Extraction of Ramie Fiber in Alkali Hydrogen Peroxide System Supported by Controlled-release Alkali Source

Summary

Presented here is a protocol for extraction of ramie fiber in alkali hydrogen peroxide system supported by controlled-release alkali source.

Abstract

This protocol demonstrates a method for ramie fiber extraction by scouring raw ramie in an alkali hydrogen peroxide system supported by a controlled-release alkali source. The fiber extracted from ramie is a type of textile material of great importance. In previous studies, ramie fiber was extracted in an alkali hydrogen peroxide system supported only by sodium hydroxide.However, due to the strong alkalinity of sodium hydroxide, the oxidation reaction speed of hydrogen peroxide was difficult to control and thus resulted in great damage to the treated fiber. In this protocol, a controlled-release alkali source, which is composed of sodium hydroxide and magnesium hydroxide, is used to provide an alkali condition and buffer the pH value of the alkali hydrogen peroxidesystem. The substitution rate of magnesium hydroxide can adjust the pH value of the hydrogen peroxide system and has great influence on the fiber properties. The pH value and oxidation-reduction potential (ORP) value, which represents the oxidation ability of alkali hydrogen peroxide system, were monitored using a pH meter and ORP meter, respectively. The residual hydrogen peroxide content in the alkali hydrogen peroxide system during the extraction process and the chemical oxygen demand (COD) value of wastewater after fiber extraction are tested by KMnO₄ titration method. The yield of fiber is measured using a precision electronic balance, and residual gums of fiber are tested by a chemical analysis method. The polymerization degree (PD value) of fiber is tested by an intrinsic viscosity method using the Ubbelohde viscometer. The tensile property of fiber, including tenacity, elongation, and rupture, is measured using a fiber strength instrument. Fourier transform infrared spectroscopy and X-ray diffraction are used to characterize the functional groups and crystal property of fiber. This protocol proves that the controlled-release alkali source can improve the properties of the fiber extracted in an alkali hydrogen peroxide system.

Introduction

Ramie, commonly known as 'China grass' is a perennial herb whose fiber can be used as an excellent material for the textile industry^1,2. It is one of the main economic crops native to China; the production of ramie in China has accounted for more than 90% of the total yield in the world^1,2. Ramie fiber is one of the strongest and longest plant fibers, lustrous with an almost silky appearance^3,4. The long length of ramie fiber make it suitable for single fiber spinning, which is seldom seen in bast fiber. The textile made from ramie fiber possesses many excellent properties, such as coolness, antibacterial, excellent thermal conductivity, ventilation, etc.^3,4

Cellulose is the main component of ramie fibers, and the other components in ramie, such as pectin, lignin, water soluble materials, are defined as gums^5,6. Ramie fiber can be extracted by dissolving the gums in solution containing chemical reagents, in a process defined as degumming^5,6. Mainly two approaches of ramie fiber extraction exist: chemical degumming and bio-degumming. The energy consumption, time consumption, and COD value of degumming wastewater in traditional chemical degumming is rather high, as cellulose fiber is extracted by scouring raw ramie in concentrated NaOH under high pressure for 6 to 8 h^7,8. Alternatively, bio-degumming is an eco-friendly option for ramie fiber extraction. Nevertheless, the harsh reaction condition and sophisticated equipment inhibit its further industrial application^9,10. Therefore, oxidation degumming with alkali hydrogen peroxide presents a valuable and alternative application to focus on, for it requires shorter degumming time and lower degumming temperature^11,12. However, due to the strong oxidation ability of the peroxides, substantial cellulose degradation may occur during the degumming process, which can cause great damage to fiber properties^13,14. This is the biggest drawback of alkali peroxide oxidation degumming of ramie.

In previous studies, ramie fiber was extracted in an alkali hydrogen peroxide system supported only by sodium hydroxide¹⁵. However, due to the strong alkalinity of sodium hydroxide, the oxidation reaction speed of hydrogen peroxide was difficult to control and thus resulted in great damage to the treated fiber⁷. To improve the properties of ramie fiber, a controlled-release alkali source, which is composed of sodium hydroxide and magnesium hydroxide, is used in this study to offer an alkali condition and buffer the pH value of alkali hydrogen peroxide system^16,17.

The rationale behind this technology can be described as follows. Magnesium hydroxide is slightly soluble in distilled water, and it can dissolve gradually into the degumming solution with the consumption of OH^- and keep the pH value and thus oxidation ability of degumming solution in an appropriate range¹⁸. The substitution rate (SR) of magnesium hydroxide is defined as the mole proportion of NaOH replaced by magnesium hydroxide under the total alkali dosage of 10%, and the substitution rate can be calculated by the following equation. Moreover, Mg²⁺ can prevent cellulose degradation caused by over oxidation^19,20.

Here, M₂ (g) is the weight of Mg(OH)₂, M₁ (g) is the weight of NaOH, 40 is the molecular weight of NaOH, 58 is the molecular weight of Mg(OH)₂, 2 is the number of OHs in Mg(OH)₂, and SR is the substitution rate.

The technology of this protocol can be extended to the extracting, bleaching, and modifying of plant materials in an alkali hydrogen peroxide system. However, it must be noted that the selection of pH value and reaction temperature of the alkali hydrogen peroxide system is key for this technology²¹. The pH value of the alkali hydrogen peroxide system can be adjusted by changing the substitution rate¹⁷. The pH value and thus oxidation ability of the alkali hydrogen peroxide system decrease with the increasing of substitution rate. When the reaction temperature is set at 85 °C, the free radical reaction plays the main role in the system and the strong oxidation of the system is suitable for dissolving materials; when the reaction temperature is set at 125 °C, the free radical reaction is inhibited and a large amount of HOO exists in the system, which makes the system suitable for bleaching¹⁹.

Protocol

1. Oxidation Degumming of Ramie

1. Preparing the oxidation degumming solution
   1. Dissolve 2 g H₂O₂, 1 g alkali (a mixture of Mg(OH)₂ and NaOH), 0.4 g Na₅P₃O₁₀, 0.1 g anthraquinone, and 0.2 g HEDP in 100 mL distilled water to make the degumming solution.
2. Oxidation degumming of ramie
   1. Immerse 10 g raw ramie in the degumming solution and scour it under 85 °C for 60 min.
   2. Raise the temperature to 125 °C (with pressure of 0.6 kg) and scour for another 60 min.
      NOTE: See the Discussion for explanation on raising the temperature.
3. Reducing the ramie fiber
   1. Dissolve 0.4 g NaHSO₃ in 100 mL distilled water to prepare the reducing solution. Then, treat the degummed fiber in the reducing solution at 90 °C for 60 min.
      NOTE: The carboxyl groups and aldehyde groups in cellulose generated in the oxidation reaction cause the reduction of hydrogen bonds and thus damage to the fiber property. Reducing can improve the property of the fiber by converting the carboxyl groups and aldehyde groups back to hydroxyl groups.
4. Follow-up treatment
   1. Wash the degummed ramie fiber thoroughly with deionized water.
   2. Immerse the fiber in degumming oil at 90 °C for 15 min and then dry the fiber in an oven (125 °C) for 4 h.

2. Testing of the Degumming Solution Property

1. Solubility test of Mg(OH)₂
   1. Dissolve 2 g Mg(OH)₂ in 100 mL distilled water.
   2. Separately, dissolve 2 g Mg(OH)₂ in 100 mL solution with completely soluble degumming additives, including 0.4 g Na₅P₃O₁₀ and 0.2 g HEDP.
   3. Raise the temperature of the solutions described in steps 2.2.1 and 2.2.2 to 85 °C.
   4. Extract the undissolved Mg(OH)₂ with sintered discs.
   5. Calculate the solubility of Mg(OH)₂ by the following formula:
      
      NOTE: Here m (g) is the weight of the undissolved Mg(OH)₂.
2. Effect of the Mg(OH)₂ substitution rate on pH value, ORP value, and residual H₂O₂ content of the degumming solution
   NOTE: ORP^12,19 is an important water chemistry parameter and it provides a measurement tool for the oxidizing or reducing capacity of the ambient water. Solutions with stronger oxidation property have a higher ORP value. The Mg(OH)₂ substitution rate refers to the mole proportion of NaOH replaced by Mg(OH)₂ under the total alkali dosage of 10% (on weight of fabric).
   1. Prepare the degumming solutions with Mg(OH)₂ substitution rate of 0%, 20%, 40%, 60%, 80%, and 100% according to step 1.1, respectively.
   2. Immerse the raw ramie in the degumming solutions described in step 2.2.1.
   3. Start the degumming process according to step 1.2.
   4. Wash the combined ORP electrode with distilled water and dry it in the air. Then immerse the combined ORP electrode meter in the degumming solutions to read the ORP value every 10 min. Immerse the pH electrode meter in the degumming solutions to read the pH value every 10 min.
   5. Test the H₂O₂ content of the degumming solutions every 10 min by the KMnO₄ titration method according to Chinese standard GB 22216-2008⁷.

3. Testing the Ramie Fiber Property

1. Yield of degumming
   1. Calculate the yield of degumming using the following equation:
      
      NOTE: Here w (g) is dry weight of fiber after degumming; W (g) is dry weight of ramie before degumming.
2. Residual gums of the fiber
   NOTE: Residual gums of fiber were tested according to Chinese standard 5889 - 86.
   1. Measure the dry weight of the fiber (about 5 g) in a weighing bottle and immerse it in a flask (with reflux condensing tube) containing 150 mL NaOH solution (20 g/L).
   2. Raise the temperature to 100 °C and keep at this temperature for 1 h.
   3. Refresh the NaOH solution.
   4. Raise the temperature to 100 °C and maintain for 2 h.
   5. Wash the fiber in a sample sieve.
   6. Measure the dry weight of the fiber in weighing bottle.
   7. Calculate the residual gums of fiber using the following equation:
      
      NOTE: Here m (g) is the dry weight of fiber; M (g) is the dry weight of ramie after NaOH scouring.
3. PD test
   NOTE: Test the PD value of ramie fiber according to Chinese standard GB 5888-86¹⁵.
   1. Degrease the ramie fiber by submerging in 2:1 (v/v) benzene and ethyl alcohol mixture.
   2. Evaporate the solvent in air at room temperature.
   3. Cut the samples into short pieces (1-2 mm, about ~20-23 mg for each sample) using scissors.
   4. Keep the samples in a controlled-humidity atmosphere (20 ± 2 °C, relative humidity = 65 ± 2%) in a weighing container until it reaches equilibrium water content before removing the materials required for test purposes.
   5. Immerse a copper wire (0.5 mm diameter) in concentrated nitric acid, followed by 98% anhydrous ethylenediamine. Then, wash the copper granule thoroughly with distilled water.
   6. Put the fiber sample and copper granule in a plastic bottle (with top).
   7. Add 10 mL distilled water and 10 mL 1 mol/L cupriethylenediamine solution into the plastic bottle, and stir using a magnetic stir bar to prepare 0.2 g/100 mL (approximately) ramie fiber cupriethylenediamine solution.
   8. Transfer 6.5 mL ramie fiber cupriethylenediamine solution to a Ubbelohde viscometer to measure its intrinsic viscosity. Calculate the relative viscosity by the following equation:
      
      NOTE: Here η_r is the relative viscosity, t (s) is the average time of the ramie fiber cupriethylenediamine solution flowing through the Ubbelohde viscometer, and t0 (s) is the average time of the 0.5 mol/L cupriethylenediamine solution flowing through the Ubbelohde viscometer.
   9. Calculate the PD value of the ramie fiber by the following equation:
      
      NOTE: Here [η]' is the intrinsic viscosity, the [η]×C value can be obtained from a table in Chinese standard GB 5888-86, and C' is the concentration of ramie fiber cupriethylenediamine solution.
4. Linear density of the fiber
   1. Calculate linear density of fiber using the following equation:
      
      NOTE: Here L_c is the cutting length (40 mm), n is the numbers of fibers, and G (g) is weight of the fiber. Linear density of the fiber refers to the weight of a 1,000 m long fiber under official regain of ramie (12%).
5. Mechanical property test
   1. Equilibrate the fiber samples in standard atmospheric condition (T = 20 ± 2 °C, RH = 65% ± 2%) for 24 h.
   2. Test the tenacity, breaking elongation, and work of rupture of the fiber using the fiber strength instrument under the following setting of 20 °C, RH 65%, and pre-tension of 0.3 cN/dtex. Set the clamping distance at 20 mm and the descending speed of the bottom clamp at 20 mm/min^7,15.
6. COD value of degumming wastewater
   1. Test the COD of degumming wastewater according to Chinese standard GB/T 15456-2008 'Industrial circulating cooling water-Determination of the COD-Potassium permanganate method'^7,15.
7. XRD test
   1. Obtain crystallinity of the fiber using X-ray diffraction. Record XRD patterns 2θ = 5-60 ° with a diffractometer equipped with a graphite monochromator and Cu Kα radiation at λ = 0.154 nm (40 kV, 200 mA).
8. FTIR analysis
   1. Obtain the FTIR pattern of fiber using spectrometer. Set the scan times at 30, the range at 4,000-400 cm^-1, and the resolution at 8 cm^-1. Determine the chemical functional groups in treated fiber using FT-IR analysis.

Results

The solubility of Mg(OH)₂ in distilled water and degumming solution was studied (Figure 1). The effect of Mg(OH)₂ substitution rate on pH value and ORP value (Figure 2) of the degumming solution was tested. The degumming yield and residual gums of fiber degummed under various Mg(OH)₂ substitution rate were calculated (Figure 3). DP value, crystallinity, tensile proper...

Discussion

The setting of Mg(OH)₂ substitution rate and reaction temperature was the key point of this protocol. Mg(OH)₂ substitution rate can influence the pH value and thus oxidation ability of degumming solution. The best Mg(OH)₂ substitution rate for ramie degumming was 20%, because cellulose cannot receive enough protection under a substitution rate below 20%, and an excessive amount of residual gums (low DP value and crystallinity) would be retained in fiber under a substitution rate above 20%...

Materials

Name	Company	Catalog Number	Comments
Hydrogen peroxide, 30%	Fisher Scientific	H325-100	Chemical for degumming
Magnesium hydroxide, 99%	Fisher Scientific	AA1236722	Chemical for degumming
Sodium hydroxide	Fisher Scientific	S318-1	Chemical for degumming
Sodium bisulfite	Fisher Scientific	S654-500	Chemical for degumming
Sodium tripolyphosphate	Fisher Scientific	AC218675000	Chemical for degumming
Anthraquinone, >98%	Fisher Scientific	AC104930500	Chemical for degumming
1-Hydroxy Ethylidene-1,1-Diphosphonic Acid	Fisher Scientific	50-901-10243	Chemical for degumming
Degumming oil	Minglong auxiliaries limited liability company, Yiyang, Hunan,China	——	Chemical for degumming
Ethyl alcohol	Fisher Scientific	A962-4	Chemical for testing
Benzene	Fisher Scientific	AA43817AE	Chemical for testing
Copper wire,0.5mm (0.02in) dia	Fisher Scientific	AA10783H4	Chemical for testing
Cupriethylenediamine solution 1mol/L	Fisher Scientific	24991	Chemical for testing, caution toxic
Nitric acid (65% ~68% )	Fisher Scientific	A200-612GAL	Chemical for testing, caution
Ethylenediamine	Fisher Scientific	AC118420100	Chemical for testing
Potassium permanganate	Fisher Scientific	P279-500	Chemical for testing
Sulphuric acid	Fisher Scientific	A300C-212	Chemical for testing
Silver sulfate	Fisher Scientific	S190-25	Chemical for testing
Raw ramie	Guangyuan limited liability company, Changde, Hunan,China	——	Raw materials
Electric-heated thermostatic water bath	Senxin Experiment equipment limited liability company,Shanghai,China	DK-S28	Equipments for degumming
High temperature lbaorator dyeing machine	Shanghai Longda chemcials Crop.	RY-1261	Equipments for degumming
Thermometer	Sichuan Shubo (group)Co.,Ltd	100 °C	Equipments for degumming
Vacuum suction machine	Yukang KNET ,Shanghai,China	SHB-IIIA	Equipments for testing Mg(OH)2 solublity
Suction flask	Sichuan Shubo (group)Co.,Ltd	1000mL	Equipments for testing Mg(OH)2 solublity
Sand-core funnels	Sichuan Shubo (group)Co.,Ltd	35mL	Equipments for testing Mg(OH)2 solublity
Oxidation reduction potential meter	Dapu instrument, Shanghai, China	MODEL 421	Equipments for testing ORP value
pH meter	Hanna instruments,Beijing,China	HI 98129	Equipments for testing pH value
Acid burette	Sichuan Shubo (group)Co.,Ltd	50mL	Equipments for testing H2O2 content
Flask	Sichuan Shubo (group)Co.,Ltd	250 mL/500 mL	Equipments for testing H2O2 content;  residual gums content
Electric furnace	Jiangyi Experiment instruments limited liability company,Shanghai,China	800-2000W	Equipments for testing residual gums content
Reflux condensing tube	Sichuan Shubo (group)Co.,Ltd	250mL	Equipments for testing residual gums content; COD value
Fiber cutter (40mm)	Changzhou No.2 Textile Machine Co.,Ltd	Y171A	Equipments for testing fiber density
Ostwald viscometer	Taizhou, jiaojiang, glass instruments company	0.6mm	Equipments for testing fiber PD value
Spherical fat extractor	Sichuan Shubo (group)Co.,Ltd	250mL	Equipments for testing fiber PD value
Soxhlet extractor	Sichuan Shubo (group)Co.,Ltd	250mL	Equipments for testing fiber PD value
Torsion balance	Liangping instrucments Co.,Ltd,Shanghai, China	JN-B	Equipments for testing fiber density
Fiber strength instrument	Xinxian instruments, shanghai,China	XQ-2	Equipments for testing fiber tensile property
Tension clamp	Depu textile technology Co.,Ltd, Changzhou, jiangsu, China	0.3cN/dtex	Equipments for testing fiber tensile property
COD thermostatic heater	Qiangdao Xuyu environment protection technology Lit company	DL-801A	Equipments for testing COD value
FTIR	Thermo Fisher, America	Nicolet	FTIR analysis
XRD	Rigaku, Japan	D/max-2550 PC	XRD analysis
Electronic balance	Shanghai jingtian Electronic instrument Co.,Ltd	FA2004A	Generral equipments
Drying oven	Tonglixinda  instruments, Tianjin,China	101-2AS	Generral equipments
Weighing bottle	Sichuan Shubo (group)Co.,Ltd	50x30	Generral equipments
Beaker	Sichuan Shubo (group)Co.,Ltd	500mL	Generral equipments
Sample sieve	Xiaojin hardware instruments Co.,Ltd, Shangyu, Zhejiang	120 mesh	Generral equipments
Glass rod	Sichuan Shubo (group)Co.,Ltd	——	Generral equipments
Cylinder	Sichuan Shubo (group)Co.,Ltd	250mL, 50mL	Generral equipments
Pipette	Sichuan Shubo (group)Co.,Ltd	5mL, 10mL	Generral equipments
Rubber suction bulb	Sichuan Shubo (group)Co.,Ltd	——	Generral equipments
Orign	OriginLab	8.0	Software for figure drawing