The ornamental design for a plasticbarrel, as shown and described.
FIG. 1 is a top view of a plastic barrel showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a rear view thereof;
FIG. 7 is a perspective view of the plastic barrel in a closed position; and,
FIG. 8 is a perspective view of the plastic barrel in an open position.
The broken line portions of the plastic barrel in FIGS. 1 through 8 are included for the purposes of illustrating unclaimed subject matter and form no part of the claimed design.