Effect of different compatibilization routes on the mechanical, thermal and rheological properties of polypropylene/cellulose nanocrystals nanocomposites

The combination of cellulose nanocrystals (CNCs) with synthetic polymers like polypropylene (PP) offers the opportunity to create advanced nanocomposites with significant advantages in terms of mechanical properties, improved thermal stability, enhanced barrier properties, and sustainability. However, a major drawback for incorporation of CNCs in polymer matrices is their poor dispersion and incompatibility with industrial processing of many composites. This work aims to improve the dispersion of hydrophilic CNCs in a hydrophobic matrix using a method which could be adapted for the industrial level. CNCs are extracted from Ampelodesmos mauritanicus (El Diss plant) (CNCD) and incorporated in a polypropylene matrix using the masterbatch method. A first nanocomposite (PP/CNC-Gr) was prepared by adding maleic anhydride (MA) to a CNCD/PP suspension, while the second nanocomposite (PP/CNC-Co) was achieved by using a MA-grafted PP (PP-g-MA) as a third component. Concentrated masterbatch underwent solution casting followed by homogenization in a Brabender mixer. Mechanical properties comparison showed that PP/CNC-Co nanocomposites exhibited greater resistance relatively to PP/CNC-Gr nanocomposites. Moreover, PP/CNC-Co nanocomposites revealed an improved thermal stability and a higher complex viscosity, particularly with 3% of CNCD. Properties enhancements are attributed to the reaction between MA groups grafted to PP chains and hydroxyl groups of CNCDs, which enables an improved interfacial adhesion, leading to more continuous materials, as perceived from the increase in viscosity and morphology observation. On the other hand, MA reaction with PP chains and CNCD induced only a partial coverage of CNCDs during nanocrystals treatment, conferring relatively lower properties to PP/CNC-Gr nanocomposites.