Porous carbons from plastic waste

Advances in Polymer Science

Volumn 266, Issue , 2013, Pages 01-26

  Bazargan, Alireza ^a   Hui, Chi Wai ^a   McKay, Gordon ^a  

^a HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY   (Hong Kong)

Author keywords

Activation methods; Plastic wastes; Polymer pyrolysis; Porous carbon

Indexed keywords

EID: 84949117732     PISSN: 00653195     EISSN: None     Source Type: Book Series    
DOI: 10.1007/12_2013_253     Document Type: Article

References (116)

1. ACCR (2004) Good practices guide on waste plastics recycling: a guide by and for local and regional authorities. Association of Cities and Regions for Recycling, Brussels.
2. PlasticsEurope (2012) Plastics-the facts 2012. PlasticsEurope, Association of Plastics Manufacturers, Brussels.
3. Williams PT (2006) Yield and composition of gases and oils/waxes from the feedstock recycling of waste plastic. In: Scheirs J, KaminskyW(eds) Feedstock recycling and pyrolysis of waste plastics: converting waste plastics into diesel and other fuels. Wiley, Chichester, pp 285-314.
4. Zia KM, Bhatti HN, Bhatti IA (2007) Methods for polyurethane and polyurethane composites, recycling and recovery: a review. React Funct Polym 67(8): 675-692.
5. Howard GT (2002) Biodegradation of polyurethane: a review. Int Biodeterior Biodegradation 49(4): 245-252.
6. Al-Salem SM, Lettieri P, Baeyens J (2009) Recycling and recovery routes of plastic solid waste (PSW): a review. Waste Manage 29(10): 2625-2643.
7. Nnamchi CI, Obeta JAN, Ezeogu LI (2006) Isolation and characterization of some polycyclic aromatic hydrocarbon degrading bacteria from Nsukka soils in Nigeria. Int J Environ Sci Technol 3(2): 181-190.
8. Kumar S, Panda AK, Singh RK (2011) A review on tertiary recycling of high-density polyethylene to fuel. Resour Conserv Recycl 55(11): 893-910.
9. Buekens AG, Schoeters JG (1998) Technical methods in plastics pyrolysis. Macromol Symp 135(1): 63-81.
10. Blaszo M (2005) Pyrolysis oils of plastic wastes. In: Müller-Hagedorn M, Bockhorn H (eds) Feedstock recycling of plastics. Selected papers presented at the third international symposium on feedstock recycling of plastics, Karlsruhe, Sept, 2005. Universitätsverlag Karlsruhe, Karlsruhe, pp 11-17.
11. Grause G, Buekens A, Sakata Y, Okuwaki A, Yoshioka T (2011) Feedstock recycling of waste polymeric material. J Mater Cycles Waste Manag 13(4): 265-282.
12. Ranzi EM, Dente M, Faravelli T, Bozzano G, Fabini S, Nava R, Cozzani V, Tognotti L (1997) Kinetic modeling of polyethylene and polypropylene thermal degradation. J Anal Appl Pyrolysis 40-41: 305-319.
13. Buekens A (2006) Introduction to feedstock recycling of plastics. In: Feedstock recycling and pyrolysis of waste plastics: converting waste plastics into diesel and other fuels. Wiley, Chichester, pp 3-41.
14. Ding W, Liang J, Anderson LL (1997) Hydrocracking of waste plastics to clean liquid fuels. ACS Division Fuel Chem Preprints 42(4): 1008-1010.
15. Cho M-H, Jung S-H, Kim J-S (2010) Pyrolysis of mixed plastic wastes for the recovery of benzene, toluene, and xylene (BTX) aromatics in a fluidized bed and chlorine removal by applying various additives. Energy Fuels 24(2): 1389-1395.
16. Bazargan A, McKay G (2012) A review-synthesis of carbon nanotubes from waste plastics. Chem Eng J 195-196: 377-391.
17. Mays TJ (2007) A new classification of pore sizes. In: Llewellyn P, RodríguezReinoso F, Rouqerol J, Seaton N (eds) Studies in surface science and catalysis, vol 160. Elsevier, Amsterdam, pp 57-62.
18. Rafsanjani HH, Jamshidi E (2008) Kinetic study and mathematical modeling of coal char activation. Chem Eng J 140(1-3): 1-5.
19. Keypour J, Haghighi Asl A, Rashidi A (2012) Synthesis of hybrid nano-adsorbent for separation of hydrogen from methane. Chem Eng J 183: 510-514.
20. Valix M, Cheung WH, Zhang K (2008) Role of chemical pre-treatment in the development of super-high surface areas and heteroatom fixation in activated carbons prepared from bagasse. Micropor Mesopor Mater 116(1-3): 513-523.
21. Cerino-Córdova FJ, Díaz-Flores PE, García-Reyes RB, Soto-Regalado E, Gómez-González R, Garza-González MT, Bustamante-Alcańtara E (2013) Biosorption of Cu(II) and Pb(II) from aqueous solutions by chemically modified spent coffee grains. Int J Envir Sci Technol 10(3): 611-622.
22. Saka C, Şahin O, Küçük MM(2012) Applications on agricultural and forest waste adsorbents for the removal of lead (II) from contaminated waters. Int J Environ Sci Technol 9(2): 379-394.
23. Zhu Y, Zhang H, Zeng H, Liang M, Lu R (2012) Adsorption of chromium (VI) from aqueous solution by the iron (III)-impregnated sorbent prepared from sugarcane bagasse. Int J Environ Sci Technol 9(3): 463-472.
24. Fallah RN, Azizian S (2012) Rapid and facile desulphurization of liquid fuel by carbon nanoparticles dispersed in aqueous phase. Fuel 95(1): 93-96.
25. Mui E, Ko D, McKay G (2004) Production of active carbons from waste tyres-a review. Carbon 42(14): 2789-2805.
26. Stavropoulos GV (2005) Precursor materials suitability for super activated carbons production. Fuel Process Technol 85: 1165-1173.
27. Alcañiz-Monge J, Illań-Gómez MJ (2008) Modification of activated carbon porosity by pyrolysis under pressure of organic compounds. Adsorption 14(1): 93-100.
28. Mahvi AH (2008) Application of agricultural fibers in pollution removal from aqueous solution. Int J Environ Sci Technol 5(2): 275-285.
29. Hussein M, Amer AA, Sawsan II (2008) Oil spill sorption using carbonized pith bagasse: trial for practical application. Int J Environ Sci Technol 5(2): 233-242.
30. Stavropoulos GG, Zabaniotou AA (2009) Minimizing activated carbons production cost. Fuel Process Technol 90(7-8): 952-957.
31. Qiao W, Yoon SH, Korai Y, Mochida I, Inoue SI, Sakurai T, Shimohara T (2004) Preparation of activated carbon fibers from polyvinyl chloride. Carbon 42(7): 1327-1331.
32. Almazań-Almazań MC, Pérez-Mendoza MJ, López-Domingo FJ, Fernańdez-Morales I, Domingo-García M, López-Garzoń FJ (2007) A new method to obtain microporous carbons from PET: characterisation by adsorption and molecular simulation. Micropor Mesopor Mater 106(1-3): 219-228.
33. Lian F, Xing B, Zhu L (2011) Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers. J Colloid Interface Sci 360(2): 725-730.
34. Lian F, Chang C, Du Y, Zhu L, Xing B, Liu C (2012) Adsorptive removal of hydrophobic organic compounds by carbonaceous adsorbents: a comparative study of waste-polymerbased, coal-based activated carbon, and carbon nanotubes. J Environ Sci 24(9): 1549-1558.
35. Abbasi M, Salarirad MM, Ghasemi I (2010) Selective separation of PVC from PET/PVC mixture using floatation by tannic acid depressant. Iran Polym J (Engl Ed) 19(7): 483-489.
36. Liu H (2000) Carbon materials based on poly(phenylene oxide): preparation, characterization and application in electrochemical devices. State University of New York, New York.
37. Kakuta N, Shimizu A, Ohkita H, Mizushima T (2009) Dehydrochlorination behavior of polyvinyl chloride and utilization of carbon residue: effect of plasticizer and inorganic filler. J Mater Cycles Waste Manag 11: 23-26.
38. Hayashi J, Yamamoto N, Horikawa T, Muroyama K, Gomes VG (2005) Preparation and characterization of high-specific-surface-area activated carbons from K2CO3-treated waste polyurethane. J Colloid Interface Sci 281(2): 437-443.
39. Lu C, Xu S, Liu C (2010) The role of K2CO3 during the chemical activation of petroleum coke with KOH. J Anal Appl Pyrolysis 87(2): 282-287.
40. Kadirova Z, Kameshima Y, Nakajima A, Okada K (2006) Preparation and sorption properties of porous materials from refuse paper and plastic fuel (RPF). J Hazard Mater 137(1): 352-358.
41. Wang H, Liu Y, Li Z, Zhang X, Zhang S, Zhang Y (2009) Glycolysis of poly(ethylene terephthalate) catalyzed by ionic liquids. Eur Polymer J 45(5): 1535-1544.
42. Marzec M, Tryba B, Kalenćzuk RJ, Morawski AW (1999) Poly(ethylene terephthalate) as a source for activated carbon. Polym Adv Technol 10(10): 588-595.
43. Mourao PAM, Cansado IPP, Carrott PJM, Carrott MMLR (2010) Designing activated carbons from natural and synthetic raw materials for pollutants adsorption. Mater Sci Forum 636-637: 1404-1409. doi: 10. 4028/www. scientific. net/MSF. 636-637. 1404.
44. Cansado IPP, Galacho C, Nunes AS, Carrott MLR, Carrott PJM (2010) Adsorption properties of activated carbons prepared from recycled PET in the removal of organic pollutants from aqueous solutions. Adsorpt Sci Technol 28(8-9): 807-821.
45. Swiatkowski A, Padee A (2007) Possibility of preparation of activated carbons from poly (ethylene terephtalate) waste. Ecol Chem Eng-Chemia I Inzynieria Ekologiczna 14(S2): 199-206.
46. Ciesinska W, Makomaski G, Zielinski J, Brzozowska T (2011) Preparation of sorbents from selected polymers. Polish J Chem Technol 13(1): 51-54.
47. Bratek W, Świątkowski A, Pakuła M, Biniak S, Bystrzejewski M, Szmigielski R (2013) Characteristics of activated carbon prepared from waste PET by carbon dioxide activation. J Anal Appl Pyrolysis 100: 192-198.
48. Lorenc-Grabowska E, Gryglewicz G, Machnikowski J, Díez MA, Barriocanal C (2009) Activated carbons from coal/pitch and polyethylene terephthalate blends for the removal of phenols from aqueous solutions. Energy Fuels 23(5): 2675-2683.
49. Barriocanal C, Díez MA, Álvarez R (2005) PET recycling for the modification of precursors in carbon materials manufacture. J Anal Appl Pyrolysis 73(1):45-51.
50. Hirogaki K, Tabata I, Hisada K, Hori T (2010) Preparation of a porous polyester fiber by foaming with supercritical carbon dioxide. Sen-I Gakkaishi 66(7):163-167.
51. Zhang FS, Itoh H (2003) Adsorbents made from waste ashes and post-consumer PET and their potential utilization in wastewater treatment. J Hazard Mater 101(3):323-337.
52. Bach C, Dauchy X, Severin I, Munoz J-F, Etienne S, Chagnon M-C (2013) Effect of temperature on the release of intentionally and non-intentionally added substances from polyethylene terephthalate (PET) bottles into water: chemical analysis and potential toxicity. Food Chem 139(1-4):672-680.
53. Cheng X, Shi H, Adams CD, Ma Y (2010) Assessment of metal contaminations leaching out from recycling plastic bottles upon treatments. Environ Sci Pollut Res 17(7):1323-1330.
54. Bhaskar T, Mitan NM, Onwudili J, Muto A, Williams P, Sakata Y (2010) Effect of polyethylene terephthalate (PET) on the pyrolysis of brominated flame retardant-containing high-impact polystyrene (HIPS-Br). J Mater Cycles Waste Manage 10(4):332-340.
55. Bóta A, Laśzló K, Nagy LGCT (1997) Comparative study of active carbons from different precursors. Langmuir 13(24):6502-6509.
56. Laśzló K, Bóta A, Nagy LG (2000) Comparative adsorption study on carbons from polymer precursors. Carbon 38(14):1965-1976.
57. Laśzló K, Tombaćz E, Josepovits K (2001) Effect of activation on the surface chemistry of carbons from polymer precursors. Carbon 39(8):1217-1228.
58. Laśzló K, Szűcs A (2001) Surface characterization of polyethyleneterephthalate (PET) based activated carbon and the effect of pH on its adsorption capacity from aqueous phenol and 2, 3, 4-trichlorophenol solutions. Carbon 39(13):1945-1953.
59. Podkościelny P, Laśzló K (2007) Heterogeneity of activated carbons in adsorption of aniline from aqueous solutions. Appl Surf Sci 253(21):8762-8771.
60. Laśzló K, Bota A, Dekany I (2003) Effect of heat treatment on synthetic carbon precursors. Carbon 41(6):1205-1214.
61. Laśzló K (2005) Adsorption from aqueous phenol and aniline solutions on activated carbons with different surface chemistry. Colloids Surfaces A Physicochem Eng Aspects 265:32-39.
62. Laśzló K, Marthi K, Rochas C, Ehrburger-Dolle F, Livet F, Geissler E (2004) Morphological investigation of chemically treated poly(ethylene terephthalate)-based activated carbons. Langmuir 20(4):1321-1328.
63. Tóth A, Novák C, Laśzló K (2009) The effect of ionic environment on the TG response of phenol loaded PET-based porous carbons. J Therm Anal Calorim 97:273-280.
64. Sych NV, Kartel NT, Tsyba NN, Strelko VV (2006) Effect of combined activation on the preparation of high porous active carbons from granulated post-consumer polyethyleneterephthalate. Appl Surf Sci 252(23):8062-8066.
65. Kartel N, Gerasimenko N, Tsyba N, Nikolaychuk A, Kovtun G (2001) Obtaining and investigation of carbon adsorbent from polyethyleneterephthalate. Russ J Appl Chem 74(10): 1711-1713.
66. Kartel MT, Sych NV, Tsyba MM, Strelko VV (2006) Preparation of porous carbons by chemical activation of polyethyleneterephthalate. Carbon 44(5):1019-1022.
67. Tamon H, Nakagawa K, Suzuki T, Nagano S (1999) Improvement of mesoporosity of activated carbons from PET by novel pre-treatment for steam activation. Carbon 37(10): 1643-1645.
68. Nakagawa K, Mukai SR, Suzuki T, Tamon H (2003) Gas adsorption on activated carbons from PET mixtures with a metal salt. Carbon 41(4):823-831.
69. Nakagawa K, Namba A, Mukai SR, Tamon H, Ariyadejwanich P, Tanthapanichakoon W (2004) Adsorption of phenol and reactive dye from aqueous solution on activated carbons derived from solid wastes. Water Res 38(7):1791-1798.
70. Almazań-Almazań MC, Pérez-Mendoza M, Domingo-García M, Fernańdez-Moralesa I, López FJ, López-Garzoń FJ (2010) The influence of the process conditions on the characteristics of activated carbons obtained from PET de-polymerisation. Fuel Process Technol 91(2):236-242.
71. Almazań-Almazań MC, Paredes JI, Pérez-Mendoza M, Domingo-García M, Fernańdez-Morales I, Martínez-Alonso A, López-Garzoń FJ (2006) Surface characteristics of activated carbons obtained by pyrolysis of plasma pretreated PET. J Phys Chem B 110(23): 11327-11333.
72. Domingo-García M, Fernańdez JA, Almazań-Almazań MC, López-Garzoń FJ, Stoeckli F, Centeno TA (2010) Poly(ethylene terephthalate)-based carbons as electrode material in supercapacitors. J Power Sources 195(12):3810-3813.
73. Parra JB, Ania CO, Arenillas A, Pís JJ (2002) Textural characterisation of activated carbons obtained from poly(ethylene terephthalate) by carbon dioxide activation. Stud Surf Sci Catal 144:537-543.
74. Parra JB, Ania CO, Arenillas A, Rubiera F, Pís JJ, Palacios JM (2006) Structural changes in polyethylene terephthalate (PET) waste materials caused by pyrolysis and CO2 activation. Adsorpt Sci Technol 24(5):439-449.
75. Arenillas A, Rubiera F, Parra JB, Ania CO, Pís JJ (2005) Surface modification of low cost carbons for their application in the environmental protection. Appl Surf Sci 252(3):619-624.
76. Cansado IPP, Mourão PAM, Falcão AI, Ribeiro Carrott MML, Carrott PJM (2012) The influence of the activated carbon post-treatment on the phenolic compounds removal. Fuel Process Technol 103:64-70.
77. Fernańdez-Morales I, Almazań-Almazań MC, Pérez-Mendoza MJ, Domingo-García M, López-Garzoń FJ (2005) PET as precursor of microporous carbons: preparation and characterization. Micropor Mesopor Mater 80(1-3):107-115.
78. Marco-Lozar J, Kunowsky M, Suárez-García F, Carruthers J, Linares-Solano A (2012) Activated carbon monoliths for gas storage at room temperature. Energy Environ Sci 5: 9833-9842.
79. Parra JB, Ania CO, Arenillas A, Rubiera F, Pís JJ (2004) High value carbon materials from PET recycling. Appl Surf Sci 238(1-4):304-308.
80. Parra JB, Ania CO, Arenillas A, Rubiera F, Palacios JM, Pís JJ (2004) Textural development and hydrogen adsorption of carbon materials from PET waste. J Alloys Compd 379:280-289.
81. Mestre AS, Pires J, Nogueira JMF, Parra JB, Carvalho AP, Ani CO (2009) Waste-derived activated carbons for removal of ibuprofen from solution: role of surface chemistry and pore structure. Bioresour Technol 100(5):1720-1726.
82. Montes-Moran MA, Menendez JA, Fuente E, Suarez D (1998) Contribution of the basal planes to carbon basicity: an ab-initio study of the H3O+ pi interaction in cluster models. J Phys Chem B 102:5595-5601.
83. Esfandiari A, Kaghazchi T, Soleimani M (2011) Preparation of high surface area activated carbon from polyethyleneterephthalate (PET) waste by physical activation. Res J Chem Environ 15(2):433-437.
84. Esfandiari A, Kaghazchi T, Soleimani M (2012) Preparation and evaluation of activated carbons obtained by physical activation of polyethyleneterephthalate (PET) wastes. J Taiwan Inst Chem Eng 43:631-637.
85. Lee J, Kim J, Hyeon T (2006) Recent progress in the synthesis of porous carbon materials. Adv Mater 18(16):2073-2094.
86. Li Z, Song D, Zhi J, Hu A (2011) Synthesis of ultrathin ordered porous carbon through Bergman cyclization of enediyne self-assembled monolayers on silica nanoparticles. J Phys Chem C 115(32):15829-15833.
87. Morishita T, Tsumura T, Toyoda M, Przepiorski J, Morawski AW, Konno H, Inagaki M (2010) A review of the control of pore structure in MgO-templated nanoporous carbons. Carbon 48(10):2690-2707.
88. Morishita T, Soneda Y, Tsumura T, Inagaki M (2006) Preparation of porous carbons from thermoplastic precursors and their performance for electric double layer capacitors. Carbon 44(12):2360-2367.
89. Morishita T, Wang L, Tsumura T, Toyoda M, Konno H, Inagaki M (2010) Pore structure and application of MgO-templated carbons. TANSO 2010(242):60-68.
90. Seredych M, Bandosz TJ (2007) Surface properties of porous carbons obtained from polystyrene-based polymers within inorganic templates: role of polymer chemistry and inorganic template pore structure. Micropor Mesopor Mater 100(1-3):45-54.
91. Walendziewski J (2006) Thermal and catalytic conversion of polyolefins. In: Scheirs J, Kaminsky W (eds) Feedstock recycling and pyrolysis of waste plastics: converting waste plastics into diesel and other fuels. Wiley, Chichester, pp 111-127.
92. Pol VG, Pol SV, Calderon-Moreno J, Gedanken A (2006) High yield one-step synthesis of carbon spheres produced by dissociating individual hydrocarbons at their autogenic pressure at low temperatures. Carbon 44(15):3285-3292.
93. Pol VG, Pol SV, Gedanken A, Sung M-G, Asai S (2004) Magnetic field guided formation of long carbon filaments (sausages). Carbon 42(12-13):2738-2741.
94. Pol VG, Pol SV, Calderon-Moreno JM, Sung M-G, Asai S, Gedanken A (2006) The dependence of the oriented growth of carbon filaments on the intensity of a magnetic field. Carbon 44(10):1913-1918.
95. Pol VG, Pol SV, Thackeray MM (2011) Autogenic pressure reactions for battery materials manufacture. US Patent 2011/0, 104, 553 A1.
96. Pol VG (2010) Upcycling: converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres. Environ Sci Technol 44(12):4753-4759.
97. Inagaki M, Park KC, Endo M (2010) Carbonization under pressure. New Carbon Mater 25(6):409-420.
98. Inagaki M, Kuroda K, Sakai M (1981) Formation of carbon spherules from polyethylene under pressure. High Temp High Press 13:207-213.
99. Inagaki M, Kuroda K, Sakai M (1983) Pressure carbonization of polyethylenepolyvinylchloride mixtures. Carbon 21(3):231-235.
100. Inagaki M, Urata M, Sakai M (1989) Morphology change in carbons prepared from pitchpolyvinylchoride mixtures under pressure. J Mater Sci 24:2781-2786.
101. Inagaki M, Washiyama M, Sakai M (1988) Production of carbon spherules and their graphitization. Carbon 26(2):169-172.
102. Ayache J, Oberlin A (1990) Mechanism of carbonization under pressure, part II: influence of impurities. Carbon 28(2-3):353-362.
103. Murata K, Sato K, Sakata Y (2004) Effect of pressure on thermal degradation of polyethylene. J Anal Appl Pyrolysis 71(2):569-589.
104. Onwudili JA, Insura N, Williams PT (2009) Composition of products from the pyrolysis of polyethylene and polystyrene in a closed batch reactor: Effects of temperature and residence time. J Anal Appl Pyrolysis 86(2):293-303.
105. Wei L, Yan N, Chen Q (2011) Converting poly(ethylene terephthalate) waste into carbon microspheres in a supercritical CO2 System. Environ Sci Technol 45(2):534-539.
106. Jia Z, Peng K, Li Y, Zhu R (2011) Preparation and application of novel magnetically separable γ-Fe2O3/activated carbon sphere adsorbent. Mater Sci Eng B 176(11):861-865.
107. Nieto-Márquez A, Romero R, Romero A, Valverde JL (2011) Carbon nanospheres: synthesis, physicochemical properties and applications. J Mater Chem 21:1664-1672.
108. Yuan D, Chen JX, Zeng J, Tan S (2008) Preparation of monodisperse carbon nanospheres for electrochemical capacitors. Electrochem Commun 10(7):1067-1070.
109. Li M, Li W, Liu S (2011) Hydrothermal synthesis, characterization, and KOH activation of carbon spheres from glucose. Carbohydr Res 346(8):999-1004.
110. Song X, Gunawan P, Jiang R, Leong SSJ, Wang K, Xu R (2011) Surface activated carbon nanospheres for fast adsorption of silver ions from aqueous solutions. J Hazard Mater 194: 162-168.
111. Funke A, Ziegler F (2010) Hydrothermal carbonization of biomass: a summary and discussion of chemical mecha nisms for process engineering. Biofuels Bioporducs Biorefining 4:160-177.
112. Hu B, Wang K, Wu L, Yu S-H, Antonietti M, Titirici M-M (2010) Engineering carbon materials from the hydrothermal carbonization process of biomass. Adv Mater 22:813-828.
113. Pol VG, Thackeray MM (2011) Spherical carbon particles and carbon nanotubes prepared by autogenic reactions: Evaluation as anodes in lithium electrochemical cells. Energy Environ Sci 4:1904-1912.
114. Zhang JH, Li J, Cao J, Qian YT (2008) Synthesis and characterization of larger diameter carbon nanotubes from catalytic pyrolysis of polypropylene. Mater Lett 62(12-13): 1839-1842.
115. Li H, Sang J, Zhao J, Fu A, Liu H, Xu M, Pang G, Zhao XS (2012) Preparation of magnetically separable mesoporous Co@carbon/silica composites by the RAPET method. New J Chem 36:2308-2315.
116. Zhao JH, Li HL, Lin Q, Li KX, Peng Z, Zhao XS (2010) Mesoporous carbon preparation by in-situ carbonization via a reaction under autogenic pressure at elevated temperature. Gaodeng Xuexiao Huaxue Xuebao/Chem J Chin Univ 31(6):1088-1092.