Nanocomposites Made from Cellulose Nanocrystals and Tailored Segmented Polyurethanes

摘要

The effect of the addition of microcrystallinecellulose nanofibers into linear segmented polyurethanes(SPU) was investigated. The polymers were synthesizedwith 4,4-methylene-bisphenyldiisocyanate (MDI) and poly(tetramethyleneglycol) (PTMG) with 1,4-butanediol (BD) aschain extender. The nanocrystals were introduced duringthe PU polymerization, which resulted in cellulose nanofi-brils covalently linked to the polymer. The interactionsbetween the cellulose nanofibrils and the matrix lead tointeresting changes in the behavior of the PU, with the hardsegment (HS) phase being more affected by these interac-tions. SPUs with different contents of HS were synthesizedto better understand these effects (23 to 45 wt %). Thermal,thermo-mechanical and mechanical characterization of thenanocomposites were performed. In general, the nanocellu-lose favored the phase separation between the soft andhard domains generating an upward shift in the melting temperatures of the crystalline phases, an increase in theYoung's modulus and a decrease in deformation at break.Comparison of the unfilled polymer responses and that ofthe nanocomposites showed that by increasing cellulosecontent, increased dynamic storage and tensile modulus aswell as melting temperatures and enthalpy of melting ofthe soft domains can be achieved. Addition of cellulose dur-ing the polymerization essentially erased the potentialshape memory behavior originally displayed by some ofthe SPU. However, a sample prepared by adding the cellu-lose nanocrystals after the reaction showed that the me-chanical properties were still improved, while the shapememory behavior of the polymer was preserved.