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In this work, poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA)/carbon fiber (CF) composites with different PDLA content were prepared by simple melt blending. The stereocomplex (SC) crystallites were in situ formed. The effects of CFs and SC crystallites on the morphology, crystallization, rheological behaviors, mechanical properties, heat resistance, thermal and electrical conductivity of composites were investigated. The SC crystallites acted as nucleating agents of PLLA to accelerate the crystallization of PLLA, improve the degree of crystallinity, and refine spherical crystals, which led to a more homogeneous and dense dispersion of CFs. For the PLLA/PDLA/CF composite with 10 wt% PDLA, attributing to the synergistic effect of CFs and SC crystallites, vicat softening temperature (VST) was increased by about 100 ℃ over neat PLLA. The thermal conductivity increased from 0.21 W (mK)−1 of neat PLLA to 0.47 W (mK)−1, and surface resistivity decreased dramatically by about 8 orders of magnitude. More importantly, an increases of 156% and 29.2% were achieved in the tensile modulus and strength of composite with 10 wt % PDLA compared to neat PLLA. Melt viscosity and elasticity were also significantly improved with the addition of CFs and PDLA. The unusual combination of the improved mechanical and rheological performances, thermal resistance, thermal and electrical conductivity established in the degradable composites meets the properties required for a wider range of PLLA applications. [ABSTRACT FROM AUTHOR]

Natural-fiber-reinforced poly(lactic acid) (PLA) is a simple and effective method to improve properties with retaining the fully biodegradability and eco-friendliness. Herein, we prepared the poly(l-lactic acid) (PLLA)/poly(d-lactic acid) (PDLA)/bamboo fiber (BF) bio-composites through melt compounding. The stereocomplex PLA (SC-PLA) was formed during the melt blending. The SC-PLA crystals combined with BFs in the PLLA/PDLA/BF bio-composites had synergistic effects that could enhance crystallization rate, rheological and mechanical properties, and heat resistance. The results showed that the SC-PLA crystals drastically increased the nucleation density and accelerated the crystallization process of the bio-composites. The rheological properties of the bio-composites were obviously enhanced by the incorporation of BFs and PDLA. Mechanical properties of the bio-composites were increased compared to neat PLLA. The bio-composite with 10 wt% PDLA showed tensile strength of 72.4 MPa, and Young's modulus of 2855 MPa, which were 9.4% and 18% higher than those of neat PLLA, respectively. Moreover, Vicat softening temperature (VST) of the bio-composites was about 90 °C higher than that of neat PLLA. Overall, this work provides an interesting strategy of fabrication of the BFs reinforced PLA composites with controllable properties. [ABSTRACT FROM AUTHOR]

Data on irradiation of poly(L-lactide) (PLLA) based active packaging is still limited. Therefore, effect of γ-irradiation on neat PLLA and active packaging with oligohexamethylene guanidine hydrochloride (OHMG·HCl) has been studied. Combined use of irradiation and active packaging technology is promising approach to maintain food safety and prolong shelf life. It has been found that regardless of the OHMG·HCl content PLLA undergoes chain scission during irradiation and this process becomes less pronounced at doses higher than 50 kGy. Slight racemization of PLLA during exposure has been observed using polarimetry and 13C NMR spectroscopy. Mechanical properties of films have been examined. Biocide addition led to a 30% decrease in films elongation at break. Irradiation either caused elongation decrease. Dose of 50 kGy and higher made PLLA active films brittle. Multiple melting behavior of irradiated PLLA has been analyzed by differential scanning calorimetry. Fraction of crystals with higher melting temperature rose with dose. Possible reason for this phenomenon is formation of α′ form with less ordered chain packaging that recrystallizes during heating. The biocide addition has not affected this process. Furthermore, in vitro antimicrobial test has shown efficacy of films with 2 wt.% of OHMG·HCl against gram-negative, gram-positive bacteria and fungi. [ABSTRACT FROM AUTHOR]

Nanocomposites prepared with a terpolymer of poly(L–lactide) (PLLA)–poly(ε–caprolactone) (PCL)–poly(ethylene glycol) (PEG) and partially oxidized carbon nanotubes (CNTspo) were synthesized and characterized to evaluate their ability to act as an effective nanocarrier of the anticancer drug methotrexate. The homopolymers of PLLA and PCL were synthesized through ring-opening polymerization (ROP) and characterized through gel permeation chromatography (GPC). The PLLA–PCL–PEG terpolymers were synthesized through a four-step chemical route using oxalyl chloride as a linker agent and analyzed with 1H–NMR, 13C–NMR, and FTIR spectroscopies. Additionally, the nanocomposites were characterized through FTIR, and X-ray photoelectron spectroscopy (XPS), as well as the differential scanning calorimetry (DSC) technique. XPS analysis revealed that PLLA–PCL–PEG terpolymer chains are grafted onto CNTspo. Moreover, evaluations through FTIR and DSC strongly suggest that the PCL-rich domains are preferentially oriented toward CNTspo. The release tests exhibited a "burst effect" profile, which was more evident in the terpolymers than in the nanocomposites. Five models were used to assess methotrexate's in vitro release. For the nanocomposites, the best fit to the experimental data was obtained using the first-order model, whereas the results obtained from the Korsmeyer–Peppas model indicated that Fickian diffusion drives methotrexate's release. [ABSTRACT FROM AUTHOR]

To overcome PLLA's poor crystallization capability, using nucleating agent as crystallization improvement strategy was performed in this study. PPAPH as PLLA's an organic nucleating agent was firstly synthesized, and then PLLA was blended with different PPAPH loading through melting blend method, the resulting influences of PPAPH on PLLA's performances were investigated using the relevant testing instruments. Melt-crystallization revealed that PPAPH played important role in promoting PLLA's crystallization through providing effective sites of heterogeneous nucleation, and effect of PPAPH loading on PLLA's melt-crystallization was very poor, indicating that low PPAPH loading could cause PLLA to possess powerful crystallization capacity. In addition, the relative low final melting temperature was beneficial for PLLA/PPAPH's crystallization. However, an increase of cooling rate during cooling stage weakened PLLA/PPAPH's crystallization capacity. PLLA/PPAPH's coldcrystallization suggested that PPAPH had an inhibition effect on cold-crystallization process to some extent. Melting behaviors depended on heating rate and previous crystallization including meltcrystallization at various cooling rates and isothermal crystallization at various crystallization temperatures. PPAPH enhanced PLLA's fluidity, tensile modulus and tensile strength. Unfortunately, PLLA's transmittance was seriously weakened as PPAPH loading increased, as well as the elongation at break continuously decreased. [ABSTRACT FROM AUTHOR]

The formation of polylactide stereocomplex (sc-PLA), involving the blending of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), enhances PLA materials by making them stronger and more heat-resistant. This study investigated the competitive crystallization behavior of homocrystals (HCs) and stereocomplex crystals (SCs) in a 50/50 PLLA/PDLA blend with added polyethylene glycol (PEG). PEG, with molecular weights of 400 g/mol and 35,000 g/mol, was incorporated at concentrations ranging from 5% to 20% by weight. Differential scanning calorimetry (DSC) analysis revealed that PEG increased the crystallization temperature, promoted SC formation, and inhibited HC formation. PEG also acted as a plasticizer, lowering both melting and crystallization temperatures. The second heating DSC curve showed that the pure PLLA/PDLA blend had a 57.1% fraction of SC while adding 5% PEG with a molecular weight of 400 g/mol resulted in complete SC formation. In contrast, PEG with a molecular weight of 35,000 g/mol was less effective, allowing some HC formation. Additionally, PEG consistently promoted SC formation across various cooling rates (2, 5, 10, or 20 °C/min), demonstrating a robust influence under different conditions. [ABSTRACT FROM AUTHOR]

A low-temperature melt blending method was adopted to prepare ternary blends of poly(L-lactide) (PLLA), poly(butylene carbonate) (PBC), and poly(D-lactide) (PDLA), aiming to obtain fully biodegradable blends with well-balanced properties. The in situ formation of stereocomplex polylactide (SC-PLA) crystals was confirmed by torque changes, differential scanning calorimetry results, and wide-angle X-ray diffraction measurements. At a PDLA concentration of 5 mass%, SC-PLA crystals formed a percolating network structure, and the rheological behavior of the blend melts transformed from liquid-like to solid-like. The viscosity ratio between PLLA and PBC melts increased due to the presence of SC-PLA crystals, resulting in an enlargement of the PBC domain size. SC-PLA crystals exhibited an excellent nucleation effect, significantly accelerating the crystallization rate of PLLA. Compared to neat PLLA with elongation at break of 5.2%, PLLA/PBC/PDLA ternary blends containing 2 mass% PDLA with elongation at break of 247.2% presented excellent toughness. This work provided a facile method to prepare PLLA-based material with outstanding crystallization ability and tailored rheological behavior as well as mechanical properties, which had the potential to replace conventional plastic products. [ABSTRACT FROM AUTHOR]

We carried out a Raman study of a series of poly(L-lactide) (PLLA) samples annealed for different periods of time and therefore having different crystallinity degree. We compared the results with our recent study of the series of poly(L-lactide-co-ε-caprolactone) (PLCL) copolymers with the ε-caprolactone (CL) content ranging from 5 to 30 mol %. X-ray diffraction (XRD) analysis showed that the crystallinity degree of the analyzed PLLA-based materials is in the range of 0–86%. We suggest using the ratio of the peak intensities of the PLLA Raman bands at 411 and 874 cm–1 to evaluate the crystallinity degree of PLLA homopolymers as well as PLLA blocks in the PLCL copolymers. This ratio does not depend on the CL content in the copolymers, it strongly depends on the crystallinity degree of PLLA (PLLA blocks in the PLCL copolymers) and it is a linear function of the crystallinity degree, measured by XRD analysis. We carried out quantum chemical calculations of the optimized geometries and Raman spectra of PLLA oligomers in the conformation of helix 103 with the number of monomeric units from 5 to 12. The results of the calculations revealed that the ratio of the intensities of the bands at 411 and 874 cm–1 weakly depends on the oligomer length for the number of the PLLA monomeric units more than 7. [ABSTRACT FROM AUTHOR]

Nanocomposites prepared with a terpolymer of poly(L–lactide) (PLLA)–poly(ε–caprolactone) (PCL)–poly(ethylene glycol) (PEG) and partially oxidized carbon nanotubes (CNTspo) were synthesized and characterized to evaluate their ability to act as an effective nanocarrier of the anticancer drug methotrexate. The homopolymers of PLLA and PCL were synthesized through ring-opening polymerization (ROP) and characterized through gel permeation chromatography (GPC). The PLLA–PCL–PEG terpolymers were synthesized through a four-step chemical route using oxalyl chloride as a linker agent and analyzed with 1H–NMR, 13C–NMR, and FTIR spectroscopies. Additionally, the nanocomposites were characterized through FTIR, and X-ray photoelectron spectroscopy (XPS), as well as the differential scanning calorimetry (DSC) technique. XPS analysis revealed that PLLA–PCL–PEG terpolymer chains are grafted onto CNTspo. Moreover, evaluations through FTIR and DSC strongly suggest that the PCL-rich domains are preferentially oriented toward CNTspo. The release tests exhibited a “burst effect” profile, which was more evident in the terpolymers than in the nanocomposites. Five models were used to assess methotrexate’s in vitro release. For the nanocomposites, the best fit to the experimental data was obtained using the first-order model, whereas the results obtained from the Korsmeyer–Peppas model indicated that Fickian diffusion drives methotrexate’s release.

Poly(lactic acid) (PLA) as a bio-based polymer with biodegradability and biocompatibility has attracted much attention. To manipulate its properties for different applications, regulation of crystal structure and crystalline morphology becomes an attractive research topic. In this work, the structure evolution of layered samples containing an amorphous poly(D-lactide) (PDLA) layer and a crystalline poly(L-lactide) (PLLA) layer with highly oriented edge-on α lamellar crystals after annealing at 150 °C or/and after melt-recrystallization has been studied by AFM, FTIR, and TEM combined with electron diffraction. The results demonstrate that melt recrystallization of the as-prepared sample leads to the formation of abundant randomly oriented PLA stereo-complex (PLA SC) crystals. Annealing at 150 °C results in the formation of a small amount of oriented PLA SC crystals at the interface. These PLA SC crystals show great impact on the recrystallization behavior of sample after melting at 190 °C and then crystallizing at 90 °C. First, they impede the mutual diffusion of the overlying PDLA and underlying PLLA, and thus reduce their stereocomplexation ability as manifested by the decreased amount of PLA SC crystals. Second, they act as substrate to initiate the epitaxial crystallization of the overlying PDLA and underlying PLLA, which ensures the production of a highly oriented structure of PDLA and PLLA after melt recrystallization again. [ABSTRACT FROM AUTHOR]

Formation of stereocomplex crystals (SCs) in enantiomeric poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA) blends is an effective way to improve the heat resistance and mechanical performance of polylactide (PLA) products. However, obtaining PLAs with high stereocomplex content is not straightforward as the homocrystal and SCs occur simultaneously and compete with one another. In this work, various amounts of epoxidized soybean oil (SO) or SO at 3%–20% by weight were added to equal amounts of the stereoisomers (PLLA/PDLA; 50/50). From differential scanning calorimetry, it was found that epoxidized SO increased the crystallization temperature, facilitated the SC crystallization, and suppressed the homecrystal formation, whereas SO did not affect the crystallization behavior for the racemic blends. Moreover, epoxidized SO reduced the glass transition temperature, cold crystallization temperature, and melting temperature of the racemic blends. We examined how epoxidized SO affected the crystallization of PLLA/PDLA at cooling rates from 2 to 20°C/min. We discovered that epoxidized SO still encouraged SC crystallization. The activation energy, calculated from Takhor and Kissinger equations, indicated that adding 5 wt% epoxidized SO effectively promoted the crystallization and facilitated the SC formation of the PLLA/PDLA blend. [ABSTRACT FROM AUTHOR]

Fully biodegradable poly(l-lactide)/poly(triethylene glycol adipate) blends with different phase behaviors and significantly increased crystallization rate were prepared for the first time in this research. Depending on PTGA content, PLLA/PTGA blends showed different phase behaviors. PLLA was completely miscible with PTGA when PTGA content was not higher than 15 mass%, while PLLA was partially miscible with PTGA when PTGA content was higher than 15 mass%. Increasing the PTGA content remarkably increased both the overall crystallization rate and spherulitic growth rate of PLLA, evidencing the plasticization role of PTGA; however, irrespective of the presence of PTGA, both the crystallization mechanism and the crystal structure of PLLA remained unchanged. [ABSTRACT FROM AUTHOR]

The formation of polylactide stereocomplex (sc-PLA), involving the blending of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), enhances PLA materials by making them stronger and more heat-resistant. This study investigated the competitive crystallization behavior of homocrystals (HCs) and stereocomplex crystals (SCs) in a 50/50 PLLA/PDLA blend with added polyethylene glycol (PEG). PEG, with molecular weights of 400 g/mol and 35,000 g/mol, was incorporated at concentrations ranging from 5% to 20% by weight. Differential scanning calorimetry (DSC) analysis revealed that PEG increased the crystallization temperature, promoted SC formation, and inhibited HC formation. PEG also acted as a plasticizer, lowering both melting and crystallization temperatures. The second heating DSC curve showed that the pure PLLA/PDLA blend had a 57.1% fraction of SC while adding 5% PEG with a molecular weight of 400 g/mol resulted in complete SC formation. In contrast, PEG with a molecular weight of 35,000 g/mol was less effective, allowing some HC formation. Additionally, PEG consistently promoted SC formation across various cooling rates (2, 5, 10, or 20 °C/min), demonstrating a robust influence under different conditions.

Poly(L-Lactide) (PLA), a fully biobased aliphatic polyester, has attracted significant attention in the last decade due to its exceptional set of properties, such as high tensile modulus/strength, biocompatibility, (bio)degradability in various media, easy recyclability and good melt-state processability by the conventional processes of the plastic/textile industry. Blending PLA with other polymers represents one of the most cost-effective and efficient approaches to develop a next-generation of PLA-based materials with superior properties. In particular, intensive research has been carried out on PLA-based blends with engineering polymers such as polycarbonate (PC), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and various polyamides (PA). This overview, consequently, aims to gather recent works over the last 10 years on these immiscible PLA-based blends processed by melt extrusion, such as twin screw compounding. Furthermore, for a better scientific understanding of various ultimate properties, processing by internal mixers has also been ventured. A specific emphasis on blend morphologies, compatibilization strategies and final (thermo)mechanical properties (tensile/impact strength, ductility and heat deflection temperature) for potential durable and high-performance applications, such as electronic parts (3C parts, electronic cases) to replace PC/ABS blends, has been made.

New tubular conduits have been developed for the regeneration of peripheral nerves and the repair of defects that are larger than 3 cm. The conduits consist of a combination of poly(L-lactide) nanofibers and chitosan composite fibers with chitin nanofibrils. In vitro studies were conducted to assess the biocompatibility of the conduits using human embryonic bone marrow stromal cells (FetMSCs). The studies revealed good adhesion and differentiation of the cells on the conduits just one day after cultivation. Furthermore, an in vivo study was carried out to evaluate motor-coordination disorders using the sciatic nerve functional index (SFI) assessment. The presence of chitosan monofibers and chitosan composite fibers with chitin nanofibrils in the conduit design increased the regeneration rate of the sciatic nerve, with an SFI value ranging from 76 to 83. The degree of recovery of nerve conduction was measured by the amplitude of M-response, which showed a 46% improvement. The conduit design imitates the oriented architecture of the nerve, facilitates electrical communication between the damaged nerve's ends, and promotes the direction of nerve growth, thereby increasing the regeneration rate. [ABSTRACT FROM AUTHOR]

In this work, the effect of uniaxial stretching on the crystallization and melting behaviors, miscibility, crystal structure, and mechanical properties of neat poly(L-lactide) (PLLA) and miscible PLLA/poly(vinyl acetate) (PVAc) blends was investigated. Stretching process could generate remarkable influence on thermal properties of neat PLLA and PLLA/PVAc blend. With stretching ratio increasing, macromolecular chains orientation and crystallization were promoted, resulting in a decrease in cold crystallization temperature and an increase in glass transition temperature, and a significant increase in crystallinity. In addition, after stretching process PVAc still inhibited the crystallization of PLLA. PLLA/PVAc blends were completely miscible blend system which had only one glass transition temperature before and after stretching process, and phase separation did not occur after stretching process. When stretch ratio increased, amorphous PVAc had greater influence on the tanδ transition peak and storage modulus increased markedly, which was benefit to the improvement of heat resistance. The α′ crystal form was produced in blends after stretching process. Stretching process with moderate stretch ratio can be utilized to improve the mechanical properties of PLLA with simultaneous enhancement of tensile strength, fracture strain and stiffness. The findings in this work provide an insightful understanding of the effect of stretching process on miscible PLLA blend and the improvement of toughness, which will facilitate the large-scale practical application of PLLA. [ABSTRACT FROM AUTHOR]

Porous films were fabricated from poly(L-lactide) (PLLA)-1,4-dioxane-dimethylacetamide ternary systems via thermally induced phase separation (TIPS) followed by using freeze extraction. The effect of processing parameters including freezing temperature, quenching time, and the film thickness was investigated on the physical, mechanical, and morphological properties of the porous films. The primary objective of increase in the film thickness is to cause a decreased temperature gradient between external layer and internal layers at the same temperature (according to Fourier's law) and to decrease the growth rate of the solvent-rich phase. The results revealed that increasing thickness from 1200 to 1600 µm at − 20 °C for 6 h resulted in producing pore sizes 200 nm and nanofibrous (> 200 nm fiber diameter) instead of 400 nm and nanofibrous (< 100 nm fiber diameter). The nanofibrous (< 100 nm) exhibit higher porosity and water absorption, and lower tensile strength than the nanofibrous (> 200 nm). As a result of the high film thickness, decreasing temperature from − 20 to − 45 °C (increasing temperature gradient), and increasing time from 6 to 24 h, it is indicated that the phase separation happens via the coarsening process and forms nanospindle structure with the pore size 800 nm. [ABSTRACT FROM AUTHOR]

Melt processing poly(L-lactide) (PLLA) with a nucleating agent has been thought to be one of the most effective route to enhance PLLA's crystallization and heat resistance. In the current work, a newly-developed organic nucleating agent named N, N'-bis(2-picolinyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NCAPH) was synthesized to investigate its effects on PLLA's crystallization and melting behaviors. It is proved that NCAPH as an organic crystallization nucleating agent could provide large number of crystallization nucleation sites to improve PLLA's crystallization, as observed from DSC and POM measurements. The result from melt-crystallization processes further showed that the final melting temperature and cooling rate were two important factors for affecting PLLA's melt-crystallization behaviors in cooling, and the theoretical calculation result of frontier orbital energy indicated there existed probable intermolecular interaction between N-H of NCAPH and C=O of PLLA, which was proposed as nucleation mechanism of NCAPH for promoting PLLA's crystallization. The melting behaviors of PLLA/NCAPH after non-isothermal crystallization or isothermal crystallization further confirmed the positive effects of NCAPH and NCAPH's loading for the crystallization of PLLA, meantime, the melting behaviors depended on the heating rate, crystallization temperature, crystallization time, etc. [ABSTRACT FROM AUTHOR]

Highly crystallized poly(L‐lactide) (PLLA) films with enhanced hydrophobicity are easily prepared by casting PLLA solution into a poor solvent like isopropyl alcohol (IPA). The crystallinity of the PLLA film can be controlled by PLLA's concentration, the kind of poor solvent, and the volume ratio of poor solvent dichloromethane (DCM). Results show the addition of poor solvents obviously accelerate the crystallization of PLLA film and enhance the crystallinity up to 48.7%. A lower volume ratio of IPA/DCM at higher PLLA concentration as well as a higher volume ratio of IPA/DCM at lower PLLA concentration is conducive to raising the crystallinity of the PLLA film. In the meanwhile, microscopy observation and wettability tests confirm the PLLA films present multidimensional microstructure including fibrils, lamellas, and flower‐like stacks or spherulite‐like superstructure, and display high porosity as well as enhanced hydrophobicity. Despite the volume ratio of IPA/DCM, the PLLA films prepared at lower concentrations display higher crystallinity, porosity as well as hydrophobicity than those prepared at higher concentrations. The highly crystalline PLLA films with enhanced porosity and hydrophobicity are supposed to be applied in oil–water separation, and so forth. [ABSTRACT FROM AUTHOR]

A biodegradable tubular poly(L-lactide) scaffold and a method for seeding and culturing mesenchymal stem cells were developed to create a tissue-engineered vascular graft. In group 1, scaffolds without pre-seeded cells were implanted into the rat abdominal aorta; in group 2, scaffolds with pre-seeded adipose-derived mesenchymal stem cells were used. The follow-up period in group 1 ranged from 2 days to 64 weeks (n = 36), while this time was up to 72 weeks in group 2 (n = 42). The graft patency in group 1 was 86%; in group 2 - 97%. Histology revealed a gradual biodegradation of the biopolymer and the replacement of the polymer fibers with connective tissue in the group 1. However, after 64 weeks complete polymer biodegradation was achieved, and in all cases, the formation of graft aneurysms was detected. In group 2, the total cells number in the graft and the thickness of the neoadventitia around it, were significantly higher, however, the grafts morphology at the late follow-up did not qualitatively differ in four out of nine cases (45%), a graft aneurysm developed. Thus, the preliminary cultivation of mesenchymal stemcells on the scaffold provoked a pronounced host cellular reaction, which probably made it possible to reduce the incidence of aneurysm formation, but did not ensure the formation of a natural vessel structure. [ABSTRACT FROM AUTHOR]

Ring‐expansion polymerizations (REPs) catalyzed by two cyclic tin catalysts (2‐stanna‐1.3‐dioxa‐4,5,6,7‐dibenzazepine [SnBiph] and 2,2‐dibutyl‐2‐stanna‐1,3‐dithiolane [DSTL]) are performed at 140 °C in bulk. Small amounts (4 vol%) of chlorobenzene or other solvents are added to facilitate transesterification reactions (ring–ring equilibration) in the solid poly(l‐lactide)s. In the mass range up to m/z 13 000 crystalline PLAs displaying a so‐called saw‐tooth pattern in the MALDI‐TOF mass spectra are obtained indicating the formation of extended‐ring crystals. The characteristics of extended‐ring crystallites and folded‐ring crystallites are discussed. Furthermore, extremely high melting temperatures (Tm's up to 201.2 °C) and melting enthalpies (ΔHm's up to 106 J g−1)) are found confirming that ΔHmmax, the ΔHm of a perfect crystal, is around or above 115 J g−1 in contrast to literature data. [ABSTRACT FROM AUTHOR]

In the present work, the attention is focused on cannulated, biodegradable olives made of poly(l -lactide) (PLLA) and PLLA with the addition of phosphate ceramics. The olive is an element expanding the intramedullary nail intended to be implantation the humerus bone. During degradation, the olive reduces the diameter of the nail, while ensuring the best conditions for the growth of bone tissue. The article examines the effect of the addition of tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) on morphology, chemical structure, physicochemical and biological properties of PLLA during storage in a degradation medium imitating the natural environment of the human body. The introduction of β-TCP+HAp into PLLA led to significant changes in both surface morphology, chemical structure and physicochemical properties, which contributed to the faster course of the biodegradation of the orthopedic implant. Due to this process, it was found that the PLLA composite with phosphate ceramics can be successfully used in this application. Clinical studies have shown that the implantation of olive made of PLLA+β-TCP+HAp does not cause any negative systemic reactions. The orthopedic implant was biodegradable and significantly contributes to bone union. [ABSTRACT FROM AUTHOR]

Amide nucleating agents have been reported to be effective in promoting poly(L‐lactide) (PLLA) crystallization, while few research efforts have focused on the structure–activity relationship of the nucleating agents which is one basic issue to develop new agents. In this work, three amide nucleating agents with different symmetry were designed and synthesized to investigate the effect of the symmetry of benzamide nucleating agents on PLLA crystallization. It is found that the C3 symmetric amide structure of N, N′, N″‐tricyclohexyl‐1,3,5‐benzenetriamine (BTCA) agent can form a highly oriented structure by a triple hydrogen bond of π–π bond and benzene ring and can act as efficient nucleation sites. In addition, the strong intramolecular hydrogen bond with PLLA would further promote the crystallization of PLLA. In general, it is the self‐assembled ability and intramolecular hydrogen bonding with PLLA affects the rate and degree of PLLA crystallinity, and we find the C3 symmetric amide structure exhibits the best performance. [ABSTRACT FROM AUTHOR]

The development of a biodegradable vascular scaffold (BVS) for the treatment of cardiovascular diseases (CVDs) still requires some improvement. Among them, re-endothelialization and anti-inflammation are clinically important to restore vascular function. In this study, we proposed a coating system to deliver hydrophilic bioactive agents to BVS using nanoemulsion and drop-casting methods. The poly(L-lactide) (PLLA) scaffold containing magnesium hydroxide (MH) was coated on the surface with bioactive molecules such as polydeoxyribonucleotide (PDRN), L-arginine (Arg, R), and mesenchymal stem cell-derived extracellular vesicles (EVs). PDRN upregulates the expression of VEGF as one of the A2A receptor agonists; and Arg, synthesized into nitric oxide by intracellular eNOS, induces endothelialization. In particular, EVs, which are composed of a lipid bilayer and transfer bioactive materials such as protein and nucleic acid, regulate homeostasis in blood vessels. Such a bioactive agent coating system and its PLLA composite suggest a new platform for the treatment of cardiovascular dysfunction. [ABSTRACT FROM AUTHOR]

• The aliphatic polyesters from 2-methyl-1,3-propanediol (MP) and dicarboxylic acids bearing 7–10 carbons were prepared, demonstrating their high biodegradability in seawater. • Poly(2-methyl-1,3-propanediyl azelate) (PMP9) showed the lowest glass transition temperature among them. • The ring-opening polymerization (ROP) of L-lactide using PMP9 as a macroinitiator gave PLLA- b -PMP9- b -PLLA (TPE9), which exhibit excellent physical properties as thermoplastic elastomers. • One-pot synthesis of a TPE9 was achieved by the successive polycondensation MP and azelaic acid followed by the ROP of L-lactide. • The TPE9s were also biodegraded in seawater. Elastic materials with high biodegradability should replace those with low biodegradability in some applications. We previously reported biodegradable thermoplastic elastomers (TPEs) composed of poly(l -lactide) (PLLA) as a hard segment and aliphatic polyesters from 2-methyl-1,3-propanediol (MP) and short aliphatic dicarboxylic acids as soft segments. In this study, we synthesized the biodegradable thermoplastic elastomers using longer aliphatic dicarboxylic acids to develop the TPEs with lower glass-transition temperature (T g) and high biodegradability. A series of aliphatic polyesters were prepared by polycondensation of MP and aliphatic dicarboxylic acids bearing 7–10 carbons. Among them, poly(2-methyl-1,3-propylene azelate) (PMP9) was found to have lower T g , amorphous nature, and high biodegradability in seawater. The ring-opening polymerization of l -lactide (LLA) using PMP9 as a macroinitiator afforded triblock copolymers, PLLA- b -PMP9- b -PLLA (TPE9). The successive addition of LLA to in-situ generated PMP9 resulted in the successful one-pot synthesis of high molecular weight TPE9. The TPE9s showed both low T g of the PMP9 segment and high melting temperature of the PLLA segment. The TPE9s exhibited elastic behavior showing elongation at break of up to 2500 % in tensile tests and also high biodegradability in seawater. Thus, we developed potentially practical TPE with tunable physical properties and high biodegradability obtainable from easily available and renewable starting materials. [ABSTRACT FROM AUTHOR]

In this paper we present the possibilities of using a femtosecond fiber laser (τ = 260 fs, λ = 1030 nm) to modify a PLLA surface. Three types of developed structures S1, S2, S3 differed significantly in topography and surface morphology. Thanks to the use of pulse overlapping in both scanning directions, the structures S1 and S2 were highly homogeneous, while in structure S3 the parallel grooves were obtained by pulse overlapping in one direction. The modified surfaces were examined for morphology (scanning electron microscopy), roughness (optical profilometry), wettability (measurement of the contact angle) and changes in the chemical structure of the polymer (infrared spectroscopy, gel permeation chromatography). The possibility of modifying these surface properties in a broad range was also discussed. The conducted cellular studies showed that there was no cytotoxicity with regard to all samples and that the pace of fibroblast colonization of samples S1 was higher compared to that of the control during the first 24 h of experiment. Moreover, the ability of S. aureus (pathogenic bacteria) and of a biotechnologically useful fungus Saccharomyces boulardii to colonize the manufactured structures was also assessed. In this case, no significant differences in the number of biofilm-forming cells were observed between the analyzed samples and the control setting. Obtained results indicate that applicability of such surface modifications should be further investigated, especially for the development of bone implants and these biotechnological processes in which microbes are used to produce the desired yield of product.

Lignin nanoparticles (LNPs), as a new type of green nanomaterial, initiate many promising applications in polymer composites. However, their heterogeneity, dissolution in organic solvents, and poor compatibility in the polymer matrix greatly limited the applications of LNPs fillers. Herein, we proposed an antisolvent precipitation of the fractionations by combining a hydrothermal treatment-assisted synthesis to fabricate self-crosslinked LNPs (ScLNPs), which have good stability in the organic solvent and controllable sizes. After surface grafting modification with d -lactide, ScLNPs- graft -poly(d -lactide) (ScLNPs- g -PDLA) exhibited excellent dispersion and compatibility in PLLA matrix. Using the rational design and addition of ScLNPs- g -PDLA fillers, the strength and toughness of the generated PLLA composite reached 31.6 MPa and 396 % (the highest value among the PLLA materials), respectively. Furthermore, the mechanical performance can also be well-tuned by the sizes and amounts of LNPs fillers. This strategy involving only green and recyclable materials provides an effective route to producing sustainable polymeric plastics with integrated strength and super-toughness. • Self-crosslinked LNPs were prepared by a crosslinker-free route. • ScLNPs have controllable sizes and good stability in the organic solvent. • ScLNPs- g -PDLA/PLLA exhibits supertough and strong performance. • The mechanical properties of the composites can be well-tuned by LNPs fillers. [ABSTRACT FROM AUTHOR]

The conventional approach for preparation of core-sheath fibers is coaxial electrospinning. Single-spinneret electrospinning of emulsions is a much less common method to obtain core-sheath fibers. Core-sheath structure may be generated by electrospinning of homogeneous blend solutions; however, reports on such cases are still scarce. Herein, the preparation of nanofibrous composites from poly(ethylene oxide) (PEO), poly(L-lactide) (PLA) and beeswax (BW) by single-spinneret electrospinning of their homogeneous blend solutions in chloroform is reported. The produced fibers had core/double-sheath structure with a PEO core, PLA inner sheath and BW outer sheath. This original fiber structure was evidenced by transmission electron microscopy, selective extraction of BW or PEO, and X-ray photoelectron spectroscopy. The PLA/BW double sheath led to hydrophobicity of the PEO/PLA/BW mats. The tensile tests revealed that PEO/PLA/BW mats had substantially improved mechanical behavior as compared to PEO, PLA and PEO/BW mats. PEO/PLA/BW mats can be used as drug carriers as evidenced by the one-pot incorporation of the model drug 5-nitro-8-hydroxyquinoline (NQ) into the fibrous materials. Microbiological tests showed that PEO/PLA/BW/NQ had antimicrobial activity. Therefore, the new materials are promising for wound healing applications. [ABSTRACT FROM AUTHOR]

The fibrous porous structure of polymers can mimic the extracellular matrix of the native tissue, therefore such polymers have a good potential for use in regenerative medicine. Organs and tissues within the body exhibit different mechanical properties depending on their functionality, thus artificial scaffolds should have mechanical behaviors similar to the extracellular matrix in conditions like living organisms, primarily in aqueous media. Several methods have been investigated in aquatic environments, including noninvasive techniques based on ultrasonic focused beams for biological objectives. In this study we explored the tensile behavior of poly(L-lactide) nonwoven polymer scaffolds using high-frequency ultrasound microscopy combined with a horizontal testing machine, which provided a visualization of the reorganization and transformation of the dynamic volume microstructure. The mechanisms of unwinding, elongation, orientation, and deformation of polymer fibers under uniaxial tension were revealed. We observed an association between the lined plastic deformation from 100 to 400% and the formation of multiple necks in the fibers, which caused stress relaxation and significant rarefaction of the fibrous microstructure. It was shown that both peaks on the stress–strain curve corresponded to the microstructure of aligned fibers in terms of initial diameter and thinning fibers. We discuss the possible influence of these microstructure transformations on cell behavior. [ABSTRACT FROM AUTHOR]

Cellulose-grafte-poly(L-lactide) (C-g-PLLA) copolymers synthesized in a CO2-switchable solvent are proposed for use as effective compatibilizers for the preparation of cellulose–PLLA composites with enhanced interfacial compatibility. The effect of the molar substitution (MSPLLA) of the grafted PLLA side chain in the C-g-PLLA copolymer and the feeding amount of this copolymer on the mechanical and thermal properties and hydrophilicity of the composites was investigated. The composites had a largely increased impact strength with the incorporation of the compatibilizer. With the increasing of MSPLLA and the feeding amount of the copolymer, the resulting composites had an increased impact strength. When 5 wt% C-g-PLLA with MSPLLA of 4.46 was used as a compatibilizer, the obtained composite containing 20 wt% cellulose presented an impact strength equal to that obtained for the neat PLLA. The composites had a slightly decreased melting temperature and thermal decomposition temperature, but increased hydrophilicity due to the incorporation of the compatibilizer. This work suggests an effective method to improve the interfacial compatibility between cellulose and PLLA for the fabrication of fully bio-based composites with high performance. [ABSTRACT FROM AUTHOR]

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Improving the crystallization performance of poly(L-lactide) (PLLA) is necessary to adapt for various applications. In the current work, N, N'-bis(isonicotinic acid) 1, 4-naphthalenedicarboxylic acid dihydrazide (NAIAH) was synthesized to be firstly aimed at promoting the crystallization of PLLA, and the NAIAH-nucleated PLLA materials were prepared using PLLA as a matrix material and NAIAH as a nucleating agent, and the crystalline nucleation, melting behavior, thermal decomposition and mechanical properties of PLLA/NAIAH samples were investigated by the relevant testing instruments. The results from the non-isothermal melt-crystallization from the melt of 190ºC indicated that the NAIHA could significantly accelerate PLLA’s crystallization, and played an efficient heterogeneous nucleation in PLLA’s crystallization. The effect of different final melting temperatures on PLLA’s melt-crystallization behavior showed that a relatively low final melting temperature was beneficial for the crystallization of PLLA, and the 170ºC was the optimum final melting temperature in this study. An increase of cooling rate could weaken PLLA/NAIAH’s crystallization ability, but the NAIAH was still able to promote PLLA’s crystallization upon the fast cooling at 50ºC/min, showing a powerful crystallization accelerating effect of NAIAH. PLLA/NAIAH’s melting behaviors after different crystallization conditions were affected by heating rate and crystallization temperature, and the double melting peaks appeared in melting DSC curves were assigned to melting-recrystallization. Thermal decomposition processes in air showed that the NAIAH decreased PLLA’s thermal stability, but the interaction of PLLA with NAIAH had an inhibition for a drop in onset decomposition temperature. Additionally, the introduction of NAIAH dramatically reduced PLLA’s tensile modulus and elongation at break. [ABSTRACT FROM AUTHOR]

The membranes of poly(l-lactide acid-p-dioxanone-glycolide) (PLPG) with stereocomplex poly(lactic acid) (sc-PLA) were prepared by the solution blending way. It was observed that sc-PLA significantly heightened the crystallizing behavior of PLLA segments of the PLPG matrix. The crystallizing behavior displayed that the temperature of crystallization shifted to a higher range than that of PLPG. Moreover, the half-time of crystallization sharply decreased in value as the sc-PLA content increased in value on account of the pre-eminent nucleation ability of sc-PLA. TGA results revealed the thermal stability of the samples with the increase of sc-PLA compared to PLPG. Meanwhile, enzymatic degradation results indicated that the mass loss rate of the membrane decreased with the introduction of sc-PLA, but the overall degradation ability was still greater than that of PLLA. In the meantime, the biological experiment indicated that the membrane possessed low cytotoxicity.

New tubular conduits have been developed for the regeneration of peripheral nerves and the repair of defects that are larger than 3 cm. The conduits consist of a combination of poly(L-lactide) nanofibers and chitosan composite fibers with chitin nanofibrils. In vitro studies were conducted to assess the biocompatibility of the conduits using human embryonic bone marrow stromal cells (FetMSCs). The studies revealed good adhesion and differentiation of the cells on the conduits just one day after cultivation. Furthermore, an in vivo study was carried out to evaluate motor-coordination disorders using the sciatic nerve functional index (SFI) assessment. The presence of chitosan monofibers and chitosan composite fibers with chitin nanofibrils in the conduit design increased the regeneration rate of the sciatic nerve, with an SFI value ranging from 76 to 83. The degree of recovery of nerve conduction was measured by the amplitude of M-response, which showed a 46% improvement. The conduit design imitates the oriented architecture of the nerve, facilitates electrical communication between the damaged nerve’s ends, and promotes the direction of nerve growth, thereby increasing the regeneration rate.

Poly(L-lactide)-b-polyethylene glycol-b-poly(L-lactide) triblock copolymer (PLLA-PEGPLLA)/boron nitride (BN) composites with BN contents of 1, 2 and 4 wt.% were prepared by melt blending. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing were carried out to characterize the phase morphologies, thermal properties and mechanical properties of composite films. The BN particles showed good distribution and dispersion throughout the film matrices as observed from SEM. DSC analysis showed that increasing crystallinity content and decreasing half crystallization-time of PLLA-PEG-PLLA/BN composites were obtained when the BN content was increased. The ultimate tensile stress significantly increased and strain at break steadily decreased with an increase in the BN content. These results showed that the BN particles enhanced crystallizability and mechanical properties of PLLA-PEG-PLLA. [ABSTRACT FROM AUTHOR]

The widely used melt-blown polypropylene (PP) non-woven fabrics had no antibacterial functions and its large-scale use also increased the burden on the environment owing to its non-degradable property. Herein, silver (I) metal organic frameworks (Ag-2MI) were prepared with AgNO 3 and 2-methylimidazole and embedded into degradable poly(l -lactide) (PLLA) to make an ultrathin filtration and antibacterial membrane by electrospinning technology with low loading of Ag-2MI. The morphology, mechanical properties, adsorption performance and antibacterial activities of the prepared films were tested and the results indicated that the addition of Ag-2MI could reduce the diameter of PLLA fibers from 910 nm to 520 nm (1.8 wt% of Ag-2MI), while the tensile strength, elongation at break of the membrane and the contact angle of the films were enhanced. Although the thickness of the prepared membranes was only about one-third of that of commercially available melt-blown cloth, they exhibited better filtering performances than the melt-blown cloth. The fiber membrane with low loading of 1.8 wt% Ag-2MI showed 99.99% inhibition rate against Escherichia coli and Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

The cartilage tissue is neither supplied with blood nor innervated, so it cannot heal by itself. Thus, its reconstruction is highly challenging and requires external support. Cartilage diseases are becoming more common due to the aging population and obesity. Among young people, it is usually a post-traumatic complication. Slight cartilage damage leads to the spontaneous formation of fibrous tissue, not resistant to abrasion and stress, resulting in cartilage degradation and the progression of the disease. For these reasons, cartilage regeneration requires further research, including use of new type of biomaterials for scaffolds. This paper shows cartilage characteristics within its most frequent problems and treatment strategies, including a promising method that combines scaffolds and human cells. Structure and material requirements, manufacturing methods, and commercially available scaffolds were described. Also, the comparison of poly(L-lactide) (PLLA) and polyethersulfone (PES) 3D membranes obtained by a phase inversion method using nonwovens as a pore-forming additives were reported. The scaffolds' structure and the growth ability of human chondrocytes were compared. Scaffolds' structure, cells morphology, and protein presence in the membranes were examined with a scanning electron microscope. The metabolic activity of cells was tested with the MTT assay. The structure of the scaffolds and the growth capacity of human chondrocytes were compared. Obtained results showed higher cell activity and protein content for PES scaffolds than for PLLA. The PES membrane had better mechanical properties (e.g. ripping), greater chondrocytes proliferation, and thus a better secretion of proteins which build up the cartilage structure. [ABSTRACT FROM AUTHOR]

Constructing stereocomplex (SC) crystallites at the interface of poly(L‐lactide) (PLLA)/elastomer blends represent a promising strategy to develop heat‐resistant and super‐tough PLLA materials because such SC crystallites can behave as not only nucleator to accelerate crystallization of PLLA matrix but also interfacial binder to strengthen interface. The properties of blends could be largely dominated by the SC interfacial layer, however, it is still unclear how the interfacial structure affects nucleating efficiency and interfacial strength. Herein, taking PLLA/poly(ethylene‐co‐methyl acrylate‐graft‐poly(D‐lactide)) (EMA‐g‐PDLA) blends as an example, EMA‐g‐PDLA bearing different chain lengths and grafting densities is prepared to tailor the size and packing density of interface‐localized SC crystallites. The results indicate that the interfacial structure and properties of the blends have been successfully manipulated. Compared with low‐graft‐density long PDLA chains, high‐graft‐density short ones can readily collaborate with PLLA chains to form numerous SC crystallites with smaller size and higher packing density at the interface and thus dramatically enhance the impact toughness and matrix crystallization rate. Moreover, the toughness is dominated by the content of SC crystallites, but the matrix crystallization is determined by their size and packing density. The work provides a new understanding of SC structure controlling the properties of PLLA/elastomer blends. [ABSTRACT FROM AUTHOR]

To improve the mechanical, crystallization performances of poly(l‐lactide) (PLLA), pristine and surface grafted chitin whiskers (CWs and g‐CWs) were introduced to PLLA via melt blending. Attributed to the good interfacial compatibility between the g‐CWs and PLLA matrix, the tensile, flexural, and impact performances of the g‐CWs/PLLA composites were better than that of the CWs/PLLA composites with the same whiskers content. The whiskers acted as nucleating agents to promote the crystallization of the PLLA matrix on the one hand, and acted as obstacles to restrict the crystals growth on the other hand. The nonisothermal cold crystallization kinetics revealed that the crystallization rate and crystallinity of the PLLA matrix were improved by the addition of the whiskers, but the promotion effect of g‐CWs was more obvious than CWs. [ABSTRACT FROM AUTHOR]

Poly(L-Lactide) (PLA), a fully biobased aliphatic polyester, has attracted significant attention in the last decade due to its exceptional set of properties, such as high tensile modulus/strength, biocompatibility, (bio)degradability in various media, easy recyclability and good melt-state processability by the conventional processes of the plastic/textile industry. Blending PLA with other polymers represents one of the most cost-effective and efficient approaches to develop a next-generation of PLA-based materials with superior properties. In particular, intensive research has been carried out on PLA-based blends with engineering polymers such as polycarbonate (PC), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and various polyamides (PA). This overview, consequently, aims to gather recent works over the last 10 years on these immiscible PLA-based blends processed by melt extrusion, such as twin screw compounding. Furthermore, for a better scientific understanding of various ultimate properties, processing by internal mixers has also been ventured. A specific emphasis on blend morphologies, compatibilization strategies and final (thermo)mechanical properties (tensile/impact strength, ductility and heat deflection temperature) for potential durable and high-performance applications, such as electronic parts (3C parts, electronic cases) to replace PC/ABS blends, has been made.

The development of a biodegradable vascular scaffold (BVS) for the treatment of cardiovascular diseases (CVDs) still requires some improvement. Among them, re-endothelialization and anti-inflammation are clinically important to restore vascular function. In this study, we proposed a coating system to deliver hydrophilic bioactive agents to BVS using nanoemulsion and drop-casting methods. The poly(L-lactide) (PLLA) scaffold containing magnesium hydroxide (MH) was coated on the surface with bioactive molecules such as polydeoxyribonucleotide (PDRN), L-arginine (Arg, R), and mesenchymal stem cell-derived extracellular vesicles (EVs). PDRN upregulates the expression of VEGF as one of the A2A receptor agonists; and Arg, synthesized into nitric oxide by intracellular eNOS, induces endothelialization. In particular, EVs, which are composed of a lipid bilayer and transfer bioactive materials such as protein and nucleic acid, regulate homeostasis in blood vessels. Such a bioactive agent coating system and its PLLA composite suggest a new platform for the treatment of cardiovascular dysfunction.

The conventional approach for preparation of core-sheath fibers is coaxial electrospinning. Single-spinneret electrospinning of emulsions is a much less common method to obtain core-sheath fibers. Core-sheath structure may be generated by electrospinning of homogeneous blend solutions; however, reports on such cases are still scarce. Herein, the preparation of nanofibrous composites from poly(ethylene oxide) (PEO), poly(L-lactide) (PLA) and beeswax (BW) by single-spinneret electrospinning of their homogeneous blend solutions in chloroform is reported. The produced fibers had core/double-sheath structure with a PEO core, PLA inner sheath and BW outer sheath. This original fiber structure was evidenced by transmission electron microscopy, selective extraction of BW or PEO, and X-ray photoelectron spectroscopy. The PLA/BW double sheath led to hydrophobicity of the PEO/PLA/BW mats. The tensile tests revealed that PEO/PLA/BW mats had substantially improved mechanical behavior as compared to PEO, PLA and PEO/BW mats. PEO/PLA/BW mats can be used as drug carriers as evidenced by the one-pot incorporation of the model drug 5-nitro-8-hydroxyquinoline (NQ) into the fibrous materials. Microbiological tests showed that PEO/PLA/BW/NQ had antimicrobial activity. Therefore, the new materials are promising for wound healing applications.

The effect of exogenous hydroxyl, carboxyl groups and/or Sn2+ on pyrolysis reactions of poly(L-lactide) (PLLA) was investigated by thermogravimetric analysis (TGA). The activation energy (Ea) of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose method. The kinetic models were also explored by the Malek method, and the random degradation behavior was determined by comparing the plots of In{-In[1 - (1 - w)0.5]} versus 1/T for experimental data from TGA with model reactions. The pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65–70 mg·kg-1 but increased appreciably in the presence of extraneous Sn2+, -COOH/Sn2+, or -OH/Sn2+. The Ea values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn2+ in different chemical environments because Sn2+ can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups, which were different in steric hindrance for the formation of activated complex between Sn2+ and PLLA. Under the catalysis of Sn2+, a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains, and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of lactide. However, it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol-1. [ABSTRACT FROM AUTHOR]

Nitrile oxide 1,3 dipolar cycloaddition is a simple and powerful coupling methodology. However, the self-dimerization of nitrile oxides has prevented the widespread use of this strategy for macromolecular coupling. By combining an in situ nitrile oxide generation with a highly reactive activated dipolarophile, we have overcome these obstacles and present a metal-free macromolecular coupling strategy for the modular synthesis of several ABA triblock copolymers. Nitrile oxides were generated in situ from chloroxime terminated poly(dimethylsiloxane) B-blocks and coupled with several distinct hydrophilic (poly(2-methyloxazoline) and poly(ethylene glycol)), and poly(N-isopropylacrylamide) or hydrophobic (poly(L-lactide) A-blocks terminated in activated dipolarophiles in a rapid fashion with high yield. This methodology overcomes many drawbacks of previously reported metal-free methods due to its rapid kinetics, versatility, scalability, and ease of introduction of necessary functionality. Nitrile oxide cycloaddition should find use as an attractive macromolecular coupling strategy for the synthesis of biocompatible polymeric nanostructures.

Polylactide is the most widely used biodegradable polymer. The high thermal stability and mechanical properties of polylactide makes permit a wide range of industrial applications. Polylactide has two isomers; Poly (L-lactide) (PLLA) and Poly (D-lactide) (PDLA). Blended PLLA and PDLA forms in a stereocomplex have melting points around 220-230°C higher than pure PLLA or PDLA 50°C. In this experiment, PLLA and PDLA were blended by a solution casting process using dichloromethane as solvent. The ratios of PLLA:PDLA were 100:0, 90:10, 70:30, 50:50, 30:70, 10:90 and 0:100. The blended films were then tested for their mechanical properties and thermal stability. The results showed that PLLA:PDLA at 50:50 had only one melting point around 225°C while the melting temperatures of neat PLLA and PDLA were about 172-175°C. Moreover, the blend materials also had higher tensile strength than pure PLLA or PDLA 55% as well as higher thermal stability than pure PLLA or PDLA.

This paper presents influence of the type of carbon nanotube functionalization on properties of poly(L-lactide) (PLLA) based nanocomposite materials. For this purpose surface modifications of multi-walled carbon nanotubes (MWCNTs) were performed by chemical and irradiation techniques, while thermo gravimetric analysis, UV-Visible and Fourier-transform infrared (FT-IR) spectroscopies confirmed successful covalent functionalization. Series of PLLA bionanocom-posites with different contents of functionalized MWCNTs (0.7; 1.6; 2.1 wt%), were synthesized via ring-opening solution polymerisation of L-lactide. FT-IR analysis confirmed that grafting of L-lactide, under controlled condition, is possible to perform starting from the surface of functionalized MWCNTs. From differential scanning calorimetry results it was concluded that even low contents of chemically and irradiation functionalized MWCNTs had a significant effect on thermal properties of the prepared nanocomposites, raising the values of melting and glass transition temperatures. Thermogravimetric analysis (TGA) has shown that the degradation onset temperature for composites with chemically functionalized MWCNTs, was much higher than that for the neat poly(L-lactide) sample and composites with irradiation functionalized MWCNTs. Morphology studies by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that poly(L-lactide) covered surfaces and separated functionalized MWCNTs. Good dispersion of carbon nanotubes in polymer matrix enabled conductivity of synthesized materials, as determined by conductivity tests. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45022 and Grant no. III 45020]