Grade variation in the rheology of white soft paraffin B.P.

Barry, Brian W.; Grace, A.J.

doi:10.1111/j.2042-7158.1970.tb08594.x

Cited by 28 publications

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“…The type of creep apparatus employed (42,43) and the method for calibration (44) are as reported. The viscometer was loaded by heating the sample to 60 ~ in a waterbath and pouring the molten material into the outer cylinder.…”

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Rheological properties of white soft paraffin

Barry

Grace

1971

Rheol Acta

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White soft paraffin has been used in pharmacy for nearly a century (1). The physical nature varies, depending upon the source of the crude petroleum, the type and degree of refining, and on any subsequent blending processes. The major constituents are n-paraffins, iso-paraffins and naphthenes (2-5), which form a colloidal gel type structure containing oil, amorphous waxes, and discrete crystals (6).Many procedures are employed to investigate the rheological properties of semisolids. Continuous shear rheometry is used widely to investigate pharmaceutical materials (7-15) although many workers have reported disadvantages for this type of procedure (16)(17)(18)(19)(20)(21)(22).Oscillatory viscometers, which operate over a wide range of shear and strain rate, have many theoretical advantages for testing pharmaceutical materials, but little work has been reported (23,24).Creep viscometry is used especially for investigation of viscoelastic materials which yield at high stresses and rates of shear, for example emulsion and semisolid systems (23,(25)(26)(27)(28)(29)(30). The theory of linear viscoelasticity (31, 32) and the method of analysing creep curves (27, 33) are documented well.There is some controversy in the reported rheologieal properties of soft paraffin, and similar paraffin-greases. The material has been reported to be elastic (34), non linear viscoelastic (35) and linear viscoelastic (36, 37) in small strain experiments. Continuous shear rheograms have been published (38) whilst ejection of the paraffin from a cone-plate gap has been reported (34). The hysteresis loop of soft paraffin rheograms may be due to thixotropy (39) or irreversible shear breakdown (40).The purpose of this work is to establish whether a sample of white soft paraffin is a) viscoelastic or non viscoelastic; b) if viscoelastic, is it linear or nonlinear? and c) *) Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14-15, 1970. whether hysteresis loops, with or without pour points, obtained in continuous shear experiments indicate thixotropy, irreversible shear breakdown, or are artifacts due to expulsion of the material from the viscometer. The influence of temperature on the rheology of the material will be considered.The sample of white soft paraffin (Loveridge, Southampton) is of B. P. standard.Melting point ranges of the crystals in the sample were determined using a Kofler hot stage mounted on a Cooke polarising microscope, and with a capillary melting point apparatus (Gallenkamp). To determine whether the shear breakdown within soft paraffin is due to thixotropy or to irreversible shear breakdown, the FerrantiShirley viscometer, with large cone, was partially loaded so that the sample did not reach the edge of the cone, thus avoiding a hysteresis loop forming due to expulsion of material from the cone-plate gap. A flow curve was obtained, using Regime (1) at 25.5 ~ The sample was left on the viscometer at this temperature and a further curve obtained after 72 h.All...

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Rheological properties of white soft paraffin

Barry

Grace

1971

Rheol Acta

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“…The base thus spreads more easily than do soft paraffins and like soft paraffins, static yield stresses gave linear Arrhenius-type plots. The linearity of such curves confirms that yield stresses are a function of some property of the material, although they may not be fundamentally significant, and they may be useful in comparative testing procedures such as quality control (Barry & Grace, 1970).…”

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confidence: 75%

“…The value for Jo at 25" (Table 1) was of the same order as those of white soft paraffin samples with and without emulsified water (Barry & Grace, 1970, 1971 but was much smaller than those of oil in water creams stabilized by mixed emulsifiers of the surfactant-long chain alcohol type (Barry, 1968;Barry & Saunders, 1970. The residual viscosity was similar to those of the lipophilic group but was higher than the self-bodied creams.…”

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confidence: 78%

“…The value for FAPG base was approximately 43 k J mol-l compared to a range of 59-105 k J mol-l for B.P. grades of white soft paraffin (Barry & Grace, 1970). The base thus spreads more easily than do soft paraffins and like soft paraffins, static yield stresses gave linear Arrhenius-type plots.…”

mentioning

confidence: 86%

“…Viscoelastic measurements were made with concentric cylinder reaction air turbine creep viscometers (Barry & Grace, 1970;Barry, 1971). Samples were loaded at 25" (f0.2") and 37" (*0.2"), temperatures representing the extremes .…”

Section: Continuous Shear Rheologymentioning

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Continuous shear, viscoelastic and spreading properties of a new topical vehicle, FAPG base

1973

Journal of Pharmacy and Pharmacology

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The rheology of a new topical vehicle FAPG base was investigated over the temperature ranges of 25-37'. Continuous shear rheograms obtained with a Ferranti-Shirley cone and plate viscometer were hysteresis loops with spur points; loop areas, yield values and apparent viscosities decreased with increase in temperature and an activation energy for viscous flow of 10.4 kcal mol-l (43.5 kJ mol-l) was derived. In creep (concentric cylinder geometry) the base was viscoelastic with a low limit of linearity with respect to strain. Creep compliance curves showed an initial elastic response, a region of retarded elasticity and a viscous region ; compliances increased and viscosities decreased with temperature rise. Patient acceptance of skin spreadability of the base was assessed using a master curve concept; the spreading properties were close to the preferred values for maximum patient acceptance. It is concluded that FAPG base deserves further study as a vehicle for dermatological use.For skin therapy, the vehicle used should have optimum physicochemical properties for assuring drug stability and release besides inhibiting microbial growth and being aesthetically satisfactory. Recently, a new topical vehicle 'FAPG base was reported to have possible significant advantages over traditional ointments and creams (British Patent No. 1,259,858 and other Patents pending; Garnier, 1971a,b;Rhodes, 1971). We have examined the rheological properties of the material in continuous shear and in creep and have attempted to assess patient acceptance of its spreadability. METHODS A N D RESULTS Material.A production sample of FAPG base was provided by Syntex Pharmaceuticals Ltd., St. Ives House, Maidenhead, Berks. It is a mixture of propylene glycol, stearyl alcohol, polyethylene glycol and glycerol combined to form a gel-like structure with a crystalline network. The product is a smooth, white, soft, non-aqueous, hydrophilic semisolid with a slight pearly sheen (Garnier, 1971b).Microscopy. The base was examined with a Kofler Micro Hot Stage attached to a polarizing microscope. At room temperature the material was anisotropic (Fig. 1A) and slight melting occurred between 32-34'. Between 47-49' the preparation melted to form an isotropic solution which recrystallized in a different form on cooling. The flocculated suspension appearance was replaced by a mosaic of thin, flat, anisotropic, polyhedral crystals (Fig. IB). This implies that FAPG base may change its crystalline form on storage to yield a product with different mechanical properties.A Ferranti-Shirley cone and plate viscometer with automatic flow curve recorder unit was used with a large cone (diameter 7 cm, Continuous shear rheology.

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Pharmaceutical Sciences—1968. A Literature Review of Pharmaceutics

Bernardo¹,

Russo²

1969

Journal of Pharmaceutical Sciences

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Grade variation in the rheology of white soft paraffin B.P.

Cited by 28 publications

References 14 publications

Rheological properties of white soft paraffin

Rheological properties of white soft paraffin

Continuous shear, viscoelastic and spreading properties of a new topical vehicle, FAPG base

Pharmaceutical Sciences—1968. A Literature Review of Pharmaceutics

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