Study of mechanical properties,oxygen permeability and AFM topography of zein films plasticized by polyols

The use of plastic for packaging has grown extensively in recent years. In this context, biodegradable films can be a source of energy saving and an important issue for environmental protection. Zein protein (prolamin of corn) is one of the best biopolymers for edible film making and polyols are convenient plasticizers for biopolymers. Polyols (sorbitol, glycerol and mannitol) at three levels (0.5, 0.7 and 1g/g zein) were used as plasticizers and the tensile properties, oxygen permeability (OP) and AFM topography of zein films were studied. Films plasticized by sorbitol had a relatively higher ultimate tensile strength (UTS) than films containing glycerol and mannitol at low levels of plasticizers (0.25, 0.7g/g zein). There was no significant difference between the strain at break values (SB) of films plasticized by sorbitol and glycerol at low levels of plasticizers, while films plasticized by sorbitol had higher SB than the films containing glycerol and mannitol at a high level of plasticizer (1g/g zein). Pure zein films had low oxygen permeability (OP), and increasing the plasticizer level to 0.5g/g zein decreased OP values in films containing sorbitol and glycerol. Films containing sorbitol and mannitol had the lowest and highest OP values, respectively. AFM images were used to evaluate the surface morphology (qualitative parameter) and roughness (quantitative parameter) of zein films. Films plasticized by glycerol had smoother surfaces and a lower roughness parameter (Rq). No relationship between OP values and the roughness of the zein films was observed. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluation of alginate and zein films as a carrier of natamycin to increase the shelf life of kashar cheese

The aim of this study was to develop alginate and zein films containing natamycin, a natural antifungal agent, in order to limit/prevent the mould growth on the surface of kashar cheeses. The films were prepared by casting, and characterized in terms of antimicrobial and mechanical properties (tensile strength, elongation-at-break, and elastic modulus), and their morphology was examined by scanning electron microscopy (SEM). Mechanical properties of the zein films were found to be weaker than the alginate films. SEM analysis indicated that alginate films have a more regular structure than zein films, and a more homogenous distribution was observed at lower concentrations of natamycin. The antifungal activities of both films increased as the natamycin concentration (100, 200, 500, 1000, 2000, and 4000 ppm) increased; however, alginate films exhibited relatively high antifungal activity. The effects of films on the shelf life of kashar cheeses inoculated with Aspergillus niger and Penicillium camemberti were investigated during their storage under refrigerator conditions for 45 days. At high-natamycin concentrations, zein films showed higher antifungal activity against both fungi at the end of the storage period.     

Preservation of sliced ham through triclosan active film

Active packaging is an alternative to preserve perishable food. In this work, polyethylene antimicrobial active films containing different levels of triclosan (0, 2000 and 4000 mg kg^?1) were developed by extrusion. The films' efficacies were evaluated against Escherichia coli, Staphylococcus aureus, Listeria innocua, Salmonella choleraesuis and Pseudomonas aeruginosa growth using agar diffusion test and by monitoring the inhibition of E. coli and S. aureus inoculated on sliced cooked ham. The mechanical characteristics of the films were also evaluated with Universal Test Machine (Instron). The incorporation of triclosan did not affect the mechanical properties of antimicrobial films compared to the control film. The average film thickness was 82.0 µm and the tensile strength and elongation to break were 30.3 N and 46.2%, respectively. Films containing triclosan showed an antimicrobial effect in vitro against E. coli and S. aureus, with formation of an inhibition halo for both. However, this result was not observed for L. innocua, S. choleraesuis and P. aeruginosa, although, a decrease in colony density occurred around the film for both incubation temperatures (7 ± 2°C and 35 ± 2°C). Sliced ham packed with the antimicrobial films showed a reduction of 1.5 logarithmic cycles in comparison to ham in contact with a control film after 12 days of storage at 7 ± 2°C, for E. coli and S. aureus. Antimicrobial films present potential for application as active packaging materials, as they showed effective against some pathogenic microorganisms that can be transmitted by foods. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal sensor properties of PANI(EB)-CSA<Subscript>x</Subscript> (X = 0.4 ±0.1 mol) polymer thin films

Films of polyaniline(EB) doped with camphor sulfonic acid (CSA) fromm-cresol on glass substrates exhibit considerable metallic properties. Such polymer metallic films have thermal sensitivity superior to ceramic metal (Cermet) films, prepared by metallo organic deposition (MOD) technique on silicon substrates. These PANI(EB)-CSA_x (X = 0.5, 0.4, 0.3 mol) polymer films were developed through controlled temperature atmosphere 60 ±2°C for 60 min, and with the help of temperature dependence of resistivity (ρ) values, high temperature coefficient of resistance (TCR) i.e. a values, and figure of merit (ρα) values of these films, thermal sensitivity were compared from that we observed. Among the three doping ratios the PANI(EB)—CSA_{0.3 mol}i film (4.4 ⧎m thick) on glass substrate resistivity (ρ) values in the range of 838–1699 Ω.⧎m with high TCR i.e. a = 10,291 ppm/°C and figure of merit (ρα) value in range of 8.62-17.48 Ωm/dgC seems to be the best. This paper deals with these superior thermal-sensing properties together with optical studies and surface topography by atomic force microscopy (AFM). These polymer films offer design advantages in developing ‘thin film polymer thermal sensor’.     

Development and evaluation of an edible antimicrobial film based on yam starch and chitosan

Edible antimicrobial films are an innovation within the biodegradable active packaging concept. They have been developed in order to reduce and/or inhibit the growth of microorganisms on the surface of foods. This study developed an edible antimicrobial film based on yam starch (Dioscorea alata) and chitosan and investigated its antimicrobial efficiency on Salmonella enteritidis. A solution of yam starch (4%) and glycerol (2%) was gelatinized in a viscoamilograph and chitosan added at concentrations of 1%, 3% and 5%. Films with and without chitosan were produced by the cast method. To evaluate the antimicrobial activity of the films, two suspensions of S. enteritidis were used in BHI medium, corresponding to counts of 2 × 10⁸ and 1.1 × 10⁶ CFU/ml. The suspensions (50 ml) were poured into flasks. The films were cut into 5 × 5 and 5 × 10 cm rectangles to be used at ratios of 1 : 1 (1 cm²/ml microorganism suspension) and 2 : 1 (2 cm²/ml). The film 30 µm thick on average. As a control, pure chitosan at an amount corresponding to that contained in the 3% and 5% films (5 × 10 cm) was added to flasks containing the microorganism suspension. Also, flasks containing only a suspension of S. enteritidis were used as control. The suspensions, in flasks, were kept at 37°C in a waterbath with agitation. Suspension aliquots were removed every hour for reading the optic density (OD₅₉₅) and plating onto PCA medium. The results showed that chitosan has a bactericidal effect upon S. enteritidis. Films treated with chitosan at different concentrations showed similar antimicrobial efficiency, in addition to being dependent on diffusion. The chitosan‐treated films caused a reduction of one to two log cycles in the number of microorganisms, whereas the pure chitosan presented a reduction of four to six log cycles compared with the control and starch film. The films showed good flexibility. Copyright © 2005 John Wiley & Sons, Ltd.     

Improvement in physical properties and cytocompatibility of zein by incorporation of pea protein isolate

A series of protein-based biocomposites was prepared from glycerol-plasticized zein (ZE) and pea protein isolate (PPI) using a hot press and moulding process. The effects of PPI content (W _PPI) on the structure and properties of ZE/PPI films were investigated. With an increase in W _PPI from 0 to 100%, the elongation at break of the films increased from 2.4 to 62.6%, and the water contact angle decreased from 31.8° to 5.8°. Cell toxicity and cytocompatibility of ZE/PPI films were evaluated in vitro. The cell viability of L929 cells cultured in extracts from ZE/PPI films containing 10–30% PPI was higher than that from other films and the control group. The L929 cells expanded very well on the surfaces of films containing 10–30% PPI. Incorporation of 10–30% PPI into ZE improved flexibility, surface hydrophilicity, cytocompatibility and its potential as biomaterials in zein-based composites.     

Development and evaluation of active packaging for sliced mozzarella preservation

Antimicrobial films were formed by the incorporation of nisin (NI), natamycin (NA) and a combination of both (NI + NA) into cellulose polymer. Film efficacies were evaluated in vitro against Staphylococcus aureus ATCC 6538, Listeria monocytogenes ATCC 15313, Penicillium sp. and Geotrichum sp. The films were also evaluated on sliced mozzarella cheese against moulds and yeasts, Staphylococcus sp. and psychrotrophic bacteria. Mechanical and microscopic properties of the films and the diffusion of the antimicrobial agents from the film to the cheese were also evaluated. Films containing NI showed an antimicrobial effect in vitro against S. aureus and L. monocytogenes, while films containing NA were effective in vitro against Penicillium sp. and Geotrichum sp. By the ninth day of storage at 12 ± 2°C, the count of yeasts and moulds on cheese covered with films containing NA decreased 2 log10 units compared with the count on cheese with control films. NI film did not show an effect against Staphylococcus sp., but it was effective against psychrotrophic bacteria for 6 days of storage of the cheese. The incorporation of antimicrobial compounds decreased the resistance and elongation of the films and caused changes in their molecular conformation. NI diffusion from the films to the cheese was not detected; however, time‐dependent diffusion of NA from the film containing NI + NA was measured. The incorporation of NI and NA together in the films did not show an effect. The film containing NA showed potential for application as active food packaging for sliced mozzarella cheese. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa₂Cu₃O_7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature T _c ,off=89 K and a critical current density j _c =2 MA/cm² (at 77 K) and were free from secondary phase particles larger than 10 nm. Pis’ma Zh. Tekh. Fiz. 24, 80–85 (February 26, 1998)     

Effectiveness of barrier film with a cellulose coating that carries nisin blends for the inhibition of listeria monocytogenes

The objective of this study was to determine the effectiveness of two nisin blend antimicrobial agents (Guardian NR 250, Novagard CBI) incorporated into a cellulose coating that was applied onto a barrier film against Listeria monocytogenes. The minimum inhibitory concentration (MIC) of the agents in solution against L. monocytogenes was found to be 2.74 mg/ml for the two nisin blends. The concentrations tested for both nisin blend treatments were 5.49, 10.9, 16.4 and 21.9 mg/ml. Guardian NR 250 resulted in wider zones of inhibition compared to the Novagard CBI at all levels tested. The MIC for Guardian NR 250 in the film was 5.49 mg/ml. Films containing Novagard CBI did not show any antimicrobial activity. A food challenge study was conducted using the film containing Guardian NR 250 at levels of 5.49 and 21.9 mg/ml. Inoculated fresh beef cubes were individually packaged with pre‐made barrier film pouches that had an interior cellulose coating containing the antimicrobial agent and stored at 4°C for 36 days. Bacterial colonies were enumerated every 6 days on modified Oxford agar. There was no significant difference in the L. monocytogenes population between two levels of Guardian NR 250 throughout the study. There was statistically significant inhibition of L. monocytogenes for both levels of Guardian NR 250 during 18–30 days of storage compared to a control film without the antimicrobial agent. Copyright © 2010 John Wiley & Sons, Ltd.     

Antimicrobial Activity of Natural Agents against Saccharomyces cerevisiae

The antimicrobial (AM) activity of starch‐based films coated with linalool, carvacrol or thymol against Saccharomyces cerevisiae in vitro and/or inoculated on the surface of Cheddar cheese was investigated. In solid medium using the agar diffusion method and in experiments involving the inoculation of the microorganism on the surface of Cheddar cheese, all the films containing these AM agents in coatings demonstrated an inhibitory effect against S. cerevisiae. The results suggest that the overall inhibitory effect of linalool, carvacrol or thymol increased significantly (p ≤ 0.05) with the concentration of each of the AM agents in the film coating and that the response is linear in the concentration range of 1 to 5% (w/w) of the AM agent. Thymol had the highest AM efficacy followed by carvacrol, whereas linalool had the lowest efficacy amongst the three systems. The zones of inhibition in the agar diffusion test method at 25°C for S. cerevisiae were found to be 7.6, 7.1 and 6.1 mm for thymol, carvacrol and linalool at 1% (w/w) loading and 13.2, 12.2 and 11.2 mm at 5% (w/w) loading of the AM agents, respectively. The death rates of S. cerevisiae on Cheddar cheese wrapped in films coated with thymol, carvacrol and linalool and stored for up to 28 days at 15°C were found to be 0.044, 0.043 and 0.038 per day at 1% (w/w) loading and 0.077, 0.073 and 0.063 per day at 5% (w/w) loading of the AM agents, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Special features in the synthesis and properties of thin Y-Ba-Cu-O high-temperature superconductor films free of secondary phases

Data on the structure and transport properties of thin Y-Ba-Cu-O (YBCO) high-temperature superconductor films obtained by magnetron sputtering of a stoichiometric target in a system with a 90° off-axis geometry are reported. It is shown that the films prepared under these conditions are free of copper-rich secondary phases and are characterized by the surface roughness height below 10 nm. The films possess a perfect structure and exhibit high superconducting properties: c-axis misorientation in microblocks FWHM(005)YBCO=0.4–0.5°; zero-resistance temperature T _co=89 K; critical (pinning) current density j _p=1.5–2 MA/cm² (77 K).     

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa₂Cu₃O_7−x (YBCO) films were fabricated on LaAlO₃ (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J _c of 3.1 MA/cm² which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.     

Evaluation of Antifungal Activity of Antimicrobial Agents on Cheddar Cheese

The antifungal activity against Aspergillus niger of the antimicrobial (AM) agents linalool, carvacrol and thymol incorporated in the coatings of starch‐based films was investigated. The activity was initially determined on a solid medium using the modified microatmosphere method and then examined on Cheddar cheese. On the solid media, all the AM films demonstrated a significant inhibitory effect against A. niger growth. The inhibitory effect of the AM films containing 2.38% (w/w) AM agents is reflected by the colony diameters that were 29.3, 25.4 and 21.3 mm for linalool, carvacrol and thymol, respectively, at 25°C after 7 days incubation compared with the control sample where the colony diameter was 85.3 mm. The AM films containing 2.38% (w/w) linalool, carvacrol or thymol reduced the population of A. niger on the surface of Cheddar cheese by 1.8, 2.0 and 2.2 log CFU/g, respectively, after 35 days of storage at 15°C. The results suggest that starch‐based film coated with an AM agent has the potential for being used as a fungicidal packaging system. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of substrate temperature on crystalline copper aluminium oxide thin films synthesized through chemical spray pyrolysis (CSP) technique

Copper aluminium oxide (CuAlO₂) of well ordered crystalline films were deposited on to glass substrates with Cu/Al ratio r = 0.8 at the substrate temperatures of 250, 300, 350, 400 and 450 °C. Films which were characterized had a thickness of the order of few micrometers. Films deposited at the optimized deposition temperature (450 °C) revealed well-crystalline CuAlO₂ phase with XRD peak at 2θ = 31.7° corresponds to (006) reflection. The peak positions of the core level XPS spectra, confirm the presence of delafossite CuAlO₂ phase. The optical transmission of 80 % has been observed in the visible spectrum. The obtained band gap energy is 4.1 eV. From the observed results it was evidenced that the substrate temperature has strong influence on the structural and optical properties of the spray pyrolysed copper aluminium oxide films.     

Dip-coating of TiO2 films using a sol derived from Ti(O-i-Pr)4-diethanolamine-H2O-i-PrOH system

Diethanolamine (DEA) can suppress the precipitation of oxides from the alcoholic titanium isopropoxide solution in its hydrolysis so that much water can be added to the Ti(O-i-Pr)₄-diethanolamine-i-propanol the solution to give a clear solution. Addition of excess water converted the solution to the gel. The conditions for the formation of the clear solution and gel are examined. Uniform transparent TiO₂ films can be prepared by dip-coating with the clear solution. The limit of the thickness of uniform films was 200 to 240 nm. Films thicker than 1 m can be prepared by repeating the coating cycle. These films were well densified. Diethanolamine has some positive effect on the densification of the TiO₂ crystals.     

Mn- and Cr-Doped InN: A Promising Diluted Magnetic Semiconductor Material

Cr- and Mn-doped InN films were successfully grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Low temperature GaN buffer layers grown by metal-organic vapor-phase epitaxy were used to accommodate the large lattice mismatch between InN and sapphire. A high n-type carrier concentration of 1.5×10²⁰ cm^–3 was measured in InN films with 3% Cr-doping. Films of this type exhibit a well-defined in-plane magnetic hysteresis loop and remanence for temperatures varying from 5 to 300K. The Mn-doped films, however, turned out to exhibit less clear magnetic properties. Thus, ferromagnetism in Cr-doped InN can be concluded from our measurements.     

Preparation of ferroelectric PZT films by thermal decomposition of organometallic compounds

Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm⁻², a saturation remanent polarization was 30.56μC cm⁻² and a coercive field was 45 kV cm⁻¹. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.     

Oriented growth of thin films of samarium oxide by MOCVD

Thin films of Sm₂O₃ have been grown on Si(100) and fused quartz by low-pressure chemical vapour deposition using an adducted β-diketonate precursor. The films on quartz are cubic, with no preferred orientation at lower growth temperatures (∼ 550°C), while they grow with a strong (111) orientation as the temperature is raised (to 625°C). On Si(100), highly oriented films of cubic Sm₂O₃ at 625°C, and a mixture of monoclinic and cubic polymorphs of Sm₂O₃ at higher temperatures, are formed. Films grown on either substrate are very smooth and fine-grained. Infrared spectroscopic study reveals that films grown above 600° C are free of carbon.     

Structural and optical characterization of c-axis textured BaTiO<Subscript>3</Subscript> thin films on MgO fabricated by RF magnetron sputtering

In this paper, BaTiO₃ thin films were prepared by RF magnetron sputtering on MgO substrates and their properties such as the crystal structure and optical waveguide properties were investigated. The optimum deposition parameters, such as substrate temperature, deposition pressure, gas flow ratio, the RF power and the after annealing temperature, were obtained in order to get the best BaTiO₃ film quality. The XRD results show that highly c-axis textured BaTiO₃ thin films were successfully grown on MgO substrate. Films obtained under the optimum deposition parameters, substrate temperature of 650°C, RF power of 50 W, deposition pressure 18 mTorr and gas flow ratio O₂/(Ar+ O₂) of 15% namely, reaches a full width at half maximum intensity (FWHM) of BaTiO₃ (002) XRD peak of 0.25°. The FWHM of BaTiO₃ (002) XRD peak was further reduced to 0.24° via post-treatment with furnace annealing (at 800°C for 2 h) which indicates the film crystal quality is further improved. The bright and sharp TE modes measured by m-line spectroscopy of the BaTiO₃ film were observed indicating its possible application in optical waveguide.     

Properties of antimicrobial plastics containing traditional food preservatives

Traditional food preservatives, sodium benzoate, sodium nitrite, potassium sorbate and sodium lactate, were incorporated into synthetic plastics, low‐density polyethylene (LDPE), poly(maleic acid‐co‐olefine), polystyrene (PS) and polyethylene terephthalate (PET), aimed at producing antimicrobial packaging material for foodstuffs. The study was undertaken on plaques (thickness 2 mm) and films (thickness 70–120 µm), whose antimicrobial test results clearly differed. Plaques containing 15% sodium nitrite inhibited both Aspergillus niger and Bacillus subtilis, whereas the same concentration of sodium benzoate and potassium sorbate had activity only against B. subtilis. Sodium lactate‐containing samples did not have any antimicrobial activity and none of the samples inhibited Escherichia coli. Antimicrobial substances added into PS and PET produced the strongest activities; however, due to the brittle structure of these materials, they were not tested further. Thus, more thorough tests for antimicrobial activity, migration and oxygen and water vapour permeability were carried out using LDPE films with 2.5–15% sodium benzoate and sodium nitrite. The effects of both substances on permeability properties were negligible. Although the total migration into food simulants measured from the films in many cases exceeded the limit value of 10 mg/dm², no antimicrobial activity was observed. Copyright © 2003 John Wiley & Sons, Ltd.