Nonisothermal crystallization kinetics of PLA/nanosized YVO₄ composites as a novel nucleating agent

Abstract

The influence of nanosized YVO 4 particles as a novel and efficient nucleating agent on the nonisothermal crystallization behaviors of poly(lactic acid) (PLA) was studied. A modified Avrami model was utilized to describe the nonisothermal crystallization kinetics of pure PLA and PLA nanocomposites. The differential isoconversional Friedmann formula was employed to calculate the effective activation energies (E X(t) ) of nonisothermal crystallization from the glass state. The results showed that modified Avrami methods describe the nonisothermal crystallization kinetics of pure PLA and PLA nanocomposites well. The crystallization rate of PLA/1 mass% YVO 4 was faster than that of pure PLA sample by factor 5 × 10 3 at a heating rate of 1 K min −1 . While the values of Lauritzen-Hoffman parameters (K g and U*) of the PLA/YVO 4 nanocomposites were lower than those of pure PLA, indicating the nucleation efficiency of nanosized YVO 4 particles for PLA. Scanning electron microscopy images reflect the uniform dispersion of 1 mass% YVO 4 in PLA matrix. Thermogravimetric analysis results revealed that the thermal degradation parameters are slightly lowered by 7 C on increasing the mass percentage of YVO 4 in the PLA nanocomposites.

Non‐isothermal crystallization kinetics of polypropylene/bamboo fiber/nano‐TiO2composites

“…The phenomenon was in line with the literature. [35] Furthermore, we could confirm from the obtained n values that nanosized TiO 2 particles had no influence on the nucleation mechanism of the PP matrix. A similar result has been reported for PP matrix with other inorganic nucleating agents.…”

“…In addition, it is worth mentioning that the value of E a is negative since the crystallization rate increases with the decrease of the crystallization temperature. El-Taweel et al [35] had reported that a large E a absolute favored the process due to the exothermic nature of the crystallization. As shown in Figure 7, the crystallization processes of PP/BF/nano-TiO 2 composites were a multistep processes and the E a values increased with increasing the X t .…”

“…The values of n for PP/BF/T0 composite ranged from 2.77 to 3.11 at different cooling rates, indicating a heterogeneous nucleation mechanism and the growth processes with three dimensional spherical. [31,33,35] However, the n values for PP/BF/T0.1, PP/BF/T0.4, and PP/BF/T0.8 composites were 3.10-3.32, 3.09-3.47, and 3.16-3.42, respectively. The difference in the n values could be attributed the confinement of the polymeric chain movement and hamper of the crystal growth owing to the addition of TiO 2 nanoparticles.…”

“…The values of 1/t 1/2 were further decreased when the TiO 2 nanoparticles loading concentration increased, which suggested that with the presence of more TiO 2 nanoparticles led to decrease in crystallization rate. [35] It was possibly due to the overloading nanoparticles with a large specific surface area and occurring the phenomenon of agglomeration. On the other hand, TiO 2 nanoparticles played an active role in inducing the interfacial bonding between BFs and matrix and inhibited crystal growth of matrix polymer.…”

“…However, it can also be applied to examine the initial stage of nonisothermal crystallization of polymers, based on assuming a constant crystallization temperature. The modified Avrami Equation ( 4) can be written as follows [35] :…”