Mechanical properties. Twelve samples, 2.54 cm wide and
10 cm long, were cut from the ISP-coated paper. Samples
were conditioned for 48 h at 25°C and 50% relative humidity
(RH) in an environmental chamber before measuring tensile
strength (TS) and elongation (E). An Instron (model 4210; Instron
Engineering Corp., Canton, MA) was used to measure
TS and E at breakage, according to ASTM standard method
D 882-88 (22). Initial grip separation and crosshead speed
were set at 50 mm and 500 mm/min, respectively. Peak loads
and extension at the breakage point were recorded for the
tested film samples. TS was calculated by dividing peak loads
by specimen cross-sectional areas. The thickness of individual
samples, required to calculate cross-sectional area, was
determined by averaging five micrometer readings taken on
each sample before testing. Extension values were divided by
the initial grip separation (50 mm) and multiplied by 100 to
yield percentage E at breakage. Units used are Pascal (Pa) and
percent (%) for TS and E, respectively.