Chemical Engineering and Processing 41 (2002) 707 – 710 Controlled release of paraquat from poly vinyl alcohol hydrogel I. Alemzadeh *, M. Vossoughi Biochemical and Bioenironmental Research Center, Sharif Uniersity of Technology, Tehran 11365 -6891, Iran Received 9 May 2001; received in revised form 20 November 2001; accepted 20 November 2001 Abstract A thorough investigation on different controlled release systems were evaluated. The required devices were constructed simultaneously and the required experiments were performed. The polymeric network and membranes of poly vinyl alcohol with cross-linking agent glutaraldehyde for preparation of hyrogel system was effected. Paraquat, a type of herbicide was introduced as solute in the system. Glutaraldehyde was utilized as cross-linking agent at different concentration. Increase in the concentration of the cross-linking agent will cause a decrease in the extent of release out of the system. The effect of temperature on hydrogel adsorption demonstrates a higher adsorption at lower temperature. © 2002 Published by Elsevier Science B.V. Keywords: Controlled release systems; Cross-linking agent; Paraquat www.elsevier.com/locate/cep 1. Introduction Diffusion of solute through non-porous gel mem- brane is important in laboratory and biological separa- tion chromatographic analysis, biomedical applications and agricultural fields. Utilization of agrochemical her- bicide, pesticide and fertilizer could lead to widespread contamination of ground water. Controlled release of the active agent is important not only for attaining the most effective use of the agent but also for the preven- tion of pollution. In recent years, a great deal of effort has been spent on developing delivery systems for agro- chemicals [1 – 5]. Controlled release of these agrochemi- cals is highly desirable not only for attaining their most effective use but also for minimizing potential pollu- tion. Different types of slow release fertilizers have been studied by various investigators, fertilizers coated with different polymers were produced and studied [6,7]. Various polymer-supported or microencapsulated biocides have been produced to prevent the contamina- tion of groundwater aquifers from their conventional applications [5]. Different types of controlled release herbicides have been studied by various investigators [3 – 5]. Herbicides that have the greatest potential for groundwater contamination are characterized by their high water solubility and moderate to long half-lives. Polymers utilizable in hydrogel preparations are pre- sented in Table 1. In this investigation, paraquat, a bipyridinium herbi- cide was evaluated as solute in controlled release devices made of a hydrogel prepared from poly vinyl alcohol (PVA) and cross-linked by glutaraldehyde in different concentrations. 2. Materials and methods Materials utilized in this investigation were analytical grade and supplied by Sigma Co. 2.1. Membrane preparation All membranes were prepared in the form of water- swollen, cross-linked polymeric networks of PVA, with molecular weight of 40 000. The herbicide was paraquat dichloride (C 12 H 14 Cl 2 N 2 ) with a molecular weight of 257.2, which is a water-soluble drug. Glutaraldehyde as cross-linking agent CHO(CH 2 ) 3 C- HO, is an active reagent. Aqueous PVA solution was prepared by dissolving 2.1 g PVA powder in 25 ml deionized water and heating then at 90 °C for 9 h. To * Corresponding author. Tel.: +98(21)6005417; fax: +91(21)6012983 E-mail address: alemzadeh@sina.sharif.edu (I. Alemzadeh). 0255-2701/02/$ - see front matter © 2002 Published by Elsevier Science B.V. PII:S0255-2701(01)00190-8