A comparative study on the mechanical and flammability properties of aluminum hydroxide and hollow glass beads-filled polypropylene composites

Lightweight polypropylene (PP) composites with high flame retardancy and high thermal stability were required for automobile, electrical and electronic applications. Aluminum hydroxide (Al(OH)₃) and two hollow glass beads (HGB) were selected as fillers for polypropylene composite fabrication. The incorporation of 10 wt% HGB (iM30K) into the PP matrix leads to a 3.5% density reduction, and 10 wt% Al(OH)₃ increased the density by 5.4%. The cone calorimeter test (CCT) showed the lowest PHRR of 536.6 kW/m² and peak smoke production rate of 0.061 m²/s was recorded for 10 wt% HGB (iM30K) loading. The formulation with 10 wt% Al(OH)₃ loading had the lowest flammability; however, the Al(OH)₃ content was not sufficient for a consistent flame-resistant performance. The incorporation of HGB and Al(OH)₃ resulted in an enhancement of both tensile and flexural modulus; however, it was observed that the tensile, flexural, and impact strengths exhibited a decrement with an increase in the concentration of HGB or Al(OH)₃. Moreover, the thermogravimetric analysis (TGA) results indicated that at the same filler content, HGB (S60HS) filled PP composites have the highest thermal stability among the prepared composites. Highlights: Effects of HGB and Al(OH)₃ on flame retardancy and thermal stability of PP. Small size HGB (iM30K) exhibited superior smoke suppression performance. Effects of HGB on density reduction of PP based composites. Mechanical properties of HGB or Al(OH)₃ filled PP were investigated. The SEM images revealed the breakage and dispersion of HGB in the composites.