Use rheology to formulate sealant formula

To understand the rheological properties, promote the research and development of sealants, and promote the process of product differentiation

Quantitative testing of the structure, flow characteristics, and rheology of sealants can help formulators understand the relationship between formula components and their effects on application characteristics
.
This article demonstrates the relationship between the raw material variables and rheology of the formulated sealant as well as the application performance
.
First, a brief introduction to the corresponding rheological conditions of the sealant is made on the coating online coatingol.
com
.

The experimental research content of the formulation components includes the ratio of pigment to base, the amount of surfactant added, the content of volatile matter and the amount of rheology modifier
.
Understanding rheological properties can significantly promote the development of sealants and promote product differentiation
.

Routine test

C920 or C834 in the American Society for Testing and Materials Standards (ASTM) of sealants stipulates the standards of sealants

The development of sealants begins with formulation; the combination of polymers and other ingredients must be consistent with product requirements
.
The next step is application; it involves applying pressure to squeeze the sealant out of the hose, and then using a tool to apply the sealant to the joint
.
Finally, the sealant must dry out within a reasonable timetable and achieve the desired curing performance; the sealant must be elastic, have good adhesion and cohesion, and have an appearance that meets the requirements
.
The traditional sealant development process is repeated over and over again, and the basis of this process is continuous experimentation, trial and failure
.

Routine tests for wet sealants include knocking and scratching
.
The tapping method is shown in Figure 1a.
The sealant sample is placed on a flat surface, and the finger taps gently on the sample to imitate the lifting and lowering action of a tool or finger pressing the sealant into the joint
.
The evaluation value from 1 to 3 is specified here.
After the finger is removed, there is no spike is 1 and the big spike is 3
.
The scribing method is shown in Figure 1b, placing a ball of sealant on a flat surface
.
It is necessary to slide the fingers gently, and to make the sealant be applied to the end.
As the fingers are quickly removed, the remaining sealant can leave trailing marks
.
This method also specifies an evaluation value from 1 to 3.
1 means that the tailing of residual sealant is the least, and 3 is the most tailing
.

Routine tests are subjective, especially these tests rely on a single finger to carry out
.
For those experienced in sealants, the one-finger method may be acceptable
.
However, what is more useful is the objective and quantitative test data of sealant material properties, which can be measured by rheological methods-especially oscillatory rheology
.

Rheology test

Oscillatory rheology provides quantification of the fluid and elastic properties of materials

Examples help to clarify the meaning of G'and G"
.
For example, water is at the end of the fluid range and is the purest liquid; when water is sheared, it deforms, and the energy brought by the shear is dissipated
.
Water.
It is completely the characteristic of G"
.

On the other hand, if the rubber band is stretched with a quantitative force, as long as it is stretched, the deformation will be maintained
.
This results in the elastic characteristic G'of the rubber band
.
Many materials have properties between water and rubber; these materials are viscoelastic
.
Sealant falls into this category
.
The relative value of G'and G" can provide all the behavioral information related to the sealant
.
Rheology is a powerful tool that connects the customer's application experience with the measurable characteristics of the material
.
The target parameters are measured by a rheometer Detection, thereby accelerating product development
.

As shown in Figure 2, the process of oscillating rheology is usually used to simulate the construction of the sealant
.
This process originated from Megz1
.
In practical applications, the process of sealant being processed by tools is shown by the sealant sample placed in the rheometer.
The rheometer simulates the processing of the sealant by the tool and provides the characteristic data of the sealant
.
The curve in Figure 2d shows the modulus, viscoelastic characteristics and fluid characteristics.
This curve is formed based on the time and stress during processing
.
At the beginning of the test, when the tool or finger starts to process the sample, the sealant characteristics are mainly dominated by the viscoelastic structure characteristics, G'>G" can confirm this
.
As time goes by, the processing process continues, and greater stress is applied Come out
.
The structure begins to be decomposed, and the sealant flows into the joint, showing G”>G'
.
When the tool/finger is withdrawn, the accompanying stress disappears and the structure (G') recovers
.

The part of the finger/tool ​​pressure on the curve in Figure 2d corresponds to the beginning of the machining process
.
The tensile force of the part with the same modulus (G'=G”, that is, the intersection point) is related to the evaluation of the tapping method
.
During the processing,
G'is reduced when the finger/tool ​​is pressed.
The reduction of G'can be Increasing the tendency of the sealant to infiltrate and adhere to the fingers or tools, leading to the formation of spikes, which is an undesirable characteristic
.
This characteristic makes the sealant the worst in the
percussion evaluation.
In order to improve the percussion evaluation results (Or it can be said to reduce the trend of peaking), the rheological sign of the modulus intersection needs to be changed to a longer time and a higher strain
.

The part of the curve in Figure 2d that represents the processing corresponds to the movement of the tool or finger along the sealant during the processing
.
In addition, the sealant is fluid in such a process, showing G">G'
.
Reduce the fluctuation of the complex viscosity or stability of the sealant, which is related to G'and G", and will improve the ease of application performance of the sealant , Because it shows that less force is required to move the sealant
.
In other words, the faster it reaches a stable state, the better the construction performance of the sealant.
In a stable state, the reaction and characteristics of the sealant will not change
.
This kind of quantification is impossible to achieve with your fingers
.

The part where the finger/tool ​​leaves on the curve in Figure 2d corresponds to the end of the machining process
.
The structural restoration of the sealant in this part of the process can be demonstrated by increasing G'to be greater than G"
.
This intersection between G'and G" can be related to the scribing method
.
Use higher stress to move the intersection point, which can improve tool application performance
.

Influence of formula design

Use experimental design to understand the influence of formula components on wet sealant characteristics and construction performance

Adjusting the level of these factors will directly affect the rheology of the sealant

Specific examples can show how rheology can provide more conclusions and directions than conventional tests

Figure 5 shows the second example, the testing of the thickener and volatile ratio in the linear region by the regular plan coating method and rheological properties G"

Powerful tool

Understanding the rheology can provide a powerful insight into the design of the sealant