Nearly every industry uses powders and other bulk solids in some form. From the inorganic powders used in polymers, to food products like milled flours and flavorings, they all share one issue: moisture.
epending on the material and how it is stored and shipped as it moves around the world, the moisture level may change. Therefore, it is important for the materials in question to be within a certain moisture range to adhere to internal and external quality standards before the final processing.
Before final processing, it is important for these materials to be within a certain moisture range to uphold internal and external quality standards. The moisture level of these products may change while being stored in intermediate warehouses or from being shipped in bulk around the world.
The conventional method of monitoring moisture levels is using standard oven and vacuum methods, and can be very accurate. The problem with these methods is the long test times that can range from 30 minutes, to several hours or even days. This is too long for the fast pace of today’s business that requires quick turn arounds and instant updates.
This standard oven method can also be applied for bulk solid analysis, using a much faster, rapid loss-on-drying (LOD) instrument:
- An empty sample pan is weighed and tared
- Sample is added and recorded as the initial starting weight
- Heat is applied to sample to evolve moisture (or other volatiles)
- Difference in sample weight is recorded and calculated as % Moisture using the equation
In the rapid LOD system, the heat source and balance are combined which allows the user to view moisture curves and rate graphs in real time as the moisture evolves. This integration makes test time significantly quicker but with the same high level of accuracy that comes with traditional oven methods.
In the following experiment, a range of powdered samples were tested using the Computrac® MAX® 4000XL Moisture Analyzer along with more traditional oven methods in order to determine moisture levels. The samples included flour, food flavorings and inorganic polymers ranging as high as 14% moisture to as low as 0.03% moisture. Built to withstand the rigor of onsite analysis using a small sample size of (<40 g), graphs can be accessed and seen in real-time, and the data collected can be stored via either Ethernet connection or USB memory stick for later graphical processing.
Sample Prep – All of the test samples were run as received from the manufacturer. So as to prevent excessive desiccation during analysis, the samples were kept in air tight Mason jars.
Test Conditions – For flour samples AOAC 925.09 or 925.10 methods were used. For all other samples a modified 925.09 or AOAC 925.45 were used.
Computrac® MAX® 4000XL – Flour Samples
Test Temperature: 150 °C–170 °C
Results Display: % Moisture (3 or 4 decimals)
Computrac® MAX® 4000XL – Food Powders
Test Temperature: 85 °C–120 °C
Results Display: % Moisture (3 or 4 decimals)
Computrac® MAX® 4000XL – Inorganic Polymers
Test Temperature: 75 °C–160 °C
Results Display: % Moisture (4 decimals)
If you require any additional information regarding sample parameters, please contact Arizona Instrument LLC.
Each of the samples were sifted over a waffle pan to ensure an even distribution and run through the Computrac® MAX® 4000XL with the above parameters. Flour samples included All-Purpose, Pastry, Whole Wheat, Soy, Black Bean, and Pinto. Food samples included Vanilla, Tomato, Blueberry, Parmesan, and 3 different cheese powders. Finally, the inorganic powders were tested and maned as polymer 1, polymer 2 and powder coating. This was so not as to appear to promote or discredit any trade or manufacturer name during the study.
Figure 1 shows the run of whole wheat flour from the described tests. There are two plots against time: the blue line is change in % Moisture, while the red line is the % loss per minute, or Rate. Once the sample had been run, the data was put into Microsoft® Excel® and plotted using the graph tool in the software. This particular test finished when the rate dropped to below a certain amount. (time, prediction, temp then rate are also other ending options that can be used)
Figure 2 shows how the flour set were analyzed in both the 4000XL and the standard oven method. All of the tests were performed three times to ensure accuracy. The error bars display the standard deviation (S.D.) of each data set.
As can be seen from the figure the 4000XL nearly exactly matches the moisture level results from the oven reference method for each of the flour samples.
The MAX® 4000XL does not just work for just flour samples however. Figures 3a &3b display the continued equivalency of the MAX® 4000XL to the oven method, while at the same time keeping a low standard deviation. Figure 3b shows how moisture levels vary within the same material and how the excellent resolution of the instrument can identify this.
Table 3 is the raw data from both the instruments highlighting the gulf in testing times between the two.
Figure 4 is the data set of inorganic powders used in the plastic/coating industries, and is the final sample set analyzed using the standard oven and rapid LOD methods. As can be seen from the error bars, the MAX® 4000XL delivers high accuracy and precision even at low moisture levels.
Table 4 represents the raw data with statistics of figure 4. Impressively, the MAX® 4000XL (4K) has a smaller S.D. than the oven even at low moisture levels when run in triplicate.
By using a rapid loss-on-drying (LOD) instrument such as the Computrac® MAX® 4000XL, the user can an accurate and precise picture of the % moisture of various samples, whether that level is high or low. This article clearly shows that test times are significantly quicker than a similar test performed using the standard oven reference method.
This does not even include the time used in preparation to purge pans or for the instrument to cool off. If the LOD unit is equipped with real-time graphing, the technician can see the rate of loss as it happens or save it externally for later analysis. This allows an appropriate end criteria to be set and the efficiency of the test to be maximized. Using the MAX® 4000XL in your factory testing will save time and money, with its robust design ensuring consistency even in the most demanding industry environment.
This information has been sourced, reviewed and adapted from materials provided by Arizona Instrument.
For more information on this source, please visit Arizona Instrument.