AOUADA, F. A.

MATTOSO, L. H. C.

MOURA, M. R. de

ORTS, W. J.

RCAAP - Repositório Científico de Acesso Aberto de Portugal

Hydrogels as carriers for the controlled release of paraquat.

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/\ .Abstracts\ \SSN 1983-7542.I..,.. ., .ICAM200911 th International Conferenceon Advanced MateriaisICAM2009Rio de daneir-o B/"'azílSoptcmber 2 O ~2SHydrogels as carriers for the controlled release of paraquatF. A. Aouada'", M. R. de Moura'", W. J. OrtS(2)and L. H. C. Mattoso(3)*(1) Chemistry Department, Federal University of São Carlos, São Carlos, SP, Brazil.(2) Bioproduct Chemistry & Engineering Research Unit, USDA-ARS-WRRC, Albany, CA, USA.(3) National Nanotechnology Laboratory for Agriculture (LNNA) Embrapa AgriculturalInstrumentation, São Carlos, SP, Brazil, e-mail: mattoso@cnpdia.embrapa.br* Corresponding author.Abstract - The objective of this work was to study the capability of hydrogels constituted by polyacrylamide andmethylcellulose for controlled release of paraquat in aqueous solution. The released amount of paraquat was measuredspectrophotometrically from the absorbance spectra applying a typical standardization curve. The results showed that the release ofparaquat becomes slower when the MC content is increased, due to the strong interaction between hydroxyl groups from MC segmentsand cationic groups from the paraquat, The mechanism of paraquat transpor! through the hydrogels synthesized with differentformulations was also explored.The aims of controlled release formulations are to protect the supply of the agent to allow theautomatic release of the agent to the target at a controlled rate and to maintain its concentration in thesystem within the optimum limits over a specified period of time, thereby providing great specificity andpersistence [1].The objective of this work was to study the capability of hydrogels constituted by polyacrylamide(PAAm) and methylcellulose (MC) for controlled release of paraquat in aqueous solution. PAAm-MChydrogels were synthesized by the free radical polymerization method. The released amount of paraquatwas measured spectrophotometrically (À = 258 nm) from the absorbance spectra applying a typicalstandardization curve. Paraquat cumulative released (CR) from the hydrogel was obtained from this Eq. - CR= (Mt I M,,) x 100, where Mt is the cumulative amount of paraquat released at time "t" and M", is the amount ofparaquat loaded onto hydrogel. Fickian and Non-Fickian diffusion can be analyzed from the Eq. developedby Ritger and Peppas [2], Mt I M", = k t n, where k is the constant characteristic of the pesticide-polymersystem, and n is the diffusion exponent characteristic of the release mechanism.It is possible to see in Fig. 1 that the paraquat release from hydrogel constituted by 6.0 % AAm is 100% after 1 day. This fast release is attributed to the weak interaction between matrix-paraquat. PAAm-MChydrogels presented values of cumulative release of 41; 73; 60 and 24 % for MC = 0.25; 0.5; 0.75 and 1.0 %(in w:v%), respectively. The values of k presented in Tab. 1 showed that the release of paraquat becomesslower when the MC content is increased, due to the strong interaction between hydroxyl groups from MCsegments and cationic groups from the paraquat. The equilibrium of release was achieved after 15-20 days.The values of n remained in a range corresponding to Fickian diffusion (n = 0.45 - 0.5) until MC = 0.5 %.After this concentration, the release of paraquat occurred through non-Fickian diffusion. Non-Fickian oranomalous diffusion occurs when the diffusion and relaxation rates are comparable. Thus, the paraquatrelease depends on two simultaneously rate processes, water migration into the beads and diffusion throughcontinuously swelling hydrogels [2].Table 1: Diffusion exponent n, constant k for the release of paraquat.Hydrogel n Mechanism k (h-i)6.0 %AAm 0.44 Fickian 0.5296.0 % AAm_O.25 % Me 0.44 Fickian 0.06786.0 % AAm_O.5 % Me 0.50 Fickian 0.04046.0 % AAm_O.75 % Me 0.63 Non-Fickian 0.05416.0 % AAm_1.0 % Me 0.58 Non-Fickian 0.0375100~:l: 80'".,Q; 60a::.,."ro 40'5E::> 20o10 20 30Time (days)40 50References[1] A. K. Bajpai and A. Giri, Reacl. Funcl. Polym. 53 (2002) 125.[2] P. L. Ritger and N. A. Peppas, J. Control. Release 5 (1987) 23.Figure 1: Release of paraquat from PAAm and PAAm-MChydrogels with different MC concentrations. [AAm] = 6.0 %(w:v%).Acknowledgements: FINEP, FAPESP, CNPq.

Hydrogels as carriers for the controlled release of paraquat.

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