Immiscibility–miscibility phase transitions in blends of poly(L‐lactide) with poly(methyl methacrylate)

BACKGROUND: The nature of phase transitions and apparently irreversible phase homogenization upon heating in blends of biodegradable poly(L ‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were proven using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and ¹H NMR spectroscopy. The complex phase behaviour in this blend system is puzzling and is a matter of debate; this study attempts to clarify the true nature of the phase behaviour. RESULTS: A PMMA/PLLA blend is immiscible at ambient temperature but can become miscible upon heating to higher temperatures with an upper critical solution temperature (UCST) at 230 °C. The blends, upon rapid quenching from the UCST, can be frozen into a quasi‐miscible state. In this state, the interaction strength was determined to be χ₁₂ = ? 0.15 to ? 0.19, indicating relatively weak interactions between the PLLA ester and PMMA acrylic carbonyl groups. CONCLUSION: The absence of chemical exchange reactions above the UCST and phase reversibility back to the original phase separation morphology, assisted by solvent re‐dissolution, in the heat‐homogenized PLLA/PMMA blend was shown. Verification of UCST behaviour, phase diagrams and solvent‐assisted phase reversibility were experimentally demonstrated in PMMA/PLLA blends. Copyright © 2008 Society of Chemical Industry     

Increasing the compatibility of poly(l‐lactide)/poly(para‐dioxanone) blends through the addition of poly(para‐dioxanone‐co‐l‐lactide)

To modify the mechanical properties of a poly(l ‐lactide) (PLLA)/poly(para‐dioxanone) (PPDO) 85/15 blend, poly(para‐dioxanone‐co‐l ‐lactide) (PDOLLA) was used as a compatibilizer. The 85/15 PLLA/PPDO blends containing 1–5 wt % of the random copolymer PDOLLA were prepared by solution coprecipitation. Then, the thermal, morphological, and mechanical properties of the blends with different contents of PDOLLA were studied via differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile testing, respectively. The DSC result revealed that the addition of PDOLLA into the blends only slightly changed the thermal properties by inhibiting the crystallization degree of the poly(l ‐lactide) in the polymer blends. The SEM photos indicated that the addition of 3 wt % PDOLLA into the blend was ideal for making the interface between the PLLA and PPDO phases unclear. The tensile testing result demonstrated that the mechanical properties of the blends containing 3 wt % PDOLLA were much improved with a tensile strength of 48 MPa and a breaking elongation of 214%. Therefore, we concluded that the morphological and mechanical properties of the PLLA/PPDO 85/15 blends could be tailored by the addition of the PDOLLA as a compatibilizer and that the blend containing a proper content of PDOLLA had the potential to be used as a medical implant material. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41323.     

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

The crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, T_g, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Crystallization behavior of biodegradable amphiphilic poly(ethylene glycol)‐poly(L‐lactide) block copolymers

Poly(ethylene glycol)‐poly(L ‐lactide) diblock and triblock copolymers were prepared by ring‐opening polymerization of L ‐lactide with poly(ethylene glycol) methyl ether or with poly(ethylene glycol) in the presence of stannous octoate. Molecular weight, thermal properties, and crystalline structure of block copolymers were analyzed by ¹H‐NMR, FTIR, GPC, DSC, and wide‐angle X‐ray diffraction (WAXD). The composition of the block copolymer was found to be comparable to those of the reactants. Each block of the PEG–PLLA copolymer was phase separated at room temperature, as determined by DSC and WAXD. For the asymmetric block copolymers, the crystallization of one block influenced much the crystalline structure of the other block that was chemically connected to it. Time‐resolved WAXD analyses also showed the crystallization of the PLLA block became retarded due to the presence of the PEG block. According to the biodegradability test using the activated sludge, PEG–PLLA block copolymer degraded much faster than PLLA homopolymers of the same molecular weight. © 1999 John Wiley amp; Sons, Inc. J Appl Polym Sci 72: 341–348, 1999     

Synthesis and characterization of poly(L‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(L‐lactic acid) copolyesters

Random copolyester namely, poly(ethylene terephthalate‐co‐sebacate) (PETS), with relatively lower molecular weight was first synthesized, and then it was used as a macromonomer to initiate ring‐opening polymerization of l ‐lactide. ¹H NMR quantified composition and structure of triblock copolyesters [poly(l ‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(l ‐lactic acid)] (PLLA‐PETS‐PLLA). Molecular weights of copolyesters were also estimated from NMR spectra, and confirmed by GPC. Copolyesters exhibited different solubilities according to the actual content of PLLA units in the main chain. Copolymerization effected melting behaviors significantly because of the incorporation of PETS and PLLA blocks. Crystalline morphology showed a special pattern for specimen with certain composition. It was obvious that copolyesters with more content of aromatic units of PET exhibited increased values in both of stress and modulus in tensile test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Disclosing the crystallization behavior and morphology of poly(ϵ‐caprolactone) within poly(ϵ‐caprolactone)/poly(l‐lactide) blends

In this work, the effect of poly(l ‐lactide) (PLLA) components on the crystallization behavior and morphology of poly(?‐caprolactone) (PCL) within PCL/PLLA blends was investigated by polarized optical microscopy, DSC, SEM and AFM. Morphological results reveal that PCL forms banded spherulites in PCL/PLLA blends because the interaction between the two polymer components facilitates twisting of the PCL lamellae. Additionally, the average band spacing of PCL spherulites monotonically decreases with increasing PLLA content. With regard to the crystallization behaviors of PCL, the crystallization ability of PCL is depressed with increase of the PLLA content. However, it is interesting to observe that the growth rate of PCL spherulites is almost independent of the PLLA content while the overall isothermal crystallization rate of PCL within PCL/PLLA blends decreases first and then increases at a given crystallization temperature, indicating that the addition of PLLA components shows a weak effect on the growth rate of the PCL but mainly on the generation of nuclei. © 2018 Society of Chemical Industry     

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     

Casting solvent effect on crystallization behavior of poly(vinyl acetate)/poly(ethylene oxide) blends: DSC study

Poly(vinyl acetate) (PVAc)/poly(ethylene oxide) (PEO) blends were prepared by casting from either benzene or chloroform. The solvent effects on the crystallization behavior and thermodynamic properties of the blends were studied by the differential scanning calorimeter (DSC). Two grades of PEO with different molecular weights (PEO200 with M_w = 200,000 g/mol and PEO2 with M_n = 2000 g/mol) were used in this work. The thermal analysis revealed that the blends cast from either benzene or chloroform were miscible in the molten state. The crystallization of PEO in the benzene-cast blends was more easily suppressed than it was in the chloroform-cast blends. Furthermore, the benzene-cast blends showed a greater negative value of Flory-Huggins interaction parameter than those cast from chloroform in the PVAc/PEO200 poly-blend system. It was supposed that the benzene-cast blends had more homogeneous morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 411–421, 1997     

Poly(para‐dioxanone)/poly(D,L‐lactide) blends compatibilized with poly(D,L‐lactide‐co‐para‐dioxanone)

The effect of poly(D ,L ‐lactide‐co‐para‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the T_g was composition dependent; when 5% PLADO was added into blend, the T_g distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

The effect of ionic interaction on the miscibility and crystallization behaviors of poly(ethylene glycol)/poly(L‐lactic acid) blends

The effect of end groups (2NH₂) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH₂)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH₃, and 2CH₃)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH₂) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH₂) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH₂)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH₂)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

Compatibilizing effect of starch‐grafted‐poly(L‐lactide) on the poly(ε‐caprolactone)/starch composites

The poly(ε‐caprolactone) (PCL)/starch blends were prepared with a coextruder by using the starch grafted PLLA copolymer (St‐g‐PLLA) as compatibilizers. The thermal, mechanical, thermo‐mechanical, and morphological characterizations were performed to show the better performance of these blends compared with the virgin PCL/starch blend without the compatibilizer. Interfacial adhesion between PCL matrix and starch dispersion phases dominated by the compatibilizing effects of the St‐g‐PLLA copolymers was significantly improved. Mechanical and other physical properties were correlated with the compatibilizing effect of the St‐g‐PLLA copolymer. With the addition of starch acted as rigid filler, the Young's modulus of the PCL/starch blends with or without compatibilizer all increased, and the strength and elongation were decreased compared with pure PCL. Whereas when St‐g‐PLLA added into the blend, starch and PCL, the properties of the blends were improved markedly. The 50/50 composite of PCL/starch compatibilized by 10% St‐g‐PLLA gave a tensile strength of 16.6 MPa and Young's modulus of 996 MPa, respectively, vs. 8.0 MPa and 597 MPa, respectively, for the simple 50/50 blend of PCL/starch. At the same time, the storage modulus of compatibilized blends improved to 2940 MPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and Properties of Poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol)/Poly(L-lactic acid) Blend Membrane

A series of poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol) (PBLG-block-PEG)/poly(L-lactic acid) (PLLA) blend membranes were prepared by casting the polymer blend solution in chloroform. Surface morphologies of the PBLG-block-PEG/PLLA blend membranes were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PBLG-block-PEG/PLLA blend membranes were studied by thermogravimetric analysis (TGA), tensile tests, and contact angle testing. It was found that the introduction of PLLA could exert outstanding effects on the morphology and the properties of polypeptide copolymer membrane.     

Nanocomposites based on vermiculite clay and ternary blend of poly(L‐lactic acid), poly(methyl methacrylate), and poly(ethylene oxide)

Vermiculite (VMT) as clay was introduced into a ternary polymer blend composed of poly(L ‐lactic acid) (PLLA), poly(methyl methacrylate) (PMMA), and poly(ethylene oxide) (PEO), whose ternary miscibility was proven within low certain contents of PMMA and PEO in PLLA. VMT was incorporated to the ternary polymer blend as matrix after proper organic modification on the clay. The organically modified vermiculite (OVMT) shows good interaction and acceptable dispersion in the ternary polymer matrix without altering the crystal structures of PLLA/PEO constituents. The effect of OVMT addition was then analyzed in isothermal crystallization by using the Avrami kinetic analysis, and the addition of OVMT is evident in altering nucleation process of the polymer blend as well as the crystal perfection. The activation energy is much lowered by the addition of OVMT, as evident from the analysis; the overall crystallization kinetic rates are increased with the incorporation of OVMT. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (T_g) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while T_g and melting temperature (T_m) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High molecular weight poly(l-lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly(l-lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

Characterization of the mechanical and thermal properties and morphological behavior of biodegradable poly(L‐lactide)/poly(ε‐caprolactone) and poly(L‐lactide)/poly(butylene succinate‐co‐L‐lactate) polymeric blends

Two series of biodegradable polymer blends were prepared from combinations of poly(L ‐lactide) (PLLA) with poly(?‐caprolactone) (PCL) and poly(butylene succinate‐co‐L ‐lactate) (PBSL) in proportions of 100/0, 90/10, 80/20, and 70/30 (based on the weight percentage). Their mechanical properties were investigated and related to their morphologies. The thermal properties, Fourier transform infrared spectroscopy, and melt flow index analysis of the binary blends and virgin polymers were then evaluated. The addition of PCL and PBSL to PLLA reduced the tensile strength and Young's modulus, whereas the elongation at break and melt flow index increased. The stress–strain curve showed that the blending of PLLA with ductile PCL and PBSL improved the toughness and increased the thermal stability of the blended polymers. A morphological analysis of the PLLA and the PLLA blends revealed that all the PLLA/PCL and PLLA/PBSL blends were immiscible with the PCL and PBSL phases finely dispersed in the PLLA‐rich phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Miscibility and phase structure of binary blends of poly(L‐lactide) and poly(vinyl alcohol)

Blend films of poly(L ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA) were obtained by evaporation of hexafluoroisopropanol solutions of both components. The component interaction, crystallization behavior, and miscibility of these blends were studied by solid‐state NMR and other conventional methods, such as Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The existence of two series of isolated and constant glass‐transition temperatures (T_g's) independent of the blend composition indicates that PLLA and PVA are immiscible in the amorphous region. However, the DSC data still demonstrates that some degree of compatibility related to blend composition exists in both PLLA/atactic‐PVA (a‐PVA) and PLLA/syndiotactic‐PVA (s‐PVA) blend systems. Furthermore, the formation of interpolymer hydrogen bonding in the amorphous region, which is regarded as the driving force leading to some degree of component compatibility in these immiscible systems, is confirmed by FTIR and further analyzed by ¹³C solid‐state NMR analyses, especially for the blends with low PLLA contents. Although the crystallization kinetics of one component (especially PVA) were affected by another component, WAXD measurement shows that these blends still possess two isolated crystalline PLLA and PVA phases other than the so‐called cocrystalline phase. ¹³C solid‐state NMR analysis excludes the interpolymer hydrogen bonding in the crystalline region. The mechanical properties (tensile strength and elongation at break) of blend films are consistent with the immiscible but somewhat compatible nature of these blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 762–772, 2001     

Morphology,rheological, crystallization behavior,and mechanical properties of poly(L‐lactide)/ethylene‐co‐vinyl acetate blends with different VA contents

Poly(L‐lactide)/ethylene‐co‐vinyl acetate (PLLA/EVA) blends with different contents of Vinyl Acetate (VA) in EVA phase were prepared through melt blending process. Although the composition of the blends was invariant (70/30), different phase morphologies were observed, namely, sea‐island morphologies for the blends with VA contents of 7.5, 18, and 28 wt %, whereas approximate co‐continuous morphology for the blend with VA content of 40 wt % was observed. The interfacial interaction between PLLA and EVA was visualized by Fourier transform infrared and rheological measurements. The nonisothermal and isothermal crystallization behaviors of the blends were investigated by wide angle X‐ray diffraction, Differential scanning calorimetry, and polarization optical microscope. Post‐thermal treatment was applied to improve the crystalline structure of PLLA. The results show that all the samples are mainly in amorphous state during the injection molding process. However, annealing promotes the second crystallization of PLLA matrix, leading to the improvement of the crystalline structure. Especially, the effect of annealing on crystalline structure of PLLA matrix is greatly dependent on the VA content of EVA. As expected, addition of EVA results in the improvement of the ductility and fracture toughness of the blends. The decreased tensile modulus and tensile strength can be enhanced through annealing process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011