Thermally activated shape memory behavior of melt‐mixed polyurethane/cellulose nanocrystal composites

Abstract

Building blocks made from renewable sources attract increasing attention for the design of new polymer systems. Recently, in this particular context, cellulose nanocrystals (CNCs) have gained great interest in both academic research and industry, mainly on account of their ability to reinforce range of polymer matrices and afford nanocomposites with attractive mechanical properties. The limited thermal stability of conventionally produced cellulose nanocrystals (CNCs) has, however, so far limited the range of polymers that could be used as basis for melt‐processed CNC nanocomposites. We herein show that a commercially accessible nanocrystal source, a particular grade of microcrystalline cellulose (MCC), can easily be converted into thermally stable CNCs by ultrasonication in phosphoric acid. A scalable melt‐mixing process was used to produce nanocomposites of these CNCs with a thermoplastic polyurethane (TPU) elastomer. A significant improvement of the room temperature storage modulus from 40 MPa (neat polymer) to 120 MPa (10% w/w CNC) was observed. The introduction of CNCs not only increased the stiffness of the polymer matrix, but also improved the shape memory properties of the nanocomposite. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45033.

Replication of annulus fibrosus through fabrication and characterization of polyurethane and cellulose nanocrystal composite scaffolds

“…As well, the minute variability within the mechanical properties obtained from tension testing led to the assumption of a high level of dispersion, as seen in the similar study by Rueda et al 52 Furthermore, research has shown the benefit of adding CNCs to a polymeric matrix for mechanical tunability. 40,53,54 Consequently, when tested dry, the samples demonstrated a drastic increase in modulus as shown in previous work, 40,[55][56][57] but significantly out of the accepted range. To mitigate this increase, the samples were swollen to reach the needed range of moduli, since the presence of CNCs in the composite increased the hydrophilicity, allowing for the absorption of water.…”

Tailoring the Properties of a Shape-Memory Polyurethane via Nanocomposite Formation and Nucleation

“…[47][48][49][50] CNCs have been used either as a switching element [51][52][53][54] or to reinforce polymers with intrinsic shape-memory effect, including a few polyurethanes. [55][56] We here report tailoring the properties of a commercially available [57][58][59][60] and widely investigated shape-memory poly(ester urethane) [61][62][63] containing crystallizable poly(1,4-butylene adipate) soft/switching segments and hard segments composed of 4,4-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol. By formulating nanocomposites with CNCs and/or influencing the crystallization of the polyester segments via the addition of a nucleating agent we were able to increase the tensile storage modulus from 150 MPa (neat polymer) to 572 MPa, improve the shape fixity at a specific fixing temperature from 47 to 75% and increase the fixing temperature from 10 to 25 ºC.…”

Polymer nanocomposites with cellulose nanocrystals made by co‐precipitation

“…Various processing schemes have been used to reinforce both polar and nonpolar polymer matrices with CNCs, such as direct melt‐mixing, solvent casting from a common solvent, or the template approach . The latter approach permits one to kinetically trap a percolating CNC scaffold by solvent‐exchange from an aqueous CNC dispersion to an organic medium and impregnating the resulting organogel with a solution of a polymer of choice, which typically results in nanocomposites with exceptional mechanical properties in comparison to the other processing approaches.…”