مروری بر الیگومرها و مونومرهای تجدیدپذیر جهت تهیه پوشش‌های تابش‌پز

نوع مقاله : مقاله مروری

نویسنده

دانشجوی دکترا، دانشکده مهندسی پلیمر و رنگ، دانشگاه صنعتی امیرکبیر

چکیده

هدف از این مقاله، معرفی انواع گونه‌های واکنش‌پذیر حساس به نور مشتق شده از زیست توده‌ها و زیست پلیمرها است که این ترکیبات می‌توانند طی فرآیند پلیمریزاسیون نوری که فرآیندی تمیز، سریع و بدون انتشار آلاینده‌ها مانند ترکیبات آلی فرار (VOC) است، پلیمر شوند و به شکل پوشش درآیند. زیست پلیمرهای اولیه می‌توانند برای به دست آوردن پلیمرهای حساس به نور اصلاح شوند. در این گزارش، ابتدا انواع الیگوهرهای تابش‌پز معرفی می‌شوند، سپس انواع اصلی پلیمرهای طبیعی مانند لیپیدها، آمینو اسیدها (پروتئین‌ها)، کربوهیدرات‌ها، پلی ان‌ها، لاستیک طبیعی و غیره توصیف خواهندشد. در ادامه نحوه استخراج، اصلاح، استفاده یا یکپارچه‌سازی آنها در سامانه‌های پلیمریزاسیون نوری و کاربرد آنها به عنوان پوشش سطوح شرح داده می‌شود. تاکنون روش‌های مختلفی نظیر آکریلاسیون با مونومرهای اکریلیکی و جفت‌کننده تیول -انی برای اصلاح این مواد اولیه تجدیدپذیر استفاده شده است. مواد تجدید پذیر اصلاح‌‌شده می‌توانند با سازوکار پلیمریزاسیون‌های مختلف مانند رادیکالی، کاتیونی، خود شروع‌کننده و عاری از شروع‌کننده، تیول انی و غیره تهیه شوند. همچنین به ویژگی‌ها، واکنش‌پذیری، سمیت، زیست تخریب‌پذیری، زیست‌سازگاری و کاربرد نهایی این ترکیبات نیز اشاره خواهد شد.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

A Review on the Renewable Oligomers and Monomers for Preparation of the Radiation Coatings

نویسنده [English]

  • Sahar Abdollahi Baghban
Polymer Engineering and Color Technology Department, Amirkabir University of Technology
چکیده [English]

The aim of this review was to describe the variety of reactive species derived from biomass that can lead to photosensitive materials through a photopolymerization process, a clean and quick process at room temperature without pollutant emission such as volatile organic compounds (VOC) to make radiation cure coatings. These biosourced macromolecules can be easily modified to obtain photosensitive or UV-reactive macromolecules. The main classes of naturally occurring molecules and macromolecules such as lipids, amino acids (proteins), carbohydrates, polyenes, natural rubber, etc. are detailed. The ways they are extracted, modified, used or integrated in photopolymerizable systems are described in relation to their applications: coatings, biomaterials, biodegradable drug delivery systems, microelectronics or optoelectronics. Different methods such as acrylation by acrylic monomers and thiol-ene coupling are used to modify these renewable feedstock use in materials. The modified renewable materials can be used in various photopolymerization such as radical, cationic, self-initiating, thiol-ene and etc. polymerization. This critical review takes into account the characteristics and reactivity of the various compounds as well as their cytotoxicity, biodegradability and their end uses.

کلیدواژه‌ها [English]

  • Radiation cure coatings
  • Renewable material
  • Vegetable oil
  • Polysaccharide
  • Protein
  1. Y. J. Park, D. H. Lim, H. J. Kim, D. S. Park, I. K. Sung, "UV- and thermal-curing behaviors of dual-curable adhesives based on epoxy acrylate oligomers", Int. J. Adhes. 29, 710–717, 2009.
  2. R. Schwalm, "Coatings basics, recent developments and new applications", Elsevier Science, 2006.
  3. C. Decker, H. Le Xuan, T .N. Thi Viet, "Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber", J. Polym. Sci. Part A Polym. Chem. 33, 2759-2772, 1995.
  4. C. Decker, K. Moussa, "Kinetic study of the cationic photopolymerization of epoxy monomers", J. Polym. Sci. Part A Polym. Chem. 28, 3429-3443, 1990.
  5. A. Asif, W. Shia, X. Shenb, K. Nie, "Physical and thermal properties of UV curable waterborne polyurethane dispersions incorporating hyperbranched aliphatic polyester of varying generation number", Polymer, 46, 11066–11078, 2005.
  6. F. Mirshahi, S. Bastani, M. Ganjaee Sari, "Studying the effect of hyperbranched polymer modification on thekinetics of curing reactions and physical/mechanical properties of UV-curable coatings", Prog. Org. Coat. 90, 187–199, 2016.
  7. X. Wang, J. Zhan, W. Xing, X. Wang, L. Song, X. Qian, B. Yu, Y. Hu, "Flame retardancy and thermal properties of novel UV-curable epoxy acrylate coatings modified by a silicon-Bearing hyperbranched polyphosphonate acrylate", Ind. Eng. Chem. Res. 52, 5548−5555, 2013.
  8. Th. Poon, "The Michael Reaction", J. Chem. Edu. 79, 264-267, 2012.
  9. W. Yin, X. Zeng, H. Li, Y. Hou, Q.iongzhi Gao, "Synthesis photo polymerization kinetics and thermal properties of UV-curable waterborne hyperbranched polyurethane acrylate dispersions", J. Coat. Technol. Res. 8, 577–584, 2011.
  10. D. James, "Unique characteristics of a dendritic polyether for radiation curing", PRA Radcure Coat. Inks, Manchester, UK, 2002.
  11. J. P. Fouassier "Photoinitiation, photopolymerization, and photocuring: fundamentals andapplications", Carl Hanser Verlag Gmbh & Co, 1995.
  12. N. Pietschmann, K. Stengel, "UV hardening and high solid binders basedon plant oil", Farbe. Lack. 110, 29-33, 2004.
  13. H. Pelletier, N. Belgacem, A. Gandini, "Acrylated vegetable oils as photocrosslinkable materials", J. Appl. Polym. Sci. 99, 3218-3221, 2006.
  14. A. Koeckritz, A. Martin,"Oxidation of unsaturated fatty acid derivatives and vegetable oils", Eur. J. Lipid. Sci. Technol. 110, 812-824, 2018.
  15. M. Desroches, S. Caillol, V. Lapinte, R. Auvergne, B. Boutevin,"Synthesis of biobased polyols by thiol-ene coupling from vegetable oils", Macromol. 44, 2489-2500, 2011.
  16. M. Stemmelen, F. Pessel, V. Lapinte, S. Caillol, J.P. Habas, J.J. Robin. "A fully biobased epoxy resin from vegetable oils: From the synthesis of the precursors by thiol-ene reaction to the study of the final material", J. Polym. Sci. Part A Polym. Chem. 49, 2434-2444, 2011.
  17. م. کرامتی نیا، ف. نجفی، م. ر. صائب",پوشش‌های تابش‌پز بر پایه پلیمرهای پرشاخه"، نشریه علمی‌ترویجی دنیای رنگ، 7، 13-23، 1396.
  18. Ch.W. Chang, K. T. Lu, "Linseed-oil-based waterborne UV/air dual-cured wood coatings", Prog. Org. Coat. 76, 1024-1031, 2013.
  19. V. Mishraa, J. Desaia, B. Kalpesh, I. Patel, "(UV/Oxidative) dual curing polyurethane dispersion from cardanol based polyol: synthesis and characterization", Ind. Crop. Prod. 111, 165–178, 2018.
  20. U. Biermann, U. Bornscheuer, M.A.R. Meier, J.O. Metzger, H.J.Schäfer, "Oils and fats as renewable raw materials in chemistry", Angew. Chem. Int. Ed. 50, 3854-3871, 2011.
  21. C. A. Teacă, D. Roşu, F. Tanasă, M. Zănoagă, F. Mustaţă,"Epoxidized vegetable oils for thermosetting resins and their Potential applications", Func. Biopolym., 27, 217-238, 2017.
  22. B. Sajjadi, W. Y. Chena, A. A. A. Raman, Sh. Ibrahimc, "Microalgae lipid and biomass for biofuel production: A comprehensive review on lipid enhancement strategies and their effects on fatty acid composition", Renewable Sustainable Energy Rev. 97, 200-232, 2018.
  23. A. Guo, D. Demydov, W. Zhang, Z.S. Petrovic, "Polyols and polyurethanes from hydroformylation of soybean oil", J. Polym. Environ. 10, 49-52, 2012.
  24. Z. S. Petrović, "Polyurethanes from vegetable oils", Polym. Rev. 48, 109-155, 2008.
  25. A. H. Mahmoud, G.S. Tay, H.D. Rozman, "A Preliminary study on ultraviolet radiation-cured unsaturated polyester resin based on palm oil", Polym. Plast. Technol. Eng. 50, 573-580, 2002.
  26. T. Eren, S. H. Küsefoğlu, "Hydroxymethylation and polymerization of plant oil triglycerides", J. Appl. Polym. Sci. 91, 4037-4046, 2004.
  27. S. N. Khot, J. J. Lascala, E. Can, S. S. Morye, G. I. Williams, G. R Palmese, S. H Kusefoglu, R. P.Wool, "Development and application of triglyceride-based polymers and composites", J. Appl. Polym. Sci. 82, 703-723, 2017.
  28. Z. Chen, B. Chisholm, R. Patani, J. Wu, S. Fernando, K. Jogodzinski, D. Webster, "Soy based UVcurable thiol-Ene coatings", J. Coat. Technol. Res. 7, 603-613, 2010.
  29. M. Lazzari, O. Chiantore, "Drying and oxidative degradation of linseed oil", Polym. Degrad. Stab. 65, 303-313, 1999.
  30. HF. Payne, "Organic Coating Technology", Vol. 1. New York: John Wiley & sons, 42-132, 1965.
  31. F. Seniha Güner, Y. Yağcı, A. Tuncer Erciyes, "Polymers from triglyceride oils", Prog. Polym. Sci. 31, 633-670, 2016.
  32. V. Sharma, P. P. Kundu, "Addition polymers from natural oils—A review", Prog. Polym. Sci. 31, 983-1008, 2006.
  33. K. Hill, "Fats and oils as oleochemical raw materials", Pure. Appl. Chem. 72, 1255-1264, 2000.
  34. B. Çakmaklı, B. Hazer, İ. Ö. Tekin, F. B. Cömert, "Synthesis and characterization of polymeric soybean oil-g-methyl methacrylate (and n-butyl methacrylate) graft copolymers: biocompatibility and bacterial adhesion", Biomacromol. 6, 1750-1758, 2015.
  35. R. P. Klaasen, R. P. C. Van der Leeuw, "Fast drying cobalt-free high solids alkyd paints", Prog. Org. Coat. 55, 149-153, 2006.
  36. A. Paramarta, X. Pan, D.C. Webster, "Synthesis and photopolymerization of highly functional acrylated biobased resins", Polym. Chem. 52, 552, 2011.
  37. S. Bovatzis, E. Ioakimoglou, P. Argitis, "UV exposure and temperature effects on curing mechanisms in thin linseed oil films: spectroscopic and chromatographic studies", J. Appl. Polym. Sci. 84, 936-49, 2002.
  38. C. E. Hoyle, C. N. Bowman "Thiol-Ene click chemistry", Angew. Chem. Int. 49, 1540-1573, 2010.
  39. S. Boileau, B. Mazeaud-Henri, R. Blackborow, "Reaction of functionalized thiols with oligoisobutenes via free-radical addition", Eur. Polym. J. 39, 1395-1404, 2003.
  40. J. Samuelsson, M. Jonsson, T. Brinck, M. Johansson, "Thiol–ene coupling reaction of fatty acid monomers", J. Polym. Sci. Part A Polym. Chem. 42, 6346-6352, 2014.
  41. C.E. Hoyle, T.Y. Lee, T. Roper, "Thiol–enes: chemistry of the past with promise for the future", J. Polym. Sci. Part A Polym. Chem. 42, 5301-5338, 2004.
  42. U. Bexell, R. Berger, M. Olsson, T.M. Grehk, P.E. Sundell, "Johansson M. Bonding of vegetable oils to mercapto silane treated metal surfaces: surface engineering on the nano scale", Thin Solid Films. 515, 838-841, 2006.
  43. B. S. Sitaramam, P. C. Chatterjee, M .A. Sivasamban,"Use of castor-based products in formulating UV-curable coatings", Paintindia, 36, 17-18, 1986.
  44. J. G. Homan, X. H. Yu, T. J. Connor, S. L. Cooper, "Castor oil-based UV-curable polyurethane-acrylate interpenetrating networks", J. Appl. Polym. Sci. 43, 2249-2257, 1991.
  45. K. I. Patel, R. J. Parmar, J. S. Parmar, "Novel binder system for ultraviolet-curable coatings based on tobacco seed (Nicotiana rustica) oil derivatives as a renewable resource", J. Appl. Polym. Sci. 107, 71-81, 2008.
  46. E. Dzunuzovic, S. Tasic, B. Bozic, D. Babic, B. Dunjic, "UV-curable hyperbranched urethane acrylate oligomers containing soybean fatty acids", Prog. Org. Coat. 52, 136-143, 2005.
  47. H. M. Kim, H. R. Kim, B. S. Kim, "Soybean Oil-Based Photo-Crosslinked Polymer Networks", J. Polym. Environ. 18, 291-7, 2010.
  48. H. M. Kim, H. R. Kim, C. T. Hou, B. S. Kim, "Biodegradable photo-crosslinked thin polymer networks based on vegetable oil hydroxy fatty acids", J. Am. Oil. Chem. Soc. 87, 1451-1459, 2010.
  49. Ch.W. Chang, K.T. Lu, "Linseed-oil-based waterborne UV/air dual-cured wood coatings", Prog. Org. Coat. 76, 1024-1031, 2013.
  50. V. Mishraa, J. Desaia, Kalpesh I. Patela, "(UV/Oxidative) dual curing polyurethane dispersion from cardanol based polyol: Synthesis and characterization", Ind. Crop. Prod. 111, 165–178, 2018.
  51. H. Gu, K. Ren, D. Martin, T. Marino, D. Neckers, "Cationic UV-cured coatings containing epoxidized soybean oil initiated by new onium salts containing tetrakis (pentafluorophenyl) gallate anion", J. Coat. Technol. 74, 49-52, 2002.
  52. R. A. Ortiz, D. P. Lopez, M. L. G. Cisneros, J. C. R. Valverde, J.V. Crivello, "A kinetic study of the acceleration effect of substituted benzyl alcohols on the cationic photopolymerization rate of epoxidized natural oils", Polymer. 46, 1535-1541, 2015.
  53. J. V. Crivello, R. Narayan "Epoxidized triglycerides as renewable monomers in photoinitiated cationic polymerization", Chem. Mater. 4, 692-699, 1992.
  54. J. Samuelsson, P. E. Sundell, M. Johansson, "Synthesis and polymerization of a radiation curable hyperbranched resin based on epoxy functional fatty acids", Prog. Org. Coat. 50, 193-198, 2014.
  55. A. H. Johnson, L. E. Meemken, M.D. Soucek, "UV-curable linseed oil based ceramers", Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 42, 747-748, 2001.
  56. N. Jiratumnukul, R. Intarat "Ultraviolet-curable epoxidized sunflower oil/organoclay nanocomposite coatings", J. Appl. Polym. Sci. 110, 2164-2167, 2008.
  57. K. Zou, M. D. Soucek,"UV-curable cycloaliphatic epoxide based on modified linseed oil: synthesis, characterization and kinetics", Macromo. Chem. Phys. 206, 967-975, 2005.
  58. J. Chen, M. D. Soucek, W. J. Simonsick, R.W. Celikay, "Synthesis and photopolymerization of norbornyl epoxidized linseed oil", Polymer. 43, 5379-5389, 2012.
  59. Z. Zong, J. He, M. D.Soucek, "UV-curable organic-inorganic hybrid films based on epoxynorbornene linseed oils", Prog. Org. Coat. 53, 83-90, 2005.
  60. R. Hoffman, P. Wells, H. Morrison,"Further studies on mechanism of coumarin photodimerization - observation of an unusual heavy atom effect", J. Org. Chem. 36, 102-108, 1971.
  61. C.H. Krauch, S. Farid, G.O. Schenck, "Photo-c4-cyclodimerisation von cumarin", Chem. Ber. 99, 625-633,1966.
  62. F.D. Lewis, S.V. Barancyk, "Lewis acid catalysis of photochemical-reactions. Photodimerization and cross-cycloaddition of coumarin", J. Am. Chem. Soc. 111, 8653-8661, 1989.
  63. A. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, "Improved utilisation of renewable resources: new important derivatives of glycerol", Green. Chem. 10, 13-30, 2008.
  64. C.H. Zhou, J.N. Beltramini, Y.X. Fan, G.Q. Lu, "Chemoselective catalytic conversion of glycerol as a biorenewable source to valuable commodity chemicals", Chem. Soc. Rev. 37, 527-49, 2008.
  65. P. D. Pham, S. Monge, V. Lapinte, Y. Raoul, J. J. Robin, "Various radical polymerizations of glycerol-based monomers", Eur. J. Lipid. Sci. Technol.115, 28-40, 2012.
  66. H. Kilambi, S. K. Reddy, L. Schneidewind, J. W. Stansbury, C. N. Bowman, "Influence of the secondary functionality on the radical-vinyl chemistry of highly reactive monoacrylates", J. Polym. Sci. Part A. Polym. Chem. 47, 4859-4870, 2009.
  67. H. Kilambi, J. W. Stansbury, C. N. Bowman, "Deconvoluting the impact of intermolecular and intramolecular interactions on the polymerization kinetics of ultrarapid mono(meth)acrylates", Macromol. 40, 47-54, 2007.
  68. J. Park, J. Eslick, Q. Ye, A. Misra, P. Spencer, "The influence of chemical structure on the properties in methacrylate-based dentin adhesives", Dent. Mat. 27, 1086-1093, 2011.
  69. P. Maciej, "Synthesis and characterization of acetyloxypropylene dimethacrylate as a new dental monomer", Dent. Mat. 27, 748-754, 2011.
  70. K.J. Zeitsch, "The Chemistry and technology of furfural and its many by-Products", Amsterdam: Elsevier Science, 2000.
  71. B.G. Amsden, A. Sukarto, D.K. Knight, S.N. Shapka, "Methacrylated glycol chitosan as a photopolymerizable biomaterial", Biomacromol. 8, 3758-3766, 2017.
  72. J. Baier Leach, K. A. Bivens, J.R. C.W. Patrick, C.E. Schmidt, "Photocrosslinked hyaluronic acid hydrogels: Natural, biodegradable tissue engineering scaffolds", Biotechnol. Bioeng. 82, 578-589, 2003.
  73. P. Granat "Synthesis of acrylated ethylcellulose for UV-curing ink", Carbohydr. Polym. 57, 225-228, 2004.
  74. R. N. Kumar, P. L. Po, H.D. Rozman, "Studies on the synthesis of acrylamidomethyl cellulose ester and its application in UV curable surface coatings induced by free radical photoinitiator. Part 1: Acrylamidomethyl cellulose acetate", Carbohydr. Polym. 64, 112-126, 2016.
  75. P. Wojciechowski, L. Okrasa, J. Ulański, M. Kryszewski, "Thermally stable optically anisotropic polymer networks obtained from mesogenic LC cellulose derivatives", Adv. Mater. Opt. Electron. 6, 383-386, 1996.
  76. S. Shimamoto, Y. Uraki, Y. Sano, "Optical properties and photopolymerization of liquid crystalline (acetyl) (ethyl) cellulose/acrylic acid system", Cellulose. 7, 347-58, 2000.
  77. L. Okrasa, G. Boiteux, J. Ulanski, G. Seytre, "Molecular relaxation in anisotropic composites based on (hydroxypropyl) cellulose and acrylic polymer", Polymer. 42, 3817-3825, 2001.
  78. A. D. Rouillard, Y. Tsui, W. J. Polacheck, J.Y. Lee, L.J. Bonassar, B.J. Kirby, "Control of the electromechanical properties of alginate hydrogels via ionic and covalent cross-linking and microparticle doping", Biomacromol. 11, 2184-2189, 2010.
  79. A. P. Vieira, P. Ferreira, J. F. J. Coelho, M. H. Gil. "Photocrosslinkable starch-based polymers for ophthalmologic drug delivery", Int. J. Biol. Macromol. 43, 325-32, 2008.
  80. J. M. Li, L. M. Zhang, "Characteristics of novel starch-based hydrogels prepared by UV photopolymerization of acryloylated starch and A zwitterionic monomer", Starch. Stärke. 59, 418-422, 2007.
  81. Y. Zhou, G. Ma, S. Shi, D. Yang, J. Nie, "Photopolymerized water-soluble chitosan-based hydrogel as potential use in tissue engineering", Int. J. Biol. Macromol. 48, 408-413, 2011.
  82. M. Liu, X. Yue, Z. Dai, L. Xing, F. Ma, N. Ren, "Stabilized hemocompatible coating of nitinol Devices based on photo-cross-linked alginate/heparin multilayer", Langmuir. 23, 9378-9385, 2007.
  83. K. Ono, Y. Saito, H. Yura, K. Ishikawa, A. Kurita, T. Akaike, M. Ishihara,  "Photocrosslinkable chitosan as a biological adhesive", J. Biomed. Mater. Res. 49, 289-95, 2000.
  84. M. Ishihara, K. Obara, S. Nakamura, M. Fujita, K. Masuoka, Y. Kanatani, B. Takase, H. Hattori, Y. Morimoto, M. Ishihara, T. Maehara, M. Kikuchi, "Chitosan hydrogel as a drug delivery carrier to control angiogenesis", J. Artif. Organs. 9, 8-16, 2006.
  85. T. M. Don, H. R. Chen, "Synthesis and characterization of AB-crosslinked graft copolymers based on maleilated chitosan and N-isopropylacrylamide", Carbohydr. Polym. 61, 334-347, 2005.
  86. C. Zhong, J. Wu, C.A. Reinhart-King, C.C. Chu, "Synthesis, characterization and cytotoxicity of photo-crosslinked maleic chitosan–polyethylene glycol diacrylate hybrid hydrogels", Acta. Biomater. 6, 3908-3918, 2010.
  87. K. Boady Djagnya; Zh. Wang; Sh. Xu, "Gelatin: A Valuable protein for food and pharmaceutical industries: Review", Crit. Rev. Food Sci. Nutr. 41, 481–492, 2010
  88. A. Tanbir; I. Amin; A. Siti Aqlima, Kh. Khalilah, A. Kumar, "Recent advances on the role of process variables affecting gelatin yield and characteristics with special reference to enzymatic extraction: A review", Food Hyrocolloids. 63, 85–96, 2017.
  89. K. Yue, G Trujillo-de Santiago, M. Moises Alvarez, A. Tamayol, N. Annabi, A. Khademhosseini, "Synthesis, properties, and biomedical applications of gelatin methacryloyl (GelMA) hydrogels", Biomater. 73, 254-271, 2015.
  90. V. Vijven, J. P. Luijsterburg, P. A. Verhagen, A. P. van Osch, G. J. Kloppenburg, M. Bierma-Zeinstra, "Symptomatic and chondroprotective treatment with collagen derivatives in osteoarthritis: a systematic review", Osteoarthritis and cartilage / OARS, Osteoarthritis Res. Socy. 20, 809–821, 2012.
  91. S. Kh. Lim, B. S. Schon, N. V. Mekhileri, G. C. J. Brown, C. M. Chia, S. Prabakar, G. J. Hooper, T. B. F. Woodfield, "New visible-light photoinitiating system for improved print fidelity in gelatin-based bioinks", Biomater. Sci. Eng. 2, 1752–1762, 2016.
  92. J. P. Van Vijven, P. A. Luijsterburg, A. P. Verhagen, G. J. van Osch, M. Kloppenburg, S.M. Bierma-Zeinstra, "Symptomatic and chondroprotective treatment with collagen derivatives in osteoarthritis: a systematic review", Osteoarthritis Res. Socy. 20,  809-21, 2012
  93. D. R. Burfield, K. L. Lim, K. S. Law, "Epoxidation of natural rubber latices: Methods of preparation and properties of modified rubbers", J. Appl. Polym. Sci. 29, 1661-1673, 1984.
  94. H. Le Xuan, C. Decker, "Photocrosslinking of acrylated natural rubber", J. Polym. Sci. Part A. Polym. Chem. 31, 769-780, 1993.