The next step is to boil the cuttings (outside, due to the odor) for 3-4 hours with soda ash, which separates the lignin, sugars, starches, waxes, and gums from the cellulose fiber, making the paper strong and archival. Boil the plant material until it is soft enough to bend, but isn't mushy. In my experience, phragmites can take up to 3-4 separate boiling sessions before it's ready to chop in a blender.
After boiling, I rinse the plants thoroughly using mesh bags from a paint store.
Then the chopping begins! This process would be quick and easy if I had a $8,000 Hollander Beater.
However, I have more time than money, so I use my sturdy KitchenAid blender in the laundry room. It can take 4 days to chop one bucket of pulp because the blender can handle only one cup of cuttings at a time. I chop each cup for 30-60 seconds and give my blender plenty of breaks so that it doesn't overheat. (Phragmites usually requires 3-4 rounds through the blender.) It's a sloooow process, but it allows for ample time to read, listen to music, and ...do laundry.
There are two invasive plants that didn't work well for paper-making. One was Dame's rocket which never broke down enough to chop, even after several boilings. The second was common buckthorn which was extremely time-consuming to prep and resulted in brittle paper.
This summer, I'm anxious to try making paper with spotted knapweed, purple loosestrife, black and pale swallow-wort, narrow-leaf cattail, eurasian water milfoil, baby's breath, and any other herbaceous or aquatic invasive plant I can get my hands on!