**2. Experiment**

*2.1. Material*

PPS, PEEK and PAEK thermoplastic polymer melts with T300 3K, 5HS, 280 gm-2 FAW (Fabric Area Weight), 43% RC (Resin Content) (50% by volume) carbon fabric (280 gsm) were compared. The coupons were manufactured by Latecoere Czech Republic, Prague using thermoforming technology. Thermoforming is used to convert a flat consolidated continuous fibre-reinforced laminate into a complex shape with no change in original laminate thickness. The laminates were heated to the required temperature and then quickly formed under ambient pressure with a few minutes dwell time (Figure 2).

**Figure 2.** Curved-beam strength samples.

Indicative properties of the compared matrices and used carbon laminates with these matrices are shown in the Tables 1 and 2. Figure 3 graphically illustrates the thermal properties of the compared thermoplastics. By comparing the properties of individual matrices in Table 1, we can see that the PAEK matrix has the highest flexural strength and elongation. On the other hand, it has the lowest compressive strength. The highest compressive strength has a PPS matrix. In tensile strength, the differences are not so large (less than 10%). The greatest differences show thermal properties. The PPS thermoplastics has glass-transition temperature (Tg) and melt temperature (Tm) that are significantly lower than the two remaining matrices. These have almost identical Tg, but PEEK has a Tm 38 ◦C higher than the PAEK matrix. When comparing the fibre-reinforced laminate with PPS, PEEK and PAEK, we find that most properties differ at the minimum. The greatest differences are in the strength properties in the 90◦ direction and in-plane shear strength; see Table 2.

**Figure 3.** Compared thermal properties of the PPS, PEEK and PAEK matrices [29].


**Table 1.** Physical, mechanical and thermal properties of the compared matrices [30–32].

**Table 2.** Mechanical properties of the carbon laminates with the PPS, polyetheretherketone (PEEK) and polyaryletherketone (PAEK) polymer melts [29–31].


The samples were divided according to Table 3 as the samples for testing at room temperature (RT) and the samples for testing at a cold temperature of −55 ◦C (CT). A temperature of −55 ◦C represents the typical operating temperature in aerospace. Show material properties at this temperature are important for airworthiness.


