Enhanced Formation of Stereocomplex Crystallites of High Molecular Weight Poly(l-lactide)/Poly(d-lactide) Blends from Melt by Using Poly(ethylene glycol)

Abstract

Melt processing of polymers is preferable in industry. Unfortunately, for high molecular weight (M w) poly­(l-lactide)/poly­(d-lactide) (PLLA/PDLA) blends, exclusive formation of stereocomplex (sc) crystallites from the melt has never been achieved. We proposed a new and simple approach to enhance the melt crystallization of sc crystallites from high M w PLLA/PDLA by using poly­(ethylene glycol) (PEG). The crystallizability of the PLLA/PDLA blend is greatly enhanced by PEG during crystallization from the melt. The resulted crystalline structures depend on the M w and content of PEG, and the crystallinity of sc crystallites increases with increasing content or decreasing M w of PEG. More importantly, exclusive formation of sc crystallites is achieved in the blends with 10% PEG having M w values of 1000 or 2000 g mol–1. Polarized optical microscopy (POM) observation shows that the spherulitic growth rates of sc crystallites are accelerated. The results demonstrate that segmental mobility of polylactides (PLA) chains plays a dominant role on the formation of sc crystallites from melt and provide a simple way to prepare sc crystallites from high M w PLA by melt blending and enlarge the applications of PLA.

Crystallization modification of poly(lactide) by using nucleating agents and stereocomplexation

“…Accordingly, plasticizers and nucleating agents were both used to promote the stereocomplexation of PLA. Bao et al reported that the formation of SC crystallites from high-M w PLLA/PDLA blends from the melt by using poly(ethylene glycol) (PEG) as a plasticizer (93). PEG could increase the segmental mobility of the polymer chains which facilitated PDLA to confront with PLLA and enhances the interaction between PLLA and PDLA macromolecules.…”

Superior Performance of Fully Biobased Poly(lactide) via Stereocomplexation-Induced Phase Separation: Structure versus Property

“…The content of SC in the cold crystallization enthalpy is expected to be very low because the temperature range of 90−110°C is unfavorable for PLA stereocomplexation but favorable for the cold crystallization of HC-PLA. 10,37 Consequently, seldom HC crystals in the PLLA/PDLA blends were detected by WAXD ( Figure 1); meanwhile, the melt enthalpy of HC-PLA (H m-hc ) from DSC measurement is comparable to the corresponding cold crystallization enthalpy (H cc ). These results evidenced that the X sc should be dominantly from the previous melt compounding process rather than from the cold crystallization.…”

“…37 Good processability, heat-resistance and optical clarity of the PLLA/PDLA/ PMMA ternary blends were achieved without a discussion in mechanical behavior. 36 A SC crystallite network was detected in asymmetric PLLA/PDLA blends with 2−5 wt % of PDLA, 38 and the SC-PLA speeded up the crystallization of the PLLA matrix.…”

Stereocomplexation kinetics of enantiomeric poly(l-lactide)/poly(d-lactide) blends seeded by nanocrystalline cellulose

“…[6][7][8][9] It is known from previous study that the crystallization of stereocomplex PLA is generally faster than the homo-crystallization of neat PLLA and PDLA and it also possesses higher nucleation density. [18][19][20][21] Tsuji et al reported that the spherulitic growth, nucleation constant (K g ) and crystallization regime of neat SC-PLA. [15][16][17] Till now, researchers are still trying to achieve high(er) efficiency in the formation of SC crystallites, e.g., by plasticizing or copolymerization.…”

“…20,28 The NCC, notably at high content, have steric hindrance and hydrogen bonds with PLA molecules, 29 which are not beneficial to the crystal growth. According to crystallization theory of polymers, the crystal growth rate is mainly controlled by chain mobility that is associated with temperatures.…”