Plastic sheets are typically made of sturdy PVC (vinyl) or more lightweight low density polyethylene. Either way, they can't be recycled.
Plastic Sheet
Plastic Drop Cloths for Painting, Clear Plastic Sheeting, Plastic Tarp, Tarpaulin Canvas, Dustproof Furniture Cover, Floor Protection Film, Ground sheet, Picnic sheet, Picnic mat
Recyclable?
Blue Bins & Chutes
Other Recycling
Recommended
Freecycle / Give Away
If the sheet is sturdy, consider giving it away at the next Really Really Free Market where such sheets are in demand to display items on offer.
Singapore Really Really Free Market
Alternative
Freecycle / Give Away
Give it to art groups or offer it online.
Art Don't Throw
Olio
GoodHood
Alternative
Trash
If not suitable for reuse, throw it away.