Carbon nanofibers in polyurethane foams: Experimental evaluation of thermo-hygrometric and mechanical performance

Polymer nanocomposites synergistically combine the good thermal properties of the hosting polymer matrix with the high mechanical performance of the fillers, providing a new class of materials with superior properties. The present study aims to evaluate in a multidisciplinary way the enhancement in mechanical and thermal-hygrometric properties of low and medium density nanophased polyurethane (PUR) foams with either randomly oriented or aligned nanofibers as compared to the neat ones. To this aim, 1% weight of carbon nanofibers (CNFs) were homogeneously dispersed into polyol of PUR foam by an ultrasonic cavitation method. In parallel, a small amount of CNFs was functionalized in advance by a co-precipitation method so as to align them into the polymer matrix through an external low intensity magnetic field. SEM analyses were used to compare the microstructure of the neat and nanophased samples. Results have shown that the addition of carbon nanofibers in the foams products a closer structure with a more uniform size and shape. Moreover, functionalized CNFs play a significant role in regulating cells shape as well as strengthening cells walls. Mechanical test results also demonstrated that CNFs increase both strength and stiffness of the samples. The alignment of carbon nanofibers within medium density nanophased foams determines the highest mechanical properties. However, the more noticeable improvement in samples performance occurred in low density nanophased foams. Finally, carbon nanoparticles decrease the thermal conductivity and increase the resistance against water adsorption.