Reversible selectivity of water/organic solvent mixtures in poly(lactic acid) film

The separation properties of water/organic solvent mixtures in poly(lactic acid) (PLA) films were investigated. The organic solvent flux increased linearly as the feed concentration increased, whereas the water flux was almost constant up to a feed concentration of 30 wt %. Interestingly, the permselectivity of PLA films was reversed from organic solvent selectivity to high water selectivity depending on the type of organic solvent. The permselectivity was strongly correlated with the solution concentration at which the solvent‐induced crystallization of the PLA films occurred. The selectivity of permeation, solution, and diffusion in water/organic solvent mixtures was determined by the expanded free volume of the PLA films as a result of the interaction between PLA and the water/organic solvent mixture. The permeability behavior of water/organic solvent mixtures in PLA films was very complex. However, it was found that this behavior could be predicted through immersion tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43822.     

The preparation and crystallization of long chain branching polylactide made by melt radicals reaction

Long chain branching (LCB) of polylactic acid (PLA) was successfully prepared by melt radicals reaction with pentaerythritol triacrylate (PETA) and bis (1‐methyl‐1‐phenylethyl) peroxide (DCP). The topological structure of the LCB was investigated by rheology and branch‐on‐branch (BOB) model was used to estimate the exact chain structures of the products, where comb‐like LCB structures were generated due to the complex coupling between different macro‐radicals. LCB structure was found to affect the crystallization of PLA products. In the temperature range of 110–130°C, the crystallization rate parameter (k) was improved sharply and the half crystallization time was decreased significantly after the grafting of PETA, which was ascribed to the enhanced hydrogen bonding in PETA‐grafted long chain branching PLA. By comparing with the LCB PLA made from chain extension using multifunctional monomer, it shows that the crystallization becomes slower in a highly branched material with extremely long relaxation time if the effect of hydrogen bonding is similar. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crystallization of amorphous poly(lactic acid) induced by organic solvents

Crystallization of amorphous poly(lactic acid) (PLA) was investigated in various organic solvents, such as acetone, ethylacetate, diethylether, tetrahydrofurane, methanol, hexane, toluene, xylene, and o‐dichlorobenene. Most of the solvents, except hexane, induced crystallization of amorphous PLA. Acetone was the most effective solvent to accelerate the crystallization among the solvents used. The crystallization was induced by permeation of acetone into the amorphous phase of PLA, and the permeation obeyed Fick type diffusion. The crystallization rate increased with increasing of conducting temperature. Crystallized PLA formed α crystalline structure. The permeated acetone in the crystallized PLA gradually evaporated as time passes, and the elimination of acetone affected thermal and mechanical properties of the crystallized PLA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Establishing a three‐dimensional diagram with solubility parameter representing the general behavior of crystallization for amorphous poly(ethylene 2,6‐naphthalate)

Supercritical fluids having different solubility parameters were obtained by changing the parameters of supercritical CO₂ and adding a cosolvent (methanol). The crystallization behavior of amorphous poly(ethylene 2,6‐naphthalate) (PEN) in these supercritical fluids covering a wide range of solubility parameter was investigated using wide‐angle X‐ray diffraction and differential scanning calorimetry. A three‐dimensional diagram of crystallization versus temperature, pressure and solubility parameter (i.e. solvent concentration) was established to represent the general behavior of crystallization for amorphous PEN. Supercritical fluids with a higher overall solubility parameter plasticized the PEN chains more effectively and thus provided moderate conditions to induce the crystallization of amorphous PEN. Copyright © 2007 Society of Chemical Industry     

Dependence of alcohol vapor‐induced crystallization on gas and vapor permeabilities of poly(lactic acid) films

The effects of methanol and ethanol vapor‐induced crystallization on vapor and gas permeabilities and on the structure of poly(lactic acid) (PLA) films were systematically investigated. At high temperature conditions, the vapor permeability of PLA films decreased with increasing exposure time. The PLA films that were exposed to alcohol vapor became slightly cloudy, and no changes in chemical structure were observed. Alcohol vapor‐induced crystallization formed α‐crystal structure. The vapor permeability decreased with increasing crystallinity. However, nitrogen permeability slightly increased after vapor‐induced crystallization. The dependence of crystallinity on vapor and gas permeabilities was different from each penetrant. Total crystalline structures, including continuous crystal structures, remaining amorphous regions, and their interface depend on vapor and gas permeabilities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40140.     

Solvent‐ and thermal‐induced crystallization of poly‐L‐lactic acid in supercritical CO2 medium

The effect of different annealing treatments with supercritical carbon dioxide (SCCO₂) on the structural and mechanical properties of semicrystalline poly‐L ‐lactic acid (L ‐PLA) was investigated. 2000, 27,000, 100,000, and 350,000 g mol^?1 molecular weight L ‐PLA polymers were used in the study. The solid‐state processing of L ‐PLA at temperatures lower than the effective melting point led to solvent‐ and thermal‐induced crystallization. Solvent‐induced and isothermal crystallization mechanisms could be considered similar regarding the increase of polymer chain mobility and mass‐transfer in the amorphous region; however, quite different microstructures were obtained. SCCO₂ solvent‐induced crystallization led to polymers with high crystallinity and melting point. On the contrary, SCCO₂ thermal‐induced crystallization led to polymers with high crystallinity and low melting point. For these polymers, the hardness increased and the elasticity decreased. Finally, the effect of dissolving SCCO₂ in the molten polymer (cooling from the melt) was analyzed. Cooling from the melt led to polymers with high crystallinity, low melting point, low hardness, and low elasticity. Distinctive crystal growth and nucleation episodes were identified. This work also addressed the interaction of SCCO₂‐drug (triflusal) solution with semicrystalline L ‐PLA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of the processing methods on the performance of polylactide films: Thermocompression versus solvent casting

Polylactide (PLA) films were prepared by the thermocompression and solvent‐casting methods, and selected properties, such as the mechanical, water‐vapor‐barrier, thermal, and thermomechanical properties, were tested. The solvent‐cast films contained 13.7% solvent, which functioned as a plasticizer, as evidenced by the results of the measurements of dry matter and thermogravimetric analysis as well as dynamic mechanical analysis. The PLA films prepared by the thermocompression method were strong and brittle, with maximum tensile strength (σ_max) and maximum elongation at break (?_max) values of 44.0 ± 2.2 MPa and 3.0 ± 0.1%, respectively; however, the solvent‐cast films were more ductile, with σ_max and ?_max values of 16.6 ± 1.0 MPa and 203.4 ± 20.8%, respectively. The water vapor permeability of the PLA films was lower than that of plastic films such as low‐density polyethylene and high‐density polyethylene but higher than that of commonly used biopolymer films. In addition, both types of tested PLA films were water‐resistant and not soluble in water. The thermocompressed films showed higher thermal stability than the solvent‐cast films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3736–3742, 2006     

Modified kaolinites‐polyalkyl methacrylate nanocomposites: Exploring relations between solubility parameters and thermal properties for in situ solution polymerization

Poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and their nanocomposites (Kao‐PMMAs and Kao‐PEMAs) with various kaolinite intercalation compounds were prepared in several solution polymerization media in order to examine relations between solubility parameters of polymerization medium including monomer and solvent/solvents and of intercalating agents and thermal properties of the resultant materials. The measurements of X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry/derivative thermogravimetry, and differential scanning calorimetry were used to characterize these materials. The increase in solubility parameter of polymerization medium improved thermal decomposition temperatures of PEMA and Kao‐PEMAs when it usually induced a decrease in those of PMMA and Kao‐PMMAs and in glass transition temperatures of all materials. These results were also examined in respect of the effects of hydrogen bonding and dispersion components of solubility parameters of intercalating agents on the thermal properties of these materials. POLYM. COMPOS., 37:2333–2341, 2016. © 2015 Society of Plastics Engineers     

Effect of nanosilver on the photodegradation of poly(lactic acid)

The poly(lactic acid), PLA, mixed with nanosilver in solution easily forms nanocomposite in solid state (after solvent evaporation), which was proved by UV–Vis spectroscopy. This work focuses on photodegradation occurring in PLA films doped with nanosilver. The changes in chemical structure of photodegraded PLA has been determined using FTIR spectroscopy. Differential scanning calorimetry of UV‐irradiated PLA samples provided information on polymer glass transition and crystallization/melting processes. It was found that PLA alone is more sensitive to photodegradation than PLA/silver nanocomposites. The mechanism of nanocomposite photodegradation and effect of nanosilver was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40144.     

Synthesis and properties of biodegradable supramolecular polymers based on polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide triblock copolymers

Biodegradable supramolecular polymers (SMPs) were synthesized by the end‐functionalization of polylactide‐block‐poly(δ‐valerolactone)‐block‐polylactide (PLA–PVL–PLA) triblock copolymers with 2‐ureido‐4[1H]‐pyrimidinone (UPy) self‐complementary quadruple hydrogen‐bonding units. The end‐functionalized PLA–PVL–PLA copolymers exhibit the typical characteristics of thermoplastic elastomers. Thermal properties, crystallization behavior, crystalline structure and other properties of SMPs can be adjusted by changing the length and stereostructure of PLA blocks. The UPy groups retard the crystallization of PLA and PVL blocks, and the crystallization of PVL blocks is also depressed with increasing PLA blocks. Tensile testing reveals that the prepared SMPs present excellent mechanical properties, and dynamic mechanical analysis indicates that the heat resistance of l ‐SMPs is better than that of d ,l ‐SMPs. Shape memory property of SMPs was also studied, and the recovery ratio of SMPs with PDLLA blocks can reach 100%. The recovery ratio of l ‐SMPs is depressed as the crystallizable PLLA blocks increase. This study has systemically investigated the effect of the composition, stereostructure and crystallizability of PLA blocks on the properties of SMPs, which would provide potential approaches for the synthesis of biodegradable SMPs with tunable properties. © 2017 Society of Chemical Industry     

Effect of different experimental conditions on biodegradable polylactide membranes prepared with supercritical CO2 as nonsolvent

There is increasing interest in the application of supercritical CO₂ (SCCO₂) in the preparation of polymer membranes. Membrane formation with SCCO₂ as a nonsolvent is analogous to the conventional immersion precipitation process using an organic nonsolvent. Polylactide membranes were prepared with SCCO₂ as the nonsolvent under different experimental conditions such as different polymer concentrations, different depressurization rates, and different nonsolvent compositions. The effects of these conditions on the cross‐sectional structure were investigated through scanning electron microscopy. In addition, solvent‐induced crystallization and CO₂‐induced crystallization were studied. The crystallinity of PLA membranes prepared with different solvents or at different pressures was characterized by wide‐angle X‐ray diffraction and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 831–837, 2005     

Physicochemical characterization of lignin recovered from microwave‐assisted delignified lignocellulosic biomass for use in biobased materials

Lignocellulosic biomass (Moso Bamboo, Chinese tallow tree wood, switchgrass, and pine wood) was subjected to a novel delignification process using microwave energy in a binary glycerol/methanol solvent. The physicochemical properties of the recovered lignin were analyzed prior to its application in the fabrication of polylactic acid (PLA)–lignin composites. The results showed that the samples had a high Klason lignin content (>75%) and retained their natural structure. Thermogravimetric analysis revealed that the recovered lignin exhibited a different thermal decomposition pattern from that of commercial lignins. All the recovered lignins had good solubility in common organic solvents (acetone, 1,4‐dioxane, THF, DMSO, and ethanol/water) and 1 mol/L NaOH solution. The addition of lignin into the PLA matrix resulted in the improvement in tensile properties of PLA–lignin composites. PLA films with low lignin content had good UV light‐resistant properties, indicating that the recovered lignin has potential in packaging of light‐sensitive products. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42635.     

Water vapor solubility of poly(lactic acid) films modified the surface by vacuum ultraviolet irradiation

Surface modification of poly(lactic acid) (PLA) film is performed via 172 nm excimer lamp irradiation. Effects on water vapor solubility and physical properties via vacuum ultraviolet (VUV) irradiation are studied systematically. After VUV irradiation, water vapor solubility increases approximately 11–43% in the low‐pressure region and approximately 20–38% in the high‐pressure region as surface hydrophilicity increased. The increase is attributed to hydrogen bonding with the carboxyl groups because of VUV radiation. The modified layer is significantly swelling after water vapor sorption. The hydrophilic layer forms a thickness of 2–3 μm from the irradiated surface via VUV radiation, but no changes are observed inside the irradiated film. Therefore, PLA film solubility after irradiation is enhanced by hydrophilicity and the swelling effect of the surface. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42200.     

Tri‐(butanediol‐monobutyrate) citrate plasticizing poly(lactic acid): Synthesis,crystallization, thermal,and mechanical properties

Tri‐(butanediol‐monobutyrate) citrate (TBBC) as a new plasticizer for poly(lactic acid) (PLA) was synthesized via a two‐step esterification. The chemical structure of TBBC was characterized by ¹H‐nuclear magnetic resonance. The studies on solubility parameters, transparence, and storage stability indicated the good miscibility between PLA and TBBC. The glass transition, crystallization, thermal, and mechanical properties of PLA plasticized by TBBC were evaluated. With an increase in TBBC content, the glass transition temperature (T_g), melting point (T_m), and the cold crystallization temperature (T_cc) of plasticized PLA gradually shifted to a lower temperature. The elongation at break and flexibility were greatly improved by the addition of TBBC. After 30 days of storage, PLA plasticized with up to 20 wt% of TBBC exhibited good storage stability and remained the original transparence and mechanical properties. The flexibility of PLA/TBBC films can be tuned by changing TBBC content. The corresponding crystalline morphology and structure were investigated by Polarizing optical microscope and X‐ray diffraction as well. This study revealed that TBBC was miscible with PLA and may therefore be a promising plasticizer for PLA‐based packaging materials. POLYM. ENG. SCI., 55:205–213, 2015. © 2014 Society of Plastics Engineers     

Preparation and characterization of poly(lactic acid)/poly(ethylene oxide) blend film: effects of poly(ethylene oxide) and poly(ethylene glycol) on the properties

Poly(lactic acid) (PLA) film plasticized with poly(ethylene oxide) (PEO) at various weight percentages (1–5 wt%) was prepared to improve the elongation, thus overcoming the inherent brittleness of the material. After optimization of the amount of PEO (4 wt%) through mechanical analysis, poly(ethylene glycol) (PEG), a well‐established plasticizer of PLA, was added (0.5–1.5 wt%) without hampering the transparency and tensile strength much, and again its amount was optimized (1 wt%). Neat PLA and PLA with the other components were solvent‐cast in the form of films using chloroform as a solvent. Improvement in elongation at break and reduction in tensile strength suggested a plasticizing effect of both PEO and PEG on PLA. Thermal and infrared data revealed that the addition of PEO induced β crystals in PLA. Scanning electron micrographs indicated a porous surface morphology of the blends. PEO alone in PLA exhibited the best optical clarity with higher percentage crystallinity, while PEG incorporation in PLA/PEO resulted in superior barrier properties. Also, the stability of the blends under a wide range of pH means prospective implementation of the films in packaging of food and non‐food‐grade products. © 2018 Society of Chemical Industry     

Improvement of microstructures and properties of poly(lactic acid)/poly(ε‐caprolactone) blends compatibilized with polyoxymethylene

Incompatibility of poly(lactic acid)/poly(?‐caprolactone) (PLA/PCL) (80:20) and (70:30) blends were modified by incorporation of a small amount of polyoxymethylene (POM) (≤3 phr). Impact of POM on microstructures and tensile property of the blends were investigated. It is found that the introduction of POM into the PLA/PCL blends significantly improves their tensile property. With increasing POM loading from zero to 3 phr, elongation at break increases from 93.2% for the PLA/PCL (70:30) sample to 334.8% for the PLA/PCL/POM (70:30:3) sample. A size reduction in PCL domains and reinforcement in interfacial adhesion with increasing POM loading are confirmed by SEM observations. The compatibilization effect of POM on PLA/PCL blends can be attributed to hydrogen bonding between methylene groups of POM and carbonyl groups of PLA and PCL. In addition, nonisothermal and isothermal crystallization behaviors of PLA/PCL/POM (70:30:x) samples were investigated by using differential scanning calorimetry and wide angle X‐ray diffraction measurements. The results indicate that the crystallization dynamic of PLA matrix increases with POM loadings. It can be attributed to the fact that POM crystals have a nucleating effect on PLA. While crystallization temperature is 100 °C, crystallization half‐time can reduce from 9.4 to 2.0 min with increasing POM loading from zero to 3 phr. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46536.     

Effect of casting solvent on characteristics of hexanoyl chitosan/polylactide blend films

Blend films of hexanoyl chitosan (H‐chitosan) and polylactide (PLA) were cast from corresponding blend solutions in chloroform, dichloromethane, or tetrahydrofuran. Thermal degradation behavior of the as‐prepared blend films was intermediate to those of the pure components and no significant effect from the type of the casting solvent was observed. All of the blend films exhibited one composition‐dependent glass transition temperature, but the results only suggested partial miscibility of the components in the amorphous phase at “low” contents of H‐chitosan. As revealed by solvent etching technique, the as‐prepared blend films prepared from the blend solutions in chloroform and dichloromethane showed extensive phase separation of the two components, with the minor phase forming into discrete domains throughout the matrix. Both thermal and X‐ray analyses showed that the apparent degree of crystallinity of the PLA component in the blends decreased monotonically with increasing H‐chitosan content and the choice of the casting solvent did not have an effect on the structure of PLA crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Fabrication of porous polylactic acid films assisted by dip‐coating and template leaching techniques

A new simple method was developed to fabricate porous polylactic acid (PLA) films coated directly on substrates. The PLA films with a controllable thickness were realized using a dip‐coating technique. The pore structure of the resulting porous PLA films was tailored by utilizing phase inversion process and template leaching techniques. The experimental results show that the resulting PLA films became thicker when using the coating solution with a higher viscosity or applying a faster withdrawal speed. The porous structures (pore size and void density) of the resulting PLA films are significantly influenced by the polymer concentration, the nonsolvents, and the addition of poly(ethylene glycol) templates. The analyses of solubility parameters was utilized to explain the porous structures of the resulting PLA films in details. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on properties and aggregation structures of deacetylated konjac glucomannan/chitosan hydrochloride absorbent blend gel films

A series of novel blend films of deacetylated konjac glucomannan (d‐KGM) and Chitosan hydrochloride (CHI·HCl) were prepared successfully by using the solvent‐casting technique with different blending ratios of the two polymers. The miscibility and aggregation structure of the blend films were studied by Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction and scanning electron microscopy. The results indicated that the blend system of d‐KGM and CHI·HCl had a conditional miscibility. A new crystal occurred and hydrogen‐bonding interaction was strengthened when the CHI·HCl content in the blend films was 40%. The effects of deacetylation degree of KGM, acids (the solvent Chitosan dissolved in), temperature, and the mix ratio on the swelling behavior of the blend films were also studied. The blend film KC3 (CHI·HCl content in the blend films was 30%) had not only the highest equilibrium swelling degree (26 times) but also the highest tensile strength, and it could be regarded as a potential absorbent film material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Three‐dimensional solubility parameters of poly(ε‐caprolactone)

The three‐dimensional solubility parameter model was applied to analyze solution thermodynamic data of 27 solutes in poly(ε‐caprolactone) (PCL) between 70 and 110 °C. A linear regression method was compared with a nonlinear least square regression method, which searches solubility parameter components by minimization of the sum of error squares. The parameters of polymers were the same by both methods. When compared with the error in predicting χRT/V, the data showed a different slope from the simple three‐dimensional model. These deviations were reduced by a different model using a smaller weight on the polar and hydrogen bonding components. In the new model, the solubility parameter components were closer to the value of a structure analogue of PCL. The confidence intervals for the parameters were estimated from a linearized equation based on the sum of error squares. The solubility parameter components obtained were different from the average values of the five solutes with the smallest χ. The inclusion of solutes with high hydrogen bonding components contributed to the increase of the component in the nonlinear regression method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2002–2009, 2006