Review and Experimental Update on Manufacturing of Hybrid Carbon Fiber Composites for Space Use

Abstract

Hybrid materials have multifunctional capabilities that are particularly attractive for space applications in order to overcome issues related to the harshness of the environment, especially during long-duration missions. Hybridization is traditionally carried out by mixing reinforcements of different natures, such as carbon with glass/kevlar fibers, or by integrating nanomaterials into the composite structure. Promising results in terms of improved toughness, ductility, and damping ability have been recorded by placing a thermoplastic interlayer between adjacent thermosetting plies reinforced with carbon fibers. These hybrid materials have additional functionalities such as thermoformability and repairability, which make them suitable for several industrial applications. In this work, a literature review on hybrid composites is presented and experimental results on the manufacturing of hybrid carbon fiber epoxy/PEEK laminates are reported. Thermoplastic films of 25 μm and 200 μm thickness have been used as well as two manufacturing procedures. The high-thickness interlayer laminate, that was compression-molded at 250 °C, showed the highest mechanical properties with a bending strength of 340 MPa and an elastic moules of 50 GPa. The other composite, that was molded at 350 °C, exhibited reduced mechanical properties.

1. Introduction

Space exploration programs encompass activities in many scientific fields such as Earth observation, satellites, connectivity, biology, human health, and engineering. In this context, the need for sophisticated structures is continuously increasing since they have to work under severe thermomechanical loads, endure harsh chemical environments, and simultaneously exhibit advanced electromagnetic properties. Therefore, advancements in the aerospace sector are strongly related to materials technology. For this reason, recent years have been characterized by the shift from monolithic to composite materials [1]. They offer significant advantages in space travel, with weight reductions ranging from 25% to 35% and cost savings of nearly 50%. Mass reduction is crucial, as space systems demand substantial weight reduction compared to traditional systems [2].

Fiber-reinforced polymers (FRPs) are typically used in launch vehicles and in satellites thanks to their high stiffness, specific strength, low thermal expansion, low conductivity, and dimensional stability. High-modulus and unidirectional carbon FRPs (CFRPs) are extensively used in the aerospace industry to manufacture structural components, such as some satellite’s support elements [3]. Aluminum-matrix hexagonal honeycomb plates are also used in satellites to improve specific properties like energy absorption and bending stiffness [4]. The presence of hot components in launch vehicles, like engines, has pushed the development of thermal protection material. Carbon–carbon composites, which have good thermal shock resistance and a low coefficient of thermal expansion, are particularly suitable for such applications; however, they tend to oxidize at temperatures above 500 °C and, thus, precious metal coatings are used to improve this aspect [5]. Moreover, good wear resistance, high thermal shock resistance, and excellent tribological performance can be obtained by nanocomposite coatings containing yttria-stabilized zirconia in a gold matrix with encapsulated nanosized reservoirs of molybdenum disulfide and diamond-like carbon [6].

Nowadays, composites are extensively used in the space industry, but further improvements in performance and material multifunctionality are still needed. Indeed, agencies and governments around the globe have established new targets for space exploration, including the creation of settlements on the Moon and on Mars, as well as long-duration missions. To achieve these goals, it is fundamental to design structures that can withstand the harshness of the space environment and, consequently, material development is of primary importance. Hybrid materials have become one of the most investigated solutions thanks to their high-performance capabilities and multi-functionality. These properties are extremely attractive not only for the space sector, but also for many other industrial fields such as automotive, defense, sport, etc. Evidence of the interest in using hybrid composites in space is demonstrated by the graph plotted in Figure 1a, where the number of published papers on this topic from 1980 to 2024 is reported (Scopus database; keywords: “hybrid composites” and “space”; selected document type: “article”). In this period, 4767 manuscripts were published, with 97.1% being published since 2001, 81.4% since 2014, and 663 papers having been published only in 2024. By restricting this analysis to only the “engineering” field, which include 160 keywords, the 10 most used are reported in Figure 1b. Excluding those which refer in general terms to “composites” and “materials”, the trend on the study of hybrid reinforcement is clear; the use of nanomaterials is of primary interest, as well as composites’ mechanical behaviors and microscopy. For comparison, the same research on Google Scholar returns a total number of papers of about 3650, almost the 77% of those obtained by Scopus.

Hybrid composite is a general term that includes composites either reinforced with different types of materials within the same matrix or one fiber material with multiple polymers [7]. Hybridization offers the possibility to achieve balance and more attractive properties and costs for the composite structure, since lower-cost fibers can be mixed with high-performance ones. Various kinds of hybrid composites used in aerospace consist in the combination of carbon and glass fibers (CFs/GFs); these composites merge the superior stiffness and strength of the former with the durability and affordability of the latter. Furthermore, a synergetic effect, due to the interaction of fibers of different nature, can also be achieved, with the hybrid laminate having superior properties than just the sum of the constituents [8]. A different approach is related to the use of thermoplastic (TP) interlayers in the thermosetting (TS)-based composite structure, which are called hybrid matrix composites. These interlayers may include nano-reinforcements, but they are also used without any filler. Hybrid matrix composites have additional functionalities with respect to neat CFR laminates and improved properties, such as ductility and toughness.

In this work, the state of the art of hybrid composites for space applications is reviewed; more specifically, Section 2 analyses hybridization methods that use reinforcements of different types whereas Section 3 investigates hybrid matrix laminates. Following this, in Section 4 a small experimental study is presented as an example. Hybrid composites made by CFRPs plies and interlayers of poly ether ether ketone (PEEK) have been manufactured by two different manufacturing routes and thermo-mechanical tests as well as microscopy have been performed to assess the performances of the laminate structure. This is the first time that high-performance PEEK has been interleaved between CFs–epoxy prepreg. These two materials, already well known in the space industry, are generally used in distinct applications to take full advantage of their properties. However, a positive hybrid effect could encourage their application in different scopes thanks to both the simplicity of the proposed manufacturing technologies and to their additional properties in terms of thermoformability, damping, and improved ductility. Finally, the conclusions of the study are reported in Section 5.

2. Composite Laminates with Hybrid Reinforcement

Hybrid fiber-reinforced materials can be developed in two distinct ways: by mixing fibers of different natures in a shared matrix or by stacking alternating layers of each type of composite. Table 1 provides a summary of the reported literature review based on the hybridizing material. Typically, hybrid composites are produced by combining high-modulus (e.g., CFs) and low-modulus (GFs or Kevlar) fibers [9]. The reinforcement can be ordinary particulate, woven or non-woven fibers, and nanoscale fillers. A dynamic shear-lag model has shown that the linear stiffness and linear density of the fibers are the two key parameters that affect the impact strength, and, in particular, fibers should have similar densities but different stiffnesses [10].

Hybridization of CFRPs with nanoscale fillers such as carbon nanotubes (CNTs), carbon nanofiber (CNFs), and graphene nanoplatelets (GNPs) allows the enhancement of both the mechanical properties and the versatility of the laminates [11]. CNTs have excellent mechanical and physical properties and, consequently, are particularly suitable for CFRPs hybridization [12]. A 3D finite element multi-scale model has been used to predict the changes in the interfacial radial stress, which is reduced by 21.3% with a CNTs content of 2 wt% [13]. Moreover, it was shown that hybridization with CNTs improves the laminates damping ability; indeed, the loss factor, loss modulus, and storage modulus improved by 454%, 529%, and 14%, respectively [14]. The addition of 0.5 wt% GNPs to a CFRPs–epoxy laminate led to a 50% increment in the electrical conductivity [15], while an increase of over 60% in interfacial strength was obtained by adding 2 wt% [16]. By combining CFs/CNTs/GNPs, an improvement of 106.7% in the transverse thermal conductivity is achieved in comparison with the neat CFRPs [17].

The combination of CFs and GFs is one of the most used hybridization methods since it permits the improvement of specific properties. Mechanical properties such as tensile modulus and compression modulus increase with the content of CFs [18]. It was shown that the ballistic limit velocity of hybrid laminates is 21% higher than CFRPs composites [19]. The laminates impact resistance, especially in terms of the extent of the damaged area, depends on the side on which the impact occurs (glass or carbon). Indeed, if the impact occurs on the CFs side, increases in resistance are obtained [20].

Manufacturing hybrid CFs/Kevlar composites allows to increase the impact resistance and to localize the damage region during impact [21]. Indeed, hybrid CFs/Kevlar laminates that underwent an impact energy of 440 J dissipated 93% of the projectile’s kinetic energy [22]. Moreover, after-impact bending tests revealed that bending properties are improved thanks to the presence of Kevlar fibers [23].

CFs tend to have a brittle fracture mode; improvements in the failure strain are achieved by the hybridization with Kevlar or GFs, but the use of tougher fibers, such as TPs ones, has led to much higher failure strains [24]. A laminate structure made up of 75% of CFs–epoxy at the front and 25% PE fibers–elastomeric matrix at the back surface showed a reduction of 20% in the compressive strength after impact and an improvement of 82% in the ballistic velocity limit [25]. In addition, the impact strength achieved by a hybrid composite having ultrahigh-molecular-weight polyethylene (UHMWPE) fibers and CFs in intra-laminar configuration was 423.3 kJ/m² for a UHMWPE fiber content of 43 wt% [26]. This combination also permits to improve the ballistic limit per areal density of 34%, but the tensile stiffness and strength decreased by 44% and 42%, respectively, in comparison with the reference carbon laminates [27]. Also, an increment of 71.43% in penetration energy has been obtained by the hybridization of CFs–epoxy composites with UHMWPE [28].

Table 1. Reported research on composite laminates having hybrid reinforcements.

Hybridization		Year	Reference
Micro-reinforcement hybridization	CFs/GFs	2020	[20]
		2018	[9,18]
		2013	[19]
	CFs/Kevlar fibers	2025	[21]
		2018	[9]
	CFs/TP fibers	2020	[27,28]
		2015	[24]
		2006	[26]
		2002	[25]
Nano-reinforcement hybridization	CFs/CNFs	2025	[11]
	CFs/CNTs	2025	[11]
		2021	[14]
		2019	[12,13]
	CFs/GNPs	2024	[15,16]
	CFs/CNTs/GNPs	2024	[17]

Table 1. Reported research on composite laminates having hybrid reinforcements.

Hybridization		Year	Reference
Micro-reinforcement hybridization	CFs/GFs	2020	[20]
		2018	[9,18]
		2013	[19]
	CFs/Kevlar fibers	2025	[21]
		2018	[9]
	CFs/TP fibers	2020	[27,28]
		2015	[24]
		2006	[26]
		2002	[25]
Nano-reinforcement hybridization	CFs/CNFs	2025	[11]
	CFs/CNTs	2025	[11]
		2021	[14]
		2019	[12,13]
	CFs/GNPs	2024	[15,16]
	CFs/CNTs/GNPs	2024	[17]

3. Hybrid Matrix Composites

This section discusses the state of the art of hybrid laminates consisting of a CFR-TS matrix and interlayers of TP polymers. The two elements have a different role in the hybrid composite structure since the former is responsible for mechanical resistance, while the latter improves capabilities like ductility and toughness, which are low in traditional CFRPs–epoxy [29]. On the other hand, the incorporation of TPs into CFR-TS may lead to a deterioration of other mechanical characteristics, such as flexural properties and interlaminar shear strength. A fundamental role is played by the surface chemistry of the composite plies which influences the crystallinity of the TP material [30]. However, in the literature, there are several examples of positive hybrid effect due to the interaction of these two classes of materials, including TP films of polyamide (PA), polyetherimide (PEI), and polymers belonging to the poly aryl ether ketone (PAEK) family. Table 2 summarizes the proposed literature review on hybrid matrix composites. The integration of PA into CF-epoxy composites has shown promising results related to the ability of the hybrid composite structure to be thermoformed [31] and repaired [32]; these properties are new for TS-based composite materials, which normally have to be cured in their final shape and are difficult to recycle. Moreover, PA films enriched with nanoparticles as CNTs have been interleaved between composite plies; the hybrid laminate exhibited an improvement in interlaminar fracture toughness, modes I and II, of 122 and 81%, respectively [33]. Also, the use of cellulose nanocrystals in PEI interlayers allowed an increase of 28% of the mode I initial fracture toughness of CFR epoxy laminates [34].

PEEK, which belongs to the PAEK family, not only has significant mechanical properties but it is also wear resistant and has a good thermal stability [35]. Thanks to its high performance, it has the potential to be a substitute for metals in some industrial applications [36]. Specific properties can be enhanced by inserting nanoparticles into a PEEK matrix. Improvements in energy dissipation have been obtained by integrating GNPs, since the nanocomposites exhibited a shockwave velocity that was 20% lower than that of the unfilled PEEK [37]; on the other hand, the presence of 3 wt% of CNTs allowed the coefficient of thermal expansion to be reduced by 18%, thus improving the thermal stability of the composite [38].

When combined with CFR epoxy, an improvement of 49% in the damping factor has been observed [39]. Furthermore, enhancements in the mode I and mode II fracture energies have been obtained, with increases of 227% and 441%, respectively [40]. Moreover, strong joints have been obtained by interleaving a layer of TP polymer between two uncured composite laminates before molding; PEEK-based joints showed the same resistance as the aerospace adhesive FM300 (by Solvay) at 22 °C (typically used in this field), while at 130°, it was four times higher [41]. An improvement of 248% in the Mode I initiation toughness has been obtained by PEEK-modified laminates, which make them particularly suitable for high-value industrial applications [42].

Table 2. Reported research on TS composite laminates with TP interlayers.

Hybridization		Year	Reference
Engineered polymers	PA	2024	[32]
		2023	[31]
		2020	[33]
High-performance polymers	PEI	2019	[34]
	PEEK	2025	[42]
		2023	[35,39,40,41]
		2022	[36]
		2021	[37]
		2020	[38]

Table 2. Reported research on TS composite laminates with TP interlayers.

Hybridization		Year	Reference
Engineered polymers	PA	2024	[32]
		2023	[31]
		2020	[33]
High-performance polymers	PEI	2019	[34]
	PEEK	2025	[42]
		2023	[35,39,40,41]
		2022	[36]
		2021	[37]
		2020	[38]

4. Manufacturing of CFR Epoxy/PEEK Hybrid Composite Laminates

In the frame of hybrid matrix composite, CF laminates have been manufactured by placing an interlayer of PEEK between adjacent plies. Both materials are commonly used in the aerospace industry and, in the following, the hybrid effect due to their interaction is investigated and correlated to the manufacturing processes used. The thickness of the interlayer severely affects the mechanical properties of the hybrid matrix composite structure [43] and, thus, films of 25 μm and 200 μm thickness have been used for experimentation. Thermo-mechanical tests as well as microscopy have been performed to evaluate the hybrid composites’ performances.

4.1. Hybrid Composites Manufacturing and Testing

4.1.1. Supplied Materials

A commercial plain wave fabric (Solvay Cycom 132 977–2) was used to manufacture the laminates; this material is supplied in the form of a prepreg with the CFs impregnated with epoxy resin. Hybridization has been performed by alternating the CFs plies with layers of PEEK of two different thicknesses: one of 200 μm (by GoodFellow) and one of 25 μm (by Solvay).

4.1.2. Laminates Manufacturing

The hybrid laminates were obtained by stacking 10 CFs plies and 9 interlayers, as shown in Figure 2. The hybrid laminate with the high-thickness interlayer was compression molded into an aluminum mold having a square cavity of 70 × 70 mm². Compression molding was performed using a hot parallel plate press at 5 bar and 250 °C for 15 min, and fluorinated ethylene propylene (FEP) was used for releasing. The low-thickness interlayer composite was compression-molded into a 140 × 140 mm² aluminum mold. A pressure of 5 bar was applied at room temperature through a steel spring, which was compressed and constrained to the mold. Subsequently, the system was placed in the oven at 350 °C for 90 min for consolidation. A layer of kapton film was placed between the composite and the mold to assist the extraction of the composite laminate from the mold. The two manufacturing procedures are shown in Figure 2.

4.1.3. Hybrid Composite Testing

Before molding, differential scanning calorimetry (DSC) was conducted on the low-thickness film with a DSC 6000 by Perkin Elmer. Double scans from 10 °C to 400 °C at 10 °C/min were performed. Compression molding was performed according to the obtained results and, after extraction from the mold, the laminates physical properties were measured, and the microscopy of the laminates cross-section was carried out with a stereomicroscope (Leica S9i by Leica). The mechanical properties were evaluated using samples of nominal size 10 × 70 mm² through four-point bending tests. A universal material testing machine (MTS Insight 5 by MTS) was used for this purpose, with a span length of 60 mm and a load span of 20 mm. Tests were performed at a speed of 1 mm/min, with a preload of 1 N and an acquisition rate of 10 Hz.

4.2. Results

4.2.1. Thermal Analysis

Calorimetry was performed on the PEEK film to investigate the characteristic temperatures of the material. The results are shown in Figure 3, where the temperature–heat flow curve is reported. In the graph, upward and downward peaks are associated with endothermic and exothermic reactions, respectively, which are correlated to phase changes in the material due to heating. In the first scan, a sharp downward peak at 176 °C is observed, as well as an upward peak at 345 °C; these critical values represent the crystallization and the melting temperature (T_c and T_m) of the material, respectively. In the second scan, the downward peak disappears and a flex point at 153 °C is observed clearly. In DSC, this behavior occurs when the glass transition temperature (T_g) of the material is reached, and it passes from a glassy to a rubbery state. As the temperature rises, the sample melts again and, thus, an upward peak is also present in the second scan, at 343 °C.

4.2.2. Morphology

Stereomicroscopy, Figure 4, shows that a good agglomeration among the layers has been achieved and voids and cavities are not visible in the cross-section, confirming the reliability of the lab-scale process.

4.2.3. Mechanical Testing

Bending tests were carried out in a four-point bending configuration to evaluate the mechanical properties of the hybrid composite laminates. As shown in

Table 3. Data extracted from the four-point bending test.

Specimens	Stiffness [N/mm]	Load Max [N]	Stress Max [MPa]	Elastic Modulus [GPa]
High-thickness interlayer	190	348	340	50
Low-thickness interlayer	110	135	140	40

, the high-thickness interlayer composite exhibited the highest bending strength and elastic modulus, being 340 MPa and 50 GPa, respectively.

4.3. Discussions

Hybrid composite laminates were obtained by compression molding; after the extraction from the mold, they showed a small amount of edge bleeding. At first, the thickness was measured, being 2.79 ± 0.11 mm and 2.35 ± 0.02 mm for the high- and low-thickness interlayers, respectively. The results of DSC, as well as the properties of the CFRP investigated in previous studies [31], were used to define the molding parameters. In this study, calorimetry of the CFR prepreg was also performed. The composite did not show any degradation until a temperature of almost 300 °C was reached. Considering that the melting range of the PEEK film is not well defined (Figure 3), it can be assumed that a certain level of melting is also present at temperatures much lower than the identified T_m. Considering these aspects, the high-thickness interlayer composite has been compression-molded at 250 °C, with the other process parameters being set according to traditional manufacturing processes. The thin-interlayer laminate was molded at 350 °C, close to the T_m, with an extended consolidation time of 1 h. These changes were made to ensure the melting of the PEEK interlayer, also considering the greater mass of the aluminum mold used for this procedure. Furthermore, because of the increase in consolidation temperature, FEP release film was substituted for Kapton, since its maximum working temperature was lower than the used consolidation temperature. The difference in the adopted manufacturing procedures is related to the necessity of finding a good balance between the necessities of the two polymers, whose characteristic temperatures are far apart. Both hybrid laminates achieved good agglomeration, with the PEEK interlayer being easily identified. Reaching a high level of adhesion between the different plies is crucial to ensure the performance of the structures. Thanks to interpenetration between the CF composite and the TP layers, a strong bonding can be achieved; during molding, the applied pressure forces the melted interlayer to flow into the valleys of the CF plies embedding the asperities at the same time. This aspect is strictly related to the prepreg surface roughness that showed an arithmetical mean height (S_a) of 23 μm and a maximum height (S_z) of 201 μm [44]. After cooling, this configuration remains fixed, and a strong adhesion is obtained. However, polymer affinity is necessary since physical mechanisms are not sufficient to ensure agglomeration. Bending tests have been performed in a four-point configuration, which allows a constant normal stress to be applied on the outer surfaces of the sample between the inner pins. This test is particularly suitable for composite materials, which tend to fracture in a brittle manner and localize on the contact surface with the punch in the case of a three-point configuration. The obtained curves have shown a big difference between the two hybrid laminates, not only in terms of mechanical properties (Table 3) but also in the fracture mode. It can be observed in Figure 5 that the high-thickness interlayer laminate breaks in a similar manner to traditional CFRPs; even though some breakage peaks are present, which indicate an improved ductility, the stress drop is sharp and occurs at small strains. On the other hand, the low-thickness interlayer composite exhibited lower mechanical properties, possibly due to degradation of the epoxy resin during compression molding at 350 °C; indeed, the stiffness, the elastic modulus, and the bending strength were the 57.9%, 40.2%, and 80.0% of those of the high-thickness composite, respectively. However, the fracture mode is ductile with the sample being able to deform severely without failing completely. The bending curve has a plateau region that starts at a displacement of 3 mm; in this area, the average load and bending strength are 63.7 ± 4.3 N and 65.8 ± 4.4 MPa, respectively. A neat laminate structure, made up of 10 CFs plies of the same prepreg, has been compression-molded and tested in a bending configuration in a previous work [31]. The obtained stiffness, the bending strength, and the elastic modulus were 90 ± 5 N/mm, 818 ± 101 MPa, and 63.1 ± 1.2 GPa. Increases in stiffness have been achieved by interleaving PEEK films between CFs plies, but lower bending strength and moduli were measured. Furthermore, improvements in ductility were obtained, as crack propagation is fast in neat laminates and, thus, a sudden failure was recorded.

The mechanical tests made clear that the selection of process parameters is crucial in hybrid composite manufacturing. Nevertheless, the use of materials having characteristic temperatures that are far from each other, as in this case, limits the achievement of high performances and, consequently, reduces the positive hybrid effect. In particular, molding at low temperatures allows the CF-epoxy layers to be preserved but the PEEK film melting is not sufficient to obtain a high level of adhesion. On the other hand, a hot consolidation temperature correctly melts the TP interlayer, but the degradation of the epoxy resin causes a strong reduction in mechanical properties.

5. Conclusions

Hybrid composite laminates are promising materials for several industrial applications and particularly for space. Depending on the nature and shape of the hybridizing material, specific properties can be improved, and even additional functionalities can be imparted to the composite structure. This characteristic is very attractive, especially for those applications in which environmental and loading conditions can change rapidly. Thus, having materials whose properties can be designed specifically for these applications and are multifunctional is crucial to obtain structures that can respond rapidly to external factors. Traditionally, hybrid composites are manufactured by combining reinforcements of different nature into the polymeric matrix. The reinforcements dimension can be either on a micro-scale, by mixing CFs with GFs and Kevlar fibers, or on a nanoscale, by using CNTs, CNFs, and GNPs. Other studies deal with the integration of TP interlayers into CF-TS composites in order to improve ductility, toughness, and damping behavior. Furthermore, through matrix hybridization, thermoforming becomes a suitable manufacturing process for TS-based composites. This is a unique property, since TS polymers retain the shape they have taken during curing. In this context, hybrid matrix laminates have been manufactured by using two materials that are commonly used in the space sector, such as CFR epoxy prepreg and PEEK films. Laminates have been made of 10 composite plies and 9 TP interlayers. PEEK sheets of 25 μm and 200 μm have been used. PEEK calorimetry has been performed, and critical temperatures have been identified; specifically, those of T_g and T_m were 153 °C and 343 °C, respectively. Composite manufacturing has been performed by following two curing strategies; hot pressing and cold compression/oven curing have been used for the high and low-thickness interlayer laminates, respectively. A good level of adhesion has been achieved for both laminates, as shown by stereomicroscopy. In manufacturing hybrid laminates, the bonding mechanism exhibits a dual character since it combines physical and chemical properties. The former is related to the roughness of the surface of the composite plies, as superficial asperities may be embedded by the molten TP interlayer, which also serves to fill the interstitial valleys. Conversely, chemical affinity refers to the intrinsic characteristics of the polymers. Additional tests could be performed to further investigate this aspect such as Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) analysis. The low-thickness interlayer showed a maximum bending strength of 140 MPa, while the high-thickness one recorded that of 340 MPa. This difference in the mechanical properties is probably due to degradation of the epoxy resin in curing at 350 °C, which lies in the melting range of the PEEK film. These results underline the importance of the selection of molding temperature. However, the big difference in the characteristic temperatures of epoxy and PEEK makes this decision very complex, since a low consolidation temperature does not allow the complete melting of the PEEK, thus reducing the effect physical adhesion mechanism, while hot temperatures can cause the degradation of the epoxy resin. To overcome this issue, further studies are needed; future works will focus on the investigation of other manufacturing strategies by analyzing different molding conditions as well as by combining different technologies. A viable solution is related to the activation of the CF prepreg plies surfaces, for example, by plasma treatment, before molding. However, ongoing investigation and advancement of PEEK-based hybrid composites could support progresses across multiple sectors, including space, aeronautic, and defense.