Using Rapid Loss-on-Drying Instrumentation to Determine Volatile Content of Coatings and Paints

Paint is a three component material composed of a pigment, vehicle, and carrier. Today, synthetic polymers, solvents, and resins are utilized for producing paints and coatings. These materials exhibit outstanding resiliency to weathering effects such as extreme heating and cooling, acid exposure, and water exposure from rain or snow.

Testing materials is essential for manufacturers to maintain the quality of the products. Manufacturers perform loss-on-drying assays to ascertain that they have the correct mix of components. This analysis determines the amount of material to be volatized upon heating.

Conventional Analysis Methods

ASTM standard D2369 describes an oven method test to determine the volatile content of coatings. Although this approach determines the volatile content effectively, it is not able to leverage new technology that shortens testing and throughput times, which would enable manufacturers to optimize the efficiency of their metrology process and lower their production times.

Further, obtaining results in real time is not possible with this method, making it incapable of immediately diagnosing potential production issues.

Rapid Loss-on-Drying Method

In 2006, ASTM International adopted method D7232, thanks to technological developments in the conventional loss-on-drying method. This method provides the same results produced by testing with method D2369, but shortens analysis time from 2+ hours to minutes. In addition, the Computrac® MAX® 4000XL Analyzer performs in-situ measurements, enabling metrologists to analyze production issues immediately.

Experimental Procedure

The analysis highlighted below involved testing of three different materials utilizing ASTM method D2369 and D7232. A convection oven was employed for method D2369, while a Computrac® MAX® 4000XL instrument was used for method D7232.

The sample testing with the MAX® 4000XL involved shaking of the coatings and pigments in their containers between tests. For each test, a 5mL plastic syringe was used to place the sample onto a flat pan with paper.

Experimental Results

The analysis results are summarized in Tables 1, 2, and 3, showing good agreement between the two methods. However, the MAX® 4000XL exhibited a much closer testing result range for two of the three sets of testing.

Table 1. Statistical Analysis of Clear Acrylic Resin.

MAX® 4000XL (% Solids) Convection Oven
Coating 1 74.644 Mean 74.404
0.111 Standard Deviation 0.400
14:17 Test time 2 hours

Table 2. Statistical Analysis of Brown Acrylic Resin.

MAX® 4000XL (% Solids) Convection Oven
Coating 1 48.429 Mean 48.198
0.261 Standard Deviation 0.377
10:01 Test time 2 hours

Table 3. Statistical Analysis of the Finish Coat with Additives.

MAX® 4000XL (% Solids) Convection Oven
Top Coat 60.317 Mean 60.028
0.111 Standard Deviation 0.035
7:20 Test time 2 hours

As can be seen in the graph shown in Figure 1, the resin starts volatilizing at around 100s, revealing that the idle temperature is cool enough to stop the material volatilizing before data collection. Furthermore, the tail of the rate graph illustrates the complete loss of the volatile content from the material, thereby allowing the test to end. This a characteristic graph for all three materials analyzed.

Determination of Solids for Brown Acrylic Resin.

Figure 1. Determination of Solids for Brown Acrylic Resin.

Conclusion

The results clearly demonstrate the advantage of using rapid loss-on-drying methods for testing paints and coatings over conventional testing methods. Although the results obtained from the two methods are similar, the analysis time is significantly less for the MAX® 4000XL, which also yields a comprehensive profile of the materials being tested.

With this instrument, manufacturing throughput times can be reduced and more information for quality improvement can be obtained to tackle formulation problems.

About Arizona Instrument

Initially known as the Quintel Corporation, Arizona Instrument LLC was founded in 1981 by a group of engineers breaking away from The Motorola Corporation who were dedicated to the idea of providing precision moisture analysis instruments that were accurate, reliable, and easy to use.

The first instrument released was the MA Moisture Analyzer, but the company quickly expanded its Computrac® moisture analysis line and became an accepted leader in moisture analysis, setting a standard that has been adopted by many Fortune 500 companies. Today the Computrac® line is comprised of three technologies: rapid loss-on-drying, high temperature loss-on-ignition, and moisture specific analysis using polymer capacitance sensor, GREEN alternative to Karl Fischer.

Arizona Instrument

This information has been sourced, reviewed and adapted from materials provided by Arizona Instrument.

For more information on this source, please visit Arizona Instrument.

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