Home Physical Sciences Effects of multiwalled carbon nanotube mass fraction on microstructures and electrical resistivity of polycarbonate-based conductive composites
Article Open Access

Effects of multiwalled carbon nanotube mass fraction on microstructures and electrical resistivity of polycarbonate-based conductive composites

  • Lijun Wang , Jianhui Qiu EMAIL logo , Eiichi Sakai and Xiaowei Wei
Published/Copyright: August 15, 2015
Download Article (PDF)
Become an author with De Gruyter Brill
Submit Manuscript Author Information
Science and Engineering of Composite Materials
From the journal Science and Engineering of Composite Materials Volume 24 Issue 2

Abstract

Four polycarbonate (PC)-based composites with 1, 2.5, 5, and 10 wt.% raw multiwalled carbon nanotubes (MWCNTs) were prepared using extrusion process followed by injection molding. The effects of MWCNT mass fraction (W) on composite mechanical, thermal, and electrical properties were examined. The mechanical properties suggested that the tensile strength of the composites with 2.5 wt.% raw MWCNTs exhibited an increase of ~5 MPa (~8.6%) at a particular injection condition. Besides, thermogravimetric analysis (TGA) indicated that the addition of 1 wt.% MWCNTs improved the thermal stability of PC by approximately 100°C. Aside from mechanical and thermal properties, the electrical resistivity of the 5 wt.% raw MWCNT composites was considerably decreased to 102 Ω/sq, a value approximately 15 orders of magnitude lower than that of PC. Furthermore, the effects of injection conditions on composite electrical properties were emphatically discussed, and it was found that electrical resistivity was sensitive to injection temperature and speed. Low electrical resistivity was achieved at high injection temperature and low injection speed. Scanning electron microscopy images revealed that electrical resistivity relied on the microstructure of the prepared MWCNT/PC composites.

Keywords: carbon nanotubes; electrical resistivity; injection condition; microstructure; polycarbonate

1 Introduction

Since the beginning of the 21st century, conductive polymer composites (CPCs) have found a wide range of applications in electronic engineering fields and/or automobile and aeronautical industries. Examples of such applications include dust-proof antistatic materials, electrostatic recording paper, overcurrent and overtemperature protection devices, electrostatic painting, and electromagnetic shielding [1], [2]. However, because of poor conductive properties of polymers, there are some problems pressing for solution in processing and applications. The most prominent is electrostatic phenomenon. It will lead to performance degradation of photographic films, and polymer products will cause catastrophic accidents in flammable and explosive occasions. To resist electromagnetic interference (EMI) and radio frequency interference (RFI), the shielding performance of the polymers also urgently needs to be solved. All these require the polymers with new conductive properties and lower surface resistivity so as to promote the rapid development of CPCs.

Generally, because of their light weight, low cost, high processing ability, and high corrosion resistance, CPCs are becoming promising candidates to be employed as EMI shields. However, most polymers have electrical conductivity values as low as 10-7–10-14 S cm-1 [3]. Therefore, CPCs have not been yet very successful in large-scale actual applications, which is attributable to the high filler loading to achieve a sufficient level of shielding. Therefore, nowadays, the most common method is to incorporate an electrically conductive filler into a polymer. Electrically conductive fillers are multifarious, such as stainless steel fibers [4], [5], carbon black [6], [7], carbon fibers [8], [9], carbon nanotubes (CNTs) [10], [11], [12], graphene [13], and so on. Recently, CNTs have been of interest as fillers for applications in CPCs due to their unique structure, high aspect ratio features, and extraordinary mechanical, thermal, and electrical properties [14], [15], [16], [17]. The prospect of advanced CPCs with multifunctional features has attracted the efforts of researchers in both academia and industry [18], [19], [20], [21], [22], [23].

In recent years, the EMI shielding capabilities of CPCs with CNTs have been studied [11], [24], [25]. Compared with conventional CPCs, composites with carbon nanofillers present lower percolation threshold and superior electrical properties. The applications of such conductive fillers are however limited because of their high processing costs, with regard to the dispersion and orientation of CNTs, and the interface interaction between CNTs and polymers. Homogeneous dispersion and strong interfacial interaction can obtain excellent property composites as compared with conventional composites. However, CNTs have large specific surface area, higher surface activation energy [26], and intrinsic van der Waals attraction between CNTs. CNT aggregates easily, and the interfacial interaction between CNTs and polymers is weak, preventing an efficient load transfer from the polymer matrix to the CNTs. Accordingly, a uniform dispersion of CNTs in a polymer matrix and a strong interfacial interaction [27], [28] between CNTs and polymers are necessary conditions to maximize the advantages of CNTs as effective reinforcing filler in polymer composites. Generally, there are two major approaches to improve the electrical properties of a polymer at a given content of conductive fillers [29] while obtaining excellent mechanical and electrical properties. One approach is to rely on surface treatment to modify and functionalize CNTs [30], [31], [32]. This method has been confirmed to not only improve the solubility and dispersibility of CNTs but also enhance the electrical properties and the interfacial interaction between CNTs and polymers [33], [34], [35]. However, the main drawbacks of this method are time consuming and environmentally unfriendly. Another approach is to prepare CPCs by different molding processes, such as melt mixing, extrusion molding, and injection molding. Many studies reported that the melt processing conditions must be optimized to achieve homogeneous multiwalled carbon nanotube (MWCNT) dispersion in the composites [36], [37], [38], [39], [40], [41], [42]. For example, Villmow et al. [41] indicated that the extrusion conditions influenced the dispersion of MWCNTs in the polylactide (PLA) matrix while using twin-screw extrusion, whereas MWCNTs were added together with the polymer when using an extruder. Besides, Lee et al. [42] found that the electrical percolation threshold of polymethyl methacrylate (PMMA)/styrene-co-acrylonitrile (SAN)/MWCNTs remained around 1.5 wt.% and the electrical conductivity increased regardless of whether the PMMA was in a continuous phase. Although MWCNT/polymer composites have been widely studied using different molding methods, there are few published reports on the effects of MWCNT mass fraction (W) on the microstructures and electrical resistivity of the composites prepared by injection molding.

In this study, with the aim to achieve excellent electrical conductivity with good mechanical and thermal properties than our previous work [43], [44], the well-dispersed MWCNT/PC composites were prepared by a two-step dispersion strategy (the twin-screw extruding and injection molding processes). The effects of raw MWCNT mass fraction (0–10 wt.%) on mechanical, thermal, and electrical properties of polycarbonate (PC)-based composites were investigated. In addition, the effects of injection conditions on the electrical resistivity and distribution of electrical resistivity from composite surface to core were also examined. Furthermore, considering the electrical properties of the composites depending on the polymer’s and the conductive filler’s properties (shape, mass fraction, and microstructure) [2], [45], the relationship between microstructure and electrical resistivity and the formation mechanism of the microstructure were elucidated. As expected, our work will achieve an enhanced composite by a two-step dispersion method and offer a potential application, such as structural materials for EMI, RFI, and the shells of electronic components. Besides, our method is an easy and green alternative method for preparing the MWCNT/PC composites with various electrical resistivity values.

2 Materials and methods

2.1 Materials

MWCNTs were provided by Denko Company (Tokyo, Japan) and used as filler without any purification processes; they had an average diameter of 10–15 nm and a mean length of 3 μm. PC from Teijin Chemicals Company (Osaka, Japan) was used as the matrix, with a melt flow index of 1.8 cm3/10 min and a density of 1.2 g/cm3.

2.2 Preparation of composites

MWCNT/PC composites with 0–10 wt.% MWCNT mass fractions were prepared at various injection conditions by a two-step dispersion method (twin-screw extruding and injection molding processes). Because of its hydroscopic behavior, PC was dried at 100°C for 8 h. In this work, a two-step dispersion strategy was adopted to ensure the homogeneous dispersion of MWCNTs in PC. In the first step, the master batches of the MWCNT/PC composites were prepared using a twin-screw extruder (KZX25TW-60MG- NH(-1200)-AKT, Technovel Co., Ltd, Osaka, Japan) at a mixing temperature of 290°C and a mixing speed of 100 rpm. In the second step, the masterbatches were dried again at 100°C for more than 5 h. Then injection molding was performed using an injection molding machine (NP7-1F, Nissei Plastic Industry Co., Ltd, Hanishina-gun, Nagano-ken, Japan) at different injection speeds (V) of 10, 40, and 80 mm/s and different injection temperatures (T) of 280°C, 305°C, and 330°C, subsequently obtaining a standard MWNT/PC composite specimen. Dumbbell-shaped specimens with dimensions of 75×10×2 mm [JIS K 7113 1(1/2)] and rectangle-shaped specimens with dimensions of 80×10×4 mm [JIS K 7171 1(1/2)] were used for tensile tests and electrical resistivity tests, respectively. The mold temperature was 80°C.

2.3 Characterization

2.3.1 Electrical property test

Electrical resistivity was measured using the rectangle-shaped specimens. A four-probe resistivity tester (SDY-4, Guangzhou Semiconductor Material Academy Co., Ltd., Guangzhou, China) was employed for measuring electrical resistivity <104 Ω/sq, and a double-loop resistance meter (UPMCP-HT450, Mitsubishi Chemical Co., Ltd, Mie-ken, Japan) was used for the measurement of electrical resistivity in the range of 104–1013 Ω/sq. The measurement of the electrical resistivity of each composite specimen was repeated more than five times, and the average value was quoted as the electrical resistivity of the composites.

2.3.2 Evaluation of distribution of the electrical resistivity

As the surface microstructures of composite specimens produced by injection molding differs from the internal microstructure, it was hypothesized that the microstructure significantly affects the surface resistivity. Therefore, the surfaces of composite specimens to be tested were repeatedly ground in the same direction using #800 sandpaper, and the surface resistivity of each ground specimen was measured to examine the distribution of electrical resistivity from the surface to the core. The grinding load was kept at 2.5 kg, and the grinding distance was fixed at approximately 250 mm.

2.3.3 Tensile test

The tensile properties were evaluated on dumbbell-shaped specimens using a universal testing machine (3360, INSTRON Co., Ltd, Kanagawa, Japan). The measurements of tensile strength and fracture strain were carried out at a room temperature of 23°C±2°C and a tensile speed of 10 mm/min (according to JIS for tensile properties testing method). At least five specimens were tested, and the average value of the tensile strength was calculated.

2.3.4 Thermogravimetric analysis

Thermogravimetric analysis (TGA) was performed on a TA Instrument (DTG-60, Shimadzu, Kyoto, Japan) by recording the weight loss as a function of temperature. During TGA, the specimens were heated from room temperature to 800°C at a heating rate of 10°C/min in nitrogen atmosphere.

2.3.5 Optical microscopy analysis

The microstructure was investigated with an optical microscope (NIKON ECLIPSE ME600D, Tokyo, Japan). Before observation, the composite specimens were cut into 5-μm slices in thickness by a Leica microtome (RM2145 LEICA Co., MN, USA).

2.3.6 Microstructure analysis

The microstructure of the fractured surface was analyzed by a scanning electron microscopy (SEM, Hitachi Ltd S-4300, Tokyo, Japan) to determine the dispersion and orientation of MWCNTs in PC. The examination surfaces were fractured by tensile tests. Before examination, the fractured surfaces were sputtered with gold using an ion sputtering apparatus (E-1030, Hitachi Science Systems Co., Ltd., Tokyo, Japan). Then the fractured surfaces were observed under an acceleration voltage of 15 kV at room temperature 23°C±2°C.

3 Results and discussion

3.1 Dispersion of MWCNTs

The excellent properties of MWCNT are attributed to their large surface area and high aspect ratios. However, these properties easily lead to significant agglomeration because of van der Waals attraction among tubes, thus preventing an efficient transfer of their superior properties to the polymer matrix. To create a composite with higher electrical conductivity, more MWCNTs should be added; however, this would lead to the additional aggregation and reduction of the attractive electrical properties of the MWCNTs. In general, for MWCNT/polymer composites, due to the lack of interfacial interactions among MWCNTs, they are aggregated in the host polymer. In the present work, homogeneously dispersed MWCNT/PC composites were prepared by a two-step dispersion method. In the first step, MWCNTs were dispersed in a twin-screw extruder machine by mechanical force. In the second step, MWCNTs were dispersed again through injection molding by mechanical force. Namely, MWCNTs were dispersed twice during the preparation process. Figure 1 shows an optical micrograph of a 2.5 wt.% MWCNT composite (T=280°C and V=10 mm/s). It is evident that the MWCNTs were homogeneously dispersed in the PC matrix with minor agglomeration, confirming that the two-step dispersion method was effective at improving the dispersibility of the MWCNTs in the host polymer.

Figure 1: Optical micrograph of 2.5 wt.% MWCNT/PC composite obtained at the injection temperature of 280°C and injection speed of 10 mm/s.
Figure 1:

Optical micrograph of 2.5 wt.% MWCNT/PC composite obtained at the injection temperature of 280°C and injection speed of 10 mm/s.

3.2 Tensile properties

The tensile properties were determined, and the tensile strength and fracture strain of the composites are shown in Figure 2 (V=10 mm/s). The tensile strength of pure PC was 58 MPa at which the yield phenomenon, a typical characteristic of ductile materials, occurred. When a small mass fraction of MWCNTs was added (W≤5 wt.%), the effect of the MWCNT mass fraction on the tensile strength was not noticeable, and the strength was the similar as that of pure PC. The tensile strength of the composites exhibited an increase of ~5 MPa (~8.6%) with the addition of 2.5 wt.% MWCNTs (V=10 mm/s and T=305°C), but the fracture strain decreased, implying that brittleness increased. When the MWCNT mass fraction was just 1 wt.%, the fracture strain dropped <100% and was easily affected by the injection temperature. Moreover, with a further increase of the MWCNT mass fraction (W>5 wt.%), the tensile strength apparently showed a lower value. For example, when the MWCNT mass fraction was 10 wt.%, the tensile strength was approximately halved. In addition, the fracture strain was sharply decreased with the increase of MWCNT mass fraction and showed greater brittleness. It was attributed to the partial transferal of tensile strain to MWCNTs embedded in the PC and strong interface interaction between MWCNT and PC, leading to the maintenance of the tensile strength when the MWCNT mass fraction was <5 wt.%. When the MWCNT mass fraction was more than 5 wt.%, more MWCNTs agglomerated in the PC matrix, and many defects were incorporated, owing to difficulties of homogeneous MWCNT dispersion during injection molding. These defects consequently lead to the decrease in tensile strength. Moreover, the tensile strength was affected by the injection temperature. The phenomenon was more evident particularly for the MWCNT mass fraction of 10 wt.%. In general, not only the MWCNT mass fraction but also the injection conditions affected the tensile properties of the composites.

Figure 2: Tensile strength and fracture strain of the PC and the MWCNT/PC composite obtained at the injection speed of 10 mm/s.
Figure 2:

Tensile strength and fracture strain of the PC and the MWCNT/PC composite obtained at the injection speed of 10 mm/s.

From Figure 2, we know that when the MWCNT mass fraction was 1 wt.%, the effect of injection temperature on fracture strain was obvious. Besides, as the MWCNT mass fraction increases from 1 to 5 wt.%, the fracture strain greatly changed under the same injection condition. Therefore, Figure 3 shows SEM micrographs of the tensile fractured surfaces of the 1 and 5 wt.% MWCNT composites prepared at different injection conditions. In Figure 3B and D, MWCNTs were dispersed homogeneously, and no agglomeration of MWCNTs was observed. The compatibility and interface interaction between MWCNTs and PCs were reasonable as there were no MWCNTs pulled out. In addition, from the observation of the whole cross section (Figure 3A and C), the specimen sizes were smaller than the original size. It was considered that some plastic deformations occurred during tensile testing, indicating that the tensile property of the 1 wt.% MWCNT composite was relatively good. However, in Figure 3E, there was a defect on the fractured surfaces. This defect was considered the cause of fracture during tensile testing, leading to a distinct decrease of fracture strain. Moreover, although the dispersibility of the MWCNTs in the PC matrix was sufficient, a few agglomerations of MWCNTs were still observed in Figure 3F. In addition, the specimen size did not change (Figure 3E), demonstrating that brittle fracture had occurred. It was inferred that the presence of more MWCNTs hindered the plastic deformation of the PC, and the MWCNT agglomeration affected the interface interaction between MWCNT and PC, thereby attenuating the tensile property of the composites.

Figure 3: SEM micrographs of the fractured surfaces of (A) 1 wt.% MWCNT/PC composites obtained at the injection temperature of 330°C and injection speed of 10 mm/s, (C) 1 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s, (E) 5 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s. (B, D, and F) Large magnification micrographs of A, C, and E, respectively.
Figure 3:

SEM micrographs of the fractured surfaces of (A) 1 wt.% MWCNT/PC composites obtained at the injection temperature of 330°C and injection speed of 10 mm/s, (C) 1 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s, (E) 5 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s. (B, D, and F) Large magnification micrographs of A, C, and E, respectively.

3.3 Thermal property

MWCNT as a reinforced filler has been reported to enhance the thermal stability of the host polymer matrices [46], [47]. TGA curves of pure PC, pure MWCNTs, and MWCNT/PC composites with 1 and 10 wt.% MWCNTs are shown in Figure 4 (T=280°C and V=80 mm/s). The pure PC possessed a single stage in the thermal degradation around 320°C–410°C. The incorporation of MWCNT exhibited significant improvements in thermal stability compared with the pure PC. The thermal degradation temperature of the 1 wt.% MWCNT composite was around 420°C–520°C, an increase of more than 100°C than that of the PC. However, when the MWCNT mass fraction increased to 10 wt.%, the degradation temperature had some decline compared with that of 1 wt.% MWCNT composite. This behavior was attributed to the breakage of MWCNT [48], resulting in the excellent properties of MWCNT not be displayed. Overall, these results demonstrated that the MWCNTs could improve the thermal stability of the pure PC, and enhanced thermal stability of the composites might testify to the homogeneous dispersion of MWCNTs in the PC matrix. In addition, these TGA results confirmed that the compatibility between MWCNTs and PCs was very good. Therefore, the incorporation of MWCNTs was a favorable method for enhancing the thermal properties of the PC.

Figure 4: TGA curves of pure PC, MWCNT, and MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s.
Figure 4:

TGA curves of pure PC, MWCNT, and MWCNT/PC composites obtained at the injection temperature of 280°C and injection speed of 10 mm/s.

3.4 Electrical properties

3.4.1 Effect of MWCNT mass fractions on the electrical resistivity

The conductivity characteristics of the composites with different MWCNT mass fractions are exhibited in Figure 5. These results showed that the electrical conductivity exponentially increased with the MWCNT mass fraction. As the MWCNT mass fraction was increased from 1 to 10 wt.%, the surface resistivity decreased by nine orders of magnitude (from 1011 to 102 Ω/sq), regardless of the injection speed and injection temperature. However, the surface resistivity trend was not the same. When the injection speed was low (i.e. V=10 mm/s, Figure 5A) and the MWCNT mass fraction ranged from 1 to 5 wt.%, the surface resistivity dropped linearly by 6–9 orders of magnitude. However, when the MWCNT mass fraction exceeded 5 wt.% (W>5 wt.%) and the injection temperature was higher (e.g. T=330°C), the effect of the MWCNT mass fraction on the surface resistivity was not noticeable and the surface resistivity decreased by only one order of magnitude. It was hypothesized that more MWCNTs agglomerated in the PC matrix, leading to the conductivity of MWCNT not being transferred to the PC. Moreover, when the injection speed was high (V=40 mm/s or 80 mm/s, Figure 5B and C), the effect of MWCNT mass fractions on the surface resistivity was also great. As the MWCNT mass fraction was increased from 1 to 10 wt.%, the surface resistivity uniformly decreased. This result implied that changing the MWCNT mass fraction could prepare composites with a wide range of electrical resistivities. In general, the effect of the MWCNT mass fraction on the electrical conductivity was such that a conductive network formed more easily for an increase in MWCNT mass fraction. In addition, a higher injection temperature was propitious to obtain a lower electrical resistivity.

Figure 5: Effect of MWCNT mass fraction on the surface resistivity of the MWCNT/PC composites obtained at injection speeds of (A) 10 mm/s, (B) 40 mm/s, and (C) 80 mm/s, respectively.
Figure 5:

Effect of MWCNT mass fraction on the surface resistivity of the MWCNT/PC composites obtained at injection speeds of (A) 10 mm/s, (B) 40 mm/s, and (C) 80 mm/s, respectively.

Figure 6A and B show SEM micrographs of the fractured surfaces of the composites with 5 and 10 wt.% MWCNTs, respectively (T=330°C and V=10 mm/s, perpendicular to the injection direction, similarly hereinafter). Comparing Figure 6A with Figure 3B, no matter the types of fractured surfaces, even if the MWCNT mass fraction was increased to 5 wt.%, MWCNT agglomeration was not observed while the electrical networks were distinctly observed. These results showed that the dispersion of MWCNTs was very good. Therefore, during the injection molding, as the high-temperature molten polymers flowed into the cold die and were cooled slowly, with a slow injection speed, MWCNTs were not oriented along the injection direction, which contributed to the formation of conductive networks. The conductive properties of the MWCNTs were the best observed at this time, and the electrical resistivity of the composites was significantly improved with the increase of the MWCNT contents. However, from Figure 6B, it was found that although the dispersion of MWCNTs was not bad, some MWCNTs agglomerated with a combined size of 150–250 nm. This observed agglomeration hampered the formation of conductive networks.

Figure 6: SEM micrographs of the fractured surfaces of (A) 5 wt.% MWCNT/PC composites and (B) 10 wt.% MWCNT/PC composites obtained at the injection temperature of 330°C and injection speed of 10 mm/s.
Figure 6:

SEM micrographs of the fractured surfaces of (A) 5 wt.% MWCNT/PC composites and (B) 10 wt.% MWCNT/PC composites obtained at the injection temperature of 330°C and injection speed of 10 mm/s.

3.4.2 Effect of injection speed on the electrical resistivity

To elucidate the effect of the injection speed on the electrical resistivity, various MWCNT/PC composites were investigated. The obtained results are shown in Figure 7. From the four plots of electrical resistivity vs. injection speed, no matter the injection temperature, the variation of surface resistivity of 1 or 10 wt.% MWCNT composite was small, although the injection speed was increased from 10 to 80 mm/s. This might be because when the MWCNT mass fraction was small (W=1 wt.%), the percolation threshold had not been reached [49], the contact probability of MWCNT was low, and conductive networks were not formed. Thus, the effect of the injection speed on the electrical resistivity was not noticeable. In addition, in the case of 10 wt.% MWCNT, although the MWCNTs had reached the percolation threshold, the MWCNTs agglomerated and the inherent conductivity of MWCN was hindered. Thus, the effect of the injection speed on the electrical resistivity was unobvious. However, when the mass fraction of MWCNTs was 2.5 or 5 wt.% (Figure 7B or C), the variation of surface resistivity with injection speed was strong. At the same injection temperature, surface resistivity increased by three orders of magnitude as the eightfold increase of injection speed. From the overall results, the electrical conductivity of the composites was improved under a lower injection speed and higher injection temperature, particularly in the case of 2.5 and 5 wt.% MWCNT composites.

Figure 7: Effect of injection speed on surface resistivity of the MWCNT/PC composites with (A) 1 wt.% MWCNTs, (B) 2.5 wt.% MWCNTs, (C) 5 wt.% MWCNTs, and (D) 10 wt.% MWCNTs.
Figure 7:

Effect of injection speed on surface resistivity of the MWCNT/PC composites with (A) 1 wt.% MWCNTs, (B) 2.5 wt.% MWCNTs, (C) 5 wt.% MWCNTs, and (D) 10 wt.% MWCNTs.

According to the formation mechanism of the internal microstructure of the composite specimens, at the same injection temperature, the formation of the composite specimen was affected by higher sheer stress under a high injection speed, and MWCNTs were easily oriented along the injection direction, resulting in a decrease in the contact probability of the MWCNTs, and consequently, the electrical conductivity of the composites was decreased. Regarding the percolation phenomenon, when the MWCNT mass fraction was <5 wt.%, the effect of the internal microstructure on the electrical resistivity was noticeable. Figure 8A and B show the SEM micrographs of fractured surfaces of the 2.5 wt.% MWCNT composites prepared at injection speed of 10 and 80 mm/s, respectively. Comparing the two micrographs showed that when the injection speed was increased from 10 to 80 mm/s, changes in the dispersion of the MWCNTs were observed, and the microstructures were markedly different. When the injection speed was low (V=10 mm/s, Figure 8A), conductive networks formed. Although the injection speed was high (V=80 mm/s, Figure 8B), many small white dots (i.e. MWCNTs) were observed. It was considered that the MWCNTs were oriented in the injection direction. Therefore, injection speed could easily affect the internal microstructure of the composite specimens, resulting in large variations in electrical resistivity between the two composite specimens.

Figure 8: SEM micrographs of the fractured surfaces of the 2.5 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C with (A) the injection speed of 10 mm/s and (B) the injection speed of 80 mm/s.
Figure 8:

SEM micrographs of the fractured surfaces of the 2.5 wt.% MWCNT/PC composites obtained at the injection temperature of 280°C with (A) the injection speed of 10 mm/s and (B) the injection speed of 80 mm/s.

3.4.3 Effect of injection temperature on the electrical resistivity

The effects of the injection temperature on the surface resistivity of various composites are shown in Figure 9. In Figure 9A, when the MWCNT mass fraction was small (W=1 wt.%), no matter the injection speed, or if the injection temperature was increased by 50°C, the variation of surface resistivity was small, in the range of 1010–1011 Ω/sq. Figure 9D shows the similar case as that previously mentioned; the surface resistivity was decreased by only one order of magnitude (W=10 wt.%). This demonstrated that regardless of the injection temperature and injection speed, the variation of surface resistivity of the 1 or 10 wt.% MWCNT composites was within two orders of magnitude. Namely, when the MWCNT mass fraction was too small or very large, the effect of the injection temperature on the electrical resistivity was not noticeable. In contrast, when the MWCNT mass fraction was 2.5 or 5 wt.% (Figure 9B or C), the electrical resistivity was greatly affected by the injection temperature. For example, the surface resistivity of the 2.5 wt.% MWCNT composites was in the range of 106–1011 Ω/sq, and the surface resistivity of the 5 wt.% MWCNT composites was in the range of 102–107 Ω/sq, both varying by five orders of magnitude. That is to say, with the appropriate MWCNT mass fraction, the injection temperature would change the internal microstructure of the composites, and this greatly affected the electrical resistivity of the composites. Moreover, comparing the resistivity plots showed that at a high injection temperature and low injection speed (T=330°C and V=10 mm/s), the composites were superior to those prepared by other injection conditions, especially at low injection temperature and high injection speed. This improvement is due to the distinctive microstructure of the composites at high injection temperature and low injection speed, which contributed to the favorable dispersion of MWCNTs for improving the electrical conductivity of PC. Therefore, composites with various electrical resistivities can be prepared by changing the injection temperature and injection speed.

Figure 9: Effect of injection temperature on surface resistivity of the MWCNT/PC composites with (A) 1 wt.% MWCNTs, (B) 2.5 wt.% MWCNTs, (C) 5 wt.% MWCNTs, and (D) 10 wt.% MWCNTs.
Figure 9:

Effect of injection temperature on surface resistivity of the MWCNT/PC composites with (A) 1 wt.% MWCNTs, (B) 2.5 wt.% MWCNTs, (C) 5 wt.% MWCNTs, and (D) 10 wt.% MWCNTs.

In general, during injection molding, while the die is being filled with a high-temperature molten polymer, a three-layer structure consisting of a skin layer, an intermediate layer, and a core layer is formed from the surface to the inside with different orientations or dispersions [50]. Figure 10 shows an SEM micrograph of the fractured surface of the 2.5 wt.% MWCNT composite prepared at an injection temperature of 330°C and injection speed of 10 mm/s. Comparing Figure 10 with Figure 8A, which is a specimen prepared at the same injection speed and MWCNT mass fraction, but using a different injection temperature (T=280°C), not much difference in MWCNT dispersion was observed. In addition, according to the formation mechanism of the internal microstructure during injection molding, when the injection temperature was lower, the viscosity of the molten polymer was higher. At the same injection speed, if the injection temperature was low (e.g. T=280°C), when the polymer was filled into the die, the solid fibrous MWCNTs were forced by high sheer stress; thus, MWCNTs were easily orientated along the flow direction of polymer, and the contact probability between MWCNTs was lower. Consequently, during the injection molding process, the change of injection temperature would cause a difference in the internal microstructure, resulting in a variation of electrical conductivity of the composite.

Figure 10: SEM micrograph of the fractured surface of the 2.5 wt.% MWCNT/PC composite obtained at the injection temperature of 330°C and injection speed of 10 mm/s.
Figure 10:

SEM micrograph of the fractured surface of the 2.5 wt.% MWCNT/PC composite obtained at the injection temperature of 330°C and injection speed of 10 mm/s.

3.4.4 Distribution of electrical resistivity from surface to core

Different electrical resistivities of the composites are likely related to the difference in dispersibility of the MWCNTs [51]. From the viewpoint of the composite formation mechanism during the injection molding, the microstructures of the specimens were most affected by the injection conditions. To illustrate the effect of the injection conditions on the electrical resistivity, the distribution of the electrical resistivity along a distance from the composite surface to core was investigated. Prior to the measurement of electrical resistivity, all specimen surfaces were ground using fine sandpaper and polished with an abrasive agent to avoid the surface roughness effects. The electrical resistivity of the composite was measured each time a certain thickness (i.e. 50 μm) was ground off the specimen and polished. Figure 11 shows the electrical resistivity distributions of the 5 and 10 wt.% MWCNT composites prepared at different injection conditions. No matter the injection conditions and the MWCNT mass fraction, the electrical resistivity of the composites dramatically increased with the increase in distance from the surface to a maximum value. After having reached this maximum value, the electrical resistivity gradually decreased and retained a constant value at an interior distance of 1000 μm.

Figure 11: Distributions of surface resistivity of the MWCNT/PC composites with (A) 5 wt.% MWCNTs and (B) 10 wt.% MWCNTs.
Figure 11:

Distributions of surface resistivity of the MWCNT/PC composites with (A) 5 wt.% MWCNTs and (B) 10 wt.% MWCNTs.

For the composite with 5 wt.% MWCNTs (Figure 11A, T=280°C), as the injection speed was increased (from 10 to 80 mm/s), the surface resistivity increased by two orders of magnitude. The position of the maximum resistivity value varied, and it was observed that with a lower injection speed, the maximum resistivity value was closer to the specimen surface. At a distance of ~1000–2000 μm from the composite surface, the order of magnitude of the electrical resistivity was the same, approximately 105 Ω/sq. As for the effect of the injection temperature, at an injection speed of 10 mm/s, when the injection temperature was increased by 50°C (from 280°C to 330°C), the surface resistivity integrally dropped by approximately three orders of magnitude, and the internal electrical resistivity also differed by three orders of magnitude. It was hypothesized that when the MWCNT mass fraction was 5 wt.%, which may be in the percolation threshold, the electrical resistivity of the core layer was easily affected by the injection temperature, and the MWCNTs were oriented easily in the PC matrix under low injection temperatures.

However, for the 10 wt.% MWCNT composite (Figure 11B), at the same injection temperature, as the injection speed was increased eightfold, the variation of the electrical resistivity was small. Although the position of the maximum resistivity value was different, the order of magnitude of the electrical resistivity was in the same range. In addition, the distribution of electrical resistivity was within an order of magnitude in the case of injection temperature of 330°C and injection speed of 10 mm/s. Moreover, although the injection temperature was increased from 280°C to 330°C, the maximum values of electrical resistivity only differed by an order of magnitude. Comparing Figure 11A and B with each other, the electrical resistivity of the 5 wt.% MWCNT composite (T=330°C and V=10 mm/s) and that of the 10 wt.% MWCNT composite (T=280°C and V=80 mm/s) had no significant difference in the order of magnitude. This also indicated that a lower injection speed and a higher injection temperature were very effective in the improvement of the electrical conductivity.

For all composite specimens, the distribution of electrical resistivity from the specimen surface to the core consisted of three regions of increasing, decreasing, and constant resistivity. It was hypothesized that this trend was attributed to the formation mechanism of the internal microstructure during injection molding. For the region of the sharp increase in the electrical resistivity, the composites were solidified quickly, and the MWCNTs were forced by sheer stress to orient along the flow direction of the polymer. For the regions where the electrical resistivity decreased or remained constant, the polymer stopped flowing, and MWCNTs were randomly dispersed. Finally, the hot polymer solidified, and then the core layer was formed. The formation of MWCNT networks was considered related to the injection conditions, which subsequently affected the electrical resistivity.

Figure 12 shows an SEM micrograph of the core layer of an MWCNT/PC composite with 5 wt.% MWCNTs (T=280°C and V=10 mm/s). Comparing Figure 12 with Figure 6A, the MWCNTs were well dispersed in both, but many small white dots and few networks could be observed in Figure 12. It was realized that when the injection temperature was low, the composite specimens were solidified quickly, and the MWCNTs were forced by high sheer stress to orient along the flow direction of the PC. In Figure 6A, more MWCNTs were observed. There was no obvious orientation of the MWCNTs, and electrical networks had formed. Therefore, when the MWCNT mass fraction was in the percolation threshold, the internal microstructure was affected by the injection conditions, and the orientation of the MWCNTs at a low injection temperature was higher than that of the MWCNTs at a high injection temperature.

Figure 12: SEM micrograph of the core layer of the 5 wt.% MWCNT/PC composite obtained at the injection temperature of 280°C and injection speed of 10 mm/s.
Figure 12:

SEM micrograph of the core layer of the 5 wt.% MWCNT/PC composite obtained at the injection temperature of 280°C and injection speed of 10 mm/s.

4 Conclusions

In this study, a twin-screw extruding and injection molding process was proposed to prepare well-dispersed MWCNT/PC composites. The mechanical, thermal, and electrical properties of various composites were investigated by performing the tensile test, TGA, and electrical resistivity measurements, respectively. The obtained results can be summarized as follows:

  1. The tensile strength of MWCNT/PC composites with 2.5 wt.% MWCNTs exhibited an increase of ~5 MPa (~8.6%) at a particular injection condition. However, with a further increase of the MWCNT mass fraction, especially when the MWCNT mass fraction was 10 wt.%, the tensile strength of the composites was approximately halved.

  2. TGA indicated that the incorporation of MWCNTs improved the thermal stability of the PC, especially only 1 wt.% addition of MWCNT resulted in an increase of more than 100°C.

  3. The electrical resistivity of the MWCNT/PC composites with 5 wt.% MWCNTs considerably decreased down to 102 Ω/sq in the case of an injection temperature of 330°C and an injection speed of 10 mm/s, and the electrical resistivity was ~15 orders of magnitude lower than that of PC.

  4. The electrical properties of the MWCNT/PC composites with 2.5 or 5 wt.% MWCNTs were more affected by the injection conditions. In addition, a lower injection speed and a higher injection temperature (i.e. T=330°C and V=10 mm/s) were conducive to obtaining the MWCNT/PC composite with lower electrical resistivity.

  5. The distribution of the electrical resistivity from the surface to the core had three regions exhibiting increasing, decreasing, and constant behaviors. The injection conditions affected the internal microstructures of the composite specimen, resulting in the differences in the maximum value of electrical resistivity and its position.

Corresponding author: Jianhui Qiu, Faculty of System Science and Technology, Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, 84-4 Tsuchiya Ebinokuchi, Yurihonjo, Akita 015-0055, Japan, e-mail:

References

[1] Amarasekera J. J. Reinf. Plast. Compos. 2005, 49, 38–41.10.1016/S0034-3617(05)70734-7Search in Google Scholar

[2] Yuan Q, Wu D. J. Appl. Polym. Sci. 2010, 115, 3527–3534.10.1002/app.30919Search in Google Scholar

[3] Gulrez SKH, Ali Mohsin ME, Shaikh H, Anis A, Pulose AM, Yadav MK, Qua EHP, Al-Zahrani SM. Polym. Compos. 2014, 35, 900–914.10.1002/pc.22734Search in Google Scholar

[4] Chang H, Kao M-J, Huang K-D, Kuo C-G, Huang S-Y. J. Nanosci. Nanotechnol. 2011, 11, 1754–1757.10.1166/jnn.2011.3358Search in Google Scholar PubMed

[5] Ameli A, Nofar M, Wang S, Park CB. ACS Appl. Mater. Interfaces 2014, 6, 11091–11100.10.1021/am500445gSearch in Google Scholar PubMed

[6] Cao Q, Song Y, Liu Z, Zheng Q. J. Mater. Sci. 2009, 44, 4241–4245.10.1007/s10853-009-3590-9Search in Google Scholar

[7] Yuan Q, Bateman SA, Wu D. J. Thermoplast. Compos. Mater. 2010, 23, 459–471.10.1177/0892705709349318Search in Google Scholar

[8] Ameli A, Jung PU, Park CB. Carbon 2013, 60, 379–391.10.1016/j.carbon.2013.04.050Search in Google Scholar

[9] Ameli A, Jung PU, Park CB. Compos. Sci. Technol. 2013, 76, 37–44.10.1016/j.compscitech.2012.12.008Search in Google Scholar

[10] Liebscher M, Krause B, Pötschke P, Barz A, Bliedtner J, Möhwald M, Letzsch A. Macromol. Mater. Eng. 2014, 299, 869–877.10.1002/mame.201300377Search in Google Scholar

[11] Arjmand M, Apperley T, Okoniewski M, Sundararaj U. Carbon 2012, 50, 5126–5134.10.1016/j.carbon.2012.06.053Search in Google Scholar

[12] Kasaliwal G, Göldel A, Pötschke P. J. Appl. Polym. Sci. 2009, 112, 3494–3509.10.1002/app.29930Search in Google Scholar

[13] Lei L, Qiu J, Zhao Y, Wu X, Sakai E. Sci. Adv. Mater. 2012, 4, 912–919.10.1166/sam.2012.1375Search in Google Scholar

[14] Filleter T, Bernal R, Li S, Espinosa HD. Adv. Mater. 2011, 23, 2855–2860.10.1002/adma.201100547Search in Google Scholar

[15] Xie X, Mai Y, Zhou X. Mater. Sci. Eng. R. 2005, 49, 89–112.10.1016/j.mser.2005.04.002Search in Google Scholar

[16] Moniruzzaman M, Winey KI. Macromolecules 2006, 39, 5194–5205.10.1021/ma060733pSearch in Google Scholar

[17] Sattler K. Carbon 1995, 33, 915–920.10.1016/0008-6223(95)00020-ESearch in Google Scholar

[18] Peng C, Zhang S, Jewell D, Chen GZ. Prog. Nat. Sci. 2008, 18, 777–788.10.1016/j.pnsc.2008.03.002Search in Google Scholar

[19] Paradise M, Goswami T. Mater. Design 2007, 28, 1477–1489.10.1016/j.matdes.2006.03.008Search in Google Scholar

[20] Kim JH, Lee KH, Overzet LJ, Lee GS. Nano Lett. 2011, 11, 2611–2617.10.1021/nl200513aSearch in Google Scholar PubMed

[21] Allaoui A, Bai S, Cheng HM, Bai JB. Comp. Sci. Technol. 2002, 62, 1993–1998.10.1016/S0266-3538(02)00129-XSearch in Google Scholar

[22] Breuer O, Sundararaj U. Polym. Compos. 2004, 25, 630–645.10.1002/pc.20058Search in Google Scholar

[23] Hossain MK, Chowdhury MMR, Salam MBA, Jahan N, Malone J, Hosur MV, Jeelani S, Bolden NW. J. Compos. Mater. 2015, 49, 2251–2263.10.1177/0021998314545186Search in Google Scholar

[24] Arjmand M, Mahmoodi M, Gelves GA, Park S, Sundararaj U-T. Carbon 2011, 49, 3430–3440.10.1016/j.carbon.2011.04.039Search in Google Scholar

[25] Yuen SM, Ma CCM, Chuang CY, Yu KC, Wu SY, Yang CC, Wei MH. Comp. Sci. Technol. 2008, 68, 963–968.10.1016/j.compscitech.2007.08.004Search in Google Scholar

[26] Kearns JC, Shambaugh RL. J. Appl. Polym. Sci. 2002, 86, 2079–2084.10.1002/app.11160Search in Google Scholar

[27] Thionnet A, Chou H, Anthony B. Appl. Compos. Mater. 2014, 22, 119–140.10.1007/s10443-014-9397-0Search in Google Scholar

[28] Mollie AB, Young WK, Randall DP. Appl. Compos. Mater. 2010, 17, 347–362.10.1007/s10443-009-9124-4Search in Google Scholar

[29] Naebe M, Hurren C, Maazouz A, Lamnawar K, Wang X. Fiber. Polym. 2009, 10, 662–666.10.1007/s12221-010-0662-zSearch in Google Scholar

[30] Tasis D, Tagmatarchis N, Bianco A, Prato M. Chem. Rev. 2006, 106, 1105–1136.10.1021/cr050569oSearch in Google Scholar PubMed

[31] Wang S, Liang R, Wang B, Zhang C. Polym. Compos. 2009, 30, 1050–1057.10.1002/pc.20654Search in Google Scholar

[32] Meng L, Fu C, Lu Q. Prog. Nat. Sci. 2009, 19, 801–810.10.1016/j.pnsc.2008.08.011Search in Google Scholar

[33] Tekin N, Beyaz SK, Kara A, Simsek E, Lamari FD, Cakmak G, Guney HY. Polym. Compos. 2012, 33, 1255–1262.10.1002/pc.22243Search in Google Scholar

[34] Xu S, Akchurin A, Liu T, Wood W, Tangpong XW, Akhatov IS, Zhong WH. J. Compos. Mater. 2015, 49, 1503–1512.10.1177/0021998314535959Search in Google Scholar

[35] Costa P, Silva J, Anson-Casaos A, Martinez MT, Abad MT, Viana J, Lanceros-Mendez S. Compos. Part B Eng. 2014, 61, 136–146.10.1016/j.compositesb.2014.01.048Search in Google Scholar

[36] Leu YY, Mohd-Ishak ZA, Chow WS. J. Appl. Polym. Sci. 2012, 124, 1200–1207.10.1002/app.35084Search in Google Scholar

[37] Andrews R, Jacques D, Minot M, Rantell T. Mater. Eng. 2002, 287, 395–403.10.1002/1439-2054(20020601)287:6<395::AID-MAME395>3.0.CO;2-SSearch in Google Scholar

[38] Krause B, Potschke P, Haussler L. Compos. Sci. Technol. 2009, 69, 1505–1515.10.1016/j.compscitech.2008.07.007Search in Google Scholar

[39] Kasaliwal GR, Pegel S, Goldel A, Potschke P, Heinrich G. Polymer 2010, 51, 2708–2720.10.1016/j.polymer.2010.02.048Search in Google Scholar

[40] Muller MT, Krause B, Kretzschmar B, Pötschke P. Compos. Sci. Technol. 2011, 71, 1535–1542.10.1016/j.compscitech.2011.06.003Search in Google Scholar

[41] Villmow T, Potschke P, Pegel S, Haussler L, Kretzschmar B. Polymer 2008, 49, 3500–3509.10.1016/j.polymer.2008.06.010Search in Google Scholar

[42] Lee M, Jeon H, Hun Min B, Kim JH. J. Appl. Polym. Sci. 2011, 121, 743–749.10.1002/app.33819Search in Google Scholar

[43] Wang LJ, Qiu JH, Sakai E. Adv. Mater. Res. 2014, 983, 94–98.10.4028/www.scientific.net/AMR.983.94Search in Google Scholar

[44] Wang LJ, Qiu JH, Sakai E, Wei X. Adv. Mater. Res. 2014, 983, 105–109.10.4028/www.scientific.net/AMR.983.105Search in Google Scholar

[45] Qiu JH, Kawagoe M, Mizuno W, Morita M. Trans. Jpn. Soc. Mech. Eng. A. 2001, 67, 1017–1023.10.1299/kikaia.67.1017Search in Google Scholar

[46] Jin Z, Pramoda KP, Xu G, Goh SH. Chem. Phys. Lett. 2001, 337, 43–47.10.1016/S0009-2614(01)00186-5Search in Google Scholar

[47] Jiang Q, Wang X, Zhu Y, Hui D, Qiu Y. Compos. Part B Eng. 2014, 56, 408–412.10.1016/j.compositesb.2013.08.064Search in Google Scholar

[48] Guo J, Liu Y, Prada-Silvy R, Tan Y, Azad S, Krause B, Pötschke P, Grady BP. J. Polym. Sci. B. Polym. Phys. 2014, 52, 73–83.10.1002/polb.23402Search in Google Scholar

[49] Potschke P, Bhattacharyya AR, Janke A. Eur. Polym. J. 2004, 40, 137–148.10.1016/j.eurpolymj.2003.08.008Search in Google Scholar

[50] Qiu J. Kobunshi Ronbunshu 2005, 62, 50–54.10.1295/koron.62.50Search in Google Scholar

[51] Krause B, Mende M, Potschke P, Petzold G. Carbon 2010, 48, 2746–2754.10.1016/j.carbon.2010.04.002Search in Google Scholar

Received: 2015-3-6
Accepted: 2015-5-18
Published Online: 2015-8-15
Published in Print: 2017-3-1

©2017 Walter de Gruyter GmbH, Berlin/Boston

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Articles in the same Issue

  1. Frontmatter
  2. Original articles
  3. Effects of multiwalled carbon nanotube mass fraction on microstructures and electrical resistivity of polycarbonate-based conductive composites
  4. Preparation and fluid drag reduction properties of superhydrophobic paper-based films comprising carbon nanotubes and fluoropolymers
  5. Studies on the structural, thermal, and dielectric properties of fabricated Nylon 6,9/CaCu3Ti4O12 nanocomposites
  6. Metal-matrix composite fabricated with gas tungsten arc melt injection and precoated with NiCrBSi alloy to increase the volume fraction of WC particles
  7. Construction of polypropylene composite multifilaments filled with sodium perborate trihydrate-treated jute microparticles
  8. Damage detection of three-dimensional braided composite materials using carbon nanotube thread
  9. An exact solution for improved metal-composite joints reinforced by FG inter-layers
  10. Effect of chemical treatment on thermal properties of bagasse fiber-reinforced epoxy composite
  11. The superior ductility of fine SiCp/Al2014 composites after extrusion
  12. Optical properties and photocatalytic activity of CdS-TiO2/graphite composite
  13. Effects of bottom ash and granulated blast furnace slag as fine aggregate on abrasion resistance of concrete
  14. Surface modification of diamond and its effect on the mechanical properties of diamond/epoxy composites
  15. Numerical simulation of strain rate effect on the inelastic behavior of metal matrix composites
  16. Electromechanical characterization of multilayer graphene-reinforced cellulose composite containing 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid
  17. The effect of hydroxyapatite reinforcement and preparation methods on the structure and mechanical properties of Mg-HA composites
  18. The effect of yttrium incorporation on the formation and properties of α-Al2O3 coatings
https://doi.org/10.1515/secm-2015-0074
Keywords for this article
carbon nanotubes; electrical resistivity; injection condition; microstructure; polycarbonate
Creative Commons
BY-NC-ND 3.0

Articles in the same Issue

  1. Frontmatter
  2. Original articles
  3. Effects of multiwalled carbon nanotube mass fraction on microstructures and electrical resistivity of polycarbonate-based conductive composites
  4. Preparation and fluid drag reduction properties of superhydrophobic paper-based films comprising carbon nanotubes and fluoropolymers
  5. Studies on the structural, thermal, and dielectric properties of fabricated Nylon 6,9/CaCu3Ti4O12 nanocomposites
  6. Metal-matrix composite fabricated with gas tungsten arc melt injection and precoated with NiCrBSi alloy to increase the volume fraction of WC particles
  7. Construction of polypropylene composite multifilaments filled with sodium perborate trihydrate-treated jute microparticles
  8. Damage detection of three-dimensional braided composite materials using carbon nanotube thread
  9. An exact solution for improved metal-composite joints reinforced by FG inter-layers
  10. Effect of chemical treatment on thermal properties of bagasse fiber-reinforced epoxy composite
  11. The superior ductility of fine SiCp/Al2014 composites after extrusion
  12. Optical properties and photocatalytic activity of CdS-TiO2/graphite composite
  13. Effects of bottom ash and granulated blast furnace slag as fine aggregate on abrasion resistance of concrete
  14. Surface modification of diamond and its effect on the mechanical properties of diamond/epoxy composites
  15. Numerical simulation of strain rate effect on the inelastic behavior of metal matrix composites
  16. Electromechanical characterization of multilayer graphene-reinforced cellulose composite containing 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid
  17. The effect of hydroxyapatite reinforcement and preparation methods on the structure and mechanical properties of Mg-HA composites
  18. The effect of yttrium incorporation on the formation and properties of α-Al2O3 coatings
Sign up now to receive a 20% welcome discount
Institutional Access
How does access work?
Have an idea on how to improve our website?
Please write us.
© 2026 De Gruyter Brill
Downloaded on 1.3.2026 from https://www.degruyterbrill.com/document/doi/10.1515/secm-2015-0074/html
Scroll to top button