Abstract—In modern agriculture, polymeric hydrogels are known as a component able to hold an amount of water due to their 3-dimensional network structure and their tendency to absorb water in humid environments. In addition, these hydrogels are able to controllably release the fertilisers and pesticides loaded in them. Therefore, they deliver these materials to the plants' roots and help them with growing. These hydrogels also reduce the pollution of underground water sources by preventing the active components from leaching. In this study, sIPN acrylamide based hydrogels are synthesised by using acrylamide free radical, potassium acrylate, and linear polyvinyl alcohol. Ammonium nitrate is loaded in the hydrogel as the fertiliser. The effect of various amounts of monomers and linear polymer, measured in molar ratio, on the swelling rate, equilibrium swelling, and release of ammonium nitrate is studied. Keywords—Hydrogel, controlled release, ammonium nitrate fertiliser, sIPN. I. INTRODUCTION ERTILISER and water are two factors which put limitations on the agricultural products [1]. Therefore, improving the utilisation of water resources and nutritive fertilisers are of a high importance. Studies show that between 40-70% of the nitrogen loaded in the fertilisers is not absorbed by the plants' roots and is permeated to the environment. This results in economical loses as well as environmental pollution. This research shows that a controlled release process can solve this problem and reduce the pollution considerably. Another problem is that in most farms located in dry lands, there is a water shortage specifically in the dry seasons while they cannot take advantage from water sources in rainy seasons due to the lack of managerial skills. An appropriate solution to this problem is to use a component which can provide water and release fertiliser in a controlled way simultaneously. Hydrogels are cross-linked polymers able to absorb and hold great amounts of water. These polymers are synthesised by using water soluble monomers through a free radical polymerisation with the help of a suitable cross linking agent. A. Hekmat and A. Barati (corresponding author, e-mail a- barati@araku.ac.ir) are with Chemical Engineering Department, Arak University, Iran. E. V. Frahani are with Biotechnology Group, Chemical Engineering Department, Tarbiat Modares University, Tehran, Iran. A. Afraz is with National Iranian Oil Company, Tehran, Iran. The water absorption characteristic of hydrogels is based on its contact with a thermodynamically fitted solution and is formed by transmitting from crystalline condition to rubbery condition. This characteristic of the hydrogels has many applications in the biomedicine production [2,3,4,5,6,7,8], tissue engineering technology [3], contact lenses production [4], and controlled release in agriculture and drug delivery systems [5,8]. Controlled release polymeric systems have many advantages in comparison with normal systems. In addition to their application in drug delivery systems, these hydrogels are used in agriculture as they reduce water consumption by reducing the numbers of irrigation [4,6]. They also reduce the plants’ death due to dehydration [3,6,7,8], stabilise fertilisers in soil, prevent active component from leaching to underground water [2,7], and improve the plants’ growth. The substitution of controlled release method with the traditional fertilizing methods have resulted in development of the best technical solution to provide local concentration of the active agents and reduction of drain piping.[1,5,8] Fertiliser release systems must be able to control the amount of leaving fertiliser as time goes by. Thus, amount of water inside the polymer network should be somehow controlled. Among the advantages of using hydrogels in controlled release of fertilisers in agriculture, mention can be made of: 1. As the water diffuses into the network, the loaded fertiliser exits slowly and feeds the plants’ roots in a longer period of time. In addition, the amount of permeation can be controlled by changing the network structure.[9] 2. Since the interactions between the fertiliser and polymeric network are weak, a higher amount of fertiliser is released by the hydrogel in comparison with the zeolites which hold the fertiliser by adsorption.[9] This article studies the water absorption and the release of ammonium nitrate as the sample chemical fertiliser in acrylamide based hydrogels. Linear polyvinyl alcohol monomers increase the strength of the gel by forming semi- interpenetrating polymer networks (sIPN) which are able to carry out the controlled release of fertilisers. The effects of changes in the amount of acrylamide monomer, ionized co- monomer, polyvinyl alcohol (PVA), and cross linking agent on the swelling rate and fertiliser release from the network have been studied. In the end, the best composition for a rigid Synthesis and Analysis of Swelling and Controlled Release Behaviour of Anionic sIPN Acrylamide based Hydrogels Atefeh Hekmat, Abolfazl Barati, Ebrahim Vasheghani Frahani, and Ali Afraz F World Academy of Science, Engineering and Technology International Journal of Chemical and Molecular Engineering Vol:3, No:8, 2009 383 International Scholarly and Scientific Research & Innovation 3(8) 2009 ISNI:0000000091950263 Open Science Index, Chemical and Molecular Engineering Vol:3, No:8, 2009 publications.waset.org/10040/pdf