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Brookfield AMETEK

Moisturizing Cream (Firmness)

Test Principle

Evaluate the firmness of two types of moisturizing creams by penetration using a hemispherical probe.

Background

Moisturising creams serve to keep the skin feeling smooth, soft, and looking radiant and healthy by retaining moisture or water in the outer most skin layer. Different moisturising creams will be defined by their consistency. Formulating moisturising creams therefore largely depends upon the required end product consistency, influencing the choice of material to use.

The penetration test, using a hemispherical probe, is an imitative test simulating the ease by which a human finger will deform the sample during application of the cream. This test allows the consistencies of creams to be assessed. Samples can also be tested in their containers directly from the production line.

Method

Equipment

  • CT3 with 4.5 kg load cell
  • Fixture base table (TA-BT-KIT)
  • Hemispherical probe (TA-43)

Settings

  • Test Type: Compression
  • Pre-Test Speed: 1.0 mm/s
  • Test Speed: 2.0 mm/s
  • Post-Test Speed: 2.0 mm/s
  • Target Type: Distance
  • Target Value: 25 mm
  • Trigger Force: 10g

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, 1mm/s test speed will require =1 mm/s pre-test speed.

The target distance chosen should be such that the probe does not deform the sample to more than 75% of sample depth otherwise the base effect may affect results.

Procedure

  1. Attach the hemispherical probe to the load cell.
  2. Align the sample centrally under the probe
  3. Start the test
  4. When the probe is pulling out of the sample and returning to the start position, firmly hold the sample down to prevent it from lifting.
  5. Ensure thorough wiping of the probe using a clean, dry cloth to remove all traces of adhering soap before proceeding onto the next test.

Note: When optimising test settings, the hardest sample would be better 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

The following is a typical Texture Analysis penetration plot of two different types of moisturizing cream.


Click to enlarge

The graph in Figure 1 shows the consistencies of two types of moisturising creams stored and tested at 21°C in a 40 mm diameter back extrusion container.

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


Click to enlarge

Figure 2 displays a graph of load verses distance comparing the hardness of two different moisturising cream formulations.

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

Observations

When a trigger force of 10 g is achieved, the probe begins to penetrate the sample to a defined distance (25 mm in this case). The maximum positive force then becomes force required to penetrate the sample to the specified distance by a finger. The higher the maximum force value, the firmer the sample. From Figure 1, sample A is firmer than sample B and is also more adhesive. The energy require to deform the samples can be quantified by selecting work done hardness 1 in the software. This is the area under the positive curve. As can be seen on the table below, sample A requires more energy than sample B to deform the sample to a defined deformation distance.

The adhesiveness of the samples can also be measured whereby the area under the negative curve is a measure of adhesiveness. From Figure 1, Sample A is more adhesive than Sample B.