Starch-based hydrogel loading with carbendazim for controlled-release and water absorption
Introduction
Fungicides are essential to disease control and maintenance of agricultural production (Singh, Sharma, & Gupta, 2009). Carbendazim, a widely used fungicide, is used to control and prevent a wide range of fungal diseases of crops (Anastassiades and Schwack, 1998, Itak et al., 1993, Wang et al., 2009, Yu et al., 2009). When applied by conventional methods, carbendazim is invariably subject to wastages like photo-degradation, leaching, etc. (Sun et al., 2014), thus, frequent application is needed. However, excessive use of carbendazim can cause undesirable effects on humans. Its detection in tomatoes and wastewater has caused public concerns (Bollmann et al., 2014, Liu et al., 2014). Therefore, there is an urgent need to develop a new method for carbendazim application. The use of various delivery systems, including microcapsules, microspheres, and beads is effective at decreasing wastage of agrochemicals (Freiberg and Zhu, 2004, Jarosiewicz and Tomaszewska, 2003, Taki et al., 2001). The fungicides thiram and tebuconazlole have been loaded into polymers for slow-release (Asrar et al., 2004, Singh et al., 2009).
Large parts of the world, especially in China, are arid and semi-arid regions. Soil in these areas has weak WHC and does not efficiently retain rain water. Hydrogels are polymeric network structures that can absorb large amounts of water and retain water for specific periods (Liu et al., 2009, Tong and Zhang, 2005). Recently, there has been an increased interest in the use of natural polysaccharides based hydrogels in the fields of agriculture (Thakur & Thakur, 2014a) due to their enormous advantages such as economic/low cost, biodegradability, acceptable specific strength, low density, good thermal properties, recyclability, no health risk, bounty and enhanced energy (Thakur et al., 2013a, Thakur et al., 2013b; Thakur et al., 2014a, Thakur et al., 2014b, Thakur et al., 2014c). Natural polysaccharides such as starch, cellulose (Thakur et al., 2014a, Thakur et al., 2014b, Thakur et al., 2014c), chitosan (Thakur & Thakur, 2014b), lignin (Thakur and Thakur, 2015, Thakur et al., 2014a, Thakur et al., 2014b, Thakur et al., 2014c), alginate and psyllium polysaccharide (Thakur & Thakur, 2014a) are well-known examples of bio-renewable resource for environmentally friendly hydrogels. Among various types of natural polymers, starch based hydrogels have attracted great attention all over the world because of economical effectiveness, environmental friendliness and easy modification with vinyl monomers onto it. The OH on the anhydroglucose unit of starch has the potential to form complex copolymer networks, which often has the property of absorbing large amounts of water (Zhang et al., 2013).
Replacement of conventional application of agrochemicals by a combination of controlled-release and water absorption systems has received much attention. Fertilizers, pesticides cypermethrin and micronutrients copper sulfate have been successfully incorporated into hydrogels (Liang and Liu, 2006, Rudzinski et al., 2003, Yang et al., 2013). However, there are few reports on hydrogels loading carbendazim.
In this work, CLH with specific WHC and slow-release properties were prepared in two steps. The release behaviors of CLH in ddH2O and phosphate buffer solution (PBS) were learnt. The effects of WA on release profiles and kinetics were investigated. What's more, the influences of pH and salt ion on the release rate were also determined.
Section snippets
Materials
Cassava starch was from Heyu (China). Acrylamide (AM), potassium peroxydisulfate (KPS), N,N′-methylenebisacrylamide (MBA), 2,2′-azobis(2-methylpropionamidine)dihydrochloride (AIBA, 99%) were from Sinopharm (China). Acrylic acid (AA) and methyl methacrylate (MMA, 99.0%) were from Aladdin (USA). Nonlabeled carbendazim (96%) was obtained from Sigma-Aldrich (Germany). 14C-carbendazim (>97% radiochemical purity and chemical purity, 5 μCi/mg specific radioactivity) was from Radiolabeled Chemicals
FTIR spectroscopy of CLH and beads
FTIR spectroscopy of the starch-g-(AA-co-MMA) beads is depicted in Fig. 2A. The strong and broad absorption band between 3200 and 3600 cm−1 in spectrum (a) is characteristic of starch. There was an intensity increment of this band in spectra (b) and (c) because of OH and COOH groups of grafted AA (Athawale & Lele, 1998). In the spectrum of starch-g-methyl methacrylate (starch-g-MMA) in Fig. 2A (spectrum a), two sharp peaks at 2997 and 2952 cm−1 represent stretching vibrations of methylene and
Conclusion
A starch-based hydrogel loading with carbendazim was synthesized in two steps, which combined slow-release with WA in one system. The WA capacities could reach 800 g of ddH2O and 160 g of tap water per gram of CLH. WA capacities strongly affected the release pattern in ddH2O and in buffer solution. The release mechanism could be tuned by WA capacity and the release duration in ddH2O could reach 240 h. Media pH played an important role in the release process of CLHs. The slowest and complete
Acknowledgements
This research was financially supported by the National Natural Science Foundation of China (no. 11275170), National High Technology Research and Development Program of China (863 Program, no. 2013AA065202), and Chinese Ministry of Agriculture Foundation (no. 201103007).
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