Starch, aspen fiber and magnesium stearate
were first mixed using a Kitchen Aid mixer with a
wire wisk attachment. Magnesium stearate acts as
a mold release agent, preventing sticking of starch
to the mold. For batters containing no PVOH,
guar gum (1% by weight of starch) was also
added to prevent settling of the starch. PVOH
solution (10% by weight, heated to 90 °C for 1 h)
and/or water and other liquid reagents were then
added so as to give the desired level of PVOH
and a total solid content of 33%. Other compounds
(see Section 2.1) were added to the batter
at 1–2% levels based on starch weights. Acetic
acid was added to batters containing the Curez or
Melrex resins to decrease the pH to nearly 5.
Mixing was continued for 20–30 min. Starch
foam trays were prepared using a laboratory
model-baking machine (model LB TRO) supplied
by Franz Haas Machinery of America, Richmond,
VA. This equipment consists of two heated
steel molds, the top of which can be hydraulically
lowered to mate with the bottom half for a set
amount of time. Dimensions of the mold were
217 mm long, 134 mm wide, 19 mm deep and 3
mm (plate separation). Baking temperatures were
set at 200–205 °C. Actual temperatures at the
mold surface were about 10 °C lower as measured
using a Temp-Sure Digital Pyrometer TS-
200 (D-M-E Co., Madison Heights, MI). Baking
times were the minimum required to avoid a soft
or bubbled tray and varied from about 80–140 s.