Case study: Measuring the texture of a shampoo

PRINCIPLE OF THE TEST

Compare the consistencies of two types of shampoo (premium shampoo and economy shampoo) by front and rear extrusion.

CONTEXT

The formulation of shampoos depends largely on the required consistency of the final product, thus influencing the choice of material to be used. Shampoos usually contain 70 to 80 % water, detergent and preservatives. Most shampoos also contain oils, sulfates, and alkanolamides to improve the texture and foaming ability of the shampoo, along with other chemicals to enhance shine and condition the hair.

Shampoos can be tested at different points in the development and production process for sample texture, among other factors. A desirable factor in product development is to have product that flows easily from a tube, leaving minimal residue on the edge of the tube after crushing. Achieving such a product requires a good sample thickness (viscosity) which produces the desired consistency.

Through the use of front and rear extrusion tests, the consistency of the samples can be assessed. The forward extrusion simulates the force required by the consumer to extrude the sample and the backward extrusion an indication of physical product failure and flow properties.

METHOD

Equipment : CT3 with 4.5 kg load cell

Luminaire base table (TA-BT-KIT)

Double extrusion cell (TA-DEC)

TexturePro CTParameters:

Type of test: Compression

Pre-test speed: 1.0 mm / s

Test speed: 2.0 mm / s

Post-test speed: 2.0 mm / s

Target value: 25 mm

Trigger force: 30g

Additional materials:

Double extrusion cell diameter 40 mm with blank plate

Plunger with disc 38 mm in diameter or less

Remarks :

It is recommended that the pre-test speed be equal to or less than the test speed for accurate trigger detection; for example, a test speed of 2 mm / s will require a pre-test speed ≤ 2 mm / s. The chosen target distance must be such that the probe does not touch the base container, otherwise the instrument will be overloaded (do not exceed 75 % depth of the sample).

PROCEDURE

Remove the sample kept at a specific temperature (eg, 21 ° C) from storage.

Fill the extrusion cell with the sample up to approximately 75 %.

Position the extrusion piston in the center of the extrusion cell.

Start the test.

RESULTS

Comparison of the consistencies of two types of shampoo by front and rear extrusion:

Figure I is a loaded graph over time showing the consistencies of two types of shampoo stored and tested at 21 ° C in a 40mm diameter extrusion container.

Data set # 1: Sample A (premium shampoo)

Data set # 2: sample B (economy shampoo)

Figure II is a load / distance graph showing the consistencies of two types of shampoo.

Data set # 1: Sample A (premium shampoo)

Data set # 2: sample B (economy shampoo)

OBSERVATIONS

When a trigger force of 10 g has been reached, the disc piston begins to penetrate a specified distance (25 mm) after which the probe returns to its starting position. The maximum force during probe descent, represented by a peak on the graph, measures firmness; the higher the value, the firmer the sample. The area below the positive part of the graph indicates the consistency of the sample (work performed up to hardness1); the higher the value, the thicker the sample and the higher the consistency. When the probe returns to its starting position, the initial lift of the sample weight onto the top surface of the disc produces the negative portion of the graph resulting from the back extrusion. This gives an indication of the cohesion and resistance of the sample to separate (flow) from the disc. The maximum negative force on the graph indicates the adhesive strength of the sample; the more negative the value, the more “sticky” the sample.

The area below the negative part of the graph is known as adhesion (the energy required to break the contact of the probe with the sample) and can give an indication of the cohesive forces of molecules in the sample. The higher the value, the more energy it takes to break the contact of the probe with the sample when the probe withdraws from the sample. From Figure 1, Sample A is firmer and has a higher consistency than Sample B. In addition, Sample A has a higher adhesive component than Sample B.