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Table 1. Chemical composition of feedstock.
Raw material
Cellulose [%]
Klason lignin [%]
Extractives [%]
Ash [%]
Hemicelluloses [%]
Eucalyptus
46.7
27.9
4.3
1.3
19.8
Hemp hurds
43.0
24.4
2.2
1.4
29.0
Bamboo
43.2
26.7
2.2
0.8
27.1
Hardwood
44.6
26.9
3.7
1.1
23.7
Softwood
46.0
28
3.0
1.0
22.0
** Constituent content calculated on a dry basis by subtracting sum of cellulose, lignin, extractives, and ash contents from 100%.
the Netherlands and Bamboo (Henon) supplied by National Bamboo, LLC. Raleigh, NC, Southern pine, eucalyptus ( E. grandis ), and mixed hardwood and softwoods from local mills. The chemical compositions of these fibers were deter- mined according to the guidance of U.S. Department of Energy, National Renewable Energy Laboratory (NREL) analytical proce- dure TP-510-42618 or the ASTM E1758-01 (2015) in agreement with previous studies [32,33] presented in Table 1 . All chemical reagents were purchased from Fisher Scientific.
methods to raise pulp yield. Despite considerable research effort, kraft and soda are still the predominant processes for producing fibers with low lignin content suitable for papermaking. [17] Almost 80% of the total chemical pulping industry employees kraft pulping, which involves digestion of wood chips in a solu- tion of sodium sulfide and sodium hydroxide at elevated tem- peratures and pressures. [18] It offers the benefit of recovering the cooking chemicals and heat, but also has some drawbacks including emissions of sodium and calcium salts particulates (flue gases) and volatilized reduced sulfur compounds. [19–24] In contrast to kraft, soda and organosolv are sulfur-free processes and thus alkali such as NaOH, KOH, and Ca(OH) 2 are widely used as pretreatment steps for pulping. [25] They can be per- formed at ambient conditions, but require longer pretreatment times. [26,27] Alkali pretreatment is most effective for biomass having low lignin contents such as leftover lignocellulosic feed- stocks, corn stover, switchgrass, bagasse, wheat, and rice straw. [28] Organosolv has been proposed based methanol, ethanol, acetic acid, acetone, etc., to remove lignin. [29] Although this technique comes with reduced emissions of sulfur dioxide and odorous gases because of the use of sulfur-free technology, it is not ready yet to be implemented on an industrial scale. [30] Thus, there is a great opportunity for an alternative pulping system to reduce eco- logical damage by minimizing waste in conventional pulping. [24] The current work discusses new types of chemical pulping where significant efforts have been made to attain sustainable utilization of natural resources. The new processes were car- ried out using very mild chemical conditions and resulted in higher yield of pulp compared to conventional methods (34%– 55%). [31] Non-conventional pulping using 4% sodium carbonate based on Na 2 O for carbonate hydrolysis and 12% active alkali (NaOH + Na 2 S, based on Na 2 O) for mild kraft were studied for five feedstocks: eucalyptus, hemp hurd, bamboo, hardwood and softwood. Fiber yield, lignin content, brightness, surface charges, hard to remove water, and crystallinity were deter- mined. Hence, the present work demonstrates how carbonate hydrolysis and mild kraft pulping can produce higher value fibers. This study will enable acceleration of the biorefinery to tune the properties different feedstock fibers.
2.2. Methods
2.2.1. Defibration
Laboratory defibration highlighting the features of sodium car- bonate and mild kraft defibration are shown in Figure 1 . The defibration process conditions are in Table 2 . A higher water-to- solids ratio of 8:1 was used for hemp due to its low bulk density compared to hardwood. The carbonate hydrolysis was carried out using 4% carbonate (based on Na 2 O). Kraft pulping was done using 12% active alkali and 25% sulfidity (NaOH + Na 2 S) (all on an Na 2 O basis). Both processes were conducted in a stainless-steel reactor under controlled temperature (160 ° C) for 3 h using a mild concentration of sodium carbonate (carbonate) and a high concen- tration of alkali charge (kraft), respectively. The pulp was washed and refined on the laboratory disc refiner (The Bauer Bros Co., Springfield, Ohio, Model 148-2, rpm 3600) at disc gaps of (0.2– 0.1–0.05) mm with three passes for hard wood pulp and disc gaps of (0.1–0.05) mm with two passes for hemp pulp before screening on a 0.15 mm slotted laboratory screen. Pulp yield, Klason lignin content, and freeness were determined using the TAPPI T222 and TAPPI T227 om-09 standard methods, respectively. For simplicity, the following sample IDs will be mentioned in the later part of the article: EU_C and EU_K (Eucalyptus fiber produced by Carbonate and Kraft process); HM_C and HM_K (Hemp fiber produced by Carbonate and Kraft process); BMB_C and BMB_K (Bamboo fiber produced by Carbonate and Kraft process); HW_C and HW_K (Hardwood fiber pro- duced by Carbonate and Kraft process) and SW_C and SW_K (Softwood fiber produced by Carbonate and Kraft process)
2. Experimental Section 2.1. Materials
2.2.2. Characterization of Different Fibers
Fiber Quality Analysis : Fiber length ( l w ), fine contents and other physical properties of the different samples were determined
Five types of feed stocks were selected: Futura 75 cultivar hemp hurds, dew retted, and decorticated procured from
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© 2020 The Authors. Published by Wiley-VCH GmbH
Global Challenges 2021 , 5 , 2000065
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