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