Cellulose nanocrystals as reinforcements in thermoplastic composites: processing routes as key
Topic(s) : Material science
Co-authors :
Mathieu BUGAUT (FRANCE), Nicolas LE MOIGNE (FRANCE), Marie-Claude HEUZEY , Pierre CARREAU (CANADA), Aurélie TAGUETAbstract :
Cellulose nanomaterials (CNM), such as cellulose nanocrystals (CNC), are expected to play a major role in the current environmental and societal transition towards a greater use of bioresources for materials applications. Due to their low density, high specific surface area and high Young's modulus, these nanomaterials have a great potential as sustainable, high-performance fillers for the development of materials with tunable rheological, thermo-mechanical, optical and barrier properties [1]. They are currently used mainly in paper manufacturing, packaging, membranes and bioengineering.
As with other nanoparticles, the dispersion of CNM in thermoplastic polymers remains a huge challenge for the development of high-performance polymer nanocomposites. In the literature, several processing methods have been studied to improve their dispersion and the mechanical properties of the nanocomposites, using solvent-based, melt processes and other more innovative processes such as chilled extrusion or wet compounding with various thermoplastic polymers as well as physico-chemical and processing aids [2], [3]. As shown in Figure 1, the different processes appear to have similar impact on mechanical improvements, and therefore potentially on the CNM dispersion, except for the combination of solvent and melt routes.
In this work, a common system to different preparation routes, based on thermoplastic polyvinyl alcohol (PVA) and CNC, is used to study the operating conditions and parameters which would make it possible to avoid the solvent-casting step. The CNC is dispersed in thermoplastic polymers by melt-processing, facilitating the preparation steps and avoiding the use of possibly harmful solvents.
In the first stage, different processing methods were compared on a laboratory scale: Solvent casting with and without a sonication step (SC and SC w/o S, respectively), melt mixing (MM) and solvent casting with a sonication step followed by melt mixing (SC-MM). The objective is identifying the key steps for obtaining a good dispersion of CNC that best improves the mechanical properties of the final composite. The impact of the processing method on the CNC dispersion in PVA is discussed, in particular by means of rheological, mechanical and microstructural analyses of PVA/CNC composites. As shown in Figure 2 , the sonication step appears to have a significant impact on increasing mechanical properties, whereas the melt mixing step does not have as much effect, and even appears to have a negative impact in the case of the combination of the solvent and melt routes. The second stage is to determine whether the process showing the most significant improvements can be transferred to a pilot scale, while focusing on the modelling and optimization of the industrially relevant extrusion processing.
As with other nanoparticles, the dispersion of CNM in thermoplastic polymers remains a huge challenge for the development of high-performance polymer nanocomposites. In the literature, several processing methods have been studied to improve their dispersion and the mechanical properties of the nanocomposites, using solvent-based, melt processes and other more innovative processes such as chilled extrusion or wet compounding with various thermoplastic polymers as well as physico-chemical and processing aids [2], [3]. As shown in Figure 1, the different processes appear to have similar impact on mechanical improvements, and therefore potentially on the CNM dispersion, except for the combination of solvent and melt routes.
In this work, a common system to different preparation routes, based on thermoplastic polyvinyl alcohol (PVA) and CNC, is used to study the operating conditions and parameters which would make it possible to avoid the solvent-casting step. The CNC is dispersed in thermoplastic polymers by melt-processing, facilitating the preparation steps and avoiding the use of possibly harmful solvents.
In the first stage, different processing methods were compared on a laboratory scale: Solvent casting with and without a sonication step (SC and SC w/o S, respectively), melt mixing (MM) and solvent casting with a sonication step followed by melt mixing (SC-MM). The objective is identifying the key steps for obtaining a good dispersion of CNC that best improves the mechanical properties of the final composite. The impact of the processing method on the CNC dispersion in PVA is discussed, in particular by means of rheological, mechanical and microstructural analyses of PVA/CNC composites. As shown in Figure 2 , the sonication step appears to have a significant impact on increasing mechanical properties, whereas the melt mixing step does not have as much effect, and even appears to have a negative impact in the case of the combination of the solvent and melt routes. The second stage is to determine whether the process showing the most significant improvements can be transferred to a pilot scale, while focusing on the modelling and optimization of the industrially relevant extrusion processing.