Applied Mechanics and Materials Vol. 469

Abstract: The Green food-packaging membranes were prepared with N-methylmorpholine-N-oxide (NMMO) as the major solvent by using L-S phase inversion technique. Scanning electron microscopy (SEM) was adopted to characterize fracture surface morphology of membrane, and tensile machine was adopted to test the membrane strength performance. Research results show with the concentration of cellulose increases from 5% to 9%, structure of membrane becomes compact, aperture size becomes small and even, value of tensile strength increases 59.6%, and value of elongation increases 67.5%. With dissolving temperature increases from 100°C to 120°C, structure of membrane becomes loose, pore size becomes big and uneven, value of tensile strength decreases 19.2%, and value of elongation decreases 13.1%. The research can provide the theoretical reference for optimizing technology, adjusting the structure of membrane, and improving the performances of membrane.

Abstract: Coefficient of thermal conductivity is an important index of performance evaluation of heat-insulated material. In order to provide theoretical reference basis for the selection of heat-insulated materials, we test the coefficient of thermal conductivity of polystyrene foamed plastic (EPS) and rigid polyurethane foam plastic (PU) in different densities at different ambient temperatures, and then determine the effect of material density and ambient temperature on the coefficient of thermal conductivity of food insulation packaging materials. According to the national standard GB/T10297-1998(Test method for thermal conductivity of nonmetal solid materials by hot-wire method), we test the coefficient of thermal conductivity of samples in different densities at different ambient temperatures. The result shows that at the same temperature, the coefficient of thermal conductivity increases first and then decrease with the increase of density. In the same density, the coefficient of thermal conductivity increases with the increase of ambient temperature.

Abstract: Starch-based nanocomposite films were fabricated by the incorporation of different amounts of nanodiamond (ND) particles. These films were characterized by SEM, FT-IR, TGA, tensile testing and water vapor permeability measurement. It was observed that at low loadings, ND dispersed well in starch matrix. However, as the loading amount increased, aggregates as large as several micrometers appeared. The physical blending of ND with starch didnt change the thermal degradation mechanisms of starch films, only increased the char residues. As the ND loading increased, the tensile strength of composite films increased but the elongation at break decreased. However, the water vapor permeability increased as the loading of ND increased due to the increased microspores in films. With further modifications, ND may be considered as a novel of biocompatible nanofillers for reinforcement of biopolymers for food packaging applications.

Abstract: Three thiol-compounds with different functionalities were synthesized through esterification reaction which was prepared by 1, 4-butanediol, trimethylolpropane, and pentaerythritol and 3-mercapto propionic acid respectively. Thiol-compounds and polyurethane-acrylate prepolymer were blended with addition of photo-initiator in certain proportions in order to form polyurethane curing film under UV irradiation. The structure and properties of the thiol-compounds and the polyurethane curing film were characterized by NMR, FT-IR, and TG. The results showed that the thiol-ene addition reaction between the urethane acrylates and the thiol-compounds was preceeded. With the increase of functionality of mercaptopropionic acid ester, the thermal stability improved, and the T-peel strength enhanced. When the moral ratio of urethane acrylates and trimethylolpropane-3-mercapto propionic acid ester was 1:1, the adhesive showed the best mechanical properties and thermal stability with curing time 40s, T-peel strength 88N/m and 50 % mass loss at 369°C, respectively.

Abstract: Water borne polyurethane /modified nano-ZnO composites packaging membranes were synthesized from modified nano-ZnO, polybutyleneadipate glycol (PBA), polycaprolactone (PCL) isophorne diisocyanate (IPDI), dimethylol propionic acid (DMPA), ethylenediamine(EDA) by self-emulsified method. The phase property, mechanical, antibacterial and anti-ultraviolet properties of the composites packaging membranes influenced by the modified nano-ZnO content were studied by scanning electron microscopy (SEM), mechanical testing, and antibacterial testing. And the relative results were analysed.

Abstract: Edible films were prepared using soy protein isolate (4g/100g), oleic acid (0-2g/100g) and stearic acid (0-2g/100g). Effects of the type and ratio of fatty acids (oleic acid and stearic acid) on the thermal properties of soybean protein isolate-based films were investigated. The results indicated that the addition of oleic acid and stearic acid take a significant effect on the thermal stability of soybean protein isolate-based films, as may attribute to that oleic acid is an amphiphilic substance that interacts with both polar and hydrophobic sites on proteins, thus it could improve the functional properties of the films. Besides, the solid state and hydrophobic nature of stearic acid could help limit water diffusion in the matrix more efficiently when it is well-integrated in the matrix through the surfactant action of oleic acid.

Abstract: The effect of rhubarb ethanol extracts (REE) and cinnamon essential oil (CEO) were used individually and in combination to maintain quality of fresh beef steaks stored for 18 days at 4±1°C was investigated. Beef characteristics, including pH, total viable counts (TVC), instrumental color (CIE a^*), lipid oxidation (TBARS) and total volatile base nitrogen (TVB-N) were determined. The treatments significantly inhibited bacterial growth (p < 0.05) and maintained the pH, TVB-N, TBARS of beefsteaks and reduced instrumental color loss (p < 0.05). The results indicated that the treatments could efficiently maintain quality of fresh beef during storage and the combination of CEO and REE antimicrobial packaging had better application potential on fresh beef preservation.

Abstract: In order to verify the effect of molecular sieve ethylene adsorbent and 1-Methylcyclopropene (1-MCP) on the shelf life of cherry tomato, two kinds of active packaging were comparatively investigated: molecular sieve sachet and 1-MCP pad with 25% Styrene-Ethylene-Butylene-Styrene (SBS) modified LDPE packaging film. LDPE was used as control. The quality properties of samples were measured over 54 days at 25±1°C and 70±2% relative humidity. The ethylene concentration in the package atmosphere and other experimental parameters were measured periodically. The experimental results show that molecular sieve is more effective in decreasing ethylene concentration in the package than 1-MCP treatment. The best result was obtained by using SBS modified LDPE film with molecular sieve sachet which could extended the shelf life of cherry tomatoes.

Abstract: This study took mung bean sprout as test materials to measure the variation of gas concentration in the film over time. This study measured the permeability coefficient of the selected LDPE film under 8°C,13°C,18°C,23°C and 28°C and calculated the respiratory rate of mung bean sprout under temperature ranges from 8°C to 28°C by the method of Osmosis system using C language. The chemical kinetics model equation was fitted to the respiration rate of bean sprouts. Experimental results: 1. Permeability coefficient of film increased with the temperature, the relationship between the permeability coefficient of the film and the temperature fitted with the Arrhenius equation. 2. With the temperature increasing, the respiratory rate of mung bean sprouts increased. By fitting chemical kinetics equation of model to the respiration rate, the results showed that the variation of respiration rate conformed to the chemical kinetics equations. The relationship between temperature and the respiration rate constant k of the chemical kinetics equations were found following of Arrhenius equation.

Abstract: The effect of modified atmosphere packaging for strawberry was discussed in this study. The best gas condition was explored to extend the shelf life of strawberry in refrigerated temperature. The 20μm PE film was used to build modified atmosphere packaging. The optimum gas condition for strawberrys modified atmosphere packaging was selected while concerned with the respiration rate, firmness, rot grade, vitamin C content, total soluble solids, titratable acidity, sensory evaluation and other quality indicators respectively. The results suggest that: In 60% O₂ + 1.5% CO₂ gas condition, it could be kept low rot grade, maintained the firmness, vitamin C content, total soluble solids, titratable acidity content, and sensory evaluation was not falling heavily. As the season in which strawberries were abundant was of high temperature, the effect of preservation was more apparent in 5±1°C. Modified atmosphere packaging discussed above could extend the strawberrys shelf life to 22 days.