Factors that affecting physical stability of high content pendimethalin capsule suspension and its optimization

Interfacial polymerization was adopted for pendimethalin 500 g/L capsule suspension. Effects of emulsifier content, wall material content, curing temperature, suspending agent and thickening agent on the average diameter, encapsulation efficiency, dispersed state, physical stability of microcapsule were investigated. Infrared spectroscopy (FT-IR) was used to characterize the encapsulation of microcapsule. It was indicated that encapsulation efficiency gradually enhanced with the amount of MDI increased. Microcapsule was prepared with encapsulation efficiency exceeding 87.0% and drug loading about 82.0% when MDI content(mass fraction) was 3.0% to 4.0%. When EL-40 content reached 1.0% and 3.0%, average diameter were 15.5 μ m and 4.00 μ m respectively and water separating proportions after thermal storage (54 ℃±2 ℃, 14 d) were 25.1% and 1.73%, respectively. The sample prepared with the curing temperature of 40, 50 and 60 ℃ were respectively severely agglomerated, agglomerated slightly and kept good morphology without agglomeration after thermal storage. Relative molecular mass and the sulfonation degree of sodium lignosulphonate were 1.0×104-1.2×104 and 0.85 mmol/g, respectively. When sodium lignosulphonate content was 3.0%, water separating proportion was only 4.76% and the particle shape kept smoothly without aggregation. Combination of xanthan gum and veegum could significantly improve the storage stability of the preparation. Water separating proportion of the preparation was only 2.12% and the flowability was fine after thermal storage when xanthan gum content was 0.07% and veegum content was 1.0%. Infrared spectroscopy results showed that the majority of pendimethalin was encapsulated in the microcapsule, but its absorption peak at 1 248 and 1 322 cm-1 were shifted to 1 231 and 1 307 cm-1.