Processing and study of novel lignin-starch and lignin-gelatin biodegradable polymeric films, JC Vengal, M Srikumar

Tags: lignin, wood chips, tensile strength, paper industry, water absorption, starch solution, viscous solution, polymer mixture, tapioca starch, Carl Hanser Publishing, Crystallinity, References, proportions, Tensile Test, M Pa, films, Young's Modulus, Text book, Preparation, glycerol, NaOH solution, M. Vert, John Wiley and Sons, Royal Society of Chemistry, R. Westling, Gelatin, polymers, polymer films, Biodegradable Polymers and Plastics, polymer science, amylose and amylopectin, biodegradable polymers, Biomedical polymers, ACS Symposium Series, Biomacromolecules, R. A. Northey, F.W. Billmeyer, morphology
Content: Trends Biomater. Artif. Organs, Vol 18 (2), January 2005
http://www.sbaoi.org
Processing and Study of Novel Lignin-Starch and Lignin-Gelatin Biodegradable Polymeric Films
Jiju Cherian Vengal and Manu SriKumar S. V. National Institute Of Technology, Surat, India E-mail: [email protected] Abstract: Synthetic plastics pose one of the biggest threats to the environment today. The most promising solution to this problem is the prospect of biodegradable polymers. In this work, we have explored the possibility of extracting lignin from waste wood chips of a paper industry and blending lignin with established biopolymers like starch and gelatin. Lignin is one of the most commonly available natural materials, yet it has been under utilized as a biopolymer. This paper reports the methodology of preparation and results of tensile and water absorption tests of different lignin- starch, lignin- gelatin and starch-gelatin-lignin polymer films. All the materials used for the polymers are bio derived and completely biodegradable. Solution blending followed by curing was the method adopted for the preparation of the films. Complete methodology of preparation of each film and the results of the tests are discussed in detail in the paper. In this paper we have explored the possibility of preparation of novel biopolymers. Novelty of the work lies in using lignin extracted from paper industry waste. Over and above bringing down the cost of lignin to almost nil, this method utilizes a waste product and the polymers prepared are potential biomaterials. Keywords: Lignin, Starch, Gelatin, Biodegradable Polymer, Water Absorption Test and Tensile Strength.
Introduction: Synthetic polymers pose one of the greatest threats to ecology today. A possible solution to the problem is the prospect of biodegradable polymers. Biodegradable polymers offer the following advantages. Firstly, they are made from renewable resources and thus do not face the problem of exhaustion. Secondly, they are biodegradable, which implies that the polymer after use will ultimately turn in to compost. Our research work concentrated on the
preparation of novel biodegradable films from lignin. For this purpose we selected ligninstarch, lignin-gelatin and lignin-starch-gelatin systems. Various films at different compositions were prepared, tested and compared with the standard values to ascertain the applicability of our new material. Lignin is a complex phenolic compound found abundantly in the Cell wall of plants in association with cellulose and hemi cellulose. Little research has gone in to preparation of
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Processing and Study of Novel Lignin-Starch and Lignin-Gelatin Biodegradable Polymeric Films
lignin based polymers. Lignin based polymers present two-fold advantage. One is that they are abundantly available as tons of lignin is thrown off as a waste product in pulp and paper industries. Secondly, lignin is completely biodegradable, though slowly. Thus it is a prospective biodegradable polymer. Starch is one of the most abundant natural compound, found widely in rice, wheat, corn, tapioca etc. It is a (14) linked poly--dglucan and is a mixture of linear amylose (poly---d-glucopyranoside) and branched amylopectin (poly- --d-glucopyranoside and --d-glucopyranoside) .the major novelty of this work is in the way lignin was obtained. Lignin for the purpose was extracted from the waste wood chips of a paper industry. This method is effective in both utilizing a waste product and in reducing the price of the product itself. Starch is an established and widely used biodegradable polymer. By blending lignin with starch it was intended to study the feasibility of preparing a lignin based film and investigate the property modifications of the starch polymer. Gelatin is most common material used for making drug capsules. By blending lignin and gelatin at various proportions we have tried to develop a cheaper drug capsule. For this purpose, we have tested the water absorption ability of the films at different pH. Experimental: Materials and Methods: Tapioca starch was obtained from a Khadi industry in Kottayam, Kerala. It was decided to extract Lignin from wood chips. The necessary wood chips were kindly supplied by Hindustan Newsprint Ltd. (HNL), Veloor, Kerala. Gelatin for the work was food grade gelatin.
Extraction of lignin from wood chips: Wood chips obtained from HNL was the source of lignin used. 12g of these wood chips were digested in 500ml of 1% NaOH solution for 5 hours at around 100oC. The solution was filtered and the filtrate, lignin solution, was concentrated to 75 ml. The weight of dry wood chips was found to be 9g. i. e, 75ml solution had almost 3 grams of lignin. Preparation of Starch-Lignin polymer: It was decided to prepare starch-lignin polymer films of the following proportions--90:10, 80:20, and 70:30(w/w). For all these three proportions, the weight of starch taken was kept constant and the weight of lignin was appropriately varied. For the 90:10starch: lignin film; 4gm of tapioca starch was mixed with 75ml water with constant stirring at 100oC until the mixture turned semi-viscous.5 drops of glycerol was added as a plasticizer. To obtain the required proportion, 10ml of lignin solution (almost 0.4g), obtained as mentioned before was added to the semi-viscous starch solution. The starchlignin mixture was stirred vigorously for another ten minutes. Later, the polymer mixture was spread on a plastic coated plate and left to cure. The other two proportions were prepared by following the same procedure, but by varying the amount of lignin taken. Preparation of Gelatin -Lignin films: 4gm of gelatin were mixed in 75ml water and were left to soak for 10 minutes. Later it was heated at 100oC till gelatin dissolved completely in water. 5 drops of glycerol was added and stirred for another 10 minutes at 100 oC. The required amount of lignin solution was added to the gelatin solution and stirred vigorously for 10 more minutes. Later, the
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Jiju Cherian Vengal and Manu Srikumar
polymer mixture was poured on a plastic coated tray and left to cure. Adopting this methodology gelatin-lignin films in the proportion 90:10 and 80:20 (w/w) were prepared.
The weights of the samples were monitored at the end of the first 30 minutes, 60 minutes and 180 minutes. The percentage increase in weight was tabulated and that was taken as a measure of the water absorption of the film.
Preparation of Starch-Gelatin-Lignin films: Two films in the proportions of 45:45:10 and 40:40:20 of starch-gelatin-lignin were prepared. For this, 2gm starch in 50ml water was heated at100oc till it formed a semi viscous solution. 3 drops of glycerol was added. Side by side, 2gm of gelatin was soaked for 10 minutes in 25ml water and later heated at 100oc till it formed a semi-viscous solution. After the addition of 3 drops of glycerol, the gelatin solution was mixed with the starch solution and the two were stirred vigorously for another 10 minutes. Required amount of lignin solution was later added to the starch-gelatin mixture and was heated for another 5 minutes. At the end of 5 minutes, the mixture was poured on to a plastic-coated plate and left to cure. Mechanical Testing: To obtain the tensile strength, the percentage elongation at break and young's modulus, a UTM test was done for all the specimens at Rubber Board, Kottayam, Kerala.
Results and Discussions:
Tensile Test: Table 1 and Table 2 show tensile strength and modulus of starch-lignin and gelatin ­ lignin films of different compositions.
Table 1: Lists the important properties obtained from the tensile test of various starch-lignin films.
Proportion Tensile % Elongation Young's
Strength
Modulus
(M Pa)
(M Pa)
90:10
4.060
357.00
1.622
80:20
0.671
112.0
1.468
70:30 0.0852
77.38
0.0387
Table 2: Lists the important properties obtained from the tensile test of various gelatin-lignin films.
Proportion 90:10 80:20 70:30
Tensile Strength (M Pa) 4.307 4.060 3.222
% Elongation 416.5 357.00 37.48
Young's Modulus (M Pa) 1.531 1.622 27.26
The important properties obtained from the tensile test of starch- gelatin-lignin film is given in table 3.
Water absorption Test: The major drawback of starch-based films is its hydrophilicity. On the other hand, the degree of absorption of water and thus swelling of gelatin-based polymers is of utmost importance, if they are to be used for biological applications. Thus, water absorption at pH 2, pH 4 and pH 6 were done. Samples of 80:20 and 90:10 starch: lignin films and 90:10 gelatin: lignin film were weighed and placed in the different solutions.
Table 3: Tensile test of starch- gelatin- lignin films.
Proportion Tensile % Elongation Young's
Strength
Modulus
(M Pa)
(M Pa)
45:45:10 5.656
44.65
67.36
40:40:20 3.2
36.9
26.5
From the tensile tests, it can be seen that starchlignin blend in the 90:10 ratio exhibits impressive strength and it is also seen that the starch-lignin blends have impressive percentage of elongation. The tensile strength and young's modulus decreases with increase
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Processing and Study of Novel Lignin-Starch and Lignin-Gelatin Biodegradable Polymeric Films
in percentage of lignin. Gelatin-lignin and starch-gelatin-lignin films also exhibit impressive tensile strengths. Water absorption test: This test was carried out as described before to ascertain the water absorption tendency of the films. This test is of prime importance as
From these data it can be inferred that the starch-lignin films and gelatin- lignin films are highly hydrophilic. The water absorption of the films increase with the increase in lignin content. It is also notable that water absorption increases with increase in pH. From the data it is seen that gelatin-lignin films show more swelling properties than starch-lignin films.
Table 4: Percentage of swelling of 90-10 % starch-lignin films at various pH
pH Initial wt
Weight
of the film (gm) after 30 min.
%of
Weight
%of
Weight .
%of Weight .
swelling after 60 min. swelling after 180 min. swelling after 24 hrs.
2
0.540
1.051
94
1.065
97
1.07
98.14 No change
4
0.465
0.7508
104
1.050
126
1.056
127.09
,,
6
0.3502
0.790
125.88
0.80
128
0.806
130.15
,,
Table 5: Percentage of swelling of 80-20 % starch-lignin films at various pH
pH Initial wt
Weight
of the film (gm) after 30 min.
%of
Weight
%of
Weight .
%of Weight .
swelling after 60 min. swelling after 180 min. swelling after 24 hrs.
2
0.539
1.646
210.5
1.75
230
1.i81
241.5 No change
4
0.4224
1.52
260
1.68
298
1.782
322
,,
6
0.275
1.11
303.5
1.20
336
1.25
347
,,
Table 6: Percentage of swelling of 90-10 % gelatin-lignin films at various pH
pH Initial wt
Weight
of the film (gm) after 30 min.
2
0.5672
2.572
4
0.6428
4.49
6
0.93
6.650
%of swelling 353 599 615
Weight
%of
Weight .
%of Weight .
after 60 min. swelling after 180 min. swelling after 24 hrs.
3.550
525
4.034
611 No change
5.142
700
5.84
808
,,
8.700
835
9.023
870
,,
they are meant for bio medical purpose, where water absorption and swelling determines the rate of drug delivery. The result of the tests are given below: The percentage of swelling of various percentage of starch-gelatin film at different pH is given in Table 4 -6.
These values are of utmost importance in the drug delivery action of the films. Conclusions: In this paper we have explored the possibility of the preparation of novel biopolymers. Novelty of the work lies in using lignin extracted from paper industry waste. Over and
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Jiju Cherian Vengal and Manu Srikumar
above bringing down the cost of lignin to almost nil, this method utilizes a waste product. It was also seen that lignin so obtained could be successfully used for the preparation of biopolymers. Starch is a widely used biopolymer, but lignin-starch systems are a relatively unexplored area in bioPolymer Research. Through this paper we have established a method of preparation lignin starch blends and found that they are comparable to normal starch films. The optimum proportion of starch: lignin is 90:10, as it shows high tensile strength and young's modulus. Increasing the proportion of lignin decreased the strength of the polymer. The water absorption tests showed that the system is highly hydrophilic. Thus, the material is suitable for internal use and for biomedical purposes. Gelatin is the most commonly used polymer for manufacture of drug capsules. Through this work we have come up with a cheaper alternative to gelatin films, by blending gelatin with lignin and starch. Amount of water absorption is a direct indicator on the pore size of the material and drug delivery systems can be designed depending on the pore size of the polymer. From the water absorption test it is clear that the pore size of the film varies with
pH. This data can be utilized in designing specific drug delivery systems. The tensile test and water absorption test results have been given in the paper and the results are comparable to those of the already existing polymers. Further work has to be done on the swelling behavior of these polymers and physiological effect. Theoretically all the components of the system are biodegradable and thus do not pose any health hazards. Study on the microscope structure on swelling is of utmost importance and is to be studied. Acknowledgements: Thanks go to Dr. Sabu Thomas, reader, school of Chemical Sciences, Mahatma Gandhi University, Kerala for providing the necessary guidance to carrying out the work. We would like to thank Mrs. Annie Mathews and Miss. Bindu K. of the post graduate department of chemistry, Baselius college, Kottayam, Kerala for their help throughout the work. We would also like to thank the management of HNL, Veloor, Kottayam, Kerala and Mr. N.J. Cherian, Surya Research and Industries, Ramapuram, Pala, Kerala for providing us waste wood chips and tapioca starch for the project.
References: 1. A R. Westling, Crystallinity and morphology in films of starch, amylose and amylopectin blends, Biomacromolecules (2001). 2. F.W. Billmeyer, Jr. John Wiley and Sons. text book of Polymer Science - Third edition. 3. Biodegradable Polymers and Plastics, Edited by M. Vert, Royal Society of Chemistry (1992). 4. R. A. Northey, Low-cost uses of lignin, emerging technology of materials and chemicals from biomass, ACS Symposium Series 476, Washington, D.C. (1992). 5. S.W. Shalaby, Biomedical polymers - designed to degrade systems, Carl Hanser Publishing (1994).
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