Study about the Effect of Addition of Carbon Nanofibers on the Strain-Rate Sensitivity of Thermoplastic Polymer Matrix Nanocomposites Manufactured by Ultrasonic Processing

Abstract

Polymer nanocomposites based on polypropylene (PP) reinforced with carbon nanofibers (CNFs) at a fixed concentration of 0.5% w/w were prepared by precipitation from liquid solutions of PP and CNFs. Ultrasonic processing was used as the primary process for mixing both PP and CNFs in the the solvent, while mechanical stirring was also used as a control process to prepare similar samples. Thermogravimetric analysis (TGA) shows that the ultrasonic processing influences little on the thermal stability of the polymer material. Moreover, ultrasonically-processed PP shows higher tensile strength and better ductility, compared to those of the neat PP. Although the mechanically-processed PP has about 10% higher tensile strength than the ultrasonically-processed one, it is observed that there is a significant deterioration in its ductility due to the dissolution of calcium carbonate which is used as an additive for the neat PP. The advantage of significantly reduced material processing time, increased mixing efficiency, and increase in thermal stability and mechanical properties of ultrasonically-processed PPs indicated that the ultrasonic processing is relatively more effective and efficient mixing process compared to mechanical stirring for preparation of the polymer and its nanocomposite. Tensile tests were also conducted using quasi-static strain rates from 10-4 to 10-1 s-1 in order to obtain the tensile strength, elongation at fracture, and the elastic modulus of injection molded polymer and its nanocomposite. PP-CNF nanocomposites exhibited higher strain-rate sensitivity within the tested strain range, compared to the neat PP.Both the neat PP and PP-CNF nanocomposite exhibited strain-rate dependent material properties, showing an increase in tensile strength, and decrease in elongation with increasing strain rates.