Adsorption natural-polymers

Enzymes can be immobilized by matrix entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to organic or inorganic polymer-carriers, or by whole cell immobilization (5 ). Particularly impressive is the great number of chemical reactions developed for the covalent binding of enzymes to inorganic carriers such as glass, to natural polymers such as cellulose or Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and... 

Gupta V., Agarwal J., Sharma S. Adsorption Analysis of Mn(VII) from Aqueous Medium by Natural Polymer Chitin and Chitosan, Asian J. of Chem., 20(8), 6195-98 (2008)... 

On the basis of the separation mechanism, restricted-access media can be classified into physical or chemical diffusion barrier types. The limited accessibility of the former type is due to the pore structure of the support that represents physical diffusion barriers for macromolecular compounds. The restricted access of the latter type is due to covalently or adsorptively bonded synthetic or natural polymers that cover the support surface, preventing macromolecules from being adsorbed on or denatured by the column packing material. 

Abstract. Several series of pyrocarbon/silica adsorbents were prepared using fumed oxides of different specific surface areas, and mesoporous silica gel Si-100, as inorganic matrices. Different synthetic and natural polymers as well as glucose were used as carbon precursors. Solutions of phosphoric acid at various concentrations were utilized to prepare functionalized hybrid carbon-silica adsorbents. Nitrogen, p-nitrophenol and Cd(II) adsorption isotherms as well as AFM, XRD and XRF methods were used to estimate the structural and adsorption characteristics of the adsorbents. 

Whatever the mechanism is, particles adhere spontaneously if, at constant temperature and pressure, the Gibbs energy G of the system decreases. The main contributions to the Gibbs energy of particle adhesion A Gad are from electrostatic, hydrophobic and dispersion forces,1 5 and, furthermore, in case of protein adsorption, from rearrangements in the structure of the protein molecule.6 9 When the sorbent surface is not smooth but hairy , additional, mainly steric, interactions come into play.4,10 12 Hairy surfaces are often encountered in nature as a result of adsorbed or grafted natural polymers, such as polysaccharides, that reach out in the surrounding medium with some flexibility. Interaction of particles with such hairy surfaces will be dealt with in section 3. 

The service performance of rubber products can be improved by the addition of fine particle size carbon blacks or silicas. The most important effects are improvements in wear resistance of tire treads and in sidewall resistance to tearing and fatigue cracking. This reinforcement varies with the particle size, surface nature, state of agglomeration and amount of the reinforcing agent and the nature of the elastomer. Carbon blacks normally are effective only with hydrocarbon rubbers. It seems likely that the reinforcement phenomenon relies on the physical adsorption of polymer chains on the solid surface and the ability of the elastomer molecules to slip over the filler surface without actual desorption or creation of voids. 

Adsorption of polymers and of polyelectrolytes—above all humic substances and proteins—is a rather general phenomenon in natural waters and soil systems that has far-reaching consequences for the interaction of particles with each other and on the attachment of colloids (and bacteria) to surfaces. 

In addition, other potential sources of variability were considered. For example, the sensor surface may potentially differently adsorb deposited polymers. Flowever, the inert nature of quartz crystal and gold sensor electrode,36 with respect to the employed solvents and polymers, resulted in no detectable irreversible adsorption of polymers to the sensor surface as measured by the recovery of the sensor baseline after washing-off deposited polymers. Thus, the sensors were completely reusable because the solvents and dissolved polymers did not chemically interact with the quartz crystal and gold electrodes of the sensor. 

Stability is based. The attractive van der Waals force depends on the size of and the distance between two bodies. The repulsive electrostatic force originates from the surface charge of the colloidal particles. Apart from this, structural forces (e.g., hydrogen bonding) can stabilize or destabilize colloidal particles depending on the nature of the particles, and adsorption of polymer material at the sulfur-solvent interface can cause steric stabilization. 

The adsorption from three-component solutions (n-hexane, benzene, and dioxane) on the hydroxylated silica surface was studied. The effect of the chemical properties of the SiC>2 surface and the nature of the solvent on the adsorption of polymers was investigated. The adsorption of macromolecules on nonporous and fairly large-pore silica is determined by their conformational transformations. The adsorption equilibrium is often established very slowly the process may take up to several months. 

Stabilization of emulsions by powders can be viewed as a simple example of structural- mechanical barrier, which is a strong factor of stabilization of colloid dispersions (see Chapter VIII, 5). The stabilization of relatively large droplets by microemulsions, which can be formed upon the transfer of surfactant molecules through the interface with low a (Fig. VII-10), is a phenomenon of similar nature. The surfactant adsorption layers, especially those of surface active polymers, are also capable of generating strong structural mechanical barrier at interfaces in emulsions. Many natural polymers, such as gelatin, proteins, saccharides and their derivatives, are all effective emulsifiers for direct emulsions. It was shown by Izmailova et al [49-52]. that the gel-alike structured layer that is formed by these substances at the surface of droplets may completely prevent coalescence of emulsion drops. 

An area of intensive research involves the interfacial aspects of diverse polymer systems. Multidisciplinary programs on the interfacial characteristics of polymers are in progress as various academic institutions e.g., Center for Interfacial Engineering at the University of Minnesota, NSF Center on Interfacial Science at Lehigh University). The projects under investigation involve the nature of interfacial adhesion, interdiffusion of diverse polymer chains, and adsorption of polymers from solution on polymer surfaces. A recent textbook on polymer blends and composites has several chapters dedicated to polymer surfaces and interfaces [Sperling, 1997]. 

The swelling of cellulose in the presence of moisture is a well known property of this material. Other protic and nonprotic solvents such as methanol, ethanol, acetonitrile, and acetone also have the capacity to swell microcrystalline cellulose. However, solvents such as benzene, toluene, or dichloromethane do not promote this effect. Therefore it is possible to control adsorption of probes on microcrystalline cellulose, either on the surface or entrapped within the natural polymer chains. After the removal of the solvent used for sample preparation, and for a swelling solvent, a chain-guest-chain interaction is promoted, replacing the previous chain-solvent-chain interaction. 

PROPERTIES OF SPECIAL INTEREST Natural resources basic polysaccharides nontoxic biodegradability bioactivity biosynthesis interesting derivatives (chitosan) toughness graft copolymerization chelating ability for transition metal cations immobilizes enzymes by chemical linking or adsorption chiral polymer. 

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