# Delayed-Expansion Capsule Sealing Material for Coal Mine Overburden Isolated Grouting
## 3 Materials and Properties
### Expansion Characteristics  
During the experiment, it was found that the colloidal mass ratio of the SAP materials with different particle sizes in water exhibited the same changes and significant segmented expansion. Moreover, as the particle size of the SAP materials decreased, the segmented expansion effect diminished. The experimental data for the SAP materials across each particle size condition revealed that the SAP with a particle size of 80 mesh reached its maximum colloidal mass ratio within 10 min of water absorption. At this point, the colloidal mass stabilized at 131.8 g. Figure 3 illustrates the colloidal mass ratio at 10 min and the time taken to reach the maximum colloidal mass ratio for SAP materials with various particle sizes. These data indicate the effect of SAP particle size on the resulting colloidal mass ratio.  
Figure 2: SAP experimental materials with different particle sizes.  
As shown in Figure 4, the colloidal mass ratios of the SAP materials with a particle size of 5 mesh, 10 mesh, 20 mesh, 30 mesh, 40 mesh, 50 mesh, 60 mesh, and 70 mesh in water for 10 min were 3.5%, 19.6%, 75.5%, 83.5%, 89.8%, 92.3%, 98.7%, and 99.8%, respectively, of that of SAP materials with a particle size of 80 mesh. The limiting colloidal mass ratios of the SAP materials of the above-mentioned particle sizes were 41.5%, 91.4%, 91.3%, 92.7%, 94.5%, 97.8%, 99.4%, and 100.0% of the colloidal mass ratios of the SAP materials with a particle size of 80 mesh, respectively. The above results reveal that the particle size on the SAP material's colloidal mass ratio is mainly observed in the range of 0-10 min, and the final colloidal mass ratios for SAP materials across different particle sizes exhibit minimal variation (except for the material with a particle size of 5 mesh). For the SAP materials with particle sizes of 10-80 mesh, smaller particle sizes exhibit stronger water absorption capacity under the same time conditions, resulting in a higher colloidal mass ratio upon water absorption and expansion.  
From the experimental results shown in Figure 5, the water absorption and expansion process of the SAP material exhibits a linear growth trend in colloid volume changes.  
Figure 4: Ratio of colloidal mass ratio of SAP materials with different particle sizes over time.  
Figure 3: Variation of colloidal mass ratio with time for SAP materials with different particle sizes.  
The variation in water absorption and expansion for SAP materials with different particle sizes lies in the differing rates of water absorption. With the particle size of 20 mesh, the expansion of colloidal volume reached its maximum within 280 s; with the particle size of 40 mesh, the expansion of colloidal volume reached its maximum within 100 s; with the particle size of 60 mesh, the expansion of colloidal volume reached its maximum within 50 s; with the particle size of 40 mesh, the expansion of colloidal volume reached its maximum within 100 s; with the particle size of 60 mesh, the expansion of colloidal volume reached its maximum within 100 s; with the particle size of 60 mesh, the expansion of colloidal volume reached its maximum within 50 s. Therefore, under identical water immersion conditions, SAP materials with smaller particle size absorbed water more quickly, resulting in a larger volume of swollen colloid produced within a shorter period. This phenomenon occurred because the thickness of the SAP material with a smaller particle size was reduced from the outer wall to the inner core, resulting in a limited capacity for water absorption and expansion. Simultaneously, because the area in contact with water was relatively larger, the particle size of the SAP material could be adjusted to control the time to reach the limiting colloidal volume and regulate the material's expansion time.