Crystallization Of Polylactide Research Articles

Entirely environment-friendly polylactide composites with outstanding heat resistance and superior mechanical performance fabricated by spunbond technology: Exploring the role of nanofibrillated stereocomplex polylactide crystals

This study aims at investigating the manufacturing and characterization of all-polylactide composites prepared by melt spunbond spinning technology. To do so, a series of asymmetric stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) was melt spun. To examine the impact of molecular structure of PDLA, the blends of linear PLLA, and low and high molecular weight as well as branched PDLAs, were subjected to a single step spunbond process. DSC thermograms of the samples showed two melting temperatures at around 170 °C and 210 °C, which were attributed to the melting of homo and stereocomplex crystals, respectively. The samples were spun at 190 °C, between the homo and stereocomplex crystals' melting temperatures, and at 230 °C, above the stereocomplex crystals' melting temperature. Morphology images showed the formation of fibers in the range of 40–50 μm. Shear rheological measurements revealed that the spun SC-PLA samples had a substantially higher viscosity and storage modulus in the low frequency region, and higher shear thinning behavior, compared to the non-spun samples. Extensional rheology measurements also showed that the spun samples demonstrated strain hardening behavior. Substantial enhancement of rheological properties was noted for the samples containing the branched and high molecular weight PDLA spun at 230 °C. After etching, the spun samples at 190 °C exhibited small spherical crystals with diameters in the range of 80–90 nm, whereas comparatively thin fibers in the size range of 60–70 nm were observed for the samples spun at 230 °C. Remarkable enhancements up to 100% and 60% was noted for the tensile modulus and strength, respectively, of the spun SC-PLA samples. The spun fibers also demonstrated a considerable reduction in boiling water and hot air shrinkage. The distinctive role of nanofibrillated stereocomplex crystals as a rheology modifier and a crystallization nucleating agent makes PLA more sustainable and paves the way for the fabricated all-PLA composites in applications requiring high heat resistance and superior mechanical performance. The present study unequivocally indicates a huge potential for the sustainable entirely all-PLA products manufactured by fiber in fiber and, indeed, unfolds unknown opportunities for PLA-based merchandises in future.

Insight into melting point depression of polylactide nanocomposites with acetylated chitin nanocrystals

Chitin nanocrystal (ChNC) was used to prepare fully biodegradable nanocomposites with polylactide (PLA). The nucleation and melting behavior of nanocomposites were studied with the objective to correlate PLA-ChNC affinity to PLA crystallization. The results disclose that the PLA nanocomposites with pristine ChNCs and the ones with acetylated ChNCs show completely different nucleation and melting behavior because the role of ChNCs is altered after acetylation. Pristine ChNC acts as inert filler, with weak nucleating activity, while acetylated ChNCs as anti-nucleation agent, restraining crystallization of PLA. Accordingly, the nanocomposites with acetylated ChNCs show melting point depression, with reduced nucleation capability. The recrystallization and self-nucleation, as well as the double-melting behaviors were then studied in terms of acetylation levels of ChNCs and annealing temperatures, in order to better understand the relations between two-phase affinity and PLA chain dynamics. This work provides interesting information around designing thermal properties of the ChNC-filled PLA nanocomposites.

Structure-Properties relationships in renewable composites based on polylactide filled with Tannin and Kraft Lignin - Crystallization and molecular mobility

Calorimetry and dielectric spectroscopy supplemented by polarized light microscopy, X-ray, infrared spectroscopy and scanning electron microscopy are employed here to assess the crystallization, interactions and molecular mobility in polylactide (PLA) filled with Tannin and kraft-Lignin prepared by melt extrusion. The direct and indirect effects of the fillers are investigated within two states of the polymer, namely, amorphous and semicrystalline (melt-crystallization annealed). The extremely slow and weak crystallization of PLA is enhanced by the fillers, mainly in the rate, via the combined effects of providing sites for crystallization and moderately enhancing polymer mobility (chains diffusion). Interestingly, the crystal structure and semicrystalline morphology were found altered in the composites as compared to the unfilled PLA. The effect on crystallization was found slightly stronger in PLA/Tannin, whereas the overall results were found in accordance to previously proposed models on the role of weak or absent interfacial interactions on promoting nucleation, such as in our case. Dielectric spectroscopy enabled the recording of the overall molecular dynamics mapping. Local dynamics was found to consist mainly of two individual processes. Regarding segmental mobility of PLA, the presence of tannin and lignin was found to impose moderate changes, namely, slight acceleration, narrowing of relaxation times range and suppression in fragility, however, not systematic changes in the calorimetric or dielectric strengths. The overall data could be rationalized exploiting known models involving as an indirect filler effect the increase in free volume. Despite the weak effects, Tannin was found again more effective and this seems to correlate with their smaller size and moderately better distribution as compared to lignin. The involvement of crystallization resulted in an expected blocking of ions transport, which, along the recorded potential for tuning semicrystalline morphology, make these materials interesting and worth to be further studied with regard to their permeation, mechanical and antioxidation performance.

Highly Tough and Thermally Stable Polylactide Blends Compatibilized with Glycidyl Methacrylate‐Grafted Polypropylene

AbstractTo attain eco‐friendly and sustainable polylactide (PLA) materials possessing highly enhanced toughness, thermal stability, and processability without significant loss in elastic modulus, for the first time, PLA‐dominant blends with 1–30 wt% glycidyl methacrylate‐grafted polypropylene (PPGMA) loadings are fabricated via an efficient masterbatch melt‐compounding process. For the purpose, PPGMA is fabricated via in situ grafting reaction of PP with GMA and styrene. The scanning electron microscope images reveal that PLA/PPGMA blends do not show recognizable phase‐separated domains, unlike immiscible PLA/PP blends. The Fourier‐transform infrared spectroscopic and melt‐rheological analyses support the presence of specific interactions between PLA and PPGMA as well as the compatibilizing effect of PPGMA‐g‐PLA formed during the melt‐compounding. The thermal analyses demonstrate that PPGMA component accelerates the crystallization of PLA in the blends and that the thermal decomposition temperatures of PLA/PPGMA blends are higher than those of neat PLA and PPGMA components. The dynamic mechanical analysis shows that a maximum storage modulus is attained for PLA‐dominant blend with 30 wt% PPGMA. Noticeably, the impact strength (≈305.6 J m−1) of PLA‐dominant blend with only 5 wt% PPGMA loading is almost three times higher than that (≈111.6 J m−1) of neat PLA and it is very comparable to the value (≈316.9 J m−1) of neat PP.

Effect of tungsten disulfide nanotubes on crystallization of polylactide under uniaxial deformation and annealing

Tungsten disulfide (WS2) nanotubes (NTs) are examined here as a filler for polylactide (PLA) for their ability to accelerate PLA crystallization and for their promising biocompatibility in relevant to biomedical applications of PLA-WS2 nanocomposites. In this work, we have studied the structural and thermal properties of PLA-WS2 nanocomposite films varying the concentration of WS2 NTs from 0 (neat PLA) to 0.6 wt%. The films were uniaxially drawn at 90 °C and annealed at the same temperature for 3 and 10 min. Using wide angle x-ray scattering, Raman spectroscopy and differential scanning calorimetry, we probed the effects of WS2 NT addition on the structure of the PLA films at various stages of processing (unstretched, stretching, annealing). We found that 0.6 wt% of WS2 induces the same level of crystallinity in as stretched PLA-WS2 as annealing in neat PLA for 10 min. These data provide useful insights into the role of WS2 NTs on the structural evolution of PLA-WS2 composites under uniaxial deformation, and extend their applicability to situations where fine tuning of PLA crystallinity is desirable.

Synergistic effect of plasticizer and nucleating agent on crystallization behavior of polylactide during fused filament fabrication

Polylactide (PLA) materials manufactured by fused filament fabrication (FFF) technique are usually in amorphous form and thereby exhibit poor mechanical properties and thermal resistance. Overcoming this issue requires a good knowledge of the crystallization behavior of PLA materials during the FFF process. In this work, a plasticizer (polyethylene glycol, PEG) and a nucleating agent (tetramethylene-dicarboxylic dibenzoyl-hydrazide, TMC-306), were added in PLA matrix, separately and synergistically, to tailor crystallization behavior of FFF-printed PLA parts. At a bed temperature of 60 °C, PEG played a stronger effect on crystallization behavior than the nucleating agent TMC and even the combination of TMC and PEG. This resulted in an increase of the crystallinity from 8% for both neat PLA and PLA/TMC samples to 18% for the samples containing PEG. With the increase of the bed temperature to 90 °C, TMC and PEG separately or synergistically had prominent effects on enhancing the crystallization ability of PLA during the FFF process, leading to the highly crystalline PLA parts with the crystallinities in the range of 30–40%. By means of wide angle X-ray diffraction and scanning electron microscopy measurements, shear-induced crystal structures were indentified at the filament surface as well as the weld interface. Nevertheless, the shear-induced effect had negligible influence on the final crystallinity of PLA parts. Instead, PLA parts with a high crystallinity can be attained, only when the material characteristics and the printing conditions are in favor of cold crystallization of PLA. The unique crystallization behavior of FFF-printed PLA materials offers guidelines for the fabrication of products with controlled crystallinity and hierarchical structures for specific applications.

Crystallization of polylactide-based green composites filled with oil-rich waste fillers

Polylactide is a highly demanded biopolymer, whose industrial application constantly increases. Its disadvantages such as brittleness and slow crystallization rate can be overcome by application of different additives. Because of environmental issues, using natural waste fillers as modifying agents for polylactide is especially interesting. In this study linseed cake, a byproduct of oil extraction from linseed, characterized by oil content of 0.9–39.8 wt.%, was added to polylactide to influence its crystallization behavior. The formation of the crystalline phase was studied by differential scanning calorimetry in isothermal and non-isothermal conditions and analyzed according to methods by Jeziorny, Ozawa, Mo and Avrami. The samples’ microstructures were observed using polarized light microscopy. The crystallization rate and Avrami exponent of samples crystallized in different conditions were evaluated. It was found that addition of 10 wt.% of linseed cake containing at least 17.7 wt.% oil notably changes the crystallization of polylactide, increasing its crystallinity and promoting the growth of crystallites.

Peculiar crystallization and viscoelastic properties of polylactide/polytetrafluoroethylene composites induced by in-situ formed 3D nanofiber network

This study comprehensively investigates the development of in-situ polylactide (PLA)/polytetrafluoroethylene (PTFE) nanofibrillated composites. PLA based composites containing 1, 3 and 5 wt% PTFE were prepared by melt compounding in a twin-screw extruder. SEM images demonstrated that interconnected PTFE nanofiber networks were generated with uniform distribution throughout the PLA matrix. Melt viscoelastic properties of nanofibrillated composites were significantly improved due to the PTFE nanofiber network. This increase was even more pronounced when the PTFE content was raised from 1 to 3 wt%, which could be considered as the percolation threshold network concentration range of PTFE fibers. However, the overall viscosity of composites was lower than that of PLA when the amount of PTFE was increased to 5 wt% due to the lubricating effect of PTFE nanofibers, which could ease PLA processing. With the increase in PTFE content, the transcrystallization of PLA around PTFE was improved and the crystallization half-time was remarkably decreased. Accordingly, the PLA crystallization kinetics was enhanced. The PLA/PTFE nanocomposite extrudates were also injection molded. SEM images of the skin layer of the injection molded nanocomposites exhibited an oriented structure in which PLA chains crystallized around the PTFE nanofibrils, whereas an amorphous structure was observed for the core layer. The crystalline structure and orientation, as well as thermal properties of the injection molded PLA/PTFE nanocomposites, were assessed by wide and small-angle X-ray scattering and differential scanning calorimetry, respectively.

Mechanical Properties, Crystallization and Biodegradation Behavior of the Polylactide/Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/Poly(butylene adipate-co-terephthalate) Blown Films

Polylactide (PLA), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), and poly(butylene adipate-co-terephthalate) (PBAT) ternary blends were prepared by extrusion blending. The biodegradable PLA/P(3HB-co-4HB)/PBAT films were successfully obtained by using blown films technique. Excellent stiffness-toughness balance was achieved for 55/10/35 PLA/P(3HB-co-4HB)/PBAT film. The tensile strength reached 33.0 MPa (MD) and 23.5 MPa (TD), the elongation at break exceeded 130 %, and tear strength exceeded 110 kN/m. The Young’s modulus as low as about 1800 MPa also met packaging applications. SEM observations revealed rough and long ligaments, indicating that the tear specimens were broken yieldingly. The addition of PBAT elastomers was the main reason for the improved toughness of the film. From DMA and SEM analysis, it was demonstrated that PLA, P(3HB-co-4HB), and PBAT were partially compatible. With increasing P(3HB-co-4HB) content, the melt and cold crystallization of PLA was promoted. The enzymatic degradation experiments indicated that the films had good biodegradability. These findings gave important implications for designing and manufacturing biodegradation package of high biological carbon content.

Effects of molecular weight and crystallizability of polylactide on the cellulose nanocrystal dispersion quality in their nanocomposites

This study investigated how cellulose nanocrystals (CNC) dispersion quality and its percolation network formation could be influenced when using polylactide (PLA) with various molecular weights and crystallizability. In this context, systematic rheological experiments were conducted on PLA/CNC nanocomposites prepared through solution casting method using dimethylformamide (DMF) as the solvent. It was found that lower CNC percolation concentrations could be obtained when a PLA matrix possesses lower molecular weight as the shorter chains and CNCs interpenetration could be facilitated during their dissolution in the solvent. On the other hand, the CNC percolation concentration was further lowered when the PLA with higher crystallizability was used. During the solvent evaporation step that occurred at 85 °C, the isothermal heterogeneous crystallization of PLA around the dispersed CNCs could prevent the driving force of the CNCs towards their re-agglomeration. Therefore, the finest CNC dispersion was appeared in the highly crystallizable low molecular weight PLA through which the rheological properties were dramatically improved and the thermal stability was significantly extended to higher temperatures. The crystallization behavior of the prepared nanocomposites was also analyzed using differential scanning calorimeter and X-ray diffractometer. The thermal degradation behavior of the PLA/CNC nanocomposites were examined through thermogravimetric and rheological analysis.

Effect of Organic Modifier and Clay Content on Non-Isothermal Cold Crystallization and Melting Behavior of Polylactide/Organovermiculite Nanocomposites.

In clay/polymer nanocomposites, the crystallization behavior and kinetics of the polymer can be affected by the presence of clay, its content and the degree of miscibility between the clay and the polymer matrix. The effect of two different organomodified vermiculites on the non-isothermal cold crystallization and melting behavior of polylactide (PLA) was studied by differential scanning calorimetry (DSC). In the presence of vermiculites, the cold crystallization of PLA occurred earlier, particularly for the highest content of the most miscible organovermiculite with PLA. The cold crystallinity of PLA decreased at low heating rates, notably at high organoclay loadings, and increased at high heating rates, especially at low vermiculite contents. According to the crystallization half-time, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP) approaches, the cold crystallization rate of PLA increased by incorporating vermiculites, with the effect being most noteworthy for the vermiculite showing better compatibility. The Mo model was successful in describing the non-isothermal cold crystallization kinetics of the PLA/vermiculite composites. The melting behavior was affected by the heating rate and the type and content of clay. The nucleating effect of the most compatible clay resulted in the less perfect crystallites. The activation energy was evaluated using the Kissinger and Takhor methods.

Ductility improvements of PLA-based binary and ternary blends with controlled morphology using PBAT, PBSA, and nanoclay

In this study, binary and ternary immiscible blends of polylactide (PLA) with poly[(butylene adipate)-co-terephthalate] (PBAT) and poly[(butylene succinate)-co-adipate] (PBSA) were prepared through an injection-molding (IM) process. Blend nanocomposites of PLA/PBAT/nanoclay were also prepared using a twin-screw extruder (TSE) followed by IM. An amorphous PLA (A-PLA), a semicrystalline PLA (SC-PLA), and their mixture were used as the matrix to investigate the matrix crystallization effect on blend morphology evolution and ductility enhancements. The results showed that in PLA/PBAT blends with 75/25 wt ratio, the increase in PLA crystallization capability caused finer and more homogenous blend morphology and hence the ductility increased significantly from around 5% to ~205%. In contrast, the ductility enhancements of co-continuous PLA/PBAT blends with 50/50 wt ratio became more profound when the PLA matrix was more amorphous. In PLA/PBSA blends, however, no ductility improvement was observed as the vitrification of PLA could hinder the PBSA crystallization which resulted in a non-uniform blend structure. In ternary blends, a matrix-core shell morphology was obtained and led to the improvements of the flexural strength and modulus. The use of nanoclay also significantly promoted the ductility of PLA/PBAT blends with 75/25 wt ratio, specifically in blends with A-PLA.

Transform poly (lactic acid) packaging film from brittleness to toughness using traditional industrial equipments

In order to produce the poly lactide (PLA) packaging film with excellent toughness, we adopted a new technological process: isothermal crystallization and then blowing film at the temperature lower than that completely melting of PLA crystals. The elongation at break of PLA film increased to around 67.50% and 104.83% in the transverse direction (TD) and machine direction (MD), respectively. Besides, the tensile strength increased to about 45.4 MPa and 78.0 MPa in TD and MD, respectively. The desirable balance between tension ductility and strength of film attributed to the introduced crystal-cross linked network. During blow molding, the crystallization fields and surrounding linked non-crystalline regions oriented and formed a network under the effect of inflating and pulling forces. The crystal network, bearing the external forces, induced the amorphous regions plastic deformation during stretching, and so improved the tension toughness and strength of PLA film.

Polylactide (PLA) and Its Blends with Poly(butylene succinate) (PBS): A Brief Review.

Polylactide (PLA), poly(butylene succinate) (PBS) and blends thereof have been researched in the last two decades due to their commercial availability and the upcoming requirements for using bio-based chemical building blocks. Blends consisting of PLA and PBS offer specific material properties. However, their thermodynamically favored biphasic composition often restricts their applications. Many approaches have been taken to achieve better compatibility for tailored and improved material properties. This review focuses on the modification of PLA/PBS blends in the timeframe from 2007 to early 2019. Firstly, neat polymers of PLA and PBS are introduced in respect of their origin, their chemical structure, thermal and mechanical properties. Secondly, recent studies for improving blend properties are reviewed mainly under the focus of the toughness modification using methods including simple blending, plasticization, reactive compatibilization, and copolymerization. Thirdly, we follow up by reviewing the effect of PBS addition, stereocomplexation, nucleation, and processing parameters on the crystallization of PLA. Next, the biodegradation and disintegration of PLA/PBS blends are summarized regarding the European and International Standards, influencing factors, and degradation mechanisms. Furthermore, the recycling and application potential of the blends are outlined.

Cellulose nanofibrils as reinforcing agents for PLA-based nanocomposites: An in situ approach

One-pot in situ polymerization approach was explored for the preparation of polylactide (PLA)-cellulose nanofibril (CNF) bio-nanocomposites. CNF were first prepared through enzymatic and mechanical treatment of bleached hardwood kraft pulp. The bio-nanocomposites- were then fabricated through ring opening polymerization (ROP) of l-lactide, in the presence of various amounts of fibrils. Molecular weight, thermal properties, surface morphology, mechanical and wettability properties of the PLA-CNF nanocomposites were evaluated. DSC analysis demonstrated the effect of CNF on crystallization and crystalline morphology of PLA. Improved modulus for the nanocomposites with respect to standard PLA was demonstrated, however, the differences in tensile stress were small probably due to the counteracting effects of reinforcement from CNF and the decreasing molecular weight as a function of CNF concentration. The absence of pulled-out fibers was assessed, highlighting the strong interface and covalent attachment of PLA chains on CNF surface. Finally, the covalent bonding of PLA chains on CNF surface was demonstrated by isolating the non-soluble part, consisting of PLA-grafted CNF, and characterization of this residue.

Crystallization behavior of polylactide matrix under the influence of nano‐magnetite

Iron oxide nanoparticle (Fe3O4) has gained remarkable research interest for various applications, from environmental to biological, because of its superparamagnetic properties and good biocompatibility. In this work, the nucleation effect of Fe3O4 in a polylactide (PLA) matrix under an influence of an alternating magnetic field was studied. The nanocomposite films that is, containing different concentrations of Fe3O4 (~8 nm) which were uniformly dispersed in the PLA matrix, were prepared via a solution casting method. The amplitude and frequency of the magnetic field impose great effects on the morphology and nucleation rate of PLA crystallization. Thermogravimetric analysis was used to study the thermal stability of Fe3O4/PLA and it showed that the thermal stability of Fe3O4/PLA was affected by the Fe3O4 content. Fourier transform infrared spectroscopy and X‐ray diffractometry indicated that Fe3O4 shows impeding effect to the crystallization of PLA. Based on the differential scanning calorimetry results, composite with 1% of Fe3O4 content could promote the crystallization of PLA but it would become an obstacle when 3% of Fe3O4 was added. The result of polarized optical microscopy also showed a good agreement that the incorporation of Fe3O4 could act as an effective nucleation regent to the composite film. POLYM. ENG. SCI., 59:608–615, 2019. © 2018 Society of Plastics Engineers

Preparation of Chitin Whisker and Effect to Crystallization of Polylactide

The aim of this study was to investigate the effect of chitin whisker (CW) to the crystallization of polylactide (PLA) nanocomposite films. CW which obtained from acidolysis reaction was compounded with PLA pellets into nanocomposite films by cast film extrusion. The morphology and crystallinity of CW were observed by TEM and XRD, illustrated that the dimension of whisker was affected by hydrolysis time. Increasing of hydrolysis time, the length of whisker was more regular with narrower distribution. Moreover, the crystallinity of whisker was obviously increased after acid hydrolysis. The nanocomposite film showed rough surface compared to pure PLA film due to some agglomeration of nanoparticles. However, CW and PLA were well-mixed with no phase separation. The introduction of 0.1 phr of CW decrease cold-crystallization temperature (Tcc) from about 121 °C to 118 °C and also increase the degree of crystallinity around 10%. There was no difference of thermal transition temperature between pure PLA and nanocomposite films with the addition of CW more than 0.1 phr which inspected by DSC. Despite the transition temperature express insignificantly different, the degree of crystallinity of nanocomposite was increase, indicating that chitin whisker would induce the crystallinity of PLA.

Crystallization kinetics of polylactide: Reactive plasticization and reprocessing effects

This work focused on the determination of crystallization kinetics of neat polylactide (PLA) and a plasticized grade of PLA obtained by reactive extrusion (pPLA), as a function of thermomechanical recycling. In particular, the materials were submitted to repeated extrusion and injection procedures to simulate recycling. Prior reprocessing, spherulitic growth rate determined by polarized light optical microscopy indicated that pPLA crystallized into much smaller spherulites as compared to PLA. This finding was explained by a lower nucleation energy barrier promoted by the plasticization of pPLA. Isothermal overall crystallization kinetics were determined by differential scanning calorimetry measurements. It was found that pPLA crystallized much faster than neat PLA due to the plasticization effect. With increasing the number of processing cycles up to 5, PLA crystallization rate gradually increased, while at the same time that of pPLA remained constant. This result was explained by more important degradation mechanisms in PLA as compared to pPLA that enhanced chain mobility, as shown by molecular weight measurements. Moreover, pPLA had a very high initial chain mobility that is maintained regardless of the number of processing cycles. However, the final crystallinity degree was lower in reprocessed pPLAs, as grafting and cross-linking reactions produced during reactive extrusion interrupt crystallizable linear crystallizable sequences and reduced the amount of crystals formed.

Effects of UV/Photo-Initiator Treatments on Enhancement of Crystallinity of Polylactide Films and Their Physicochemical Properties

Effects of UV/photo-initiator treatments on crystal formation and properties of polylactide (PLLA) films are investigated. Camphorquinone and riboflavin photo-initiator solutions in methanol are employed in the treatment of amorphous quenched PLLA films. Results from FTIR, ATR-FTIR, DSC, XRD, and SEM show evidence of crystalline domain formation dispersed throughout the film. 1H NMR and GPC results suggest that the molecular weights of the polymer slightly decrease after the treatment. This indicates that the treatment leads to a diffusion of the photo-initiators molecules through the film matrix, resulting in a low degree of PLLA chain scissions, and formation of carboxylic acid and hydroxyl polar end groups. This, in turn, induces PLLA crystallization, which imposes profound effects on surface wettability and physical and mechanical properties of the samples. The process can be applied in optimizing properties of PLLA films with shorter treatment times, compared to other methods, which is suitable for use in various fields; especially those that require specific characteristics like biomedical, packaging and environmental applications.

Ring opening precipitation polymerization for preparing polylactide particles with tunable size and porous structure and their application as chiral material

Polylactide (PLA) particles become increasingly important for practical applications as typical sustainable polymeric materials; however, their preparation still remains as a big challenge due to lacking effective preparation method directly starting from monomer lactide (LA) and lactic acid. In this study, we established an unprecedented strategy for preparing PLA particles in a high yield (>90 wt%) — precipitation polymerization of LA in ethyl acetate at 0 °C. The method provides PLA particles with narrowly distributed size. Phase separation occurred in the course of precipitation polymerization and endowed the PLA particles with interesting porous structures. The particles and their formation process were investigated by SEM, CD, XRD and DSC analyses. Noticeably, the size of PLA particles and the porous structure can be tuned through controlling the crystallization of PLA by adding D-LA in the polymerization system of L-LA. We further explored chiral recognition ability of the PLLA particles. The established strategy provides promising approaches for preparing novel PLA-based materials.