The existing seal is not designed with a special sand retaining structure, and it is difficult to discharge the mud particles after entering, resulting in serious wear of the seal and premature failure. Therefore, a special-shaped sealing structure for sand blocking of roller cone bits is proposed to solve the problem of sealing wear. Starting from the structural principle, the structural parameters of the special-shaped seal of the sand-retaining flap are designed based on the O-ring, and the sealing principle is analyzed, the formula of grease leakage is derived, and the simulation and optimization analysis are completed with the aid of APDL. This proved the feasibility of the design. The influence law of structural parameters on contact pressure and leakage is obtained, and the formula of leakage is verified; The influence of structural parameters on the contact gap of the sand flap is obtained. Under the condition of optimal combination of structural parameters, the grease leakage is 43 mg/h, a decrease of 85%. Theoretically, it takes 580 h to exhaust the grease, and the contact gap of the sand flap is 0.00019479 mm, a decrease of 95%, which can greatly reduce the wear of the main seal. This study opens up a new idea for seal design.

Polylactic acid (PLA) is derived from renewable resources and can be composted under controlled industrial conditions, but its flammability and brittleness limit wider use. This study combined Ti₃C₂T_x MXene with surface terminations and an intumescent flame retardant (IFR) system based on ammonium polyphosphate and pentaerythritol (4:1, w/w). A styrene–butadiene–styrene (SBS) elastomer was then added to improve toughness. At a total flame retardant loading of 10 wt%, PLA/8.5IFR/1.5MXene reached a limiting oxygen index (LOI) of 30.32% and a UL-94 V-0 rating without dripping. Compared with PLA/10IFR, the peak heat release rate (PHRR) and total heat release (THR) decreased by 18.6% and 28.8%, respectively, and the residue at 600 °C increased from 5.88 to 6.75 wt%. The composite containing MXene formed a denser char and showed a slightly lower Raman D/G intensity ratio. Adding 10 wt% SBS increased notched impact strength by 48% for PLA/IFR and 31% for PLA/IFR/MXene, but reduced tensile strength and modulus. MXene therefore improved the barrier in the condensed phase at a lower IFR content, while SBS partly recovered toughness.