Mechanical behaviour of poly(lactic acid)/cellulose nanocrystal nanocomposites: A comparative study between conventional tensile test and small punch test

Abstract

The use of nanocomposites is increasingly frequent as a way to improve the mechanical behaviour of polymers. In the specific case of poly(lactic acid) (PLA), the use of cellulose nanocrystals (CNC) as a reinforcing material is an interesting option, once the tendency of CNCs to agglomerate has been solved. One of the possible solutions to this problem is a superficial modification of CNC’s nanocrystals through a ring-opening polymerization (ROP) process. This work analyzes the use of CNC nanocrystals modified using ROP (mCNC) as a reinforcement of PLA. The mechanical properties of PLA/CNC nanocomposites are evaluated using tensile tests and small punch tests (SPT) on films prepared by extrusion calendering and post processed by compression molding. The addition of non-modified CNC promotes multiple crazing in PLA, increasing its ductility. mCNC leads to a more dispersed nanocomposite, a slight increase in the elastic modulus and a drastic decrease of crazing in tensile tests. The same tendency has been observed with SPT, and the applicability of this test in the prediction of the tensile modulus (E) of polymeric nanocomposites has been demonstrated. However, more work is needed to find the ideal SPT parameter to estimate the yield point.

Keywords

• biopolymers, biocomposites
• material testing
• poly (lactic acid) (pla)
• cellulose nanocrystals (cnc)
• small punch tests (spt)