In order to further investigate the porous structure inside the ethylcellulose microspheres and the effect of the content of ethyl cellulose in the oil phase solution on the internal structure of the obtained powder, the pore size distribution of the ethylcellulose microspheres under different mass ratios of ethyl cellulose/ethyl acetate was measured by mercury injection apparatus. The mass ratios of ethyl cellulose to ethyl acetate were 0.4/10, 0.8/10 and 1.2/10, respectively. Figure 129 shows the pore size distribution curves of three kinds of ethyl cellulose microspheres. During the mercury injection test, the mercury liquid is first pressed into the stacking gap of the ethyl cellulose microspheres, and with the continuous increase of pressure, the mercury liquid begins to be pressed into the internal structure of the ethyl cellulose microspheres [135]. Therefore, the pore size distribution curve of the microspheres shows a typical bimodal distribution, and the pore size of the accumulation gap of the ethylcellulose microspheres is larger than the internal pore size of the microspheres. It can be seen from the pore size distribution curve that with the increase of the addition of ethyl cellulose in the oil phase solution, the pore size of the obtained powder particles increases gradually. It also indicates that with the increase of the mass ratio of ethyl cellulose to ethyl acetate, the particle size of the obtained powder gradually increases. In addition, according to the pore size distribution curve inside the microspheres, the three kinds of ethyl cellulose microspheres showed a large cumulative pore volume, which indicated that there were a large number of connected pores inside the microspheres, which was also consistent with the conclusion obtained from the observation of the cross section of the microspheres. The calculated porosity of the three kinds of microspheres is 72%, 74% and 68%, respectively.
