The role of PLLA-g-montmorillonite nanohybrids in the acceleration of the crystallization rate of a commercial PLA

Abstract

Employing the hydroxyl groups on the surface of Cloisite® 30B montmorillonite (Cl30B), the ring-opening polymerization of L-lactide was performed with a metal-free catalyst to yield a PLLA-g-Cl30B nanohybrid with low M n grafted PLLA chains (i.e., 9 kg mol −1 ). This nanohybrid was then melt mixed with PLA 4032D from NatureWorks, which is a slow-crystallizing PLA as it contains 2% D-isomers and has a high M n value (i.e., 123 kg mol −1 ). The samples were characterized by TEM, WAXS, SAXS, DSC and Polarized Light Optical Microscopy (PLOM) in order to study their crystallization kinetics in depth. The dispersion of the nanoclay was excellent and much better in the PLA/PLLA-g-Cl30B nanocomposites in comparison to PLA/Cl30B blends prepared as reference. In order to ascertain the role of the nanoclay, analogue PLA/PLLA blends without Cl30B were also prepared. The spherulitic crystallization kinetics from the melt was determined for all samples. The growth rate of neat PLA was accelerated approximately 3 times by incorporating the PLLA-g-Cl30B nanohybrid with an inorganic content of 5%. The overall crystallization kinetics from the glassy state of PLA was also accelerated in a similar way by the nanohybrid addition. Nevertheless, the PLA/ PLLA blends crystallized even faster indicating that the dominant effect that causes the acceleration of the crystallization of PLA is the plasticization of PLA by the low M n PLLA molecules. The changes in T g of PLA also support this explanation. In the case of the PLA/PLLA-g-Cl30B nanocomposites, even though the plasticizing effect of the PLLA chains still dominates, their action is counterbalanced by their tethering on one end, as they are grafted to the surface of the exfoliated clay nanoplatelets.

Poly(lactic acid)–thermoplastic poly(ether)urethane composites synergistically reinforced and toughened with short carbon fibers for three‐dimensional printing

“…Moreover, a small amount of d ‐lactic acid in the PLA seriously slows down the crystallization process. As a result, the neat PLA showed almost no crystallization peak upon cooling and no significant melting peak, as observed in Figure ; this was consistent with the experimental results of Li and Huneault and Zaldua et al . After the addition of a small amount of TPU, a sharp crystal peak and wide melting peak occurred; this indicated that the flexible chains of TPU were conducive to improving the kinetic capability and accelerating the crystal growth of PLA.…”

Synergistic effects of polyethylene glycol and organic montmorillonite on the plasticization and enhancement of poly(lactic acid)

“…Moreover, the OMMT lamellas were dispersed in PLA matrix well, more nucleation sites formed that contributed to give a high degree of overall crystallinity (X c ). At >3.0 wt % OMMT, the effect of aggregation of nanoclay was enhanced and the number of nucleation sites decreased, which was consistent with the XRD results.…”

Influence of Chain Topology (Cyclic versus Linear) on the Nucleation and Isothermal Crystallization of Poly(l-lactide) and Poly(d-lactide)

“…In order to calculate the value of the lamellar thickness (l), we have employed the approximation l = Xv L, where Xv is the crystal volume fraction (see the Supporting Information for the procedure employed to calculate the crystal volume fractions). 62 Using the lamellar thickness values and the experimental melting points of the isothermally crystallized samples, the Thompson-Gibbs equation can be applied. 59 Therefore, 0 is higher in cyclic PLAs than in their linear analogues and D or L stereoregularity has no influence on this thermal property.…”