Toughening of poly(lactic acid) with the renewable bioplastic poly(trimethylene malonate)

The aim of this work was to enhance poly(lactic acid)'s (PLA) flexibility and ductility by blending it with another bioplastic. Poly(trimethylene malonate) (PTM), developed as part of this study, was synthesized from 1,3‐propane diol and malonic acid via melt polycondensation. Blend films of PLA and PTM were prepared by solvent casting from chloroform. Differential scanning calorimetry and thermogravimetric analysis were used to show shifted phase transitions and a single glass‐transition temperature, indicating miscibility of PTM in the blend films. Morphology and mechanical characterizations of the PLA/PTM blend films were performed by atomic force microscopy using a quantitative nanomechanical property mapping mode, tensile testing, and scanning electron microscopy. Miscible blends exhibited Young's modulus and elongation at break values that can significantly extend the usefulness of PLA in commercial applications. The blending of PTM with PLA resulted in films with a 27‐fold increase in toughness compared with neat PLA film. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40888.     

The effect of solvent mixture on the properties of solvent cast polylactic acid (PLA) film

The objective of this study was to investigate the effects of various solvents on the crystallinity and thermal expansion stability of PLA film. Three different PLA films were produced by the solvent casting technique; PLA in chloroform (PLA‐C), PLA in methylene chloride (PLA‐M), and PLA in methylene chloride: acetonitrile = 50: 50 (PLA‐MA). The PLA‐MA had higher % crystallinity, 46.15, than the PLA‐C, 24.03, and the PLA‐M, 14.25. With this increase in crystallinity, the PLA‐MA had improved thermal expansion stability as shown by very low accumulated dimensional changes at 20 to 100°C. Wide‐angle X‐ray diffraction identified multiple crystalline structures for the PLA‐MA. Film barrier properties were also measured. PLA‐MA had the lowest oxygen permeability. However, there was no significant difference in water vapor permeability among the three PLA films. The mechanical property tests revealed that the PLA‐C and PLA‐M were ductile while the PLA‐MA was brittle in behavior. The PLA‐MA was very hazy as compared with the PLA‐C and PLA‐M. This work has shown that the PLA‐MA had increased % crystallinity and, more importantly, it had improved thermal expansion stability which can be very beneficial for the flexible packaging industry. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

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     

Fabrication of honeycomb‐structured porous films from poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) via the breath figures method

Formation of porous films from poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) using the breath figures (BF) method was investigated by evaporating solutions in chloroform in humid air and examining film structure using optical and scanning electron microscopy (SEM). BF films were successfully fabricated from PHB (M_w = 486,000 g/mol) and displayed hexagonal arrays of pores, which varied in diameter (D = 7–2 μm) with solution concentrations (0.5–2.00%). SEM of fractured films also showed subsurface closed nano‐pores (D = 500–700 nm). BF films cast from PHBV (5% HV) formed arrays with smaller pores and apparent surface defects. Differential scanning calorimetry showed that porous PHB and PHBV films produced using the BF method were more crystalline than nonporous solvent cast films of PHB and PHBV. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Bicontinuous networks made of polyphosphates and of thermoplastic polymers

Composite films are obtained by casting aqueous dispersions obtained by admixture of PVAc or styrene-acrylic latexes with aluminium or iron polyphosphate powders. Film extraction with solution of aqueous EDTA (a solvent for polyphosphate) yields a dense polymer film, but using a polymer solvent (chloroform) a porous monolithic solid is obtained. Composite and solvent-extracted films were characterized by SEM coupled to energy dispersive X-ray analysis, and by Raman microspectrophotometry. The results from morphological, spectral and gravimetric experiments show that the cast films are bicontinuous, indicating a strong compatibility of the organic and inorganic phases. This is assigned to ionic bonds at the interfaces, in which aluminium ions act as bridging groups. © 1997 Elsevier Science Ltd.     

Effect of incorporation of graphene oxide and graphene nanoplatelets on mechanical and gas permeability properties of poly(lactic acid) films

Nanocomposite thin films of poly(lactic acid) (PLA) were produced incorporating small amounts (0.2 to 1 wt%) of graphene oxide (GO) and graphene nanoplatelets (GNP). The films were prepared by solvent‐casting. Mechanical properties were evaluated for plasticized (by residual solvent) and unplasticized films. Plasticized nanocomposite films presented yield strength and Young's modulus about 100% higher than those of pristine PLA. For unplasticized films improvements in tensile strength and Young's modulus were about 15 and 85%, respectively. For both film types, a maximum in mechanical performance was identified for about 0.4 wt% loadings of the two filler materials tested. Permeabilities towards oxygen and nitrogen decreased, respectively, three‐ and fourfold in films loaded with both GO or GNP. The glass transition temperature showed maximum increases, in relation to unloaded PLA films, of 5 °C for 0.4 wt% GO and 7 °C for 0.4 wt% GNP, coinciding with the observed maxima in mechanical properties. Copyright © 2012 Society of Chemical Industry     

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     

Morphological control of porous ethylene‐vinyl acetate copolymer membrane obtained from a co‐continuous ethylene‐vinyl acetate copolymer/poly(ϵ‐caprolactone) blend

Ethylene‐vinyl acetate copolymer (EVA)/poly(?‐caprolactone) (PCL) blend (50/50 w/w) with co‐continuous morphology was prepared via melt mixing for fabricating microporous EVA membrane materials through selective solvent extraction. Shear flow and quiescent annealing techniques were employed to control co‐continuous phase size in the EVA/PCL blend, and the time‐ and temperature‐dependent relations of phase size were then evaluated theoretically. Using these techniques, microporous EVA membrane materials with various pore sizes ranging from 2 µm to more than 200 µm were obtained. In contrast to the porous EVA membrane prepared by the traditional way of solvent casting/particulate leaching, the as‐obtained microporous membrane shows a higher level of interconnectivity and much narrower pore size distribution with uniform pore structure. © 2013 Society of Chemical Industry     

豌豆淀粉/聚乳酸双层膜的制备与性能表征

采用溶液流延法以豌豆淀粉（PS）和聚乳酸（PLA）为原料制备了豌豆淀粉/聚乳酸（PS/PLA）双层薄膜。通过对双层薄膜的吸水性、溶解性、水蒸气透过性、拉伸性能、表面形貌等进行测试,研究了薄膜的力学性能、疏水性能以及水蒸气阻隔性能。结果表明：随着双层膜中聚乳酸层的比例增加,双层薄膜的吸水性、溶解性和水蒸气透过性逐渐降低,拉伸强度和拉伸模量逐渐增加,断裂伸长率逐渐下降,表明水蒸气阻隔效果明显,增加了膜的韧性,降低了膜的强度。当PLA和PS的质量比为50：50时,PS/PLA双层膜的拉伸强度为（13.47±0.75）MPa,拉伸模量为（0.848±0.002）GPa;断裂伸长率为（16.11±0.16）%,水蒸气透过系数为0.27×10^-10 g·cm/（cm²·s·Pa）。     

Preparation of superhydrophobic silica‐based films by using polyethylene glycol and tetraethoxysilane

Preparation of superhydrophobic silica‐based films via sol‐gel process by adding polyethylene glycol (PEG4000) in the silica sol precursor solution has been developed. The casting films were prepared by casting the above solution on the glass and adding poor solvent on it or not. Surface roughness of the films was obtained by removing polymer from the films at high temperature. Then, the hydrophobic group on the surfaces was obtained by reaction with hexamethyldisilazane (HMDS). Characteristic properties of the as‐prepared surface of the films were analyzed by contact angle measurement, scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared (FT‐IR) spectrophotometer, and X‐ray photoelectron spectrometer (XPS). The results showed that the contact angles of the films were varied with the PEG weight fraction of the films, the solvent for the PEG solution, the reaction temperature and time, and adding poor solvent (n‐hexane) or not. However, the surface roughness has been controlled by adjusting the experimental parameters during the early period. The contact angle of the film that prepared by spraying the poor solvent (n‐hexane) onto each coating layer for four times after casting process was greater than 150°. It was difficult to obtain superhydrophobic surface without adding n‐hexane onto any coating layer in this system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Long‐range‐ordered,hexagonally packed nanoporous membranes from degradable‐block‐containing diblock copolymer film templates

Polystyrene (PS)‐b‐polylactide (PLA) diblock copolymers with different molecular weights and fractions were synthesized through a combination of living anionic polymerization and controlled ring‐opening polymerization. Then, the PS–PLA films were guided to phase‐separate by self‐assembly into different morphologies through casting solvent selection, solvent evaporation, and thermal and solvent‐field regulation. Finally, perpendicularly oriented PS–PLA films were used as precursors for PS membranes with an ordered periodic nanoporous structure; this was achieved by the selective etching of the segregated PLA domains dispersed in a continuous matrix of PS. Testing techniques, including IR, ¹H‐NMR, gel permeation chromatography, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were used to determine the chemical structure of the PS–PLA copolymer and its film morphology. AFM images of the self‐assembled PS‐PLA films indicate that vertical tapers of the PLA domains were generated among PS continuum when either toluene or tetrahydrofuran was used as the annealing solvent. The SEM images certified that the chemical etching of the PLA component from the self‐assembled PS–PLA films led to a long‐range‐ordered array of hexagonally packed nanoporous membranes with a diameter about 500 nm and a center‐to‐center distance of 1700 nm. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39638.     

Synthesis and properties of ultralow dielectric constant porous polyimide films containing trifluoromethyl groups

In this research, a series of porous copolyimide (co‐PI) films containing trifluoromethyl group (CF₃) were facilely prepared via a phase separation process. The co‐PI were synthesized by the reaction of benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride (BTDA) with two diamines of 4,4′‐diaminodiphenyl ether (ODA) and 3‐trifluoromethyl‐4,4'‐diaminodiphenyl ether (FODA) with various molar ratios. The flexible and tough porous co‐PI films with about 300 μm thickness and 8～10 μm average diameter could be obtained by solution casting conveniently. The thermal properties of the obtained porous co‐PI films were excellent with a glass transition temperature at 270 °C ～ 280 °C and only 5% weight loss in temperature from 530 °C to 560 °C under nitrogen atmosphere. In addition, the dielectric and hydrophobic properties of porous co‐PI films were remarkably improved owing to the presence of trifluoromethyl groups (CF₃) in the polymer chains. Moreover, our synthesized porous co‐PI films also showed good mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44494.     

Benign route for the modification and characterization of poly(lactic acid) (PLA) scaffolds for medicinal application

Scaffolds fabricated from polymers have imprinted its wide applicability in the field of tissue engineering. The surface of electrospun poly(lactic acid) (PLA) nanofibers was modified to improve their compatibility with living medium. PLA film were treated with alkali solution to introduce carboxyl groups on the surface followed by covalent grafting of gelatin using Xtal Fluoro‐E as coupling agent. The gelatin g‐PLA polymer synthesized via ‘graft‐onto’ method exhibit fascinating properties as studied by contact angle measurement, fourier transformed infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, water vapor transmission rate(WVTR), swelling studies and differential scanning calorimetry. The fabricated gelatin g‐PLA scaffolds were further characterized to conduct the study on hydrolytic degradation, and extent of biodegradation at ambient temperature. It was observed from the in‐vitro analysis that the gelatin g‐PLA nanofiber (with hemolytic percentage, 0.56 ± 0.13%) was cytocompatible with fibroblast cell and does not impair cell growth. The WVTR obtained for the electrospun mat around 2900 ± 100 g/m². 24 h signifies the optimal moist environment required for tissue engineering especially wound healing. Notably, many of these strategies resulted in porous hydrophilic scaffolds with human cell growth and proliferation for medical applications of various types. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46056.     

Casting solvent effect on crystallization behavior and morphology of poly(ethylene oxide)/poly(methyl methacrylate)

Poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were prepared by casting from either chloroform or benzene solvents. After casting from solvents, all samples used in this study were preheated to 100°C and held for 10 min. Then, the solvent effect on the crystallization behavior and thermodynamic properties were studied by differential scanning calorimeter (DSC). Also, the morphology of spherulite of casting film was studied by polarized optical microscope. From the DSC and polarizing optical microscopy (POM) results, it was found that PEO/PMMA was miscible in the molten state no matter which casting solvent was used. However, the crystallization of PEO in the chloroform‐cast blend was more easily suppressed than it was in the benzene‐cast blend. Relatively, the chloroform‐cast blend showed the greater melting‐point depressing of PEO crystals. Also, the spherulite of chloroform‐cast film showed a coarser birefringence. It was supposed that the chloroform‐cast blend had more homogeneous morphology. It is fair to say that polymer blends, cast from solvent, are not necessarily in equilibrium. However, the benzene‐cast blends still were not in equilibrium even after preheating at 100°C for 10 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1627–1636, 2000     

Development and properties evaluation of bio‐based PLA/PLGA blend films reinforced with microcrystalline cellulose and organophilic silica

The preparation and properties of hybrid materials based on poly(lactic acid)/poly(lactic acid‐co‐glycolic acid) (PLA/PLGA) blends using microcrystalline cellulose (MCC) and organophilic silica (R972) as fillers have been investigated. Hybrid materials were manufactured by solution casting using chloroform as solvent to prepare films. R972 was incorporated in a ratio of 3 wt%, and MCC was added in ratios of 3, 5, or 7 wt% with respect to the weight of the polymeric matrix. Films were prepared with only MCC addition or with MCC and R972 combined. Properties of the films were evaluated by X‐ray diffraction (XRD), nuclear magnetic resonance, differential scanning calorimetry (DSC) and mechanical property measurements. The results show that each filler, when added individually or in combination, affects the structure and final properties of the films differently. MCC acts as a nucleating agent for the crystallization of the polymeric matrix. An increase in the MCC content increased the crystallinity of the films. This effect became more pronounced with silica addition. The domain distribution curves showed PLA/PLGA blends to be homogeneous, which was further confirmed by DSC. An improvement in the mechanical performance was observed with MCC addition, especially when silica was added together with cellulose. POLYM. ENG. SCI., 57:464–472, 2017. © 2016 Society of Plastics Engineers.     

A facile method of preparing highly porous polylactide microfibers

Highly porous polylactide (PLA) microfibers with the diameter of about 14 µm are prepared by melt‐spinning and stretching core–sheath PLA fibers (CSF) and sequent treatment of ethyl acetate. The resultant pores are regular and elliptical. The average values of length of major axis and minor axis of elliptical pores are around 1 and 0.5 μm, respectively. This new and facile method can prepare porous PLA fibers on industrial scale, and nearly overcome all the shortcomings of melt‐spinning and stretching method. In addition, highly porous structure in partially oriented poly(l ‐lactide) yarn (POY) can be also formed by treating POY using ethyl acetate. The obtained pores are irregular. In addition, the formation mechanism of pore structure in CSF is different with the one in POY. The former is the separation of row‐nucleated lamellae induced by stretching while the latter is swelling and subsequent solvent‐induced crystallization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45860.     

Gamma radiation induced property modification of poly(lactic acid)/hydroxyapatite bio‐nanocomposites

Poly(lactic acid)/hydroxyapatite (PLA/HAP) nanocomposite films with various compositions, 2 ? 70 parts HAP per 100 of the PLA polymer (pph), were made via the solution casting method. Transmission electron microscopy images of the PLA/HAP films exhibited spherical particles in the size range from nearly 10 nm to 100 nm dispersed within the polymeric matrix. Fourier transform infrared spectra of the nanocomposites revealed an interaction between PLA and HAP nanoparticles by carbonyl group peak shift. Incorporation of HAP nanoparticles in the PLA matrix stimulated crystal growth verified by differential scanning calorimetry. The films irradiated with γ‐rays at a dose of 30 kGy also showed an increase in crystallinity. The X‐ray diffraction patterns of the irradiated PLA exhibited two new peaks at around 16° and 19°, assigned to the α crystalline phase of PLA; these were absent in the unirradiated nanocomposites. Significant ductile behavior was observed in both irradiated and unirradiated PLA nanocomposites containing 2 and 10 pph of HAP. However, the irradiated nanocomposites had higher tensile strength. © 2013 Society of Chemical Industry     

Rapid formation of flexible silk fibroin gel‐like films

Flexible silk fibroin gel‐like films with microporous morphology were prepared from B. mori silk fibroin fibers directly solubilized in formic acid/CaCl₂ solvent. These films were characterized by several analysis techniques to determine the structure and properties of films. The pore size of gel‐like films can be adjusted through SF concentration and Ca ions concentration. The controllable pore size in gel‐like films was grew from 3–5 μm to 100 μm under the increase of fibroin concentration from 1.0 wt % to 8.0 wt %. At the same time, the water content of silk fibroin gel‐like film decreased from 83.5 ± 3.4% to 68.2 ± 2.6%. With increasing Ca ions contents from 2.0 wt % to 10.0 wt % in dissolution process, the pore size and water content of silk fibroin gel‐like films grew larger, especially its water content values reached 86.2 ± 4.0% at 10.0 wt % Ca ions concentration. At wet condition, the gel‐like film with β‐sheet structure showed higher breaking stress (4.26 ± 0.31 MPa) and elongation (45.45 ± 15.79%) at 8.0 wt % concentration. With the preparation method, the membrane is hydrophilic and the pore size is adjustable, which contributes to high toughness and favorable cell growth environment, suggesting that these silk fibroin gel‐like films can be a potential candidate scaffold for biomedical applications, such as wound dressing, facial mask, contact lenses, etc. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41842.     

Effect of nonsolvent coagulant on the morphology and radionuclide detection efficiency of CAYS‐impregnated polysulfone films

Single‐ or double‐layered porous films consisting of polysulfone (PSF) and cerium‐activated yttrium silicate (CAYS) were prepared through the phase inversion of polymeric solutions. For a single‐layered structure, a casting solution including n‐methylpyrrolidone (NMP) as a solvent was cast on a glass substrate and solidified by immersing into a nonsolvent bath. In a double‐layered structure, the bottom layer is a dense PSF film, prepared by vacuum coagulation of a methylene chloride/PSF solution. The top layer was formulated by coagulating the NMP solution, cast over the dense film, in a nonsolvent bath. The morphology and the radionuclide detection efficiency of the prepared films were significantly affected by the nonsolvent coagulants used. The water‐coagulated, double‐layered film showed a relatively clear‐cut interface between the two layers, indicating the rapid coagulation of the second layer. On the contrary, the film coagulated by isopropanol retained well‐developed sponge structures highly intertwined in the interface, associated with the delayed precipitation of the second layer. When spotted on the prepared films, radionuclides stayed mainly on the top surface of the isopropanol‐coagulated film, but went deep into the substructure of the film coagulated with water. In comparison with the mono‐layered films, the double‐layered ones improved the detection capacity of the spotted radionuclides, owing to the dense support layer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1903–1909, 2006