Testing and Interface Modeling of the Mechanical and Damping Behavior of Nanocrystalline Cellulose Reinforced Bio-based Polyamides

Abstract

Bio-based polyamide 610 (PA610) reinforced with micro- and nanocellulose were manufactured by melt compounding followed by injection molding. The resulting composites had fiber sizes ranging from nanoscale to 100 μm at 2.5%, 5% and 10% fiber mass fractions. These composites were mechanically characterized by tensile tests followed by scanning electron microscopy to examine the tensile fracture surface. The primary focus of the work was the damping behavior of these nanocomposites, which was found to be substantial. Damping was characterized using the damping ratio extracted from the measured decay of mechanical vibrations. Cellulose nanocrystal-reinforced PA610 at 10% mass fraction was found to produce a 210% increase in damping ratio compared to control PA610. Larger fiber sizes and lower mass fractions resulted in smaller, but significant, increases in damping. Comparison to cellulose reinforced polypropylene composites showed that PA610/cellulose composites produced significantly greater relative damping. Additionally, since both cellulose and PA610 are hydrophilic materials, a study was made on the effects of moisture absorption on the damping. It was found that the pronounced effect of the filler on damping was diminished by absorbed moisture and did not return after removing moisture from the samples. The origin of the damping increase and the effects of moisture were discussed in the dissertation. A damping model was developed based on the mechanism of interfacial interaction in nanoscale particle reinforced composites. The model included the elasticity of the materials and the effects of interfacial adhesion hysteresis. The presence of hydrogen bonding at the interface between the particle and matrix and the large interfacial area due to the filler’s nano size were shown to be the main causes of the high damping enhancement. The influence of other parameters, such as interfacial distance and stiffness of the matrix materials were also discussed. The modeling work can be used as a guide in designing composites with good damping properties.