The extent of long-term biodegradat

The extent of long-term biodegradation of polymeric materials
in contact with soil was determined based on ASTM D5988-03 [24].
These included PP þ 2% additive, polystyrene (PS) þ 2% additive,
polyethylene terephthalate (PETE) þ 1% additive, plastarch, a copolyester
þ corn-based plastic, a wheat starch-derived plastic and
PHA (Tables 2 and 3). Six natural fiber composite materials were
also tested: paper pulp, paper pulp þ asphalt, coconut coir, rice hull,
composted cow manure and peat fiber. All samples were incubated
in triplicate for a period of 660 days.