Enhanced thermal stability, flame retardancy, and thermal conductivity of self-healing natural rubber composites reinforced surface treated halloysite clay nanotubes

This study introduces acrylic acid treated halloysite clay nanotubes (m-HNTs) as an innovative nanofiller for self-healing natural rubber (SHNR) nanocomposites. The m-HNTs were synthesized using acrylic acid (AA), effectively increasing its compatibility with non-polar natural rubber, also generates massive Zn 2+ salt bonding between zinc thiolate and carboxylic groups of m-HNTs which enable electrostatic interaction and allows additional reversible ionic networks. The effects of the m-HNTs obtained on the thermal stability, flame retardancy, and thermal conductivity of SHNR was investigated using thermogravimetric analysis, thermal constants analyzer, differential scanning calorimetry, flammability test, and limiting oxygen index (LOI) measurements. The incorporation of m-HNTs into the self-healing natural rubber nanocomposites enhanced 17.5% of their thermal conductivity, 19% of thermal stability, 27.7% of LOI, and 29% reduction in burn rate compared to the unfilled SHNR nanocomposite. A two-phase Lewis–Nielsen model was also utilized to simulate efficiency of the thermal conductivity of SHNR containing functionalized halloysite nanotubes. The experimental data was accurately fitted by two-phase model with a confidence level of >95%. The utilization of m-HNTs as a reinforcement in SHNR is promising for rubber products that experience high temperature environments especially for automotive hoses, seals and belts.