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Brookfield AMETEK

Toothpaste

Test Principle

Compare the firmness / “force to extrude” of two toothpaste formulations.

Background

Toothpastes that meet consumer expectations will have no lumps, graininess or air bubbles, and good consistency. These qualities are in turn influenced by the selection of raw materials, manufacturing procedure and quality control.

Toothpastes should have a good thickness (viscosity) and a low thixotropy so that, when squeezed out of a tube, a clean break off is achieved when the desired amount has been extruded. The toothpaste should also be firm enough as not to sink in, but stand up well on the brush.

Binders in toothpaste play a crucial role in sample texture as they control or modify toothpaste rheology in terms of viscosity, thixotropy, and yield value. Binders will often be used in combination to achieve a desired consistency. The texture and consistency of a toothpaste is therefore controlled by adjusting the binder content, as well as the solids-to-liquids and water-to-humectants ratios. The abrasive surface area and particle size will also affect the concentration of binder necessary to achieve a desired viscosity.

The CT3 Texture Analyser extrusion test is an imitative test for the ease of extrusion of toothpaste. Results are influenced by product formulation and extrusion temperature.

Method

Equipment

  • CT3 with 4.5kg load cell
  • Toothpaste Extrusion Jig
  • Product Catchment Tray

Settings

  • Test Type: Compression
  • Pre-Test Speed: 1.0 mm/s
  • Test Speed: 1.0 mm/s
  • Post-Test Speed: 10.0 mm/s
  • Target Value: 15 mm
  • Trigger Force: 5g

Note: It is recommended that the pre-test speed be the same as or less than the test speed for accurate trigger detection; for example, 2mm/s test speed will require =2 mm/s pre-test speed.

The target distance chosen should be such that the probe does not touch the base of the container, otherwise the instrument will be overloaded (do not exceed 75 % of sample depth).

Sample Preparation

Equilibrate selected samples (with no prior deformation or squeezing) at a controlled temperature.

Procedure

  1. Set-up the extrusion rig with the hemispherical probes in line with each other.
  2. Adjust the extension bar on the lower fixture to a distance enough to separate it from the hemispherical probe and support the toothpaste tube such that it is squeezed around its central point.
  3. Support the base of the tube cap with the extension bar.
  4. Place the product catchment tray below the toothpaste cap to collect the extruded sample.

Note: For comparison purposes, use standard tube size and support distance to ensure that tubes are always squeezed at the same position; e.g., 40 mm for a 50ml tube.

For differing diameters and toothpaste tube sizes, the distance of compression in the Texture Analyser settings may need to be adjusted relative to the sample.

The distance set should be such that upon compression, the two sides of the tube do not meet as this may cause a force overload and wrong interpretation of the maximum force.

When optimising test settings the hardest sample would be tested first in order to anticipate the maximum testing range required. This will ensure that the force capacity covers the range for other future samples.

Results

A comparison of an extrusion test on 2 toothpaste formulations:


Click to enlarge

The Figure 1 graph shows the work of extrusion and firmness of two formulations of toothpaste in 100 mL tubes tested at 21°C. For comparison purposes, a constant support distance of 80 mm between the extension bar and the lower hemispherical probe was used.

Data Set #1: Sample A (Premium toothpaste)
Data Set #2: Sample B (Budget toothpaste)


Click to enlarge

The graph in Figure 2 shows the load verses distance for the work of extrusion and firmness of two formulations of toothpaste

Data Set #1: Sample A (Premium toothpaste)
Data Set #2: Sample B (Budget toothpaste)

Observations

When a 5g trigger force has been achieved, the upper fixture begins to compress the tube to a distance of 15 mm. The force required to extrude (squeeze) the toothpaste out of the tube to a specified compression distance provides the peak force value. The higher the resulting force for a sample, the more difficult it is to extrude. Hence from the graph, Sample B is more firm and therefore requires more force to extrude the toothpaste out of the tube than Sample A. The premium sample demonstrates a greater ease of extrusion than the budget sample as shown by the energy required to extrude sample (Hardness work done1).

Toothpaste containing air pockets typically show a sharp drop in force as seen with Sample B (see Figure 1 at 2.5 seconds or Figure 2 at 2mm) as the air bubble is extruded.

Test results for 3 toothpaste samples give mean maximum force and mean area values as follows:


Click to enlarge