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OCR for page 59
A-5 Figure A-4. DSC curve for a mixed-color recycled HDPE. From the equation in Figure A-3, the heat of fusion for PP for each of the five specimens. Then, the displacement corre- from 139.1C to 175C is 78.4 J/g. The percentage PP is then sponding to a 2% strain in the outside surface was calculated by: 3.18/78.4 100 or 4.0%. D = rL2 6d A.2.7 Tensile Properties (ASTM D638) where: The tensile properties were evaluated according to ASTM D = displacement at 2% strain (in), D638, Standard Test Method for Tensile Properties of Plastics. r = strain (in/in), Type IV dumbbell specimens were used with a cross-head L = support span (in.), and speed of 50.8 mm/min (2 in./min). The gage length for break d = specimen thickness. strain was 50.8 mm (2.0 in.). The displacement was measured by cross-head travel. The tensile yield stress and the strain- The required displacement varies with the thickness of the at-break were determined. Five replicates were tested. specimen. Therefore, each of the five test replicates will likely have a different displacement representing 2% strain. Once the displacement is determined, the corresponding load is A.2.8 Flexural Modulus (ASTM D790) found and the flexural stress at 2% strain is calculated by: The flexural modulus was determined in accordance to = 3PL 2 bd 2 ASTM D790, Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. Pro- where: cedure B was used according to ASTM D3350. The specimen was a bar, 12.7-mm wide by 7.63-mm long (0.5 in. 3 in.). The = stress at 2% strain (psi), thickness varied within the sample, which was a compression P = load at 2% strain (lbf), molded plaque of a nominal thickness of 0.125 mil (3.175 mm). L = support span (in.), The test span was 2.0 in. and the cross-head rate of deflection b = specimen width (in.), and was 0.5 in. per minute. A Load vs. Deflection plot was obtained d = specimen thickness.