Toothpaste Compound Science Project?

Well it goes like this I have a science project and I remembered an experiment where the toothpaste pack is empty and after heating a little bit it inflated I want to know why it inflates and what compound is responsible fot the inflating of the pack.

Toothpaste Compound Science Project?
i can%26#039;t find the experiment, but maybe this info. will help you figure things out. good luck.





CHEMTECH


December 1995


Copyright © 1995 by the American Chemical Society.





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Squeezing out a better toothpaste


Michael Prencipe James G. Masters


K. Penny Thomas James Norfleet





Dental creams are complex mixtures. They contain ingredients


that provide important therapeutic and cosmetic


benefits, such as fluoride, triclosan, and tartar


control agents. The trick is getting them to still taste good


and stand up on your toothbrush.


Formulating dental creams for consumer acceptance requires optimizing many physical and chemical attributes. Much work has been done to develop toothpastes that are not stringy, do not show separation of a liquid phase from the dentifrice, and do not increase in viscosity on aging (1-5). Dentifrices also must have an appealing taste for consumers to keep buying the product. Along with consumer tests and sensory evaluations, analytical data on flavor composition and flavor release is usually obtained using gas chromatography while new dental creams are being created. These quantitative data can show the interactions between flavor and other dentifrice components and are a very useful tool in the formulation process. Finally, active ingredients such as fluoride, tartar control agents, and triclosan must be blended in such a way that their activity is not lost.





Dental creams are complex dispersions. Toothpastes are mixtures of abrasives and surfactants; anticaries agents, such as fluoride; tartar control ingredients, such as tetrasodium pyrophosphate and methyl vinyl ether/maleic anhydride copolymer; pH buffers; humectants, to prevent dry-out and increase the pleasant mouth feel; and binders, to provide consistency and shape (Table 1). Binders keep the solid phase properly suspended in the liquid phase to prevent separation of the liquid phase out of the toothpaste. They also provide body to the dentifrice, especially after extrusion from the tube onto the toothbrush. Table 2 lists typical ingredients used in formulations; the final combination will depend on factors such as ingredient compatibility and cost, local customs, and desired benefits and quality to be delivered in the product.








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TABLE 1. Components of toothpaste


Ingredients Wt%


Humectants 40-70


Water 0-50


Buffers/salts/tartar control 0.5-10


Organic thickeners (gums) 0.4-2


Inorganic thickeners 0-12


Abrasives 10-50


Actives (e.g., triclosan) 0.2-1.5


Surfactants 0.5-2


Flavor and sweetener 0.8-1.5





Fluoride sources provide 1000-15000 ppm fluorine.





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TABLE 2. List of typical ingredients


Gums Inorganic Thickeners Abrasives Surfactants Humectants Tartar Control Ingredient


Sodium carboxymethyl cellulose Silica thickeners Hydrated silica Sodium lauryl sulfate Glycerine Tetrasodium pyrophosphate


Cellulose ethers Sodium aluminum silicates Dicalcium phosphate digydrate Sodium N-lauryl sarcosinate Sorbitol Gantrez S-70


Xanthan Gum Clays Calcium carbonate Pluronics Propylene glycol Sodium tri-polyphosphate


Carrageenans Sodium bicarbonate Xylitol


Sodium alginate Calcium pyrophosphate Sodium lauryl sulfoacetate Polyethylene glycol


Carbopols Alumina











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Know the flow


Toothpaste must have certain flow properties to be accepted and liked by the consumer. The formulation should not separate into liquid and solid phases with aging. The dentifrice must be easy to dispense from a toothpaste tube yet have excellent ribbon qualities, which enable it to stand up after it is extruded onto toothbrush bristles. Furthermore, the ribbon should not exhibit a long string. This is particularly important because stringy toothpastes contribute to messiness around the cap, which the consumer dislikes. To predict these consumer-perceivable attributes, we study the rheology of the toothpaste.





Rheological properties are measured at a constant temperature of 25 degrees C using a parallel plate geometry. The plates are 4 cm in diameter with a constant gap distance of 1000 micro meter. Three types of measurements are conducted with the rheometer: The first involves creating a flow curve in which the shear rate is measured as a function of applied stress. This measurement is used to predict ease of dispensing from a toothpaste tube and the stand-up properties. The flow curves (shear stress vs. shear rate) yield information on the strength of structure at rest (yield stress) and how easily the three-dimensional network will break down (shear thinning) at high applied stresses. An apparent yield stress can be obtained at a very low shear rate (%26lt;0.10/s), which approximates conditions at rest. With higher apparent yield stress, the product exhibits more structure and is less likely to be runny.





Creep studies are performed to monitor changes in strain or structural deformations in response to a constant applied stress over a period of time. The linear portion of creep curves yields the Newtonian viscosity. Measured at high applied stresses (400-500 Pa), the Newtonian viscosity can be used to predict ease of squeezing; at low applied stresses (50 Pa), it can be used to predict how runny the toothpaste will be when squeezed out of a tube.





Dynamic oscillatory experiments are also conducted on toothpaste. An oscillatory stress is imposed on the material, and the resulting shear strain response (degree of deformation) is measured. The stress measurement has two components: one in phase with the displacement (elastic modulus, G%26#039;) and one 90|SD out of phase (loss modulus, G%26quot;). The ratio of G%26quot;/G%26#039; is known as the tangent delta and is a measure of the relationship between the elastic and viscous natures of the dentifrice. Highly elastic structures (tangent delta %26lt;1) are less subject to phase separation during the aging process. They also recover more quickly after a stress is imposed on the toothpaste.





Additionally, dental cream viscosity measurements are conducted to gain information on the overall thickness of the product.





The string properties of dental creams may be important not only as a contributor to the messiness of the product but also in how they affect the processing of the product, for example, in the latter stages of tube filling. This attribute can be qualitatively determined in the laboratory by measuring the conductivity of toothpaste sandwiched between two separating plates. The stringiness index is measured on the basis of current versus time curves and is unitless: High stringiness values indicate messy dentifrices.





Runny is not good


Toothpaste formulations exist as a three-phase system: the continuous phase, which contains humectants, water and dissolved salts; the dispersed phase, made up of an emulsion (surfactants and flavor oils) and the binders (gums) used to gel the continuous phase; and the solid phase, which is mainly the abrasive system of the dentifrice. The solid phase is suspended throughout the continuous phase by the gel network formed with the binder system. To study the effects within the continuous phase, factorial design experiments were performed to identify how continuous phase ingredients control or affect the rheological properties of dental creams. The design focused on simultaneously varying the water and humectant levels; a D-optimal design was chosen (D-optimal designs are optimizations of a particular set of parameters based on a model fitted using iterative methods). The systems investigated included simple gel phases and complete dental creams. Optimization of humectant systems revealed that higher water levels in the formula yielded dentifrices with lower stringiness, as shown in Figure 1. At constant humectant levels, increasing the water in the formula resulted in a significant decrease in the toothpaste string properties, leading to a more desirable, low-string toothpaste (6).











To Enlarge Figure 1


Figure 1.


At constant humectant levels, increasing the water in the formula resulted in a siginificant decrease in the toothpaste string properties. Factorial design experiments were performed simultaneously varying the water and humectant levels to determine string value.








In parallel studies, systems were formulated with carboxymethyl cellulose (CMC) and iota carrageenan (IC) binders.





Preparations containing these two polymers were compared. CMC is a carbohydrate polymer that is sufficiently water soluble to swell and thicken aqueous solutions. The carboxylate anion imparts this feature; it is readily soluble in water and inhibits intramolecular association through electrostatic repulsion. Carrageenans%26#039;s solubility is from nonuniformity in the repeating structure and the sulfate ester groups. Carrageenans are extracted seaweed that have galactopyranosyl repeating units where the anomeric linkage varies between beta (1 - 3) and alpha (1 - 4) (7). Its three-dimensional helical structure allows the gum to form gels and to have a yield point (the stress below which no flow occurs).





In simple gel systems, CMC provides viscosity primarily through thickening, where the tangent delta is %26gt;1. IC produces thermally reversible elastic gel networks because of its three-dimensional helical structure. Simple systems formulated with IC binder exhibit a tangent delta %26lt;1.





Tangent delta


Gum Simple gels Complete dentifrice


CMC 1.08 0.49


Iota 0.36 0.28











Additionally, when the elastic modulus is plotted as a function of frequency at constant strain, the more elastic IC-thickened gel produces an elastic modulus (G`) that is less dependent on frequency than CMC. This indicates more robust, solidlike structure characteristic of gel structures with IC rather than simply thick solutions (8). However, the optimized tangent delta values for complete dentifrices are %26lt;1 for both gums, indicating that interactions of the binders with other ingredients play a major role in defining rheology of toothpastes.





An example of a toothpaste formulated with all the desirable rheological properties is Colgate%26#039;s Micro Cleansing Tartar Control Formula (MCTC), which contains a new abrasive called Micro Cleansing Crystals for enhanced cleaning and a desirable mouth feel (9, 10). This toothpaste was particularly challenging to formulate because of the special silica abrasive, which was engineered to clean dental stains but not impart the usual thickening effect observed from regular silica particles. MCTC was formulated with an optimal amount of water, to minimize stringiness, and a dual-gum system, which comprises a combination of CMC and IC to obtain all the desired consumer-perceivable attributes. Table 3 contains a summary of the effect of gums on the rheological properties of MCTC with an optimized water level for reduced string. The gums were used in concentrations based on standard toothpaste compositions. Data indicate that the dual-gum system currently being used in MCTC is preferred over IC or CMC alone.











TABLE 3. Rheological properties of Colgate%26#039;s Micro Cleansing Tartar Control formula with different binder systems


Binder NV at 50 Pa applied stress,Pa.s Shear stress at 0.01s-1, Pa NV at 450 Pa applied stress, Pa.s Tangent delta Brookfield viscosity, x10,000 cps Stringiness Index


CMC and IC 3422 32 59 0.398 30 4.7


CMC 1380 11 47 0.380 23 5.9


IC 139 18 4 0.186 12 6.1





NV, Newtonian viscosity; CMC, carboxymethyl cellulose binder; IC, iota carrageenan binder. Brookfield viscosity is measured using the Brookfield viscometer, model DV-11, with spindle E, at 5 rpm. Stringiness index is measured on the basis of current versus time curves and is unitless.








At 0.01 s -1 shear rate, the corresponding stress for the CMC-and-IC formulation is significantly higher compared with the CMC- or IC-thickened dentifrice (Table 3). These data confirm results obtained from the creep experiments, which showed that the dual-gum system has more structure at rest, will not be runny, and will exhibit excellent stand-up properties. MCTC with the dual-gum system has a comparatively low Newtonian viscosity at high applied stresses (450 Pa), as does the CMC dental cream, indicating that it will be easy to squeeze out of a tube. All the dentifrices listed in Table 3 have highly elastic networks that yield products more stable against phase separation and that exhibit a quicker rate of recovery after being sheared. Increasing the gum levels of the CMC dentifrices and the IC dentifrices to decrease runniness will result in products that are more stringy and harder to extrude from a tube than the dual-gum toothpaste. In addition, IC is a more expensive gum and therefore will increase the cost of a paste made with it alone.





An undesirable property of some dentifrice formulations is an increase in viscosity as a function of time, also known as progressive thickening. The Brookfield viscosity of MCTC with the dual-gum system was measured as a function of time.








Time Tangent delta Brookfield viscosity,


X10,000 cps


72 h 0.431 31


1 week 0.398 30


2 weeks 0.291 30


4 weeks 0.248 29











Tangent delta values were determined from oscillatory measurements taken at 1.00 rad/s. Data show that no undesirable changes in the rheological properties of the MCTC formula occur over long periods of time and that the product is very stable.





Flavor release


Flavor influences whether the consumer will like the product enough to purchase it again. The extent to which dentifrice flavor interacts with the product%26#039;s continuous phase and the abrasive profoundly affects how the flavor will be perceived by the consumer. The effect of various types of surfactants on dentifrice systems can also be important. Previous work has shown that volatile flavor components of toothpastes diluted with water were significantly reduced by surfactants such as alkyl polyglycosides compared with sodium lauryl sulfate, methyl cocoyl taurate, and sodium dodecylbenzene sulfonate (12). This in vitro work has also been found to correlate well with sensory studies.





Flavor release measurements, along with sensory evaluations from flavorists and consumers, constitute another method the formulation chemist can use to achieve the optimal dentifrice preparation. The analytical technique used to measure the effect of dentifrice components on flavor release also yields insights into the interactions occurring in the dental cream (13). Different continuous-phase compositions can have an effect on flavor release that can ultimately change taste perceptions.





Headspace gas chromatography is often used to measure the flavor release from neat dentifrices as well as from toothpaste slurries diluted with water (11). Gas chromatographic profiles of complex flavor mixtures show many peaks. A mathematical technique called principal component analysis is used to better visualize and represent the changes that occur as a function of the different toothpaste ingredients. A plot of the first two principal components (those with the greatest variance) obtained from the headspace profile of neat dental creams and of creams diluted 1/1 and 1/3 (wt/wt) with distilled water is shown in Figure 2. The value represented by the principal component on the y-axis relates to the interaction between flavor components and other toothpaste ingredients, such as the abrasive. The principal component along the x-axis is related to the effect that dilution has on the flavor release profiles. For example, the dentifrice containing dicalcium phosphate dihydrate as the abrasive exhibits more flavor release in to the headspace than toothpastes formulated with silica. Thus the calcium-based abrasive does not interact to any significant extent with the flavor components compared with silica. Also, the low-water silica formula released more flavor than the high-water formula. However, because the water has an effect on both stringiness and flavor release, these two parameters must be carefully balanced to achieve the optimal toothpaste composition.











To Enlarge Figure 2


Figure 2.


Dicalcium phosphate dihydrate-containing toothpastes interact with flavor compounds to a lesser degree than silica dentifrices. Low water silica formulations (middle) have a better flavor release than high-water silica formulas (bottom). Arbitrary values indicate variance from normal (N) readings








To Enlarge Figure 3


Figure 3.


Hydroxyapatite has the highest affinity for and is the least compatible with sodium fluoride, whereas silica has the smallest heat of adsorption. The heats of adsorption of sodium fluoride with the abrasive systems were measured by first equilibrating the solids with a humectant-water solution and then injecting a solution containing humectant, water, and 1500 ppm ionic fluorine from sodium fluoride at pH 6.8.





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Active agents


Another important consideration when formulating dentifrices is the incorporation of active ingredients. Currently marketed dentifrices are complex, multifunctional formulations that not only provide basic cleaning of the tooth and gum surfaces but also are used as delivery vehicles for ingredients active against diseases such as caries and gingivitis. Fluoride salts have been used extensively for the past 25 years to reduce the incidence of caries in the general population. More recently, the introduction of triclosan in toothpaste (15-17) has made formulation even more challenging. Dentifrice components commonly used in toothpaste must be formulated so that they do not interfere with the activity of these ingredients.





Sodium fluoride, sodium monofluorophosphate, and stannous fluoride are the most common fluoride sources used in toothpaste. Great care must be taken in the formulation of these agents so that their anticaries activity is not reduced by other dentifrice ingredients, such as the abrasive system. For example, whereas sodium monofluorophosphate is compatible with both silica and dicalcium phosphate dihydrate abrasives, sodium fluoride is most compatible with the silica abrasive at neutral pH values. This can be shown by measuring heats of interactions between an active ingredient and a solid surface under steady-state flow conditions. The exothermic heats measured for dicalcium phosphate dihydrate, silica, and hydroxyapatite are presented in Figure 3. The results indicate that, because hydroxyapatite has the largest heats of adsorption per unit area measured (-277 mJ/m2), it has the highest affinity for and is the least compatible with sodium fluoride, whereas silica has the smallest heat of adsorption (-0.10 mJ/m2) and is the most compatible. The absence of interactions between sodium fluoride and abrasive means that the active agent will not be trapped at the abrasive surface, but will be released in the saliva during the brushing process.





Sodium fluoride, which in aqueous solutions dissolves to give ionic fluoride, can be trapped by the silica abrasive at pH values significantly %26lt;7. The significance of pH on fluoride availability is demonstrated by the loss of soluble fluoride in supernatants of toothpaste/water slurries. This loss is most noticeable when soluble fluoride is measured using minimal water dilution. For example, dentifrices at pH 5.8 that were diluted 1/1 by weight with water showed a 47% reduction in soluble fluoride compared with the same formula at pH 7. At a dilution of 1/3, a 20% reduction was found. It is important to note that, with saliva in the mouth, the final dilution of toothpaste encountered during brushing is about 1/3.





Triclosan is a noncationic antibacterial agent now being used by all the major toothpaste manufacturers as a way of reducing gingivitis, a disease that can lead to redness and bleeding of gums. Colgate Palmolive has developed a delivery system that can enhance the efficacy of triclosan (18). Surfactants play a significant role in inhibiting or enhancing its activity; strong surfactant triclosan interactions will not allow the antibacterial agent to be effectively delivered to the oral tissues. Figure 4 shows the comparative heats of solubilization of triclosan with two types of surfactants: sodium lauryl sulfate, which is an anionic surfactant, and Tween 80, which is nonionic in nature. Curves obtained with a batch calorimeter indicate that much stronger interactions exist between triclosan and Tween 80 than between triclosan and sodium lauryl sulfate. In fact, nonionic surfactants can bind so strongly to triclosan that they can completely inactivate it.











To Enlarge Figure 4


Figure 4.


Curves obtained with a batch calorimeter indicate much stronger interactions exist between triclosan and Tween 80 than those that exist between triclosan and sodium lauryl sulfate.








Complexity


Not very long ago, dentifrice formulations were fairly simple and contained only a few ingredients. They have become far more complex because of the incorporation of agents that provide important therapeutic and cosmetic benefits, such as fluoride, triclosan, and tartar control agents. These ingredients usually are not inert and require careful selection of toothpaste components with which they are compatible. Additionally, toothpaste must still taste terrific and display the excellent physical properties to which the customer is accustomed. Meeting these needs is increasingly more difficult. Preparing such dental creams requires formulation experience and a sound knowledge of the physicochemical properties of the raw materials, surface and colloid chemistry, and rheology.











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