The following instructions describe the sample preparation steps for fiber analysis.
- The LFT samples were cut into ~2 in. × 2 in. pieces.
- The polymer matrix of the sample was removed by burning in an oven at 800 °C for 3 minutes. If the sample contains HFFR, the polymer digestion method is used as described separately below.
- 0.1 g of fibers was dispersed in 1 L of deionized water with a few drops of surfactant to mitigate fiber aggregation.
- The fiber/water solution was stirred for at least 10 minutes to achieve uniform dispersion, then poured into a Petri dish for imaging using FASEP.
- More than four images were taken for each sample to obtain the average fiber length and distribution, which were automatically calculated by the FASEP software.
- In this project, weight-average fiber length (Lp) is used rather than number-average fiber length (Ln) because Lp provides a more representative measure of fiber length distribution in LFT materials.
Polymer Digestion Method by Sulfuric Acid
- Rinse the flask with two washes of ~75 mL each of 98.5% H₂SO₄.
- Rinse the flask with at least three washes of ~100 mL each of water.
- Do NOT use the same vacuum flask for both rinses. Extremely dangerous splashing and vapor will occur.
- Add ~1 g of sample and a stir bar to a 150 mL Erlenmeyer flask.
- Fill the flask with 75–100 mL of 98.5% H₂SO₄.
- Place on a stirring hot plate and heat on medium (liquid temperature of ~220 °C) while stirring vigorously. Cover with a watch glass.
- Allow at least 4 hours for full digestion.
- After 4 hours, let cool to 50–60 °C.
- Filter by vacuum filtration using a Whatman GF/F (or equivalent, 0.7 microns) filter.
- Dry the fibers and filter in an aluminum tray at 105 °C until the weight no longer changes (at least 1 hour).
Sample Preparation Steps Using a Furnace and Sulfuric Acid for Fiber Length Analysis
Example of Results
