3. Results and discussion
3.1. Morphology
Fig. 1 shows a SEM micrograph of CNF. The diameter of fibers was in the range of 5–80 nm with an average of 28 10 nm. The SEM micrographs of fractured surfaces of the PLA and its nanocomposites are presented in Fig. 2. The surface of PLA/CNF1 and PLA/CNF3 nanocomposites showed no significant differences compared to that of neat PLA. PLA/CNF5 had the roughest surface (Fig. 2D). This can be explained by higher loading of CNF resulting in aggregation
of nanofibers, leading to the reduced compatibility with the biopolymer. Generally, relatively good dispersion
was achieved in composites with low fiber contents (1 and 3 wt%).
The atomic force microscopy (AFM) technique is a powerful tool for studying surfaces and has been used to provide qualitative and quantitative information about biopolymers at the nanometer scale that are often inaccessible
by any other experimental techniques [29]. AFM was used to examine the actual surface characteristics of
the neat PLA and PLA/CNF nanocomposites. The surface model of different samples including neat PLA is depicted
in Fig. 3. Surface topographical evaluation of samples confirmed the overall results that were obtained by SEM
and mechanical tests. Neat PLA film has a smooth and uniform surface with an Rrms roughness of 74.5 nm. Addition
of CNF increased the Rrms roughness of samples by