Startseite Preparation of PEEK-NH2/graphene network structured nanocomposites with high electrical conductivity
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Preparation of PEEK-NH2/graphene network structured nanocomposites with high electrical conductivity

  • Huizhi Liu , Qilin Mei EMAIL logo , Guomin Ding EMAIL logo , Han Xiao , Shuhui Chen und Zhixiong Huang
Veröffentlicht/Copyright: 12. September 2022
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e-Polymers
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Abstract

The percolation thresholds of poly ether ether ketone/graphene (PEEK/Gr) composites in most studies are high due to the random distribution of Gr in the matrix. Here, aminated poly-ether-ether-ketone/graphene network (PEEK-NH2/GN) nanocomposites were prepared by electrostatic adsorption of PEEK-NH2 with positive charges and graphene oxide with negative charges, followed by in -situ reduction and hot-pressing. The GN structure of composites was well presented in the images of scanning electron microscope. The PEEK-NH2/GN nanocomposites exhibited excellent electrical conductivity with a maximum conductivity of 0.0634 S·cm−1 and a percolation threshold as low as 0.25 vol%. In addition, the maximum tensile strength of nanocomposites was reached at 93 MPa when the Gr content was 0.5 wt%. We believe that this approach is a new avenue for the production of low filler high conductive polymer composites with potential commercial prospects in various fields.

Keywords: aminated poly ether ether ketone; graphene; electrostatic adsorption; conductive network; electrical property

1 Introduction

As an engineering plastic with good thermal stability, chemical resistance, and excellent mechanical properties, poly ether ether ketone (PEEK) shows great advantages in areas such as aerospace and information technology (1,2,3). However, the non-conductive property of PEEK severely limits its application in electromagnetic shield, static protection, and lightning protection (4), which does not meet the needs of integration of material structure and function and equipment light-weighting (5). In recent years, many efforts have been made to dope conductive nanomaterials into PEEK matrix, especially graphene (Gr) with high electrical conductivity, high thermal conductivity, and large specific surface area as fillers. The mechanical properties, and electrical and thermal conductivity of the nanocomposites are significantly improved after the incorporation of Gr (6,7,8).

As is well known that the dispersion of nanofillers in the matrix is closely related to the performance of nanocomposites (9). But it is difficult to exfoliate Gr nanosheets by stirring, and Gr is also not dispersed in the matrix via melt blending because of the low melt index of PEEK. In comparison, solution blending is the ideal dispersion process for graphene-reinforced conventional thermoplastic composites (10). However, the interaction forces between Gr sheets result in poor dispersion in most solvents, and even its derivative graphene oxide (GO) only shows good dispersion in water. In contrast, the dispersion of PEEK in organic solvents such as dimethylformamide (DMF) and N-methylpyrrolidone is much better than in water. To solve the above contradictions, polymer-based dispersants, such as silane coupling agent KH550 (11), polyether-sulfone (12), and polyvinyl alcohol (13), are nowadays mostly grafted on the surface of GO or Gr to improve their dispersibility in organic solutions. Nevertheless, the contact resistance between Gr sheets is increased by these dispersants on the surface. And some dispersants may be decomposed at high molding temperature to introduce defects in the composites and reduce the mechanical properties.

The construction of conductive pathways in the matrix is the key to achieve high conductivity of the composites (14). Gr sheets are randomly distributed in poly ether ether ketone/graphene (PEEK/Gr) composites prepared through simple blending methods resulting in percolation thresholds of composites as high as 1–9 vol% (11,15,16,17,18). To obtain higher conductivity, large amounts of Gr nanosheets are added to the PEEK matrix, which not only leads to wasted resources and higher costs but also makes processing more difficult because of the increasing melt viscosity. To date, challenges for the preparation of PEEK/Gr composites with high performance by solution blending still exist.

In this article, aminated poly-ether-ether-ketone (PEEK-NH2) with positive charges was prepared by introducing amino groups in the amination reaction. A binary solvent system of DMF/H2O was provided to get rid of the dependence on dispersants and enable good dispersion of PEEK-NH2 and GO in solution. PEEK-NH2@Gr particles were obtained by electrostatic adsorption of GO sheets and PEEK-NH2 and then in situ reduction. The graphene network (GN) structure was constructed in the nanocomposites by hot pressing. The electrical and mechanical properties of the PEEK-NH2/GN composites were investigated.

2 Materials and methods

2.1 Materials

Graphite (5,000 items), ascorbic acid, and tin chloride dihydrate were provided by Shanghai Aladdin Biochemical Technology Co., Ltd (Shanghai, China). PEEK (085PF) was purchased from Jinlin Jusep Special Plastics Co., Ltd (Jilin China). DMF was provided by Tianjin Beichen District Fangzheng Reagent Factory (Tianjin, China). Sulfuric acid (98 wt%), nitric acid (65 wt%), and hydrochloric acid (37 wt%) were obtained from Sinopharm Chemical Reagent Co., Ltd.

2.2 Fabrication of PEEK-NH2 particles

PEEK powder was first placed in the vacuum drying oven for 24 h at 120°C to remove the water. Nitric acid (40 mL) and sulfuric acid (10 mL) were poured into the 250 mL round-bottom flask in turn. Later, the PEEK powder (4 g) was added to the mixed solution which was being stirred. The mixture was stirred for 10 min at low temperature (15°C) to diminish the nitrification of PEEK. After that, the mixture was vacuum-filtered through a PTFE membrane (with a diameter of 50 mm and a pore size of 0.22 mm) and then washed several times with distilled water and ethanol to obtain PEEK-NO2. Next, tin chloride dihydrate (16 g) was dissolved in a mixture of hydrochloric acid (100 mL) and ethanol (50 mL), and stirred for 15 min at room temperature. PEEK-NO2 powder (4 g) was added in the mixture which was being stirred and then stirred for 4 h at 65°C. Finally, the mixture was vacuum-filtered, washed with deionized water, and dried overnight at 80°C to obtain PEEK-NH2 powder.

2.3 Preparation of PEEK-NH2/GN composite

GO was prepared from pristine graphite powder according to a modified hummers method as reported in our previous study (19,20). GO (0.1, 0.5, 1, 2, 3, and 5 wt% of PEEK-NH2) and PEEK-NH2 were added into a mixture of the binary solution of DMF (95 mL) and H2O (5 mL). The mixture was sonicated for 30 min in a water bath and then stirred at room temperature for 30 min. Next, ascorbic acid (four times the weight of GO) was dissolved to reduce GO in the mixture. The suspension solution was kept stirring continuously at 90°C for 4 h. After that, the mixture was vacuum-filtered and washed several times with distilled water and ethanol. The PEEK-NH2@Gr composite particles were taken from the membrane and dried at 80°C for 12 h.

The metal mold was coated with a release agent which was high temperature-resistant. The composite particles were overfilled into the metal mold and then pre-pressed at room temperature for 3 min under 0.1 MPa to diminish the gas in the particles. Finally, the PEEK-NH2/GN nanocomposites were prepared at 360°C for 5 min under 3 MPa.

2.4 Characterization

Fourier transform infrared spectroscopy (FTIR) was carried out with an intelligent Fourier transform infrared spectrometer model Nexus from Therno Nicolet, USA, in the range 4,000–400 cm−1. The chemical structure of the surface was detected with an X-ray photoelectron spectroscopy (XPS) from Thermo Fisher Scientific. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were tested by a comprehensive thermal analyzer model STA449F3 from NETZSCH, Germany (nitrogen atmosphere, 10°C·min−1 ramp-up rate, room temperature – 1,000°C). Scanning electron microscopic (SEM) images were taken using an SEM model JSM-7500F from Nippon Electron Co at an accelerating voltage of 5.0 kV. Metallographic images were taken with a Phoenix Optical model M3230Bd metallographic microscope. The conductivity was measured through the RTS-8 digital four-probe tester. The tensile strength was characterized using an electronic universal testing machine, model RGM4100, manufactured by Shenzhen Rigel.

3 Results and discussion

3.1 Modified of PEEK

Scheme 1 shows a schematic illustration of the fabrication of the PEEK-NH2/GN composite. The PEEK was nitrated and reduced, respectively, so the –NH2 was introduced on the surface of PEEK particles (Scheme 1a–c). On the other hand, in order to improve the dispersion of GO in DMF, a little water was added (Scheme 1d and e). Then, the GO nanosheets and PEEK-NH2 particles were mixed well in the DMF-H2O binary solution, and a self-assembly of GO nanosheets on the surface of PEEK-NH2 was formed due to electrostatic attraction (Scheme 1f). Next, the PEEK-NH2@GO was reduced in situ by vitamin C at 90°C, and the PEEK-NH2@Gr composite particles were obtained (Scheme 1g). Finally, the GN was proactively built in the PEEK matrix by means of the core–shell structure of PEEK-NH2@Gr, and the PEEK-NH2/GN composite was fabricated by hot-pressing, which was expected to show high conductivity (Scheme 1h).

Scheme 1 Schematic illustration of the experiment route to prepare PEEK-NH2/GN composites. (a–h) Experimental steps described in the text of this article (Section 3.1).
Scheme 1

Schematic illustration of the experiment route to prepare PEEK-NH2/GN composites. (a–h) Experimental steps described in the text of this article (Section 3.1).

For understanding the self-assembly of GO nanosheets on the matrix particles, the PEEK was modified by amino-functionalization to introduce electrostatic attraction. However, the common technology adopting strong nitration to generate –NO2 during the amination process would damage seriously the molecules structure of PEEK, which caused a decrease dramatically of the property (21). Therefore, a mild nitrated reaction at low temperature (15°C) and short term (10 min) was used to make a minimal amination on the PEEK surface in our study.

The chemical characteristics of the PEEK and PEEK-NH2 were confirmed using the FTIR spectra. As shown in Figure 1a, the appearance of PEEK does not change after minimal amination treatment, and the FTIR curves of PEEK and PEEK-NH2 are the same. However, the survey scan of XPS spectra shows that compared with that of PEEK, a new, small peak of N 1s appears at 400 eV (Figure 1b). This change also agrees with the C 1s spectra of both. As shown in Figure 1c and d, the double peak structure of the C 1s spectrum of PEEK is deconvolved into four chemically shifted components which are the C–C (284.8 eV), C–O (286.3 eV), C═O (287.4 eV), and C═C (291.2 eV) bonds (22). After the amination modification, there is a new peak at 286 eV for C–N bond and a little N atom (1.25%) in the C 1s spectrum, which suggests the presence of –NH2. The difference in change degree of FTIR and XPS is due to the data gathered by the FTIR test containing the chemical information from a large depth of surface (several microns). However, the XPS test detects the chemical information of the surface to be ≈5 nm. This indicates that the amination of PEEK occurs in a very shallow range of the surface, which is advantageous to maintain the high performance of the material.

Figure 1 (a) FTIR spectra of PEEK and PEEK-NH2, (b) XPS survey spectrum, (c) C 1s peek-fitting curves of PEEK, and (d) PEEK-NH2 from XPS spectra.
Figure 1

(a) FTIR spectra of PEEK and PEEK-NH2, (b) XPS survey spectrum, (c) C 1s peek-fitting curves of PEEK, and (d) PEEK-NH2 from XPS spectra.

3.2 Dispersion of PEEK-NH2 and GO in solution

The good dispersion of PEEK-NH2 and GO in the solvent is one of the important prerequisites to prepare the PEEK-NH2/GN composites by solution blending. But PEEK-NH2 is poorly dispersed in H2O, and it floats on the surface of solution (Figure 2a). On the contrary, GO is badly dispersed in DMF, and it deposits in the solution (Figure 2b). To improve the dispersion in the solution, we propose a binary solvent combined H2O which is the good solvent for GO and DMF which is the good solvent for PEEK-NH2, and the volume ratio of binary solvent is 5:95. As shown in Figure 2c, the solution is a white suspension indicating PEEK-NH2 is homogeneously dispersed in the DMF/H2O solvent. Similarly, a yellow solution is presented in Figure 2d, indicating the good dispersion in the DMF/H2O solvent for GO.

Figure 2 (a) Digital photographs of PEEK-NH2 in H2O, (b) GO in DMF, (c) PEEK-NH2 in DMF/H2O, and (d) GO in DMF/H2O, and (e) metallographic micrographs of PEEK-NH2 in H2O, (f) GO in DMF, (g) PEEK-NH2 in DMF/H2O, and (h) GO in DMF/H2O.
Figure 2

(a) Digital photographs of PEEK-NH2 in H2O, (b) GO in DMF, (c) PEEK-NH2 in DMF/H2O, and (d) GO in DMF/H2O, and (e) metallographic micrographs of PEEK-NH2 in H2O, (f) GO in DMF, (g) PEEK-NH2 in DMF/H2O, and (h) GO in DMF/H2O.

The dispersion states of PEEK-NH2 and GO in different solvents were characterized using metallographic microscope. PEEK-NH2 are aggregated white particles in H2O, and the image is blurred due to a large height difference in the aggregation (Figure 2e). This is because there is a strong hydrophobic force between PEEK-NH2 and H2O, and PEEK-NH2 particles clump together in hydrophobic force to create a minimal contact area (23). From Figure 2f, GO in DMF is a huge lustrous sheet with a length of beyond 40 µm and a width of 26 µm. However, the average size of graphite to prepare GO is about 2.6 µm, indicating GO sheets are agglomerated in DMF caused by the van der Waals forces between the GO sheets (24). In comparison, PEEK-NH2 is a single white particle with a size of 10 µm in DMF/H2O that is consistent with the size of PEEK, and GO presents translucent lamella with an average size of about 10 µm in DMF/H2O (Figure 2g and h). We consider that the good dispersion in DMF/H2O is attributed to two aspects. First, small amounts of H2O can be interspersed between the GO nanosheets because of a large number of hydrophilic oxygen-containing functional groups on the surface of GO. Second, as a result of the miscible system of H2O and DMF, the dispersion of PEEK-NH2 is not affected by small amounts of H2O. Based on the above results, the binary solvent system of DMF and H2O realizes a good dispersion for GO and PEEK-NH2 and is chosen as the solvent to prepare the PEEK-NH2@Gr composite particles by solution blending.

3.3 Preparation of PEEK-NH2@Gr particle

Figure 3a shows the schematic illustration of the preparation of PEEK-NH2@Gr particles by solution blending. First, GO with negative charges was adsorbed on the surface of positively charged PEEK-NH2 by electrostatic force. The electrostatic force almost disappeared after reduction, and then, the π–π conjugation between Gr and PEEK-NH2 played an important role to hold the position of Gr (25).

Figure 3 (a) Schematic illustration of electrostatic adsorption between PEEK-NH2 and Gr, (b) FTIR spectra of GO and Gr, (c) digital photographs of same content PEEK/Gr and PEEK-NH2@Gr in solution and schematic illustration of volume state, (d) SEM images of PEEK-NH2, (e) PEEK-NH2@0.5 wt% Gr, (f) PEEK-NH2@1 wt% Gr, (g) PEEK-NH2@3 wt% Gr, (h–k) TEM images of PEEK-NH2@2 wt% Gr, and (l) C 1s peek-fitting curve of PEEK-NH2@2 wt%Gr.
Figure 3

(a) Schematic illustration of electrostatic adsorption between PEEK-NH2 and Gr, (b) FTIR spectra of GO and Gr, (c) digital photographs of same content PEEK/Gr and PEEK-NH2@Gr in solution and schematic illustration of volume state, (d) SEM images of PEEK-NH2, (e) PEEK-NH2@0.5 wt% Gr, (f) PEEK-NH2@1 wt% Gr, (g) PEEK-NH2@3 wt% Gr, (h–k) TEM images of PEEK-NH2@2 wt% Gr, and (l) C 1s peek-fitting curve of PEEK-NH2@2 wt%Gr.

Figure 3b shows the FTIR spectra of GO before and after reduction. There are O‒H stretching vibration (3,424 cm−1), C═O stretching vibration (1,725 cm−1), and C‒OH stretching vibration (1,355 cm−1) for GO (26,27,28). After the reduction, the intensity of the characteristic peaks related to the oxygen-containing functional group is significantly weakened, indicating that GO is reduced to Gr.

The states of the same content PEEK/Gr and PEEK-NH2@Gr composite powder in solution were taken by digital camera. As shown in Figure 3c, there is a stratification in the PEEK/Gr powder which is the white PEEK and the black Gr, indicating that Gr is randomly distributed in the matrix. On the contrary, stratification does not occur in the PEEK-NH2@Gr powder which is only gray powder suggesting that Gr sheets are well dispersed in the matrix. Larger volume of PEEK-NH2@Gr than that of the PEEK/Gr is noteworthy. This is probably related to the appropriate Hansen solubility parameters of DMF molecules. Due to the sum of δ p (polarity cohesion parameter) and δ h (hydrogen bonding cohesion parameter) in the range of 13–29, DMF shows a good affinity for the surface of Gr and is able to intersperse between the Gr sheets (29,30). When Gr is uniformly distributed over the surface of the PEEK-NH2, the PEEK-NH2@Gr particles are segregated by the DMF molecules.

The micromorphology of PEEK-NH2 and PEEK-NH2@Gr particles were characterized using SEM and transmission electron microscope (TEM). Figure 3d shows that PEEK-NH2 are irregular particles with a size of about 5–10 µm and smooth on the surface. But some lighter-colored sheets appear on the surface of PEEK-NH2@Gr particles, indicating that the Gr sheets are coated on the PEEK-NH2 by electrostatic force (Figure 3e). Moreover, the Gr sheets on the PEEK-NH2 surface increase as the content of Gr increases, and Gr could be distributed over the surface of multiple PEEK-NH2 particles, which forms a bridge of connection (Figure 3f and g). Figure 3h–k shows the TEM image of PEEK-NH2@Gr particles. Gr sheets are observed on the surface of particles, which is consistent with the results of the SEM images. From the above results, SEM and TEM can provide visual evidence of the presence of Gr on the surface of PEEK-NH2.

In addition, the surface chemical structure of PEEK-NH2@Gr was detected using XPS. Compared to the PEEK-NH2, the disappearance of the C–N peak and N atom in the C 1s spectrum of PEEK-NH2@Gr composite particles are observed (Figure 3l). There is an increase of 1.58% for C atom in the element content of PEEK-NH2@Gr. It is attributed to the fact that the surface of PEEK-NH2@Gr is covered with Gr sheets. Thus, we consider the result of the XPS spectrum also confirms the presence of Gr on the surface of PEEK-NH2.

3.4 Thermal properties

To investigate the influence of modification and different content of Gr on the thermal properties, PEEK, PEEK-NH2, and PEEK-NH2@Gr were analyzed using DSC and TG. The data on thermal properties are collected (Table 1). As shown in Figure 4a, there is a significant exothermic peak at 343.6°C corresponding to melting temperature (T m) in the DSC curve of PEEK. After amination modification, the T m of PEEK-NH2 is 1.2°C lower than PEEK. This is because the –NH2 destructs the regularity in the molecular structure leading to a decrease of the crystallinity, which is similar to other PEEK derivatives with substituent groups (31). With the addition of Gr, it is a tendency to increase first and then decrease for the T m of PEEK-NH2@Gr ascribed to the nucleation effect and the restriction of molecular chain movement (32). When the content of Gr is low, the crystallization is promoted by nanofillers which are able to be the center of the crystallization process. By contrast, the crystallization is reduced at the high content of Gr resulting from impeding the molecular chains of PEEK-NH2.

Table 1

Thermal properties of PEEK, PEEK-NH2, and PEEK-NH2@Gr

Sample Filler content (wt%) T m (°C) T max (°C)
PEEK — 343.6 590.3
PEEK-NH2 — 342.4 561.0
0.1 Gr 0.1 345.5 566.6
1 Gr 1 345.4 569.2
3 Gr 3 346.2 578.0
5 Gr 5 345.7 582.4
Figure 4 (a) DSC and (b) TG curves of PEEK, PEEK-NH2, and PEEK-NH2@Gr composite powder.
Figure 4

(a) DSC and (b) TG curves of PEEK, PEEK-NH2, and PEEK-NH2@Gr composite powder.

In addition, PEEK has a sharp heat absorption peak at 590°C which is the maximum degradation temperature (T max) (33). The T max of PEEK-NH2 is decreased by 29.3°C due to the decomposition of -NH2. As the content of Gr increases, the T max of PEEK-NH2@Gr is gradually increased and up to 582.4°C at 5 wt% Gr. The addition of Gr results in a better thermal stability of the PEEK-NH2@Gr composite particles due to the large specific surface area of Gr that is a good barrier to the thermal decomposition gases (34).

Figure 4b shows the TG curves of PEEK, PEEK-NH2, and PEEK-NH2@Gr. Compared to PEEK, there is a decrease in the thermal stability of PEEK-NH2 after amination modification. With the addition of Gr, the thermal stability of PEEK-NH2@Gr increased. The above results are consistent with DSC, and all of them indicate that the PEEK-NH2@Gr has good thermal stability performance.

3.5 Electrical conductivity

As we all know, the electrical conductivity of the nanocomposites is closely related to the distribution of Gr. The SEM images of PEEK-NH2 and PEEK-NH2/GN nanocomposites prepared under 10 MPa at room temperature were used to characterize the GN in the matrix. As shown in Figure 5a and b, it is obvious that Gr sheets are attached to the surface of the PEEK-NH2/GN compared to PEEK-NH2. The shells of PEEK-NH2@Gr are in close contact under pressure, which form a continuous GN structure. The conductive pathways are made up of matrix and Gr in conventional polymer/Gr composites caused by the random distribution of Gr in the matrix (Figure 5c). However, based on the PEEK-NH2@Gr core–shell structure, electrons only transport in the GN which can greatly improve the conductivity of nanocomposites (Figure 5d).

Figure 5 (a) SEM images of PEEK-NH2 and (b) PEEK-NH2/GN nanocomposites pressed at room temperature, (c) schematic illustration of the conductive pathways in substrates for random distribution and (d) GN, (e) electrical conductivities of PEEK-NH2/GN nanocomposites as a function of volume fraction of Gr, and (f) double logarithmic curve of conductivity versus (φ–φ c ).
Figure 5

(a) SEM images of PEEK-NH2 and (b) PEEK-NH2/GN nanocomposites pressed at room temperature, (c) schematic illustration of the conductive pathways in substrates for random distribution and (d) GN, (e) electrical conductivities of PEEK-NH2/GN nanocomposites as a function of volume fraction of Gr, and (f) double logarithmic curve of conductivity versus (φ–φ c ).

Figure 5e and f shows the relationship between the electrical conductivity of the PEEK-NH2/GN composites and the Gr content. The conductivity of nanocomposites can be described by the power law equation of the percolation theory in Eq. 1.

(1) σ = σ 0 ( φ − φ c ) t

where σ is the conductivity of the composite, σ 0 is the intrinsic conductivity of the filler, φ is the volume fraction of the filler, φ c is the volume fraction of the filler at the percolation threshold which is the sharp increase in the electrical conductivity of a composite with the addition of a certain amount of conductive fillers, and t represents the criticality index which describes the conductivity change factor at the critical point.

The electrical conductivity of the PEEK-NH2/GN composite increases rapidly after the incorporation of Gr and reaches 0.0634 S·cm−1 at a Gr content of 2.912 vol%. Moreover, the percolation threshold of the PEEK-NH2/GN composites is 0.25 vol%, which indicates that at Gr content of 0.25 vol% the GN is formed in the composite. The conductive properties of the PEEK/Gr nanocomposites in the recent years of research are summarized in Table 2. The percolation threshold of our PEEK-NH2/GN composites is much lower than other PEEK/Gr nanocomposites. The reason for this result is that a small amount of Gr could construct a continuous GN in the matrix due to the PEEK-NH2@Gr core–shell structure. The method in this study is well suited for the preparation of PEEK/Gr nanocomposites with a lower percolation threshold and higher electrical conductivity.

Table 2

A comparison of fabrication method, electrical percolation threshold, and maximum electrical conductivity of PEEK/Gr nanocomposites

Composition Fabrication methoda Percolation threshold (φ c) (vol%) Maximum filler content (wt%) Maximum electrical conductivity (S·cm−1) Ref.
PEEK/m-TRG U + HCM 0.76 5 2.0 × 10−3 (11)
PEEK/GNP/CLF HCM — 9 9.4 × 10−3 (16)
PEEK/GNP SB + HCM 1.76 6 1.0 × 10−3 (17)
PEEK/GNP EPM 2.91 10 4.3 × 10−3 (18)
PEEK/GPEI1 U + EM 1.11 5 1.0 × 10−2 (15)
This work SB + HCM 0.25 5 6.3 × 10−2 This work

aU – ultrasonication; HCM – hot compression molding; SB – solution blending; EPM – electric powder mixer; and EM – extrusion molding.

3.6 Mechanical properties

Tensile strength and modulus of PEEK, PEEK-NH2, and PEEK-NH2/GN composites are presented in Figure 6a and b. Compared to the unmodified PEEK, tensile strength and modulus of PEEK-NH2 are decreased by 6.3% and 7.4%, respectively, related to the decrease in crystallinity (31). With the addition of Gr, the trend of tensile strength is increased first and then decreased, and the optimal performance is 93 MPa obtained at the 0.5 wt% Gr. But tensile modulus of composites has been increasing with increasing Gr. We consider that the mechanical strength of composites is related to crack deflection and agglomeration caused by nanofillers which could be observed in the tensile section of the composite (35,36).

Figure 6 (a) Tensile strength and (b) modulus of PEEK, PEEK-NH2, and PEEK-NH2/GN composites, (c) schematic illustration of crack propagation mechanism in PEEK-NH2/GN composite, (d) SEM images from tensile fracture surfaces of PEEK-NH2, (e) PEEK-NH2/0.5 wt% GN, (f) PEEK-NH2/1 wt% GN, and (g) PEEK-NH2/3 wt% GN.
Figure 6

(a) Tensile strength and (b) modulus of PEEK, PEEK-NH2, and PEEK-NH2/GN composites, (c) schematic illustration of crack propagation mechanism in PEEK-NH2/GN composite, (d) SEM images from tensile fracture surfaces of PEEK-NH2, (e) PEEK-NH2/0.5 wt% GN, (f) PEEK-NH2/1 wt% GN, and (g) PEEK-NH2/3 wt% GN.

Figure 6c–f shows the SEM images of the tensile section of the composites. It is apparent that there is flat and smooth on the cross section without the nanofiller. But the cracks are found in the cross section of PEEK-NH2/GN composites, and the number of cracks is more with the increase in filler content. It is due to the fact that cracks bifurcate and bypass along the surface of Gr sheets when they encounter Gr sheets (Figure 6g). As the deflection of cracks, there is a height difference from the original cracks, which makes a tortuous crack path and corresponds to the rough surface observed from SEM images (37). Due to the energy absorption of crack deflection, the mechanical properties of nanocomposites are increased at the low content of Gr. When the content of nanofillers is high, the height difference of cracks is larger, indicating Gr sheets agglomerate in the matrix leading to a decrease in mechanical properties.

4 Conclusion

In this study, –NH2 was introduced on the surface of PEEK to obtain PEEK-NH2 with positive charges. A binary solvent of DMF/H2O was used to improve the dispersion of PEEK-NH2 and GO in the solution. Then, GO was coated on the surface of PEEK-NH2 via electrostatic adsorption in the DMF/H2O. After in-situ reduction and hot-pressing, a 3D conductive GN was formed in the composite. The prepared PEEK-NH2/GN nanocomposites exhibited excellent electrical conductivity with a percolation threshold as low as 0.25 vol%. The maximum conductivity was 0.0,634 S·cm−1 when the content of Gr reached 2.912 vol%. In addition, the composites showed relatively good thermal and mechanical properties. The method of building the GN is a new route, which is also applicable to other engineering plastics, for the production of nanocomposites with a low percolation threshold.

Acknowledgment

We are grateful for the constructive comments and valuable advice from all the reviewers for further improvement of our work.

  1. Funding information: This work was supported by the National Natural Science Foundation of China (No. 52003120), the Fundamental Research Funds for the Central Universities (WUT: 2022VIA004), and Jiangsu Province Shuangchuang Project.

  2. Author contributions: Huizhi Liu: writing – original draft, writing – review and editing, methodology, formal analysis; Qilin Mei: writing – review and editing, project administration; Guoming Ding: writing – review and editing, funding acquisition; Han Xiao: investigation; Shuhui Chen: resources; and Zhixiong Huang: supervision.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Received: 2022-04-20
Revised: 2022-07-17
Accepted: 2022-07-18
Published Online: 2022-09-12

© 2022 Huizhi Liu et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

  1. Research Articles
  2. The effect of isothermal crystallization on mechanical properties of poly(ethylene 2,5-furandicarboxylate)
  3. The effect of different structural designs on impact resistance to carbon fiber foam sandwich structures
  4. Hyper-crosslinked polymers with controlled multiscale porosity for effective removal of benzene from cigarette smoke
  5. The HDPE composites reinforced with waste hybrid PET/cotton fibers modified with the synthesized modifier
  6. Effect of polyurethane/polyvinyl alcohol coating on mechanical properties of polyester harness cord
  7. Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties
  8. Development, characterization, and in vitro evaluation of adhesive fibrous mat for mucosal propranolol delivery
  9. Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites
  10. Preparation of highly water-resistant wood adhesives using ECH as a crosslinking agent
  11. Chitosan-based antioxidant films incorporated with root extract of Aralia continentalis Kitagawa for active food packaging applications
  12. Molecular dynamics simulation of nonisothermal crystallization of a single polyethylene chain and short polyethylene chains based on OPLS force field
  13. Synthesis and properties of polyurethane acrylate oligomer based on polycaprolactone diol
  14. Preparation and electroactuation of water-based polyurethane-based polyaniline conductive composites
  15. Rapeseed oil gallate-amide-urethane coating material: Synthesis and evaluation of coating properties
  16. Synthesis and properties of tetrazole-containing polyelectrolytes based on chitosan, starch, and arabinogalactan
  17. Preparation and properties of natural rubber composite with CoFe2O4-immobilized biomass carbon
  18. A lightweight polyurethane-carbon microsphere composite foam for electromagnetic shielding
  19. Effects of chitosan and Tween 80 addition on the properties of nanofiber mat through the electrospinning
  20. Effects of grafting and long-chain branching structures on rheological behavior, crystallization properties, foaming performance, and mechanical properties of polyamide 6
  21. Study on the interfacial interaction between ammonium perchlorate and hydroxyl-terminated polybutadiene in solid propellants by molecular dynamics simulation
  22. Study on the self-assembly of aromatic antimicrobial peptides based on different PAF26 peptide sequences
  23. Effects of high polyamic acid content and curing process on properties of epoxy resins
  24. Experiment and analysis of mechanical properties of carbon fiber composite laminates under impact compression
  25. A machine learning investigation of low-density polylactide batch foams
  26. A comparison study of hyaluronic acid hydrogel exquisite micropatterns with photolithography and light-cured inkjet printing methods
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  33. Simultaneously enhance the fire safety and mechanical properties of PLA by incorporating a cyclophosphazene-based flame retardant
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  35. The role of natural rubber endogenous proteins in promoting the formation of vulcanization networks
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  37. A wood-mimetic porous MXene/gelatin hydrogel for electric field/sunlight bi-enhanced uranium adsorption
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  81. Mechanical, thermal, and tribological characterization of bio-polymeric composites: A comprehensive review
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  83. Influence of filler material on properties of fiber-reinforced polymer composites: A review
  84. Rapid Communications
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https://doi.org/10.1515/epoly-2022-0067
Schlagwörter für diesen Artikel
aminated poly ether ether ketone; graphene; electrostatic adsorption; conductive network; electrical property
Creative Commons
BY 4.0

Artikel in diesem Heft

  1. Research Articles
  2. The effect of isothermal crystallization on mechanical properties of poly(ethylene 2,5-furandicarboxylate)
  3. The effect of different structural designs on impact resistance to carbon fiber foam sandwich structures
  4. Hyper-crosslinked polymers with controlled multiscale porosity for effective removal of benzene from cigarette smoke
  5. The HDPE composites reinforced with waste hybrid PET/cotton fibers modified with the synthesized modifier
  6. Effect of polyurethane/polyvinyl alcohol coating on mechanical properties of polyester harness cord
  7. Fabrication of flexible conductive silk fibroin/polythiophene membrane and its properties
  8. Development, characterization, and in vitro evaluation of adhesive fibrous mat for mucosal propranolol delivery
  9. Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites
  10. Preparation of highly water-resistant wood adhesives using ECH as a crosslinking agent
  11. Chitosan-based antioxidant films incorporated with root extract of Aralia continentalis Kitagawa for active food packaging applications
  12. Molecular dynamics simulation of nonisothermal crystallization of a single polyethylene chain and short polyethylene chains based on OPLS force field
  13. Synthesis and properties of polyurethane acrylate oligomer based on polycaprolactone diol
  14. Preparation and electroactuation of water-based polyurethane-based polyaniline conductive composites
  15. Rapeseed oil gallate-amide-urethane coating material: Synthesis and evaluation of coating properties
  16. Synthesis and properties of tetrazole-containing polyelectrolytes based on chitosan, starch, and arabinogalactan
  17. Preparation and properties of natural rubber composite with CoFe2O4-immobilized biomass carbon
  18. A lightweight polyurethane-carbon microsphere composite foam for electromagnetic shielding
  19. Effects of chitosan and Tween 80 addition on the properties of nanofiber mat through the electrospinning
  20. Effects of grafting and long-chain branching structures on rheological behavior, crystallization properties, foaming performance, and mechanical properties of polyamide 6
  21. Study on the interfacial interaction between ammonium perchlorate and hydroxyl-terminated polybutadiene in solid propellants by molecular dynamics simulation
  22. Study on the self-assembly of aromatic antimicrobial peptides based on different PAF26 peptide sequences
  23. Effects of high polyamic acid content and curing process on properties of epoxy resins
  24. Experiment and analysis of mechanical properties of carbon fiber composite laminates under impact compression
  25. A machine learning investigation of low-density polylactide batch foams
  26. A comparison study of hyaluronic acid hydrogel exquisite micropatterns with photolithography and light-cured inkjet printing methods
  27. Multifunctional nanoparticles for targeted delivery of apoptin plasmid in cancer treatment
  28. Thermal stability, mechanical, and optical properties of novel RTV silicone rubbers using octa(dimethylethoxysiloxy)-POSS as a cross-linker
  29. Preparation and applications of hydrophilic quaternary ammonium salt type polymeric antistatic agents
  30. Coefficient of thermal expansion and mechanical properties of modified fiber-reinforced boron phenolic composites
  31. Synergistic effects of PEG middle-blocks and talcum on crystallizability and thermomechanical properties of flexible PLLA-b-PEG-b-PLLA bioplastic
  32. A poly(amidoxime)-modified MOF macroporous membrane for high-efficient uranium extraction from seawater
  33. Simultaneously enhance the fire safety and mechanical properties of PLA by incorporating a cyclophosphazene-based flame retardant
  34. Fabrication of two multifunctional phosphorus–nitrogen flame retardants toward improving the fire safety of epoxy resin
  35. The role of natural rubber endogenous proteins in promoting the formation of vulcanization networks
  36. The impact of viscoelastic nanofluids on the oil droplet remobilization in porous media: An experimental approach
  37. A wood-mimetic porous MXene/gelatin hydrogel for electric field/sunlight bi-enhanced uranium adsorption
  38. Fabrication of functional polyester fibers by sputter deposition with stainless steel
  39. Facile synthesis of core–shell structured magnetic Fe3O4@SiO2@Au molecularly imprinted polymers for high effective extraction and determination of 4-methylmethcathinone in human urine samples
  40. Interfacial structure and properties of isotactic polybutene-1/polyethylene blends
  41. Toward long-live ceramic on ceramic hip joints: In vitro investigation of squeaking of coated hip joint with layer-by-layer reinforced PVA coatings
  42. Effect of post-compaction heating on characteristics of microcrystalline cellulose compacts
  43. Polyurethane-based retanning agents with antimicrobial properties
  44. Preparation of polyamide 12 powder for additive manufacturing applications via thermally induced phase separation
  45. Polyvinyl alcohol/gum Arabic hydrogel preparation and cytotoxicity for wound healing improvement
  46. Synthesis and properties of PI composite films using carbon quantum dots as fillers
  47. Effect of phenyltrimethoxysilane coupling agent (A153) on simultaneously improving mechanical, electrical, and processing properties of ultra-high-filled polypropylene composites
  48. High-temperature behavior of silicone rubber composite with boron oxide/calcium silicate
  49. Lipid nanodiscs of poly(styrene-alt-maleic acid) to enhance plant antioxidant extraction
  50. Study on composting and seawater degradation properties of diethylene glycol-modified poly(butylene succinate) copolyesters
  51. A ternary hybrid nucleating agent for isotropic polypropylene: Preparation, characterization, and application
  52. Facile synthesis of a triazine-based porous organic polymer containing thiophene units for effective loading and releasing of temozolomide
  53. Preparation and performance of retention and drainage aid made of cationic spherical polyelectrolyte brushes
  54. Preparation and properties of nano-TiO2-modified photosensitive materials for 3D printing
  55. Mechanical properties and thermal analysis of graphene nanoplatelets reinforced polyimine composites
  56. Preparation and in vitro biocompatibility of PBAT and chitosan composites for novel biodegradable cardiac occluders
  57. Fabrication of biodegradable nanofibers via melt extrusion of immiscible blends
  58. Epoxy/melamine polyphosphate modified silicon carbide composites: Thermal conductivity and flame retardancy analyses
  59. Effect of dispersibility of graphene nanoplatelets on the properties of natural rubber latex composites using sodium dodecyl sulfate
  60. Preparation of PEEK-NH2/graphene network structured nanocomposites with high electrical conductivity
  61. Preparation and evaluation of high-performance modified alkyd resins based on 1,3,5-tris-(2-hydroxyethyl)cyanuric acid and study of their anticorrosive properties for surface coating applications
  62. A novel defect generation model based on two-stage GAN
  63. Thermally conductive h-BN/EHTPB/epoxy composites with enhanced toughness for on-board traction transformers
  64. Conformations and dynamic behaviors of confined wormlike chains in a pressure-driven flow
  65. Mechanical properties of epoxy resin toughened with cornstarch
  66. Optoelectronic investigation and spectroscopic characteristics of polyamide-66 polymer
  67. Novel bridged polysilsesquioxane aerogels with great mechanical properties and hydrophobicity
  68. Zeolitic imidazolate frameworks dispersed in waterborne epoxy resin to improve the anticorrosion performance of the coatings
  69. Fabrication of silver ions aramid fibers and polyethylene composites with excellent antibacterial and mechanical properties
  70. Thermal stability and optical properties of radiation-induced grafting of methyl methacrylate onto low-density polyethylene in a solvent system containing pyridine
  71. Preparation and permeation recognition mechanism of Cr(vi) ion-imprinted composite membranes
  72. Oxidized hyaluronic acid/adipic acid dihydrazide hydrogel as cell microcarriers for tissue regeneration applications
  73. Study of the phase-transition behavior of (AB)3 type star polystyrene-block-poly(n-butylacrylate) copolymers by the combination of rheology and SAXS
  74. A new insight into the reaction mechanism in preparation of poly(phenylene sulfide)
  75. Modified kaolin hydrogel for Cu2+ adsorption
  76. Thyme/garlic essential oils loaded chitosan–alginate nanocomposite: Characterization and antibacterial activities
  77. Thermal and mechanical properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/calcium carbonate composite with single continuous morphology
  78. Review Articles
  79. The use of chitosan as a skin-regeneration agent in burns injuries: A review
  80. State of the art of geopolymers: A review
  81. Mechanical, thermal, and tribological characterization of bio-polymeric composites: A comprehensive review
  82. The influence of ionic liquid pretreatment on the physicomechanical properties of polymer biocomposites: A mini-review
  83. Influence of filler material on properties of fiber-reinforced polymer composites: A review
  84. Rapid Communications
  85. Pressure-induced flow processing behind the superior mechanical properties and heat-resistance performance of poly(butylene succinate)
  86. RAFT polymerization-induced self-assembly of semifluorinated liquid-crystalline block copolymers
  87. RAFT polymerization-induced self-assembly of poly(ionic liquids) in ethanol
  88. Topical Issue: Recent advances in smart polymers and their composites: Fundamentals and applications (Guest Editors: Shaohua Jiang and Chunxin Ma)
  89. Fabrication of PANI-modified PVDF nanofibrous yarn for pH sensor
  90. Shape memory polymer/graphene nanocomposites: State-of-the-art
  91. Recent advances in dynamic covalent bond-based shape memory polymers
  92. Construction of esterase-responsive hyperbranched polyprodrug micelles and their antitumor activity in vitro
  93. Regenerable bacterial killing–releasing ultrathin smart hydrogel surfaces modified with zwitterionic polymer brushes
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