High moisture strength of cassava starch/polyvinyl alcohol-compatible blends for the packaging and agricultural sectors

Effect of high amylose starch on the incorporation of thymol into electrospun pullulan nanofibers

High amylose starch (HAMS) was employed as an effective carrier to incorporate thymol within pullulan nanofibers. Aqueous solutions with HAMS concentrations of 0 % - 5 % were investigated to study their effect on the incorporation of thymol during electrospinning. As a result, the loading capacity was significantly improved by the addition of HAMS, increasing from 2.38 % to 6.15 %. Thymol-starch mixture with an irregular structure was embedded within pullulan nanofiber according to SEM and TEM results. The HAMS-1, HAMS-3 and HAMS-5 were endowed with good anti-microbial inhibition against Escherichia coli and Bacillus cereus. Additionally, HAMS-5 exhibited sustained release of thymol, while the addition of HAMS improved the mechanical properties of HAMS-1. Further investigation into the interaction between HAMS, pullulan, and thymol in the nanofibers was conducted. HAMS proved effective in enhancing the bioavailability of thymol and provides a promising material for developing edible, sustainable polysaccharide antimicrobial nanofibrous films for the food industry.

De- and Re-Structuring of Starch to Control the Melt and Solid State Visco-Elasticity as Method for Getting New Multi Component Compounds with Scalable Properties

The aim of the article was to design and develop new thermodynamically stable starch-based compounds, with scalable properties, that are melt-processable into finished products by classic or 3D printing methods. This is based on phenomena of de-structuring, entanglement compatibilization, and re-structuring of starch, along with the modification of the polymer, polyvinyl alcohol (PVA), by following an experimental sequence involving pre-treatment and melt compounding in two stages. The new compounds selection was made considering the dependence of viscoelastic properties on formulation and flowing conditions in both the melted and solid states. Starting from starch with 125 °C glass transition and PVA with a Tg at 85 °C, and following the mentioned experimental sequence, new starch-PVA compounds with a high macromolecular miscibility and proven thermodynamic stability for at least 10 years, with glass transitions ranging from -10 °C to 50 °C, optimal processability through both classical melt procedures (extrusion, injection) and 3D printing, as well as good scalability properties, were achieved. The results are connected to the approaches considering the relationship between miscibility and the lifetime of compounds with renewable-based polymer content. By deepening the understanding of the thermodynamic stability features characterizing these compounds, it can be possible to open the way for starch usage in medium-life compositions, not only for short-life applications, as until now.

Mechanical activation-enhanced metal-organic coordination strategy to fabricate high-performance starch/polyvinyl alcohol films by extrusion blowing

The production of high-performance starch-based packaging films by extrusion blowing is challenging, ascribed to poor processability of the blend precursors. In this study, a new strategy of mechanical activation (MA)-enhanced metal-organic coordination was proposed to improve the processability of starch (St)/polyvinyl alcohol (PVA) blend precursor, with calcium acetate (CA) as a chelating agent and glycerol as a plasticizer. MA pretreatment activated the hydroxyl groups of starch and PVA for constructing strong metal-organic coordination between CA and St/PVA during reactive extrusion, which effectively enhanced the melt processing properties of the blend precursor, contributing to the fabrication of high-performance St/PVA films by the extrusion-blowing method. The as-prepared St/PVA films exhibited excellent mechanical properties (tensile strength of 34.5 MPa; elongation at break of 271.8 %), water vapor barrier performance (water vapor permeability of 0.704 × 10-12 g·cm-1·s-1·Pa-1), and oxygen barrier performance (oxygen transmission rate of 0.7 cm3/(m2·day·bar)), along with high transmittance and good uniformity. These outstanding characteristics and performances can be attributed to the improved interfacial interaction and compatibility between the two matrix phases. This study uncovers the mechanism of MA-enhanced metal-organic coordination for improving the properties of starch-based films, which provides a convenient and eco-friendly technology for the preparation of high-performance biodegradable films.

Poly(butylene adipate-co-terephthalate)/Polylactic Acid/Tetrapod-Zinc Oxide Whisker Composite Films with Antibacterial Properties

Biodegradable composite films comprising of poly(butylene adipate-co-terephthalate) (PBAT), polylactic acid (PLA), and tetrapod-zinc oxide (T-ZnO) whisker were prepared by a melt-extrusion and blow molding process. The effect of the incorporation of the T-ZnO whisker (1 to 7 wt.%) in the PBAT/PLA blend film was studied systematically. The composite films with an optimal T-ZnO whisker concentration of 3 wt.% exhibited the highest mechanical (tensile strength ~32 MPa), rheological (complex viscosity~1200 Pa.s at 1 rad/s angular frequency), and gas barrier (oxygen permeability~20 cc/m2·day) properties, whereas the composite films with 7 wt.% T-ZnO whiskers exhibited the highest antibacterial properties. The developed composite films can find potential application as antibacterial food packaging materials.

Fabrication of biodegradable and cold-water-soluble starch/polyvinyl alcohol films as inner packaging materials of pesticides: Enhanced emulsification, dispersibility, and efficacy

Developing environmentally friendly film materials for packaging pesticides is significant yet challenging. The use of native starch for preparing inner packaging materials of pesticides is limited by its physicochemical properties. In this study, a novel strategy of synergetic mechanical activation (MA)-enhanced solid-phase esterification of starch and cooperative combination of starch and polyvinyl alcohol (PVA) was proposed to fabricate biodegradable and cold-water-soluble starch (St)/PVA films. The appropriate esterification of starch and favorable compatibility between starch and PVA contributed to the production of St/PVA films by the extrusion-blowing method. The as-prepared film with St/PVA ratio of 4:6 exhibited outstanding mechanical properties (tensile strengths of 21.0 MPa; elongation at break of 213.9 %), cold-water solubility (dissolution time of 90 s), and oxygen barrier performance (oxygen transmission rate of 1.41 cm3/(m2·day·bar)). The dissolved St/PVA films with amphiphilic groups were conducive to the emulsification of butachlor (a fat-soluble liquid pesticide) and the dispersibility of oxyfluorfen (a fat-soluble solid pesticide). Furthermore, a mechanism of the interaction between pesticides and the surface of weed leaves was proposed to reveal the enhanced efficacy of St/PVA films-packaged pesticides. The strategy based on MA-enhanced esterification and PVA blending is efficient to produce starch-based films suitable for inner packaging materials of pesticides.

Fabrication and Testing of Crop Waste Ceiba pentandra Shell Powder Reinforced Biodegradable Composite Films

Ceiba pentandra shell powder (CPSP) biowaste is chosen as a biofiller combined with poly(vinyl alcohol) (PVA) as a matrix to make biofilms to increase the exploitation of biowaste materials and reduce the use of plastic materials. FTIR plots indicated no significant chemical reaction or formation of new functional groups during interaction between PVA and CPSP. XRD diffractograms showed that the crystallinity index (35.3, 38.6, 42.3, 46.4, and 48.5%) and crystalline size (18.14, 20.89, 23.23, 24.87, and 26.34 nm) of biofilms increased with CPSP loading (5-25 wt %). The PVA/CPSP films are thermally stable up to 322 °C. The peak highs of AFM images showed that the films' surface roughness gradually increased from 94.75 nm (5 wt % CPSP) to 320.17 nm (25 wt % CPSP). The FESEM micrographs clarify the homogeneous distribution of CPSP in the PVA matrix. Tensile strength and tensile modulus are noticeably increased by 26.32 and 37.92%, respectively, as a result of the loading of CPSP from 5 to 20 wt % in the PVA matrix. The PVA/CPSP films outperform pure PVA films in UV shielding (350-450 nm). The 59% weight loss of films was estimated during 60 days of burial. The fabricated biofilms maintained their suitable structural, thermal, morphological, and mechanical properties. Additionally, they exhibited consistent performance in ultraviolet (UV) barrier, opacity, water absorption, water vapor permeability, soil burial, and antimicrobial characteristics over time. Overall, PVA/CPSP (5-25 wt %) films are biodegradable and have promising applications as good packaging materials.

Intermolecular interactions between starch and polyvinyl alcohol for improving mechanical properties of starch-based straws

Starch/polyvinyl alcohol (PVA) degradable straws with different PVA contents were prepared by the twin-screw extrusion method. The results showed that the starch/PVA straws with 40 % PVA (PS4) had the highest dispersion uniformity of starch and PVA to achieve the best compatibility, and the compatibility size was below the micron level. Molecular interactions between starch and 40 % polyvinyl alcohol reached the highest due to the highest strength of hydrogen bonds, hence resulting in the highest texture densities. Consequently, the largest compatibility and molecular interactions significantly improved the mechanical properties and water resistance of PS4. Compared to the starch/PVA straw with 0 % PVA (PS0), swelling volume of PS4 decreased by 45.5 % (4 °C) and 65.2 % (70 °C), respectively. After soaking, the diameter strength increased by 540.1 % (4 °C, 1 h) and 638.7 % (70 °C, 15 min), respectively. Water absorption decreased by 45.3 % (4 °C, 30 min) and 27.6 % (70 °C, 30 min).

Investigation of Morphological, Chemical, and Thermal Properties of Biodegradable Food Packaging Films Synthesised by Direct Utilisation of Cassava (Monihot esculanta) Bagasse

The utilisation of edible sources of starch such as corn, wheat, potato, and cassava has become the common approach to develop biodegradable food packaging. However, the future food security issue from the wide application of such edible starch sources has become a major concern. Consequently, exploring non-edible sources of starch for starch-based biodegradable food packaging and their property enhancement have become one of the common research interests. Although there has been a great potentials of synthesising biodegradable food packaging by direct utilisation of agro-industrial waste cassava bagasse, there have been very limited studies on this. In this context, the current study investigated the potential of developing biodegradable food packaging by directly using cassava bagasse as an alternative matrix. Two film-forming mixtures were prepared by incorporating glycerol (30% and 35%), powdered cassava bagasse and water. The films were hot-pressed at 60 °C, 100 °C, and 140 °C temperatures under 0.28 t pressure for 6 min. The best film-forming mixture and temperature combination was further tested with 0.42 t and 0.84 t pressures, followed by analysing their morphology, functional group availability and the thermal stability. Accordingly, application of 35% glycerol, with 100 °C, 0.42 t temperature and pressure, respectively, were found to be promising for film preparation. The absence of starch agglomerates in film surfaces with less defects suggested satisfactory dispersion and compatibility of starch granules and glycerol. The film prepared under 0.42 t exhibited slightly higher thermal stability. Synthesised prototypes of food packaging and the obtained characterisation results demonstrated the high feasibility of direct utilisation of cassava bagasse as an alternative, non-edible matrix to synthesise biodegradable food packaging.

Preparation of hydroxypropyl starch/polyvinyl alcohol composite nanofibers films and improvement of hydrophobic properties

Starch-derived edible films have great potential as biodegradable food packaging and biomedical materials, in this study, we adopted a green method to prepare starch-based composite electrospun nanofibers films. The hydroxypropyl starches (HPS) were prepared to improve native starch solubility and properties, and a series of blend solutions were prepared with different HPS/polyvinyl alcohol (PVA) weight ratios. The comparison of the properties of HPS/PVA (HPA) nanofibers with different amylose contents were evaluated, and the fibers fabricated from hydroxypropyl high amylose starch (HP-HAS) had more continuous and homogeneous morphologies compared to the other starch fibers, it was also found that the addition of HP-HAS in the film has better mechanical properties than pure PVA film. Thus, to improve the hydrophobicity of the film, the HP-HAS/PVA (HPA(H)) nanofiber was selected for the hydrophobic study by the citric acid (CA) treatment. The hydrophobic surface was formed on the HPA(H) film by CA self-assembled coating with a water contact angle changed from 30.95° up to 100.74°. This study successfully prepared the modified starch/PVA composite nanofibers and established a simple method of self-assembled hydrophobic modification to improve water stability. Therefore, this green strategy is an alternative candidate in further study for food packaging and relative areas.

Effect of polyvinyl alcohol and carboxymethylcellulose on the technological properties of fish gelatin films

The objective of this work was to develop biodegradable films by mixing gelatin/carboxymethylcellulose (FG/CMC) and gelatin/polyvinyl alcohol (FG/PVOH) and to evaluate the effect of adding these polymers on the properties of fish gelatin films. The films FG/CMC and FG/PVOH were produced in the proportions 90/10, 80/20 and 70/30 and characterized their physical, chemical and functional properties. The addition of CMC and PVOH improved the mechanical strength, barrier property and water solubility of gelatin films. FG/CMC films showed greater tensile strength and greater solubility than FG/PVOH. The maximum concentration of CMC promoted the highest mechanical resistance, while the highest PVOH content produced the film with the lowest solubility. The proposed mixing systems proved to be adequate to improve the properties of fish gelatin films, with potential for application in the packaging sector.

Preparation of carboxymethyl starch/polyvinyl-alcohol electrospun composite nanofibers from a green approach

A green approach for the preparation of starch-based composite nanofibers using electrospinning was developed. The water-soluble sodium carboxymethyl starch (CMS) with DS 0.31 was prepared. The addition of co-blending polymer polyvinyl-alcohol (PVA) was attempted to improve the CMS solution spinnability, which blends from aqueous solution were prepared at different CMS/PVA weight ratios. The solution parameters including viscosity, surface tension and conductivity were measured and the morphologies of nanofibers were observed by SEM. Smooth, continuous, and defect-free nanofibers were successfully obtained range from the blend of CMS/PVA weight ratios of 10:90 to 80:20. Diameter distribution diagrams suggested that the diameter of the nanofibers reduced with the concentration of CMS increasing. This is the first report that the thin nanofiber (135.29 nm) with bead-free was obtained at the maximal CMS content of 50.0 wt% in the CMS/PVA blend. This study provided a green approach to produce starch-based nano-scale fibers.

Antimicrobial biodegradable film based on corn starch/Satureja khuzestanicaessential oil/Ag-TiO2nanocomposites

Biosynthesis of nanoparticles (NPs) using plant extract is an eco-friendly method, in which natural materials are used and is a simple, non-toxic, and environmentally friendly green synthesis. In this study, corn starch (CS) film containingSatureja khuzestanicaessential oil (SEO) and Ag-TiO₂nanocomposites (size: nearly 30-60 nm) were prepared and its antimicrobial, morphological, physical, and mechanical characteristics were investigated. Ag-TiO₂nanocomposites with different molar percentages were synthesized byS. khuzestanicaextract and based on the best antibacterial results against Gram-negative bacteria (Escherichia coliATCC 25922 andSalmonella typhimuriumATCC 14028) and Gram-positive bacteria (Staphylococcus aureusATCC 25923), were chosen to prepare the films. Four types of biodegradable films were provided: simple CS film, the film incorporated with SEO (essence film), the film incorporated with Ag-TiO₂nanocomposites (nanofilm), and nano/essence film. The scanning electron microscopy (SEM) was employed for investigating the morphology of the films. The combined energy-dispersive x-ray spectroscopy with SEM was applied to analyze the near-surface elements. Physical characteristics of the films containing water vapor permeability (%) and their moisture content, mechanical tests, and antibacterial properties were examined. Antimicrobial evaluation of the films revealed a 3-4 log and 6-7 log (CFU ml^-1) reduction inS. aureusandE. colispecies respectively, compared to the control group. The bio-polymer film incorporated with extracted essential oil ofS. khuzestanicaand Ag-TiO₂nanocomposites are effective to package foods and can delay chemical, physical, and microbial spoilage.

Development and characterization of corn starch/PVA active films incorporated with carvacrol nanoemulsions

An active film was prepared by corn starch (CS), polyvinyl alcohol (PVA) and carvacrol nanoemulsions (CNE). The microstructure and properties of CNE/corn starch/PVA (CNE/CSP) films were characterized and investigated. Scanning electron microscopy (SEM) revealed the uniform distribution of CNE and discontinuity of the film matrix. Fourier transform infrared (FT-IR) and rheological analysis indicated that CNE could weaken molecular interaction of the film matrix. X-ray diffraction (XRD) show that the films are amorphous and CNE has no effect on crystal structure of the films. Incorporation of CNE significantly increased the tensile strength, Young's modulus, elongation at break, barrier (water vapor and ultraviolet), antioxidant and antifungal activity. With the CNE incorporated, the optimal tensile strength, Young's modulus, elongation at break and antioxidant activity of the films can reach 12 MPa, 11 MPa, 133%, 81%, respectively. Minimum water vapor permeability was 3.1 × 10^-12 gd^-1m^-1Pa^-1. Notably, films incorporated with CNE (≥20%) had good DPPH free radical scavenging ability (>50%) when stored up to 6 days. Films with 25% CNE exhibited excellent antifungal activity against Trichoderma sp. and its inhibitory zone was 47 mm. Overall, the CSP films loaded with CNE (>15%) could be used as food packing materials with good antioxidant and antimicrobial activities.

Dendrite Integration Mimicked on Starch-Based Electrolyte-Gated Oxide Dendrite Transistors

Emulation of dendrite integration on brain-inspired hardware devices is of great significance for neuromorphic engineering. Here, solution-processed starch-based electrolyte films are fabricated, demonstrating strong proton gating activities. Starch gated oxide dendrite transistors with multigates are fabricated, exhibiting good electrical performances. Most importantly, dendrite modulation, spatiotemporal dendrite integration, and linear/superlinear dendrite algorithm are demonstrated on the proposed dendrite transistor. Furthermore, a low energy consumption of ∼1.2 pJ is obtained for triggering a synaptic response on the dendrite transistor. Accordingly, the signal-to-noise ratio is still as high as ∼2.9, indicating a high sensitivity of ∼4.6 dB. Such artificial dendrite transistors have potential applications in brain-inspired neuromorphic platforms.

Chitosan/Cellulose Nanofibril Nanocomposite and Its Effect on Quality of Coated Strawberries

The aim of this study was to develop a chitosan/cellulose nanofibril (CNF) nanocomposite and evaluate its effect on strawberry’s postharvest quality after coating. From the results of color, thickness, and scanning electron microscopy (SEM) and permeability to water vapor analyses, the best film formulation for coating strawberries was determined. Three coating formulations were prepared: 1% chitosan, 1% chitosan + 3% CNF, and 1% chitosan + 5% CNF. The strawberries were immersed in the filmogenic solutions and kept under cold storage (1 ± 1°C). The color of the film was not affected by increased concentration of cellulose nanofibrils; however, the thickness and water vapor permeability were affected by the CNF addition. The coating with the highest CNF concentration performed better in reducing fruit mass and firmness loss. The color was positively influenced by the addition of the coating, regardless of formulation, as well as soluble solid content, PG enzymatic activity, and the fruit appearance. The pH and titratable acidity showed no significant difference among treatments. It was observed that the vitamin C, phenolic compounds, and anthocyanin content, as well as the PAL activity and the antioxidant activity (except for % protection), were affected by chitosan coating, however not by the addition of CNFs.