Case Study: Lipstick Texture Measurement

PRINCIPLE OF THE TEST

The objective was to compare the bending force of two brands of lipsticks; premium lipstick and economical lipstick.

CONTEXT

For lipstick users, there is a general preference for a product that will not crease, crumble, crack or break during application. As such, the basic ingredients become of prime importance in formulating a product endowed with strength and physical strength capable of withstanding the application of firm lipstick by the user.

The cantilever test is a mimic test using a hemispherical edge probe to simulate the bending action caused during application.

METHOD

Equipment: CT3 with 4.5 kg load cell

Cantilever Lipstick (TA-LC)

TexturePro CTParameters:

Type of test: Compression

Pre-test speed: 1.0 mm / s

Test speed: 1.0 mm / s

Post-test speed: 10.0 mm / s

Target type: Distance

Target value: 7 mm

Trigger force: 20 grams

Note: It is recommended that the pre-test speed be the same or slower than the test speed for accurate trigger detection; for example, a test speed of 1 mm / s will require a pre-test speed ≤ 1 mm / s.

SAMPLE PREPARATION

Condition the sample to temperature before testing. In this test, the samples were conditioned at 21 ° C overnight.

PROCEDURE

Attach the fixture base table to the machine base and install the cantilever base plate onto the fixture base table.

Secure the sample in the hole of the holder device.

Unroll lipstick to its maximum length

Position the upper bending device so that it hits the sample approximately 3-4mm from the tip. This will allow the sample to bend in response to the force applied by the hemispherical lip-shaped probe mimicking the application of lipstick to the lips.

RESULTS

A typical TexturePro CT plot of bending force on two different lipsticks:

The graph in Figure I shows the flexural strength of two different 4g lipsticks tested at 21 ° C and 3mm from the tip of the lipstick.

Data set # 1: Sample A (premium lipstick)

Data Set # 2: Sample B (Economical Lipstick)

The graph in Figure II shows the load versus distance for the bending force of two different 4g lipsticks.

Data set # 1: Sample A (premium lipstick)

Data Set # 2: Sample B (Economical Lipstick)

OBSERVATIONS

When a trigger force of 20 g is reached, the probe begins to descend to a strain distance of 7 mm. During this time, the sample is bent until it comes off (in some cases).

The hardness of the sample can be obtained from the maximum force value on the graph and the stiffness of the sample (apparent modulus) from the gradient of the slope during the bending action. The distance at which the fracture occurs (strain at peak load) gives an indication of the brittleness of the sample. Typically, a brittle specimen has a short bend distance. The energy required to bend the lipstick can be quantified by selecting (work done hardness1 in the software), this also gives a good indication of the consistency of the lipstick. From the graph, sample A (premium lipstick) is twice as hard as sample B (economy lipstick). Sample B is also more fragile than sample A which ruptures in two seconds.

The test results of two lipstick samples give the following values: