PSI - Issue 68

Carlos Fernandes da Silva et al. / Procedia Structural Integrity 68 (2025) 1252–1258 C. F. das Silva et al. / Structural Integrity Procedia 00 (2024) 000–000

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4

4. Tensile testing

The tensile testing was performed in a electromechanical Kratos universal testing machine (polymer lab., Depart ment of Metallurgical and Materials Engineering, Escola Polite´cnica da USP) under controlled ambient with room temperature 23 ± 2 ◦ C (300 ± 2 K), and a relative humidity of 50%. The tests were conducted with a 1000 N load cell, under displacement control, at a constant displacement rate of the grips ( ∆ ˙ ℓ ) of 5mmmin − 1 . A special device was constructed for film fixation in the grips. Details of this device will be published elsewhere, Figure 1(b) shows an example of a sample fixed in the machine.

5. Results and discussion

5.1. Properties of the base resins

Figure 2(a) shows the result of the second heating cycle of the DSC experiments for the base resins. PET and PA 66, as expected, show a prominent endothermic heat e ff ect corresponding to melting of the crystalline phase around 250 and 260 ◦ C (523 to 533 K), with PA 66 presenting a slightly higher melting temperature compared with PET. PA 6T6I, being an amorphous resin, show no sign of melting, but the curve shows a definite heat e ff ect around 120 ◦ C (393 K) believed to correspond to the glass transition temperature in this resin, with the e ff ect being more visible in this resin since the amorphous phase corresponded to its entirety, while in the other resins a considerable volume fraction of the crystalline phase existed. These temperatures supported the temperature setting used in the extruder.

0.2 0.4

45

PET PA 66 PA 6T6I

PET

σ

y

40

-1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0

35

-1 ]

σ

d

30

25

20

σ [MPa]

15

endothermic

heat flow [W g

10

second heating cycle

5

0 50 100 150 200 250 300

0

0 1 2 3 4 5 6 7

o

T [

C]

(a) (b) Fig. 2. Result of the second heating cycle of the DSC experiments in the base resins (a) and Example of load displacement curve obtained for the PET films, in the present case the thickness was 0.35 mm (b). Figure 2(b) a typical load - displacement curve obtained in the tensile testing for the PET films. The curve shows a maximum which is associated with the yield strength ( σ y ) of the film, and a second e ff ect, which is associated with the drawing stress ( σ d ) of the specimen ligament. All tested films presented a yield strength, and some presented also a drawing stress (sometimes, multiple) depending mainly on the width of the film (thicker films resulted is a tendency to present a more evident ligament drawing stage). The decrease in load after the drawing stage corresponds to the ligament tearing. This shape of curve is also observed in other amorphous and semi-crystalline polymers like MDPE Peres and Scho¨n (2008), iPP Maspoch et al. (1999), Poly(ethylene naphtalate), PEN Karger-Kokcis and Moskala (2000). ∆ l [mm]

5.2. Properties of the blends

Table 2 summarizes the results obtained for all sets of samples. During the production of the films it was observed that the final thickness ( t ) varied from batch to batch. By analysing the obtained data, it was concluded that the thickness did not a ff ect the mechanical properties for films thicker than 0.15 mm, therefore only these results were used in the present analysis.