As a large agricultural country, China has innumerable crop straw resources, with the highest output for crop straw worldwide; its annual output is about 700 million tons, accounting for 24% of the world’s total output, of which CS is approximately 250 million tons, accounting for 41% of the total output of crop straw (Privas and Navard 2013; Li et al. 2019). CS is used as a fuel and feed, as well as for panels, etc. (Widyorini et al. 2005a; Mancera et al. 2012; Nagarajan et al. 2013; Yuan et al. 2019). However, straw is currently found widely in several industrial outlets due to the decline in its demand and prices over the past 15 years. Developed countries as well as countries with high demand for agricultural modernization are increasing their attention to the recycling and full use of crop straw to promote agricultural resource utilization and environmental protection (Mancera et al. 2012; More 2021).
Along with China’s economic development and accelerating pace of agricultural modernization, steady development of the rural economy and society, a considerable change in the farmers’ way of life, and a fundamental change in agricultural production, crop straw is rarely used in wet compost and cooking, which is used less than 5%. The problem of straw overstocking in rural areas is difficult to handle. Incineration of straw in situ causes serious air pollution and other environmental problems, as well as wastage of these resources (Ravindra et al. 2019). To solve the above problems and enhance the added value of straw-derived products, straw treatment technology is being developed. Crops comprise a high amount of a wax layer and ash on their surface due to growth characteristics, making their utilization difficult (Li et al. 2010). The surface treatment of straw raw materials reduces the effects of different components such as silicon and other mineral content on the bonding phase and substrate, and the interface compatibility between straw and the bonding phase can be improved (Zhang et al. 2003).
Pretreatment technologies include mechanical treatment (Yousefi 2009), humid heat and steam treatment (Widyorini et al. 2005b; Kaushik et al. 2010), biological treatment (Zeng et al. 2011; Ko et al. 2019), chemical treatment (Martelli-Tosi et al. 2017; Lazorenko et al. 2020), and physical treatment (Li et al. 2012). There are two problems with traditional pretreatment methods: (1) physical methods such as heat treatment and steam blasting not only destroy the surface structure of straw but also reduce the strength of straw to a certain extent; (2) biological methods have a long cycle and high costs. Related research has focused on kenaf, soybean, and wheat straw materials (Zhang et al. 2003; Kalaycıoglu and Nemli 2006; Ye et al. 2007; Nyambo et al. 2010; Tabarsa et al. 2011), while CS has been investigated to a relatively low extent (Wang and Sun 2002; Zhou et al. 2010; Wu et al. 2011). Hence, it is crucial to seek efficient green pretreatment methods for CS.
In this study, CS was selected as the raw material, and oxalic acid, oxalic acid + ultrasound, NaOH, and NaOH + ultrasound were selected as pretreatments. The changes in the chemical composition, surface elements, aggregation structure, and microstructure of CS were investigated to select suitable pretreatment methods, which might serve as a theoretical guide for further research and practice.
EXPERIMENTAL
Materials
Corn stalks obtained from Anda (Heilongjiang Province, China) were reduced into smaller particles using a flaker (FW-100 high-speed shredder, Changzhou, China). The obtained particles were dried to a moisture content of 5% and passed through a 40- to 60-mesh sieve for separation. Pure analytical-grade oxalic acid and NaOH were purchased from Tianjin Guangfu Chemical Reagent Co., Ltd. (Tianjin, China).
Table 1. Experimental Design of Corn Stalk Pretreatment
Methods
Pretreatment of corn stalks
The effects of oxalic acid, oxalic acid + ultrasound, NaOH, and NaOH + ultrasound pretreatment on the waxy layer and SiO2 on the CS surface were investigated. Table 1 shows the specific experimental design. First, 3 g of CS was dispersed into a 5% oxalic acid or a NaOH solution to form a slurry with a 3% mass concentration. Pretreated CS was dried at 60 °C for 24 h after mechanical stirring at 50 °C or ultrasonication for 1 h. The ultrasonic treatment was carried out by an ultrasonic cleaning (KQ-300DE ultrasonic cleaning machine, Kunshan, China). The CS was treated with ultrasonic wave of 300 W at 50 °C for 1 h in the ultrasonic volume of 10 L. The control group represented CS without pretreatment. Oxalic acid pretreatment, oxalic acid + ultrasound pretreatment, NaOH pretreatment, and NaOH + ultrasound pretreatment were referred to as CSE, CSEUS, CSN, and CSNUS, respectively.
GC-MS analysis
Organic components of CS under different pretreatment conditions were investigated by gas chromatography-mass spectrometry (GC-MS). Chloroform was used for extraction. One microliter of the sample was automatically injected with a split ratio of 2:1 and a split flow rate of 1 mL/min. The inlet temperature was set to 280 °C. The oven was programmed for ramp from 130 to 320 °C at a ramp rate of 10 °C/min and maintained constant at 320 °C for 18 min. The resulting mass spectrum was analyzed using the NIST 20 Library.
Surface characterization of CS
X-ray photoelectron spectroscopy (XPS) was employed to scan the surface chemistry of CS before and after pretreatment, and changes in the C, N, O, and Si content on the sample surface were measured. Table 2 summarizes the chemical shifts and existing valence states of relevant elements. XPS analysis was conducted using MgK (1253.6 eV) as the X-ray source at a pass energy of 20 eV and a vacuum degree for the analysis room of 3.2 × 107 Pa.
Table 2. Chemical Shifts and Structures of Surface Elements of Samples
FTIR and XRD analyses
Fourier transform infrared (FTIR; Thermo Fisher Scientific, Waltham, MA, USA) spectroscopy was employed to analyze changes in functional groups of the samples. The KBr tablet method was employed, and powder samples were used. FTIR spectra were recorded from 4000 to 500 cm−1 at a resolution of 4 cm−1, with a scanning time of 40. X-ray diffraction (XRD) was employed to analyze the crystal structure and relative crystallinity of the samples. The scanning range was 5° to 50° at a scanning speed of 5°/min, and the step distance was 0.02°. The crystallinity index of the sample was calculated in accordance to a previous study (Segal et al. 1959).
Surface morphological analysis
Scanning electron microscopy (SEM) images were recorded to evaluate morphology changes of the CS surface under different pretreatments on a Sirion 200 instrument (FEI, Hillsboro, Oregon, USA). The samples were sprayed with gold to increase the conductivity of the samples. The high-vacuum mode was adopted for tests, and SEM images were recorded at a beam voltage of 12.5 kV.
RESULTS AND DISCUSSION
Analysis of Wax Compounds of the CS Surface after Pretreatment
As key components of the water barrier, epidermal waxy CS was attached to the outermost layers of the plant hydrophobic material (Bourgault et al. 2019). According to GC-MS analysis, the wax compounds of CS under different pretreatment conditions were well isolated. From the mass spectrometry database, a total of 16 epidermal wax compounds were identified, including alkanes, primary alcohols, aliphatic aldehydes, fatty acids, and diketones (Liao et al. 2021). Among these compounds, four alkanes were present, mainly with an odd number of carbon atoms with a carbon chain length of C25–C31 alkanes. Four primary alcohols were present, mainly with even carbon atoms and carbon chain lengths ranging from C22 to C30. Six fatty acids, mainly with an even number of carbon atoms and carbon chain lengths ranging from C22 to C32, were present. Two diketones, viz. β-diketones with a carbon chain length of C31 and their derivatives. Figure 1 shows the quantitative analysis of the total wax layer and contents of each component in the control, CSE, CSEUS, CSN, and CSNUS. Compared to the control (11.26 μg/cm2), the total wax content decreased in the order of CSNUS > CSEUS > CSN > CSE. Fatty acids were the main wax components of the outer surface of CS, and the fatty acids of the control, CSNUS, CSEUS, CSN, and CSE reached 9.86, 3.66, 3.89, 4.16, and 5.37 μg/cm2, respectively.
Fig. 1. Absolute content of the total wax and components of corn stalk after various pretreatments
Table 3. Relative Contents of Wax Components of Corn Stalk
The relative content of epidermal wax components of CS raw materials revealed 87.6% of fatty acids, followed by 7.4% of primary alcohols, 4.1% of alkanes, and 0.92% of diketones. The wax components of CS epidermis were different under different pretreatment conditions. The fatty-acid content of wax exhibited a decreasing trend, and the relative contents of fatty acids reached the minimum after the oxalic acid + ultrasound treatment. The primary alcohol and alkane content increased marginally and reached the maximum after NaOH and oxalic acid + ultrasound treatments. The relative content of dione increased, while the dione content reached the maximum after the NaOH + ultrasound treatment. The results revealed that the effect of the pretreatment of the wax layer of the CS surface is particularly important to improve wettability on the straw surface.
Effect of Pretreatment on Chemical Elements and Lignin Content of CS
X-ray photoelectron spectroscopy is an efficient modern analytical method to characterize the chemical composition of material surfaces (Popescu et al. 2009). Unlike wood, CS contains a certain amount of a wax layer and Si on its surface, in addition to the three main components (i.e., cellulose, hemicellulose, and lignin). The distribution and valence states of C, O, Si, and N in CS were determined. The O/C ratio on the CS surface was calculated by XPS spectroscopy at a low resolution, and the relative content of C1s in different oxidation states was calculated by XPS at a high resolution to further determine changes in the lignin content on the CS surface. Figure 2 shows low-resolution spectra of the control, CSE, CSEUS, CSN, and CSNUS.
Fig. 2. Low-resolution spectra of C1s, O1s, and Si 2p of corn stalk after various pretreatments
Table 4. Surface Element Content and O/C Ratio of Corn Stalk after Various Pretreatments
Table 4 shows the surface elemental contents of each sample. Compared with the O/C ratio of the control, the O/C ratios of oxalic acid and NaOH pretreatment were higher, indicative of a low lignin content of CSE and CSN. The higher O/C ratio on the CS surface may be related to the dominant effect of the depolymerization of lignin on the CS surface (Ström and Carlsson 1992). However, the O/C ratio did not change significantly in synergistic ultrasound treatment, indicating that ultrasound treatment does not affect the lignin content on the CS surface. For Si, the chemical environment of Si in the sample was mainly in the form of SiO2 (binding energy of 103.2 eV). Pretreatment could effectively reduce the content of SiO2 in the straw, and the reduction degree followed the order of CSEUS > CSE > CSNUS > CSN. Compared with that in the control, the N content of all pretreated samples reduced, and that of CSN was the least, possibly because NaOH could remove protein compounds in CS, leading to the reduction of N.
Fig. 3. High-resolution spectra of C1s of corn stalk after various pretreatments
Table 5. Binding Energies and Peak Area of Samples
The high-resolution C1s spectra of corn straw under different pretreatment conditions were fitted (Fig. 3). Table 5 summarizes the C1–C4 chemical binding energies and relative absorption peak area of C1s with different oxidation states. The relative absorption peak area of C1 (C–C and C–H only exist in lignin or in the extract of CS but not in cellulose and hemicellulose) in the control was 46.6%. The peak area of CSE, CSEUS, CSN, and CSNUS decreased to 35.7%, 46.0%, 38.9%, and 44.2%, respectively. Compared to CSE and CSN, CSEUS and CSNUS exhibited lower C1 peak areas, indicating that oxalic acid + ultrasound and NaOH + ultrasound treatments can remove a small amount of lignin from the CS surface; this result is consistent with that of the reduction of lignin content in the low-resolution spectrogram. The peak area of C2 (C-O, which exists in carbohydrate components of CS), increased after different pretreatments compared to the control, indicating that carbohydrate on the CS surface increase after pretreatment and that the increasing increase degree in the order of CSEUS > CSNUS > CSN > CSE. The peak area of C3 (C=O or O-C-O) increased only in CSE after different pretreatments compared to the control, which may be related to the oxalic-acid degradation of cellulose/hemicellulose in CS. The peak area of C4 (O-C=O, mainly in carboxylic acid) decreased compared to the control, CSEUS, and CSNUS, and it increased in CSE and CSN. These results are thought to be related to the increase in the carboxylic-acid components in the sample during pretreatment and the fact that ultrasound treatment potentially remove a part of the carboxylic-acid components, leading to two changes in the carboxylic acid components (Popescu et al. 2009).
Analysis of Chemical Components of CS after Pretreatment
The chemical compositions of samples were determined according to GB/T 2677. Compared with that of wood, the main chemical composition of CS was similar to that of poplar and broadleaf forest (Yuan and Guo 2017), but its ash content and extract content were greater than that of wood (Rodríguez et al. 2010). Compared with other crop straws, corn straws exhibited a higher lignin content (Reddy and Yang 2005). Changes in the main chemical components on the CS surface before and after pretreatment were observed (Table 6).
Table 6. Main Chemical Components of Samples
The contents of ash and solution extract considerably affected the production of non-wood-based panels. Ash is an inorganic residue of straw after high-temperature combustion, and SiO2 is its main component. A high ash content not only causes dust pollution but also increases the cost of adhesive raw materials. The cold-water extract mainly contains tannins, pigments, alkaloids, soluble mineral components, and some sugars, while the benzene–alcohol extract mainly contains oils, waxes, and fats, as well as a small number of soluble tannins and pigments. The 1% NaOH extract contains protein, amino acid, and a small amount of oil, wax, and essential oil, in addition to the components of the hot-water extract. The higher the solution extract content, the more difficult the bonding with the adhesive, and the size deviation of the panel can easily occur. Moreover, with long-term storage, rotting can easily occur, and mildew and moisture again affect the composite panel, which in turn affects its performance. Compared to the control, the benzene-alcohol extract and ash content decreased after pretreatment, which was consistent with the results obtained from GC-MS and XPS; this result indicated that pretreatment can be an effective to treat the wax layer and ash content of CS.
The main characteristic peaks observed in the IR spectrum of the CS surface were as follows (Fig. 4): 3317 to 3331 cm−1 corresponding to OH stretching, which is generally thought to represent cellulose, hemicellulose, and polysaccharide monosaccharide; 2888 to 2904 cm−1 corresponds to the anti-symmetric peak of -CH stretching vibration in cellulose; 1640 to 1730 cm−1 corresponds to the C=O stretching vibration peak of lignin or hemicellulose-related carboxylic esters and ketones. The C-O-C asymmetric stretching vibration peak of aliphatic compounds was observed at 1159 cm−1, and the Si-O stretching vibration of inorganic materials such as SiO2 was observed at 1016 cm−1. A significant change in the IR spectra of CS after pretreatment was not observed, indicating that it does not significantly affect the principal components of CS and that it plays a role in surface removal rather than in modification.
Fig. 4. FTIR spectra of corn stalk surface after pretreatment
Compared with untreated CS, some characteristic absorption peaks on the CS surface without pretreatment were changed. After four types of pretreatment (viz. oxalic acid, oxalic acid + ultrasound, NaOH, and NaOH + ultrasound, respectively), the intensity of absorption peaks corresponding to OH stretching and C-H stretching vibrations increased, and the amplitude of enhancement decreased in the order of CSN > CSNUS > CSE > CSEUS, which may be oxalic acid + ultrasound caused to the cellulose structure least damage. After NaOH treatment, the number of bands decreased most clearly at 1640 to 1730 cm−1, which basically disappeared at 1728 cm−1, indicating that NaOH treatment destroys C-O and dissolves lignin and hemicellulose; hence, cellulose content increases (Pang et al. 2012). The absorption vibration peak of CS treated with oxalic acid, oxalic acid and ultrasound increased slightly at 1640 to 1730 cm−1, indicating that oxalic-acid treatment could increase the relative contents of hemicellulose and lignin. After pretreatment, compared to the untreated CS surface, the intensity of the peaks was weakened, i.e., bands were observed at 1159 cm−1 and 1064 cm−1, and the order was as follows: CSN > CSNUS > CSE > CSEUS. The results revealed that the oxalic acid + ultrasound pretreatment could effectively reduce the lipid and SiO2 on the CS surface, thus reducing the waxy layer and ash content on the CS surface and improving its wettability; this result is consistent with those of GC-MS and XPS.
Changes to Crystallinity and Microstructure of CS after Pretreatment
Figure 5 shows changes in the crystal shape and crystallinity of CS before and after pretreatment. Diffraction peaks were observed at 2θ equal to 18.8° and 22.1°, corresponding to typical cellulose I. Therefore, in pretreatment, irrespective of the addition of oxalic acid or NaOH, CS can maintain the integrity of the original crystal, and its diffraction peak is similar to that of natural cellulose (Yao et al. 2008). The crystal structure of CS did not change significantly before and after pretreatment. The crystallinity of the CS of control was 55.3%. The crystallinity of CN was increased after pretreatment. The crystallinities of CSE, CSEUS, CSN, and CSNUS were 62.22%, 64.10%, 60.06%, and 60.83%, respectively. This result indicated that the oxalic acid + ultrasound pretreatment is suitable for the growth of crystallinity; meanwhile, a positive effect on the CS lignin-activated treatment was observed.
Fig. 5. XRD patterns and relative crystallinity of corn stalks after pretreatment
Fig. 6. SEM images of corn stalks before and after pretreatment (a: untreated corn stalks, b: oxalic acid treatment, c: oxalic acid + ultrasonic treatment, d: NaOH treatment, e: NaOH + ultrasonic treatment)
The outer surface of CS without pretreatment was dense and smooth, and the surface wax layer was clearly visible (Fig. 6). After oxalic acid and oxalic acid + ultrasound pretreatments, the surface gloss of CS decreased, indicating that the cuticle and siliceous layers are partially removed, albeit the overall surface is relatively smooth. After oxalic acid + ultrasound pretreatment, the approximately rectangular thin-walled cells on the inner surface of CS were exposed clearly, similar to enzymatic treatment (Ko et al. 2019). After NaOH and NaOH + ultrasound treatment, the silky layer on the CS surface was almost dissolved, and the fibers were exposed. Notably, after NaOH + ultrasonic treatment, a part of flower-like SiO2 was broken and dispersed on the CS surface, further confirming that pretreatment can remove lipid substances on the CS surface, which is consistent with the results obtained from GC-MS, XPS, and FTIR.
CONCLUSIONS
- Compared with the control, the benzene-alcohol extract and ash content decreased after pretreatment. Si in the samples was mainly present as SiO2. Pretreatment effectively reduced the SiO2 content of corn stalk (CS), and the reduction followed the order of CSEUS > CSE > CSNUS > CSN, where the subscripts have the following meanings: E = oxalic acid extraction; US = ultrasonic treatment; N = NaOH extraction
- Four pretreatments effectively reduced the waxy layer and ash content on the corn straw surface and improved its wettability. The total amount of wax decreased in the order of CSNUS > CSEUS > CSN > CSE. Fatty acids were the main wax components of the outer surface of corn stalk. The crystallinity of CS was clearly improved after pretreatment in the following order: CSEUS > CSE > CSNUS > CSN.
- The optimal pretreatment conditions of CS were oxalic acid + ultrasound treatment, i.e., 5% oxalic acid and ultrasound treatment at 50 °C for 1 h.
ACKNOWLEDGMENTS
The authors are grateful for the support of Fund Project of Guangxi Central Guiding development of local science and technology in 2021 (Grant No. ZY21195056), Scientific Research Project of Scientific Research Talents Small Highland of Wuzhou University in Liubao Tea Industry of Guangxi (No.1 paper of Guicha Rengao [2020]), the Project of Wuzhou Liubao Tea Industry in 2020 and the National Natural Science Foundation of China (Grant No. 31801313).
REFERENCES CITED
Bourgault, R., Matschi, S., Vasquez, M., Qiao, P., Sonntag, A., Charlebois, C., Mohammadi, M., Scanlon, M., Smith, L., and Molina, I. (2019). “Constructing functional cuticles: Analysis of relationships between cuticle lipid composition, ultrastructure and water barrier function in developing adult maize leaves,” Annals of Botany 125(1), 79-91. DOI: 10.1093/aob/mcz143
Kalaycıoglu, H., and Nemli, G. (2006). “Producing composite particleboard from kenaf (Hibiscus cannabinus L.) stalks,” Industrial Crops and Products 24(2), 177-180. DOI: 10.1016/j.indcrop.2006.03.011
Kaushik, A., Singh, M., and Verma, G. (2010). “Green nanocomposites based on thermoplastic starch and steam exploded cellulose nanofibrils from wheat straw,” Carbohydrate Polymers 82(2), 337-345. DOI: 10.1016/j.carbpol.2010.04.063
Ko, C.-H., Yang, C.-Y., Chang, F.-C., and Lin, L.-D. (2019). “Effect of Paenibacillus cellulase pretreatment for fiber surface,” Journal of Environmental Management 241, 1-11. DOI: 10.1016/j.jenvman.2019.03.133
Lazorenko, G., Kasprzhitskii, A., Yavna, V., Mischinenko, V., Kukharskii, A., Kruglikov, A., Kolodina, A., and Yalovega, G. (2020). “Effect of pre-treatment of flax tows on mechanical properties and microstructure of natural fiber reinforced geopolymer composites,” Environmental Technology and Innovation 20, 101105. DOI: 10.1016/j.eti.2020.101105
Li, F. H., Hu, H. J., Yao, R. S., Wang, H., and Li, M. M. (2012). “Structure and saccharification of rice straw pretreated with microwave-assisted dilute lye,” Industrial and Engineering Chemistry Research 51(17), 6270-6274. DOI: 10.1021/ie202547w
Li, S., Yuan, Y., Wang, J., and Guo, M. (2019). “Fabrication and characterization of a novel corn straw/modified ammonium lignosulfonate bio-composite strengthened by polyethylenimine pretreatment,” RSC Advances 9(60), 34754-34760. DOI: 10.1039/C9RA06237H
Li, X., Cai, Z., Winandy, J. E., and Basta, A. H. (2010). “Selected properties of particleboard panels manufactured from rice straws of different geometries,” Bioresource Technology 101(12), 4662-4666. DOI: 10.1016/j.biortech.2010.01.053
Liao, J., He, S., Mo, L., Guo, S., Luan, P., Zhang, X., and Li, J. (2021). “Mass-production of high-yield and high-strength thermomechanical pulp fibers from plant residues enabled by ozone pretreatment,” Journal of Cleaner Production 296, 126575. DOI: 10.1016/j.jclepro.2021.126575
Mancera, C., El Mansouri, N.-E., Pelach, M. A., Francesc, F., and Salvadó, J. (2012). “Feasibility of incorporating treated lignins in fiberboards made from agricultural waste,” Waste Management 32(10), 1962-1967. DOI: 10.1016/j.wasman.2012.05.019
Martelli-Tosi, M., Assis, O. B. G., Silva, N. C., Esposto, B. S., Martins, M. A., and Tapia-Blácido, D. R. (2017). “Chemical treatment and characterization of soybean straw and soybean protein isolate/straw composite films,” Carbohydrate Polymers 157, 512-520. DOI: 10.1016/j.carbpol.2016.10.013
More, A. P. (2021). “Flax fiber–based polymer composites: A review,” Advanced Composites and Hybrid Materials. DOI: 10.1007/s42114-021-00246-9
Nagarajan, V., Mohanty, A. K., and Misra, M. (2013). “Sustainable green composites: Value addition to agricultural residues and perennial grasses,” ACS Sustainable Chemistry and Engineering 1, 325-333. DOI: 10.1021/sc300084z
Nyambo, C., Mohanty, A. K., and Misra, M. (2010). “Polylactide-based renewable green composites from agricultural residues and their hybrids,” Biomacromolecules 11(6), 1654-1660. DOI: 10.1021/bm1003114
Pang, C., Xie, T., Lin, L., Zhuang, J., Liu, Y., Shi, J., and Yang, Q. (2012). “Changes of the surface structure of corn stalk in the cooking process with active oxygen and MgO-based solid alkali as a pretreatment of its biomass conversion,” Bioresource Technology 103(1), 432-439. DOI: 10.1016/j.biortech.2011.09.135
Popescu, C.-M., Tibirna, C.-M., and Vasile, C. (2009). “XPS characterization of naturally aged wood,” Applied Surface Science 256(5), 1355-1360. DOI: 10.1016/j.apsusc.2009.08.087
Privas, E., and Navard, P. (2013). “Preparation, processing and properties of lignosulfonate–flax composite boards,” Carbohydrate Polymers 93(1), 300-306. DOI: 10.1016/j.carbpol.2012.04.060
Ravindra, K., Singh, T., and Mor, S. (2019). “Emissions of air pollutants from primary crop residue burning in India and their mitigation strategies for cleaner emissions,” Journal of Cleaner Production 208, 261-273. DOI: 10.1016/j.jclepro.2018.10.031
Reddy, N., and Yang, Y. (2005). “Properties and potential applications of natural cellulose fibers from cornhusks,” Green Chemistry 7(4), 190-195. DOI: 10.1039/B415102J
Rodríguez, M., Rodríguez, A., Jb, R., Vilaseca, F., and Mutjé, P. (2010). “Determination of corn stalk fibers’ strength through modeling of the mechanical properties of its composites,” BioResources 5(4), 2535-2546. DOI: 10.15376/biores.5.4.2535-2546
Segal, L., Creely, J. J., Martin, A. E., and 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. DOI: 10.1177/004051755902901003
Ström, G., and Carlsson, G. (1992). “Wettability of kraft pulps-effect of surface composition and oxygen plasma treatment,” Journal of Adhesion Science and Technology 6(6), 745-761. DOI: 10.1163/156856192X01088
Tabarsa, T., Jahanshahi, S., and Ashori, A. (2011). “Mechanical and physical properties of wheat straw boards bonded with a tannin modified phenol–formaldehyde adhesive,” Composites Part B: Engineering 42(2), 176-180. DOI: 10.1016/j.compositesb.2010.09.012
Wang, D. H., and Sun, X. S. (2002). “Low density particleboard from wheat straw and corn pith,” Industrial Crops and Products 15(1), 43-50. DOI: 10.1016/s0926-6690(01)00094-2
Widyorini, R., Higashihara, T., Xu, J., Watanabe, T., and Kawai, S. (2005a). “Self-bonding characteristics of binderless kenaf core composites,” Wood Science and Technology 39(8), 651-662. DOI: 10.1007/s00226-005-0030-0
Widyorini, R., Xu, J., Watanabe, T., and Kawai, S. (2005b). “Chemical changes in steam-pressed kenaf core binderless particleboard,” Journal of Wood Science 51(1), 26-32. DOI: 10.1007/s10086-003-0608-9
Wu, J. G., Zhang, X., Wan, J. L., Ma, F. Y., Tang, Y., and Zhang, X. Y. (2011). “Production of fiberboard using corn stalk pretreated with white-rot fungus Trametes hirsute by hot pressing without adhesive,” Bioresource Technology 102(24), 11258-11261. DOI: 10.1016/j.biortech.2011.09.097
Yao, F., Wu, Q., Lei, Y., and Xu, Y. (2008). “Rice straw fiber-reinforced high-density polyethylene composite: Effect of fiber type and loading,” Industrial Crops and Products 28(1), 63-72. DOI: 10.1016/j.indcrop.2008.01.007
Ye, X. P., Julson, J., Kuo, M., Womac, A., and Myers, D. (2007). “Properties of medium density fiberboards made from renewable biomass,” Bioresource Technology 98(5), 1077-1084. DOI: 10.1016/j.biortech.2006.04.022
Yousefi, H. (2009). “Canola straw as a bio-waste resource for medium density fiberboard (MDF) manufacture,” Waste Management 29(10), 2644-2648. DOI: 10.1016/j.wasman.2009.06.018
Yuan, Y., Sidan, L., Feng, J., Guinan, S., Lei, Y., and Weidong, W. (2019). “Dimensional stability improvement of corn stalk biocomposites using two-part lignin-derived binder optimized with response surface methodology,” BioResources 14(3), 5923-5942. DOI: 10.15376/biores.14.3.5923-5942
Yuan, Y., and Guo, M. (2017). “Do green wooden composites using lignin-based binder have environmentally benign alternatives? A preliminary LCA case study in China,” The International Journal of Life Cycle Assessment 22(8), 1318-1326. DOI: 10.1007/s11367-016-1235-1
Zeng, J. J., Singh, D., and Chen, S. L. (2011). “Biological pretreatment of wheat straw by Phanerochaete chrysosporium supplemented with inorganic salts,” Bioresource Technology 102(3), 3206-3214. DOI: 10.1016/j.biortech.2010.11.008
Zhang, Y., Lu, X., Pizzi, A., and Delmotte, L. (2003). “Wheat straw particleboard bonding improvements by enzyme pretreatment,” European Journal of Wood and Wood Products 61(1), 49-54. DOI: 10.1007/s00107-002-0349-2
Zhou, X. Y., Zheng, F., Li, H. G., and Lu, C. L. (2010). “An environment-friendly thermal insulation material from cotton stalk fibers,” Energy and Buildings 42(7), 1070-1074. DOI: 10.1016/j.enbuild.2010.01.020
Article submitted: February 20, 2022; Peer review completed: April 25, 2022; Revised version received: May 8, 2022; Accepted: May 30, 2022; Published: June 1, 2022.
DOI: 10.15376/biores.17.3.4395-4409