Molecular modeling study on surface,thermal, mechanical and gas diffusion properties of chitosan

The motivation of this work is to provide reliable and accurate modeling studies of the physical (surface, thermal, mechanical and gas diffusion) properties of chitosan (CS) polymer. Our computational efforts have been devoted to make a comparison of the structural bulk properties of CS with similar type of polymers such as chitin and cellulose through cohesive energy density, solubility parameter, hydrogen bonding, and free volume distribution calculations. Atomistic modeling on CS polymer using molecular mechanics (MM) and molecular dynamics (MD) simulations has been carried out in three dimensionally periodic and effective two dimensionally periodic condensed phases. From the equilibrated structures, surface energies were computed. The equilibrium structure of the films shows an interior region of mass density close to the value in the bulk state. Various components of energetic interactions have been examined in detail to acquire a better insight into the interactions between bulk structure and the film surface. MD simulation (NPT ensemble) has also been used to obtain polymer specific volume as a function of temperature. It is demonstrated that these V–T curves can be used to locate the volumetric glass transition temperature (T_g) reliably. The mechanical properties of CS have been obtained using the strain deformation method. Diffusion coefficients of O₂, N₂, and CO₂ gas molecules at 300 K in CS have been estimated. The calculated properties of CS are comparable with the experimental values reported in the literature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1260–1270, 2007     

Computation of density of perfluoroalkyl methacrylates: a molecular modeling approach

Molecular dynamics simulations have been carried out on different perfluoroalkyl methacrylates to predict their densities. Density calculations on selected perfluoroalkyl methacrylates have been performed using molecular dynamics in the NPT ensemble by employing COMPASS force field. The calculated density values compared quite well with the experimental data reported in the literature.     

Preferential Interactions on Polystyrene Divinylbenzene Copolymeric Sorbents

The adsorption of picric acid, naphthalene-sulfonic acid, and toluenesulfonic acid onto a polystyrene divinylbenzene copolymeric sorbent in methanol-water systems at 25°C was studied by reverse-phase high performance liquid chromatography. The observed peak asymmetry and increase in capacity factor at high methanol concentrations in the mixture was attributed to preferential interactions of the solutes at the surface. The phenomena were not as pronounced for octadecyl silane bonded phases.     

Polymerized Lightweight Fibrous Composites

Industrial, agricultural, and naturally occurring waste materials in conjunction with liquid epoxy resin, asbestos, and silica have been employed to make lightweight engineering composite materials. To bring down the cost of epoxy resin, phenol formaldehyde was used as a binding material. Various physicomechanical properties of these composites were investigated. This study advocates elegant, economical, and lighter alternative materials for structural applications, reducing the deadweight of the structure and thereby resulting in lighter foundations. Furthermore, an attempt has been made to find a suitable fibrous material as an alternative substitute for asbestos to meet hygienic requirements.     

Lightweight Polymer Composites from Waste Materials: A Solution to Environmental Pollution

Several new lightweight polymer concretes derived from industrial, agricultural, and naturally occurring waste materials were investigated. Various physicomechanical properties of these materials were studied. Such inexpensive and lightweight polymer composites, which have properties superior to ordinary reinforced cement concrete, may find wide applications in building technology and related areas and may serve as better substitutes for cement. Furthermore, recycling of such wastes from various sources may help to solve the present environmental pollution problems.     

Enhanced Environmental Degradation of Plastics

Intensive research in the last two decades on the degradation of commercial plastics has led to the development of new methods of degradation and innumerable experimental techniques to characterize the degraded products. During the period 1970–1980, there have been substantial advances in most of the important aspects of polymer degradation including that induced by heat, light, oxygen, high energy radiation, photooxidation, and biological factors; and accounts have been given at various times of the current position in most of these [1–30].     

TRANSPORT STUDIES ON MACROMOLECULES USED AS DRUG CARRIERS

Abstract

Modecular transport of drugs through carier polymeric materds has been an active area of research. A number of soluble polymers have been used to deliver the drugs selectively to specific parts of the body. The literature in this area of research is extensive and diverse. An effort has been made to review the transport of drug molecules through physiological systems via polymeric materials. A brief introduction to the fundamentals and concepts which are frequently used in the drug-delivery area are covered in the following sections. Various aspects of the problems related to polymer-drug complexes, carrier molecules, and their degradability have been discussed. Both natural and synthetic biopolymers have been included in the discussion. Only representative references during the period 1977–1989 have been used in the discussion of results, and thus the reader is advised to look further into the original literature for greater information.     

Dehydration of 1,4-dioxane through blend membranes of poly(vinyl alcohol) and chitosan by pervaporation

Blend membranes prepared from poly(vinyl alcohol) (PVA) and chitosan (CS) were crosslinked with glutaraldehyde and used in the pervaporation dehydration of 1,4-dioxane. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (X-RD) to assess, respectively, the intermolecular interactions, thermal stability and crystallinity. Equilibrium sorption studies were carried out in pure liquids and binary mixtures of different compositions of water + 1,4-dioxane mixtures to assess the polymer–liquid interactions. The crosslinked membrane showed a good potential in breaking the azeotrope of 82 wt.% aqueous 1,4-dioxane giving a selectivity of 117 with a reasonable water flux of 0.37 kg/m² h. The effect of operating parameters such as feed composition, membrane thickness and permeate pressure was evaluated.