humectant.pptx

Humectant

1. HUMECTANTS

2. Introduction Definition – Humectant is a hygroscopic substance used to keep things moist . They are used in many products , including food cosmetic and medicines . A humectant attracts and retains moisture in the air nearby via absorption ,drawing the water vapour into or beneath the object’s surface. In pharmaceuticals and cosmetics , humectants can be used in topical dosage form to increase the solubility of a chemical compounds , active ingredients, increasing the active ingredients ability to penetrate skin or its activity time.

3. Humectants are added to cosmetic creams partiularly of the oil-in-water type, with a view to reducing the drying out of such creams on exposure to the air. In addition , the hygroscopic properties of the film of humectant which remains on the skin may be an important factor in influencing the feel and condition of the skin after application. A humectant also provides control in use, by helping to reduce the rate at which water disappers and fluidity decreases.

4. Drying out : Drying out may occur either between the time of packing and the time of use , or else during the usage period. During the first of these periods the most important means of preventing drying out is an efficient closure , and the humectant present plays a subsidiary role since there is only the small space above the product to be sturated with water vapour . In the case of emulsion products, the type of emulsion will have a big effect in respect of water loss. Water-in-oil emulsion such as all purpose creams were successfully marketed for many years in slip lid tins , with the surface of the cream covered by a disk of metal foil , since they dry out at much lower rates than oil-in-water creams which, even if of similar composition , require at least a screw cap with a compressible wad. In tropical climates, even thus will often not avoid drying with shrinkage, cavitation or crust formation. In case of full exposure to the atmosphere during use . Ex. By incomplete closure , the quantities of humectant that can be incorporated seem. Theoretically to be insufficient to prevent drying out. They appear much more likely to affect in retaining moisture in the residual film on the skin.

5. The case of toothpaste is somewhat different. As a system it contains from 30-60% solid and he problems of drying out during storage is mnimal if the tube is properly closed, but drying out during use by failing to replace the tube cap is much more likely and leads to serious difficulties in extrusion and use. In pressurized packs there is the additional problem of the exposed paste blocking the delivery orifice even with normal use.

6. Properties required : Hygroscopicity : The product must attract and retain an appreciable amount of water under nomal conditions of atmospheric humidity. Viscosity : A low viscosity humectant has advantages in easy mixing but conversely a high viscosity will tend to hinder unmixing , or separation of emulsion phases. Viscosity index : Change in viscosity with temperature should be small. Compatibility : Good compatibility, solubility, or solvent power for a wide range of materials , are advantages. Colour, Odour, Taste : The material should have a good colour , odour, and taste. Toxicity : The material should be non-toxic and non-irritant. Corrosion : The material should be non-corrosive. Stability : The material must be non-volatile and should not solidify nor deposite crystals at low temperatures. Reaction : The material should preferably be neutral in reaction. Availability : The material should be freely available and as inexpensive as possible.

7. TYPE OF HUMECTANTS : In general , humectants are divided into three classes: Inorganic humectant Metal-organic humectant Organic humectant

8. Inorganic humectant : Considering inorganic humectants, exemplified by calcium chloride, viscosity characteristics are favorable . They are non-volatile but not always non- crystalizable . They are frequently low in cost , but fail badly on the points of corrosion and compatibility . They find only limited use. Ex. Calcium chloride. 2. Metal organic humectant : The principal metal organic humectant is sodium lactate. This material has greater hygroscopic power than glycerine but it is incompatible with a few materials , can be corrosive has a pronounced taste and may discolor . It has not found a wide application in cosmetics but, has been recommended for use in skin creams to prevent crust formation, particularly becomes lactates are naturally in the body and sodium lactate carries no risk of toxicity or dermatities . The problem of pH can be overcome by admixture with lactic acid which is also fairly hygroscopic.

9. 3. Organic humectants : Organic humectants , which are the most widely used type , are usually polyhydric alcohols, sometimes their esters and ethers. Ethylene glycol is the simplest polyhydric alcohols and we may progress from it in several ways. Considering the main family of polyhydric alcohols the progression is via glycerol, sorbitol . Another pregression is along the sries of alkanes with two terminal hydroxy group. HYGROSCOPICITY : Hygroscopicity is the tendency of a solid substance to absorb moisture from the surrounding atmosphere. The process can take on a number of forms. Thus, with a porous solid such as activated carbon, water vapor will be physically adsorbed, both on the external surface and within the pores, to form a condensed layer. The process may initially take place at "active sites" from which spreading then occurs. With other solids, such as silica gel, the interaction at the surface may not be entirely of a physical nature and some loose chemical bonds may be established. Many cellulosic materials, including hair, cotton and wool, are hygroscopic and change their physical dimensions as a result of the take-up of water. Such materials may be used as the active elements in hygrometers (see Humidity Measurement ).

10. The method most frequently used to determine hygroscopic qualities is to construst a curve of relative humidity of atmosphere against humectant concentration in equilibrium. This is done by exposing small weighed amount of solutions of known composition in atmosphere of controlled humidity and weighing periodically. The controlled humidity can be achieved in small desiccators charged with crystals wetted with their own saturated solutions. STABILITY : Polyols , glycerine, sorbitol and propylene glycol were not interchangable in that in a W/O cream the sample containing propylene glycol had the greater stability whilst that containing glycerene showed the most oil separation. Conversely in an o/w emulsion , the sample containing glycerine remained fluid whilst those contaning propylene glycol and sorbitol would not after storage. On the basis of such observation it would appear that glycerine promoted the formation of an o/w emulsion and whilst propylene glycol favoured a w/o emulsion , their use in wrong types leading to instability. Sorbitol was apparently midway , in such properties, between these other two humectants.

11. Safety : The three humectants widely employed in the cosmetic and toilet industry at present time and which have been discussed in this chapter –namely glycerine , sorbitol , propylene glycol are non-toxic and dermatologically innocuous. Ethylene glycol is not considered safe , since it is oxidised in the body to oxalic acid and any absorption through the skin might lead to renal calculus; for the same reason diethylene glycol is considered toxic. The mono-ethyl ether diethylene glycol has been widely used in cosmetic and toilet preparation. Skin moisturizing : It is not possible to define satisfactorily the role of humectants in skin care. It would appear that the presence of a humectant may be expected to stabilze the water content of the residual film from a cream on the skin and prevent excessive drying out. However , the manner in which adjustment is made with changes in the ambient humidity, and whether the skin is dried or moistened , will depend on the relative transfer rate of water between the atmoshere and the film ,and the film and the skin. The use of humectant in skin products both for the probable benefit to the product while it remains in its container , and the possible benefit to the skin during use appears to be justified.