Effects of Filler Size and Crystallinity on Thermal Performance and Flammability of Polymer Nanocomposites

The flammability of polymers can be inhibited by loading the polymeric matrix with a flame-retardant filler. The mixing quality of the filler in the matrix (filler-to-filler averaged distance) affects its overall performance; therefore, a detailed characterization of the composite can be valuable when a high filler loading is required. We studied the morphology of a composite, focusing on how the filler particle size and mixing quality effect polymer crystallinity. Small- and wide-angle x-ray scattering provided information on the degree of filler aggregation in the semicrystalline polymer matrix, which was complemented by an imaging study. This approach was applied to a commercial polymer loaded by various types of fillers (brominated molecules, brominated polymers, and crystalline particles) and to hybrid systems that include an additional second filler (e.g., antimony trioxide). For those hybrid systems, imaging and spectroscopic techniques were employed to distinguish between the fillers. We compared the thermal stability and the flammability of the various composites using thermogravimetry and micro combustion calorimetry, respectively, and found that the filler particle size and distribution and the polymer crystallinity play major roles. The sensitivity of thermogravimetry and micro combustion calorimetry to these parameters is discussed. These flame-retardant fillers, when incorporated into the polymer matrix, decrease flammability parameters by more than 60% compared to the flame-retardant-free matrix.