Abstract:
The oil-in-water (O/W) microemulsion of menthol in mineral oil was first prepared in the presence of 1:1 mixture of a low HLB surfactant, poly(oxyethylene-2-stearyl ether) (HLB=4.9) and a high HLB co-surfactant, cetyl-stearyl alcohol (HLB=15) using a homogenizer with a stirring speed of 16,000 rpm. The menthol microemulsion coated by chitosan was then solidified by ionic crosslinking with sodium tripolyphosphate (TPP). As characterized by laser light scattering particle size analyzer, the chitosan-menthol microcapsules had a size in a range of 0.5 40 µm. The shape and morphology of the microcapsules were analyzed by optical microscopy. The optimum preparative condition that yielded stable microcapsules with a narrow size distribution was as follows: homogenizing speed of 16,000 rpm, homogenizing time of 3 min, concentration of surfactant of 5.0%(w/w), pH of 4.9, mol ratio between chitosan and TPP of 2:1, crosslinking time of 120 min and weight ratio of oil to chitosan of 8:1. The microcapsules containing menthol in the microemulsion were stable at high temperature at 40oC under three sweep cycles of control stress at 1.0 Pa evidenced by G/ and G// values measured by the rheometer. As determined by gas chromatography, the encapsulation efficiency of menthol in microcapsules was approximately 25%. The amount of menthol encapsulated in the microcapsules was equal to 2%(w/w). The amount of the released menthol can be varied as a function of the mol ratio between chitosan and TPP and the weight ratio between oil and chitosan. At 80% relative humidity and 32oC, the total amount of menthol release from the microcapsules was in a range of 60-80%. As evidenced from scanning electron micrographs, the microcapsule added in the leave-on hair condition was found attached to the hair surface. Furthermore, not only the leave-on conditioner containing the chitosan-menthol microcapsules helped increasing the thermal stability of the hair, but it also made hair softer and easy to comb.