jrups
Abstract : Modification of Nanocrystalline Cellulose for Bioactive Loaded Films
|
|
Abstract: Despite the use of petrochemical derived packaging, many problems such as browning and food spoilage still happen in food after harvesting. There is an increasing consumers concern for food shelf life to be extended as much as possible along with a big interest in green and bioactive materials, that could be used in direct contact with aliments. In order to reach public demand, biopolymers coming from natural sources such as plants or animals have been used to replace synthetic materials. Even though natural polymers are biodegradable, they do not reach regulations required with respect to mechanical properties in commercial applications. However, the mechanical properties can be improved when reinforced with nanoparticles. Several reinforcing nanoparticulessuch as clays, silica or silver have been used for industrial applications, but cellulose nanocrystals (CNCs) are a better choice for food industry due to their biodegradable and biocompatible nature as well as their outstanding potential in improving mechanical and barrier properties of nanocomposites. CNCs consist of anhydroglucopyranose units (AGU) linked together and several functional hydroxyl groups found on its surface. Modifications of the CNC surface chemistry can give to cellulose new functionalities that open the way to the development of new bioactive reinforcement in food packaging. The present review will be focused on covalent and non covalent modifications that can be achieved on surface CNC with the aim of adding functionalities to be applied for food industry. Keywords: Food packaging, cellulose nanocrystals, CNC, acetylation, polymer grafting, TEMPO oxidation, layer-by-layer, cationic surfactants, radiation-induced polymer grafting. Download Full Article |
|
|
Abstract: Molecular characteristics of chitosan in diluted water solutions of acetic and hydrochloric acids were studied by viscometry, dynamic light scattering, and thin layer chromatography. Chitosan molecules were found to undergo destruction in the solutions of hydrochloric acid and its mixtures with acetic acid. The structure of the chitosan films cast from these solvents was studied by DSC, TGA, and SEM. As shown by electron microscopic data, all the films had an amorphous-crystalline structure but the films prepared from chitosan solutions in diluted hydrochloric acid were characterized by a higher degree of crystallinity. It was supposed that a lower molecular mass of chitosan molecules in the hydrochloric acid solutions results in more extended conformations providing a higher capability of self-organization and formation of regular supermolecular structure. The difference in crystal modification in structure of the films cast of these acids was observed. It was found that the films prepared from the mixtures of acids had a spherulite structure and the crystal modification like ones cast from hydrochloric acid, but with a lower degree of crystallinity. Keywords: Chitosan, water solutions of acids, viscosity, destruction, mixtures of acids solutions, chitosan film structure.Download Full Article |
|
|
Abstract: Gold nanoparticles (Au NPs) have been successfully biosynthesized by Chenopodium murale (C. murale) leaf extract. Au NPs were incorporated within polyethylene oxide (PEO)/polyvinyl pyrrolidone (PVP) polymer blend by casting method. Scanning electron microscope (SEM), Differential scanning calorimetry (DSC), and DC electrical resistivity were used to investigate the morphological, thermal, and electrical properties of blend/Au nanocomposite before and after gamma-irradiation at different doses (1, 2, 3, 4 and 5 MR).SEM micrographs confirmed the dispersion of Au NPs within the polymeric matrix due to effect of irradiation process. DSC analysis showed that the thermal stability for irradiated samples was improved as compared with pure blend and its nanocomposite. DC measurements revealed nonlinear behavior for electrical resistivity versus temperature. The electrical resistivity values for blend/Au nanocopmosite and its high irradiated samples were less compared to pure blend. Keywords: Gamma-irradiation, Au NPs, SEM, DSC, electrical resistivity. |
|
|
Abstract: Fibres are preimpregnated by solutions of mono- and bis-maleimides with comonomers. Imides alone polymerize to resins with too low energies of fracture. In the presence of Methylene dianiline or Aniline Diphenylmethylenebismaleimide reacts via Michael addition to equimolar addition products. When fibres are preimpregnated with these addition compounds alone or in combination with flame retardants, B-prepregs are obtained, which after curing show high glass temperatures and sufficient energies of fracture. 2.5 moles of Diphenylmethylene bismaleimide and 1mol Methylene dianiline or 1mole Aniline react to resins with glass temperatures of 350 and 380°C and energies of fracture of 75 and 100J/m2. The resins contain no carcinogen or blood harming free amines. A one pot reaction starting from Methylene dianiline and Maleic anhydride is possible and more economic. As polymerized bismaleimides possess their imide bonds in the side chain, they are strictly spoken no polyimides with imide bonds in the main chain. Diphenylmethylenebismaleimide and styrene as copolymer react to an insoluble crosslinked polymer. Fibres are preimpregnated with equimolar mixtures of 2- Bromophenylmaleimide and styrene. After curing laminates with 285°C glass temperature and sufficient energies of fracture are obtained. The heat resistant resins are charring polymers and display higher Limiting Oxygen Indices, when the heats of combustion are increased. Differential Scanning Calorimetry determines the temperatures and the heats of glass transition, which indicate that the glass temperature is raised, when the enthalpy is increased and the entropy reduced, which is achievable by Diphenylbismaleimide and 2-Bromophenylmaleimide with their large side groups appropriate for intermolecular forces and steric hindrance. Keywords: Thermodynamic, heat resistant, burning behaviour, brittleness, toxicity. |
|
|
Abstract: The morphology evolution of hydroxyl zinc monomethacrylate (HZMMA) in hydrogenated nitrile rubber (HNBR) during its formation, and effect of synergistic behavior of HZMMA and carbon black (CB) in HNBR on its properties, were investigated. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to probe the reaction of in-situ polymerized HZMMA. The results showed that an ionic polymer interpenetrating HNBR, due to homo-polymerization or graft polymerization of HZMMA solid monomer occurred, and poly-HZMMA particles, confirmed by FTIR and TEM, were formed during the HNBR vulcanization process. This kind of morphology for the HNBR composites played a very significant role in the HNBR reinforcement. At ambient temperature, the mechanical properties of HNBR composite filled with pure PHZMMA was much superior to those of the HNBR/PHZMMA/CB composites; however, when the temperature was increased to above 50°C, the decrease of the tensile strength for the latter was slower, and the tensile strength was always higher than that of the HNBR composites reinforced with pure PHZMMA at the same temperature. The elongation at break above 80°C was also always higher than that of the HNBR/PHZMMA sample. The HNBR/PHZMMA/CB composites showed excellent air oven aging resistance. Keywords: hydrogenated nitrile rubber, hydroxyl zinc monomethacrylate, morphology, properties.Download Full Article |