Biopolymer-based Nanocomposites: Processing and Properties
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The aim of this study was to produce biopolymer-based nanocomposites using extrusion as an industrially adaptable manufacturing process, and to study how this production process influenced the structure and properties of the nanocomposites produced. Cellulose nanowhiskers (CNWs) were prepared and used as nanoreinforcement in two different biopolymers, polylactic acid (PLA) and cellulose acetate butyrate (CAB). The CNWs were added to PLA and CAB in order to improve the thermal and mechanical properties of these polymers. Two different preparation methods of CNWs were used; isolation by sulfuric acid hydrolysis and isolation by hydrochloric acid hydrolysis. Different feeding procedures were used and evaluated during compounding. The CNW suspension was either freeze-dried and dry-mixed with the polymer prior the extrusion, or fed as a suspension directly into the extruder during compounding. However, the CNW suspension required modification in order to prevent re-aggregation of the whiskers as the dispersing medium was removed and to uniformly disperse the whiskers in the polymer matrix. In order to improve the dispersion of the CNWs in the matrix, a surfactant and a water soluble polymer were used for PLA, and a plasticizer was used for CAB. No major improvements in mechanical or thermal properties were seen for the PLA/CNW nanocomposites, either because of degradation of the matrix or poor dispersion of the whiskers. The material system of CAB/CNW was more successful and showed great improvements in mechanical and thermal properties. This study demonstrated that it is possible to produce nanocomposites by pumping a suspension of CNWs into the extruder during compounding, but compatibility between the CNWs and the matrix is required.
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