Cellulose derivative

Cellulose derivative biopolymers have mucus adhesive properties and pH dependent solubility, which makes their use extremely interesting to delivery 

O-methylated and 0-(2-hydroxypropylated) cellulose is available in several grades that vary in viscosity and extent of substitution. It is widely used in pharmaceutical formulations in film-coating and as a controlled-release matrix, in oral products and tablet binder (between 2-5% w/w), and in either wet or dry granulation processes. High-viscosity grades can be used to retard the release of water-soluble drugs from a matrix [2]. 

Sodium carboxymethyl cellulose is an anionic water-soluble polymer and is widely used in oral and topical pharmaceutical formulations because of its viscosity-increasing properties. Viscous aqueous solutions are used to suspend powders intended for topical, oral, or parenteral applications [13]. It is also used as a tablet binder and to stabilize emulsions [14]. 

Cellulose acetate (CA), the acetate ester of cellulose, is one of the most commonly used biocompatible materials for the preparation of semi-permeable membranes to be used for dialysis, ultrafiltration, and reverse osmosis. CA membranes have very low absorption characteristics and thermal stability with high flow rates. Cellulose-based materials are also widely used in the bio-pharmaceutical industry as the matrix for adsorbent beads and membranes. Moreover, CA nanofibers can be used as carrier for delivery of vitamins or pharmaceutical products [15]. 

Cellulose itself is virtually insoluble in water, but aqueous solubility can be conferred by partial methylation or carboxymethylation. 

Ethylcellulose is an ethyl ether of cellulose containing 44-51% of ethoxyl groups. It is insoluble in water but soluble in chloroform and in alcohol. It is possible to form water-soluble grades with a lower degree of substitution. 

Methylcellulose is thus a methyl ether of cellulose containing about 29% of methoxyl groups it is slowly soluble in water. A 2% 

Sinicture IX Highly methylated region of methylcellulose chain 

Derivative Percentage -OCH3 Percentage -OCHjCHpHjCHs Gel point (°C) Surface tension (mN m ) Interfacial tension (mN m ) 

Hypromellose or hydroxypropylmethylcellulose is a partly O-methylated and 0-(2-hydroxypropylated) cellulose [25]. It is used from 10% up to 80% w/w for controlled drug release in solid dosage form and from 2% to 20% w/w as coating solution for tablets and pellets [25,30,31 ]. Hydroxypropylmethylcellulose is a nonionic polymer with pH of a 2% w/w aqueous solution ranging from 5 to 8. It is soluble in water. Being nonionic, it will not form complexes with metallic salts or ionic compounds that can possibly lead to the precipitation of insoluble compounds [32]. Hydroxypropylmethylcellulose matrix hydrates and swells into a gel layer in the direction of matrix surfaces to core when it is contacted with the dissolution medium [14,20,33]. Erosion of gel takes place thereafter and may occur simultaneously with the subsequent phases of matrix hydration and swelling [14]. The swelling and erosion properties of a solid matrix made of 

Cellulose can be alkylated into a number of derivatives with good swelling properties and improved solubility. Such derivatives have a wide 

The reaction of cellulose with methylchloride or propylene oxide in the presence of a strong alkali introduces methyl or hydroxypropyl groups into cellulose (cf. Reaction 4.160). The degree of substitution (DS) is dependent on reaction conditions. 

This is a hard tough material made by the acetylation of cellulose. It is sensitive to moisture pickup and is dimensionally unstable. It is resistant to weak acids and alkalies but is decomposed by strong ones. Both the triacetate and the secondary cellulose acetate give crystal clear films with high gas and water vapour permeabilities. 

Thicker section secondary acetate film is used for the manufacture of rigid food containers and vacuum drawn cellulose acetate containers are used in packaging sweets and chocolates at the high price end of the market. 

This is manufactured by reacting cellulose with ethyl chloride. It is tough and retains flexibility and impact strength down to -40 °C and has a similar moisture pickup to cellulose acetate. It is widely used as a moulding material and in film manufacture. 

Typical degrees of substitution for plastics applications [21] are DS(acetate) = 2.5 for cellulose acetate, DS(propionate) = 2.6 andDS(acetate) = 0.1 for cellulose acetate propionate (CAP), and DS(butyrate) = 1.8 and DS(acetate) = 1.1 for cellulose acetate butyrate (CAB). In the industrial process of catalysed esterification, chain scission is a competitive reaction that can, however, be fairly well controlled under appropriate conditions [22]. Degrees of polymerization of commercial products can be estimated from literature data [22-25] to be in the range of 200 to 300. 

The supermolecular structure of cellulose derivatives - in the present case cellulose esters -is strongly influenced by the degree of substitution and the substitution pattern. With the exception of cellulose triacetate (CTA, tully substituted, DS = 3), most commercially used cellulose esters have a DS of less than three or, in the case of mixed esters, do not have a regular substitution pattern. Therefore, a proper crystallization with well defined X-ray interferences is normally not observed and the materials appear amorphous. 

The two parallel chains on the u-axis can be transformed by the symmetry operations to their antiparallel counterparts shown on the right side of the unit cell. Hydrogen bonds are no longer formed because all hydroxyl groups are substituted by acetyl moieties and CTA becomes a thermoplastic. 

Single crystals of regioselective, fully substituted mixed esters with acetate, propionate und butyrate substituents and DPs between 46 and 84 were synthesised and structurally investigated by Iwata et al. (see [28] for references). Results are summarized by Zugenmaier [27] and many structures resemble the CTA II chain arrangement. 

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N. M. Bikales and L. Segal, Cellulose and Cellulose Derivatives, Parts 4—5, Wiley-Interscience, New York, 1971. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Plant stmctural material is the polysaccharide cellulose, which is a linear P (1 — 4) linked polymer. Some stmctural polysaccharides iacorporate nitrogen iato thek molecular stmcture an example is chitin, the material which comprises the hard exoskeletons of kisects and cmstaceans. Chitki is a cellulose derivative whereki the OH at C-2 is replaced by an acetylated amino group (—NHCOCH ). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both ki monomer units and the nature of thek linkages. 

The Diacel columns can be used for the separation of a wide variety of compounds, including aromatic hydrocarbons having hydroxyl groups, carbonyls and sulfoxides, barbiturates, and P-blockers (35,36). There are presendy nine different cellulose derivative-based columns produced by Diacel Chemical Industries. The different columns each demonstrate unique selectivities so that a choice of stationary phases is available to accomplish a separation. 

Cellulose Deriva.tives, Cellulose can be derivatized to make both water-soluble gums and hydrophobic polymers. The preparation of the hydrophobic cellulose esters (qv), cellulose acetates and cellulose nitrates, has already been mentioned. The water-soluble cellulose derivatives are cellulose ethers (qv). 

Unit cells of pure cellulose fall into five different classes, I—IV and x. This organization, with recent subclasses, is used here, but Cellulose x is not discussed because there has been no recent work on it. Crystalline complexes with alkaU (50), water (51), or amines (ethylenediamine, diaminopropane, and hydrazine) (52), and crystalline cellulose derivatives also exist. Those stmctures provide models for the interactions of various agents with cellulose, as well as additional information on the cellulose backbone itself. Usually, as shown in Eigure la, there are two residues in the repeated distance. However, in one of the alkah complexes (53), the backbone takes a three-fold hehcal shape. Nitrocellulose [9004-70-0] heUces have 2.5 residues per turn, with the repeat observed after two turns (54). 

Many cellulose derivatives form Hquid crystalline phases, both in solution (lyotropic mesophases) and in the melt (thermotropic mesophases). The first report (96) showed that aqueous solutions of 30% hydroxypropylceUulose [9004-64-2] (HPC) form lyotropic mesophases that display iridescent colors characteristic of the chiral nematic (cholesteric) state. The field has grown rapidly and has been reviewed from different perspectives (97—101). 

Antiredeposition agents contribute to the appearance of washed fabrics. Sodium carboxymethylceUulose [9004-32-4], NaCMC is the most widely used, and on cotton fabrics, the most effective. With the advent of synthetic fabrics, other cellulose derivatives, eg, methylceUulose [9004-67-5], hydroxybutjiceUulose, hydroxypropyl- and mixed methyl and hydroxybutyceUulose ethers have been shown to be more effective than NaCMC (8) (see... 

Cellulose Derivatives. Chemical modification markedly alters the physical properties of ceUulose. Common derivatives iaclude methylceUulose ethylceUulose [9004-57-3] ptopylceUulose /7(9(93 -/ -7/, hydroxyethjlceUulose /7(9(94- 52-(97, hydtoxyptopylceUulose [9004-64-2],... 

Many cellulose derivatives have been prepared of which the esters and ethers are important. In these materials the hydroxyl groups are replaced by other substituent groups. The degree of substitution is the term given to the average number of hydroxyl groups per anhydroglucose unit that have been replaced. 

Carbon, hydrogen and possibly oxygen Resin and derivatives Natural drying oils Cellulose derivatives Alkyd resins Epoxy resins (uncured) Phenol-formaldehyde resins Polystyrene Acrylic resins Natural and synthetic rubbers Carbon monoxide Aldehydes (particularly formaldehyde, acrolein and unsaturated aldehydes) Carboxylic acids Phenols Unsaturated hydrocarbons Monomers, e.g. from polystyrene and acrylic resins... 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

Oridation. This is caused by contact with oxidising acids, exposure to u-v, prolonged application of excessive heat, or exposure to weathering. It results in a deterioration of mechanical properties (embrittlement and possibly stress cracking), increase in power factor, and loss of clarity. It affects most thermoplastics to varying degrees, in particular polyolefins, PVC, nylons, and cellulose derivatives. 

In this context, the enantiomeric pair containing the eutomer of cyclothiazide can be resolved by HPLC on cellulose-derived coated CSPs. Nevertheless, the poor solubility of this compound in solvents compatible with this type of support makes this separation difficult at preparative scale. This operation was achieved with a cellulose carbamate fixed on allylsilica gel using a mixture of toluene/acetone as a mobile phase [59]. 

Cellulose derivatives Amylose derivatives Brush-type... 

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