Application

Health & Personal Care

 Introduction

Toothpastes are complex formulations. Their composition is a mixture of abrasives,
binders to keep the solid particles in suspension and to manage ribbon properties on
the toothbrush, active ingredients (fluoride…) and flavour components, amongst
many others…
The viscoelastic behaviour of toothpastes drives several end-use properties such as:

- Ribbon stand-up behaviour ;                             
- Recovery after extrusion from the tube ;
- Mouth feel;
- Storage stability (particles suspendability) ;

Rheolaser Master enables us to analyse these properties by measuring the viscoelastic
behaviour of the ribbon just after the tube extrusion.
In this note, ribbon stand-up properties of 4 toothpastes have been analysed
simultaneously with Rheolaser Master at 25°C during 10 minutes just after tube
extrusion, in order to characterise mouth feel .

 Objective

Analyse the ribbon shape stability of various toothpastes on the toothbrush, and their mouth feel.

Device

Rheolaser Master

shape stability). Indeed, the ribbon has to sit on the top of the toothbrush without losing its
shape and leak into the toothbrush.
The Figure 1 (below) reports the Solid Liquid Balance (SLB) of each sample. The
SLB ranges from 0 (pure solid behaviour) to 1 (pure liquid behaviour), when SLB
equals 0.5, there is a perfect equilibrium between solid and liquid behaviour in the
product. Thus a product having a low SLB has a good stand-up property as it
behaves more as a solid. The lower is the SLB value, the better is the shape stability
of the ribbon on the brush, and the less the paste will flow into the toothbrush bristles.

Sample 4 has a weak shape stability as the liquid behaviour dominates during the
first minutes after extrusion. The paste sinks into the toothbrush. Sample 1 has the lowest
SLB meaning a better shape stability. Samples 2&3 have an intermediate behaviour,
and during the first 2 minutes, sample 3 has a better behaviour than sample 2.

 The shape stability of the 4 toothpastes studied in this example can then be ranked
as follows:

Note: during the sampling, both viscosity and elasticity decrease because of the
shear which is applied as the paste is extruded from the tube. Then, the paste
recovers its structure to guaranty a good shape stability. The recovery time is very
toothbrush), and we can see in the Figure 1 that samples 3 and 1 have a very short
recovery time (SLB is almost immediately at an equilibrium value), while sample 4
takes a very long time to recover (still not at the equilibrium after 10 minutes).

Mouth feel properties
Formulators must find a good compromise             
between a good ribbon stand-up behaviour
(strong solid like-behaviour, low SLB value),
and a good mouth feel ranging from hard
(stiff) to soft (creamy).
The Figure 2 reports the evolution of Elasticity Index (EI) of the 4 studied samples
during the first 10 minutes after tube extrusion.

 Sample 4 is the softest compared to the other toothpastes, while Sample 3 is the
stiffest. Samples 1 and 2 have an intermediate behaviour.
It is noticeable that the elasticity increases for Samples 2, 3 and 4, while it is almost
constant immediately for Sample 1, meaning that the structure has been less
affected by the shear for this last one. 

Rheolaser Master offers:
- 1-click experiment & results ;
- Measurement at rest ;
- Non intrusive measurement ;
- Ageing analysis on the very 
  same sample ;

Summary
Monitoring the viscoelastic properties of the toothpastes right after the extrusion from
the tube enables the user to characterize key end-use properties of the formulated
product such as stand-up of the paste on the toothbrush and mouth feel during 
brushing. The use of Rheolaser Master will allow the user to adjust the formulation and easily
monitor the effect on the toothpaste.
Rheolaser Master is a powerful tool, which can fully and easily characterize, in real
time, the viscoelasticity of such products during the processes. The measurement is
is a non-contact method and analyse the sample without any
external influence over ageing time.