It should have MLA Format and Works Cited page and it should be 6 or 7 pages long.
The outline should be something similar to this
II. Background of Plastic Material
B. Composition or how is it made
E. Innovative uses
F. Every-day uses (intro to plastic bags and bottles)
III. Plastic Bags and Bottles
C. Time of decomposition
It does not need to have a concluding paragraph.