Qualitative and Quantitative Analysis with Grinding Polymers

This article discusses an application where polymer and compact synthetic (such as webbing fabric, pellets, textile etc.) yarn, filaments (such as polyester or polyethylene, polypropylene (PP)), and fleece material were ground using the 6750 Freezer/Mill® (Figure 1).

Accurate qualitative and quantitative analysis of additives present in synthetic materials such as antioxidants using HPLC and INOC-Test need grinding. As the Freezer/Mill is capable of reducing the particle size to the desired level in a considerably short period of time, it is suitable for this application.

6750 Freezer/Mill

Figure 1. 6750 Freezer/Mill

Example: PP Fleece Materials

The material is cut into squares measuring approximately 2 mm and transferred into grinding vials, which are filled half way with the sample. The material is then ground according to the following program:

Pre-cooling : 15 minutes
Run : 1.5 minutes
Cycle cool : 2 minutes
Cycles : 5
Rate : 10 Hz

For this particular analysis, the method mentioned above was discovered to be the most effective grinding program for PP fleece materials. In this program, the material does not become warm enough to decompose or lose its brittleness during short grinding and it provides a yield of between 80 and 90%.

The required final particle size and the quantity of material determine the number of grinding cycles. The fleece material can be sieved through a 500 µm sieve in order remove the particles that are too coarse.

A) Sample Preparation for HPLC Analysis of Additives

Ground material weighing approximately 2.0 g is transferred into a 125 ml flask to an accuracy of 1 mg. 40 ml of toluene is then added to the material. The material is constantly stirred while it is boiled and fully dissolves in 30 minutes, after which it is slowly cooled to a temperature of 50°C.

40 ml of methanol is introduced into the sample with additional stirring to precipitate the polymer. After this addition, the material is cooled to room temperature. The cooled material is then filtered using a Nutsche (suction) filter and the filtrate is passed through a 0.45 µm filter. The material now contains the stabilizers essential for analysis and is ready for oxidation and HPLC separation.

B) Material Analysis: INOC-Test

Depending on the stabilizer content, 10.0 mg of AIBN (initiator) and 200 to 400 mg of sample material are added into the reaction vessel. After this, 10.0 ml of cumol is introduced into a pipette.

The vessel is then attached to the oxidation apparatus as shown in Figure 2. The stabilizer in the pulverized fleece material is effectively removed by the cumol, enabling AIBN oxidation.

Oxidation apparatus

Figure 2. Oxidation apparatus

The time-dependent oxygen consumption that takes place during the reaction is determined by the INOC test. A diagram is created with the obtained data to enable visual evaluation of the samples’ stabilizer content.

Conclusion

The 6750 Freezer/Mill* can be used for an efficient reduction of particle size of materials that are hard to grind. The particle size of fleece material used in the study for example, was reduced to less than 500 µm.

The increase in the brittleness of the sample at extremely low temperatures significantly reduces sample preparation time to less than 15 minutes.

This information has been sourced, reviewed and adapted from materials provided by SPEX SamplePrep.

For more information on this source, please visit SPEX SamplePrep.

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