Fig. 3: Effect of the nanofibrillar network on nucleation, low-strain melt properties, and high-temperature dimensional stability.
a PCL crystallization half times, τ1/2, from isothermal DSC measurements at 45 °C after cooling from the melt at 10 °C/min, show that polymer crystallization is about six times faster in mPCL than in PCL, up to twenty-five times faster in mPCL/A than in PCL, and about nine times faster in mPCL/A than in the corresponding PCL/A reference blends at low A contents. b According to oscillatory shear rheometry cooling scans (strain 0.5%, frequency 1 rad/s, cooling rate 1 °C/min), both mPCL/A (blue) and PCL/A (orange) exhibit rheological onset temperatures for aggregate formation, Tagg, defined as the temperature at which the melt storage modulus, G’, and loss modulus, G”, start to deviate significantly from those of pure PCL on cooling, that are in excellent agreement with the onset temperatures of the corresponding DSC exotherms (Fig. S3). However, at low A contents, rubbery elastic behavior (G’ > G”, light blue area) is only observed for mPCL/A. The corresponding rubbery plateau extends from the PCL crystallization temperature up to the rheological softening temperature, Ts (G’ = G”). Within this temperature window, G’ is about an order of magnitude higher for mPCL/A than for PCL/A. c, d Ts and the effective plateau modulus (G’ at 60 °C) increase systematically with A content up to about 5 wt% A. e Dogbone specimens of mPCL/A (5 wt%) remain dimensionally stable for several hours at 95 °C, whereas specimens of PCL or PCL/A fail within a few seconds. f A thermoformed mPCL/A (5 wt%) cup retains its shape when filled with boiling water, although it becomes transparent, indicating a loss of crystallinity in the PCL matrix. However, cups prepared from PCL and PCL/A fail within a few seconds. (See Figs. S13–15 for details).
