Solution-cast Films Research Articles

Optimum Blend of Chitosan and Poly-(ε-caprolactone) for Fabrication of Films for Food Packaging Applications

The present work deals with the preparation and characterization of the chitosan and poly-e-caprolactone (PCL) solution-casted blended films in various proportions (chitosan–PCL ratio 90:10, 80:20, and 70:30). The films were casted and dried at 55 °C, which were characterized based on the mechanical, barrier, thermal, and microscopic properties. The film prepared from chitosan to PCL ratio 80:20 resulted in increase percentage elongation by 20.56% as compared to pure chitosan film. Fourier transform infrared spectrum indicated a shift in peak of absorption from 1743.9 to 1724.8 cm−1 due to carbonyl group of PCL indicating the miscibility and interaction between the PCL and chitosan. Scanning electron microscopy revealed that PCL appeared as a co-continuous phase with chitosan for ratio 80:20, confirmed the interaction between chitosan and PCL. The above study indicated that the properties of chitosan films can be modified with the addition of PCL and may find its versatile use in food packaging.

Purple red and luminescent polyiminoarylenes containing the 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) chromophore

New DPP-containing polyiminoarylenes were prepared from 1,4-diketo-2,5-dihexyl-3,6-di(4′-bromophenyl)pyrrolo[3,4-c]pyrrole and various arylamine derivatives using palladium-catalyzed amination reactions. The arylamine comonomers were aniline (ANI), t-butylaniline (TBA), 2-aminoanthracene (AAN), 1-aminopyrene (APY) and N,N′-diphenyl-p-phenylenediamine (PDA). Purple red polymers with good solubility in common organic solvents and molecular weights between 4.4 and 35.8kDa were obtained. Polymer solutions were readily fluorescent with quantum yields between 19 and 62%, while solution-cast films only showed a weak fluorescence. All polymers exhibit low band gaps of approximately 1.9eV. Cyclovoltammetric studies indicate quasireversible oxidation for polymers with TBA, APY and PDA as comonomer units, and quasireversible reduction for the polymer with AAN comonomer unit. Polymers with APY and PDA comonomer units are electrochromic and can be switched between red in the neutral and greenish grey in the oxidized state.

Volatile electrical switching in a functional polyimide containing electron-donor and -acceptor moieties

A solution-processable functional polyimide (PYTPA-PI), containing triphenylamine-substituted diphenylpyridine moieties (PYTPA, electron donors) and phthalimide moieties (PI, electron acceptors), was synthesized. The copolymer exhibits a high glass transition temperature of 342 °C. A switching device, based on a solution-cast thin film of PYTPA-PI sandwiched between an indium-tin oxide (ITO) bottom electrode and an Al top electrode, exhibits two accessible conductivity states and can be switched from the low-conductivity (OFF) state to the high-conductivity (ON) state, with an ON/OFF current ratio of more than 103, at the threshold voltage of about 2.7 V. The ON state is volatile and relaxes readily to the OFF state. However, it can be electrically sustained by a refreshing voltage pulse of 2 V. The ON state can also be reset to the initial OFF state by a reverse bias of −0.9 V. The ability to write, erase, read, and refresh the electrical states fulfills the functionality of a dynamic random access memory. The electronic transitions and transport mechanisms associated with the memory effect were elucidated from molecular simulation. In comparison with that of other functional polyimides, the electrical switching performance in PYTPA-PI illustrates the possibility of tuning memory properties in imide polymers via molecular design and synthesis.

Thermal transitions and heat‐sealing of glycerol‐plasticized whey protein films

AbstractTransparent, flexible whey protein‐based edible films plasticized with glycerol were produced by wet (solution‐casting) and dry (twin‐screw extrusion followed by compression‐molding) processes. The relationship between the thermal transitions and the heat‐sealability of the whey protein‐based edible films was investigated. Differential Scanning Calorimetry showed the existence of endothermic peaks with an onset transition temperature of 156.3 ± 1.4°C for both the solution‐cast and extruded films. Films were heat‐sealed using an impulse heat‐sealer at an effective jaw pressure of 293.31 kPa, a voltage of 15 V and a cooling time of 4 s. Various impulse times, ranging from 1.5 to 2.5 s, were used to heat‐seal the films. A thermocouple was used to measure the heat‐sealing temperatures at each impulse time. Heat‐sealing temperatures ranged between 126.1 ± 9.0 and 204.0 ± 5.4°C for the shortest and longest impulse times, respectively. Seal strengths were determined using an Instron Universal Testing Machine. Film thickness appeared to have an effect on seal strength; higher strengths were achieved for thinner films, which, in this case, were the solution‐cast films. Thicker (extruded) films required a longer minimum impulse time to achieve a heat‐seal. The highest seal strength (433.07 ± 39.37 N/m) was obtained with solution cast films (thickness of 0.13 ± 0.01 mm) sealed with an impulse time of 2 s (164.6 ± 5.1°C). Impulse times above 2.5 s (204.0 ± 5.4°C) resulted in degradation of both solution‐cast and extruded films. Copyright © 2009 John Wiley & Sons, Ltd.

Interactions between endothelial cells and electrospun methacrylic terpolymer fibers for engineered vascular replacements

A compliant terpolymer made of hexylmethacrylate (HMA), methylmethacrylate (MMA), and methacrylic acid (MAA) intended for use in small diameter vascular graft applications has been developed. The mechanical properties and in vitro biostability of this terpolymer have been previously characterized. The goal of this investigation was to examine the interactions between endothelial cells and the new terpolymer and to evaluate endothelial cell function. Electrospinning was used to produce both oriented and random terpolymer fiber scaffolds. Smooth solution cast films and tissue culture polystyrene were used as negative and positive controls, respectively. Human blood outgrowth endothelial cells and human umbilical vein endothelial cells were incubated with the test and control samples and characterized with respect to initial cell attachment, proliferation, viability, and maintenance of the endothelial cell phenotype. It was found that the terpolymer is cytocompatible allowing endothelial cell growth, with random fibers being more effective in promoting enhanced cellular activities than oriented fibers. In addition, endothelial cells cultured on these substrates appeared to maintain their phenotype. The results from this study demonstrate that electrospun HMA:MMA:MAA terpolymer has the potential to be used successfully in fabricating small diameter blood vessel replacements.

Banded spherulites grown from poly(trimethylene terephthalate) solution-cast film

Various morphologies of poly(trimethylene terephthalate) (PTT) solution-cast thin films at different crystallization temperatures were investigated by polarized light microscopy (PLM), atomic force microscopy (AFM) and transmitted electron microscopy (TEM). In the range of 110–150 °C, banded spherulite occurred and banding space gradually decreased along the radial direction from the primary nucleation site. Between 160 and 170 °C, normal non-banded spherulite was found. Above 170 °C, banded configuration occurred again. Lamellar growth direction of banded spherulite was determined to the crystal a-axis.

Highly soluble and colorless fluorinated poly(ether imide)s based on 4,4’-(2,5-tolylenedioxy)diphthalic anhydride and trifluoro methyl-substituted aromatic bis(ether amine)s

AbstractA series of novel fluorinated poly(ether imide)s (PEIs) IVa-h were synthesized from 4,4’-(2,5-tolylenedioxy)diphthalic anhydride (I) and various trifluoromethyl-substituted aromatic bis(ether amine)s (IIa-h) via a conventional two-step method with thermal or chemical imidization of the precursor poly(amic acid)s. These PEIs were readily soluble in a variety of organic solvents; they were soluble with a concentration higher than 10% in amide-type polar solvents, ether type solvents, and chlorinated hydrocarbons. The solution-cast films showed a high optical transparency and low color intensity, with an ultraviolet-visible absorption edge of 371- 377 nm and low b* values (a yellowness index) of 4.9-7.5. These films were strong and tough with tensile strength of 90-103 MPa. They exhibited glass-transition temperatures (Tg) in the range of 207-293oC, with 10% weight loss temperature in excess of 500oC in air or nitrogen atmosphere. They also showed low-dielectric constants (2.95-3.37 at 1 MHz) and low moisture absorption (0.20- 0.67 wt %).

Enzyme-catalyzed degradation of poly( l-lactide)/poly(ɛ-caprolactone) diblock, triblock and four-armed copolymers

Poly( l-lactide)/poly(ɛ-caprolactone) diblock, triblock and four-armed copolymers with the same monomer feed ratio (50/50) were synthesised by two step ring opening polymerisation of successively added ɛ-caprolactone and l-lactide, using isopropanol, ethylene glycol, or pentaerythritol as initiator and zinc lactate as co-initiator. The resulting copolymers were characterised by 1H NMR, DSC, SEC, and FT-IR, which confirmed the blocky characteristic of the copolymers. Solution cast films were allowed to degrade at 37 °C in the presence of proteinase K, and the degradation was monitored by gravimetry, DSC, SEC, 1H NMR and ESEM. The effects of chain structure, block length and crystallinity on the degradation are discussed. The four-armed block copolymer degrades the most rapidly, while the diblock copolymer exhibited the slowest degradation rate. The difference was related to the crystallinity depending on both the molecular structure and block length. Little compositional or molar mass changes were obtained during degradation, which strongly supports a surface erosion mechanism, in agreement with ESEM observations.

Electrical Properties of Disk-Shaped Molecules Embedded with Three Dipole N,N',N''-Tri-n-heptyl-1,3,5-benzenetricarboxamide

We report the electrical properties of N,N',N''-tri-n-heptyl-1,3,5-benzenetricarboxamide (T7B), a phenyl compound embedded with triple amide dipoles. A solution-cast thin film of T7B exhibited current–electric field (I–E) hysteresis. The I–E trace had double switching peaks at temperatures lower than 45 °C, while it had single peak at higher temperatures. The residual polarization was 8.8 mC/m2 at 25 °C. On the other hand, the annealed thin film did not exhibit hysteresis. The dielectric spectrum had a dielectric anomaly at 100 °C, at which the dielectric relaxation strength was as small as 0.1 at 10 Hz frequency. Temperature-dependent IR absorption spectroscopy showed that the material consisted of a crystalline phase and an amorphous phase, and the degree of crystallinity increased during annealing. It was concluded that the polar conformations of the amide dipoles in both the amorphous and crystalline phases were associated with the formation of the polarization.

A Novel Bone Scaffolds Based on Hyperbranched Polyglycerol Fibers Filled with Hydroxyapatite Nanoparticles: <i>In Vitro</i> Cell Response

A novel bone scaffolding material was successfully fabricated by electrospinning from hyperbranched polyglycerol (HPGL) solutions containing nanoparticles of hydroxyapatite (HA). The potential use of the electrospun fibrous HPGL-HA scaffolds for bone regeneration was evaluated in vitro with human osteoblasts in terms of alkaline phosphatase (ALP) activity of the cells that were cultured directly on the scaffolds. The results were compared with those on corresponding HPLG-HA solution-cast film scaffolds. It was found that all of the fibrous scaffolds promoted much better adhesion and proliferation of cells than the corresponding film scaffolds.

Synthesis and Electronic Properties of Conjugated Pentacene Dimers

Conjugated pentacene dimers 1-3 were synthesized in two steps from readily available precursors. Noteworthy is the initial step, which assembles five independent fragments to form the carbon-rich molecular framework. Solution-cast films of these materials are air stable. Photocurrent measurements for solution-deposited thin films show that dimer 3 exhibits photoconductive gain >10.

Study on Different Solution-Cast Films of PMMA and PVAc

Transparent films of PMMA (poly methyl methacrylate) and PVAc (polyvinyl acetate), previously dissolved in chloroform, toluene and tetrahydrofuran (THF), were prepared by using solution-cast technique. FT-IR transmission spectra were obtained from the samples. Also, different concentrations of PMMA/PVAc blend, dissolved in chloroform, were prepared by the same method. From absorption, transmission and specular reflection spectra, the absorption coefficient (α) and refractive index (n) have been calculated at room temperature and also after heating. The values of the optical band gap (Eg) have been obtained from the direct allowed transitions in k-space. In addition, the values of width of the tails of localized states in the band gap (Eu) were evaluated from Urbach edges.

Morphology and properties of thermoplastic polyurethanes with dangling chains in ricinoleate-based soft segments

In our previous publication on the structure–property behavior of segmented polyurethanes based on castor oil [Petrović ZS, Xu Y, Zhang W. Polymer Preprints 2007;48(2):852–3.], the results showed that these materials which possessed a soft segment weight concentration (SSC) of 70% have both low tensile strength and elongation at break. This behavior is distinctly different from segmented polyurethanes of comparable soft segment content obtained from petrochemical polymeric diols that possess terminal hydroxyl groups. The poor elastic properties of these segmented polyurethanes were ascribed to the low molecular weight of the polymers as well as due to the presence of the six-carbon “dangling chain”, which may influence the morphology of the resulting segmented polyurethanes. To further understand this behavior, four segmented polyurethanes with the SSC of 70, 60, 50, and 40%, respectively, were synthesized from a polyricinoleate diol with an Mn of 2580, diphenylmethane diisocyanate (MDI) and butanediol. The objective of this work was to study the effect of SSC on the morphology of the resulting polyurethanes, and to correlate the morphology with the properties of these bio-based segmented polyurethanes. Polymers were characterized by GPC, viscometry and spectroscopic methods. Thermal and mechanical properties of the polymers indicated good microphase separation. Microphase morphology was also noted by SAXS and AFM. Finally, “spherulitic-like” superstructures were noted in the solution cast films that are believed to arise from the nucleation and crystallization of the hard segments.

Synthesis of Novel Multifunctional Polyisobutylenes at Chain End(s) and Their Application to AnB Asymmetric Star and AnBAn Pompom Polymers by Combination of Living Cationic and Anionic Polymerizations

The synthesis of an array of ω- or α,ω-multifunctional polyisobutylenes (PIBs) with 2, 4, and 8 benzyl bromide moieties has been demonstrated by an iterative divergent methodology using ω- or α,ω-functional PIBs with allyl halide moiety (moieties) as starting materials. The multifunctional PIBs were successfully applied for the synthesis of A2B, A4B, and A8B asymmetric star polymers as well as A2BA2, A4BA4, and A8BA8 pompom polymers where A and B were poly(methyl methacrylate) (PMMA) and PIB segments, respectively. The synthetic method involved the coupling reaction of living PMMA with multifunctional PIBs in tetrahydrofuran at −40 °C. The coupling efficiencies were virtually quantitative in all cases. The well-defined structures of the resulting branched polymers were confirmed by size exclusion chromatography−right angle laser light scattering and 1H NMR analyses. The microphase-separated morphologies of all AnBAn type pompom polymers were supported by differential scanning calorimetry. The stress−strain plots of solution-cast films of AnBAn type pompom polymers showed good elastomeric properties (279−444% elongations at break and 12.6−20.7 MPa tensile strengths).

The influence of 4HB content on the properties of poly(3‐hydroxylbutyrate‐co‐4‐hydroxylbutyrate) based on melt molded sheets

AbstractA series of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)s[P(3HB‐co‐4HB)s] sheets with the 4HB contents from about 9 to 34 mol % were prepared via melt molding. Their crystallinity, crystalline structures, thermal and mechanical properties were characterized by differential scanning calorimetry, X‐ray diffraction, thermogravimetric analysis, dynamic mechanical analysis, and tensile test. It was found that the melt temperatures (Tm), glass transition temperatures (Tg), and storage modulus (E′) of all the [P(3HB‐co‐4HB)s] copolymers investigated decreased continuously with increasing the amount of the 4HB; the yield stress and breaking stress nearly decreased with the increase of the 4HB contents while the elongation at the yield and break points increased; and the thermal stability of the P(3HB‐co‐4HB)s improved with increasing 4HB contents. The results suggest that the mechanical properties and crystal lattice parameters of the melt molded sheets are somewhat different from those of the solution cast films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Contact-induced crystallinity for high-performance soluble acene-based transistors and circuits

The use of organic materials presents a tremendous opportunity to significantly impact the functionality and pervasiveness of large-area electronics. Commercialization of this technology requires reduction in manufacturing costs by exploiting inexpensive low-temperature deposition and patterning techniques, which typically lead to lower device performance. We report a low-cost approach to control the microstructure of solution-cast acene-based organic thin films through modification of interfacial chemistry. Chemically and selectively tailoring the source/drain contact interface is a novel route to initiating the crystallization of soluble organic semiconductors, leading to the growth on opposing contacts of crystalline films that extend into the transistor channel. This selective crystallization enables us to fabricate high-performance organic thin-film transistors and circuits, and to deterministically study the influence of the microstructure on the device characteristics. By connecting device fabrication to molecular design, we demonstrate that rapid film processing under ambient room conditions and high performance are not mutually exclusive.

Synthesis and Properties of Polyetherketone-block-Polybenzobisthiazole-block-Polyetherketone ABA Triblock Copolymers

As an approach to rigid-rod molecular composites, a series of PEK-b-PBZT-b-PEK ABA triblock copolymers were synthesized. Three different types of polyetherketones (PEKs) as coil A-block units and the carboxylic acid-terminated polybenzobisthiazoles (PBZTs) with two different molecular weights as rigid-rod B-block units were utilized to afford the targeted ABA triblock copolymers. The resulting triblock copolymers were insoluble in common polar aprotic solvents such as N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide but showed greatly improved solubility in strong acids such as trifluoroacetic acid, methanesulfonic acid (MSA), trifluoromethanesulfonic acid, and sulfuric acid. Good quality films could be cast from solutions. Alternatively, we could also process these copolymers by the compression molding technique. The block copolymer samples were simply heated above the transition temperatures of the coil components and pressed into articles with desired shapes. The wide-angle X-ray diffraction study of the selected solution-cast film exhibited a long-range ordering, which is indicative of microphase separation. This was further confirmed by the results from small-angle X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In addition, the UV−vis absorption behavior of the copolymer solutions implied that the ground state conformations of PBZT in MSA were greatly dependent on the amorphous or the semicrystalline nature of the PEK unit, which has little or no effect on the emission properties.

MWNT Polymer Nanocomposites Based on P3HT

Thin and short multi walled carbon nanotubes (MWNTs) were used to prepare nanocomposites based on poly(3-hexylthiophene) (P3HT). The MWNTs were characterized by TEG, SEM, TEM and Raman spectroscopy following deposition of films from stable dispersions of MWNT in chloroform. Non-covalent interaction between MWNT and P3HT dissolved in chloroform allowed the preparation of solution-cast composite films. Composite thermal events such as glass transition, melting temperature and heat of fusion were investigated by DSC and compared with pure polymer. Conductivity of composite bulk films was measured as a function of temperature by 2-point probe DC-resistance measurements. Loadings of MWNTs above 0.1 weight percent (wt%) in the conjugated polymer significantly increased the conductivity of P3HT composites. Interplay between charge transport through the semiconductor polymer and carbon nanotube network allowed the increase of conductivity after percolation to values close to 10-2 S cm-1, an improvement of four orders of magnitude over that of films cast from pure P3HT.

Enzymatic degradation of block copolymers obtained by sequential ring opening polymerization of l-lactide and ɛ-caprolactone

Copolymers of ɛ-caprolactone and l-lactide with different molar ratios were prepared via sequential ring opening polymerization (ROP) of both monomers. The resulting PCL–PLLA–PCL triblock copolymers were characterized by using NMR, SEC, DSC and XRD. One melting peak corresponding to the PCL block was detected, but the presence of PLLA decreased the crystallinity of PCL. Enzyme-catalyzed biodegradation of solution cast films was investigated at 37 °C in the presence of Pseudomonas lipase. It was observed that the PLLA component retarded the degradation of the block copolymer as compared to the PCL homopolymer. Therefore, the enzymatic degradation rate can be adjusted by varying the composition of the copolymers. 1H NMR and SEC data showed no significant chemical composition or molecular weight changes during degradation, indicating that the degradation proceeded according to a surface erosion mechanism. ESEM confirmed surface erosion with appearance of a rugged morphology.

Influence of film structure on mobilities of charge carriers in conducting polymers

Two sorts of poly(3-hexylthiophene) (PHT) films with the same chemical compositions were prepared, and their electrochemical, spectroscopic, and transport properties were studied with a special interest in a possible influence of film structure on mobilities of charge carriers. One of the PHT films was electrochemically synthesized using 3-hexylthiophene as a monomer (as-grown film) and the other was obtained by dissolving the as-grown film in chloroform and then casting the polymer solution (cast film). A clear difference was observed in the mobility versus doping level plot between the two sorts of PHT films, demonstrating that the difference is caused only by a distinction in film structure. An initial decreasing feature of the mobility plot observed for the cast films was accounted for in terms of swelling of the films at an early stage of doping.