Polymer nanocomposites with cellulose nanocrystals made by co‐precipitation

Abstract

A premixing method to produce polymer nanocomposites with cellulose nanocrystals (CNCs) is reported. This method involves the dissolution and dispersion of a polymer and CNCs in an organic solvent, co‐precipitation into water, drying of the resulting particles, and subsequent melt processing. The key aspect of the method is that it allows the kinetic trapping of well‐dispersed CNCs in the polymer. Although the nanocomposite must be dried before subsequent melt‐processing, the organic solvent can be removed by extraction in water and recycled, leaving only residual water in the composite, which is easily eliminated. This process presents numerous advantages compared with the time‐consuming solvent casting process, which often suffers from incomplete organic solvent evaporation. As a testbed, polyurethane (PU) composites with up to 30% of CNCs were prepared. These materials were either melt‐processed as produced or used as a masterbatch, i.e., they were diluted via melt‐mixing with neat polymer toward nanocomposites with lower filler content. All nanocomposites prepared using this approach had a homogeneous appearance. They displayed similar mechanical properties as the corresponding reference materials made by solvent casting, and significantly better properties than materials prepared by direct melt mixing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45648.

Functionally Graded Polyurethane/Cellulose Nanocrystal Composites

“…The increase of the Young's modulus from 4.3 MPa for the neat PU to 33 MPa for the 15% w/w PU/CNC nanocomposite was less pronounced than the increase of the storage modulus. This trend has previously been observed and may be attributable to the different thermal history of nanocomposites measured by DMA, which were cooled to −100 °C before the storage modulus was measured at 25 °C, and nanocomposites characterized by stress–strain measurements, which have never been cooled; as a result, the PU's soft segments may crystallize differently. In this work, the difference in crystallization might be more pronounced with increasing CNC content, as shown by the similar values for Young's and storage modulus for the neat polymer, and more than 100% difference for 15% w/w PU/CNC nanocomposites.…”

Chemical Modification of Reducing End‐Groups in Cellulose Nanocrystals

“…properties of the nanocomposite were found to gradually increase with the content of end-functionalized CNCs (2.5-15 wt %) and exceeded the reinforcement achieved with unmodified CNCs.F or instance,t he storage modulus E' (at 25 8 8C) increased from 1MPa for the unmodified rubber to 12 MPa upon incorporation of 10 wt %e nd-modified CNCs. Compared to that, the aggregation tendency of unmodified CNCs (especially at loadings > 7.5 wt %) resulted in weaker composites.W hile the covalent integration of end-functionalized CNCs clearly led to improved reinforcement, ac omparison with the results achieved with nanocomposites made with poly(vinyl alcohol)-adsorbed CNCs [158][159][160] suggests that there is further room for improvement. Afollow-up study by Linsg roup was published very recently,i nw hich the CNC REGs were modified with cysteamine (NH 2 CH 2 SH) via ar eductive amination.…”

“…Compared to that, the aggregation tendency of unmodified CNCs (especially at loadings >7.5 wt %) resulted in weaker composites. While the covalent integration of end‐functionalized CNCs clearly led to improved reinforcement, a comparison with the results achieved with nanocomposites made with poly(vinyl alcohol)‐adsorbed CNCs [158–160] suggests that there is further room for improvement. A follow‐up study by Lin's group was published very recently, in which the CNC REGs were modified with cysteamine (NH 2 CH 2 SH) via a reductive amination [90] .…”

Chemische Modifizierung der reduzierenden Enden von Cellulosenanokristallen

“…Demgegenüber resultierte die Aggregationstendenz der unmodifizierten CNCs, besonders bei einem Gehalt von >7.5 Gew.‐%, in schwächeren Kompositen. Während die kovalente Integration von endfunktionalisierten CNCs die Verstärkung deutlich verbesserte, zeigt ein Vergleich der Ergebnisse zu Nanokompositen mit Polyvinylalkohol‐adsorbierten CNCs, [158–160] dass immer noch Verbesserungspotential besteht [158–160] …”

“…Während die kovalente Integration von endfunktionalisierten CNCs die Verstärkung deutlich verbesserte,z eigt ein Vergleich der Ergebnisse zu Nanokompositen mit Polyvinylalkohol-adsorbierten CNCs, [158][159][160] dass immer noch Verbesserungspotential besteht. [158][159][160] Eine nachfolgende,k ürzlich verçffentlichte Studie von Lins Gruppe beschreibt die CNC-REG-Modifizierung mit Cystamin (NH 2 CH 2 SH) über eine reduktive Aminierung. [90] Die selektive Thiolierung wurde genutzt, um CNCs kovalent in ein thermoplastisches Elastomer…”