Abstract
Goaf sealing wall is set in the roadway close to the stop line of working face in an underground coal mine. However, the sealing wall is prone to crack or fracture under serious mining stress, resulting in water and air leakage from goaf. In this study, the combination of polymethylene polyphenyl polyisocyanate (PAPI) and methylene diphenyl diisocyanate (MDI) as component A and polyether polyols, catalysts, surfactants, chain extenders, and plasticizers as component B were investigated to optimize the exothermic, foaming, and mechanical properties of modified polyurethane (PU) as the filling material for goaf sealing wall. Firstly, the reaction temperature of specimens with different contents of polyether polyols was monitored using a dynamic acquisition system; secondly, the effect of polyether polyols, catalysts, and surfactants on foaming property was studied; then, uniaxial compression tests were developed to obtain compressive behavior; finally, the microstructure after uniaxial compression was observed by using a scanning electron microscope (SEM). The results indicate that the pure chemical slurry is superior to the combination of chemical slurry and sand in compressive strength and deformation behavior. The optimal mass ratio of polyether triols, polyether tetraols, catalysts, surfactants, chain extenders, and plasticizers is 11 : 9 : 1.0 : 0.5 : 1.2: 6 in component B due to the maximum reaction temperature of 121.4°C, the expansion ratio of 2.6, and the compressive strength of 7.97 MPa at the strain of 10% in this study. The research provides a solution for the construction of the sealing wall, which is of great significance to safety production in an underground coal mine.
Highlights
In recent years, polymer materials have developed in the field of engineering, considering their foaming and mechanical properties, in reservoir dam [1, 2], traffic tunnel [3, 4], underground coal mine, and other underground construction [5, 6]
Materials. e PU materials are composed of isocyanates, polyols, catalysts, surfactants, plasticizers, crosslinkers, chain extenders, flame retardants, and smoke suppressants. e above materials are divided into component A and component B; among them, isocyanates belong to component A and the rest belong to component B
E data suggest that the maximum reaction temperature of specimens in four groups were quite different, which fluctuates within the range of 110°C to 138°C. e materials reached the maximum temperature within 6 minutes, but the heat dissipation was slow, and it has taken about 2 hours to return to room temperature
Summary
Polymer materials have developed in the field of engineering, considering their foaming and mechanical properties, in reservoir dam [1, 2], traffic tunnel [3, 4], underground coal mine, and other underground construction [5, 6]. Polymer materials are mainly used for reinforcing coal and rock mass as grouting material, plugging water seepage as grouting material, sealing caving cavity or abandoned roadway as filling material, and preventing air leakage as spraying material in an underground coal mine [7,8,9,10]. Some organic-inorganic composite materials [16,17,18] and modified materials [19,20,21] are under continuous development Among these polymer materials, PU materials have been widely used in an underground coal mine. The chemical slurry is injected into the caving cavity or enclosed space, which expands into a sealing solid in a short time due to its outstanding foaming, mechanical properties, and high chemical reaction rate. Gypsum sealing walls, brick sealing walls, and concrete sealing walls are prone to crack or fracture under mining stress, which leads to water and air leakage from goaf. erefore, P-type PU filling materials suitable for the composite sealing wall were proposed in this study
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