The Graft Copolymerisation of Acrylamide onto Cellulose using Enhanced Fe 2+ / H 2 O 2 redox initiator system

Transcription

1 JASEM ISSN All rights reserved Full-text Available Online at J. Appl. Si. Environ. Mgt. September, 6 Vol. (3) 11-1 The Graft Copolymerisation of Arylamide onto Cellulose using Enhaned Fe 2+ / H 2 O 2 redox initiator system 1 JIDEONO, A; * 2 ADIMULA, H A 1 Department of Chemistry, University of Benin, Benin City, Nigeria 2 Department of Industrial Safety and Environmental Siene, Petroleum Training Institute, Effurun, Delta State. ABSTRACT: Graft opolymers of arylamide onto holoellulose derived from ooa (Theobroma aao) wood meal have been produed using hydroquinone enhaned Fe 2+ /H 2 O 2 redox system. The addition of hydroquinone to the redox system affeted the effetiveness of the redox system to initiate graft opolymer formation. The effets of time, monomer onentration, initiator onentration, and temperature were studied to determine the optimum ondition for graft opolymer Cellulose is frequently modified in the preparation of a wide range of new materials that have proved to be very useful in several and diverse fields of appliation (Onishi et al, 4; Heinrih and Mishnik, 1999; Kato et al, 1999). The presene of three reative hydroxyl groups on eah gluan unit of ellulose makes it relatively easy to modify. One method of modifying ellulose that has been studied extensively is graft opolymerization (Ouajai, et al., 4). Cellulose graft opolymers are very attrative beause their produts an readily be made to posses any number of the required properties (Hodano et al, 3; Okieimen, 3). Great numbers of grafting methods have been developed, but the free radial methods of generating radials on the ellulose bakbone before grafting have reeived the greatest attention (Fernandez et al., 199). The use of eri ions to generate free radials whih initiate grafting reations has been one of the most reported (Gupta and Khandekar, 2). The limitations of this graft opolymerization of arylamide on ellulose using hydroquinone enhaned Fe 2+ /H 2 O 2, initiating system. MATERIALS AND METHODS Ferrous ammonium sulphate, % H 2 O 2 and hydroquinone were reagent grade BDH, England, hemials. Arylamide was obtained from Burgoyne Urbidges, India and was used without extration of the polymerization inhibitor. The water used in the reations was re-distilled. Preparation of Holoellulose: In a typial experiment ooa wood waste was obtained from farms in Idanre, Ondo State, Nigeria. The dried wood hunks were ground and sieved and material retained on a 6-mesh sreen olleted. The material was de-waxed by Soxhlet extration for 24 hrs using a 1:1 v/v mixture of benzene and ethanol. The extrative free wood was washed thoroughly with distilled water and air dried. g portion of the extrative free wood was initiating system, the relatively large amount of homopolymers formed, have been reported (Okieimen and Idehen, 1989). Redox initiating systems whih redue the formation of homopolymers have also been developed. Fe 2+ /H 2 O 2 is one of the best and most effetive redox systems (Mateva and Nikolov, 1991). Reports exist whih show that the effiieny of grafting parameters ould be inreased by the addition of a suitable reduing agent suh as hydroquinone into redox initiating systems. Mateva and Nikolov reported in their work the use of hydrazine hydrate to inrease the effiieny of the redox system. Although several workers have reported on the graft opolymerization of vinyl monomers on ellulosi material, no information has been found however on the graft opolymerisation to ellulose obtained from ooa wood waste. Beause of the large availability of this material as agriultural wastes, researh was initiated on the possible prodution of simple value added produts from it. This work reports on the heated with 16ml H 2 O ontaining.ml aeti aid and 1.g NaClO 2 for 4 hours at 7-8 C..ml aeti aid and 1.g NaClO 2 were added eah hour until a total of 2ml aeti aid and 6.g NaClO 2 have been added. The holoellulose obtained was filtered, washed thoroughly and dried. Graft Copolymerization: Graft opolymerization of arylamide onto the holoellulose was ahieved by an adaptation of the methods desribed by Mateva and Nikolov (1991), and, Vazquez et al., (1989), for the radial graft opolymerization of vinyl monomers onto polysaharide using the Fe 2+ /H 2 O 2 redox system. In a typial reation, 1 gram of the holoellulose was dispersed in a ml 1% w/v aqueous ferrous ammonium sulphate solution for 1 hour at o C. The exess Fe 2+ salt was drained off by filtration and the holoellulose rinsed with distilled water. The holoellulose on to whih Fe 2+ was adsorbed was *Correspondene:

2 12 dispersed in ml of arylamide solution of predetermined onentration for another one hour at the reation temperature to allow for adequate interation of the holoellulose fiber with the monomer..g of hydroquinone and the required amount of H 2 O 2 were then added. The grafting reation was allowed to proeed with stirring for the pre-determined duration. The graft opolymer obtained was washed several times with distilled water. Extration of the homopolymer was done in a Soxhlet extrator with ethanol until onstant weight was obtained. The graft opolymer was washed with distilled water again and dried first in air and later at C in an oven to a onstant weight. Determination of grafting parameters: The grafting parameters were determined by weighing. The effet of hanges in the reation ondition: initiating system, time, monomer onentration, H 2 O 2 onentration, and temperature on the grafting parameters: grafting effiieny, grafting yield, total monomer onversion into polymers and graft onversion were alulated. Grafting parameters: Apparent grafting yield, G is the weight ratio of grafted polymer to original ellulose: g = x Grafting effiieny, GE, is the fration of the total syntheti polymer that is grafted to ellulose: E = g p - x Total onversion of monomer to polymer, C t, is the monomer fration that polymerizes: p C t = x m Graft onversion, Cg, is the monomer fration that affords grafted polymer: g = weight of graft opolymer sample after extrating the arylamide homopolymer; = weight original ellulose; m = weight of arylamide monomer; p = weight of rude opolymer produt before extrating the homopolymer g g = m RESULTS AND DISCUSSION The effet of the addition of the reduing agent, hydroquinone, into the initiator system on grafting parameters is presented below: Table 1: The effet of hydroquinone on the effiieny of H 2 O 2 /Fe 2+ redox system. [H 2 O 2 ]M = x 2 ; polymerization temperature 6 o C; reation time 2hr. Initiator E t g system Fe 2+ /H 2 O Fe2+ / H 2 O 2, hydroquinone Results show that the addition of hydroquinone to the Fe 2+ /H 2 O 2 redox system inreased all the grafting parameters studied:, E, t and the g. The results agree with reports by other workers whih showed similar inreases in graft yields on the addition of a reduing agent to the redox system (Mateva and Nikolov, 1991). It is onsidered that the addition of hydroquinone ats in two ways: (I) the redution of the inative Fe 3+ to the ative Fe 2+ state as follows: + Fe 3+ + Fe 2+ + H + It is thought that some of the Fe 2+ adsorbed onto the ellulose would have been oxidized to Fe 3+ by the atmospheri oxygen. This to be expeted sine the reation was not arried out in an oxygen-free environment. The addition of a reduing agent, hydroquinone, thus regenerates the Fe 2+ / H 2 O 2 system ausing the initiation and grafting to ontinue or (ii) the hydroquinone may also deompose the H 2 O 2 thus: HO Hydroquinone O. O. + H 2 O 2 + H + HO.

3 13 The radials generated ould be thought to be apable of initiating graft opolymerisation by the prodution of radials on the ellulose as well as on the monomer. In both ases the graft yield would improve essentially beause the hydroquinone has been added into the initiator system. G raftin g Yield Time (min) Fig. 1: Effet of Reation Time on and E E Conentration of arylamide used.2m; polymerization temperature 6 C The effet of reation time on perent graft yield and perent graft effiieny is presented in Fig. 1. An inrease in graft yield is observed initially as the reation time inreases from to 6 minutes and less rapidly to 1 minutes when a leveling off is observed. The optimum reation time for grafting is thus 1 minutes and a longer reation time will not produe higher graft yield. The amount of polymerization inreases with time and this aount for the initial rise in graft yields. But the rate would be expeted to slow as the arylamide is used up and the initial radials generated on the holoellulose bakbone are depleted by grafting. The grafting effiieny was atually observed to fall after 1 minutes indiating that more homopolymers are formed in preferene to opolymers after 1 minutes. Stopping the reation at 1 minutes will thus prevent signifiant quantity of homopolymer formation. Grafting Yield Monomer Conentration (M) Fig. 2: Effet of Monomer Conentration on and E E Polymerization temperature 6 o C; reation time 2hours Fig. 2 shows the effet of monomer onentration on the graft yield and graft effiieny. The graft yield inreased as the monomer onentration is inreased up to a maximum monomer onentration of.m. At a higher monomer onentration,.6m, the graft yield was observed to fall. The initial rise in graft yield with monomer onentration is expeted as there is a higher amount of the arylamide available for opolymerization. But above.m the exess monomer onentration did not result in graft opolymerization produt. This is onsidered to be due to the fat that under a given initiator onentration the available number of ative sites for grafting is onstant and the arylamide moleules ompete for the limited sites for grafting, thus at high monomer onentration there is an exess of the monomer moleules relative to the available sites for graft formation hene more of the monomer moleules partiipate in homopolymerisation. Fig. 2 also shows that the graft effiieny (GE) dereased with inreasing monomer onentration. This may be due to an inreasing formation of the homopolymer as the onentration of the monomer is inreased. Even though the reation onditions were hosen to maximize the formation of the opolymer, the formation of homopolymers may not have been prevented. raft Conversion (Cg) Monomer Conentration (M) Fig. 3: Effet of Monomer Conentration on g The dependeny of graft onversion (Cg) on onentration is presented in Fig. 3 as plot of raft onversion against monomer onentration. The result shows that the fration of the monomer that resulted in graft opolymerisation is highest at low onentrations. At this relatively low onentration the few monomer moleules available are readily onverted to opolymers. As the arylamide onentration inreased, however, more of arylamide forms homopolymers resulting in less onversion to the graft opolymer. This onfirms the

4 14 earlier observation that higher onentration of the monomer results in more moleules of the monomer being available to form the homopolymers. raft Conversion (Cg) Time (min) Fig. 4: Effet of Reation Time on t and g The dependeny of Cg and Ct on time is shown in Fig. 4. Results showed that the amount of monomer that polymerized (Ct) inreased with time. Result showed an initial rapid inrease up to 6 minutes and then less rapidly thereafter for the duration of the experiment, 18 minutes. This is expeted sine polymerization theoretially should ontinue until all the monomer moleules have been onverted given the presene of initiators, although the rate of polymerization would be expeted to slow as the initial onentration of initiators are used up. Fig. 4 also showed that the fration of monomers onverted to graft opolymers (Cg) inreased rapidly up to 6 minutes and then less rapidly up to 1 minutes when it leveled off. ith more grafts formed there is inreasingly less amount of ative sites for grafting on the ellulose bakbone and it would be expeted that fewer grafts should result with time. % G raft G raft Y ield Temperature (degrees Celius) Fig. : Effet of Temperature on and E The effet of temperature on graft yield and grafting effiieny is presented in Figure. Graft yield (G) E inreased with rise in temperature probably due to inreased deomposition of H 2 O 2, greater mobility of monomer moleules and enhanement of rates of the reations. The formation of graft opolymers at low temperatures is probably due to inreased deomposition of H 2 O 2 by the addition of hydroquinone to the redox system, and the abstration of H from hydroquinone to generate a radial apable of initiating grafting. The grafting effiieny (GE) was observed to derease after 6 C. This was probably due to termination reations aused by the inreased number of radials generated in the reation medium as temperature is raised thus the number of ative sites for grafting on the ellulose is dereased. % Graft Graft Yield Conentration of Hydrogen peroxide (M) Fig. 6: Effets of Hydrogen peroxide onentration on and E The result of the variation of [H 2 O 2 ] on the graft yields and graft effiieny is presented in figure 6. The and E dereased progressively with rising [H 2 O 2 ] until it levels off at x 2 M H 2 O 2. At high [H 2 O 2 ] there are more radials produed whih may ombine to promote termination of radial on the ellulose bakbone and the termination of the polymerization reations. A mehanism for the graft opolymerization of a vinyl monomer, onto a polysaharide, initiated by Fe (II) / H 2 O 2 has been proposed (Vazquez et al (1989). The results obtained in this study onfirm that a high [H 2 O 2 ] will not inrease the graft yields even though there may be an inrease in total polymers produed. Conlusion: Results from this work showed that holoellulose derived from ooa (Theobroma aao) wood meal are a good substrate for opolymerisation. Cellulose graft opolymers have proved useful in several fields thus value added produts ould fairly easily be obtained from agriultural wastes that otherwise pose environmental hallenge. The addition of hydroquinone to the redox system has resulted in signifiant improvements in the grafting parameters.

5 1 REFERENCES Fernandez M. J; Casinos I; Guzman G. M. (199) Effet of the way of Addition of the Reatants in the Graft Copolymerization of a Vinyl Methyl Arylate mixture onto Cellulose. J. Polym Si. A, 28, Gupta K. C; Khandekar K. (2) Graft Copolymerization of Arylamide-Methylarylate Comonomers onto Cellulose using eri ammonium nitrate. J. Appl. Polym. Si. 86, Heinrih J; Mishnik P. (1999) Determination of the Substitution Patterns in the Polymer hains of Cellulose aetates J. Polym. Si. A, 37, Hodano S; Onimura K; Tsutumi H; Yamasaki H; Oishi T. (3) Synthesis of Chemialmodified Cellulose obtained from aste pulp. J. Appl. Polym. Si. 9, 9-6 Kato K; Vasilets V. N; Fursa M. N; Meguro M; Ikada Y; Nakame K. (1999) Surfae Oxidation of Cellulose fibers by Vauum ultra-violet Irradiation J. Polym Si. A, 37, Mateva R and Nikolov K. (1991) On some Regularities of Grafting of Vinyl Pyridine Derivatives on Aetyl Cellulose J. Polym. Si. A, 29, Okieimen F. E. (3) Preparation, Charaterisation and Properties of Cellulose-polyarylamide Graft Copolymers. J. Appl. Polym. Si. 89, Okieimen F. E and Idehen K. I. (1989) Studies in the Graft Copolymerisation of Vinyl Monomers on Cellulosi Materials. J. Appl. Polym. Si. 37, Onishi Y; Butler G. B; Hogen-Esh T. E (4) 1,2- propanediol-ellulose- arylamide Graft Copolymers. J. Appl. Polym. Si. 92, Ouajai S; Hodzi A; Shanks R. A. (4) Morphologial and Grafting Modifiations of Natural Cellulosi fibres. J. Appl. Polym. Si. 94, Vazquez B; Goni I; Gurruhaga M; Valero M; Guzman G. M. (1989) A study of the Graft Copolymerization of Metharyli aid onto Starh using the H 2 O 2 / Fe 2+ Redox system. J. Polym. Si., A. 27, 9-63