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ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 14, 2006 Rheological Properties of Carbomer Dispersions University of Bahrain, Isa Town, Bahrain Email: almalah@eng.uob.bh, Email: almalah@just.edu.jo at hand. It can be used in cosmetic products, Rheological properties of carbomer like lotions, gels, and hair products. solutions were investigated as a function of carbomer concentration. Carbomer is an polymers like carbomer for ocular drug emulsion stabilizer. The shear stress was delivery was the subject of several studies measured as a function of shear rate and published during the last decade and several shearing time. Both dynamic and static yield review articles are available1. Carbomer, a stress, τo, values were also measured. It was polyacrylic acid polymer, is available in a wide range of molecular weights and either content, carbomer dispersion behave as a being linear, branched or cross-linked2. The Newtonian fluid, whereas at or above 0.45 acidic carboxyl groups partially dissociate in thinning and rheopectic behaviour. The thought, upon the addition of alkaline yield stress results are in harmony with the compounds, solvation, salt formation and shear stress- rate experiments that below electrostatic repulsion between the anionic reported and a non-zero value at or above surfactant, with the aim of achieving better used in hair gels, and other gels, lotions, and creams. It is suitable for formulating containing various amounts of surfactant sparkling and clear gels as well as (from 0.01 to 1.0% w/w) was used stabilizing emulsions. The typical use level throughout their study. For the hydrophobic, is 0.1-0.5% depending on the type of modified carbomer, they reported an formulation and final desired viscosity. It is increase in viscosity and texture profile a cost effective thickener and is pH parameters with increasing Polysorbate 80 sensitive. Carbomer is a water and alcohol concentration up to 0.3% w/w, followed by soluble polymer. It is a mildly acidic and a decrease in the gel network strength at forms a loose network when partially higher surfactant concentrations. On the neutralized to pH 5-8. Carbomer requires a long time to swell properly for use. It is best to make a pre-gel before beginning the batch changes in the network structure with the increasing concentration of surfactant; of AMP, 1.5g of TEA). It is advisable to add hence the interactions between emulsifier strong bases previously diluted into water at and surfactant are of a hydrophobic nature, properly for use. It is best to make a pre-gel dependent release or the bioavailability of the active ingredient being used in drug delivery systems. For example, Esposito et al.5 investigated the influence of liposomal distilled water at room temperature. The formulations on the in vitro absorption of methyl nicotinate (MN), which was taken as temperature. The next day, the sample was model drug. Their results indicated that MN stirred to assure homogeneity and dispersity permeability was directly related to soybean of carbomer in the aqueous solution. The phosphatidylcholine concentration and following concentrations of carbomer were inversely related to liposome size and to used: 0.15, 0.30, 0.45, 0.6, and 0.90 wt %. In this research, the rheological Accuracy of Viscosity Measurements varied concentration, will be examined. The shear stress vs. shear rate and vs. shearing measure fluid parameters of shear stress and time, in addition to the yield stress viscosity at given shear rates. The principle measurement will be exploited. Viscosity of operation of the LDV-III Ultra is to drive and yield stress measurements are useful in a spindle (which is immersed in the test telling the effects of processing, formulation viscous drag of the fluid against the spindle is measured by the spring deflection. Spring range of the LDV-III Ultra (in centipoises or Carbomer, type 940, carboxyvinyl cP) is determined by the rotational speed of polymer; average equivalent weight: ca.76; spindle, the container the spindle is rotating water dispersion): 2.7-3.5 was used. It was in, and the full scale torque of the calibrated spring. The LDV-III Ultra can also measure Wyoming; U.S.A. Carbomer must be measurement of viscosity of carbomer thoroughly mixed and hydrated. Increasing dispersions: LV#1, with an entry code of 61, the pH to 7.0, gives a gel structure. and LV#2, with an entry code of 62. For Neutralization can be carried out with LV#1 spindle, the spindle range coefficient inorganic bases (such as NaOH, KOH, is 6,000 while for LV#2 spindle it is 30,000. NH4OH) or with organic amines, such as Such numbers are used to evaluate the full rheometer/spindle/speed combination. The Propane-Diol (AMPD). To neutralize 1 g of accuracy of viscosity measurement for the Carbomer to pH 7, ca. 0.01 equivalent of LDV-III Ultra rheometer is ±1.0% of its full base are required (e.g. 0.4g of NaOH, 0.9g scale range for a specific spindle running at rate (i.e., different RPM) both in the forward (increasing) and backward IA is subscripted by γ& to indicate that the instrument accuracy is a function of the spindle speed, RPM (i.e., γ& ). The higher stepwise decrement in RPM value till the starting point is reached. At each step 30 seconds was allowed for the sample to reach its steady value at the given RPM. concerned, the sample was subjected to a accuracy of measurement will be ±0.01*600=±6 cP (mPa.s). For LV#2, constant shear rate for 4 minutes to see if there is a time-dependent flow behavior. The measurement was taken for each 30 second elapsing period. If the torque reading is beyond the upper limit (i.e., spindle is replaced by a smaller spindle size to assure that the torque reading lies According to the operating 100% torque reading, in general). number M/98-211-B0104, Appendix D1, pages 94-97, Table 1 shows the results for III is equipped to measure yield stress vs. values and the shear rate constant (SRC) yield strain. The yield point is the point at which is used to calculate shear rate and associated properties are the yield stress and yield strain. The yield stress is the critical shear stress, applied to the sample at which the material begin to flow as a liquid. The spindle LV1 with entry code 61 which has material, resulting from the applied stress prior to the start of flow. The operating given as 0.09373 (Table D2 of Brookfield principle is to drive a vane spindle through the calibrated spiral spring connected to a Laboratories, has n value of 4940 cP. The spindles are suitable for most fluids and are ideal for paste-like materials, gels, fluids with suspended solids, and a variety of so- called “soft solid” materials (puddings, material due to the increasing force imparted sauces). The primary benefit of the vane spindle is that it imparts minimal disruption value is the yield point. An algorithm in the to the sample during spindle immersion. The resistance of the material to movement is value into a yield stress value, expressed in values as the LDV-III Ultra motor rotates. The amount of shaft rotation is measured by the deflection of the calibrated spiral spring inside the instrument. Spring deflection is measured with a rotary transducer. There is Table1: Calculation of SMC and SRC for a particular set of spindle/container. Spindle LV#1 with entry code of 61 was used in a plastic cylinder with a radius of 22.175 mm Note: η = n for a standard solution. Table 2: Spindle codes used in yield stress yield stress values is defined as follows: Note: If the secondary immersion mark is For example, if spindle V-71 is used while the spindle is completely immersed up to constant which is given in Table 2. Thus: experiment, IAγ varied between 0.67 and 1.2 cP, with a mean IA value of 0.95 cP. In this case, carbomer dispersion up to this concentration and within the instrumental fluid. Figure 2 shows the plot of η vs. γ& at apparent viscosity value was found to be such a level of carbomer content. Again, one can see how the distribution of data standard deviation for η under the variable falls within the margin of the instrumental shear rate, γ& , experiment. The smallest value of IAγ is 0.32 cP. This simply 0.30 wt % Carbomer Dispersion
implies that within the instrument accuracy essentially constant with γ& . Figure 1 η, ( 14.75
shows the plot of η vs. γ& at such a level of distribution of data falls within the margin γ′, (1/s)
Figure 2: The apparent viscosity, η, as a 0.15 wt % Carbomer Dispersion
function of shearing rate, γ& , (s-1) for 0.30 are the same as those of Fig. 1. The IA apparent viscosity has an average value of 107.7±28.5 cP. For the variable shear rate experiment, IAγ varied between 2.8 and Figure 1: The apparent viscosity, η, as a 12.0 cP, with a mean IAγ value of 7.4 cP. function of shearing rate, γ& , (s-1) for 0.15 In this case, the variation in viscosity with γ& is significant at this stage and it is about cylinder with a radius of 22.175 mm. The IAγ margin is bounded between the two can argue that the viscosity is no longer a constant with γ& and the carbomer dispersion started to behave as a non- Newtonian fluid. Thus, there is a necessity apparent viscosity has an average value of to analyze the data in the light of this 15.06±0.51 cP. For the variable shear rate function of γ& for 0.60 wt% carbomer η, as a function of shearing rate, γ& , for dispersion. η decreases with increasing γ& ; an indication of a pseudo-plastic or shear- seen that η decreases with increasing γ& ; this type of behaviour is referred to as a 0.45 wt% Carbomer Dispersion
emulsions, and dispersions of many types. Such a behaviour may be attributed to the .s 125 Backward
carbomer molecules in a way they will be destroyed and the molecule formation will be oriented more parallel to the spindle surface. So, the hindering of the spindle structure damage is done and the less the γ′, s-1
structure of molecules slide in together, the Figure 3: The apparent viscosity, η, as a function of shearing rate, γ& , (s-1) for 0.45 are the same as those of Fig. 1 The IAγ concentration or less there is no significant rheopectic (an increase of η with shearing time) or thixotropic (a decrease of η with 0.6 wt% Carbomer Dispersion
some kind of a hysteresis loop; i.e., the exactly coincide, nevertheless, this can be P 2000 Forward
η, m 1000
accuracy. Here, the largest difference in η directions ∆η = 5.94 cP which is definitely less than the mean value of IAγ under the Figure 4: The apparent viscosity, η, as a function of shearing rate, γ& , (s-1) for 0.60 cP. For the variable shear rate experiment, IAγ varied between 11.65 and 171.40 cP implies that the variation in η with γ& is obvious than that in Figure 3. and the viscosity difference between the forward very significant. Figure 4 shows η as a than the corresponding value of IA backward direction values is larger than evaluated at the same RPM (or γ& ). For the corresponding value of IA evaluated at the same RPM (or γ& ). For example, ∆η RPM=0.35 (γ& =0.09 sec-1) is equal to evaluated at RPM=8 (γ& =2.04 sec-1) is 3257.77-2850.55=407.22 cP which is about 2.4 larger than the corresponding IA pseudo-plastic effect is prominent at such obviously larger than IAγ =30 cP, same time, the rheopectic behaviour which LV#2 at this time, unlike previous cases can be expressed in terms of the viscosity difference between shear rate forward and 0.9 wt% Carbomer Dispersion
Spindle : LV#2
regarding the effect of shearing time on η are not presented here, simply to make the increased with shearing time; an indication η, m 1800
breakdown/alignment of polymer chains or segments, whereas rheopectic behaviour Figure 5: The apparent viscosity, η, as a segments6. Shear-thinning and rheopectic function of shearing rate, γ& , (s-1) for 0.90 (or, non-thixotropic) behaviour of the pharmaceutical properties of estradiol gels has an average value of The Yield Stress, τo, Results shear rate experiment, IAγ varied between found for such dispersions, which is in line 25 and 37.5 cP with a mean value of 31.2 apparent viscosity measurements. Figure 6 η with γ& is very significant. Figure 5 shows a typical plot for the shear stress shows η as a function of γ& for 0.90 wt% versus strain for 0.45 wt% carbomer dispersion, where the sample was pre- shorn for 30 s at RPM=10 and the test was increasing γ& ; an indication of a pseudo- plastic or shear-thinning behaviour. The hysteresis loop is wide and extends over the entire range of γ& . The viscosity o, with pre-shearing is 0.17±0.009 Pa. without a pre-shearing step and the yield step of zeroing the torque reading which is usually done as a priori for the sake of comparison and treating samples equally. yields properties. This process beaks down means moving or rotating the shaft clock- the sample’s structure. It is particularly or counter-clock wise in a way to diminish the torque reading and is usually carried out at a specified constant speed (i.e., RPM) which of course results in a shearing before testing and observe the structural effect in addition to the pre-shearing step. rebuilding of the sample. The yield stress Table 3: The yield stress, τo, value for “dynamic yield”, while the yield stress 0.45 wt% Carbomer Dispersion
pre-Shear RPM=10 for 30 s
Run Speed RPM=5; Secondary Mark
τ, ( 0.075
Strain (rad)
Figure 6: The stress vs. strain for 0.45 wt% carbomer dispersion, pre-shorn for 30 s at RPM=10 and the test was carried out at RPM=5, using spindle LV#71. The dispersion at different concentrations. One behave as a Newtonian fluid, whereas for a dispersions start to exhibit a shear-thinning behavior with shear rate and a rheopectic with the highest concentration, the yield behavior with shear time. Finally, the yield stress did not change with pre-shearing. At stress results are in harmony with the shear high concentration of carbomer (i.e. 0.9 wt stress shear rate experiments in a way that below 0.45 wt%, a zero-yield stress value higher value of yield stress; an indication above 0.45 wt% of carbomer content. As a (entanglement/build-up of polymer result of shearing, the yield stress segments) took place. It should be noticed “dynamic yield”, was found to be larger dispersions”, Food Hydrocolloids, 14,
originally un-disturbed material, the “static head”; an indication of network stiffening estradiol gels”, Arzneim Forsch, 48,
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