Case Study: Lipstick Curvature and Hardness Test

PRINCIPLE OF THE TEST

To determine the firmness of lipstick by folding samples with a Lipstick Cantilever Device (TA-LC) using a CTX texture analyzer.

CONTEXT

Lipstick is a cosmetic product applied to the lips to add texture, color and protective benefits. Lipsticks come in many shades and styles. The ingredients include wax for the structure, oils for a shiny or shiny appearance, pigments for the color and emollients to smooth and soften the skin.

Lipsticks were stored at room temperature for 24 hours before testing. A CTX texture analyzer with a 1.5 kg load cell was used with a TA-LC apparatus to perform a bend test.

This test bends the lipstick a set distance and measures the force required to bend the lipstick. This folding test measures the firmness of the lipstick. As the probe retracts, the stickiness of the lipstick will be measured. The lipstick samples will be placed inside the lower TA-LC holder, attached to the base table of the holder (TA-BT-KIT). When the probe is lowered over the sample, it will make contact and bend the lipstick. This will provide data on the hardness of the lipstick.

METHOD

Equipment : CTX with 1.5 kg load cell (XCTX)

Luminaire base table (TA-BT-KIT)

Lipstick Cantilever Fixing (TA-LC)

Texture Pro Software (SWL-02-111)

Settings :

Type of test: Compression

Test speed: 1.0 mm / s

Target type: Distance

Target value: 7 mm

PROCEDURE

1. Attach the TA-LC probe to the CTX texture analyzer.
2. Insert two table bolts into the slots in the analyzer base.
3. Place the fixture base table on the CTX and lightly tighten the bolt nuts.
4. Adjust the table so that the probe is in the center of the table. Attach the TA-LC bottom to the base table. Lightly tighten the side screws.
5. When alignment is complete, secure the base table by tightening the bolt nuts.
6. Place the lipstick sample in the hole on the TA-LC bottom. Extend the lipstick 12.5mm beyond the tube and tighten the screw.
7. Align the sample under the probe in the center.
8. Position the probe approximately 3 mm above the sample.
9. Set the test parameters using Texture Pro software.
10. Start the test.
11. Wipe the probe with a dry cloth after testing each sample.
12. Repeat steps 1 through 11 for all test samples.

OBSERVATION

When a trigger load of 10g is detected on the surface of the sample, the probe begins to bend the lipstick sample at a test speed of 1mm / s for a specified distance of 7mm. Once the distance of 7 mm is reached, the probe returns to the starting position.

The Load vs. Time (Fig. 6) indicates the hardness of the sample (maximum load) and the stickiness (adhesive force). The adhesion is the total area under the negative curve found in the Load vs Distance graph (Fig. 7). It indicates the work done on the sample to bend it a defined distance and the adhesion of the sample.

Typical load versus time graph. The axes are the Load (g) vs. Dry weather)

Typical load vs. Distance. The axes are Load (g) vs Distance (mm)

DISCUSSION

The maximum force value is the maximum load. It is a measure of the "hardness" of the sample. The higher the value, the harder the sample. The higher the maximum load, the more work is required to bend the sample. Adhesive strength is the amount of force required to overcome the attractive bonds between the sample (lipstick) and the external surfaces in contact with it (probe). Stickiness is the amount of work required to move the sample away from these external surfaces.

DATA REPORT

TexturePro software is used to program and control the CTX Texture Analyzer during experimental testing. It automatically calculates the maximum load values and the hardness work performed. Multiple samples can be analyzed if desired, and the calculated values for the standard deviation can be reported.