Materials tested included plastics designed to be biodegradable,
conventional plastics amended with additives that are meant to
enhance biodegradability, bio-based plastics and natural fiber
composites (Tables 2 and 3). The positive and negative controls
used for all experiments were cellulose paper (Fisher Scientific, PA,
U.S.) and 100% conventional polypropylene (PP), respectively. Materials
were tested both after grinding (a preliminary soil experiment
only) and as 1 1 cm squares (thicknesses shown in Table 3)