Any vestment piece that has been used liturgically must be disposed of properly when it becomes either worn-out or damaged. Rubrics specify that blessed items are to be burned or buried, but disposing of a large mass of synthetic fabric can pose a bit of a challenge, so here is my solution:
Purchase a large zinc tub from your local garden store or hardware shop (they are inexpensive-about $15). Place on a concrete patio or pad, out of doors in a well-ventilated area. NEVER BURN LITURGICAL FABRICS INDOORS-THEY CAN OFFGAS TOXIC CHEMICALS. Even when burning outside, keep well away from the fumes and wear a respirator if you are burning for more than a few minutes.
Place some dirt in the bottom of the zinc tub to help insulate (I fill mine halfway full with dirt). Place the worn-out/damaged vestments on top and light them with a match. Burn only one piece at a time as these fabrics can flare easily and you want the fire very small in order to contain it.
Once you are done, you will have only ashes and small metal pieces like buttons and cuff rings left, which can then be buried (do not bury them near a vegetable garden as these will have petrochemical residue).