Strain recovery and stress relaxation behaviour of multiblock copolymer blends physically cross-linked with PLA stereocomplexation

Soft, Formstable (Co)Polyester Blend Elastomers

“…Stretching and relaxation to different strains showed a small hysteresis of extension and recovery curves as well as a small permanent deformation in the first extension and very low further permanent deformation in subsequent experiments (see also Figure 5) [54]. This means that the blends behaved as semicrystalline polymers that show plastic deformation of crystals at the investigated strains [23] and highest ε b and form stability when the crystallinity is very low. R rec values determined from the experiment shown in Figure 4b and from manual experiments documented by photos (such as Figure 5 and Supplementary Materials Figure S8) were in the range of 66-85% for the blends already in the first cycle.…”

“…This is a bit higher than typically observed in physical networks such as multiblock copolymers (R rec = 55-85%) [55], thermoplastic polyurethanes (R rec~7 0%) [56]; (R rec = 47-80%) [57], poly(butylene 1,4-cyclohexanedicarboxylate) (R rec = 11-64%) [58], or poly(butylene terephthalate)/ethylene rubber blends (R rec~6 0%) [59]. In PCL-PLLA multiblock copolymers blended with PDLA, only at crystallinities below 6% and limited strains full form stability was found [23]. In most samples investigated here, this crystallinity was exceeded by far, except for B95-PLC-58-4.8-156, while B90-PLC-56-5.4-145 and B90-PLC-62-7.2-180 were close to this mark, and all of these samples showed low E and high ε b .…”

“…(1) The generation of physical netpoints in a PLA containing polymer system can exploit the strong tendency of poly(L-lactide) (PLLA) to preferentially form crystallites with poly(D-lactide) (PDLA), the so called stereocomplexes (SC) [19][20][21], due to the lower rate of isotactic PLA crystallization [22]. The fast crystallization, high melting temperature, and high mechanical stability of SCs facilitate reduction of absolute crystallinity (φ c ) and weight content of crystallites in comparison to homocrystallite-based systems without affecting the physical network stability [23]. Such stereocrystallites display, e.g., in PLLA/PDLA blends a lamellar triangular microstructure, with an edge length of~350 nm [24], though confinement effects may lead to smaller crystallite sizes [23].…”

“…The fast crystallization, high melting temperature, and high mechanical stability of SCs facilitate reduction of absolute crystallinity (φ c ) and weight content of crystallites in comparison to homocrystallite-based systems without affecting the physical network stability [23]. Such stereocrystallites display, e.g., in PLLA/PDLA blends a lamellar triangular microstructure, with an edge length of~350 nm [24], though confinement effects may lead to smaller crystallite sizes [23]. The formation of PLLA/PDLA stereocrystals can be analytically detected, e.g., by differential scanning calorimetry (DSC), as sufficiently large stereocrystallites show higher melting transitions ≥190 • C compared to the PLA homocrystallites (HC) (T m ≤ 180 • C), and by wide angle X-ray scattering (WAXS), as distinctive signals at 2 θ = 12 • , 21 • , and 24 • are observed that do not occur in the scattering of crystalline isotactic PLA [25].…”

Functionalizable coaxial PLLA/PDLA nanofibers with stereocomplexes at the internal interface

“…The rate of isotactic crystallization of PLA is in any case often quite slow [21]. Interestingly, the two isotactic polymers PLLA and PDLA crystallize together in socalled stereocomplexes (SC), which show a higher rate of crystallization as well as higher thermal transitions [22], mechanical stability [23] and hydrolytic resistance [24] than the isotactic crystals (homocrystallites, HC). Blends of PLLA-PDLA have been investigated in electrospinning [25][26][27] and also as composites [28][29][30].…”