Plasticity and spreadability

The most important functionality of a solidified oil and fat is its plasticity, consistency or spreadability . A shortening or margarine product may appear to be in a homogeneous solid state, but it consists of discrete solid (crystal 

Specific gravity (25°C) Refractive index, n 5 Specific refraction, r 0 Viscosity (centipoises at 25°C) Solidification point (°C) Specific heat (cal/g at 19.7°C) Heat of combustion (cal/g) Smoke point (°C) 

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The rheological characteristics of finished margarines are expressed in terms such as consistency, texture, plasticity, hardness, structure, and spreadability (1). 

Most emulsions, unless very dilute, display hoth plastic and pseudoplastic flow behaviour rather than simple Newtonian flow. The flow properties of fluid emulsions should have little influence on their biological behaviour, although the rheological characteristics of semisolid emulsions may affect their performance. The pourability, spreadability and syringeability of an emulsion will, however, be directly determined by its rheological properties. The high viscosity of w/o emulsions leads to problems with intramuscular administration of injectable formulations. Conversion to a multiple emulsion (w/o/w), in which the external oil phase is replaced by an aqueous phase, leads to a dramatic decrease in viscosity and consequent improved ease of injection. 

Gels and emulsions show plastic and pseudo-plastic behaviour. At rest, these systems are more viscous than when they flow. Creams and ointments should be easily spreadable, but they should not drip from the skin. Emulsions and suspensions should be as stable as possible and pouring should be easy. 

Fats that melt close to 30 °C and have a plastic or spreadable consistency at room temperature. 

Butter has a limited plastic range. At refrigerator temperature ( 1-0°C), butter behaves essentially as a solid and lacks spreadability, whereas at room temperature (21-25°C), it oils off and exhibits moisture exudation. 

Low-fat squeezable spreads and soft products (e.g., soft cheese, spreadable margarine) require a ratio of plastic stress to maximum stress of 0.95 to 1.0 (Kasapis, 2000). Typically around 15% of a high-dp fraction ( 25 dp) can be used in these products. Interestingly, the physical structure of the material does not develop immediately with formulation but requires 1 to 2 days of storage. 

Plastisol is a specialized technique for making flexible vinyl products. It is also sometimes called paste or dispersion technology. Basically, powdered PVC is stirred into liquid plasticizer at room temperature to form a viscous liquid or spreadable paste. This can be poured or spread into the shape of the final product, heated to fuse, and cooled to gel into the final solid product. Simple pouring or gentle spreading require no heavy equipment, and do not damage delicate substrates such as... 

Margarine can be served by preloading on to plastic serving spoons for flavor evaluations. If margarines are to be evaluated for their spreadability properties, they should be served in a small plastic or paper cup (25-30 mL) with a plastic knife and a slice of white bread. Bland crackers can also be used, although these are less desirable than bread in evaluating spreadability due to their limited size and ease of breaking. 

Body and Texture. By means of appropriate qualifications of the terms body and texture, butter graders describe the physical properties of butter that are noted by the senses. The exact meanings of these terms have not been clearly outlined. Frequently, they are used as if they had the same meaning. Certain properties such as hardness and softness refer to the body of butter, whereas properties such as openness refer to texture. However, some of the properties, such as leakiness or crumbliness, are confusing. Usually, most body and texture terms are used to describe a defect, e.g., gritty, gummy, and sticky (86). Good butter should be of fine and close texture have a firm, waxy body and be sufficiently plastic to be spreadable at cold temperatures. 

Table I shows that a 3x3.5 cm dorsal skin wound on a Wistar rat can ooze out 2.2 ml of serous fluid in about 3 days. This fluid volume is reduced to 1.2 ml, if the wound is exposed for 3 hr before treatment. Beyond the 3 hr exposure, there may be further reduction in oozing, but the chance of eschar formation will also increase. Various compositions of the AgN03 medicated dextran hydrogel paste have been evaluated. The one with a good spreadability and fluid absorption has been used in the present study. Measurements by a simple hygrometric method showed that the medicated paste on the wound reduced evaporative loss by almost 50% as compared to an open wound which had a rate of 93 mg H20/cm /hr (7.). On subsequent days, the relatively steady value of 12.5 mg H20/cm /hr was about 2x higher than the evaporative loss of the paste spread over a plastic sheet used as a control. The higher evaporative rate of the paste on the wound site might be due to the transmission of excess moisture from the wound surface. The oozing serous fluid had apparently been first absorbed into the paste, because no exudate accumulation was ever observed under the paste coating. The humectant in the paste which retained moisture obviously must have kept the wound surface sufficiently moist to prevent eschar formation.

Uses Lubricant and plasticizer in oils and polymers o/w emulsifier for min. and veg. oils, and soivs., cosmetic and industrial applies. improves flow and leveling of coatings increases spreadability of personal care prods. defoamer... 

Most oil-based paints contain polymer binders dissolved in organic solvents. These polymer molecules float about separately in the liquid solvent. For the preparation of water-insoluble paints, appropriate solvents are required. Enough solvent is added to make the paint spreadable and solvents usually exceed 25% of the paint s weight. When the paint is applied to a surface, the solvent molecules evaporate into the air, and the polymer molecules are left behind as a thin plastic layer. Most acrylic paints are of this type. 

Contact angle measurements indicate the capability of a surfactant to spread a desired formulation on a given surface. For example, for developing printing ink for a plastic surface, the surfactant should result in a very low contact angle with the surface. In a way, contact angle measuranents also explain the wetting of the surface, besides the spreadability of paints, inks, and polishes on the surface to be coated. 

The combination of less mechanical shear and lower bed pressure allows for a thicker binder deposit, especially when the binder is poured into the granulation unit instead of sprayed. This thicker film often dries to a more effectively spreadable film during the compression of these granules to form tablets. This increased plasticity is especially true at the lower compression forces (Fig. 1). The tablets also have... 

Texture has been defined as the way in which various constituents and structural elements are arranged and combined into a micro- and macrostructure and this structure is externally manifested in terms of flow and deformation [1], The structural elements of fats consist of solid fat crystals. They are suspended in liquid oil and when present in sufficient quantity form a three-dimensional network that imparts plastic properties to the fat. The external manifestations of this network structure include a number of physical and mechanical properties such as hardness, softness, spreadability, brittleness, shortening power, and aeration properties. 

Uses Surfactant surf. tens, depressant wetting agent emulsifier foam builder humectant softener used for producing flexible slab stock urethane foam plasticizer for hair resins imparts spreadability. It. nongreasy feel, and detackification to hair sprays, shampoos, skin care lotions, perfumes, shaving soaps lubricant, antistat on polyamide/polyester/spandex fibers Properties Gardner 2 hazy, vise, liq. sol. in water, alcohol, hydroalcoholic systems, propylene glycol, IPM sp.gr, 1,07 vise. 465 cs HLB 13.6 f.p. 50 F b.p. > 200 C flash pt. (COC) 149 C pour pt, 52 F ref. index 1.454 100% cone. 

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