Lactic Acid Oligomers Research Articles

Preparation of silver nanoparticles by using the hydrolyzates of poly(lactic acid) and their application for the antibacterial functionalization of poly(lactic acid) non-woven fabric

Poly(lactic acid) (PLA) fiber, owning to its biodegradability and biocompatibility, has extensive applications in many fields including textiles, and an enhanced antibacterial function can increase its application value. This work presents an innovative approach to prepare silver nanoparticles (AgNPs) using the hydrolytic degradation products of PLA fiber in the scouring process that contain reducing hydrolyzates (lactic acid and oligomers of lactic acid), and to functionalize PLA non-woven fabric using the resulting AgNPs. The preparation and application conditions of AgNPs were discussed. AgNPs with an average size of 80 nm were obtained at pH 9 and 90 °C with no use of an additional reducing agent in the presence of the use of polyvinyl pyrrolidone as a stabilizer, and exhibited good storage stability. PLA non-woven fabric was successfully treated with AgNPs using an impregnation technique at pH 4 and 70 °C, and the treated fabric exhibited excellent antibacterial activity against Escherichia coli and Staphylococcus aureus, even in the case of a low amount of Ag loading.

Sustained Dye Release Using Poly(urea-urethane)/Cellulose Nanocrystal Composite Microcapsules.

The aim of this study is to develop methods to reinforce polymeric microspheres with cellulose nanocrystals (CNCs) to make eco-friendly microcapsules for a variety of applications such as medicines, perfumes, nutrients, pesticides, and phase change materials. Surface hydrophobization treatments for CNCs were performed by grafting poly(lactic acid) oligomers and fatty acids (FAs) to enhance the dispersion of nanoparticles in the polymeric shell. Then, a straightforward process is demonstrated to design sustained release microcapsules by the incorporation of the modified CNCs (mCNCs) in the shell structure. The combination of the mCNC dispersion with subsequent interfacial polyurea (PU) to form composite capsules as well as their morphology, composition, mechanical properties, and release rates were examined in this study. The PU microcapsules embedded with the mCNC were characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The morphologies of the microcapsules were characterized by optical microscopy (OM) and scanning electron microscope (SEM). The rupture stress and failure behavior of the microcapsules were determined through single-capsule compression tests. Oil-soluble Sudan II dye solution in mineral oil was utilized as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency was measured spectroscopically. The release rates of the encapsulated dye from the microcapsules were examined spectroscopically by both ethanol and 2-ethyl-1-hexanol medium at room temperature. The concentration of released dye was determined by using UV-vis absorption spectrometry (UV-vis). The mCNC embedded poly(urea-urethane) capsules have strong and dense walls, which function as excellent barriers against leakage due to their extended diffusion path length and ensure enough mechanical strength from rupture for handling or postprocessing.

Functional Properties of Plasticized Bio-Based Poly(Lactic Acid)_Poly(Hydroxybutyrate) (PLA_PHB) Films for Active Food Packaging

Fully bio-based and biodegradable active films based on poly(lactic acid) (PLA) blended with poly(3-hydroxybutyrate) (PHB) and incorporating lactic acid oligomers (OLA) as plasticizers and carvacrol as active agent were extruded and fully characterized in their functional properties for antimicrobial active packaging. PLA_PHB films showed good barrier to water vapor, while the resistance to oxygen diffusion decreased with the addition of OLA and carvacrol. Their overall migration in aqueous food simulant was determined and no significant changes were observed by the addition of carvacrol and OLA to the PLA_PHB formulations. However, the effect of both additives in fatty food simulant can be considered a positive feature for the potential protection of foodstuff with high fat content. Moreover, the antioxidant and antimicrobial activities of the proposed formulations increased by the presence of carvacrol, with enhanced activity against Staphylococcus aureus if compared to Escherichia coli at short and long incubation times. These results underlined the specific antimicrobial properties of these bio-films suggesting their applicability in active food packaging.

Influence of Water and Humidity on Wood Modification with Lactic Acid

Impregnation of dry wood with pure lactic acid oligomers (OLAs) followed by heat treatment confers promising properties to wood because of OLA's good diffusion, in-situ polymerization and persistence in cell walls. Treatment provides drastic reduction of the equilibrium moisture content, high dimensional stability and good durability. The presence of water during treatment has been evaluated. Curing of OLA impregnated dry wood in humid atmosphere leads to a strong and global degradation of the material. OLA treatment of wet wood only impacts the water leaching rate negatively. Treatment of dry wood with OLA diluted in water additionally decreases the biological resistance and is not efficient for decreasing hygroscopicity. Treatment of dry wood with lactic acid solution leads to a lower polymerization level but confers good properties.

Equilibrium condition and stabilization kinetics of lactic acid oligomers in aqueous solutions

Lactic acid is one of the most important compounds in the field of bio‐renewable chemicals. Lactic acid is present in nature but can also be produced by chemical synthesis or by fermentation of biomass. It can be used as raw material for the production of biodegradable and environmentally friendly polymers or copolymers, such as poly lactic acid (PLA).In this work, the equilibrium distribution of monomer and low molecular weight oligomers of lactic acid in aqueous solutions at different overall concentrations of lactic acid (from 0.09 g/g to 0.94 g/g) and temperatures (423 K and 453 K), was investigated.In addition, a kinetic study of monomer and oligomer esterification reactions, of a lactic acid aqueous solution at about 0.09 g/g, was carried out at 423, 433, 443, and 453 K. The values of the kinetic constants were successfully correlated through Arrhenius’ law.

Thermal degradation of poly(lactic acid) oligomer: Reaction mechanism and multistep kinetic behavior

This study was aimed to reveal the kinetic and mechanistic features of the thermal degradation of linear poly(lactic acid) oligomer (PLAO) by analyzing the evolved gases and overall rate behavior during mass-loss processes. The thermal degradation reaction involved two partially overlapping mass-loss steps. The first mass-loss step started right after the reactant melted and was accompanied with the release of lactides as the main gaseous products while maintaining the microscopic appearance of molten PLAO. The mass-loss rate behavior was controlled by a diffusion process with an apparent activation energy (Ea) of approximately 90 kJ mol–1, with the diffusional transfer of lactides from the reaction sites to the top surface of the molten PLAO being considered as the rate-limiting step. The second mass-loss step became noticeable at reacting system temperatures above the boiling point of lactides. During this dramatically accelerated mass-loss step, carbon oxides, aldehydes, lactides, and cyclic PLAO with large molecular weights were simultaneously evolved with frequent formation and disappearance of gaseous bubbles in the molten reacting system. In this step, the overall rate behavior was largely influenced by the bubbling phenomena for which the Ea value was determined to be approximately 155 kJ mol–1. The changes in the chemical mechanism and the physico-geometrical reaction behavior midway through the thermal degradation reaction were both illustrated by the change in the molten reacting system in view of degradation-polymerization equilibrium via the boiling points of lactides.

Poly(lactic acid)‐based nanocomposites filled with cellulose nanocrystals with modified surface: all‐atom molecular dynamics simulations

AbstractPolymer bio‐nanocomposites are widely used nowadays in various applications. One of the most promising polymers for producing such materials is poly(lactic acid) (PLA) filled with cellulose nanocrystals (CNCs). To increase the compatibility of hydrophobic PLA and hydrophilic cellulose, the surface of the latter can be chemically modified. Among the various surface modifications, the grafting of lactic acid oligomers (OLAs) is of special interest. In this paper, the first all‐atom molecular dynamics simulation of nanocomposites of PLA filled with CNCs with surface‐grafted OLAs is presented. The influence of the degree of modification of the CNCs with OLA chains on the PLA structure near the CNC surface and on the grafted OLA, as well as on the thermal and mechanical properties of the nanocomposites is studied. It is demonstrated that a 50% modification of CNCs with OLA chains leads to PLA expulsion from the CNC surface. © 2016 Society of Chemical Industry

Biodegradable polyesters based on star-shaped lactic acid oligomers

Catalytic polymerization of ε-caprolactone and copolymerization of maleic anhydride and propylene or ethylene oxide carried out in the presence of star-shaped L-lactic acid oligomers were studied. The analysis of the reaction products by means of GPC, MALDI ToF and 1H NMR show that the applied processes allowed to combine oligomers with polyesters produced by ring opening polymerization and obtain a new type of lactic acid copolymers of relative molar masses in the range 15–60 kg/mol. DSC studies revealed that the formed polyesters segments were fully or partially miscible with poly(lactic acid) core causing the reduction of its glass transition temperature. Selected copolymers were subjected to enzymatic degradation, which indicated that all of these compounds underwent partial decomposition. An analysis of weight loss showed, however, that the degradation occurred more slowly than in the case of poly(lactic acid) of similar molar masses and chain architecture.

Enhanced in Vitro Mineralization and in Vivo Osteogenesis of Composite Scaffolds through Controlled Surface Grafting of L-Lactic Acid Oligomer on Nanohydroxyapatite.

Nanocomposite of hydroxyapatite (HA) surface grafted with L-lactic acid oligomer (LAc oligomer) (op-HA) showed improved interface compatibility, mechanical property, and biocompatibility in our previous study. In this paper, composite scaffolds of op-HA with controlled grafting different amounts of LAc oligomer (1.1, 5.2, and 9.1 wt %) were fabricated and implanted to repair rabbit radius defects. The dispersion of op-HA nanoparticles was more uniform than n-HA in chloroform and nanocomposites scaffold. Calcium and phosphorus exposure, in vitro biomineralization ability, and cell proliferation were much higher in the op-HA1.1 wt %/PLGA scaffolds than the other groups. The osteodifferentiation and bone fusion in animal tests were significantly enhanced for op-HA5.2 wt %/PLGA scaffolds. The results indicated that the grafted LAc oligomer of 5.2 or 9.1 wt %, which formed a barrier layer on the HA surface, prevented the exposure of nucleation sites. The shielded nucleation sites of op-HA particles (5.2 wt %) might be easily exposed as the grafted LAc oligomer was decomposed easily by enzyme systems in vivo. Findings from this study have revealed that grafting 1.1 wt % amount of LAc oligomer on hydroxyapatite could improve in vitro mineralization, and 5.2 wt % could promote in vivo osteogenesis capacity of composite scaffolds.

Composition dependence of the synergistic effect of nucleating agent and plasticizer in poly(lactic acid): A Mixture Design study

Blends consisting of commercial poly(lactic acid) (PLA), poly(lactic acid) oligomer (OLA8) as plasticizer and a sulfonic salt of a phthalic ester and poly(D-lactic acid) as nucleating agents were prepared by melt extrusion, following a Mixture Design approach, in order to systematically study mechanical and thermal properties as a function of composition. The full investigation was carried out by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile tests. The crystallization half-time was also studied at 105°C as a function of the blends composition. A range of compositions in which the plasticizer and the nucleation agent minimized the crystallization half-time in a synergistic way was clearly identified thanks to the application of the Mixture Design approach. The results allowed also the identification of a composition range to maximize the crystallinity developed during the rapid cooling below glass transition temperature in injection moulding, thus allowing an easier processing of PLA based materials. Moreover the mechanical properties were discussed by correlating them to the chemical structural features and thermal behaviour of blends.

A New Effective, User-friendly Bacterial Vaginosis Treatment: A Randomized Multicenter Open-label Parallel-group Two-part Study with a Novel Sustained-release Pessary Containing Oligomeric Lactic Acid

A New Effective, User-friendly Bacterial Vaginosis Treatment: A Randomized Multicenter Open-label Parallel-group Two-part Study with a Novel Sustained-release Pessary Containing Oligomeric Lactic Acid

Scale-Up of Polymerization Process of Biodegradable Polymer Poly(lactic acid) Synthesis Using Direct Polycondensation Method

Environmental problems from petroleum-based plastic wastes have been rapidly increasing in recent years. The alternative solution is focus on the development of environmental friendly plastic derived from renewable resource. Poly(lactic acid) (PLA) is a biodegradable polymer synthesized from biomass having potential to replace the petroleum-based non-degradable polymers utilizations. PLA can be synthesized by two methods: (1) ring-opening of lactide intermediate and (2) direct polycondensation of lactic acid processes. The latter process has advantages on high yields and high purity of polymer products, materials handling and ease of process treatments. The polymerization process of PLA synthesis has been widely studied in a laboratory scale. However, the mass scale production using direct polycondensation of lactic acid has not been reported. We have investigated the kinetics and scale-up process of direct polycondensation method to produce PLA in a pilot scale. The order of reaction is 2 and activation energy of lactic acid to lactic acid oligomers is 61.58 kJ/mol. The pre-polymer was further polymerized in a solid state polymerization (SSP) process. The synthesized PLA from both the laboratory and pilot scales show the comparable properties such as melting temperature and molecular weight. The appearance of synthesized PLA is yellow-white solid powder.

Photocurable bioadhesive based on lactic acid.

Novel photocurable and low molecular weight oligomers based on l-lactic acid with proven interest to be used as bioadhesive were successfully manufactured. Preparation of lactic acid oligomers with methacrylic end functionalizations was carried out in the absence of catalyst or solvents by self-esterification in two reaction steps: telechelic lactic acid oligomerization with OH end groups and further functionalization with methacrylic anhydride. The final adhesive composition was achieved by the addition of a reported biocompatible photoinitiator (Irgacure® 2959). Preliminary in vitro biodegradability was investigated by hydrolytic degradation in PBS (pH=7.4) at 37 °C. The adhesion performance was evaluated using glued aminated substrates (gelatine pieces) subjected to pull-to-break test. Surface energy measured by contact angles is lower than the reported values of the skin and blood. The absence of cytoxicity was evaluated using human fibroblasts. A notable antimicrobial behaviour was observed using two bacterial models (Staphylococcus aureus and Escherichia coli). The cured material exhibited a strong thrombogenic character when placed in contact with blood, which can be predicted as a haemostatic effect for bleeding control. This novel material was subjected to an extensive characterization showing great potential for bioadhesive or other biomedical applications where biodegradable and biocompatible photocurable materials are required.

Synergistic effect of lactic acid oligomers and laminar graphene sheets on the barrier properties of polylactide nanocomposites obtained by thein situpolymerization pre‐incorporation method

ABSTRACTNanocomposites of polylactide (PLA) and functionalized graphene sheets (FGS) were obtained via melt compounding. Pre‐incorporation of the FGS fillers into lactic acid oligomers (OLLA) byin situmelt polycondensation was performed with the aim of improving the FGS dispersion and distribution into the polymeric matrix. To evaluate the effect of the pre‐incorporation step, a comparison with direct addition of the filler to the melt mixing process was carried out. Addition of OLLA and FGS led to enhanced better barrier properties. Specifically, reductions of up to 45% and 41% in oxygen and water vapor permeability were achieved, respectively. Mechanical and electrical properties of the PLA and its nanocomposites were also studied and correlated with both the addition of oligomers and the incorporation method. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2016,133, 42661.

Bioactive composites produced in situ on the basis of calcium phosphates and lactic acid oligomers

Composites based on lactic acid oligomers, calcium hydrophosphate and hydroxyapatite synthesized under the action of microwave radiation were obtained in situ. The appearance of a new band associated with stretching vibrations of >C=O in spectra of the chloroform-insoluble fraction is indicative of the chemical interaction between lactic acid and hydroxyapatite. To determine whether a calcium phosphate layer can be formed on the surface of composite samples, biomimetic studies in a physiological SBF solution were carried out during 28 days at 37°C. It was found that all samples containing calcium phosphates promote active formation of a new calcium phosphate layer, whereas lactic acid oligomer in samples containing no inorganic component undergoes destruction in the SBF solution as a result of hydrolysis. The estimate of the resorption rate demonstrated that the solubility of calcium phosphates contained in the composites at 20°C in the physiological solution is 3–7 times that of pure hydroxyapatite.

Plasticization of poly(lactic acid) through blending with oligomers of lactic acid: Effect of the physical aging on properties

Two oligomers of lactic acid (OLAs), carboxyl (OLA-COOH) or hydroxyl (OLA-OH) end capped, were employed to modulate physical and mechanical properties of poly(lactic acid), PLA. Blends up to 25wt.% by weight of OLAs were prepared by melt mixing. Mechanical, thermal and transport properties of the materials were tested as a function of OLA functional moieties and blend composition. Moreover, the effect of physical aging on structure and properties of blends was studied by storing the samples in controlled temperature and humidity conditions, up to 8weeks.OLAs significantly affect mechanical properties of PLA; blends showed an interesting ductility even after aging, suggesting their use as flexible films. Moreover, gas transport and total migration properties of blends are suitable for packaging applications.

Bioactivity and Physico-Chemical Properties of Composites on Basis of Hydroxyapatite with Lactic and Glycolic Acids Oligomers

A new methodin situfor producing of biocompatible composites based on hydroxyapatite and oligomers of lactic and glycolic acid is described. Their thermo-mechanical, physical-chemical and biological properties are studied as well. The formation of bonds between hydroxyapatite with lactic and glycolic oligomers in composites are confirmed by IR spectroscopy of the samples, including those obtained in the Soxhlet apparatus. The formation of calcium-phosphate layer on the composite's surface containing hydroxyapatite was shown by SBF-investigation. The scaffolds based on lactic acid oligomer do not stimulate formation of a calcium-phosphate layer and they are subjected to destruction by the way of hydrolysis.

Melt polycondensation to improve the dispersion of bacterial cellulose into polylactide via melt compounding: enhanced barrier and mechanical properties

Nanocomposites of polylactide (PLA) and bacterial cellulose nanowhiskers (BCNW) with improved properties were obtained through melt compounding. Prior to melt processing, and with the aim of improving BCNW dispersion, lactic acid oligomers (OLLA) were in situ polymerized in the presence of the nanofiller (both freeze-dried and partially hydrated). This in situ polymerization reaction enhanced the compatibilization between hydrophilic cellulose and hydrophobic PLA, even leading to chemical grafting of the OLLA onto the surface of BCNW, when this was used in a partially hydrated form. The optimized dispersion attained through this pre-incorporation strategy was confirmed by comparison with materials obtained through direct melt compounding of PLA with BCNW. Differential scanning calorimetry experiments showed that although cellulose content had not effect on melting temperatures, the degree of crystallinity was significantly affected. Addition of grafted BCNW also resulted in improved mechanical properties increasing the elastic modulus and tensile strength up to 52 and 31 %, respectively, mainly ascribed to the promotion of filler–filler and filler–matrix interactions. Moreover, the developed nanocomposites showed improvements in the water and oxygen barrier properties (measured at 80 % RH), respectively, which make them attractive for food packaging applications. This could be explained by well-dispersed nanocrystals acting as blocking agents within the polymeric matrix, reducing the diffusion through the nanocomposite films and, hence, the water and oxygen permeability. Therefore, this work offers a new route for incorporating well dispersed nanocellulose within a hydrophobic PLA matrix, overcoming the dispersion problems that this entails, especially when working with melt compounding methods.

Copolymers from epoxidized soybean oil and lactic acid oligomers for pressure-sensitive adhesives

Corn based lactic acid oligomers and soybean based epoxidized oil were copolymerized under UV irradiation for biobased pressure-sensitive adhesives (PSA).

Vacuum Effect on the Lactide Yield

The vacuum effect on the yield and purity of lactide obtained by catalytic lactic acid oligomer depolymerization was investigated. As raw material for the lactic acid oligomer synthesis the L-lactic acid aqueous solution was used. It was shown that the highest yield of raw-lactide takes place via distillation under a vacuum. The raw-lactide in all fractions was purified by recrystallization from dry ethyl acetate. The highest yield of raw-lactide is observed at a vacuum of 10 ... 15 mbar. The distillation process of raw-lactide is complicated with chemical reactions. Control of the reaction, raw materials and products was performed using DTA, gel permeation chromatography, infrared spectroscopy and high performance liquid chromatography.