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Pre-irradiation grafting of temperature sensitive hydrogel on cotton cellulose fabric
Radiation Physics and Chemistry
PERGAMON
Radiation Physics and Chemistry 55 (1999) 55±59
Pre-irradiation grafting of temperature sensitive hydrogel on cotton cellulose fabric Liu Jianqin, Zhai Maolin, Ha Hongfei * Department of Technical Physics, Peking University, Beijing, 100871, People's Republic of China Received 5 October 1998
Abstract Temperature sensitive polymer (poly-N-isopropylacrylamide)was grafted on the surface of cotton cellulose fabric by g-pre-irradiation-induced grafting. The eect of absorbed dose, dose rate, grafting temperature and concentration of monomer on grafting yields were investigated. In order to explain the characteristic of active points and the location of grafting site, the peroxides formed during irradiation in air and the eects of store time at various temperatures after irradiation were measured. It was found that grafting reaction was induced mainly by trapped radicals located in the interphase between crystal and amorphous regions, but for the monomer of Nisopropylacrylamide the peroxides also made some contribution to grafting yields. The results showed that the surface of grafted fabric has temperature sensitivity as well. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Pre-irradiation grafting copolymerization; N-isopropylacrylamide; Cotton cellulose fabric; Temperature sensitivity; Trapped radical; Peroxide
1. Introduction Radiation induced grafting of vinyl monomer onto cotton cellulose has been widely investigated (Sharda, 1972; Chye and Garnett, 1982; Zahran, 1980; Ha Hongfei et al., 1995). Among them, there were some reports concerning pre-irradiation grafting (Kabanov, 1989; Garnett et al., 1995). The study on characteristics of active points of grafting reaction and location of grafting site was rare and taken attention seriously up to now. Cotton cellulose is a kind of nature polymer with high crystallinity. When it is irradiated in air at room temperature, the radicals produced in amorphous regions would react with oxygen and produce peroxides rapidly, so both these free radicals and peroxides should make no contribution to the grafting yields at room temperature. On the other hand, the trapped radicals in the crystalline regions could not induce grafting reaction because the monomer could
* Corresponding author.
not enter into these regions. Then, where and how can the high grafting yields be initiated? In this work, pre-irradiation grafting of N-isopropyacrylamide (NIPAAm) and acrylamide (AAm) on cotton cellulose fabric was researched in details. The results showed that the grafting reaction was mainly induced by the trapped radicals in interphase located between the crystalline and amorphous regions.
2. Experimental 2.1. Materials Cotton cellulose fabric bought from market was used. It was extracted by boiling ethanol for 5 h and then boiled in 1% sodium hydroxide solution for three hours. After washed by distilled water until neutrality, it was dried and stored in desiccator for future use. NIPAAm and AAm are the products of Wako Pure Chemical Industries Ltd, Japan. Puri®cation of monomer was carried out by recrystallization. The other re-
0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 3 1 1 - 9
56
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
agents used are domestic products, analytical grades without further puri®cation. Triplet distilled water was used for preparation of all solutions. 2.2. Method 2.2.1. Radiation grafting A piece of treated fabric (12 cm2.0.1±0.15 g) was irradiated in air by 60Co-g ray (Department of Technical Physics, Peking University) and then immersed in grafting solution at desired temperature with bubbling N2 for various periods of time. After removing homopolymers by extraction with ethanol for 12 h, the grafting yields were measured gravimetrically. 2.2.2. Determination of oxidation products The content of oxidation products (alkyl peroxides and hydroperoxides) was determined by the conventional iodide method (Kulik et al., 1995). The density of oxidation products was calculated from the optical density of sample solution at 360 nm (756 type visibleUV spectrophotometer, Shanghai, China).
3. Results and discussion 3.1. Measurements of main grafting conditions 3.1.1. Equilibrium time of grafting reaction Measurements of equilibrium time of grafting reaction after the samples were irradiated in air showed that under dierent grafting temperature 3 h of graft-
Fig. 1. Grafting yield (G.Y.%) as a function of reaction time at dierent temperature. Total dose : 32.3 kGy. Dose rate : 270 Gy/min [NIPAAm]: 6% in water. Q 50.58C. R 40.58C. . 32.08C.
Fig. 2. Grafting yield as a function of monomer concentration. Total dose: 32.3 kGy. Dose rate: 270 Gy/min. Temperature: 208C.
ing reaction would be enough to reach the equilibrium of reaction (Fig. 1) 3.1.2. Eect of monomer concentratiion The results in Fig. 2 indicated that the concentration of monomer had strong in¯uence on grafting yields. The grafting reaction took place in a heterogeneous system, so it is a diusion-controlled reaction. Because of limiting of solubility of NIPAAm in aqueous solution (only can reach 010%), so the monomer concentration was kept at 6% in the experiments of this work. 3.1.3. Eects of total dose and dose rate Figs. 3 and 4 represented the eects of absorbed dose and dose rate on grafting yields. The grafting yields increased with total dose and tended to level o
Fig. 3. Grafting yield as a function of total dose. [NIPAAm]: 6%. Temperature 208C.
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
Fig. 4. Grafting yield as a function of dose rate. [NIPAAm]: 6%. Temperature: 208C. Total dose: 32.3 kGy.
around 30 kGy. The dose rate has no eect on grafting yields reasonably. 3.2. The trapped radicals, the main active points of grafting The pre-irradiated samples were stored for various times at 40 and 808C respectively, and then reacted with monomer solution at room temperature or 718C separately. The results were shown in Figs. 5 and 6. From Fig. 5, it can be seen that if the samples were stored at lower temperature, 408C, and then reacted with monomer solution at room temperature, the normalized G.Y.% almost became zero after 4 h store. It indicated that under this condition, the grafting reaction is induced only by trapped radicals which decay with store time and tended to zero up to 4 h. In the mean time the oxidation products were stable at that temperature. If the grafting reaction took place at higher temperature, 718C, the grafting yields maintained around 35.1% after 5 h store. These parts of grafting yields should be contributed by oxidation pro-
Fig. 5. Normalized grafting yield as a function of store time at 408C. Q 208C. . 718C.
57
Fig. 6. Normalized grafting yield as a function of store time at 808C. Q 208C. . 718C.
ducts, which decomposed at higher temperature, 718C. Further, the irradiated samples were stored at high temperature, 808C, the grafting yields tended to zero after 2 h store in both cases of reaction temperature at 20 or 718C. Because the oxidation products formed during irradiation in air were decomposed out rapidly as well. From these results a reasonable conclusion could be given, that the grafting reaction was mainly initiated by trapped radicals which were located in the interphase between crystal and amorphous regions. Because, in this case, both trapped radicals in crystal regions (monomer could not enter in) and free radicals in the amorphous regions (became peroxides during irradiated in air) could not make contributions to grafting yield. 3.3. Eect of oxidation products Decomposition of oxidation products and eect on grafting yield depend on the temperature of store and grafting reaction. Generally as increasing of reaction temperature the grafting yield would decrease just like pre-irradiation grafting of acrylamide (AAm) on cotton cellulose fabric (Fig. 7). For NIPAAm, however,
Fig. 7. Grafting yield as a function of temperature. Total dose: 32.3 kGy. [Monomer]: 6% Q NIPAAm. . AAm.
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L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
Fig. 9. DSC spectrum of the fabric grafted with poly NIPAAm.
Fig. 8. (a) Amount of peroxides as a function of measurement temperature. (b) Amount of peroxides as a function of absorbed dose.
its grafting yield was increasing with reaction temperature (Fig. 7) although the grafting reaction was induced mainly by trapped radicals as discussed above. It may be due to the special structure of NIPAAm which induces following reaction:
. The RO radicals produced in this reaction could induce the extra grafting reaction which can compensate the decrease of grafting yield due to the decay of trapped radicals. So in pre-irradiation grafting system
of NIPAAm, the oxidation products could also make some contribution to the grafting yield with increasing of grafting temperature. The amount of oxidation products formed in the irradiation of cotton cellulose fabric in air as the function of absorbed dose and measurement temperature were given at Fig. 8. The oxidation products contain alkyl peroxides (ROOR) and hydroperoxides (ROOH), the later is more unstable (Kashiwabra and Seguchi, 1992). which make more contribution to grafting yield.
3.4. The surface property of grafted samples NIPAAm is an important monomer used to prepare environmental sensitive polymers or hydrogels (Wu et
al., 1992; Morita and Kaetsu, 1992). Fig. 9 showed the result of DSC measurement of the cotton cellulose fabric grafted by polyNIPAAm. From this picture it can be seen that the grafted fabric had also the tempera-
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
ture sensitivity which LCST was 35.48C closing to that of pure polyNIPAAm.
4. Conclusion 1. PolyNIPAAm was successfully grafted onto the cotton cellulose fabric by pre-irradiation technology. The surface of grafted fabric also has temperature sensitivity, its LCST is 35.48C. 2. The main active particles initiating reaction were the trapped radicals located in the interphase between the crystal and amorphous regions. 3. The hydroperoxides which was one of oxidation products produced during irradiation of samples in air are easy to decompose at lower temperature in the presence of NIPAAm and make some contribution to grafting yield as well.
Acknowledgements This Research is supported by Nuclear Foundatiion, China Y719FY006 and IAEA 9565/RO.
59
References Chye Ang, H., Garnett, J.L., 1982. Acid eect in UV and radiation-induced grafting of styrene to cellulose. ACS Symp Ser 187, 141. Garnett, J.L., Dworjangn, P.A., Bett, S.J. et al., 1995. Grafting and curing on polymer surfaceÐrole of additives, IAEA-TECDOC-834. Advanced Radiation Chemistry Research: Current Status October, 129±140. Ha, Hongfei, Wu, Liju, Tai, Hong et al, 1995. Study on radiation grafting of styrene on cotton cellulose. Radiat. Phys. Chem. 46 (4±6), 823±827. Kabanov, V.Ya, 1989. Radiation-induced graft copolymerization in the USSA. Radiat. Phys. Chem. 33, 51. Kashiwabara, H., Seguchi, T., 1992. Radiation-induced oxidation of plastics. In: Singh, A., Silverman, J. (Eds.). Radiation Processing of Polymers, Chap. II. Hanser, Oxford University Press, New York, pp. 221±253. Kulik, Eduard, A., Ivanchenko, Maria I. et al, 1995. Peroxides generation and decomposition on polymer surface. J. Polym. Sci. Part A: Polym. Chem. 33 (2), 323±330. Morita, Y., Kaetsu, I., 1992. Synthesis of stimule sensitive hydrogels. Radiat. Phys. Chem. 39 (6), 473. Sharda, Dasgupta, 1972. Industrial application of radiation induced grafted cotton. J. Polym. Sci. (C) 37, 333. Wu, Xueshen, Homan, Allen S., Yager, Paul, 1992. Synthesis and characterization of thermally reversible macroporous poly(N-Isopropylacrylamide) hydrogels. J. Polym. Sci. (A), Polymer Chemistry 30, 2121±2129. Zahran, A.H., 1980. Radiation grafting of acrylic and methacrylic acid to cellulose fabric to impart high water absorbency. J. Appl. Polym. Sci. 33, 5.
PERGAMON
Radiation Physics and Chemistry 55 (1999) 55±59
Pre-irradiation grafting of temperature sensitive hydrogel on cotton cellulose fabric Liu Jianqin, Zhai Maolin, Ha Hongfei * Department of Technical Physics, Peking University, Beijing, 100871, People's Republic of China Received 5 October 1998
Abstract Temperature sensitive polymer (poly-N-isopropylacrylamide)was grafted on the surface of cotton cellulose fabric by g-pre-irradiation-induced grafting. The eect of absorbed dose, dose rate, grafting temperature and concentration of monomer on grafting yields were investigated. In order to explain the characteristic of active points and the location of grafting site, the peroxides formed during irradiation in air and the eects of store time at various temperatures after irradiation were measured. It was found that grafting reaction was induced mainly by trapped radicals located in the interphase between crystal and amorphous regions, but for the monomer of Nisopropylacrylamide the peroxides also made some contribution to grafting yields. The results showed that the surface of grafted fabric has temperature sensitivity as well. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Pre-irradiation grafting copolymerization; N-isopropylacrylamide; Cotton cellulose fabric; Temperature sensitivity; Trapped radical; Peroxide
1. Introduction Radiation induced grafting of vinyl monomer onto cotton cellulose has been widely investigated (Sharda, 1972; Chye and Garnett, 1982; Zahran, 1980; Ha Hongfei et al., 1995). Among them, there were some reports concerning pre-irradiation grafting (Kabanov, 1989; Garnett et al., 1995). The study on characteristics of active points of grafting reaction and location of grafting site was rare and taken attention seriously up to now. Cotton cellulose is a kind of nature polymer with high crystallinity. When it is irradiated in air at room temperature, the radicals produced in amorphous regions would react with oxygen and produce peroxides rapidly, so both these free radicals and peroxides should make no contribution to the grafting yields at room temperature. On the other hand, the trapped radicals in the crystalline regions could not induce grafting reaction because the monomer could
* Corresponding author.
not enter into these regions. Then, where and how can the high grafting yields be initiated? In this work, pre-irradiation grafting of N-isopropyacrylamide (NIPAAm) and acrylamide (AAm) on cotton cellulose fabric was researched in details. The results showed that the grafting reaction was mainly induced by the trapped radicals in interphase located between the crystalline and amorphous regions.
2. Experimental 2.1. Materials Cotton cellulose fabric bought from market was used. It was extracted by boiling ethanol for 5 h and then boiled in 1% sodium hydroxide solution for three hours. After washed by distilled water until neutrality, it was dried and stored in desiccator for future use. NIPAAm and AAm are the products of Wako Pure Chemical Industries Ltd, Japan. Puri®cation of monomer was carried out by recrystallization. The other re-
0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 9 8 ) 0 0 3 1 1 - 9
56
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
agents used are domestic products, analytical grades without further puri®cation. Triplet distilled water was used for preparation of all solutions. 2.2. Method 2.2.1. Radiation grafting A piece of treated fabric (12 cm2.0.1±0.15 g) was irradiated in air by 60Co-g ray (Department of Technical Physics, Peking University) and then immersed in grafting solution at desired temperature with bubbling N2 for various periods of time. After removing homopolymers by extraction with ethanol for 12 h, the grafting yields were measured gravimetrically. 2.2.2. Determination of oxidation products The content of oxidation products (alkyl peroxides and hydroperoxides) was determined by the conventional iodide method (Kulik et al., 1995). The density of oxidation products was calculated from the optical density of sample solution at 360 nm (756 type visibleUV spectrophotometer, Shanghai, China).
3. Results and discussion 3.1. Measurements of main grafting conditions 3.1.1. Equilibrium time of grafting reaction Measurements of equilibrium time of grafting reaction after the samples were irradiated in air showed that under dierent grafting temperature 3 h of graft-
Fig. 1. Grafting yield (G.Y.%) as a function of reaction time at dierent temperature. Total dose : 32.3 kGy. Dose rate : 270 Gy/min [NIPAAm]: 6% in water. Q 50.58C. R 40.58C. . 32.08C.
Fig. 2. Grafting yield as a function of monomer concentration. Total dose: 32.3 kGy. Dose rate: 270 Gy/min. Temperature: 208C.
ing reaction would be enough to reach the equilibrium of reaction (Fig. 1) 3.1.2. Eect of monomer concentratiion The results in Fig. 2 indicated that the concentration of monomer had strong in¯uence on grafting yields. The grafting reaction took place in a heterogeneous system, so it is a diusion-controlled reaction. Because of limiting of solubility of NIPAAm in aqueous solution (only can reach 010%), so the monomer concentration was kept at 6% in the experiments of this work. 3.1.3. Eects of total dose and dose rate Figs. 3 and 4 represented the eects of absorbed dose and dose rate on grafting yields. The grafting yields increased with total dose and tended to level o
Fig. 3. Grafting yield as a function of total dose. [NIPAAm]: 6%. Temperature 208C.
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
Fig. 4. Grafting yield as a function of dose rate. [NIPAAm]: 6%. Temperature: 208C. Total dose: 32.3 kGy.
around 30 kGy. The dose rate has no eect on grafting yields reasonably. 3.2. The trapped radicals, the main active points of grafting The pre-irradiated samples were stored for various times at 40 and 808C respectively, and then reacted with monomer solution at room temperature or 718C separately. The results were shown in Figs. 5 and 6. From Fig. 5, it can be seen that if the samples were stored at lower temperature, 408C, and then reacted with monomer solution at room temperature, the normalized G.Y.% almost became zero after 4 h store. It indicated that under this condition, the grafting reaction is induced only by trapped radicals which decay with store time and tended to zero up to 4 h. In the mean time the oxidation products were stable at that temperature. If the grafting reaction took place at higher temperature, 718C, the grafting yields maintained around 35.1% after 5 h store. These parts of grafting yields should be contributed by oxidation pro-
Fig. 5. Normalized grafting yield as a function of store time at 408C. Q 208C. . 718C.
57
Fig. 6. Normalized grafting yield as a function of store time at 808C. Q 208C. . 718C.
ducts, which decomposed at higher temperature, 718C. Further, the irradiated samples were stored at high temperature, 808C, the grafting yields tended to zero after 2 h store in both cases of reaction temperature at 20 or 718C. Because the oxidation products formed during irradiation in air were decomposed out rapidly as well. From these results a reasonable conclusion could be given, that the grafting reaction was mainly initiated by trapped radicals which were located in the interphase between crystal and amorphous regions. Because, in this case, both trapped radicals in crystal regions (monomer could not enter in) and free radicals in the amorphous regions (became peroxides during irradiated in air) could not make contributions to grafting yield. 3.3. Eect of oxidation products Decomposition of oxidation products and eect on grafting yield depend on the temperature of store and grafting reaction. Generally as increasing of reaction temperature the grafting yield would decrease just like pre-irradiation grafting of acrylamide (AAm) on cotton cellulose fabric (Fig. 7). For NIPAAm, however,
Fig. 7. Grafting yield as a function of temperature. Total dose: 32.3 kGy. [Monomer]: 6% Q NIPAAm. . AAm.
58
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
Fig. 9. DSC spectrum of the fabric grafted with poly NIPAAm.
Fig. 8. (a) Amount of peroxides as a function of measurement temperature. (b) Amount of peroxides as a function of absorbed dose.
its grafting yield was increasing with reaction temperature (Fig. 7) although the grafting reaction was induced mainly by trapped radicals as discussed above. It may be due to the special structure of NIPAAm which induces following reaction:
. The RO radicals produced in this reaction could induce the extra grafting reaction which can compensate the decrease of grafting yield due to the decay of trapped radicals. So in pre-irradiation grafting system
of NIPAAm, the oxidation products could also make some contribution to the grafting yield with increasing of grafting temperature. The amount of oxidation products formed in the irradiation of cotton cellulose fabric in air as the function of absorbed dose and measurement temperature were given at Fig. 8. The oxidation products contain alkyl peroxides (ROOR) and hydroperoxides (ROOH), the later is more unstable (Kashiwabra and Seguchi, 1992). which make more contribution to grafting yield.
3.4. The surface property of grafted samples NIPAAm is an important monomer used to prepare environmental sensitive polymers or hydrogels (Wu et
al., 1992; Morita and Kaetsu, 1992). Fig. 9 showed the result of DSC measurement of the cotton cellulose fabric grafted by polyNIPAAm. From this picture it can be seen that the grafted fabric had also the tempera-
L. Jianqin et al. / Radiation Physics and Chemistry 55 (1999) 55±59
ture sensitivity which LCST was 35.48C closing to that of pure polyNIPAAm.
4. Conclusion 1. PolyNIPAAm was successfully grafted onto the cotton cellulose fabric by pre-irradiation technology. The surface of grafted fabric also has temperature sensitivity, its LCST is 35.48C. 2. The main active particles initiating reaction were the trapped radicals located in the interphase between the crystal and amorphous regions. 3. The hydroperoxides which was one of oxidation products produced during irradiation of samples in air are easy to decompose at lower temperature in the presence of NIPAAm and make some contribution to grafting yield as well.
Acknowledgements This Research is supported by Nuclear Foundatiion, China Y719FY006 and IAEA 9565/RO.
59
References Chye Ang, H., Garnett, J.L., 1982. Acid eect in UV and radiation-induced grafting of styrene to cellulose. ACS Symp Ser 187, 141. Garnett, J.L., Dworjangn, P.A., Bett, S.J. et al., 1995. Grafting and curing on polymer surfaceÐrole of additives, IAEA-TECDOC-834. Advanced Radiation Chemistry Research: Current Status October, 129±140. Ha, Hongfei, Wu, Liju, Tai, Hong et al, 1995. Study on radiation grafting of styrene on cotton cellulose. Radiat. Phys. Chem. 46 (4±6), 823±827. Kabanov, V.Ya, 1989. Radiation-induced graft copolymerization in the USSA. Radiat. Phys. Chem. 33, 51. Kashiwabara, H., Seguchi, T., 1992. Radiation-induced oxidation of plastics. In: Singh, A., Silverman, J. (Eds.). Radiation Processing of Polymers, Chap. II. Hanser, Oxford University Press, New York, pp. 221±253. Kulik, Eduard, A., Ivanchenko, Maria I. et al, 1995. Peroxides generation and decomposition on polymer surface. J. Polym. Sci. Part A: Polym. Chem. 33 (2), 323±330. Morita, Y., Kaetsu, I., 1992. Synthesis of stimule sensitive hydrogels. Radiat. Phys. Chem. 39 (6), 473. Sharda, Dasgupta, 1972. Industrial application of radiation induced grafted cotton. J. Polym. Sci. (C) 37, 333. Wu, Xueshen, Homan, Allen S., Yager, Paul, 1992. Synthesis and characterization of thermally reversible macroporous poly(N-Isopropylacrylamide) hydrogels. J. Polym. Sci. (A), Polymer Chemistry 30, 2121±2129. Zahran, A.H., 1980. Radiation grafting of acrylic and methacrylic acid to cellulose fabric to impart high water absorbency. J. Appl. Polym. Sci. 33, 5.