- Email: [email protected]
A method for determining reactive hydroxyl groups in natural fibers: application to ramie fiber and its modification
Carbohydrate Research 348 (2012) 95–98
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research journal homepage: www.elsevier.com/locate/carres
Note
A method for determining reactive hydroxyl groups in natural fibers: application to ramie fiber and its modification Liping He a,⇑, Xinqi Li a, Wenjun Li a, Jianmin Yuan b, Haiye Zhou a a
State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body (Hunan University), College of Mechanical and Vehicle Engineering, Hunan University, Changsha, Hunan 410082, PR China b College of Materials and Engineering, Hunan University, Changsha, Hunan 410082, PR China
a r t i c l e
i n f o
Article history: Received 11 October 2011 Received in revised form 22 October 2011 Accepted 23 October 2011 Available online 29 October 2011 Keywords: Natural fiber Isocyanate group backtitration Methodology Modification NF/polymers
a b s t r a c t The hydrophilic features of natural fibers (NFs) hinder the widespread application of natural fiber/polymer composites due to the hydroxyl groups (–OH) presented in the cellulose molecule. Detecting reactive hydroxyl groups in NFs is very important for optimizing the modification process of natural fibers. This paper proposes a simple and practical methodology to measure reactive hydroxyl groups in NFs using a isocyanate group, a method we term the isocyanate group back titration (IBT) method. Application of the IBT method to ramie fiber with toluene-2,4-diisocyanate (TDI) and hexadecanol indicated that the measured value of reactive hydroxyl groups was about 150 mg KOH/g, which was less than the theoretical value of hydroxyl groups in the ramie fiber being tested. The FTIR analysis revealed that the TDI and hexadecanol were grafted onto the surface of the ramie fiber, leading the modified ramie fiber to be hydrophobic. Thus, the IBT method is also useful for modifying the surface properties of NFs and improving their compatibility with polymers, and finally leading to good mechanical properties of NF/polymer composites. Ó 2011 Elsevier Ltd. All rights reserved.
Natural fiber (NF) reinforced polymer composites have attracted much attention for their wide potential applications in the automobile and construction industries because NFs present advantages such as high specific strength and modulus, low price, low weight, biodegradability, recyclability, and so on. However, NFs are hydrophilic and have poor compatibility with hydrophobic polymers due to the hydroxyl groups (–OH) presented in cellulose, the main composition of natural fibers. Consequently, there has been a long history of research on modifying NFs with chemical reagents attempting to decrease the number of hydroxyl groups present in cellulose.1–5 Thus it is necessary to be able to measure the number of hydroxyl groups that can be reactive in a chemical treatment (modification). Determining reactive hydroxyl groups in NFs is undoubtedly helpful for optimizing the stoichiometric ratio between NFs and their modifiers (chemical treatment agents). Currently available methods of determining the number of hydroxyl groups, such as the acetic anhydride–acetone method, and the imidazole–phthalic anhydride method, are limited to determining the hydroxyl value of alcohols6–8 and cannot be applied to determine the number of hydroxyl in NFs because these methods result in the degradation of NFs.9 Therefore, in this work we have developed a simple method for accurately determining the number of ⇑ Corresponding author. Tel.: +86 0731 88823863; fax: +86 0731 88822051. E-mail addresses: [email protected], [email protected] (L. He). 0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.10.035
reactive hydroxyl groups in NFs, which we have named isocyanate group backtitration (IBT). Application of the IBT method to measure reactive hydroxyl groups in ramie fiber and its modification were also investigated. The mechanism of the proposed isocyanate group backtitration (IBT) method for measuring reactive hydroxyl groups in NFs is based on the reaction scheme shown in Figure 1. First, the isocyanate group attacks the active hydroxyl groups in the tested NF catalyzed by dibutyltin (DBT), which leads to the formation of complex I. Second, an excess of n-butylamine reacts with the complex I and the remaining isocyanate groups. Finally, the resultant solution is titrated to neutrality with hydrochloric acid solution. A blank test, which lacks the NF, is used as a comparison. Therefore, a derivation formula for measuring the reactive hydroxyl (mg KOH/g) of NFs with the IBT method can be given as:
mg KOH=g ¼
ðMKOH =MHCl ÞC HCl ðV 2 V 1 Þ 1000 m
Where m is the mass of the tested fiber in g; V1 and V2 are the volumes of hydrochloric acid solution used in the sample test and blank test, respectively, in mL; MKOH and MHCl are the molecular weights of KOH and HCl, respectively; and CHCl is the concentration of hydrochloric acid solution in g/mL. The measured number of reactive hydroxyl groups in the tested ramie fiber with IBT method is shown in Table 1. The results indi-
96
L. He et al. / Carbohydrate Research 348 (2012) 95–98
NCO
OH
O
H
C
N
NCO
O
Catalyst
NCO ( Complex I )
Natural Fiber O H O C N
NCO
NCO
NCO
H3C
2 H3C
H3C
CH 2
CH2
CH 2
3
NH 2
3
NH 2
3
H3C
H3C
NH 2
CH 2
H3C
HCl
CH 2
3
CH 2
3
H
O
H
N
C
N
H
O
H
N
C
N
3
NH 3Cl
Figure 1. Mechanism of the proposed isocyanate group backtitration (IBT) method.
Table 1 Measured number of reactive hydroxyl groups in the tested ramie fiber Reaction time (h) Number of reactive hydroxyl (mg KOH/g)
1 72.36
2 115.3
3 150.7
4 153.5
cate that number of reactive hydroxyl groups involved in the modification reaction was about 150 mg KOH/g, which was much less than that of the theoretical hydroxyl value (1037 mg KOH/g). This suggested that some of the hydroxyl groups could not be reacted with the chemical modifier due to chemical interactions within the cellulose itself and the strong hydrogen bonding between the cellulose chains. The mechanism of applying the IBT method to ramie fiber with toluene-2,4-diisocyanate (TDI) and hexadecanol is presented in Figure 2. Figure 3 shows the FTIR spectra of the ramie fiber before and after modification. It was found that after modification two new characteristic bands appeared at 1605 and 1543 cm1, which arise from stretching vibration modes of the benzene ring. This suggested that TDI was grafted onto the ramie fiber. Bands at 2852 and 2920 cm1 indicate the symmetric and asymmetric stretching vibrations of C–H groups, respectively.10 The sub-peak phenomenon around 2900 cm1 was assigned to the stretching vibration
Figure 3. FTIR spectra of ramie fiber before and after modification.
of –CH2– groups resulting from the grafted hexadecanol. Bands at 970–1240 cm1 correspond to the stretching vibration of C–O
NCO DBT
OH
OCN
O
CH 3
O
H
C
N
Ramie Fiber
O
O
H
C
N
NCO CH 3 H O H
NCO CH 3
H3C
CH2
3
NH 2
O
O H
N C N
C N
CH 3
CH 2
3
CH3
CH 2
3
CH3
H O H H O H
NCO OCN
CH 3
H3C
CH 2
2 H3C
CH2
NH 2
HCl
3
3
NH 2
H3C
H3C
CH2
CH 2
3
3
N C
N C N
NH 3Cl
Figure 2. Application of IBT method to ramie fiber with TDI and hexadecanol.
CH 3
N
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L. He et al. / Carbohydrate Research 348 (2012) 95–98
NCO DBT
OH
OCN
CH 3
O
O
H
C
N
NCO CH 3
Ramie Fiber
O
O
H
C
N
NCO OH
CH 3
O
O
H
C
N
H
O
N
C
O
CH 3
Hexadecanol Figure 4. Modification mechanism of ramie fiber with TDI and hexadecanol.
Table 2 Contact angle test results of the modified ramie fiber Contact angle (°)
1 101
2 110
3 108
result in hydrophobic features of the modified natural fiber, which are favorable for improving the compatibility between NFs and polymers and leading good properties of NF/polymer composites.
4 102
1. Experimental 1
groups in cellulose. The bands at 1647 cm and between 981 and 1203 cm1 became stronger and sharper after modification, which indicate that the modification produced some additional C–O groups. Literature reports11 indicated that only one –NCO of TDI would react with the hydroxyl groups of the NF if there are no bands of – NCO at 2340 cm1. This implied that another –NCO should have already reacted with the hydroxyl group of hexadecanol. The modification mechanism of the ramie fiber with TDI and hexadecanol can be elucidated as in Figure 4. In Figure 4, the reactive hydroxyl in ramie fiber first reacts with TDI catalyzed by dibutyltin in acetone. Another isocyanate group of TDI, which is grafted onto the surface of ramie fiber would further react with the hexadecanol. This undoubtedly increases the length of the grafted chain, which could result in a hydrophobic feature of the modified NF. This is verified by the contact angle (CA) test carried on a KRUSS DSA100 tester by dropping off water droplets onto the surfaces of the modified and unmodified ramie fiber. The contact angle (CA) results showed that water droplets were immediately absorbed by the unmodified fiber, while water droplets stayed on the surface of the modified fiber for a long time. The CA test results of the modified ramie fiber are listed in Table 2, which showed that the average contact angle of the modified fiber is about 105°. In summary, the present work reports the isocyanate group backtitration method (IBT) for determining reactive hydroxyl groups in NFs. Applying the IBT method to ramie fiber and its modification with TDI and hexadecanol verified that the IBT method is not only useful for measuring the number of reactive hydroxyl groups in natural fibers, but is also useful for modifying the surface properties of NFs. The results also show that the measured value of reactive hydroxyl groups is less than the theoretical value of hydroxyl groups in the tested fiber as the result of chemical interactions in and between cellulose molecules. Toluene-2,4-diisocyanate (TDI) and hexadecanol can be grafted onto the surface of ramie fiber and
TDI Ramie fiber
Vacuum drying
Anhydrous ramie fiber
The proposed IBT method was applied to test the number of reactive hydroxyl in a commercial ramie fiber and its modification with toluene-2,4-diisocyanate (TDI) and hexadecanol. Commercial ramie fiber was from Hunan Guangyuan Fiber Company, China. The used chemical reagents, such as TDI, hexadecanol, acetone, nbutylamine, dibutyltin (DBT) were all in analytical grade. The concentration of the hydrochloric acid used in the sample test and blank test was of 0.00049 g/mL. 1.1. Determining the number of reactive hydroxyl groups The flow chart for determining the reactive hydroxyl group in ramie fiber is described in Figure 5. The ramie fiber (RF) was dried in a vacuum oven for 24 h before the test. About 5 g dried RF and 5 g TDI were dissolved in 250 mL anhydrous acetone in a threeneck flask. After the complete dissolution, 2–3 droplets of DBT were added dropwise. The mixture, in the three-neck flask, was reacted at 60 °C. During the reaction, 10 mL solution was drawn off the three-necked flask and added into an iodine flask once every hour. The extracted solution was cooled to room temperature and then reacted with 0.4996 g n-butylamine for about 15– 20 min at room temperature. The resultant solution in the iodine flask was finally titrated with hydrochloric acid until the solution changed to a slight yellow using bromocresol green as the indicator. Repeating the reaction process without adding the ramie fiber was as a blank test. 1.2. Modification of ramie fiber Anhydrous ramie fiber (5 g) and 2.5 g TDI were dissolved in 250 mL anhydrous acetone in a three-necked flask and DBT was added dropwise. The solution was heated at reflux at 60 °C for 4 h and then reacted with 6 g hexadecanol over 5 h. Finally, the modified ramie fiber was dried in a vacuum chamber.
n-butylamine
DBT
Reaction solution Acetone
Figure 5. Flow-chart of determining the reactive hydroxyl in the tested ramie fiber.
Indicator
Titration
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L. He et al. / Carbohydrate Research 348 (2012) 95–98
1.3. Characterization of the modified ramie fiber
References
The modified and unmodified ramie fibers were analyzed with a Perkin Elmer 2000 FTIR instrument. The ramie fibers were dried in vacuum chamber for 48 h before FTIR analysis.
1. Torres, F. G.; Cubillas, M. L. Polym. Test. 2005, 24, 694–698. 2. Zhang, X.; Do, M. D.; Kurniawan, L.; Qiao, G. G. Carbohydr. Res. 2010, 345, 2174– 2182. 3. Paul, A.; Joseph, K.; Thorna, S. Compos. Sci. Technol. 1997, 51, 67–79. 4. Paquet, O.; Krouit, M.; Bras, J.; Thielemans, W.; Belgacem, M. N. Acta Mater. 2010, 58, 792–801. 5. He, L.; Tian, Y.; Wang, L. Adv. Mater. Res. 2008, 42–43, 313–316. 6. Jin, Y.; Jin, X. Phys. Test. Chem. Anal. Part B: Chem. Anal. 2004, 40, 237–241. 7. Song, K. J. Mater. Sci. Eng. 2003, 21, 901–902. 8. Wei, M.; Yan, L.; Jiang, J. Biomass Chem. Eng. 2006, 40, 18–20. 9. Chand, N.; Verma, S.; Khazanchi, A. J. Mater. Sci. Lett. 1989, 8, 1307–1309. 10. Dong, Y. Polym. Anal. Handbook (in Chinese); China Petrochemical Press: Beijing, 2004. Chapter 7, pp 265–268. 11. Yang, M.; Wang, J.; Chen, W. Polym. Mater. Sci. Eng. 2007, 23, 45–48.
Acknowledgements This work is financially supported by the Natural Science Foundation of China (Project No. 51073051), ‘863’ high-tech project (No. 2008AA030905) from the Ministry of Scientist and Technology, the fundamental Research Funds for the Central Universities, Hunan University, and the Science Fund of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body No. 71075009 and No. 30815003, and the Chinese automobile independent innovation capacity building project.
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research journal homepage: www.elsevier.com/locate/carres
Note
A method for determining reactive hydroxyl groups in natural fibers: application to ramie fiber and its modification Liping He a,⇑, Xinqi Li a, Wenjun Li a, Jianmin Yuan b, Haiye Zhou a a
State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body (Hunan University), College of Mechanical and Vehicle Engineering, Hunan University, Changsha, Hunan 410082, PR China b College of Materials and Engineering, Hunan University, Changsha, Hunan 410082, PR China
a r t i c l e
i n f o
Article history: Received 11 October 2011 Received in revised form 22 October 2011 Accepted 23 October 2011 Available online 29 October 2011 Keywords: Natural fiber Isocyanate group backtitration Methodology Modification NF/polymers
a b s t r a c t The hydrophilic features of natural fibers (NFs) hinder the widespread application of natural fiber/polymer composites due to the hydroxyl groups (–OH) presented in the cellulose molecule. Detecting reactive hydroxyl groups in NFs is very important for optimizing the modification process of natural fibers. This paper proposes a simple and practical methodology to measure reactive hydroxyl groups in NFs using a isocyanate group, a method we term the isocyanate group back titration (IBT) method. Application of the IBT method to ramie fiber with toluene-2,4-diisocyanate (TDI) and hexadecanol indicated that the measured value of reactive hydroxyl groups was about 150 mg KOH/g, which was less than the theoretical value of hydroxyl groups in the ramie fiber being tested. The FTIR analysis revealed that the TDI and hexadecanol were grafted onto the surface of the ramie fiber, leading the modified ramie fiber to be hydrophobic. Thus, the IBT method is also useful for modifying the surface properties of NFs and improving their compatibility with polymers, and finally leading to good mechanical properties of NF/polymer composites. Ó 2011 Elsevier Ltd. All rights reserved.
Natural fiber (NF) reinforced polymer composites have attracted much attention for their wide potential applications in the automobile and construction industries because NFs present advantages such as high specific strength and modulus, low price, low weight, biodegradability, recyclability, and so on. However, NFs are hydrophilic and have poor compatibility with hydrophobic polymers due to the hydroxyl groups (–OH) presented in cellulose, the main composition of natural fibers. Consequently, there has been a long history of research on modifying NFs with chemical reagents attempting to decrease the number of hydroxyl groups present in cellulose.1–5 Thus it is necessary to be able to measure the number of hydroxyl groups that can be reactive in a chemical treatment (modification). Determining reactive hydroxyl groups in NFs is undoubtedly helpful for optimizing the stoichiometric ratio between NFs and their modifiers (chemical treatment agents). Currently available methods of determining the number of hydroxyl groups, such as the acetic anhydride–acetone method, and the imidazole–phthalic anhydride method, are limited to determining the hydroxyl value of alcohols6–8 and cannot be applied to determine the number of hydroxyl in NFs because these methods result in the degradation of NFs.9 Therefore, in this work we have developed a simple method for accurately determining the number of ⇑ Corresponding author. Tel.: +86 0731 88823863; fax: +86 0731 88822051. E-mail addresses: [email protected], [email protected] (L. He). 0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2011.10.035
reactive hydroxyl groups in NFs, which we have named isocyanate group backtitration (IBT). Application of the IBT method to measure reactive hydroxyl groups in ramie fiber and its modification were also investigated. The mechanism of the proposed isocyanate group backtitration (IBT) method for measuring reactive hydroxyl groups in NFs is based on the reaction scheme shown in Figure 1. First, the isocyanate group attacks the active hydroxyl groups in the tested NF catalyzed by dibutyltin (DBT), which leads to the formation of complex I. Second, an excess of n-butylamine reacts with the complex I and the remaining isocyanate groups. Finally, the resultant solution is titrated to neutrality with hydrochloric acid solution. A blank test, which lacks the NF, is used as a comparison. Therefore, a derivation formula for measuring the reactive hydroxyl (mg KOH/g) of NFs with the IBT method can be given as:
mg KOH=g ¼
ðMKOH =MHCl ÞC HCl ðV 2 V 1 Þ 1000 m
Where m is the mass of the tested fiber in g; V1 and V2 are the volumes of hydrochloric acid solution used in the sample test and blank test, respectively, in mL; MKOH and MHCl are the molecular weights of KOH and HCl, respectively; and CHCl is the concentration of hydrochloric acid solution in g/mL. The measured number of reactive hydroxyl groups in the tested ramie fiber with IBT method is shown in Table 1. The results indi-
96
L. He et al. / Carbohydrate Research 348 (2012) 95–98
NCO
OH
O
H
C
N
NCO
O
Catalyst
NCO ( Complex I )
Natural Fiber O H O C N
NCO
NCO
NCO
H3C
2 H3C
H3C
CH 2
CH2
CH 2
3
NH 2
3
NH 2
3
H3C
H3C
NH 2
CH 2
H3C
HCl
CH 2
3
CH 2
3
H
O
H
N
C
N
H
O
H
N
C
N
3
NH 3Cl
Figure 1. Mechanism of the proposed isocyanate group backtitration (IBT) method.
Table 1 Measured number of reactive hydroxyl groups in the tested ramie fiber Reaction time (h) Number of reactive hydroxyl (mg KOH/g)
1 72.36
2 115.3
3 150.7
4 153.5
cate that number of reactive hydroxyl groups involved in the modification reaction was about 150 mg KOH/g, which was much less than that of the theoretical hydroxyl value (1037 mg KOH/g). This suggested that some of the hydroxyl groups could not be reacted with the chemical modifier due to chemical interactions within the cellulose itself and the strong hydrogen bonding between the cellulose chains. The mechanism of applying the IBT method to ramie fiber with toluene-2,4-diisocyanate (TDI) and hexadecanol is presented in Figure 2. Figure 3 shows the FTIR spectra of the ramie fiber before and after modification. It was found that after modification two new characteristic bands appeared at 1605 and 1543 cm1, which arise from stretching vibration modes of the benzene ring. This suggested that TDI was grafted onto the ramie fiber. Bands at 2852 and 2920 cm1 indicate the symmetric and asymmetric stretching vibrations of C–H groups, respectively.10 The sub-peak phenomenon around 2900 cm1 was assigned to the stretching vibration
Figure 3. FTIR spectra of ramie fiber before and after modification.
of –CH2– groups resulting from the grafted hexadecanol. Bands at 970–1240 cm1 correspond to the stretching vibration of C–O
NCO DBT
OH
OCN
O
CH 3
O
H
C
N
Ramie Fiber
O
O
H
C
N
NCO CH 3 H O H
NCO CH 3
H3C
CH2
3
NH 2
O
O H
N C N
C N
CH 3
CH 2
3
CH3
CH 2
3
CH3
H O H H O H
NCO OCN
CH 3
H3C
CH 2
2 H3C
CH2
NH 2
HCl
3
3
NH 2
H3C
H3C
CH2
CH 2
3
3
N C
N C N
NH 3Cl
Figure 2. Application of IBT method to ramie fiber with TDI and hexadecanol.
CH 3
N
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L. He et al. / Carbohydrate Research 348 (2012) 95–98
NCO DBT
OH
OCN
CH 3
O
O
H
C
N
NCO CH 3
Ramie Fiber
O
O
H
C
N
NCO OH
CH 3
O
O
H
C
N
H
O
N
C
O
CH 3
Hexadecanol Figure 4. Modification mechanism of ramie fiber with TDI and hexadecanol.
Table 2 Contact angle test results of the modified ramie fiber Contact angle (°)
1 101
2 110
3 108
result in hydrophobic features of the modified natural fiber, which are favorable for improving the compatibility between NFs and polymers and leading good properties of NF/polymer composites.
4 102
1. Experimental 1
groups in cellulose. The bands at 1647 cm and between 981 and 1203 cm1 became stronger and sharper after modification, which indicate that the modification produced some additional C–O groups. Literature reports11 indicated that only one –NCO of TDI would react with the hydroxyl groups of the NF if there are no bands of – NCO at 2340 cm1. This implied that another –NCO should have already reacted with the hydroxyl group of hexadecanol. The modification mechanism of the ramie fiber with TDI and hexadecanol can be elucidated as in Figure 4. In Figure 4, the reactive hydroxyl in ramie fiber first reacts with TDI catalyzed by dibutyltin in acetone. Another isocyanate group of TDI, which is grafted onto the surface of ramie fiber would further react with the hexadecanol. This undoubtedly increases the length of the grafted chain, which could result in a hydrophobic feature of the modified NF. This is verified by the contact angle (CA) test carried on a KRUSS DSA100 tester by dropping off water droplets onto the surfaces of the modified and unmodified ramie fiber. The contact angle (CA) results showed that water droplets were immediately absorbed by the unmodified fiber, while water droplets stayed on the surface of the modified fiber for a long time. The CA test results of the modified ramie fiber are listed in Table 2, which showed that the average contact angle of the modified fiber is about 105°. In summary, the present work reports the isocyanate group backtitration method (IBT) for determining reactive hydroxyl groups in NFs. Applying the IBT method to ramie fiber and its modification with TDI and hexadecanol verified that the IBT method is not only useful for measuring the number of reactive hydroxyl groups in natural fibers, but is also useful for modifying the surface properties of NFs. The results also show that the measured value of reactive hydroxyl groups is less than the theoretical value of hydroxyl groups in the tested fiber as the result of chemical interactions in and between cellulose molecules. Toluene-2,4-diisocyanate (TDI) and hexadecanol can be grafted onto the surface of ramie fiber and
TDI Ramie fiber
Vacuum drying
Anhydrous ramie fiber
The proposed IBT method was applied to test the number of reactive hydroxyl in a commercial ramie fiber and its modification with toluene-2,4-diisocyanate (TDI) and hexadecanol. Commercial ramie fiber was from Hunan Guangyuan Fiber Company, China. The used chemical reagents, such as TDI, hexadecanol, acetone, nbutylamine, dibutyltin (DBT) were all in analytical grade. The concentration of the hydrochloric acid used in the sample test and blank test was of 0.00049 g/mL. 1.1. Determining the number of reactive hydroxyl groups The flow chart for determining the reactive hydroxyl group in ramie fiber is described in Figure 5. The ramie fiber (RF) was dried in a vacuum oven for 24 h before the test. About 5 g dried RF and 5 g TDI were dissolved in 250 mL anhydrous acetone in a threeneck flask. After the complete dissolution, 2–3 droplets of DBT were added dropwise. The mixture, in the three-neck flask, was reacted at 60 °C. During the reaction, 10 mL solution was drawn off the three-necked flask and added into an iodine flask once every hour. The extracted solution was cooled to room temperature and then reacted with 0.4996 g n-butylamine for about 15– 20 min at room temperature. The resultant solution in the iodine flask was finally titrated with hydrochloric acid until the solution changed to a slight yellow using bromocresol green as the indicator. Repeating the reaction process without adding the ramie fiber was as a blank test. 1.2. Modification of ramie fiber Anhydrous ramie fiber (5 g) and 2.5 g TDI were dissolved in 250 mL anhydrous acetone in a three-necked flask and DBT was added dropwise. The solution was heated at reflux at 60 °C for 4 h and then reacted with 6 g hexadecanol over 5 h. Finally, the modified ramie fiber was dried in a vacuum chamber.
n-butylamine
DBT
Reaction solution Acetone
Figure 5. Flow-chart of determining the reactive hydroxyl in the tested ramie fiber.
Indicator
Titration
98
L. He et al. / Carbohydrate Research 348 (2012) 95–98
1.3. Characterization of the modified ramie fiber
References
The modified and unmodified ramie fibers were analyzed with a Perkin Elmer 2000 FTIR instrument. The ramie fibers were dried in vacuum chamber for 48 h before FTIR analysis.
1. Torres, F. G.; Cubillas, M. L. Polym. Test. 2005, 24, 694–698. 2. Zhang, X.; Do, M. D.; Kurniawan, L.; Qiao, G. G. Carbohydr. Res. 2010, 345, 2174– 2182. 3. Paul, A.; Joseph, K.; Thorna, S. Compos. Sci. Technol. 1997, 51, 67–79. 4. Paquet, O.; Krouit, M.; Bras, J.; Thielemans, W.; Belgacem, M. N. Acta Mater. 2010, 58, 792–801. 5. He, L.; Tian, Y.; Wang, L. Adv. Mater. Res. 2008, 42–43, 313–316. 6. Jin, Y.; Jin, X. Phys. Test. Chem. Anal. Part B: Chem. Anal. 2004, 40, 237–241. 7. Song, K. J. Mater. Sci. Eng. 2003, 21, 901–902. 8. Wei, M.; Yan, L.; Jiang, J. Biomass Chem. Eng. 2006, 40, 18–20. 9. Chand, N.; Verma, S.; Khazanchi, A. J. Mater. Sci. Lett. 1989, 8, 1307–1309. 10. Dong, Y. Polym. Anal. Handbook (in Chinese); China Petrochemical Press: Beijing, 2004. Chapter 7, pp 265–268. 11. Yang, M.; Wang, J.; Chen, W. Polym. Mater. Sci. Eng. 2007, 23, 45–48.
Acknowledgements This work is financially supported by the Natural Science Foundation of China (Project No. 51073051), ‘863’ high-tech project (No. 2008AA030905) from the Ministry of Scientist and Technology, the fundamental Research Funds for the Central Universities, Hunan University, and the Science Fund of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body No. 71075009 and No. 30815003, and the Chinese automobile independent innovation capacity building project.