| Summary: | 碩士 === 國立雲林科技大學 === 化學工程與材料工程系 === 107 === Periodic and excessive applications of fertilizers could lead to high cost of agricultural production and pollute the environment. Montmorillonite (MMT) has been used as a release carrier due to its large specific surface area and high cation exchange capacity. In this study, quaternary ammonium chitosan (QCS) was synthesized by graft copolymerization of monomers with quaternary ammonium groups onto chitosan (CS) to increase the water solubility of CS. MMT was then mixed with QCS and urea to form MMT/QCS/Urea composites as controlled release carriers for urea. The effects of the amount of QCS in composites on the swelling ratio, urea release profiles, water retention and antimicrobial activity were investigated.
The grafting of cationic monomers onto CS chains was confirmed by Fourier transform infrared spectroscopy. The grafting yield estimated by the gravimetric analysis was approximately 31.4%. The X-ray diffraction analysis demonstrated that the interlayer distance of MMT increased from 1.37 nm to 1.70 nm and 2.01 nm for the intercalation of urea and QCS, respectively. Moreover, the incorporation of QCS into MMT increased the encapsulation efficiency of urea from 4.6% to 21.7%. The water absorption capacity and water retention of soil of MMT/Urea/QCS composite increased with increasing the amounts of QCS in composites.
The release of urea from the composites was evaluated in water and soil. The results revealed that the release rate of urea was significantly decreased and the release period was significantly prolonged after the incorporation of QCS into MMT. Moreover, the higher amounts of QCS in composites, the slower the release rate of urea. The composites exhibited a slow and sustained release over a period of 14 days in soil.
The antimicrobial activities of MMT/Urea/QCS composites against Agrobacterium sp and Rhizoctonia solani were examined. The results revealed that MMT/Urea composite could not inhibit the growth of Agrobacterium sp, while MMT/Urea/QCS composites effectively inhibited the growth of Agrobacterium sp. The antibacterial ratio of MMT/Urea/QCS composites with QCS/MMT weight ratios of 2 and 4 reached 86% after 48 hr of contact, even at a concentration of only 1000 ppm. Additionally, they at a concentration of 1 wt% inhibited Rhizoctonia solani growth by over 80% in 48 hr. Therefore, these results indicate that the MMT/Urea/QCS composites could be used as urea controlled release carriers with excellent antimicrobial properties.
|
|---|
