The elongation at break of untreated and treated PLA/CSP ecocomposites is shown in Fig. 5. The result shows that the elongation at break of both PLA/CSP ecocomposites decreased as the CSP content increased. This result was expected, because the addition of CSP reduced the chain mobility of PLA matrix and resulted in more rigid and brittle ecocomposites. The incorporation of wood flour, pine wood flour, and acorn powder in PLA ecocomposites showed a similar trend on the elongation at break [28–30]. Nevertheless, the treated PLA/CSP biocomposites with MA exhibit lower elongation at break compared to untreated PLA/CSP ecocomposites. The MA treatment enhanced the interfacial interaction and adhesion between CSP and PLA matrix. The stronger interfacial adhesion induced the restriction of PLA chain mobility and due to the reduction of flexibility.