Cast Films Research Articles

Exploring stabilizer formulations for light-induced yellowing of polystyrene by high-throughput experimentation and machine learning

In this study, a high-throughput experimental protocol was established for yellowing inhibition of transparent plastics on the basis of solution film casting on microplates and ultraviolet/visible (UV/Vis) spectroscopic evaluation using a microplate reader. A combination of the protocol and a genetic algorithm realized a large-scale exploration of stabilizer formulations that consist of commercially available hindered amine stabilizers and UV absorbers, etc. The found formulations were highly effective in inhibiting the photo-induced yellowing of polystyrene, compared to the most efficient single stabilizer at the fixed concentration. The obtained data, which corresponded to seven years of aging (when sequentially acquired), were analyzed and validated based on decision tree classification, force-directed network visualization, and so on. A formulation design guideline was successfully derived that it is essential to combine as many stabilizers that are complementary and synergistic with each other as possible.

Chitin nanocrystal based aqueous inks for 3D printing via direct ink writing

Chitin nanocrystal (ChiNC), a kind of rod-like nanoparticle, exhibits a high elastic modulus, high mechanical strength, good biocompatibility, and biodegradability. Its aqueous dispersion behaves with a prominent shear thinning and concentration-related sol-gel transition characteristics, which has feasibility of extrusion-based 3D printing, that is, direct ink writing (DIW). Based on this, herein, ChiNC was chosen as matrix material to explore its printability via DIW. A kind of waterborne polycitrate prepolymer (pre-POFC) was introduced into the ChiNC aqueous dispersion inks. On the one hand, pre-POFC was as rheology modifier to tune the flow behavior of the inks; on the other hand, the cured POFC component was as adhesive agent to glue ChiNC nanoparticles, aiming to improve water-stability and remove brittleness of the ChiNC-based materials. The results showed the optimal loading ratio of POFC component was 30–50 wt% determined via water-stability tests. The rheological analyses showed that the ChiNC/pre-POFC aqueous inks exhibited a prominent shear thinning behavior, thixotropy, modulus recovery ability, and higher dynamical yield stress ( σy), meaning such systems had a good DIW printability theoretically. Actually, DIW results showed that only ChiNC/pre-POFC-6/4–30wt% and ChiNC/pre-POFC-5/5–30wt% inks exhibited optimal printability, in consideration of minimal contraction and superior shape retention after dehydration and thermocuring. However, the mechanical properties of printed films were weaker than that of cast films due to the limited printing precision and lower density.

Composites of cellulose nanocrystals in combination with either cellulose nanofibril or carboxymethylcellulose as functional packaging films

Cellulose nanocrystals (CNC) were mixed with either cellulose nanofibril (CNF) or carboxymethylcellulose (CMC) in variable proportions (0/100, 20/80, 40/60, 50/50, 60/40, 80/20 and 100/0) to obtain cast films with acceptable barrier and mechanical properties as replacements for food packaging plastics. Both CNF and CMC improved tensile strength, elongation, UV opacity, air resistance, hydrophobicity (WCA-water contact angle), water vapor transmission rate (WVTR) and oxygen impermeability in pure CNC. WVTR and oxygen permeability were strongly dependent on relative humidity (RH). Interestingly, the greatest effect on WVTR was observed at RH = 90% in films containing CMC in proportions above 60%. CMC- and CNF-containing films had oxygen impermeability up to an RH level of 80% and 60%, respectively. The previous effects were confirmed by food packaging simulation tests, where CMC-containing films proved the best performers. The composite films studied were biodegradable—which constitutes a major environmental related advantage—to an extent proportional to their content in CMC or CNF.

Physical and active properties of poly (vinyl alcohol) films with phenolic acids as affected by the processing method

Poly (vinyl alcohol) (PVA) films containing cinnamic acid (C) and ferulic acid (F) at 1% w/w and 2% w/w were successfully produced by solvent-casting the polymeric solution and melt blending and compression moulding. The effect of the processing method and the phenolic acid content on the microstructure, crystallinity and the optical, thermal, barrier and mechanical properties of partially hydrolysed PVA based films have been analysed, as well as the antioxidant and antimicrobial properties of the films. The processing method influenced the microstructural arrangement of the matrix, leading to differences in the degree of crystallinity and in the tensile and barrier properties of the films. Cast films were more stretchable and more resistant to break, while thermoprocessed films exhibited values of oxygen and water vapour permeability significantly higher than those obtained by casting. The incorporation of phenolic acids, especially ferulic acid, enhanced the barrier properties of the materials without affecting their thermal stability. The presence of phenolic acids in the films clearly induced the inhibition of Listeria innocua growth and had a positive antioxidant response, thus suggesting the great potential of these active materials for food packaging applications.

The effect of melt drawing ratio on the crystal structural change and performance of polyketone extrusion cast film

In this paper, the polyketone (POK) extrusion cast film is manufactured by melt stretching method, and the evolution process of the crystal morphology and mechanical properties with the increase of melt drawing ratio (MDR) are followed. The results show that the melt stretching process produces many micro shish-kebab crystals in the POK. The length of the shish crystal and the thickness of the kebab crystal hardly increase with MDR, but the lateral length of the kebab crystal shows linear growth when MDR exceeds 40. The crystalline morphology of POK is mainly affected by melt relaxation. The molecular chain has sufficient relaxation during cooling at a low MDR (20–40). At this time, micro shish-kebab crystals are mainly randomly arranged. When MDR exceeds 40, the rapid melt stretching shortens the relaxation time of the tie chain between the neighborhood shish crystal, and the atomic force microscopy image shows a typical shish-kebab structure. This experimental result indicates that the formation of the oriented lamella structure may be related to the relaxation of the molecular chains between the micro-shish. When the length of the shish axis and the thickness of the kebab lamellae are similar, it is difficult to distinguish the two.

PHB/PLA plasticized by olive oil and carvacrol solvent-cast films with optimised ductility and physical ageing stability

Polylactic acid (PLA) is a bio-based polyester, widely used in various compostable food packaging film applications. Polyhydroxybutyrate (PHB), the most commercialised polymer of the PHA polyesters family, is one of the preferred bio-based polymers for food packaging, mainly because of its biodegradability in natural and controlled environments, and its good gas barrier properties. PHB, being a rather brittle polymer, is suitable for rigid packaging applications, mainly through injection molding processes. PHB may also be used for manufacturing flexible packaging by film casting and film blowing extrusion, through blending or co-extrusion with selected bio-based polymers such as PLA and additives. The potential development of blends of PHB with selected bio-based polymers that may be used for food packaging film applications was investigated in this work. Films made of various blends of PHB with other bio-based biodegradable polymers and additives were produced by the solvent casting method at laboratory scale and evaluated in terms of their mechanical properties and stability, used as “pass-fail” selection criteria. Following the development and evaluation of a second series of selected PHB/PLA blends suitable for films production, it was possible to achieve optimised compositions of PHB/PLA (10/90) blends with olive oil (OO) and carvacrol (CAR) as plasticizing and stabilising additives. The excellent mechanical performance of the selected blends with high ductility and stability against physical ageing, was analysed in depth in terms of their chemical structure and thermal behaviour.

Sum-Frequency Generation and Scanning Electron Microscope Studies on Second-Harmonic Generation Active Structures of Sacran Aggregates

Optical second-harmonic generation (SHG) in self-assembled ampholytic mega-molecule polysaccharide sacran is an interesting phenomenon but its origin has not been clarified. SHG-active sacran aggregates in dried cast films made from ultrasonicated 0.5 wt% sacran aqueous solutions were studied at microscale using the scanning electron microscope and the energy dispersive X-ray technology. Hexagonal morphology was observed frequently with the size of a few to tens of micrometers. The calcium density was higher in the area showing the SHG signals. In sum-frequency generation spectra of the SHG-active sacran aggregates, vibrational modes of functional groups such as CH3, CH2, and −COOH of the sacran molecules and OH of the water molecules were identified. The structure of the SHG-active sacran aggregates was modeled from the observed facts.

Linear stability analysis of nonisothermal glass fiber drawing

We present a model of the draw resonance instability for glass fiber drawing including inertia, gravity, surface tension, and temperature. Using linear stability analysis, we have evidenced, through an alternative scaling, the crucial role of the fiber aspect ratio as a control parameter. It appears that a strong destabilization of the system occurs as this parameter increases. We also show the significant influence of nonhomogeneous ambient temperature on system stability. Contrary to the film casting problem, the high critical draw ratio in industrial applications could be rationalized only for a heat transfer coefficient dependent on both the velocity and cross-sectional area of the fiber.

Effects of Surfactants on Zein Cast Films for Simultaneous Delivery of Two Hydrophilic Active Components.

In order to prepare edible films with outstanding antimicrobials and antioxidants utilized in applications of food and pharmaceutics, in this study, effects of surfactants on zein cast films for simultaneous delivery of lysozyme (LY) and ascorbic acid (AA) were investigated, where sodium alginate (SA), soy lecithin (SL), and Pluronic f-68 (PF-68) were selected as surfactants. FT-IR tests indicated that SL or PF-68 dramatically changed secondary structure of zein composite films, which heightened the irregularity of the composite film and inhibited LY crystallization. Mechanical tests showed that highly flexible films exhibiting elongations between 129% and 157% were obtained when adding PF-68. Compared with the film without emulsifier, zein film containing SL and PF-68 showed approximately 7.51 and 0.55 times lower initial release rates for LY and AA respectively, which significantly improved the controlled release and heightened the anti-microbial and anti-oxidant activities of the film. Finally, emulsified mechanisms of the surfactants in zein films were proposed.

Research on the Preparation and Application of Chitosan Composite Membrane

In this study, an edible chitosan/castanopsis powder/essential oil ternary composite film was prepared by the casting film forming method. Prepare 1.5% chitosan (CTS) solution and 3% Castanopsis sclerophylla powder (ST) gelatinization solution respectively, and measure the CTS solution and ST gelatinization solution according to different mass ratios of chitosan and Castanopsis sclerophylla powder. Mix the liquid uniformly, add 15% glycerin to plasticize, then add different content of essential oil (EO) and Tween 80, high-speed shear mixing, vacuum defoaming, quantitative casting in the mold, drying at 45 °C to form a film .Through the study of the physicochemical properties and antibacterial ability of the composite film, the results show that the addition of an appropriate amount of Castanopsis sclerophylla powder can improve the physical and chemical properties of the composite film, and the essential oil can effectively improve the water barrier and antibacterial properties of the film. The edible film is used for fresh-keeping packaging of fresh meat, and the result shows that the edible film has good antibacterial and antioxidant effects.

Effects of ZnO and SiO<sub>2</sub> Nanoparticle Additions on the Structural, Water Absorption and Mechanical Properties of Polyvinyl Alcohol (PVA) Films

Nanocomposite films were prepared with polyvinyl alcohol (PVA) as a base matrix and ZnO, SiO2 nanoparticles as a filler material. SiO2 and ZnO nanoparticles were synthesized using sol-gel and co-precipitation methods, respectively. PVA-ZnO, PVA-SiO2, and PVA-ZnO-SiO2 hybrid nanocomposite films were prepared by a solution film casting method. The presence of ZnO and SiO2 nanoparticles within the films has been confirmed by structural and morphological analysis of the films. Water solubility, water absorption and tensile strength was evaluated for all the films produced. The addition of both types of nanoparticles in the PVA matrix led to a reduction in water absorption in addition to the water solubility capability of the material when compared to the pure PVA film. Addition of nanoparticles resulted in an increase in the tensile strength of the composite films compared to the pure PVA films by 14%, 23%, and 66% for the PVA-ZnO, PVA-SiO2, and PVA-ZnO-SiO2 films respectively. This work provides a simple route to tune the properties of PVA embedded with metal oxide nanoparticles for food packaging and medical applications.

Effects of an industrial graphene grade and surface finishing on water and oxygen permeability, electrical conductivity, and mechanical properties of high-density polyethylene (HDPE) multilayered cast films

Graphene-based composites are promising candidates to improve properties in flexible packaging to protect electronic devices. However, the literature hardly addresses the industrial scale requirements. In this context, high-density polyethylene (HDPE), a common packaging material, and an industrial grade graphene (G) were used to prepare multilayered composites by cast film coextrusion, a flexible-packaging-industry compatible technique. The effects of G content and surface finishing on HDPE films’ properties were investigated. Experimental results showed that a maximum permeability reduction of 43% at 0.5 wt% of G was achieved. Such result was associated with a good dispersion efficiency and with the filler’s aspect ratio. However, as the concentration of G increased both barrier and mechanical properties worsened due to a poor dispersion of G within the composite. Additionally, it was found that surface finishing induced defects increasing permeability despite improvements in visible light transmittance and reduction of surface roughness. These defects can be successfully prevented using a proper design of layers during coextrusion. In summary, the present study showed the feasibility of G-based flexible packaging film applications at an industrial scale. The importance of G dispersion and of layer design to achieve improved barrier properties should be emphasized.

In vitro evaluation of porous poly(hydroxybutyrate-co-hydroxyvalerate)/akermanite composite scaffolds manufactured using selective laser sintering.

Incorporation of a bioactive mineral filler in a biodegradable polyester scaffold is a promising strategy for scaffold assisted bone tissue engineering (TE). The current study evaluates the in vitro behavior of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/Akermanite (AKM) composite scaffolds manufactured using selective laser sintering (SLS). Exposure of the mineral filler on the surface of the scaffold skeleton was evident from in vitro mineralization in PBS. PHBV scaffolds and solvent cast films served as control samples and all materials showed preferential adsorption of fibronectin compared to serum albumin as well as non-cytotoxic response in human osteoblasts (hOB) at 24h. hOB culture for up to 21days revealed that the metabolic activity in PHBV films and scaffolds was significantly higher than that of PHBV/AKM scaffolds within the first two weeks of incubation. Afterwards, the metabolic activity in PHBV/AKM scaffolds exceeded that of the control samples. Confocal imaging showed cell penetration into the porous scaffolds. Significantly higher ALP activity was observed in PHBV/AKM scaffolds at all time points in both basal and osteogenic media. Mineralization during cell culture was observed on all samples with PHBV/AKM scaffolds exhibiting distinctly different mineral morphology. This study has demonstrated that the bioactivity of PHBV SLS scaffolds can be enhanced by incorporating AKM, making this an attractive candidate for bone TE application.

Anticorrosive waterborne polyurethane coatings derived from castor oil and renewable diols

Although vegetable oil-based waterborne polyurethane (WPUs) possesses unique advantage like environmental friendliness, the shortcomings of low mechanical properties havehampered its practical implementations. In this work, sustainable diols, isosorbide (IS) and L-tyrosine derived cyclic dipeptide (L-CD), were employed into the anionic castor oil based WPU backbones via a molecular design strategy respectively (denoted as WPU-A and WPU-B). Their impact on the stability of the dispersion as well as the performance of casting films were investigated thoroughly. Result shown that the tensile strength of the films reached up to 29.56 MPa, while the toughness remained at 20.12 MJ/m−3, outperforming the state-of-art castor oil-based WPU systems. Specifically, WPU-B films exhibited superior performance than WPU-A ones possessing the similar hard segment contents, which presumably attribute to a higher density of hydrogen bonds within the network. The glass transition temperature (Tg) of WPUs were tailored in the range of 5.93 °C to 57.23 °C, and the highest value was prominent in the reported systems. Interestingly, the incorporation of sustainable diols into WPUs improved the anticorrosion performance towards 45# steel, which stemmed from the robust, hydrophobic properties of the WPU films. This study offered strategies for tailoring the physical properties of environmental benign WPUs and paved the ways towards developing high performance coatings for anticorrosion applications.

Ag Nanoparticle-Coated Polystyrene Microspheres for Electromagnetic Interference Shielding Films with Low Metal Content

The fabrication of thin composite films incorporating metal-based fillers with a delicate structure to achieve high electromagnetic interference shielding effectiveness (EMI SE) at low metal content remains a great challenge. In this work, benefiting from the excellent electrical conductivity of Ag nanoparticles, Ag nanoparticle-coated polystyrene (PS@Ag) microspheres with a large PS core were selected as electrically conductive fillers, and the volume exclusion effect guaranteed the construction of an electrically conductive network with low silver loading. A spontaneous process to construct a segregated laminar structure with a three-dimensional electrically conductive network happened with the assistance of a gravity-driven effect. The flexible thin films with a low amount of silver exhibited outstanding EMI SE per unit thickness (SE/d). To further investigate the effect of the structure on the EMI SE efficiency, it is found that the alternate interfaces play a critical role in enhancing shielding performance by stacking multiple films compared to the bulk films obtained by casting. The EMI SE for an only 0.3 mm triple-piece stacking film with 6.3 wt % Ag loading could reach 55.3 dB compared to 37.2 dB for the triple-thickness casting film. Using the stacking process results in easy accessibility for tailored composites with the desired EMI SE, which supplies a new strategy for the design of shielding materials in the next-generation electronics.

Alginate Biofunctional Films Modified with Melanin from Watermelon Seeds and Zinc Oxide/Silver Nanoparticles.

Bioactive films find more and more applications in various industries, including packaging and biomedicine. This work describes the preparation, characterization and physicochemical, antioxidant and antimicrobial properties of alginate films modified with melanin from watermelon (Citrullus lanatus) seeds at concentrations of 0.10%, 0.25% and 0.50% w/w and with silver and zinc oxide nanoparticles (10 mM film casting solutions for both metal nanoparticles). Melanin served as the active ingredient of the film and as a nanoparticle stabilizer. The additives affected the color, antioxidant (~90% ABTS and DPPH radicals scavenging for all melanin modified films) and antimicrobial activity (up to 4 mm grow inhibition zones of E. coli and S. aureus for both zinc oxide and silver nanoparticles), mechanical (silver nanoparticles addition effected two-fold higher tensile strength), thermal and barrier properties for water and UV-vis radiation. The addition of ZnONP resulted in improved UV barrier properties while maintaining good visible light transmittance, whereas AgNP resulted in almost complete UV barrier and reduced visible light transmittance of the obtained films. What is more, the obtained films did not have an adverse effect on cell viability in cytotoxicity screening. These films may have potential applications in food packaging or biomedical applications.

3ω techniques for measurement of volumetric heat capacity and anisotropic thermal conductivity of a solution processable, hybrid organic/inorganic film, Te-PEDOT:PSS

Measuring the thermal properties of anisotropic films of hybrid materials poses a challenge to existing metrology techniques. We have developed a new approach for measuring the volumetric heat capacity and anisotropic thermal conductivity of these systems using the 3ω method. While there exist many avenues for measuring the thermal properties of thin films, most carry with them difficult requirements such as smooth surfaces or advanced lithography. Here, we present measurements of a film's in-plane and cross-plane conductance and its volumetric heat capacity using relatively simple sample configurations, each requiring a single heater. For the measurement of volumetric heat capacity, we present a new model fitting method, relying on a standard film-on-substrate configuration. For the measurement of in-plane thermal conductance by 3ω, we have developed the use of an embedded micro-wire heater in suspended drop cast films, allowing for a 12 μm wide heater without the need for advanced lithography. We also expose the surprisingly significant effect of thermal radiation in the suspended film measurement and its associated error. Our measurements reveal a large anisotropy in the thermal conductivity of our test material, Te-PEDOT:PSS, of kin-plane/kcross-plane = 19, consistent with the nanoscale morphology of the material.

Solution-Processable Colorless Polyimides Derived from Hydrogenated Pyromellitic Dianhydride: Strategies to Reduce the Coefficients of Thermal Expansion by Maximizing the Spontaneous Chain Orientation Behavior during Solution Casting.

In this study, practically useful colorless polyimides (PIs) with low coefficients of thermal expansion (CTEs) and other desirable properties were prepared from hydrogenated pyromellitic dianhydride (1-exo,2-exo,4-exo,5-exo-cyclohexanetetracarboxylic dianhydride, H-PMDA). A modified one-pot polymerization method afforded a high-molecular-weight PI with sufficient film-forming ability from 2,2′-bis(trifluoromethyl)benzidine (TFMB) with a rod-like structure and H-PMDA. However, the PI film cast from its homogeneous solution did not have low CTEs, similar to the analogous system using meta-tolidine. To solve this problem, a series of amide- and amide-imide-containing diamines were designed and synthesized. The modified one-pot polymerization of H-PMDA and the diamines in γ-butyrolactone produced homogeneous, viscous, and stable solutions of high-molecular-weight PIs with high solid contents. The cast films of certain systems examined in this study simultaneously achieved low CTEs, high optical transparency, considerably high glass transition temperatures (Tgs), and sufficient ductility. A possible mechanism for the generation of low CTEs, which is closely related to the spontaneous in-plane orientation behavior during solution casting, was proposed. Certain H-PMDA-based PIs developed in this study are promising colorless heat-resistant plastic substrates for use in image display devices and other optical applications.

Research on the implementing conditions of inverse emulsion‐breath figure method

AbstractThe relationships between three steps of the inverse emulsion‐breath figure (Ie‐BF) method, including emulsion preparation, film casting and hydrophilic component loading, are explored by adjusting the experimental factors of the three implementing processes. For emulsion preparation step, the influence of the ultrasonification, the concentration of emulsifier and the addition of polymer on the size of the emulsion droplets are investigated. For film casting step, the influence of environmental humidity and several factors concerning the emulsion preparation on the porous structure of the resultant films are studied. It has been proved that high humidity is a necessity for obtaining surface pores, and multi‐layered pores with disordered distribution can be formed in the bulk layer of the film when high water/oil ratio is used in making the emulsion. Bovine serum albumin is loaded into the emulsion water droplets, and by implementing the Ie‐BF method under the condition of water/oil ratio being as low as 0.02 vol%, selective protein enrichment within the interior of the top‐layer pores is still realized. It reflects the characteristics of “high efficiency, targeted assembly” in the step of hydrophilic component loading.

“Dontcha Wanna Boogie Woogie”

ABSTRACT Building upon Mecca Jamilah Sullivan’s theory of the choreopoem as a queer form emphasizing a poetics of difference, as well as Omi Osun Jones’s concept of theatrical jazz, this article reassesses Ntozake Shange’s boogie woogie landscapes to argue that the choreopoem serves as an embodied futurist solution for resolving cisgender bias, as well as femme phobia and transphobia in theater, film, and television casting and performance training.