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ХИМИЧЕСКИЕ НАУКИ
Synthesis of hydrogels based on polyvinyl alcohol and methylcellulose and their physico-chemical studies Kuanova A.1, Nurpeissova Zh.2, Mangazbayeva R.3 Синтез гидрогелей на основе поливинилового спирта и метилцеллюлозы и их физико-химические исследования Куанова А. О.1, Нурпеисова Ж. А.2, Мангазбаева Р. А.3
'Куанова Айман Омирбековна /Kuanova Aiman Omirbekovna — магистрант;
2Нурпеисова Жансая Абиировна /Nurpeissova Zhansaya Abiirovna - доктор философии, старший преподаватель;
3Мангазбаева Рауаш Амантаевна /Mangazbayeva Rauash Amantayevna - кандидат химических наук,
старший преподаватель, кафедра химии и технологии органических веществ, природных соединений и полимеров, факультет химии и химической технологии, Казахский национальный университет имени аль-Фараби, г. Алматы, Республика Казахстан
Abstract: in this research, characteristics of polyvinyl alcohol (PVA)/methylcellulose (MC) hydrogels modified with two crosslinking methods are investigated. The first method is the use of a glutaraldehyde (GA) crosslinker to promote hemi-acetal linkages between MC and PVA chains. The second one is gamma irradiation to form insoluble PVA/MC gel by intermolecular crosslinking. The effects of the GA concentration and irradiation dose on the degree of crosslinking, degree of swelling, gel content were determined. The results indicate that the chemically crosslinked PVA/MC hydrogels showed lower polarity than the radiation crosslinked hydrogels.
Аннотация: в работе изучена характеристики гидрогелей на основе поливинилового спирта (ПВС) / метилцеллюлозы (МЦ) модифицированных с двумя методами сшивки. Первый метод - использование глутарового альдегида (ГА) в качестве сшивающего агента для развития геми-ацетальных связей между цепями МЦ и ПВС. Вторым из методов является гамма-облучение для образования нерастворимых ПВС/МЦ гелей путем межмолекулярного сшивания. Было определено влияние концентрации глутарового альдегида и дозы радиации на степень сшивания и набухания. Результаты показали, что химически сшитые ПВС/МС гидрогели имеют меньшую набухаемость, чем радиационно сшитые гидрогели.
Keywords: gamma radiation, crosslinking, polyvinyl alcohol, methylcellulose, glutaraldehyde, hydrogel. Ключевые слова: гамма-излучение, сшивание, поливиниловый спирт, метилцеллюлоза, глутаровый альдегид, гидрогель.
1. Introduction
Currently, polymeric materials on the basis of natural polysaccharides and synthetic polymers find more and more broad application in the most various areas of the industry, such as pharmaceutical industry, medicine, agriculture. In this regard, the increasing value is gained by development o f new composite materials on the basis of natural polysaccharides and synthetic polymers.
Poly (vinyl alcohol) (PVA) has a wide commercial application due to its unique chemical and physical properties. It is a nontoxic, highly crystalline, and water-soluble polymer and has good film forming and high hydrophilic properties. Poly (vinyl alcohol) could be considered as a good host material due to good thermo-stability, chemical resistance and film forming ability [1]. Due to their simple structure and unique properties , PVOH polymers have found applications in different industries including textile, paper, adhesives, food, biomedical and pharmaceutical in particular [2].
Commercial MC is a heterogeneous polymer consisting of highly substituted hydrophobic zones and less substituted hydrophilic zones. Gelation is therefore an intermediate non-equilibrium metastable state in which a three-dimensional network structure is formed due to secondary valence forces [3]. MC is used primarily because it has high viscosity, it is non-toxic, and is non-allergenic. MC has a wide range of applications due to its low cost. Because of its polymeric structure and high molecular Wight; it can be used as filler in bio- composite films [4].
Taking into consideration these properties of polyvinyl alcohol and methylcellulose, relevant is the study and creation of new composite materials based on this class of polymeric substances.
2. Experimental
2.1. Materials
In our work, we used methylcellulose (MC) powder with molecular weight M1=4 *104 g/mol, purchased from Aldrich (USA). PVA (number average molecular weight 70 *104 g/mol) was purchased from Merck KGaA (Germany) used without purification. Glutaraldehyde (GA) solution (25wt%) product of "Renal" company, was used without further purification.
2.2. Preparation of Chemically Crosslinked Polyvinyl alcohol/Methylcellulose Hydrogels
To obtain the hydrogels 10% aqueous solutions of polyvinyl alcohol and methylcellulose were used. GA contents were varied at 1-5 wt%. Hydrogels were obtained in the following proportions 9PVA: qMC: 9GA = 5:3:2; 2:2:1 and 3:5:2. Aqueous solutions of PVA and MC was mixed in chemical glass, then pH was adjusted to pH ~ 3 by adding hydrochloric acid (0,1 N). Therefore in this solution a certain amount of GA was added. The mixture was stirred until obtaining of homogeneous mass using a magnetic stirrer at 700 rpm. Duration of reaction was 2 hr. The obtained hydrogels were washed by distilled water to neutralize the hydrogels. The washed hydrogels were dried for several days at room temperature, then dried to constant weight in a vacuum oven.
2.3. Preparation of Radiation Crosslinked Polyvinyl alcohol/Methylcellulose Hydrogels
10% aqueous solutions of polyvinyl alcohol and methylcellulose were prepared in was prepared in the following proportions 9pva: 9mc=70:30, 50:50, 30:70. About 20 ml of the obtained PVA/MC solution was poured into a Petri dish. Gamma radiation experiment was performed at the Institute of Nuclear Physics (INP) of the Ministry of Energy of the Republic of Kazakhstan, Almaty. Gamma ray was radiated on PVA/MC solutions at various doses of 40, 80 and 120 kGy.
2.4. Swelling Behaviour of Polyvinyl alcohol/Methylcellulose Hydrogels
The swelling degree of radiation and chemically crosslinked PVA/MC hydrogels by gravimetric methods was determined. 0,1 g samples of composite materials was placed in 10 ml distilled water, then every 15 min was measured by the steady mass of the sample on an analytical balance. The degree of swelling (1) was calculated using the following equation:
m0
where, mo - initial mass of sample, g;
mt is the mass of the swollen sample in t time, g.
2.5. Gel content
The gel of hydrogels was measured by extraction in hot distilled water at 100°C for 48 h and dried at 70°C for 48 h until they reached constant weight. The gel content was defined as in equation below (2); where Wd is the dried gel weight after extraction, and W0 is the initial weight of polymer.
Gel = —xlOO (2)
Wo ( )
2.6. Scanning electron microscopy
Scanning electron microscopy (SEM) of the PVA/MC hydrogels was performed using Hitachi TM3030: Tabletop Scanning Electron Microscope (Japan). The sample was frozen and the fracture was coated with gold before being measured.
3. Results and Discussion
3.1. Swelling Behaviour of Polyvinyl alcohol/Methylcellulose Hydrogels
Hydrogels are hydrophilic three-dimensional (3D) networks that are chemically crosslinked or physically entangled with excellent water swelling capacity [5]. Hydrogels are characterized as soft material with high water content, which is similar to soft tissue, so they have good biocompatible properties and have been exploited in many fields such as food additives, pharmaceuticals, cell culture and biomedical implants [6].
Swelling characteristics of polymers, usually presented as weight of solvent absorbed per 1 g of dried gel, strongly depends on hydrophilicity of the polymer, density of intermolecular links i.e. molecular weight of chain part between crosslinks and others [7].
a, g/g
a, g/g
1,3 1
0,7 0,4 0,1
A A A A 3
[GA] = 1%
a, g/g
AAA 3
[GA] = 3%
a, g/g
2 4 6 8
0 2 4 6 8
t, h
t, h
[GA] = 2%
a, g/g
0 2 4 6 8
0 2 4 6 8
t, h
t, h
[GA] = 4%
A—A—A—A
2 4 6 8
t, h
[GA] = 5% [PVA] = [MC] = 10 %; 9pva:9MC:9GA = 3:5:2 (1); 2:2:1 (2); 5:3:2 (3)
Fig. 1. The kinetics of swelling ofPVA/MC hydrogels at various contents ofglutaraldyhyde
0
2
1
3
2
1
0
9pva:9MC = 70:30
2 4 6 8
t, h
9pva:9MC = 50:50
a, g/g
4 3,5 3 2,5 2 1,5 1
0,5 0
8
t, h
9pva:9MC = 30:70 [PVA] = [MC] = 10 %; 40 kGy (1); 80 kGy (2); 120 kGy (3) Fig. 2. The kinetics of swelling ofPVA: MC hydrogels with different doses ofgamma ray
In this study, the relationship between the degree of swelling of PVA/MC hydrogel samples with doses of gamma ray as well as with contents of a GA crosslinker is illustrated in Fig. 1,2. According to the study of the kinetics of swelling has been proven that gels obtained by chemical crosslinking and radiation methods in all volume ratios were proven. From the figure 1, it was clearly seen that the degree of swelling of the crosslinked PVA/MC hydrogels increased with increasing the contents of a GA crosslinker. For example, in contents of a 1% GA crosslinker at the maximum equilibrium degree of swelling was 1,3; at 5% it was 6. Additionally, as can be seen from this figure, swelling capabilities of hydrogel compositions are increased by increasing the PVA content. This is due to the fact that the conformation of PVA compared to the conformation of MC is simple and hydroxyl groups binding with GA is located close and often. In the case of the radiation crosslinking, from the figure 2, the degree of swelling increased with decreasing doses of radiation. The maximum equilibrium degree of swelling of PVA/MC hydrogels at 40 kGy was 3,5, and at 120 kGy was 1,8.
In comparison on the swelling values between radiation crosslinked and chemically crosslinked hydrogel samples, the swelling values of gamma irradiation crosslinked MC films were greater than that of GA crosslinked MC films. From these results, it is likely that the gamma irradiation crosslinking process should maintain more hydrophilic groups on the methylcellulose gel network than the GA crosslinking process thus resulting in the higher degree of swelling of the former process. This statement could be corresponded to the
0
2
4
6
research of Florin et al. who studied about the effect of gamma radiation on the structure of MC and reported that the radiation induced chain cleavage, demethylation, carbonyl and acid group formation in MC, leading to enhanced hydrophilic behaviors [8].
3.2. Gel Content of Crosslinked PVA/MC hydrogels
Gel content is defined as the amount of insoluble polymer in any solvent. Gel contents of PVA/MC hydrogels at various doses of gamma ray (kGy) and those obtained at different contents of a GA crosslinker (wt %) is presented in Fig. 3.
100
OS
15 u
80
60
(a)
20 40 60 80 100 120
Dose of Gamma Ray(kGy)
£
"3 80
UJ
60
40
20
(b)
2 4
Glutaraldyhyde content (wt%)
Fig. 3. Gel content of crosslinked PVA/MC gels at various doses ofgamma ray (a) and contents ofglutaraldyhyde (b)
In figure 3 (a), it was clearly seen that the gel contents of the crosslinked increased with an increase of the doses of the gamma ray. The high gel fraction of hydrogels; caused by enhanced irradiation dose as a result of higher degree of crosslinking onto polymer network which cause higher gel content. In the PVA/MC samples the gel content increased from 67% using a radiation dose of 40 kGy to the value of 87% using a radiation dose of 120 kGy. The same trend was observed in the chemically crosslinked PVA/MC hydrogels with increasing the contents of a GA crosslinker. In the chemical crosslinking process, the gel content changed from 49% at the GA level of 1wt% to the gel content value up to 72% at the maximum GA content of 5wt%. Gamma irradiation on cellulose derivatives typically lead to the random formation of free radicals on polymer chains and hydrogen atoms. These free radicals are responsible for such reactions as grafting and intermolecular crosslinking [9].
3.3. Scanning electron microscopy
In general, the scanning electron microscopy (SEM) shows microstructure morphologies of hydrogels.The surface morphology of chemically and radiation crosslinked PVA/MC hydrogels was detected by scanning electron microscopy (SEM).
D5,0 X100 1 mm
D3,1 x2,0k 30 urn
0
0
Fig. 4. Micrographs of chemically (a) and radiation (b) crosslinked PVA/MC hydrogels
In fig. 4 we can see that the pore structure of a hydrogel obtained by chemical cross linking is different from the gel produced by radiation method. Radiation crosslinked PVA/MC hydrogel shows a larger pore structure compared with the chemically crosslinked hydrogel and this affect on the degree of swelling. 4. Conclusion
Crosslinked PVA/MC hydrogels prepared by gamma irradiation and GA addition were achieved. The effects of the GA concentration and irradiation dose on the degree of crosslinking, degree of swelling were determined. Degree of swelling of the crosslinked PVA/MC hydrogels increased with increasing the contents of a GA crosslinker was determined. In the case of the radiation crosslinking, the degree of swelling increased with decreasing doses of radiation. The results showed that the swelling values of gamma irradiation crosslinked PVA/MC hydrogels were greater than that of GA crosslinked PVA/MC hydrogels. The gel fraction increases with increasing irradiation dose, the same trend was observed in the chemically crosslinked PVA/MC hydrogels with increasing the contents of a GA crosslinker.
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