PLLA Matrix Research Articles

Introduction of stereocomplex crystallites of PLA for the solid and microcellular poly(lactide)/poly(butylene adipate-co-terephthalate) blends.

Solid and microcellular poly(l-lactide)/poly(butylene adipate-co-terephthalate) (PLLA/PBAT) blends with or without poly(d-lactide) (PDLA) were prepared via melt blending and batch foaming process with supercritical carbon dioxide, respectively. The introduction of PDLA on the rheological properties, crystallization behavior and dynamic mechanical properties of the PLLA matrix were investigated. The formed PLA stereocomplex between PLLA and PDLA enhanced the storage modulus and complex viscosity of PLLA/PBAT blends efficiently. Interestingly, the addition of 5 wt% or 10 wt% PDLA in the PLLA/PBAT blends was unfavorable for the PLLA crystallization behavior. The potential reason can be sc-PLA crystallites acting as the physical crosslinking points, which constrained the molecular mobility of the PLLA matrix and even blocked the nucleating effect of PBAT domains. Both the enhanced melt strength and decreased crystallinity of the PLLA matrix are favorable for the cell nucleation and growth and the gas adsorption, respectively. The designed partially foaming of PLLA/PBAT with or without PDLA was carried out to investigate the foaming mechanism. The final cell morphology of PLLA/PBAT foams exhibited typical open-cell structure mainly attributed to the soft immiscible PBAT phase as separated domains. With further addition of PDLA in the PLLA/PBAT blends, the microcellular morphology exhibited decreased average cell size and increased cell density. The sc-PLA crystallites networks in the PLLA matrix acted as cell nucleating agents, which meanwhile resisted the force of cell growth and then prevented the cell collapse.

Synthesis of Janus POSS star polymer and exploring its compatibilization behavior for PLLA/PCL polymer blends

Synthesis of hybrid hetero-arms star polymer with precisely defined arms distribution in three dimensional (3D) space is still a challenge. Herein, we have employed cubic polyhedral oligomeric silsesquioxane (POSS) nanoparticle as a scaffold to synthesize a biodegradable Janus POSS star polymer (oom-T8PLLA5PCL3), which contains an inorganic rigid POSS core, three poly(ε-caprolactone) (PCL) arms and five poly(l-lactide) (PLLA) arms on the POSS cage two sides, respectively. The chemical structure of oom-T8PLLA5PCL3 was confirmed by NMR, SEC, and FTIR spectra. As an example of application for the Janus POSS star polymer, oom-T8PLLA5PCL3 was used for the compatibilization of biodegradable PLLA/PCL (w/w = 70/30) blends. It was found that oom-T8PLLA5PCL3 could reduce the dispersed PCL phase size in PLLA matrix and enhance the properties of PLLA/PCL polymer blends, which was reflected in the increase of Izod impact strength and tensile performance of the polymer blends.

Poly(L-lactide) nanocomposites containing poly(D-lactide) grafted nanohydroxyapatite with improved interfacial adhesion via stereocomplexation.

Biodegradable organic-inorganic composites composed of polylactide (PLA) and hydroxyapatite (HA) are important bone repairing materials, while the dispersibility of nanoscaled HA in PLA and the interfacial adhesion between HA and PLA remained unsatisfactory. In this study, poly(D-lactide) (PDLA) oligomers with different molecular weights were grafted onto HA nanorods (HA-PDLA), and the HA-PDLA hybrids were mixed with poly(L-lactide) (PLLA). Dispersibility of HA-PDLA hybrids in PLLA matrix was investigated, and the formation of PDLA/PLLA stereocomplex at the interface of HA-PDLA and PLLA was studied by characterizations including crystallization, mechanical and thermal properties, taking PLLA grafted HA (HA-PLLA) and unmodified HA as comparisons. Surface grafting of PLLA or PDLA oligomers both significantly improved the dispersibility of HA nanorods in PLLA matrix. Benefiting from PDLA/PLLA stereocomplexation, HA-PDLA could increase the tensile strength and the elongation of resulting PLLA/HA nanocomposites more significantly than HA-PLLA. The interfacial interaction between HA-PDLA and PLLA matrix could be further strengthened by increasing the molecular weights of those grafted PDLA chains on HA, which was verified by changes in crystallization and glass transition behaviors. To sum up, the concept of using PDLA/PLLA stereocomplexation was feasible and effective in preparing PLA-based organic-inorganic nanocomposites targeting bone repairing.

Poly(l-lactic acid)-polyethylene glycol-poly(l-lactic acid) triblock copolymer: A novel macromolecular plasticizer to enhance the crystallization of poly(l-lactic acid)

Different from traditional small molecular plasticizers, poly(l-lactic acid) (PLLA)-polyethylene glycol (PEG)-PLLA triblock copolymers were synthesized by ring-opening polymerization of L-lactide on the end hydroxyls of PEG and blended with PLLA, to enhance the crystallization of PLLA. Non-isothermal and isothermal crystallization studies show that the triblock copolymer enhances the crystallization of PLLA due to the nucleation effect from PLLA segments and the plasticization effect from PEG segments, which strongly depends on the structure of copolymers. With shorter PLLA segment and longer PEG segment of the triblock copolymer, the glass transition temperature and cold crystallization temperature of the blends decrease, and the degree of crystallinity and spherulite growth rate increase owing to the higher content of PEG. However, triblock copolymers with relatively longer PLLA segment and shorter PEG segment show unique nucleation effects for PLLA, leading to the elevation of crystallization temperature of PLLA. The results confirm that the crystallization acceleration of PLLA can be ascribed to the nucleation and plasticization effect, and the plasticization effect is more significant. What’s more, the introduction of triblock copolymers improves the compatibility and durability due to the good interfacial interaction with PLLA matrix even at a high loading.

Crystallization and melting behavior of poly(L-lactic acid) modified with salicyloyl hydrazide derivative

This work evaluated the influence of a novel organic nucleating agent, salicyloyl hydrazide derivative (BS), on the crystallization and melting behavior of poly(L-lactic acid) (PLLA). Differential scanning calorimetry revealed that the incorporation of BS (0.2 to 3 wt %) significantly promoted the crystallization of PLLA on cooling at 1 °C/min. At BS content of 1.5 wt % in PLLA matrix, the highest effectiveness of crystallization process was observed, this result was further demonstrated by X-ray diffraction analysis of non-isothermal crystallization behavior at different cooling rate and measurements after isothermal crystallization. X-ray diffraction studies showed also that the addition of BS did not change the crystalline structure of PLLA. Based on the effect of the predetermined melting temperature on the crystallization behavior of PLLA/BS, the optimum process temperature of 190 °C was found. The comparative study on the melting behavior of PLLA/BS composite under different conditions (cooling rate, melting temperature) also confirmed the ability of BS to promote the nucleation of PLLA crystallization. The crystallization of PLLA/BS composite depends on the concentration of BS additive, crystallization temperature and time as well as heating rate.

Regulating performance of poly(L-lactic acid) by Addition of N, N′-Bis(Salicyloyl) p-phthalic acid dihydrazide

Within this work, the influence of a crystallization accelerator N, N′-bis(salicyloyl) p-phthalic acid dihydrazide (PAS) on the non-isothermal crystallization behavior, melting behavior, thermal stability, and light transmittance of poly(L-lactic acid) (PLLA) was investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), thermogravimetric analysis (TGA), and light transmittance meter. Comparative analysis of the non-isothermal crystallization behavior of the primary PLLA and PLLA/PAS samples revealed an important role of PAS in promoting the crystallization of PLLA in cooling. Additionally, the concentration of PAS and cooling rate also exhibited significant effect on the non-isothermal crystallization process, and the 3 wt% PAS causes the PLLA to have the highest the onset crystallization temperature and the crystallization peak temperature, and the largest non-isothermal crystallization enthalpy. However, the increase of cooling rate resulted in the decrease of crystal growth ability, weakening the crystallization of PLLA. The investigating on the melting behavior under different conditions further confirmed the crystallization promoting effect of PAS for PLLA, and the crystallization temperature, resulting from the different crystal growth rate, affected remarkably the melting behavior of PLLA/3%PAS sample. The addition of PAS could not change the thermal decomposition behavior of the primary PLLA, but decreased the onset decomposition temperature with an increase of PAS concentration in PLLA matrix. Similarly, the incorporation of PAS is unfavourable to the light transmittance of the primary PLLA.

Fully bio-based, highly toughened and heat-resistant poly(L-lactide) ternary blends via dynamic vulcanization with poly(D-lactide) and unsaturated bioelastomer

Inherent brittleness and low heat resistance are the two major obstacles that hinder the wide applications of poly(L-lactide) (PLLA). In this study, we report a fully bio-based, highly toughened and heat-resistant PLLA ternary blend, which was prepared by dynamic vulcanization of PLLA with poly(D-lactide) (PDLA) and an unsaturated bioelastomer (UBE). The results indicated that during dynamic vulcanization PDLA cocrystallized with PLLA to form stereocomplex (SC) crystallites, which not only enhanced the molecular entanglement but also accelerated the crystallization rate of PLLA matrix. With increase in the content of PDLA, the matrix molecular entanglement increased while phase-separation was enhanced, which enabled the impact strength to increase first and then decrease. The ternary blends containing 10 wt.% PDLA showed the highest impact strength. The presence of SC crystallites makes it possible to achieve a fully sustainable PLLA/VUB/PDLA ternary blend with highly crystalline matrix under conventional injection molding, due to the high nucleation efficiency of SC towards crystallization of PLLA. The highly crystalline ternary blend showed excellent heat resistance and better impact toughness than high impact polystyrene.

Design of gefitinib-loaded poly (l-lactic acid) microspheres via a supercritical anti-solvent process for dry powder inhalation

To develop a safer, more stable and potent formulation of gefitinib (GFB), micro-spheres of GFB encapsulated into poly (l-lactic acid) (PLLA) have been prepared by supercritical anti-solvent (SAS) technology in this study. Operating factors were optimized using a selected OA16 (45) orthogonal array design, and the properties of the raw material and SAS processed samples were characterized by different methods The results show that the GFB-loaded PLLA particles prepared were spherical, having a smaller and narrower particle size compared with raw GFB. The optimal GFB-loaded PLLA sample was prepared with less aggregation, highest GFB loading (15.82%) and smaller size (D50=2.48μm, which meets the size of dry powder inhalers). The results of XRD and DSC indicate that GFB is encapsulated into PLLA matrix in a polymorphic form different from raw GFB. FT-IR results show that the chemical structure of GFB does not change after the SAS process. The results of in vitro release show that the optimal sample release was slower compared with raw GFB particles. Moreover, the results of in vitro anti-cancer trials show that the optimal sample had a higher cytotoxicity than raw GFB. After blending with sieved lactose, the flowability and aerosolization performance of the optimal sample for DPI were improved, with angle of repose, emitted dose and fine particles fractions from 38.4° to 23°, 63.21% to >90%, 23.37% to >30%, respectively.

Emulsion based microencapsulation of proteins in poly(L-lactic acid) films and membranes for the controlled release of drugs

The aim of this study was to develop micro- or macro-porous substrates of poly(L-lactic acid) (PLLA) for the sustained release of water-soluble proteins. A model protein, bovine serum albumin (BSA), was incorporated into the hydrophobous PLLA matrix by emulsifying an aqueous BSA solution into an organic PLLA solution. The work focused on the effect of the fabrication procedure on substrates' microstructure and protein delivery kinetics. The films were prepared by solvent casting or freeze-extraction, after which the protein release profiles from both matrices were compared. A homogeneous distribution of BSA in the PLLA-films and membranes was obtained. In vitro release of the protein from the freeze-extraction membranes was more significant than the release from the solvent cast films. BSA was found to be released from the freeze-extraction membranes in two stages: an initial fast release followed by a sustained release. The release from the solvent cast films was more moderated and accompanied by the polymer degradation.These materials can find applications in wound healing by local delivery of proteins known to have a positive effect on the regeneration of basal lamina. They can also be used to produce macroporous scaffolds able to deliver growth factors during bone or cartilage regeneration.

Shape memory polymers with interconnected nanopores and high mechanical strength

ABSTRACTThe fabrication of shape memory polymers with both interconnected nanopores and high mechanical strength is challenging. In this work, porous shape memory polymers (PSMPs) were prepared based on the combination of crystallization and phase separation in a ternary blend of poly(l‐lactic acid)/polyvinyl acetate/poly(ethylene oxide) (i.e., PLLA/PVAc/PEO). The phase separation between the PLLA and PVAc/PEO resulted in bicontinuous structures in microscale including a PLLA‐rich phase and a mixed PVAc/PEO phase. On one hand, the continuous PLLA‐rich phase contributed to the high mechanical strength and shape memory performance, in which tiny crystals and amorphous matrix of PLLA act as the shape fixed phase and reversible phase, respectively. On the other hand, the crystallization of PEO in the miscible PVAc/PEO blend produced submicrometer bicontinuous structures. The interconnected nanopores have been obtained by selective etching of the PEO. Our strategy opens a new avenue for fabricating PSMPs with both interpenetrated channels and high strength. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 125–130

Graphene Oxide-Graft-Poly(l-lactide)/Poly(l-lactide) Nanocomposites: Mechanical and Thermal Properties.

The surface modification of graphene sheets with polymer chains may greatly hinder its aggregation and improve its phase compatibility with a polymer matrix. In this work, poly(l-lactic acid)-grafted graphene oxide (GO-g-PLLA) was prepared via a simple condensation polymerization method, realizing its dispersion well in organic solvents, which demonstrated that the surface of GO changed from hydrophilic to hydrophobic. GO-g-PLLA can disperse homogeneously in the PLLA matrix, and the tensile test showed that the mechanical properties of GO-g-PLLA/PLLA were much better than that of GO/PLLA; compared with GO, only 3% GO-g-PLLA content can realize a 37.8% increase in the tensile strength for their PLLA composites. Furthermore, the differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results demonstrated that GO-g-PLLA shows a nucleating agent effect and can promote the crystallization of PLLA.

Effect of MIL‐53 (Al) MOF particles on the chain mobility and crystallization of poly(L‐lactic acid)

ABSTRACTPolymer‐filler interactions significantly influence morphology, functionality, and various desirable properties of mixed matrix membranes (MMMs). In this study, chain mobility and crystallization of poly(l‐lactic acid) (PLLA) MMM films prepared by solvent casting PLLA with 1, 5, 10, and 20% wt/wt of MIL‐53(Al) metal organic framework (MOF) were evaluated. The fabricated MMMs were characterized using differential scanning calorimetry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Differential scanning calorimetry studies indicated that the addition of MOF particles in the PLLA matrix reduces the polymeric chain mobility, which affects the crystallization process. The percent crystallinity of neat PLLA was found to decrease from 4% in neat PLLA to completely amorphous structures in PLLA‐10% and PLLA‐20% MMMs, as observed in the second heating cycle. Fourier transform infrared spectroscopy data supports these observations. Thermogravimetric analysis results showed that PLLA‐MOF films are thermally less stable than neat PLLA suggesting that MOF particles act as a depolymerization catalyst for PLLA. Partial agglomeration of MOF particles was observed in the samples using scanning electron microscopy studies. This study indicates strong PLLA‐MIL‐53(Al) MOF interactions. In addition, this study also provides insight into the effect of MOF particles on the segmental mobility and morphology of PLLA‐MIL‐53 (Al) composite films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45690.

Biocomposites based on poly(lactic acid) and superabsorbent sodium polyacrylate

ABSTRACTIn this research work, biocomposites based on crosslinked particles of sodium polyacrylate, commonly used as superabsorbent polymer, and poly(l‐lactic acid) (PLLA) were developed to obtain superabsorbent thermoplastic products, and to elucidate the role of this type of filler (i.e., polymeric crosslinked particles) on their overall physical‐mechanical behavior. Samples prepared by melt‐blending components with different ratios showed a biphasic system with a uniform distribution of particles, with diameters up to about 50 μm, within the PLLA polymeric matrix. The polymeric biphasic system, coded PLASA, that is, superabsorbent PLLA, showed excellent swelling properties, demonstrating that crosslinked particles retain their superabsorbent ability even if distributed in a thermoplastic polymeric matrix. The thermal characteristics of the biocomposites evidenced enhanced thermal stability in comparison with neat PLLA and also mechanical properties are markedly modified by addition of crosslinked particles, revealing a regular stiffening effect. Furthermore, in aqueous environments the particles swell and are leached from PLLA matrix generating very high porosity. These new open‐pore foams coded PLASAW, that is, PLASA after water treatment, produced in absence of organic solvents and chemical foaming agents, with good physicomechanical properties appear very promising for several applications, for instance in tissue engineering for scaffold production. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45655.

Fabrication of Hierarchical Macroporous Biocompatible Scaffolds by Combining Pickering High Internal Phase Emulsion Templates with Three-Dimensional Printing.

Biocompatible and biodegradable porous scaffolds with adjustable pore structure have aroused increasing interest in bone tissue engineering. Here, we report a facile method to fabricate hierarchical macroporous biocompatible (HmPB) scaffolds by combining Pickering high internal phase emulsion (HIPE) templates with three-dimensional (3D) printing. HmPB scaffolds composed of a polymer matrix of poly(l-lactic acid), PLLA, and poly(ε-caprolactone), PCL, are readily fabricated by solvent evaporation of 3D printed Pickering HIPEs which are stabilized by hydrophobically modified silica nanoparticles (h-SiO2). The pore structure of HmPB scaffolds is easily tailored to be similar to natural extracellular matrix (ECM) by varying the fabrication conditions of the Pickering emulsion or adjusting the printing parameters. In addition, in vivo drug release studies which employ enrofloxacin (ENR) as a model drug indicate the potential of HmPB scaffolds as a drug carrier. Furthermore, in vivo cell culture assays prove that HmPB scaffolds that possess good biocompatibility as mouse bone mesenchymal stem cells (mBMSCs) can adhere and proliferate well on them. All the results suggest that HmPB scaffolds hold great potential in bone tissue engineering applications.

Morphology, rheology property, and crystallization behavior of PLLA/OMMT nanocomposites prepared by an innovative eccentric rotor extruder

An innovative eccentric rotor extruder, which can generate continuous elongation flow, was used to fabricate the poly(L‐lactide) (PLLA)/organo‐modified montmorillonite (OMMT) nanocomposites in different OMMT concentrations. The morphology of the nanocomposites was characterized by thermal gravimetric analyzer, X‐ray diffractometer, and transmission electron microscope. The results showed that the OMMT nanoparticles were uniformly dispersed in the PLLA matrix and mainly existed in intercalation mode. The intercalation and exfoliation process of OMMT in the eccentric rotor extruder may be a double‐side exfoliation, which is more effective than the layer‐by‐layer peeling mechanism based on the shear flow. The influence of OMMT on the rheological behavior of PLLA was investigated by dynamic rheological measurements, showing greater improvement of rheological properties for the nanocomposites. The thermo‐mechanical properties analysis indicated that significant enhancement of E′ can be seen for all the nanocomposites. Presence of intercalated OMMT platelets did not lead to a significant shift of the E″ and tan δ curves compared with that of pure PLLA. The crystallization and melting behavior was studied by differential scanning calorimetry, which indicated that the incorporation of OMMT nanoparticles slightly increased the crystallinity of PLLA matrix. The polarizing microscope was further carried out and showed that the dispersed OMMT nanoparticles acted as a heterogeneous nucleating agent to promote the crystallization of PLLA.

Tailor-Made Dispersion and Distribution of Stereocomplex Crystallites in Poly(l-lactide)/Elastomer Blends toward Largely Enhanced Crystallization Rate and Impact Toughness.

Stereocomplex (SC) crystallites, formed between poly(l-lactide) (PLLA) and poly(d-lactide), exhibit great potential to substantially enhance crystallization rate of PLLA-based materials as an eco-friendly nucleating agent. However, the nucleation efficiency of the SC crystallites is still far below an expected level, mostly on account of their strong aggregation tendency in PLLA/PDLA melts. Herein, taking PLLA/poly(ethylene-methyl acrylate-glycidyl methacrylate) (E-MA-GMA) blends as an example, we report a unique and facile strategy to control the dispersion and distribution of SC crystallites within the PLLA matrix by using elastomeric E-MA-GMA as carrier for the incorporation of PDLA. To do this, PDLA was first blended with E-MA-GMA or chemically grafted onto the E-MA-GMA. During subsequent melt-blending of PLLA and the E-MA-GMA/PDLA master batch, the PDLA chain clusters predispersed in the E-MA-GMA phase can gradually migrate into PLLA matrix and then collaborate with the matrix chains to form large amounts of tiny and well-dispersed SC crystallites. Compared with the SC-crystallite agglomerates formed by the direct melt-blending of PLLA and PDLA components, such tiny SC crystallites are much more effective in accelerating PLLA matrix crystallization. More interestingly, when PDLA chains are grafted onto the EMA-GMA, the formed SC crystallites tend to preferentially distribute at the blend interface and thus induce not only optimal nucleation efficiency but also superior impact toughness because these interface-localized SC crystallites can also serve as bridges to enhance interface adhesion. This work could open a new avenue in designing heat-resistant and supertough PLLA blends via controllable construction of SC crystallites.

Increase the elongation at break of poly (lactic acid) composites for use in food packaging films

Poly (3-hydroxy butyrate) (PHB), cellulose nano crystal (CNC) and a plasticizer (TBC) are mixed together with PLLA with the aim to increase the elongation at break for use in the food packing sector. Spherical (CNC) and fibril nano crystal (CNF) were prepared by hydrolysis of microcrystalline cellulose (MCC) in distilled water, and then stirred using a magnetic stirrer for 15 days and ultrasonic treatment without using any acids as green method. The morphology, thermal, and mechanical properties were studied using POM, DSC, WAXD, SEM and tensile testing, respectively. DSC demonstrated that the addition of PHB, CNC and TBC to PLLA matrix lead to reduce Tg, TCC and Tm than pure PLLA. FT-IR verified that the carbonyl group C=O appeared broad and some peaks in the PLLA composites 5, 6 and 7 shifted from 3.98 × 108 to 4.07 × 108 Hz, at 3.54 × 108 to 3.44 × 108 Hz, at 3.19 × 108 to 3.13 × 108 Hz. Mechanical testing shows that pure PLLA is brittle, and the elongation at break of PLLA composites reaches up to 205%, making it suitable to use in food packaging.

Chemical modification and plasma-induced grafting of pyrolitic lignin. Evaluation of the reinforcing effect on lignin/poly(l-lactide) composites

Pyrolitic lignin was modified through two methods. First, it was grafted with polylactide chains via a solvent-free process by ring-opening polymerization of l-lactide using calcium hydride as a catalyst. The efficiency of grafting was determined by infra-red, nuclear magnetic resonance and time-of-flight secondary ion mass spectrometry analyses. Then, lignin particles were oxygen plasma-treated and immersed in l-lactide solution. Infra-red and X-ray photoelectron spectroscopy revealed that chains bearing ester groups similar to that of lactide were covalently grafted onto the lignin. Composite cast films based on poly(l-lactide) matrix containing ungrafted lignin (lignin/PLLA), chemically-grafted lignin copolymer (PLA-g-lignin/PLLA) and plasma-treated lignin (plasma-treated lignin/PLLA) were investigated. Differential scanning calorimetry and dynamical mechanical analyses revealed that plasma-treated lignin preserved the crystalline structure of PLLA matrix and had a significant reinforcing effect compared with lignin and PLA-g-lignin. Results were compared with literature data.

Highly Biodegradable and Tough Polylactic Acid–Cellulose Nanocrystal Composite

Poly(l-lactide) cellulose nanocrystals-filled nanocomposites were fabricated by blending of cellulose nanocrystals-g-rubber-g-poly(d-lactide) (CNC-rD-PDLA) and commercial PLLA, in which CNC-g-rubber was synthesized by ring opening polymerization (ROP) of d-lactide and a e-caprolactone mixture to obtain CNC-P(CL-DLA), followed by further polymerization of d-lactide to obtain CNC-rD-PDLA. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and solubility tests confirmed successful grafting of the rubber segment and the PDLA segment onto CNC. Stereocomplexation between CNC-rD-PDLA nanofillers and PLLA matrix was confirmed by FT-IR, XRD, and differential scanning calorimetry (DSC) characterization. The PLLA/CNC-rD-PDLA nanocomposites exhibited greatly improved tensile toughness. With 2.5% CNC-rD-PDLA loading, strain at break of PLLA/CNC-rD-PDLA was increased 20-fold, and the composite shows potential to replace poly(ethylene terephthalate). SEM and small-angle X-ray scattering (SAXS) investigations rev...

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

AbstractPoly(l‐lactic acid) (PLLA) was blended with a series of four‐armed poly(ϵ‐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‐PCL5k‐b‐PDLA5k/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