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Reclamation of Waste Polystyrene by Sulfonation† Yasuhito Inagaki,* Miyuki Kuromiya, Tsutomu Noguchi, and Haruo Watanabe Center for Environmental Technology, Sony Corporation Research Center, 2-1-1, Shinsakuragaoka, Hodogaya-ku, Yokohama-shi 240-0036, Japan Received September 8, 1998. In Final Form: December 31, 1998 Waste polystyrene containing additives was converted into a polymeric flocculant by a chemical modification. Specifically, waste polystyrene and waste high-impact polystyrene (HI-PS) containing rubber components or a coloring agent were sulfonated to produce a water-soluble polymer whose molecular weight ranged from 400 000 to 700 000. The polymer provides superior purification of the supernatant after flocculating a kaolin suspension than a conventional polymeric flocculant such as a partially hydrolyzed polyacrylamide (hereafter abbreviate PAA). Moreover, using the polymer and a PAA together provides a higher sedimentation rate and a purer supernatant in the treatment of actual wastewater than using each one separately. A new reclamation technology to convert waste plastic into a functional polymer is reported.
Introduction Polystyrene and high-impact polystyrene (HI-PS) are moderate in price and have excellent mechanical and insulating properties. They are utilized in resin-molded articles such as TV cabinets, video cassette shells, and polystyrene foam used for packing household electric appliances. Consumption of the polystyrene and HI-PS used in electrical products is about 20% of the total consumption of polystyrene in Japan.1 Unfortunately, most used polystyrene and HI-PS are disposed of in landfills or by incineration and are hardly ever recycled.2 This is because polystyrene and HI-PS are relatively low in price and conventional recycling methods3 turn waste polystyrene and HI-PS into less valuable material such as fuel oil or recycled resin. We have been focusing our attention on the polystyrene used in household electric appliances and working on ways to recycle waste polystyrene.4 Our object is to find a way to convert waste polystyrene into a functional polymer which is more valuable than virgin polystyrene. We report the reclamation of waste polystyrene into a water-soluble polymer, sodium poly(styrenesulfonate) (SPS). Conventional SPS, whose molecular weight is less than 100 000, has many applications, such as a dispersant for coal-water mixtures5 and cement.6 So there are many reports on low molecular weight (less than 100 000) SPS. * To whom correspondence may be addressed. E-mail:
[email protected]. † Presented at Polyelectrolytes ‘98, Inuyama, Japan, May 31June 3, 1998. (1) Plastics Age 1995, 41 (12), 113. (2) PLASPIA, “the 25th anniversary Plastic Waste Management Institute”, No. 97, Winter 1997. (3) Ehring, R. J. Plast. Recycl. 1992. (4) (a) Inagaki, Y.; Kuromiya, M.; Noguchi, T.; Watanabe, H. Proc. IEEE Int. Symp. Electron. Environ. 1997, 121. (b) Inagaki, Y.; Kuromiya, M.; Noguchi, T.; Watanabe, H. Prepr. 74th Spring Meet. Jpn. Chem. Soc. 1998, 2, 1152. (c) Kawate, Y.; Ishikawa, K.; Inagaki, Y.; Kuromiya, M. Prepr. 74th Spring Meet. Jpn. Chem. Soc. 1998, 2, 1152. (d) Inagaki, Y.; et al. Proc. Sony Res. Forum, 7th 1998, 431. (e) Inagaki, Y.; et al. Gosei Jushi 1998, 44 (1), 58. (f) Inagaki, Y.; et al. Kagaku to Kogyo, 1997, 50 (9), 1363. (g) Inagaki, Y.; et al. Kagaku Sochi 1997, 39 (7), 66. (h) Inagaki, Y.; et al. Kogyo Zairyo 1997, 45 (7), 54. (i) Inagaki, Y.; et al. Clean Technol. 1997, 7 (7), 31. (j) Inagaki, Y.; Kuromiya, M.; Noguchi, T.; Watanabe, H. Polym. Prepr. Jpn. 1997, 46 (5), 1015. (k) Inagaki, Y.; et al. Eco INDUSTRY 1998, 3 (11), 24. (5) (a) Ukigai, T.; Sugawara, H.; Tobori, N. Chem. Lett. 1995, 5, 371. (b) Furusawa, K.; Ueda, M.; et al. Colloid Polym. Sci. 1995, 273 (5), 490. (c) Ogura, T.; Tanokura, M.; Hiraki, A. Bull. Chem. Soc. Jpn. 1993, 66 (5), 1343.
However, there are few reports on high molecular weight SPS used as a polymeric flocculant.7-9 This is because of the following: (1) It is hard to convert conventional polystyrene into high molecular weight SPS,10-12 the high molecular weight SPS made from sodium styrenesulfonate (monomer) is more expensive than conventional flocculants, and it is not practical as a polymeric flocculant. (2) SPS is less advantageous than PAA in cases where flocculation is by hydrogen bonding.13,14 (3) Since SPS is a strong electrolyte, it is easy to generate repulsive forces among the particles on which it is adsorbed and to redisperse the particles. Despite these reasons, we attempted to used waste polystyrene and waste HI-PS as raw material to produce a polymeric flocculant. The focus of our research is to convert waste polystyrene and waste HI-PS into watersoluble SPS and to develop a way to utilize SPS as a polymeric flocculant. Experimental Section (a) Chemical Modification of Waste Polystyrene. Virgin polystyrene [molecular weight (MW) ) 280 000] was obtained from Aldrich, and waste polystyrene was obtained from video cassette shells, TV cabinets, and polystyrene foam used for packing. The waste from video cassette shells and TV cabinets was HI-PS, containing butadienes as a comonomer and additives such as carbon-black coloring material. The molecular weight of the polystyrene and the waste HI-PS were measured using gel permeation chromatography (GPC) in an Ultra Styragel Plus MX (N22115) column from Waters Ltd. with chloroform as the mobile phase. The molecular weight of the waste polystyrene and the waste HI-PS ranged from 195 000 to 217 000. The butadiene content in HI-PS was calculated using Fourier transformation nuclear magnetic resonance spectroscopy (FTNMR). The butadiene contents ranged from 1.3 to 4.9 mol %. The carbon-black content in HI-PS was calculated by measuring the residue after burning the HI-PS. (6) El-Hosiny, F. I.; Gad, E. A. M. J. Appl. Polym. Sci. 1995, 56 (2), 153. (7) Walles, W. E. J. Colloid Interface Sci. 1968, 27 (4), 797. (8) Nashima, T.; Sudo, H.; Furusawa, K. Colloids Surf. 1992, 67, 95. (9) Sussman, D. L.; Jenq, T. Prepr. Pap. Natl. Meet., Div. Environ. Chem., Am. Chem. Soc. 1975, 15 (1), 245. (10) Tubak, A. F. Ind. Eng. Chem. Prod. Res. Dev. 1962, 1 (4), 275. (11) Goldstein, S.; Schmuckler, G. Ion Exch. Membr. 1972, 1, 63. (12) Akovali, G.; Ozkan, A. Polymer 1986, 27, 1277. (13) Michaels, A. S. Ind. Eng. Chem. 1954, 46, 1485. (14) Michaels, A. S.; Morelos, O. Ind. Eng. Chem. 1955, 47, 1801.
10.1021/la981185e CCC: $18.00 © 1999 American Chemical Society Published on Web 03/19/1999
4172 Langmuir, Vol. 15, No. 12, 1999
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Table 1. Sulfonation of Waste Polystyrene and the Resulting SPS starting materials resin
MWa
virgin PS PS foam PS foam video cassettef video cassettef TV cabinetf
288 000 215 000 215 000 217 000 217 000 195 000
sulfonation
butadieneb
(mol%)
none none none 1.2 1.2 4.9
sulfonated compounds
solventc
time (h)
temp (°C)
% sulfonationd
MWe
EDC EDC CH EDC CH EDC
2 2 2 2 2 2
25 25 50 25 50 25
87 107 75 89 72 89
553 000 442 000 582 000 552 000 679 000 606 000
a Determined by gel permeation chromatography(GPC) in CHCl . b Determined by nuclear magnetic resonance (NMR) in CDCl . c EDC: 3 3 1,2-dichloroethane/CH: cyclohexane. d Determined by titration of NaOH aqueous solution. e Determined by GPC in H2O/CH3CN ) 80/20. f Containing carbon black of 1 wt % in it.
Table 2. Water Quality after Treating with Sulfonated Waste Polystyrene and PAA item
unit
this work
regulation
hydrogen ion concentration biochemical oxygen demand (BOD) suspended solid (SS) extractive substance in n-hexane total chromium cadmium nickel soluble iron tetrachloroethyrene 1,2-dichloroethane
pH ppm ppm ppm ppm ppm ppm ppm ppm ppm
6.4-6.7 3-5 14-17
