Objectives To develop a slow-release system using xanthan gum (XG) as the main substrate with longer release time comparing to current relative research.
Methods Salicylic acid (SA) was used as a pattern release target. A total of 29 formulas were designed and divided into 4 groups: XG + PVA + SA, XG + PVA + acetate starch (AS) + SA, XG + PVA + stearic acid + SA, XG + PVA + chitosan (CS) + SA. According to the designed formula, the materials were grinded and mixed with polyvinyl alcohol (PVA) solution as the binder for granulation. Firstly, five kinds of sustained-release granules (in diameter of 6-10 mm) and three kinds of sustained-release granules granulated with PVA solution of different concentrations of 4%, 5%, 6% (w/v) were prepared to study the effect of concentration of PVA solution and granulation diameter on the release behavior of the sustained-release granules. After determining the granulation conditions, the effects of different formulas on the particle release behavior were studied. The release effect of the obtained particles was studied in water and soil. The indicator was the release ratio of SA and the amount of released SA.
Results The release curves of prepared slow release granules all followed a trend that the release percentage of salicylic acid raised quickly in the former period, then the curve eventually tended to be flat. According to the experimental results, XG with larger particle size swelled more slowly, therefore the release of the contents was slower. The smaller the granule was, the higher the percentage of final release was. However, the release behavior end more quickly at the same time due to its larger specific surface area. When the granule too large, the duration of the release was not prolonged. The final selection of the granulation diameter (D) was 8 mm. The study on three different kinds of concentration of PVA solution showed that PVA solution with the concentration of 4% was the best to be used as binder. The appropriate ratio between mixed powder and 4% PVA solution (w/w) was 1.1∶1. After comparing the release behavior of 29 formulas, 4 formulas were selected. They were listed as below. Formulation 1∶XG∶SA = 3∶1, the release in deionized water lasted about 2.5 days. Formulation 2: XG∶AS∶SA = 3∶1∶1, the release in deionized water lasted about 2.5 days. Formulation 3∶XG∶stearic acid∶SA = 1∶1∶1, the release in deionized water lasted about 3 days. Formulation 4: XG∶CS∶SA = 3∶1∶1, the release behavior lasted for 4 days in deionized water and up to 36 days in soil column.
Conclusions In combination with the cost and the release effect, the selected formula is XG∶ CS∶ SA = 3∶1∶1 (the particle size of XG is 0.178 mm), D = 8 mm, 4% PVA. This obtained slow release system has the characteristics of low cost, simple production method and environment friendliness.
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