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Title: Continuous processing of cellulose nanofibril sheets through conventional single-screw extrusion

Source: ACS Applied Polymer Materials. 2(8): 3365-3377.

Author(s)El Awad Azrak, Sami M.; Costakis, William J.; Moon, Robert J.; Schueneman, Gregory T.; Youngblood, Jeffrey P.

Publication Year: 2020  View PDF »

Category: Journal Articles
Associated Research Project(s):   FPL-4707-3B

Abstract: Extrusion-based processes are one of the most widely used continuous polymer processing techniques because of their commercial availability, versatility, and cost-effective scal-ability. For these reasons, conventional single-screw extrusion was investigated and used for continuously processing mechanically fibrillated cellulose nanofibrils (CNFs) into wet sheets. A high shear mixing procedure was used to process highly loaded CNF pastes with up to ∼25 wt % solids, composed of ∼91 wt % CNF and ≤∼9 wt % of a processing aid like carboxymethyl cellulose (CMC), xanthan gum (XG), or anionic polyacrylamide (aPAM). Validation of the mixing procedure proved that highly loaded CNF/processing aid pastes can be processed in under 40 min. The higher solid loadings significantly reduced the preparation and drying time. The water-retention ability and stability of CNF suspensions containing different processing aids were assessed through centrifugation and zeta potential analysis. Extrusion of the prepared pastes showed that cohesive sheets could be produced continuously at output rates of 7.45 ± 0.47 kg/h (or 1.14 ± 0.072 dry) without the introduction of surface defects. Wet extrudates with an average width of ∼5 cm and thickness of 1.46 ± 0.05 mm were continuously processed, with the length limited only by the lack of collection rolls. A viscosity−shear rate dependence analysis linked extrudate homogeneity and reduced defects to a stronger Newtonian response for CNF/CMC pastes when compared to pure CNFs. On the other hand, CNF/XG and CNF/aPAM pastes experienced a much stronger shear thinning response, which correlated with a stronger appearance of observable aggregates and pinhole defects in the extrudates. Tensile testing of the pressed and heated CNF/CMC extrudates revealed equivalent mechanical properties to cast CNF films prepared through conventional solution casting. Lastly, preliminary calendering results for CNF/CMC extrudates showed that full consolidation can be achieved, thus providing a way to continuously dry and press the wet extrudates.

Keywords: Nanocellulose; extrusion; carboxymethyl-cellulose; CNF; torque rheometer

Publication Review Process: Formally Refereed

File size: 3,072 kb(s)

Date posted: 09/04/2020

This publication is also viewable on Treesearch:  view
RITS Product ID: 98795
Current FPL Scientists associated with this product (listed alphabetically)
Moon, Robert J.
Materials Research Engineer
Schueneman, Gregory
Supervisory Research Materials Engineer
 

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