Biomedical Engineering Reference
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were taken out from the chambers and weighed using a PGB200 model
analytical balance.
The moisture uptake at any time points as a result of moisture absorp-
tion was determined by
Moisture uptake =
Wh - Wo
Wo
× 100
where Wh and Wo denote the weight of humid specimens and the
original dry value, respectively. All data from three repeated tests were
averaged.
9.2.5 SOIL BURIAL DEGRADATION EXPERIMENTS
Under moisture controlled conditions soil burial degradation experiments
were carried out at ambient temperature. Specimens of each composite
were placed in a series of boxes containing moisturized soil. The speci-
mens (30 × 10 mm) were buried 100 mm beneath the surface of soil, which
was regularly moistened with distilled water. At predetermined time points
the samples were removed, carefully washed with distilled water in or-
der to ensure the stop of the degradation, dried at room temperature to a
constant weight and then were stored in darkness. The specimens were
weighed on the PGB200 model analytical balance in order to determine
the average weight loss:
Weight loss =
Wo - Wt
Wo
× 100
where Wo is the initial mass and Wt is the remaining mass at any given
time t. All results are the average of three experimental values.
9.2.6 MECHANICAL STRENGTH
Tensile strength, Young
'
s Modulus and Elongation at break were measured
according to the ASTM standard method D882-Test method A (ASTM
1997) with application of an Lloyd universal testing machine with a 5 KN
capacity at 23±2 °C and 48±5% RH. Test specimens with a length of 10
cm and a width of 2.5 cm were cut from composite sheets. All specimens
were equilibrated in a chamber kept at 18 °C and 35% relative humid-
ity for 24 hr before testing. All these tests were conducted at ambient
temperature and an average value of four repeated tests was taken for each
material. Specimen used for this test can be observed in the Fig. 9.3.
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