Extrusion of Polylactic acid (PLA) Nanocomposites using Liquid Feeding of Cellulose Nanocrystals

The purpose of this work was to prepare, polylactic acid (PLA) based nanocomposites with cellulose nanocrystals (CNCs) as reinforcement and triethyl citrate (TEC) as an additive using compounding extrusion. The final nanocomposites thermal- and mechanical properties, as well as the crystallinity, the transparency and the morphology were characterized. Prior the extrusion process, CNC suspensions were prepared by dispersing the CNCs in TEC and water:ethanol or TEC:ethanol mixtures to facilitate their dispersion and distribution in the final composite. The prepared suspensions were then liquid fed into the extruder. After the compounding process, the obtained nanocomposites were compression molded to sheets, from which test samples were cut. The feeding of the liquid suspensions resulted in nanocomposites with CNCs content 1 and 5 wt% and the TEC content varied between 4 and 17 wt%. The study showed that is possible to prepare nanocomposites using liquid feeding of CNCs, although it was found that the high liquid phase content in the suspensions together with a high feeding rate affected the final composition of the materials. It was also demonstrated that the presence of water in the feeding suspensions improves the CNCs dispersion in the nanocomposite matrix. OM and SEM microscopy showed the presence of CNCs agglomerations in the obtained nanocomposites although the materials produced with low content of CNCs resulted in better CNC dispersion and higher transparency. The nanocomposite containing 5 wt% CNCs and prepared by CNCs aqueous suspension presented increased tensile strength and E-modulus values respect to the reference material. The elongation was completely affected by the amount of plasticizer since values up to 295% for 17 wt% TEC content were detected. Finally, X-ray diffraction study revealed low crystallinity in almost all the obtained nanocomposites; only one material exhibited a crystalline structure since, in this case, CNCs were expected to act as nucleating agents, facilitating the crystallization of the PLA matrix.Validerat; 20140930 (global_studentproject_submitter