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Formation of Polypropylene/Functional Graphene Oxide Nanocomposites With Different FGs Loading in Elongation Flow Condition.

INTRODUCTION

Over the past few years, graphene, due to its unique conductivity, thermal and superior mechanical properties, has been identified as a promising candidate for reinforcing polymer composites [1-4]. Polymer nanocomposites based on graphene nanoplatelets attract researchers much attention owing to their excellent physical and chemical properties these days [5-7]. It has been found that significant variations of mechanical, thermal, electrical and barrier property occurred even if incorporated nanofillers at a very low loading [8-10]. The properties of graphene filled polymer materials are obviously dependent on the filler amount but above all, they are related to the distribution, orientation and interfacial adhesion in the matrix. However, there is a strong van der Waals force between the layers and layers of graphene, because graphene is a 2D nanomaterial with a large specific surface area, which is unstable in thermodynamics [11]. These forces make graphene easy to aggregate so that it is difficult to disperse homogeneously in polymers, resulting in rather poor mechanical, electro-conductive properties and other performance [12-14]. In order to achieve excellent properties of the polymer/graphene composites, we focus on improving the dispersion and enhancing the interfacial interaction between graphene and polymer matrix. Graphene is a one-dimensional inorganic nano-filler with an inert surface and poor interaction with polymer chains. Therefore, by grafting different polar/non-polar groups on the surface of the graphene to improve the activity of the graphene surface [15-17]. On the one hand, the presence of graphene surface groups can improve the interaction with different polymer molecular chains, on the other hand, it can also prevent the agglomeration of graphene sheets, thus achieving better dispersion of graphene in the polymer matrix. In our previous work, a kind of functional graphene sheets (FGs) with alkyl chains has successfully produced to improve interfacial adhesion in iPP matrix [18].

Isotactic polypropylene (iPP) is one of main engineering plastics in commercial importance because of its cost effectiveness as well as intrinsic properties of low density, high stiffness, good tensile strength, and inertness toward acid, alkalis, and solvents [19]. Materials based on iPP have been used in a wide range of applications including automobile, electronic devices, packaging, household appliances and construction industries. Moreover, for advanced applications, many functionalized iPP composites have been developed by introducing graphene [20, 21]. Lin et al. [17] prepared well dispersion PE/graphene oxide nanocomposites using the melting-blending method by adopting PE-grafted-graphene oxide. Kim et al. [22] have recently also fabricated exfoliated graphene/PE nanocomposites via employing PE functionalized analogs with thermally reduced graphene. Yuan et al. [10]. prepared functionalized graphene oxide by reacting graphene oxide with maleic anhydride grafted polypropylene and then melted blending with polypropylene to obtain the functionalized graphene oxide/polypropylene nanocomposites. Thus, to realize the graphene homogeneously dispersed in polymer matrix is the main challenge to fabricate the excellent performance nanocomposites.

It is not an economical and environmentally friendly way to fabricate graphene nanocomposites by chemical solution in large scale, so a simple and effective melt blending method is used to prepare the graphene nanocomposites in this study. Moreover, polymer processing equipment plays an important role in the preparation of high performance graphene composite materials. Conventional mixers and plastic processing machines mainly operate in the shear flow field. It had been theoretically shown that mixing process dominated by elongational flow has many advantages such as well dispersion, reduced mixing temperature, and wide adaptability [23-26]. Polymer melt drops are more efficiently broken under elongation flow than the shear flow in polymer processing [27-29]. Qu [30] invented a new type of none screw plasticizing processing equipment, known as vane extruder, which based on extensional deformation. Jia et al. [31] have shown that better mechanical properties and finer dispersion particles have been achieved because of the extensional flow field of vane extruder compared with those of the traditional twin-screw extruder. Zhang et al. [32] take the comparison of a novel extruder generating continuous elongation flow and traditional twin-screw extruder to fabricate PP/OMMT nanocomposites shows the tensile properties and impact performance of the nanocomposites prepared by novel extruder are better than the nanocomposites prepared by the twin-screw extruder. Many studies to achieve uniform dispersion of graphene are complicated. Here, we demonstrate a facial route to realize the FGs uniformly dispersed in iPP matrix for fabricating FGs/iPP nanocomposites.

In this work, the iPP/functionalized graphene sheets (FGs) composites have been prepared using vane mixer which is a novel polymer processing equipment based on elongation flow field. The plasticizing and conveying mechanism and the structure have been reported in detail on our previous work [33, 34]. The morphology, mechanical and thermal stability properties of the composites will be investigated and discussed together with the FGs dispersion in iPP matrix under elongational flow field.

EXPERIMENTAL

Materials

The iPP, model T30S, was provided by Lanzhou Petroleum Chemical Incorporation (Gansu, China), with a melt flow index of 2.5 g/10 min (190[degrees]C, 2.16 kg), [M.sub.w] = 399 000, [M.sub.w]/[M.sub.n] = 4.6, and a density of 0.90-0.91 g/[cm.sup.3]. The mixed nanoparticles are functionalized graphene oxide sheets (FGs), which exhibit good dispersion and strongly interfacial interactions in the polymer matrix. FGs were synthesized from nature flake graphite by the modified Hummers' method and then functionalized by 4, 4'-diphenylmethane diisocyanate and stearic acid. The details of this preparation can be found in our previous work [17].

Preparation of Nanocomposites

A novel polymer processing equipment known as the vane mixer was employed to compound iPP/FGs nanocomposites in this research. The structure schematic diagram of the vane mixer is shown in Fig. 1 [35, 36]. The structure and working principle of the unit were introduced in detail

in the previous study [37, 38].

The FGs particles and iPP pellets were dried to remove moisture in a vacuum before processing. The iPP with different FGs percentages (0.1, 0.2, 0.5, 1.0, and 2.0 wt%) were melt-blending by the vane mixer at the rotation speed of 30 rpm at 180[degrees]C for 6 min, and then compression molded at 200[degrees]C under a pressure of 10 MPa into sheets with a thickness of 1 mm.

Characterizations

Scanning Electron Microscopy. The FGs in iPP matrix was evaluated by scanning electron microscope (SEM S4800 Hitachi) at 20 kV. The samples were firstly cryogenically fractured in liquid nitrogen and then coated with a layer of gold before observation.

Transmission Electron Microscopy. Transmission electron microscopy (TEM) observation was performed to observe the dispersion of nanoparticles in iPP matrix with JEOL (JEM2100PLUS) field emission transmission electron microscopy (TEM) at an acceleration voltage of 210KV.

Dynamic Rheological Measurements. Dynamic viscoelastic properties of the pure iPP and its nanocomposites were analyzed by using a rheometer of Anton Paar Physica MCR 302. The measurements were performed in the linear viscoelastic region with dynamic oscillatory mode and 25 mm parallel cone-plate with a gap setting of about 1 mm. All experiments were carried out nitrogen atmosphere at 200[degrees]C. Frequency scans were taken at low strain (1%) at the frequency range between 0.01 and 100 rad [s.sup.-1].

Differential Scanning Calorimetry. The crystallization behavior of the composites was also investigated by differential scanning calorimetry (Netzsch DSC 204) using nitrogen as a purge gas. The non-isothermal crystalline melting behavior of the specimens was obtained through melting the samples (about 5 mg) from 25 to 220 [degrees]C at a heating rate of 10[degrees]C/min and maintained at 220[degrees]C for 5 min to erase the thermal history, and cooled down to 25[degrees]C at the cooling rate of 10[degrees]C /min, then heated to 220[degrees]C at the rate of 10[degrees]C /min. The fractional crystallinity [X.sub.c] was calculated using the following equation:

[X.sub.c](%) = ([DELTA][H.sub.c]/[DELTA]Ho) x (100/[phi])

where [X.sub.c] is the crystallinity of iPP in the composites, [DELTA][H.sub.c] is the measured heat of crystallization, [DELTA][H.sub.o] (J [g.sup.-1]) is the heat of crystallization of a 100% crystalline iPP, and [phi] is the weight fraction of iPP in the composites.

X-Ray Diffraction. The FGs/iPP composites samples were characterized by X-ray diffraction (XRD) (Bruker, D8 ADVANCE) with Cu K[alpha] radiation ([lambda] = 1.5418 [Angstrom]) at room temperature. Scanning was performed over the range of 5[degrees] [less than or equal to] 2[theta] [less than or equal to] 30[degrees] with a scanning rate of 2[degrees]/min.

Thermogravimetric Analysis. The thermal stability of the FGs/iPP composites samples were performed by a thermogravimetric analysis (TGA) (Netzsch TG209 thermogravimetric analyzer) under nitrogen flow (50 mL/min) with a temperature range from 20 to 800[degrees]C at a scanning rate of 10[degrees]C/min.

Dynamic Thermomechanical Analysis. Dynamic mechanical analysis (Netzsch DMA242c) tests of the FGs/iPP composites samples were performed from -50 to 150[degrees]C in a nitrogen atmosphere. The samples were deformed in tension at a fixed frequency of 1 Hz and a heating rate of 3[degrees]C/min. The FGs/iPP composites samples (25 x 4 x I mm) were prepared from the compressed sheets.

Tensile Testing. Mechanical properties of the FGs/iPP composites samples were measured using a tensile testing machine (INSTRON 5566) at a cross-head speed of 20 mm/min. All the measurements were performed at room temperature (23 [+ or -] 2[degrees]C) and the average value was obtained from at least five samples.

RESULTS AND DISCUSSION

Morphology of FGs/iPP Nanocomposites

As we know, the dispersion and distribution of graphene layers in the polymer matrix, as well as their interfacial bonding are the two key factors of influencing the high macroscopic properties of the nanocomposites. In this work, SEM and TEM were employed to assess the dispersion of FGs and interfacial bonding strength in the iPP matrix.

Figure 2 shows the cryogenically fractured surface of the iPP/FGs composites with different FGs loadings. When the FGs content is <2%, it is difficult to find the FGs in the iPP matrix (Fig. 2a-d). The FGs are almost single platelet exist and uniformly distributed in the iPP matrix (Fig. 2e-h), which indicates that continuous volume extensional flow generated in the vane extruder has good effects on the dispersion of FGs in iPP matrix. Moreover, there is almost no delamination between FGs and iPP matrix manifest they have a strong interfacial interaction, as shown in Fig. 2e-h.

The morphology of FGs and FGs/iPP nanocomposites are investigated by TEM. Figure 3a and b shows the FGs are exfoliated and wrinkled with a lateral dimension of a few microns. It also exhibits the layer structure of FGs has been maintained after the chemical modification. After melt-blending by elongation flow of the vane mixer, the FGs are found dispersed by iPP matrix, as shown in Fig. 3c-f. The FGs/iPP nanocomposite cut into nanofilms by microtome for TEM observation. These images demonstrate the FGs are several hundred nanometers at the lateral size and homogeneous distribution in iPP matrix.

The possible dispersing mechanism for FGs particles under the steady and elongation flow field is shown in Fig. 4. Under the circumstance of the steady flow, the velocity gradient is perpendicular to the flow direction. The nanoparticles are apt to aggregates in the steady flow (as shown in Fig. 4a). However, according to recently published works, the melt drops of polymer are more efficiently broken under elongational flow than shear flow [39-42]. Logically, we believe that the aggregated nanoparticles will be easily separated if they withstand a strong stretched force during the polymer processing (as shown in Fig. 4a). In our work, the vane extruder has improved elongation flow significantly during polymer processing. This is attributed to the uniform dispersion of FGs in iPP matrix.

Crystallization Behavior

The crystallization properties of these composites investigated by DSC and XRD. Figure 5 shows the nonisothermal crystallization and melting curves of pure iPP and iPP/FGs composites. Table 1 shows the crystallization temperature ([T.sub.c]), melting temperature ([T.sub.m]) and crystallization ([X.sub.c]) of pure iPP and iPP/FGs composites. From Fig. 5a and Table 1, interestingly, the crystallization temperature of the iPP/FGs composites first increase from 121.6[degrees]C (pure iPP) to 122.1[degrees]C (iPP/0.2 wt% FGs) and then decrease to 120.9[degrees]C (iPP/2.0 wt % FGs). The high crystallization temperature of the iPP/FGs samples with low FGs loading is ascribed to the good dispersion and nucleating in iPP matrix. When the content of FGs nanoparticles reach a certain value, they may play a role as lubricate plasticizer in the polymer matrix, which can improve the motion ability of the molecular chains and reduce the crystallization temperature of the composites. As shown in the Fig. 5b and Table 1, the melting curves show that the iPP has the highest melting temperature (165.2[degrees]C) and the iPP/1.0 wt % FGs exhibits the lowest melting temperature (164.0[degrees]C). The melting temperatures values of the others are between the two temperatures. The crystals developed well structure will have a high melting temperature. The decrease of melting temperature illustrates the fillers will influent iPP's crystallization degree of perfection. The crystallinity of composites was calculated from DSC results and summarized in Table 1. The crystallinity of the composites varied with the increasing FGs content, and the variation was irregular. The reason for this phenomenon may be the competition result between heterogeneous nucleation and space confinement effects in iPP matrix [43].

XRD was used to evaluate the effects of FGs on the crystalline structure of iPP matrix. The XRD patterns of the composites with FGs are almost identical to that of pure iPP, as shown in Fig. 6. There is no [beta]-form crystal found in all samples, which indicates FGs just acting as [alpha]-nucleating agent for iPP crystallization. It is very hard to find the characteristic peaks of FGs in the iPP/FGs composites. The reason is the FGs well dispersion and exfoliation under the elongation flow during polymer processing in iPP matrix.

Thermal Stability

The degradation behavior of pure iPP and iPP/FGs composites in nitrogen atmosphere were investigated by TGA. Figure 7 gives weight loss curves of pure iPP and iPP/FGs composites. The 5 wt % weight loss temperature ([T.sub.5%]) defined here as the initial decomposition temperature, 50 wt% weight loss temperature ([T.sub.50%]) and the temperature at the maximum rate of weight loss ([T.sub.Max]) are summarized in Table 2. It can be seen from Fig. 7 that incorporation of FGs can improve the [T.sub.5%] and [T.sub.50%] compared with pure iPP, and increased with FGs content adding. Neat iPP starts to degrade at 407[degrees]C and [T.sub.50%] occurs at about 452.3[degrees]C. After incorporation of 2 wt% FGs, [T.sub.5%]. and [T.sub.50%] of the iPP/FGs nanocomposites are increased by 8 and 9.1[degrees]C, respectively. Moreover, the [T.sub.max] values are also enhanced by 7.6[degrees]C for 0.2 wt % FGs loading. The increased thermal stability of composites is probably due to the fillers acting as the physical barrier and delaying the escape of degradation products. On the other hand, the high thermal conductivity of graphene can dissipate the external heat effectively. Therefore, the dispersion particles become important to improve the thermal stability of the composites.

Dynamic Mechanical Analysis

Figure 8 shows the temperature dependence of storage modulus E', loss modulus E" and tan [delta] of the pure iPP and various iPP/FGs composites. As shown in the Fig. 8a, the E' of all the samples decreased with an increase of temperature. It decreased slowly in the range from -60 to -25[degrees]C, but between -25 and 25[degrees]C dropped quickly due to the glass transition. Between -25 and 100[degrees]C, E' decreased slowly again. When compared with pure iPP, iPP/0.1%FGs showed significant improvement of E'. When the FGs loading was 0.1 wt%, the storage modulus reached the maximum value (1.96 GPa) which was 35% higher than that of neat iPP (1.49 GPa). The magnitude of increase of storage modulus is lower than that of Young's modulus, which ascribed to the difference of measurement modes and resolution of instruments.

Tan 6, the ratio of E"/E', is used to evaluate the energy loss of materials from segment rearrangements and internal friction during the test. Figure 8b shows the tan [delta] of the pure iPP and iPP/FGs composites as a function of temperature. The glass transition temperature ([T.sub.g]) is widely determined by the tan [delta] peak temperature in DMA. It is clear to note that the [T.sub.g] for iPP/FGs composites with 0.1 and 2 wt% is 17.4 and 15.25[degrees]C, respectively, which is higher than that of neat iPP (14.2[degrees]C). There is a slight increase in [T.sub.g] (ca. 3.2[degrees]C) at 0.1 wt% of FGs than that of neat iPP, indicating the movements of polymer chain are restricted to a certain degree. However, the [T.sub.g] gradually reduces with increasing FGs loadings, the results may be explained by the plasticization effect of FGs sheets in iPP matrix. Due to the surface of FGs nanoparticles functionalized with alkane chains, they have good compatibility with the iPP matrix. When at a low FGs loadings, its plasticization can be ignorable relative to the restriction of FGs to the polymer chains. With the increase of FGs content, they play the role of plasticizer to improve the motion ability of matrix molecule chains and reduce the Tg gradually.

Rheology Properties

Neat iPP and iPP/FGs composites were submitted to a small amplitude deformation test by the parallel disc oscillatory shear at 200[degrees]C in the frequency range [10.sup.-1] to [10.sup.3] Hz. The measured dynamic storage modulus G', loss modulus G" and dynamic viscosity ([eta]*) are depicted in Fig. 9a-c, respectively. According to the linear viscoelastic theory, it is generally believed that G' and G" of polymer based materials increased monotonously with an increase of the frequency. As Fig. 9a and b shows that the theory is applicable in this work with the G' and G" of pure iPP and iPP/FGs composites which increased with an increase of frequency. Based on Seo and Park [44]. the rheological behavior at low frequencies is sensitive to the structure of the composites. At low frequencies, the composites with 0.2 and 0.5 wt% of FGs show lower storage modulus values than the neat iPP, while the composites containing higher amounts of FGs show higher storage modulus, also compared with the neat iPP. The increase of G' and G" in the composites with a higher concentration of FGs indicates the existence of an interaction between the polymer matrix and FGs.

The complex viscosity [eta]* of pure iPP and iPP/FGs composites as a function of frequency at 200[degrees]C is shown in Fig. 9c. It can be seen that the iPP/FGs composites had a similar dependence on the frequency as the pure iPP. All the samples show the typical thinning behavior, the viscosity decreases as the shear rate increases. Nevertheless, the remarkable drop in viscosity at high frequencies is similar for all samples, illustrating that the composites filled with FGs in the range from 0.1 to 2.0 wt% could be processed at higher shear rates without any difficult. With analysis of the effects on melt rheology when FGs are added to the polymer matrix, shows that composites tend to reduce the viscosity may ascribe to the presence of FGs with alkane chains on the surface and the lamella structure. Furthermore, the decrease of viscosity in these composites is attributed to the dispersion of FGs in the iPP matrix and a strong interaction between the matrix and FGs, which means that the alkane chains on the surface and lamellar structure of FGs can reduce shear stresses and relaxation times to flow.

On the grounds of Verma et al. [45]. the storage modulus is high when the molecular mobility is limited or restricted. The lower viscosity and modulus showed the 0.2 and 0.5 wt% of FGs samples may be the alkane chains on the surface of graphene that can induce to a greater local chain mobility. As a matter of fact, it is depicted that the reduction of complex viscosity at low frequencies of the neat iPP, as a result of the alkane chains may generate more imperfect crystals within the polymer matrix. On account of alkane chains on FGs surface, it could loosen the molecular packing and then increase the free volume.

Mechanical Properties

Table 3 shows the detailed data of tensile properties of pure iPP and iPP/FGs composites. Clearly, incorporation of FGs results in a significant enhancement in the tensile strength and Young's modulus at low FGs loadings, herein, not exceeding 1.0 wt%. However, the elongation at break of the composites reduces with increasing FGs loading level. Upon adding 0.1 wt% FGs, the tensile strength and Young's modulus are increased up to 43.5 MPa (by 6.6%) and 1.14 GPa (12.8%), respectively. Furthermore, the elongation at break is almost unchanged, manifesting no reduction for the composites toughness. When the FGs loading adds to 1.0 wt%, all tensile strength and Young's modulus reach the maximum values. The tensile strength (44 MPa) and Young's modulus (1.55 GPa) are increased by 7.8% and 53.4%, respectively. These improvements are ascribed to the homogeneous dispersion of graphene nanosheets and effective load transfer from matrix to FGs due to their strong interfacial adhesion. However, when the content of FGs increases at 2.0%, both the tensile strength and the Young's modulus of iPP/FGs composites show a significant decrease, it is due to a critical point of the mechanical properties similar to electrical percolations [6].

CONCLUSION

In summary, a novel polymer processing equipment vane mixer which dominated by elongational flow field is used to prepare different FGs contents of iPP/FGs nanocomposites. The FGs, which is prepared by graphene oxide sheets reacting with the diisocyanate and the stearic acid, can physically tangle with the polypropylene molecular chains and enhance the interface interaction with iPP matrix. The dispersion of nanoparticles and mechanical properties of iPP/FGs are investigated in detail. Results show that FGs nanoparticles are well dispersed and exfoliated under the elongation flow during polymer processing in iPP matrix. XRD results are very hard to find the characteristic peaks of FGs in the iPP/FGs composites. The DMA shows that increased glass transition temperature due to the presence of FGs to some extent restricts the movement or relaxation of the polymer chains. The thermal oxidative stability of iPP was improved by the addition of FGs because of the barrier effect of sheets structure. Compared with our previous work, the mechanical properties of iPP are improved obviously by vane mixer. Consequently, it can be used for developing graphene nanocomposites with many potential applications.

ACKNOWLEDGMENTS

We acknowledge the National Key Research and Development Program of China (Grant No. 2016YFB0302300), the Key Program of National Natural Science Foundation of China (Grant No. 51435005), the National Natural Science Foundation of China (Grant No. 51505153), the PhD Start-up Fund of Natural Science Foundation of Guangdong Province, China (Grant No. 2016A030310429), the Science and Technology Program of Guangzhou, China (Grant No. 201607010240), the Natural Science Foundation of Guangdong Province (2016A030313486 and 2018A030313275), the Program of Nanhai Talented Team (201609180006) and the Program of Foshan Innovative Entrepreneurial Team (2016IT100152).

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Feng Qiu, Xiaochun Yin, Jin-Ping [iD]

National Engineering Research Center of Novel Equipment for Polymer Processing, Key Laboratory of Polymer Processing Engineering, Ministry of Education, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China

Correspondence to: J.-P. Qu; e-mail: jpqu@scut.edu.cn Contract grant sponsor: Science and Technology Program of Guangzhou, China; contract grant number: 201607010240. contract grant sponsor: Special-funded Program on National Key Scientific Instruments and Equipment Development of China; contract grant number: 2012YQ230043. contract grant sponsor: Natural Science Foundation of Guangdong Province, China; contract grant number: 2016A030310429. contract grant sponsor: National Natural Science Foundation of China; contract grant numbers: 51505153; 51435005.

DOI 10.1002/pen.25017

Caption: FIG. 1. Schematic drawing of the vane mixer. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 2. SEM images of the cryogenically fractured surface of the iPP/0.1 wt% FGs composites (a), iPP/0.2 wt% FGs composites (b), iPP/0.5 wt % FGs composites (c), iPP/1.0 wt% FGs composites (d), and iPP/2.0 wt% FGs composites (e-h). [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 3. TEM images of the FGs (a, b), iPP/2.0 wt% FGs composites (c, d), and iPP/0.1 wt% FGs composites (e, f). [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 4. The schematic diagram of dispersing processing for the nanoparticles in different flow field (a) steady shear flow and (b) volume elongational flow. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 5. (a) Melt-crystallization DSC curves and (b) Second-heating DSC curves of pure iPP and different iPP/FGs composites. [Color figure can be viewed at wiIeyonlinelibrary.com]

Caption: FIG. 6. The XRD spectra of the iPP and iPP/FGs composites. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 7. TGA curves of the pure iPP and iPP/FGs composites under [N.sub.2] atmosphere. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 8. Temperature dependence of (a) storage modulus E' and (b) tan [delta] of the pure iPP and iPP/FGs composites. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 9. (a) Storage modulus (G'), (b) loss modulus (G"), and (c) complex viscosity ([eta]*) versus frequency of iPP and iPP/FGs composites with different weight fractions of FGs at 200[degrees]C. [Color figure can be viewed at wileyonlinelibrary.com]
TABLE 1. The crystallization temperature ([T.sub.c]),
melting temperature ([T.sub.m]), and crystallization
([X.sub.c]) of pure iPP and iPP/FGs composites.

Samples         [T.sub.c]      [T.sub.m]      [DELTA]    [X.sub.c]
               ([degrees]C)   ([degrees]C)   [H.sub.m]      (%)
                                               (J/g)

iPP               121.6          165.2         102.6       49.1
iPP/0.1%FGs       122.1          164.1         99.24       47.5
iPP/0.2%FGs       121.4          165.0         110.2       52.8
iPP/0.5%FGs       121.5          164.8         85.21       41.0
iPP/1.0%FGs       121.6          164.0         100.8       48.7
iPP/2.0%FGs       120.9          164.7         101.4       49.5

TABLE 2. The 5 wt% weight loss temperature ([T.sub.5%]),
50 wt% weight loss temperature ([T.sub.50%]), and maximum
decomposition temperature ([T.sub.max]) from TGA results
of pure iPP and iPP/FGs composites.

Samples         [T.sub.5%]    [T.sub.50%]    [T.sub.max]
               ([degrees]C)   ([degrees]C)   ([degrees]C)

iPP               407.9          452.3          458.7
iPP/0.1%FGs       410.0          458.6          464.6
iPP/0.2%FGs       411.8          460.3          466.3
iPP/0.5%FGs       412.9          459.5          465.5
iPP/1.0%FGs       413.7          460.2          464.7
iPP/2.0%FGs       415.9          461.4          465.9

TABLE 3. The mechanical properties of pure iPP and iPP/FGs composites.

               Tensile             Young's
Samples        strength (MPa)      modulus (GPa)

iPP            40.8 [+ or -] 0.6   1.01 [+ or -] 0.13
iPP/0.1%FGs    43.5 [+ or -] 1.3   1.14 [+ or -] 0.10
iPP/0.2%FGs    43.4 [+ or -] 0.8   1.21 [+ or -] 0.12
iPP/0.5%FGs    43.7 [+ or -] 0.7   1.35 [+ or -] 0.15
iPP/1.0%FGs    44.0 [+ or -] 0.8   1.55 [+ or -] 0.21
iPP/2.0%FGs    42.6 [+ or -] 0.6   1.42 [+ or -] 0.18

               Elongation at
Samples        break (%)

iPP            1080 [+ or -] 100
iPP/0.1%FGs     980 [+ or -] 75
iPP/0.2%FGs     466 [+ or -] 60
iPP/0.5%FGs     320 [+ or -] 30
iPP/1.0%FGs     179 [+ or -] 25
iPP/2.0%FGs      20 [+ or -] 10
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Title Annotation:functional graphene
Author:Qiu, Feng; Yin, Xiaochun; Qu, Jin-Ping
Publication:Polymer Engineering and Science
Article Type:Report
Date:Apr 1, 2019
Words:5541
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