Cellulose plastic

Cellulose is a polymer which occurs abundantly in nature, constituting about one-third of the vegetable matter of the world. Cotton is almost pure cellulose, whereas wood contains about 50% of the polymer. Cotton linters and wood pulp are the usual raw materials for cellulose polymers. The former is digested at 120-150°C with dilute caustic soda, and bleached to give 99% pure cellulose, and wood pulp cellulose is extracted by a variety of chemical processes to a product of 88-90% purity, which can be enhanced by alkaline digestion and bleaching. 

Cellulose is the most abundant polymer constituting the cell walls of all plants. Oven-dried cotton consists of lignin and polysaccharides in addition to 90% cellulose. On digesting it under pressure and a temperature of 130-180°C in 5-10% NaOH solution, all impurities are removed. The residual a-cellulose has the following structure  

Every glucose ring of cellulose has three —OH functional groups that can further react. For example, cellulose trinitrate, an explosive, is obtained by nitration of all OH groups by nitric acid. Industrial cellulose nitrate is a mixture of cellulose mononitrate and dinitrate and is sold as celluloid sheets after it is plasticized with camphor. Although cellulose does not dissolve in common solvents, celluloid dissolves in chloroform, acetone, amyl acetate, and so forth. As a result, it is used in the lacquer industry. However, the polymer is inflammable and its chemical resistance is poor, and its usage is therefore restricted. 

Among other cellulosic polymers, one of the more important ones is cellulose acetate. The purified cellulose (sometimes called chemical cellulose) is pretreated with glacial acetic acid, which gives a higher rate of acetate 

Sodium carboxymethyl cellulose (CMC) is prepared through an intermediate alkali cellulose. The latter is obtained by reacting cellulose [X—(OH)3] with sodium hydroxide as follows  

Commercial grades of CMC are physiologically inert and usually have a degree of substitution between 0.5 and 0.85. CMC is mainly used in wallpaper adhesives, pharmaceutical and cosmetic agents, viscosity modifiers in emulsions and suspensions, thickener in ice cream industries, and soil- suspending agents in synthetic detergents. 

---

Ethyl Cellulose. Ethyl cellulose is prepared by reacting cellulose with caustic to form caustic cellulose, which is then reacted with chloroethane to form ethyl cellulose. Plastic-grade material contains 44 to 48% ethoxyl. 

Typical physical properties of celluloid are compared with other cellulose plastics in Table 22.2. 

Table 22.2 Typical physical properties of cellulosic plastics. (It is necessary to quote a range of figures in most instances since the value of a particular property is very dependent on formulation)...

Typical values for the principal properties of cellulose acetate compounds are tabulated in Table 22.2 in comparison with other cellulosic plastics. Since cellulose acetate is seldom used today in applications where detailed knowledge of physical properties are required these are given without further comment. 

Cellulose Plastics Cellulose Acetate 1912 M P All conventional processes Excellent vacuumforming material for blister packages, etc. 

Cellulosic plastics Group of plastics composed of cellulose compounds for example, esters (e.g., cellulose acetate) and ethers (e.g., ethyl cellulose). 

Cellulose plastics These old established materials have limited chemical resistance. Ethyl cellulose is, however, often used in conjunction with... 

Cellulosic plastics are usually used for the membrane, but any water vapor permeable material is a good possibility, provided the film has good mechanical properties. 

Thermoplastics ABS, acetal and polyacetal, acrylic (methyl methacrylate), cellulose plastic, EVA, fluorocarbon, PTFE,... 

An organic material which occurs in the woody tissues of plants. It is a by-product in the preparation of cellulose for the manufacture of paper, rayon and the cellulose plastics, and its use has been proposed as a reinforcing filler for rubber. 

Oxygen Availability in Degrading Films. A major difference between natural materials and starch-plastic or cellulose-plastic blends is that the hydrophilic and relatively permeable matrix of materials like wood and hydrated polysaccharide films allows diffusion of O2 and release of nutrients from sites at a distance from the invasion site. As colonization proceeds, pore enlargement occurs when the pore walls are degraded (8) or as the polymer matrix of amylose or PVA films is hydrolyzed (10.12). In contrast, the LDPE matrix supplies no nutrients, hinders diffusion of water and O2, and the pore diameter cannot be increased. The consequence of impermeability is that the sole means of obtaining O2 and nutrients is by diffusion through water-filled pores. 

Cellophane is, after chemical modification, obtained from the cellulose in wood, just as paper (from cellulose and lignin), cellulose fibres ( rayon ), and cellulose plastics. Leather is made from animal hides in a tanning process. 

Strain rate sensitivity of (or the effect of press speed on) the formulation is of primary concern in scale-up. Whether the product development work was performed on a single-stroke press or a smaller rotary press, the objective in operations will be to increase efficiency, in this case the tablet output rate and, therefore, the speed of the press. For a material that deforms exclusively by brittle fracture, there will be no concern. Materials that exhibit plastic deformation, which is a kinetic phenomenon, do exhibit strain rate sensitivity, and the effect of press speed will be significant. One must be aware that although specific ingredients (such as calcium phosphate and lactose) may exhibit predominately brittle fracture behavior, almost everything has some plastic deformation component, and for some materials (such as microcrystalline cellulose) plastic deformation is the predominant behavior. The usual parameter indication is that target tablet hardness cannot be achieved at the faster press speed. Slowing the press may be the only option to correct the problem. 

In the most general sense, all plastics are engineering materials, in that they offer specific properties which we judge quantitatively in the design of end-use applications. Among die large-volume established thermoplastics, we should certainly pay tribute to the engineering performance of the polyolefins, polystyrene, impact styrene, ABS, vinyls, acrylic, and cellulosic plastics. 

Although Lhe first cellulose plastic (cellulose nitrate plastic-based on an inorganic ester of cellulose) was developed in 1865. the first organic cellulose ester plastic was not offered commercially until 1927. In that year, cellulose acetate plastic became available as sheets, rods, and tubes. Two years later, in 1929. it was offered in the form of granules for molding. It was the first thermoplastic sufficiently stable to be melted without excessive decomposition, and it was the first thermoplastic to be injection molded. Cellulose acetate butyrate plastic became a commercial product in 1938 and cellulose propionate plastic followed in 1945. The latter material was withdrawn after a short time because of manufacturing difficulties, but it reappeared and became firmly established in 1955. 

Cellulosic plastics are used in a niunbei of outdoor applications with signs being one of the principal areas of use. This plastic can be stabilized reasonably well with the aryl esters of salicyclic acid. It is of interest to note that these esters undergo a photochemical rearrangement in the plastic to derivatives of hydroxy benzophenone. The hydroxy benzophenones may be added initially to effect stabilization. 

Acetic anhydride is one of the most important esters. The major market for acetic anhydride is in the production of cellulose acetate Other important uses Include production of cellulosic plastics, vinyl acetate, and aspirin. Acetic anhydride is u mature commercial product enjoying a stable price situation and steady growth... 

Regenerate cellulose Plastics directive Ceramics directive... 

The use of monohydric alcohol esters as PVC plasticizers had its beginning in the decade of the thirties. Plasticization of PVC was first demonstrated by W. D. Semon of B. F. Goodrich(1). Semon s patent gave examples of plasticizers such as dibutyl phthalate and other unrelated compounds. However, the claims were limited to non specific aromatic substances, liquid aromatic nitro compounds, and specific aromatic nitro compounds. The first commercially used plasticizers for PVC were those already available and used as cellulosic plasticizers, such as the monohydric alcohol ester—dibutyl phthalate. 

---