Polymer blends with ordered distribution of conductive filler

This review highlight approaches to the formation of an ordered distribution of conductive filler in polymer blends. This distribution leads to a significant decrease of the percolation threshold in the polymer mixture, i.e. to a decrease in the critical concentration of the filler, at which the transition of the system from a non-conductive to a conductive state occurs. This improves the mechanical properties of the composition and its processability. It is shown that the ordered structure of the filler is formed in the polymer blend upon mixing the components in the melt under the action of three factors - thermodynamic (the ratio between the values of the interfacial tension of the filler-polymer A and filler-polymer B, as well as between polymers A and B), kinetic (the ratio between viscosities of polymer components A and B) and technological (the intensity and temperature of processing, as well as the order of introduction of a filler into a heterogeneous polymer matrix, which can enhance or suppress the effect of thermodynamic or kinetic factors). On the example of the works performed by the author on mixtures of thermoplastics filled with electrically conductive carbon fillers such as carbon black and carbon nanotubes, as well as a metal filler - dispersed iron, with the involvement of literature data on filled polymer blends, the influence of each of the factors on the formation of an ordered structure of the conducting phase in polymer blends is shown.

Deformation and Failure Mechanism of Particulate Filled and Short Fiber Reinforced Thermoplastics: Detection and Analysis by Acoustic Emission Testing

Acoustic emission, the detection of signals during deformation, is a frequently used method for the study of local deformation processes occurring in heterogeneous polymer systems. Most of these processes result in the evolution of elastic waves which can be detected by appropriate sensors. The analysis of several parameters characterizing the waves offers valuable information about the possible deformation mechanism. The acoustic emission testing of composites may yield very different number of signals from a few hundred to more than 100,000. This latter was proved to be affected mainly by particle size, interfacial adhesion and composition, but other factors, such as matrix modulus and specimen size, also influence it. Local deformation processes are claimed to have a strong effect on macroscopic properties. Indeed, a close correlation was found between the initiation stress of the dominating particle related process derived from acoustic emission testing and the tensile strength in both polypropylene (PP) and poly(lactic acid) (PLA) composites. However, in polyamide (PA)-based heterogeneous polymer systems, deformations related to the matrix dominated composite properties. Besides forecasting failure, the method makes possible the determination of the inherent strength of lignocellulosic fibers being around 40 MPa as well as the quantitative estimation of adhesion strength for composites in which interactions are created by mechanisms other than secondary forces. The proposed approach based on acoustic emission testing proved that in PP/CaCO3 composites, the strength of adhesion can be increased by ten times from about 100 mJ/m2 to almost 1000 mJ/m2 in the presence of a functionalized polymer.

Valorization and Mechanical Recycling of Heterogeneous Post-Consumer Polymer Waste through a Mechano-Chemical Process

In this paper, a sustainable strategy to valorize and recycle heterogeneous polymer-based post-consumer waste is proposed. This strategy is based on a high-energy mechano-chemical treatment and has been applied to a polyolefin-rich fraction, coded as FIL/S, deriving from household plastic waste collection. This processing, performed in a planetary ball mill, allowed us to obtain fine grinding and, consequently, to induce an intimate mixing of the different polymer fractions and contaminants composing the FIL/S, as demonstrated by SEM analysis. As a result, an improvement in the deformability of the treated material was obtained, recording values for elongation at the break which were two and half times higher than the neat FIL/S. Finally, the addition of small amounts of organic peroxide during mechano-chemical treatment was tested, determining a more homogeneous morphology and a further improvement in mechanical parameters.