Semisolid characteristics

Almost black, thick liq or semisolid characteristic odor. A small portion of coal tar dissolves in water all or almost all dissolves in benzene or nitrobenzene partly dissolves in alcohol, ether, chloroform, carbon disulfide, methanol, acetone, petr ether, or sodium hydroxide soln. Practically insol in water, Sol in 20 parts alcohol miscible with abs alcohol, acetone, patrolatum, oils and fats. 

Of all these formulations, it is the diverse semisolids that stand out as being uniquely topical. Semisolid systems fulfill a special topical need as they cling to the surface of the skin to which they are applied, generally until being washed off or worn off. In contrast, fluid systems have poor substantivity and readily streak and run off the desired area. Similarly, powders have poor staying properties. Importantly, the fundamental physicochemical characteristics of solutions, liquid emulsions and suspensions, and powders are independent of their route of application, and are discussed adequately elsewhere in this text and need not be reconsidered. This is not to say the compositions of such systems cannot be uniquely topical, for there are chemicals that can be safely applied to the... 

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

Dewatered sludge, or filter cake, is a highly viscous material in which the remaining water is mechanically trapped within the cake. For further drying, the cake must be broken up before heating to expose as much surface area as possible. This is difficult, because semisolid filter cake often takes on the characteristics of a heavy, sticky paste when efforts are made to break it up (PACE 1986). 

Tar sands are composed of a mixture of 84-88% sand and mineral-ricli clays, 4% water, and 8-12% bitumen. Bitumen is a dense, sticky, semisolid that is about 83% carbon. The substance does not flow at room temperature and is heavier than water. At higher temperatures, it flows freely and floats on water. Characteristics of tar sands important to mining, recovery, and processing indude grain size, composition, sortability, porosity, permeability, and microscopic habitat. 

The physical form of a drug product that is pourable displays Newtonian or pseudoplastic flow behavior and conforms to its container at room temperature. In contrast, a semisolid is not pourable and does not flow at low shear stress or conform to its container at room temperature [12], According to its physical characteristics, liquid dosage forms may be dispersed systems or solutions. 

Gels are of central importance for most semisolid food products. A gel can contain more than 99% water and still retain the characteristics of a solid. The network structure will determine whether the water will be firmly held or whether the gel will behave more like a sponge, where water is easily squeezed out. The gel structure will also have a major impaet on the texture as well as diffusion of water and soluble compounds. Many food matrixes are based on colloidal gels such as yoghurts, cheeses, many desserts, sausages etc (see also Chapters 19 and 20). In whole foods, there is often a combination of colloidal structures and fragments of biological tissues or gel structures in combination with particles, emulsion and foam structures. This level of complexity of composite food structures will not be dealt with here. 

The various means of photostabilization of solid and semisolid dosage forms, based on the principle of spectral overlay and opacification, have been reviewed and presented. Selection of one particular technique will depend on the particular drug substance or ingredients causing the photodegradation and its particular spectral characteristics. 

Palm oil is an edible oil referred to by the FAOAVHO Codex Alimentarius (1) as being derived from the fleshy mesocarp of the oil palm fruit. In the unprocessed form palm oil is reddish brown in color, and it has a semisolid consistency at ambient temperature. Readers should not confuse palm oil with palm kernel oil, which is another product obtained from the kernel of the oil palm fruit while palm oil is derived from the mesocarp or fruit flesh. The two oils have different chemical composition and physical characteristics, and they are used and marketed separately according to their own supply and demand situations. 

Knowledge about the detailed structures of the triglycerides present in palm oil is important because they define some of the physical characteristics of the oil. The melting points of triglycerides are dependent on the structures and position of the component acids present. They also affect the crystallization behavior of the oil. The semisolid nature of palm oil at room temperature has been attributed to the presence of the oleo-disaturated fraction. 

Hydrogenation is a chemical process in which hydrogen gas is reacted with oils to increase their oxidative and thermal stability by converting liquid components to semisolid fractions. The melting and crystalline characteristics developed are essential for formulating shortenings with specific desirable physical and functional properties. 

Use of the term gel as a classification originated during the late 1800s as chemists attempted to classify semisolid substances according to their phenomenological characteristics rather than their molecular compositions. At that time, analytical methods needed to determine chemical structures were lacking. The defines gels (sometimes called jellies) as... 

Boylan, J.C. Rheological estimation of the spreading characteristics of pharmaceutical semisolids. J. Pharm. Sci. 1967, 56, 1164-1169. 

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