Effect of multi‐branched PDLA additives on the mechanical and thermomechanical properties of blends with PLLA

Stereocomplex formation between poly(l ‐lactic acid) (PLLA) and poly(d ‐lactic acid) (PDLA) in the melt state was investigated and altered via the addition of multi‐branched poly(d ‐lactide) (PDLA) additives. Two different multi‐branched PDLA additives, a 3‐arm and 4‐arm star‐shaped polymeric structure, were synthesized as potential heat resistance modifiers and incorporated into PLLA at 5, 10, and 20 (w/w) through melt blending. Mechanical and thermomechanical properties of these blends were compared with linear poly(l ‐lactide) (PLLA) as well as with blends formed by the addition of two linear PDLA analogs that had similar molecular weights to their branched counterparts. Blends with linear PDLA additives exhibited two distinct melting peaks at 170–180°C and 200–250°C which implied that two distinct crystalline domains were present, that of the homopolymer and that of the stereocomplex, the more stable crystalline structure formed by the co‐crystallization of both d ‐ and l ‐lactide enantiomers. In contrast, blends of PLLA with multi‐branched PDLA formed a single broad melting peak indicative of mainly formation of the stereocomplex, behavior which was confirmed by X‐ray diffraction (XRD) analysis. The heat deflection temperature determined by thermal mechanical analysis was improved for all blends compared to neat PLLA, with increases of up to180°C for 20% addition of the 3‐arm PLLA additive. Rheological properties of the blends, as characterized by complex viscosity (η*), remained stable over a wide temperature range. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42858.     

Stereocomplexation and morphology of enantiomeric poly(lactic acid)s with moderate‐molecular‐weight

The thermal behavior and spherulitic morphologies of poly(L ‐lactic acid) (PLLA)/poly(D ‐lactic acid) (PDLA) 1/1 blend with weight‐molecular‐weight of 10⁵ order, together with those of pure PLLA and PDLA, were investigated using differential scanning calorimetry and polarized optical microscopy. It was found that in the blend, stereocomplex crystallites could be formed exclusively or coexisted with homocrystallites depending on thermal history. Banded to nonbanded spherulitic morphological transition occurred for melt‐crystallized PLLA and PDLA, while the blend presented exclusively nonbanded spherulitic morphologies in the temperature range investigated. The spherulite growth of the blend occurred within a wider temperature range (≤180°C) compared with that of homopolymers (≤150°C), while the spherulite growth rates were comparable for both the blend and homopolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Isothermal crystallization and spherulite growth behavior of stereo multiblock poly(lactic acid)s: Effects of block length

Stereo multiblock poly(lactic acid)s (PLA)s and stereo diblock poly(lactic acid) (DB) with a wide variety of block length of 15.4–61.9 lactyl units are synthesized, and the effects of block length sequence on crystallization and spherulite growth behavior are investigated at different crystallization temperatures, in comparison with neat poly(L ‐lactide) (PLLA), poly(D ‐lactide) (PDLA), and PLLA/PDLA blend. Only stereocomplex crystallites as crystalline species are formed in the stereo multiblock PLAs and DB, irrespective of block length and crystallization temperature. The maximum crystallinities (33–61%), maximum radial growth rate of spherulites (0.7–56.7 μm min^?1), and equilibrium melting temperatures (182.0–216.5°C) increased with increasing block length but are less than those of PLLA/PDLA blend (67 %, 122.5 μm min^?1, and 246.0°C). The spherulite growth rates and overall crystallization rates of the stereo multiblock PLAs and DB increased with increasing block length and are lower than that of PLLA/PDLA blend. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of poly(l‐lactide)/poly(d‐lactide) block length ratio on crystallization behavior of star‐shaped asymmetric poly(l(d)‐lactide) stereoblock copolymers

Effect of Poly(l ‐lactide)/Poly(d ‐lactide) (PLLA/PDLA) block length ratio on the crystallization behavior of star‐shaped poly(propylene oxide) block poly(d ‐lactide) block poly (l ‐lactide) (PPO–PDLA–PLLA) stereoblock copolymers with molecular weights (M_n) ranging from 6.2 × 10⁴ to 1.4 × 10⁵ g mol^?1 was investigated. Crystallization behaviors were studied utilizing differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Only stereocomplex crystallites formed in isothermal crystallization at 140 to 156°C for all samples. On one hand, the overall crystallization rate decreased as PLLA/PDLA block length ratio increased. As PLLA/PDLA block length ratio increased from 7:7 to 28:7, the value of half time of crystallization (t_1/2) delayed form 2.85 to 5.31 min at 140°C. On the other hand, according to the Lauritzen–Hoffman theory, the fold‐surface energy (σ_e) was calculated. σ_e decreased from 77.7 to 73.3 erg/cm² with an increase in PLLA/PDLA block length ratio. Correspondingly increase in nucleation density was observed by the polarized optical microscope. Results indicated that the PLLA/PDLA block length ratio had a significant impact on the crystallization behavior of PPO–PDLA–PLLA copolymers. POLYM. ENG. SCI., 55:2534–2541, 2015. © 2015 Society of Plastics Engineers     

Poly(L‐lactide)/Poly(D‐lactide)/clay nanocomposites: Enhanced dispersion,crystallization, mechanical properties,and hydrolytic degradation

Poly(L ‐lactide) (PLLA)/poly(D ‐lactide) (PDLA)/clay nanocomposites are prepared via simple melt blending method at PDLA loadings from 5 to 20 wt%. Formation of the stereocomplex crystals in the nanocomposites is confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction (WAXD). The internal structure of the nanocomposites has been established by using WAXD and transmission electron microscope analyses. The dispersion of clay in the PLLA/PDLA/clay nanocomposites can be improved as a result of increased intensity of shear during melt blending. The overall crystallization rates are faster in the PLLA/PDLA/clay nanocomposites than in PLLA/clay nanocomposite and increase with an increase in the PDLA loading up to 10 wt%; however, the crystallization mechanism and crystal structure of these nanocomposites remain unchanged despite the presence of PDLA. The storage modulus has been apparently improved in the PLLA/PDLA/clay nanocomposites with respect to PLLA/clay nanocomposite. Moreover, it is found that the hydrolytic degradation rates have been enhanced obviously in the PLLA/PDLA/clay nanocomposites than in PLLA/clay nanocomposite. POLYM. ENG. SCI., 54:914–924, 2014. © 2013 Society of Plastics Engineers     

Stereocomplexed polylactides (Neo‐PLA) as high‐performance bio‐based polymers: their formation,properties, and application

Polymeric materials prepared from renewable natural resources are now being accepted as “bio‐based polymers”, because they are superior to the conventional petroleum‐based polymers in reducing the emission of carbon dioxide. Among them, poly(L ‐lactide) (PLLA) prepared by fermentation and polymerization is paid an immediate attention. Although PLLA exhibits a broad range of physico‐chemical properties, its thermal and mechanical properties are somewhat poorer for use as ordinary structural materials. For improving these inferior properties, a stereocomplex form consisting of PLLA and its enantiomer poly(D ‐lactide) (PDLA) has high potential because of showing high melting nature (230 °C). It can be formed by simple polymer blend of PLLA and PDLA or more easily with stereoblock polylactides (sb‐PLA) which are PLLA/PDLA block copolymers. These novel PLA polymers, named “Neo‐PLA”, can provide a wide range of properties that have never be attained with single PLLA. Neo‐PLA retains sustainability or bio‐based nature, because both monomers L ‐ and D ‐lactic acids are manufactured from starch by fermentation. Copyright © 2006 Society of Chemical Industry     

Unique crystallization behavior of poly(l-lactide)/poly(d-lactide) stereocomplex depending on initial melt states

A unique crystallization behavior of poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) stereocomplex was observed when a PLLA/PDLA blend (50/50) was subjected to specific melting conditions. PLLA and PDLA were synthesized by ring opening polymerization of l- or d-lactide using zinc lactate as catalyst. PLLA/PDLA blend was prepared through solution mixing followed by vacuum drying. The blend was melted under various melting conditions and subsequent crystallization behaviors were analyzed by using DSC, XRD, NMR and ESEM. Stereocomplex was exclusively formed from the 50/50 blend of PLLA and PDLA with relatively low molecular weights. Surprisingly, stereocomplex crystallization was distinctly depressed when higher melting temperature and longer melting period were applied, in contrast to homopolymer crystallization. Considering predominant interactions between PLLA and PDLA chains, a novel model of melting process is proposed to illustrate this behavior. It is assumed that PLLA and PDLA chain couples would preserve their interactions (melt memory) when the stereocomplex crystal melts smoothly, thus resulting in a heterogeneous melt which can easily crystallize. The melt could gradually become homogeneous at higher temperature or longer melting time. The strong interactions between PLLA and PDLA chain segments are randomly distributed in a homogeneous melt, thus preventing subsequent stereocomplex crystallization. However, the homogeneous melt can recover its ability to crystallize via dissolution in a solvent.     

Stereocomplex formation between enantiomeric PLA–PEG–PLA triblock copolymers: Characterization and use as protein‐delivery microparticulate carriers

Two enantiomeric triblock ABA copolymers composed of poly(L ‐lactide)–poly(ethylene glycol)–poly(L ‐lactide) (PLLA–PEG–PLLA) and poly(D ‐lactide)–poly(ethylene glycol)–poly(D ‐lactide) (PDLA–PEG–PDLA) were synthesized with two different middle‐block PEG chain lengths by ring‐opening polymerization of L ‐lactide and D ‐lactide in the presence of PEG, respectively. A pair of enantiomeric triblock copolymers were combined to form a stereocomplex by a solvent‐casting method. The triblock copolymers and their stereocomplexes were characterized by ¹H‐ and ¹³C‐NMR spectroscopy and gel permeation chromatography. Their crystalline structures and crystalline melting behaviors were analyzed by the wide‐angle X‐ray diffraction method and differential scanning calorimetry. The stereocomplex formed between a pair of enantiomeric triblock copolymers exhibited a higher crystalline melting temperature with a distinctive 3/1 helical crystalline structure. PLLA–PEG–PLLA and its stereocomplex with PDLA–PEG–PDLA were used to fabricate a series of microspheres encapsulating a model protein drug, bovine serum albumin (BSA). They were prepared by a double‐emulsion solvent‐evaporation method. The morphological aspects of the microspheres were characterized and BSA release profiles from them were investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1615–1623, 2000     

Non‐Isothermal Crystallization Behavior of Poly(L‐lactic acid) in the Presence of Various Additives

Summary: The effects of various additives: poly(D ‐lactic acid) (PDLA), talc, fullerene C₆₀, montmorillonite, and various polysaccharides, on the non‐isothermal crystallization behavior of poly(L ‐lactic acid) (PLLA), during both the heating of melt‐quenched films from room temperature, and the cooling of as‐cast films from the melt, was investigated. When the melt‐quenched PLLA films were heated from room temperature, the overall PLLA crystallization was accelerated upon addition of PDLA or the stereocomplex crystallites formed between PDLA and PLLA, the mixtures containing PDLA, and the mixture of talc and montmorillonite. No significant effects on the overall PLLA crystallization were observed for talc, C₆₀, montmorillonite, and the mixtures containing C₆₀. Such rapid completion of the overall PLLA crystallization upon addition of the aforementioned additives can be ascribed to the increased density (number per unit volume or area) of PLLA spherulites. When the as‐cast PLLA films were cooled from the melt, the overall PLLA crystallization completed rapidly, upon addition of PDLA, talc, C₆₀, montmorillonite, and their mixtures. Such rapid overall PLLA crystallization is attributable to the increased density of the PLLA spherulites and the higher nucleation temperature for PLLA crystallization. In contrast, the addition of various polysaccharides has no significant effect, or only a very small effect, on the overall PLLA crystallization during heating from room temperature or during cooling from the melt. This finding means that the polysaccharides can be utilized as low‐cost fillers for PLLA‐based materials, without disturbing the crystallization of the PLLA. The effect of additives in accelerating the overall PLLA crystallization during cooling from the melt, decreased in the following order: PDLA > talc > C₆₀ > montmorillonite > polysaccharides.

Polarization optical photomicrographs of pure PLLA, and the PLLA‐F film, with the fullerene additive, during cooling from the melt (Process IIB). Both of the photomicrographs were taken at 120 °C.     

Investigation of poly(lactide) stereocomplexation between linear poly(L‐lactide) and PDLA‐PEG‐PDLA tri‐block copolymer

In this study, stereocomplexed poly(lactide) (PLA) was investigated by blending linear poly(l ‐lactide) (PLLA) and tri‐block copolymer poly(d ‐lactide) ? (polyethylene glycol) ? poly(d ‐lactide) (PDLA‐PEG‐PDLA). Synthesized PDLA‐PEG‐PDLA tri‐block copolymers with different PEG and PDLA segment lengths were studied and their influences on the degree of sterecomplexation and non‐isothermal crystallization behaviour of the PLLA/PDLA‐PEG‐PDLA blend were examined in detail by DSC, XRD and polarized optical microscopy. A full stereocomplexation between PLLA and PDLA‐PEG_4k‐PDLA200 could be formed when the L/D ratio ranged from 7/3 to 5/5 without the presence of PLA homocrystals. The segmental mobility and length of both PEG and PDLA are the dominating factors in the critical D/L ratio to achieve full stereocomplexation and also for nucleation and spherulite growth during the non‐isothermal crystallization process. For fixed PEG segmental length, the stereocomplexed PLA formed showed first an increasing and then a decreasing melting temperature with increasing PDLA segments due to their intrinsic stiff mobility. Furthermore, the effect of PEG segmental mobility on PLA stereocomplexation was investigated. The results clearly showed that the crystallization temperature and melting temperature of stereocomplexed‐PLA kept increasing with increasing PEG segmental length, which was due to PEG soft mobility in the tri‐block copolymers. However, PEG was not favourable for nucleation but could facilitate the spherulite growth rate. Both the PDLA and PEG segmental lengths in the tri‐block copolymers affect the crystallinity of stereocomplexed‐PLA and the stereocomplexation formation process; they have a different influence on blends prepared by solution casting or the melting method. © 2015 Society of Chemical Industry     

Unique Homo-Crystallization and Melting Behavior of Poly(L-lactic acid): Influence of Stereocomplex with Varied Structure

Homo-crystallization and melting behavior of poly(L-lactic acid) (PLLA) with poly(D-lactic acid) (PDLA) (≤10 wt.%) was studied. The different thermal history had been applied to exert structural variation on stereocomplex (SC). The PLLA/PDLA blend showed different crystallization and melting behavior when cooled from 250°C or 200°C. Double melting peaks were observed after the blend was cooled from 250°C. SC annealing at different temperatures exhibited significant effect for melt-crystallization of PLLA. Influence of initial melting condition before cooling was also investigated. The cold crystallization of amorphous blend initially was studied and some novel results had been observed.     

Enhanced toughness and strength of poly (d‐lactide) by stereocomplexation with 5‐arm poly (l‐lactide)

The enhancement of mechanical properties were achieved by solution blending of poly(d ‐lactide) (PDLA) and 5‐arm poly(l ‐lactide) (5‐arm PLLA). Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5‐arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5‐arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5‐arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42857.     

Crystallisation and spherulite morphology of polylactide stereocomplex

In this study we investigated the crystallisation behaviours of stereocomplex crystals in poly(l ‐lactic acid)/poly(d ‐lactic acid) ( PLLA/PDLA) blends (LD blends) of various weight ratios. The crystallisation and melting behaviours were studied using DSC, and the crystal structure was analysed through wide‐angle X‐ray diffraction. The morphology of homocrystals and stereocomplex crystals in the blends was examined using a hot‐stage polarising microscope and a scanning electron microscope. The DSC results showed that homocrystals and stereocomplex crystals were present in all LD blends except that with 50 wt% PLLA/50 wt% PDLA; in this blend, only stereocomplex crystals were present. The regime II → III transition temperature of stereocomplex crystals in a Lauritzen–Hoffman plot of the LD blends was determined to be 165 °C. A concentric spherulite consisting of stereocomplex crystals and homocrystals formed under two‐step isothermal crystallisation conditions with three growth stages was observed. The confined spherulitic growth rate in the concentric spherulite and the unrestricted spherulitic growth rate in individual spherulites were also analysed. © 2018 Society of Chemical Industry     

Crystallinity and mechanical properties of optically pure polylactides and their blends

Nonisothermal solidifications of medical‐grade polylactides were conducted on compression molding sheets, resulting in a variety of crystalline forms and different amounts of crystallinity. Both optically pure polylactides, poly (L‐lactide) (PLLA) and poly (D‐lactide) (PDLA), were found to crystallize at a low melting temperature α crystalline form. PLLA/PDLA blends were found to yield both α homocrystallites and 50°C higher melting temperature stereocomplex crystallites. The effects of processing conditions and blend composition on crystal heterogeneity and degree of crystallinity were studied. Tensile tests reveal for these polylactides Young's modulus values of 3.5–4.2 GPa, strength values of 62–71 MPa, and elongations at break of 1–5%, depending on blend composition and crystallinity. POLYM. ENG. SCI. 45:745–753, 2005. © 2005 Society of Plastics Engineers     

Effect of the melting temperature on the crystallization behavior of a poly(l‐lactide)/poly(d‐lactide) equimolar mixture

The effect of the final melting temperature (T_f) on the crystallization of poly(l ‐lactide) (PLLA)/poly(d ‐lactide) (PDLA) was studied via a combination of differential scanning calorimetry, wide‐angle X‐ray scattering, polarized optical microscopy, and Fourier transform infrared (FTIR) spectroscopy. We observed that a residual stereocomplex (SC) crystal induced the formation of SC crystals during cooling from a T_f (230°C) just above the melting peak of the SC crystals. On cooling from a T_f (240°C) just above the endset temperature of SC crystal melting [T_m(S)(E)], the possible order structure and the strong interchain interaction promoted the preferential crystallization of SC crystals; this enhanced the formation of α crystals. During cooling from a T_f (≥250°C) far above T_m(S)(E), the crystallization peaks of α and SC crystals converged. The FTIR results indicated that the residual SC crystals, possible ordered structure, and interchain interactions in the melt might have been the key factors for the different crystallization of PLLA/PDLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43015.     

The toughening behavior of PLLA and its asymmetric PLLA/PDLA blends with lower optical purity

Linear poly(d ‐lactide) (PDLA) with various molecular weights is synthesized and incorporated into commercial poly(l ‐lactide) (PLLA) with different optical purities. And then, the crystallization, mechanical and thermal properties of the PLLA and PLLA/PDLA cast films are investigated. In the PLLA and PDLA/PLLA specimens with lower optical purity, few homochiral crystallites (HC) form in all the specimens and only a small amount of PLA stereocomplex crystallites (SC) are observed in the blends. The elongation at break of all the specimens is extraordinary high, >300%. Dynamic mechanical analyses indicate that the destruction temperature increases at first, and then depresses as enlarging the molecular weight of PDLA in these blends. For the PLLA and PLLA/PDLA with higher optical purity, more content of HC develops in neat PLLA, and both SC and HC produce in the PLLA/PDLA specimens. However, the strains of neat specimens and binary blends are much lower than that of specimens with lower optical purity. The specimens with higher optical purity exhibit higher destruction temperatures and lower loss factors. The high content of crystals (SC and HC) would act as the physical cross‐linking points and provide a key factor to impede the deformation of neat PLLA and binary blends during stretching, which should result in the fragile behavior of the PLLA and PLLA/PDLA blends with higher optical purity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44730.     

Properties of a poly(L‐lactic acid)/poly(D‐lactic acid) stereocomplex and the stereocomplex crosslinked with triallyl isocyanurate by irradiation

A poly(L ‐lactic acid) (PLLA)/poly(D ‐lactic acid) (PDLA) stereocomplex was prepared from an equimolar mixture of commercial‐grade PLLA and PDLA by melt processing for the first time. Crosslinked samples were obtained by the radiation‐induced crosslinking of the poly(lactic acid) (PLA) stereocomplex mixed with triallyl isocyanurate (TAIC). The PLA stereocomplex and its crosslinked samples were characterized by their gel behavior, thermal and mechanical measurements, and enzymatic degradation. The crosslinking density of the crosslinked stereocomplex was described as the gel fraction, which increased with the TAIC content and radiation dose. The maximum crosslinking density was obtained in crosslinked samples of PLA/3% TAIC and PLA/5% TAIC irradiated at doses higher than 30 kGy. The stable crosslinking networks that formed in the irradiated PLA/TAIC substantially suppressed the segmental mobility for the crystallization of single crystals as well as stereocomplex crystals. The crosslinking network also significantly improved the mechanical properties and inhibited the enzymatic degradation of crosslinked PLA/3% TAIC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Stereocomplexation of solvent‐cast poly(lactic acid) by addition of non‐solvents

Equimolar blends of poly(L ‐lactic acid) (PLLA) and poly(D ‐lactic acid) (PDLA) were obtained by solution casting from chloroform/methanol mixed solvents and analyzed using wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarizing optical microscopy. Chloroform and methanol are a solvent and non‐solvent, respectively, for poly(lactic acid). The WAXD and DSC results showed that stereocomplex crystallization between PLLA and PDLA occurred in addition to homo‐crystallization. On adding methanol to the casting solution, the stereocomplexation was gradually enhanced while the homo‐crystallization was suppressed. When a large amount of methanol was added, the homo‐crystallization was fully suppressed and the degree of stereocomplex crystallinity reached 90%. Similar results were obtained when another non‐solvent, hexane, was added to the casting solution in place of methanol. The effect of the addition of good and poor solvents such as tetrahydrofuran, ethanol, acetone and ethyl acetate was also studied. Copyright © 2011 Society of Chemical Industry     

Enhanced crystallization rate and mechanical properties of poly(l‐lactic acid) by stereocomplexation with four‐armed poly(ϵ‐caprolactone)‐block‐poly(d‐lactic acid) diblock copolymer

Poly(l ‐lactic acid) (PLLA) was blended with a series of four‐armed poly(? ‐caprolactone)‐block ‐poly(d ‐lactic acid) (4a‐PCL‐b ‐PDLA) copolymers in order to improve its crystallization rate and mechanical properties. It is found that a higher content of 4a‐PCL‐b ‐PDLA copolymer or longer PDLA block in the copolymer lead to faster crystallization of the blend, which is attributed to the formation of stereocomplex crystallites between PLLA matrix and PDLA blocks of the 4a‐PCL‐b ‐PDLA copolymers. Meanwhile, the PDLA block can improve the miscibility between flexible PCL phase and PLLA phase, which is beneficial for improving mechanical properties. The tensile results indicate that the 10% 4a‐PCL_5k‐b ‐PDLA_5k/PLLA blend has the largest elongation at break of about 72% because of the synergistic effects of stereocomplexation between enantiomeric PLAs, multi‐arm structure and plasticization of PCL blocks. It is concluded that well‐controlled composition and content of 4a‐PCL‐b ‐PDLA copolymer in PLLA blends can significantly improve the crystallization rate and mechanical properties of the PLLA matrix. © 2017 Society of Chemical Industry     

Melt preparation and nucleation efficiency of polylactide stereocomplex crystallites

A melt blending procedure was developed for the preparation of poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) stereocomplex crystallites dispersed in a PLLA matrix. All PLLA/PDLA blends were prepared in a batch melt mixer with ≥95% PLLA. Three PDLA homopolymers with a range of molecular weights were used as the minority (≤5%) component. The presence of the stereocomplex in the PLLA matrix was verified by differential scanning calorimetry (DSC) and optical microscopy. The effectiveness of the in situ formed stereocomplex crystallites for nucleating PLLA crystallization was evaluated using self-nucleation and non-isothermal DSC methods. With only 3 wt% of the 14 kg mol⁻¹ PDLA, nucleation efficiencies near 100% could be obtained. In addition, fast crystallization kinetics were observed in isothermal crystallization experiments at 140 °C. The stereocomplex crystallites were much more effective at enhancing the crystallization rate of PLLA compared to talc, a common nucleating agent.