Effects of epoxy resin crosslinking networks on stereocomplexation of poly(l‐lactic acid)/poly(d‐lactic acid) racemic blends

Abstract

In contrast to existing methods that add specific substances to poly(L-lactic acid)/poly(D-lactic acid) racemic blends to enhance stereocomplexation, in this study, a crosslinkable epoxy resin (EP) was introduced into a racemic blend. The results showed that, when the mass ratio of EP to racemic blend was 0.2:1 (EP:racemic blend = 0.2), regardless of the amount of diethylenetriamine (DETA) curing agent, homo-crystals in the racemic blend were essentially inhibited. With a fixed EP content, a 0.05:1 DETA to EP mass ratio resulted in a homogeneous poly(L-lactic acid)/poly(D-lactic acid)/EP/DETA mixture. Uniformly dispersed EP network promoted the stereocomplexation of the racemic blend from the melt, but delayed the lamellar thickening of the stereocomplex crystals during heating. Thus, the constrained chain diffusion caused by the uniformly dispersed EP network was likely responsible for these contradictory results. Introducing uniformly dispersed network into poly(L-lactic acid)/poly(D-lactic acid) racemic blends is presumably a promising approach for gaining more insight into poly(lactic acid) stereocomplexation.

Insights into Stereocomplexation of Poly(lactic acid) Materials: Evolution of Interaction between Enantiomeric Chains and Its Role in Conformational Transformation in Racemic Blends

“…One can find that the conformation transformation time (CTT) at T i near the melting point of HC (T m,H ) or T g is longer than that at T i around 120 °C (Figure 3e), which has been proven to be the fastest crystallization or nucleation temperature for PLA racemic blends with similar molecular weights. 10,24 Whether this is a coincidence or if there is a relationship between the structural evolutions of different scales requires further investigation. However, this was not the focus of this study.…”

“…However, when PLA racemic blends with higher molecular weight crystallize below the melting point of HC, the growths of SC and HC compete. , There have been many efforts to regulate the content of SC in PLA racemic blends, including specific processing paths, − chemical design of the PLA chains, − and adding extra substances. − Among them, the interaction between the PLA enantiomers − is considered one of the most important factors for SC enhancement. Presently, the interaction between opposite enantiomers of other polymers is also considered as the driving force for their stereocomplexation .…”

Synergistic effect of star‐shaped architecture and poly(ethylene glycol) moieties on poly(lactic acid) stereocomplex crystallization behaviors

“…PLA stereocomplex (scPLA) crystal formation subsequently grants higher melting temperature, 16 improved thermal resistance, 17 enhanced mechanical properties 18 and anti‐hydrolysis ability, 19 thus expanding the potential applications of PLA‐based materials 20–27 . It is found that the formation of stereocomplex crystals is selective and competitive, largely influenced by many parameters including molecular weight, 28,29 enantiomeric blending ratio, 30,31 preparation routes, 32,33 chain architectures 34 and the presence of additives 35,36 . While high molecular weight PLA confers greater mechanical properties, a low molecular weight is more conducive to encouraging stereocomplex crystallization to occur 37 …”

“…[20][21][22][23][24][25][26][27] It is found that the formation of stereocomplex crystals is selective and competitive, largely influenced by many parameters including molecular weight, 28,29 enantiomeric blending ratio, 30,31 preparation routes, 32,33 chain architectures 34 and the presence of additives. 35,36 While high molecular weight PLA confers greater mechanical properties, a low molecular weight is more conducive to encouraging stereocomplex crystallization to occur. 37 In recent years, a variety of star-shaped and branched PLAs have been reported, allowing an understanding about the effect of chain architecture on scPLA properties.…”