Cast Films Research Articles

Heterogenity of graphite oxide particles obtained with wet oxidative exfoliation

Wet oxidative exfoliation of graphite is one of the most frequently applied techniques to obtain aqueous dispersions of hydrophilic graphene derivatives as required, e.g., in 3D printing, wet spinning or film casting. Due to the harsh conditions of the process, the resulting suspension is a mixture of particles with a wide distribution range both of physical dimensions and chemical properties. An aqueous graphite oxide suspension was obtained by an improved Hummers method and separated into five fractions by controlled centrifugation. The fractions were characterized and compared by various methods, revealing their diversity in size, chemical properties and application-related viscosity. The characterization methods (powder XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, potentiometric titration, rheology) exhibited subtle but measurable differences that exceeded the standard deviation of the techniques employed, but no systematic trend was found across the fractions in any of the properties investigated. The conditions of our centrifugal separation hardly meet the constrains of the ideal of Stokes’s law, the polydispersity of the high aspect ratio particles as well as their concentration close to the percolation limit challenge the independent sedimentation of the platelets.

Determination of the Sterilization Dose of Gamma-Ray Irradiation for Polyvinyl Alcohol-Collagen-Chitosan Composite Membrane as a Material for Periodontal Regenerative Surgery.

Membrane sterility is very necessary considering its function as an implant material. Therefore, this research aims to determine the dose of gamma-ray irradiation for the sterilization of polyvinyl alcohol (PVA)-collagen-chitosan composite membranes used as regenerative surgery materials. A total of 100 pieces of the composite membranes were prepared in a size of 2.0 × 1.5 cm by mixing 7.5% PVA, 3% collagen, and 2% chitosan using the film casting method in three batches. Furthermore, the bioburden test was performed to determine the initial microbial count in the sample by following ISO 11737-1. The results were used to ascertain the dose of gamma-ray irradiation on the sample according to ISO 11137-2. The dose verification test was then performed at the sterility assurance level 10-6. The average result of the bioburden test from three batches was 6.6 colony forming unit; hence, the verification dose was 4.8 kGy. In the verification dose test, since there was only one contaminated sample, the sterility dose test was continued. The sterile gamma-ray irradiation dose for PVA-collagen-chitosan composite membrane was 17.1 kGy.

Self-Standing Thin Films of Cellulose Nanocrystals and Graphene Quantum Dots for Detection of Trace Iron(III)

Cellulose nanocrystal (CNC) thin films have gained attention for application in green optoelectronics devices. However, the dependence on plasticizers, external cross-linkers, or auxiliary polymers can impair the full exploration of the nanomaterials’ properties. Herein, we report on the evaluation of a surface-oxidized CNCs ultrathin film, made from a formulation that excludes the use of auxiliary compounds, to be used as a sensing platform. The physicochemical characterizations using UV–vis, Fourier transform infrared , and Raman spectroscopies, nuclear magnetic resonance, zeta potential, transmission electron and field emission scanning electron microscopies, X-ray diffraction, thermogravimetric analysis, and contact angle measurement showed that the adopted procedure led to (i) the modification of the CNC surface and (ii) the formation of smaller CNCs. The production of casting films from highly diluted CNC-modified aqueous suspensions showed that a very thin, transparent, self-supporting, and manipulable film could be obtained, which was not the case for diluted unmodified CNC suspension. Additionally, the CNC thin film has been demonstrated to be a suitable platform for hosting graphene quantum dots, based on which an optochemical sensor was successfully employed to detect iron(III) in a dynamic range from 1 fM to 2 pM, yielding a limit of detection of 0.8 fM.

Simple Correlations for Thickness Profiles in Melt Casting

Neck-in during melt casting of polymeric film and extrusion coating along with the related issue of edge bead formation, has been widely studied. However, one aspect of this problem that has received relatively little attention is empirical correlations for the thickness profile near the edges of the sheet. The correlations given here may prove useful for industrial operations as well as provide benchmarks for numerical studies of the myriad factors that influence neck-in.

Sulfonate-Grafted Metal–Organic Framework─A Porous Alternative to Nafion for Electrochemical Sensors

Nafion, a polymer containing negatively charged sulfonate groups, is commonly used as a thin film cast on the electrode to adjust the selectivity of complicated electrochemical reactions involving charged reactants or analytes in the electrochemical sensing and electrolytic systems. Herein, a highly porous and chemically stable metal–organic framework (MOF) with enriched sulfonate groups in its pores is synthesized by performing the postsynthetic immobilization of the sulfonate-based ligand within a zirconium-based MOF, MOF-808, and the resulting sulfonate-grafted MOF (SO3-MOF-808) is proposed as a “porous Nafion”─an appealing alternative to the conventional Nafion coating for modulating the selectivity of electrochemical reactions. As a demonstration, the electrochemical sensing of dopamine (DA), which usually suffers from interference caused by the oxidation of the coexisting negatively charged ascorbic acid (AA) and uric acid (UA), is implemented. With the use of the SO3-MOF-808 thin film deposited on the active electrode surface, both the current signal for DA oxidation and the selectivity toward the oxidation of DA against those of AA and UA remarkably outperform those achieved by the Nafion thin film with an optimized film thickness. Findings here suggest the new role of such sulfonate-grafted MOFs as an advanced alternative to Nafion in a range of electrochemical sensing systems and other complicated electrochemical reactions.

PH-sensitive liposomes bearing a chemotherapeutic agent and a natural apoptosis modulator for effective intracellular delivery to the solid tumor.

The intracellular delivery of the drug to the solid tumor is a major challenge in the treatment of solid tumors. This project aims to increase cytosolic drug delivery using the endosomal escape of drugs. Topotecan (TPT) and capsaicin were used for the treatment of solid tumors. The pH-dependent conversion of active lactone form to inactive carboxylic form is a major problem of TPT that limits its therapeutic use. Liposomal encapsulation of TPT improved the stability of active lactone form and increased the therapeutic efficacy of TPT. Endosomal degradation of liposomes may reduce the content in the target cells. To solve these problems, pH-sensitive liposomes (pSLPs) were developed which improved the intracellular drug delivery by the endosomal escape of drugs. The liposomes (LPs) bearing the drug(s) were prepared using the cast film method and optimized for various formulation and process variables using the Design-Expert 7 software by employing the Box-Behnken design (BBD). The developed hyaluronic acid (HA)-conjugated pSLPs (HA-pSLPs) displayed a vesicle size of 166.5 ± 2.31nm, zeta potential - 30.53 ± 0.91, and entrapment efficiency of 44.39 ± 1.78%, and 73.48 ± 2.15% for TPT and CAP, respectively. HA-pSLPs displayed better cytotoxicity in comparison to free drugs either single or in combination on the MCF-7 cell line. The apoptosis and cellular uptake of HA-pSLPs were increased ⁓ 4.45-fold and ⁓ 6.95-fold as compared to unconjugated pSLPs, respectively. The pharmacokinetic studies in Balb/c mice demonstrated that HA-pSLPs increased the half-life, MRT, and AUC in comparison to the free drug solution. The HA-pSLPs formulation has shown remarkable tumor regression as compared to PpSLPs, pSLPs, and free drug combinations. These results demonstrated that TPT- and CAP-loaded HA-pSLPs offer a potential platform for targeted drug delivery to solid tumors.

Pharmaceutical characterization and dissolution behavior of ibuprofen/Soluplus solvent cast films

Purpose: To characterize the physicochemical and dissolution properties of Soluplus®/ibupofen solid dispersions prepared by solvent casting technique.
 Methods: Soluplus® was used as a film-forming agent whereas ibuprofen served as a poorly soluble biopharmaceutics classification system (BCS) class II active pharmaceutical ingredient (API). The solution casting of ethanolic Soluplus®/ibuprofen was carried out on a release liner and dried under a vacuum. The crystallinity of crushed films was examined using powder x-ray diffraction (PXRD), while a USP Type II apparatus was used to determine their dissolution behaviour.
 Results: Ibuprofen was uniformly distributed in an amorphous form into the cast films. The PXRD-based confirmation of crystalline peaks' absence revealed a significantly higher dissolution rate in alkaline and acid media when compared to the pure drug.
 Conclusion: Soluplus® (polymeric dispersant)-based solvent casting is a simple and efficient technique to prepare highly water-soluble solid dispersions of ibuprofen. This film cast technique may be suitable for various applications where a film or powder form of a drug with enhanced solubility in different aqueous media is desired.

Structure evolution and properties enhancement of polyamide‐6/polyamide‐1010 films under uniaxial and biaxial stretching

AbstractThe effect of stretching process on the structures and properties of the stretch‐oriented PA6/PA1010 film was investigated during the uniaxial and biaxial stretching. The results showed that the PA6/PA1010 cast film exhibited β‐form crystals, and the uniaxial stretching induced the β → α + γ phase transition and preferential orientation along the stretching direction, while the β → α phase transition and no preferential orientation were observed during the biaxial stretching process. Meanwhile, the melting temperature and crystallinity of PA6 in uniaxially and biaxially stretched PA6/PA1010 films were improved with the increasing stretching ratios, thus creating a much more tortuous pathway for the diffusion of oxygen molecules to enhance the oxygen barrier property of the stretched films after uniaxial and biaxial stretching. The morphological analysis showed that the PA1010 particles were oriented and deformed along the stretching direction and no obvious debonding and voids were observed at the interface. In addition, the mechanical properties of the stretched films were closely dependent upon the stretching ratios. It was found that the tensile strength of the biaxially stretched PA6/PA1010 films with stretching ratio of 3.5 × 3.5 in MD and TD exhibited about 1.7 times and 2.2 times higher than that of the PA6/PA1010 cast film, respectively.

Synthesis of Multiblock Copolymer Composed of Biodegradable Poly(butylene succinate) and Poly(2-pyrrolidone): Impact of Each Block Length on the Mechanical Properties.

A series of multiblock copolymers comprising a systematic combination of biomass-originated and biodegradable poly(butylene succinate) (PBS) and poly(2-pyrrolidone) (PA4) units is synthesized with various mean degrees of polymerization (mDP) of each unit. Despite the inherent immiscibility of PBS and PA4, multiblock structure allows to mix the two components in the solution-cast films from solution. The mechanical properties of the cast films are highly dependent on the mDP of each unit, as demonstrated by tensile tests. The film of the copolymer with the lowest mDP of each unit (PBS: 17, PA4: 10) is transparent and exhibits extremely high elongation at break (> 400%) and high tensile stress (39.5MPa) with strain hardening. The films with 50% or higher crystallinity are brittle and opaque, while a decrease in crystallinity can result in higher elongation, as revealed by wide-angle X-ray diffraction measurements.

Improving water resistance property of starch straw by synergistic effects of chemical crosslinking, physical barrier, and surface modifications

AbstractStarch straws are developed by focusing on improving the critical weakness of all starch‐based materials: moisture sensitivity. Various technologies including blending (with hydrogel carrageen), chemical crosslinking (using citric and boric acids, and furfural), physical barrier (using talc), and surface modifications (by adding stearic acid, or hot oxalic acids) are evaluated, and then synergized in this study. The materials and products are characterized by Fourier transform infrared spectroscopy, contact angle, mechanical properties, water solubility and water absorption. All the trends of individual modification are similar to previous work but it was found that the influence of some modifications on the extruded straws was significantly different from that of the casting films reported previously since extrusion with high shear stress can destroy chemical and physical crosslinking or network formed. It was found that there was a maximum acid content to improve the water sensitivity since the excessive amount of acid could degrade starch and have more damage to the crosslinking during extrusion, resulting in decreasing mechanical properties and increasing solubility. On the other hand, some synergic functions, like crosslinked by additional citric acid and surface treatment by hot oxalic acid, were observed. The promising starch straws are developed based on synergic methodologies, in which typical samples were prepared by crosslinking using citric (1 w%), boric (2 w%), talc (3 w%), and stearic acids (1 w%) and treated with hot oxalic acids for 2 s. The optimized straw can be smoothly processed, reduced water absorption significantly (55.3%), and mechanical properties (modulus) increased about 54% compared with neat starch one after being immersed in water at room temperature (25°C) for 20 min. This synergic strategy provides a useful guideline for developing starch‐based materials with low moisture sensitivity.

Spraying-assisted construction of robust polyvinylidene fluoride membrane with superhydrophobic property for water-in-oil emulsions purification

Construction of the hierarchical surface topographies is advantageous to develop the highly-permeable membrane with super hydrophobicity, which is conductive to the precise purification of water-in-oil emulsions. Herein, the robust superhydrophobic poly(vinylidede) fluoride (PVDF) membrane with the artificially tunable surface topographies was constructed by spraying the hydrophobic silicon dioxide (SiO2) particles onto the nascent cast film prior to the thermally induced phase separation. Benefiting from the self-adhesive property of PVDF, the SiO2 particles of two different sizes were firmly immobilized to the membrane surface, endowing resultant membranes with the micro-nano coarse structure and therefore the specific characteristic of super-hydrophobicity. The resulted membrane prepared at the optimal conditions exhibited the water contact angle and the water sliding angle of 160 ± 4° and 3 ± 2° respectively, accompanied with the averaged pore size of 330.8 ± 11.0 nm. Accordingly, it displayed the improved permeation fluxes of 1698 ± 119 L∙m−2∙h−1 and 2000 ± 129 L∙m−2∙h−1 with regard to the separation of the water-in-toluene and water-in-chloroform emulsions respectively, along with the separating efficiencies of 99.0 ± 0.2% and 98.7 ± 0.2% in terms of the oil purity in the penetrated solutions. Besides, the favorable reusability and stability of fabricated membranes demonstrated by the destructive experiments and cyclic performance tests might provide guarantee for the industrial water-in-oil emulsions purification.

One-pot synthesis of cellulose ester–graft–polylactide copolymers in an ionic liquid and the effect of graft-chain composition on their thermoplasticities and enzymatic degradabilities

With the aim of developing polymers having controlled thermoplasticities and biodegradabilities, a series of cellulose ester–graft–polylactide copolymers was synthesized using a homogeneous one-pot system in which the reaction medium was the ionic liquid 1-ethyl-3-methylimidazolium diethylphosphate (EmimDEP). The structures and compositions of the copolymers were controlled by varying the feed ratio of the carboxylic anhydride (acetic (C2), propionic (C3), or hexanoic (C6)) and L-lactide. In terms of side-chain substitution, the copolymers exhibited DSAcyl values of 0.7–2.7 and MSPLA values of 3.2–14.2. With increasing DSAcyl, the copolymers presented enhanced thermal stability and thermoplasticity due to the intermolecular interactions between the acyl groups and polylactide side-chains. The effect of graft-chain composition on mechanical properties and biodegradability was investigated using homogeneous cast films prepared with the copolymers. The mechanical properties were found to be affected by the carbon number of the acyl group (C2–C6), with higher carbon numbers imparting better plasticization. To investigate biodegradability, a two-step enzymatic degradation was performed using proteinase K and then cellulase. The copolymers with DSAcyl values below 1.3 exhibited enzymatic biodegradability with weight losses in the range 15.2%–34.6% (cf. 58.4% for polylactide).

Dual‐Additive‐Driven Morphology Optimization for Solvent‐Annealing‐Free All‐Small‐Molecule Organic Solar Cells

AbstractAll‐small‐molecule organic solar cells (ASM‐OSCs), which consist of small‐molecule donors and acceptors, have recently been studied extensively to eliminate the batch‐to‐batch variation from polymer‐based donor or acceptor. On the other hand, the control of their active layer morphology is more challenging due to the similar chemical structure and miscibility of small‐molecule donor and small‐molecule accepter. Hence, this study develops a dual‐additive‐driven morphology optimization method for ASM‐OSCs based on BTR‐Cl:Y6. One solid additive – 1,4‐diiodobenzene (DIB) and one liquid additive – diiodomethane (DIM) are selected, making use of their distinct interaction mechanisms with Y6 and BTR‐Cl. It is found that DIB can form a eutectic phase with Y6, which can increase the intermolecular interactions and modulate the acceptor phase separation, while the simultaneous volatilization of DIM suppresses the over‐aggregation of BTR‐Cl during the film casting process. As a result of the synergistic morphology tuning, the optimized device delivers a power conversion efficiency (PCE) as high as 15.2%, among the highest PCE reported to date for binary ASM‐OSCs without solvent annealing treatment. This work demonstrates the potential of morphology tuning via the incorporation of dual additives into ASM‐OSCs, enabling them to achieve comparable efficiencies to those of conventional polymer/small‐molecule based OSCs.

Effect of neutralization treatment on properties of chitosan/bamboo leaf flavonoids/nano-metal oxide composite films and application of films in antioxidation of rapeseed oil

Neutralization treatment improved the slow-release antioxidant food packaging function of chitosan (CS)/bamboo leaf flavone (BLF)/nano-metal oxides composite films. The film cast from the CS composite solution neutralized by KOH solution had good thermal stability. The elongation at break of the neutralized CS/BLF film was increased by about 5 times, which provided the possibility for its packaging application. After 24 h of soaking in different pH solutions, the unneutralized films swelled severely and even dissolved, while the neutralized films maintained the basic structure with a small degree of swelling, and the release trend of BLF conformed to the logistic function (R2 ≥ 0.9186). The films had a good ability to resist free radicals, which was related to the release amount of BLF and the pH of the solution. The antimicrobial neutralized CS/BLF/nano-ZnO film, like the nano-CuO and Fe3O4 films, were effective in inhibiting the increase in peroxide value and 2-thiobarbituric acid induced by thermal oxygen oxidation of rapeseed oil and had no toxicity to normal human gastric epithelial cells. Therefore, the neutralized CS/BLF/nano-ZnO film is likely to become an active food packaging material for oil-packed food, which can prolong the shelf life of packaged food.

Polyhydroxyalkanoates-based Cast Film as Bio-based Packaging for Fresh Fruit and Vegetables: Manufacturing and Characterization

Polyhydroxyalkanoates-based Cast Film as Bio-based Packaging for Fresh Fruit and Vegetables: Manufacturing and Characterization

Production of nanocellulose from corn husk for the development of antimicrobial biodegradable packaging film

Packaging is a potential way of keeping food products safe from various environmental pollutants, and biological, chemical, & physical deterioration. Hence, the demand for an effective antimicrobial active packaging material is increasing tremendously to improve the shelf-life of food products. Thus, we extracted nanocellulose from corn husks and developed a eugenol-incorporated biodegradable antimicrobial active packaging film. The extracted nanocellulose showed a particle size of 149.67 ± 3.56 nm and an overall surface charge of −20.2 mV ± 0.76 V. The film casting method is one of the promising methods to fabricate biodegradable films using plant-based biopolymers. Therefore, different concentrations of eugenol (0.5–5 % v/v) were incorporated to formulate the functional film (FF0.5-FF5) by employing the casting process. FF exhibited comparable tensile strength as compared to the control film (CF), however, FF5 showed the least tensile strength (85 MPa). Based on the mechanical characterization, the FF3 film sample was further selected for characterization. The morphological evaluation revealed that the surface of the film was smooth and non-porous with reduced moisture content and density. The film exhibited high thermal stability as the degradation occurred above 400 °C, indicating the strong hydrogen bonding between the hydroxyl groups of the film. The Fourier transform infrared spectroscopy analysis revealed the existence of -COOH vibration and COC stretching groups of cellulose and eugenol. The antimicrobial studies showed high efficacy against Staphylococcus aureus followed by Salmonella typhmurium, Pseudomonas aeruginosa, and Klebsiella pneumoniae bacteria. Overall, eugenol-incorporated nanocellulose-based biodegradable packaging film could be an excellent candidate as an alternative to active packaging material and provide an opportunity for the efficient utilization of corn husk.

A Novel Porous Butyryl Chitin-Animal Derived Hydroxyapatite Composite Scaffold for Cranial Bone Defect Repair.

Bone defects, a common orthopedic problem in clinical practice, are a serious threat to human health. As alternative materials to autologous bone grafts, synthetic cell-free functionalized scaffolds have been the focus of recent research in designing scaffolds for bone tissue engineering. Butyryl chitin (BC) is a derivative of chitin (CT) with improved solubility. It has good biocompatibility, but few studies have investigated its use in bone repair. In this study, BC was successfully synthesized with a degree of substitution of 2.1. BC films were prepared using the cast film method and showed strong tensile strength (47.8 ± 4.54 N) and hydrophobicity (86.4 ± 2.46°), which was favorable for mineral deposition. An in vitro cytological assay confirmed the excellent cell attachment and cytocompatibility of the BC film; meanwhile, in vivo degradation indicated the good biocompatibility of BC. Hydroxyapatite (HA), extracted from bovine cancellous bone, had good cytocompatibility and osteogenic induction activity for the mouse osteoblast cell line MC3T3-E1. With the aim of combining the advantages of BC and HA, a BC-HA composite scaffold, with a good pore structure and mechanical strength, was prepared by physical mixing. Administered into skull defects of rats, the scaffolds showed perfect bone-binding performance and effective structural support, and significantly promoted the regeneration of new bone. These results prove that the BC-HA porous scaffold is a successful bone tissue engineering scaffold and has strong potential to be further developed as a substitute for bone transplantation.

Effect of roll temperature on the structure and properties of oriented polypropylene cast film and stretched microporous membrane

AbstractThe effect of roll temperature from 60 to 120°C on the crystalline structure and properties of oriented polypropylene (PP) cast films and the stretched microporous membrane was studied. It was found that the long period, the thickness of the crystalline and amorphous phase increase with the increasing roll temperature. And the regularity of the lamellar structure also improves with the increasing roll temperature. In comparison, the lamellae lateral dimension is nearly unchanged at 50 nm. The orientation of the lamellar structure slightly decreases from 0.81 to 0.76 with increasing roll temperature. The increase of the long period and the improvement of the regularity of the lamellar structure lead to the increase of the elastic recovery value of PP cast film. The corresponding microporous membrane also shows a smaller thickness of lamellar clusters, larger pores, better air permeability and better thermal shrinkage resistance. The higher roll temperature is beneficial to the perfection of the lamellar structure, obtaining the higher‐performance microporous membrane.

Unidirectional Nanopore Dehydration Induces a Highly Stretchable and Mechanically Robust Silk Fibroin Membrane Dominated by Type II β-Turns.

Aqueous silk fibroin solution is dehydrated by evaporation into a water-soluble cast film (SFME) with poor mechanical properties but becomes by unidirectional nanopore dehydration (UND) into silk fibroin membrane (SFMU) with water-stable and good mechanical robustness. The thickness and tensile force of the SFMU are almost twice those of the MeOH-annealed SFME. The UND-based SFMU has a tensile strength of 15.82 MPa, an elongation of 665.23%, and a type II β-turn (Silk I) that accounts for 30.75% of the crystal structure. Mouse L-929 cells adhere, grow, and proliferate well on it. The UND temperature can be used to tune the secondary structure, mechanical properties, and biodegradability. UND induced the oriented arrangement of the silk molecules, which led to the formation of the SFMU dominated with Silk I structure. The silk metamaterial by controllable UND technology has great potential in medical biomaterials, biomimetic materials, sustained drug release, and flexible electronic substrates.

A Novel Alginate Film Based on Nanocoating Approach for Enteric-Release Tablets.

The objective of this study was to propose a new coating film for biodegradable polymers and environmentally friendly processing. Here, a novel implementation of solid lipid nanoparticles (SLN) into a biodegradable alginate (ALG) film composition created a new gastric-resistant film for an enteric-release tablet. Experiments were performed on a water-soluble substance (thiamine nitrate) to characterize the effects of SLN upon the addition of the ALG coating formulation. The coated tablets or cast films were characterized based on delayed-release properties, surface morphology, moisture resistance, and chemical interactions. The SLN-ALG film displayed gastric-resistant properties (< 10% drug substance dissolved at pH 1.2) and rapid disintegration in the intestinal medium (pH 6.8). Morphological analysis using a microscope and scanning electron microscope confirmed the uniformity and smoothness of the SLN-ALG film, which improved the mechanical properties of the film. Fourier transform infrared spectroscopy and differential scanning calorimetry indicated that SLN contributed to the formation of the film, which maintained free carboxylic groups, making the SLN-ALG film a higher acid resistance, but soluble in pH 6.8 buffer. These promising results suggest a novel nanotechnology-based coating formulation for various enteric-release dosage forms. Because of their biodegradability, the proposed ingredients and processes are safe and environment-friendly.