关键词: 复凝聚法, 微胶囊, 交联, 昆虫激素, 可控缓释

Acacia gum (GA) and gelatin (GE) were coacervated with presence of dodecanol (C12OH) in order to prepare microcapsules with C12OH encapsulated. C12OH was chosen for the encapsulated core material in consideration of its structural similarity to authentic insect sex pheromones, which are mainly consisting of unsaturated alcohol, acetate ester and aldehyde of hydrocarbons with carbon numbers between 10 and 24. In a first step, Zeta potential and transmittance of the solution mixture of GA and GE during the coacervation were followed in order to determine the optimum ratio of GA and GE. It was observed that maximum coacervation was achieved at GA/GE weight ratio at unity. In the presence of formaldehyde or glutaraldehyde as the crosslinker of the wall materials, microcapsules were prepared at different crosslinking level. With increase of glutaraldehyde from 1% to 4% relative to total polymer mass, the crosslinking significantly increased from 27.8% to 78.5%, similar performance was seen when formaldehyde was used instead of glutaraldehyde. Particle size and size distribution data showed that particle size decreased with a narrower size distribution when crosslinking agent was increased. C12OH encapsulation by this complex coacervation was examined for capsules prepared with C/W (core/wall) ratio of 1/2. It was revealed that crosslinking could remarkably enhance C12OH encapsulation. For the microcapsules without crosslinking agent, only 16% of the added C12OH was detected encapsulated, which led to a C12OH loading of 7%. Compared with the capsules without crosslinking agent, those prepared with 1% glutaraldehyde gave capsules with increased C12OH loading up to 20%. And C12OH loading was relatively constant while the crosslinking agent varied from 1% to 4%. It was found that capsules prepared using formaldehyde produced similar crosslinking, however, a much higher C12OH loading was observed when compared with those prepared using same levels of glutaraldehyde. To investigate C12OH release from the capsules, samples were placed into an incubator with constant temperature (30℃) and relative humidity (50% RH), and taken out for C12OH examination by gas chromatography and weighing the samples. It was found that all samples manifested a three-step-release profile, i.e. a quick start followed by a constant plateau region, representing a very low release rate or stopped release, and terminated by a release increase. C12OH expressed by percentage of capsules showed that all glutaraldehyde crosslinked capsules had a higher release rates than the sample without crosslinking; and the higher the crosslinking, the lower the release rate for all crosslinked samples. This gave a longest time and the most constant release rate in the capsules done with 4% glutaraldehyde. This work indicates that release of C12OH can be well controlled through capsule structure design, this is of great importance for our on-going study on controlled release of authentic insect semiochemicasls.

Key words: Complex Coacervation, Microcapsules, Crosslinking, Insect pheromone, Controlled release