Effect of chitosan on Bacillus cereus inhibition and quality of cooked rice during storage

Improper cooling of cooked rice at an inappropriate temperature or leaving cooked rice at room temperature can cause food poisoning attributed to Bacillus cereus. Natural food preservative of either squid or crab polymer chitosan solution was added to examine their antibacterial properties against Bacillus cereus in cooked rice during storage at 37 and 4 °C. Both types of chitosan could retard the growth of B. cereus and total aerobic counts in cooked rice stored at 37 °C up to 1 day. In addition, the effect of chitosans on the physical and textural properties of cooked rice during storage was studied. Both chitosans slightly increased the moisture content of cooked rice. However, chitosans had no effect on the whiteness and hardness of cooked rice during storage (P > 0.05). Therefore, both chitosans have a potential to be used as food preservative for cooked rice with no negative effects on rice quality.     

Relationship between cell morphology and impact strength of microcellular foamed high‐density polyethylene/polypropylene blends

Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher‐value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell‐population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well‐developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well‐developed microcellular morphology. Polym. Eng. Sci. 44:1551–1560, 2004. © 2004 Society of Plastics Engineers.     

Robust model predictive control with time-varying tubes

This paper focuses on the problem of robustly stabilizing uncertain discrete-time systems subject to bounded disturbances. The proposed tube-based model predictive controller ensures that all possible realizations of the state trajectory lie in the time-varying tubes so robust stability and satisfaction of the state and input constraints are guaranteed. The time-varying tubes are computed off-line so the on-line computational time is tractable. At each sampling time, the precomputed time-varying tubes are included in the optimal control problem as the constraints in the prediction horizon and only a quadratic programming problem is solved. In comparison to the algorithm that calculates the time-varying tubes on-line, the proposed algorithm can achieve the same level of control performance while the on-line computational time is greatly reduced.     

Facile fabrication of polyethylene/silver nanoparticle nanocomposites with silver nanoparticles traps and holds early antibacterial effect

Antibacterial polyethylene (PE)/silver nanoparticle (AgNP) nanocomposites containing AgNPs at concentrations of 5 × 10^?5, 5 × 10^?4, and 5 × 10^?3 wt % were fabricated and tested. Transmission electron microscopy revealed an even dispersion of surface AgNPs in the PE/AgNP nanocomposites. No AgNP agglomeration was observed. The tensile strength, elongation at break, and Young's modulus of these PE/AgNP nanocomposites were similar to those of neat PE. Differential scanning calorimetry demonstrated that the PE/AgNP nanocomposites and neat PE had similar melting and crystallization temperatures of 126 ± 0.5 and 109 ± 0.6°C, respectively. The heats of fusion of the PE/AgNP nanocomposites containing AgNPs at concentrations of 5 × 10^?5 and 5 × 10^?4 and of 5 × 10^?3 wt % were lower than those of neat PE by 5 and 7%, respectively. These PE/AgNP nanocomposites were immersed in shaking liquid cultures of the potential pathogenic bacteria Escherichia coli, Bacillus subtilis, and Salmonella typhimurium in the lag phase. The results show that the growth rates of all of the tested bacteria were restricted effectively after 1.5, 3, and 6 h of cultivation, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43331.     

Microcellular foam of polymer blends of HDPE/PP and their composites with wood fiber

In this study, the effects of batch processing conditions (foaming time and temperature) and blend composition as well as the effect of incorporating wood fiber into the blends on the crystallinity, sorption behavior of CO₂, void fraction, and cellular morphology of microcellular foamed high‐density polyethylene (HDPE)/polypropylene (PP) blends and their composites with wood fiber were studied. Blending decreased the crystallinity of HDPE and PP and facilitated microcellular foam production in blend materials. The void fraction was strongly dependent on the processing conditions and on blend composition. Foamed samples with a high void fraction were not always microcellular. The addition of wood fiber inhibited microcellular foaming. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2842–2850, 2003     

Synthesis and characterization of carboxymethyl cellulose powder and films from Mimosa pigra

Mimosa pigra peel was sun‐dried for 2 days and then ground before being boiled with 30%w/v sodium hydroxide (NaOH) at 100°C for 3 h, washed and then dried at 55°C to constant weight. The cellulose was then synthesized using different NaOH concentrations and monochloroacetic acid (MCA) in isopropyl alcohol (IPA). Effects of various NaOH concentrations on degree of substitution (DS), viscosity and thermal of carboxymethyl cellulose from Mimosa pigra peel (CMC_m) were investigated. The increasing of NaOH concentration resulted in increasing DS and viscosity. However, viscosity of CMC_m decreased as temperature increased. Thermal properties were studied using differential scanning calorimetry (DSC). The melting point of the samples decreased as %NaOH increased. The effects of various NaOH concentrations in CMC_m synthesis on the mechanical properties and water vapor permeability (WVP) of the CMC_m films were investigated as well. With increasing NaOH concentrations (30–50%) were also found to result in improved mechanical properties. However, when the level of NaOH concentration was 60%, the mechanical properties of the CMC films decreased. This result indicates that the highest mechanical properties were found for 50% NaOH‐synthesized CMC_m films. The WVP of the CMC_m films increased as %NaOH increased. In addition, the CMC_m films were tested to determine the effect of glycerol as a plasticizer on the mechanical properties. Increasing the amount of glycerol showed an increase in elongation at break but also led to a decrease in tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Salt-free dyeing of cotton cellulose with a model cationic reactive dye

A model cationic reactive dye based on an anthraquinone chromophore was prepared. The synthesis of this dye was achieved by the modification of the a free amino group of an anthraquinone-based dye, reacting first with cyanuric chloride and then with N -(2-aminoethyl)pyridinium chloride. TLC analysis was employed to follow the chemical reactions. The application of the prepared dye to cotton fabric was carried out using the exhaustion method without the addition of electrolytes. The results showed that, despite no electrolytes being present in the dye bath, a high percentage of dye exhaustion could be obtained. The high percentage of dye exhaustion was attributed to the attractive force between positive charges on the dye molecule and the negatively charged fibre surface. A high degree of dye fixation with excellent wash fastness was also achievable. Advantageously, it was found that this cationic reactive dye showed promising fastness to light when compared with that of analogous conventional basic dye on cotton. It is believed that the pyridinium cationic moiety, which attached separately to the chromophore via aliphatic spacer groups, was later eliminated during the washing-off process, hence causing an insignificant effect on the photofading of the dyed fabric.     

Thermoplastic polymers as modifiers for urea‐formaldehyde (UF) wood adhesives. II. Procedures for the preparation and characterization of thermoplastic‐modified UF wood composites

Wood composites were prepared by using wood flour (sugar maple, Acer saccharum March) and thermoplastic‐modified urea‐formaldehyde (UF) suspensions. Thermoplastic (5–10% w/v) was introduced into the UF suspension as an aqueous solution, a self‐stabilized dispersion in water, or as a surfactant‐stabilized latex. The modified suspension was blended with wood flour, and the blend was cured by using a cure cycle that was suitable for all the thermoplastic‐modified UF formulations and unmodified UF controls. The wood flour composites were tested by using a notched Izod impact strength test. All formulations containing surfactant decreased the impact strength by ～ 30–40% relative to the unmodified UF control, whereas the water‐soluble thermoplastic had no effect on the impact strength. The formulations with self‐dispersed thermoplastics all increased the notched Izod impact strength, with the greatest increase being 69% more than the UF control, except in a single instance when the molecular weight of the thermoplastic was very high, which decreased resin flow. Increasing the thermoplastic content from 5 to 10% w/v did not further improve the impact test results. Scanning electron microscopy of the fracture surfaces showed morphological differences in the systems that varied with the thermoplastic and method of thermoplastic addition to the UF suspension.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 898–907, 2003     

Conductive Poly(3-methylthiophene) Thin Films

The work described herein represents an efficient method in the deposition of poly(3-methylthiophene),P3MeTh,thin films utilizing a microwave plasma system in combination with a simultaneous doping with iodine.It was envisaged that,an alternative poly(3-methylthiophene),P(3MeTh),with an electron donating methyl substituent,would reduce the degree of ring opening which reportedly occur to a certain extent during the plasma polymerization process of its parent compound polythiophene.An alkyl substituent would also increase the solubility of the materials.P(3MeTh)thin film deposition has been performed utilizing microwave-induced plasma polymerization in order to directly grow films on glass substrates.Moreover,simultaneous doping of the so-formed polymer with iodine has been carried out as opposed to the post-synthesis doping method.This is aimed to prolong electrical conducting lifetime of the materials.The synthesized films were characterized by attenuated total reflection fourier transform infrared(ATR FT-IR)spectroscopy and energy dispersive X-ray spectroscopy(EDS)to confirm the incorporation of iodine dopant into the films.Scanning electron microscopy showed uniformly deposited films.It has been observed that the electrical conductivity of the doped film is 2 orders of magnitude higher than the undoped counterpart.The doped fabricated films exhibited UV-vis spectra indicative of increased π-conjugation(536 nm).Furthermore,electrical conductivity of the in situ doped P(3MeTh)is more highly sustained over a longer period of time.     

Factors Affecting Migration of Vanillin from Chitosan/Methyl Cellulose Films

ABSTRACT:  The diffusion kinetics and factors affecting the migration of vanillin from chitosan/methyl cellulose (Chi/MC) films into water, cantaloupe juice (CJ), pineapple juice (PJ), and citrate buffer adjusted to pH values of 3.5, 5, and 6.5 were studied. Vanillin was incorporated into the Chi/MC films to provide an inhibitory effect against microorganisms. Initial vanillin concentration in the films, temperature, and pH of extracting solvent impacted the migration behavior of vanillin. The diffusion coefficients (D) followed the Arrhenius equation and increased as temperature increased for all the solvents. As temperature rose, the rate increment of the diffusion of vanillin into pineapple juice was higher than that into water and cantaloupe juice. Films containing lower vanillin content had a higher diffusion coefficient than those containing high vanillin content. Migration of vanillin was affected by pH rather than acid concentration. Lower pH resulted in a higher migration rate.