Chemically modified cellulose-based

Among various chemical treatments, alkali treatment with NaOH solution is often chosen to modify cellulose-based materials. Since NaOH reacts with -OH groups of cellulose and reduces hydrophilicity and impurities from cellulose fiber, it improves the compatibility between the cellulose and the polymer matrix. Consequently, significant improvement in the mechanical and morphological properties of composite such as MOE, MOR, compressive modulus, SEM morphology and XRD pattern are observed for the alkali-treated composite materials. Benzene diazonium salt is also an important chemical, which reacts with cellulose in fiber and produces 2,6-diazo cellulose by a coupling reaction. 

Chiral stationary phases in tic have been primarily limited to phases based on normal or microcrystalline cellulose (44,45), triacetylceUulose sorbents or siHca-based sorbents that have been chemically modified (46) or physically coated to incorporate chiral selectors such as amino acids (47,48) or macrocyclic antibiotics (49) into the stationary phase. 

The principal chemical iadustry based on wood is pulp and paper. In 1995, 114.5 x 10 metric tons of wood were converted iato - 60 x 10 metric tons of fiber products ranging from newsptint to pure cellulose ia the United States (1,76). Pure cellulose is the raw material for a number of products, eg, rayon, cellulose acetate film base, cellulose nitrate explosives, cellophane, celluloid, carboxymethylceUulose, and chemically modified ceUulosic material. 

Synthetic polymer materials are so ubiquitous in modem life that we now take them for granted. But, the first commercially significant, completely synthetic plastic was only introduced at the beginning of the 20th century. This was Bakelite, invented by Leo Baekeland and a short account of his contributions will form the subject of one of our Polymer Milestones in the next chapter. The introduction of this new material was preceded by roughly 40 years of the development of what can be called semi-synthetics based on chemically modified forms of cellulose. 

ATER-SOLUBLE POLYMERS (WSPs) are an important class of industrial polymers. They have many applications in solution and in the solid state. In solution, they are widely used as thickeners to control the rheology of various water-based formulations, such as latex paints, drilling muds, foods, cosmetics, and building materials. Chemically modified natural polysaccharides such as starch, cellulose, and guar are a large class of commercial water-soluble polymers. The appropriate chemical modification of these polysaccharides can lead to the modified solution properties needed for specific applications. 

A variety of polymers and copolymers are used for gas separation membranes. To be suitable for gas separation, the polymer must have good permeability and selectivity and the material must be capable of forming a strong, thin, defect-free membrane with good chemical and thermal stability. Commercial gas separation membranes are based on modified cellulose, treated polysulfone or a substituted polycarbonate polymer. Membranes... 

Ibach RE, Clemons CM. Biological resistance of polyethylene composites made with chemically modified fiber or flour. Proceedings of the 6th Pacific Rim Bio-based Composites Symposium and Workshop on the Chemical Modification of Cellulosics 2002 Nov 10-13 Portland, OR. Portland (OR) Oregon State University 2002. p 574. 

Cellulose UF membranes are used in applications where low fouling characteristics are required. Cellulose has a very regular structure and is able to form strong intermolecular hydrogen bonds between the several hydroxy groups. As a result, cellulose is practically insoluble in almost all solvents. The only exceptions are dilute solutions in DM Ac or NMP with addition of lithium chloride. Cellulose membranes are prepared by methods that basically involve precipitation from a solution of chemically modified native cellulose (from cotton linters, etc.). Until some years ago the three main methods were based on cellophane, cuprophane and cuenophane. 

The first macromolecular substances which fotmd technical interest were based on chemically modified natural materials, for example cellulose nitrate (Celluloid) or crosslinked casein (Galalith). Only with the onset of industrialisation in the nineteenth century did these renewable raw materials become the limiting factor for further growth, and chemists began developing artificial macromolecules based on fossil carbon sources like coal, oil, and gas. Polymers like condensation products from phenol and formaldehyde (Bakelite) started the plastics age in 1910 and polymers of styrene or vinyl chloride were used since about 1930 and until nowadays as important plastics. Presently, worldwide more than 260 million tons polymers per year are produced and used as plastics, films, fibres, and synthetic rubber. 

Wang, J., T. Golden, and R. Li (1988). Cobalt phthalocyanine/cellulose acetate chemically modified electrodes for electrochemical detection in flowing streams Multifunctional operation based upon the coupling of electrocatalysts and permselectivity. AnoZ. Chem. 60(15), 1642-1645. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

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