The Effect of Uniaxial Extrusion on the Degree of Reinforcement of Nanocomposites Polyvinyl Chloride/Boron Nitride

Abstract

The influence of uniaxial extrusion on the structure, molecular characteristics, and properties of polymer/2D nanofiller nanocomposites is elucidated by example of polyvinyl chloride/boron nitride nanocomposites. The extrusion is found to cause a drastic (by 2.5 times) increase in statistical rigidity of polymer chains in the nanocomposite matrix determined by their characteristic ratio. The characteristic ratio for unoriented samples is less than that for a polymer precursor, but exceeds the values for oriented specimens. Nanofiller particles (or their aggregates) form a fractal network (“skeleton”) in the polymer matrix, whose dimension increases upon uniaxial extrusion. This effect leads to a linear reduction of the percolation index in the percolation model of reinforcement of nanocomposites, which significantly affects the degree of their reinforcement. When the dimension reaches its threshold of 2.8, the percolation index changes values from positive to negative values, meaning the transition from the “ant” to the “termite” limit. This yields an abrupt (to ~150) increase in the degree of reinforcement of polymer nanocomposites at low nanofiller contents. The characteristic ratio of polymer chains of the nanocomposite matrix is closely related to the aggregation level of the 2D nanofiller, which depends on the number of boron nitride slabs in a “package” (tactoid). The relative fraction of interfaces serving as reinforcing elements in a nanocomposite structure by analogy with nanofillers is also a function of statistical rigidity of polymer chains in the matrix and increases with the characteristic ratio. The theoretical estimates in the context of the percolation model of reinforcement reveal the prospects in the improvement of the properties of polymer/2D nanofiller nanocomposites.