Flammability of Thermoplastic polyurethane (TPU) limits its application in automotive, wires and cables, sports and textile coatings. Endowing TPU with simultaneously improved flame retardancy and smoke-suppressant will be highly beneficial. Herein, a novel green and efficient condensed phase GO/ MgÀ Al layered double hydroxides (LDHs) flame retardant for TPU was synthesized by the co-precipitation of Mg 2 + and Al 3 + and assembled with graphene oxide (GO) by electrostatic interaction. The unique two-dimensional layered structure of GO/LDHs has a large specific surface area, which can form a dense and uniform char layer during the combustion process, thus hindering mass and heat transfer between gaseous and condensed phases. The XRD, TEM, SEM and EDS results showed that MgÀ Al LDHs and GO/LDHs were successfully synthesized. The thermal, flame retarding and smoke suppression properties of TPU/GO/MgÀ Al LDHs were determinated by UL-94, limiting oxygen index (LOI), cone calorimeter (CCT) and smoke density (SDT). UL-94 testing results showed that all the TPU/GO/MgÀ Al LDHs samples had a vertical combustion rating of V-0. Compared with pure TPU (19.1 � 0.2 %), the LOI value of all TPU/GO/MgÀ Al LDHs composites are above 27 %. CCT results showed TGAL3 sample displayed the lowest peaks of heat release rate (pHRR) value of 142.9 � 9.3 Kw m À 2 . The total heat release (THR) value of TGAL5 is almost 70 % lower than that of pure TPU. In addition, compared to pure TPU, GO/MgÀ Al LDHs materials has excellent performance in smoke suppression. The digital photos and Raman spectra of char residue demonstrated that TPU/GO/MgÀ Al LDHs materials has a denser carbon layer after combustion. Apart from flame retarding and smoke suppression, the mechanical properties of TPU/GO/MgÀ Al LDHs can maintain more than 80 % of the original TPU after addition of GO/LDHs. These results indicates that GO/LDHs composites is a kind of two-dimensional layered material with unique structure and excellent flame retardant and smoke suppression.
Controlling the surrounding rock in soft rock roadways under deep high stress, strong rheology, and intensive mining is critical for the safety, efficiency, and economy of mine production. In this study, the mechanical properties, large deformation mechanism, and support countermeasures of surrounding rock in the high-stress roadway in the Yuwu coal mine were systematically explored through laboratory tests, numerical calculations, and field measurements. It is shown that mudstone and sandstone are mainly composed of chlorite and kaolinite, respectively. Also, mudstone features elastoplasticity and experiences argillization and swelling in water. The mechanism of surrounding rock deformation in the high-stress roadway in the Yuwu coal mine was determined. As the V-shaped shear zone in the side corner expanded to the deep under high deviatoric stress, large-scale tensile damage occurred in the shallow surrounding rock. Consequently, discontinuous stresses in deep and shallow parts induce the expansion and fracturing of the roadway. The deformation velocity and damage degree of surrounding rock rise exponentially under different stress release coefficients, so the reduced distance of the face roof under control and timely support is important for restricting the free surface. An idea of “timely and active reinforcing the side and strengthening the bottom” was proposed. This approach made the loads on all the support objects within the working range. The overall deformation of the surrounding rock was controlled within 350 mm, ensuring the long-term stability of the roadway.
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