Tensile Properties of Glass Fiber/Carbon Fiber ...

Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition IMECE2016 November 11-17, 2016, Phoenix, Arizona, USA

IMECE2016-66270

TENSILE PROPERTIES OF GLASS FIBER/ CARBON FIBER REINFORCED POLYPROPYLENE HYBRID COMPOSITES FABRICATED BY DIRECT FIBER FEEDING INJECTION MOLDING PROCESS Xiaofei YAN The Department of Bio-based Materials Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan

Masuo MURAKAMI Tradition Mirai Education Research Center, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan

Putinun UAWONGSUWAN The Department of Materials and Production Technology Engineering, King Mongkut's University of Technology North Bangkok , Bangkok, 10800, Thailand

Akihiko IMAJO

Yuqiu YANG

The Department of Advanced-fibro Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan

Key Laboratory of Textile Science &Technology, Ministry of Education, College of Textiles, Donghua University, Shanghai, 201620,China

ABSTRACT This paper mainly discusses the effect of coupling on the tensile properties of glass fiber (GF)/carbon fiber (CF) reinforced polypropylene (PP) hybrid composites which were made through a new injection molding process named direct fiber feeding injection (DFFIM) process. It is mainly divided into two parts which discusses the functional of coupling agent in the composites system, and the different contents of coupling agent (PA6 and MAPP) on the tensile properties of composites. DFFIM progress is a new method that by directly feeding of continuous carbon fiber into the barrel of injection molding machine to make the hybrid composites. The continuous CF roving strands are guided into the vent of devolatilizing unit of injection barrel and fed into the melt by the shearing motion of the screw during plasticization process. By using DFFIM process to make composites, the fiber attrition during extrusion compounding will be eliminated. It is a great improvement in reduction of material cost. And also the cost of reinforcing compounded pellet in the traditional composites market value chain could be lower. Polyamide 6 (PA6), Maleic anhydridegrafted polypropylene (MAPP) or both of them were mixed with pellets during the DFFIM process and PA6 and MAPP were used as coupling agent for CF/GF reinforced PP system.

Hiroyuki HAMADA Tradition Mirai Education Research Center, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan

The CF and GF contents in each hybrid composites were tested to analysis the influence of fiber contains on the tensile properties of composites. Usually, better interfacial bonding between fiber and matrix in composites, better tensile properties of composites. So the effect of coupling agent (PA6 and MAPP) on the interfacial bonding between CF and PP in hybrid composites were firstly analyzed. And then the influence different contents of PA6 and MAPP on the tensile properties of GF/PP composites and GF/CF reinforced PP hybrid composites were investigated. It is found that the addition of PA6 did not improve the interfacial bonding but the addition of MAPP has shown a little improvement to the bonding between CF and PP. And when using PA6 and MAPP together as co-coupling agent, the tensile properties of composites has greatly increased. And, there is fiber aggregation in the core layer of the hybrid composites which made by DFFIM process, while there is no such phenomenon happened in the condition of normal injection molding process. It is the main reason that the tensile strength of hybrid composites without coupling agent is weaker than the GF/PP composites. And the tensile modulus of composites would be increased considerably. That is due to the addition of the carbon fiber which has high tensile modulus. In the condition of composites with 1wt.% PA6, the 1wt.% PA6 shows

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control the feeding rate of matrix. By direct feeding of continuous fiber into the barrel of injection molding machine, the fiber attrition during extrusion compounding will be eliminated. Furthermore, the reduction of material cost can be the most effective cost reduction route. This is a fundamental industry change that eliminates the compounding step and also the cost of reinforcing compounded pellet in the traditional composite market value chain. The continuous fiber roving strands are guided into the vent of the devolatilizing unit of injection barrel and fed into the melt by the shearing motion of the screw during plasticization process. There are three important parameters that controlled the content of reinforcing fiber. Increasing the number of fiber roving increased the feeding content of fiber. The amount of matrix is controlled by the adjustment of screw speed of the adjustable feeding hopper. In addition, by changing the rotational speed of injection screw unit the content of both fiber and matrix are changed [18].

positives effect on tensile properties and while PA6 has negative role when the amount of PA6 has improved. Within a certain range, the larger amount of MAPP in the system of MAPP-PA6 composites, the better on the tensile properties of composites is. And MAPP has positive effect on the tensile properties of composites. 1. INTRODUCTION Polypropylene (PP) has shown a widespread range of using in composites material science due to its moderate cost, low density and favorable properties [1]. To improve the rigidity and stiffness of PP, usually, short fiber especially the high modulus and high stress fibers such as glass fiber (GF) and carbon fiber (CF) were added to PP to make the PP based composites [2-3]. Thus it makes the application of PP, GF and CF extended. Hybrid composites is a hot topic in the composites material designs because it can make the full use of material and it can find the balance between the advantage and disadvantage of two or more material. The advantage of one type of material could complement with what are lacking in other fiber or matrix and the cost of composites material would be also decrease [4-6]. And hybrid composite which made by glass fiber and carbon fiber is popular those days especially in automobile industry such as fan blades of engine cooling system, dashboard, door, front-end module frame and so on. And after improvement the rigidity and stiffness of hybrid composites, the application of composites in the automobile industry will be wider [7-8]. For making the fiber reinforced thermoplastics (FRTP), injection molding is extremely popular because it can be more cost-effective compared with other molding process. And the molds required for injection molding process are generally considered to be lightweight and low cost compared with conventional compression molding and other molding process, resulting in a lower investment to enter production [9-11]. The mechanical properties of FRTP is determined by fiber–matrix interfacial adhesion, fiber orientation, dispersion of fiber, and also fiber aspect ratio (the ratio of fiber length over diameter as a measurement of fiber relative) [12-15]. But, in general, the attrition of fibers can occur during injection molding process. So it is important to select the right molding process conditions to avoid or decrease the excessive fiber attrition. And also, the extrusion compounding for preparing fiber filled polymer pellets, has a practical processing limit on the fiber attrition problem. It could decrease the reinforcement efficiency of the fibers and affect the properties of composites [16-17]. The direct fiber feeding injection molding (DFFIM) process is an improvement of the injection molding (IM) process and it is aim is to improve the fiber dispersion with minimum fiber breakage during molding process. As it is shown in Figure 1. The general vented barrel, which is typically used for releasing the volatile gasses of the hydroscopic materials, is adapted as the direct fiber feeding unit. The normal hopper was replaced with the controllable feeding speed hopper in order to

Fig.1 Schematic drawing of direct fiber feeding injection molding process. Truckenmueller and Fritz H Gin [19] firstly done the research work about DFFIM process and found that the specimens which made by direct incorporation of continuous fibers onto injection molding machine exhibit very good fiber dispersion, minimal fiber breakage, and full retention of mechanical properties including impact toughness. M. J. A. V. et.al and K.H. Wong et.al [20-23] found that the reinforcing potential of the fiber was increased by improving the interfacial adhesion between the fiber and PP matrix and this was done by the addition of maleic anhydride grafted polypropylene (MAPP) coupling agents and indicated that the mechanical properties of hybrid composites is greatly influenced by the fiber–matrix interface characteristics. Karsten Brast et.al [24] reveals the influence of production parameters on the quality of composites. The shear stresses exerted by the screw or ram will break the fibers and result finally in a fiber length distribution with an asymmetric character with a tail at the long fiber end. The fiber length is governed by a number of factors including fiber content and processing conditions, etc. [25]. And fiber aspect ratio is not fixed. It has the distribution characteristics. This paper mainly discusses the tensile properties of GF/CF reinforced PP hybrid composites which used polyamide

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Japan) were selected as the coupling agent for carbon fiber and polypropylene. In this study, the single coupling and cocoupling agent were used for the modification of interfacial bonding between fiber and matrix as list in Table 1.

6 (PA6) and Maleic anhydride-grafted polypropylene (MAPP) as coupling agent. Generally, better interfacial bonding between fiber and matrix in composites, better properties of composites. Thus it is very important to express the effect of coupling agent on the mechanical properties of GF/CF reinforced PP hybrid composites. This article is divided into two parts: Part I Effect of coupling agents on the interfacial bonding between CF and PP in hybrid composites; Part II Effect of different content of PA6 and MAPP on the tensile properties of hybrid composites.

2.2 Method Tensile tests were conducted on Instron universal testing machine (model 4206) in accordance with ASTM D638. The testing speed was 1 mm/min with at least 5 samples were tested. Scanning electron microscope (SEM, JSM 5200) was conducted on fracture surface to observe the failure surface. The specimen was mounted on aluminum holder and gold sputtered for 6 minutes prior observation. The fiber content in hybrid composites were measured by using the ignition loss method at 600℃ for 6 hours under the air atmosphere according the ASTM D3171-15.

PART I EFFECT OF COUPLING AGENTS ON THE INTERFACIAL BONDING BETWEEN CF AND PP IN HYBRID COMPOSITES 2. MATERIALS AND TESTING METHODS 2.1 Materials and Preparation of the specimen Pre-compounded glass fiber polypropylene (GF/PP, diameter of GF=9 um) pellet (grade R-150G, Prime Polymer Co., Ltd.) with 10 wt.% loading content was used for injection molding process. The carbon fiber (CF: grade TR50S12L, 1200 Tex, diameter=7um, Mitsubishi rayon, Japan) was used as hybrid fiber. The 18-tons injection molding machine (Sumitomo: model iM18) with a vented barrel was used for the fabrication of testing specimens. A single roving carbon fiber was guided into the vent of the devolatilizing unit of the barrel and fed into the melt by the shearing action of the injection screw during plasticization process as presented in Figure 1. The barrel temperature and mold temperature were set at 200 and 30℃, respectively. The screw plasticization speed was fixed at 130 rpm. The 10 wt.% GF/PP pellets were fed at controllable feeding hopper with constant rate 50 r/min. The GF/PP and CF/GF/PP hybrid composites were fabricated based on the composition which listed in Table 1.

Code G0 G1 G2 G3 H0 H1 H2 H3

Table 1 Specimen code Composition 10wt.% GFPP 10wt.% GFPP+5wt.%PA6 10wt.% GFPP+2wt.%MAPP 10wt.% GFPP+2wt.%MAPP+5wt.%PA6 10wt.% GFPP+ as-received CF 10wt.% GFPP+5wt.%PA6+as-received CF 10wt.% GFPP+2wt.%MAPP+asreceived CF 10wt.% GFPP+2wt.%MAPP+5wt.%PA6+asreceived CF

3. RESULTS AND DISCUSSION Table 2 Composites of GF/PP and GF/CF/PP hybrid composites Code Matrix Glass fiber Carbon fiber (wt.%) (wt.%) (wt.%) G0 90 10 0 G1 90.5 9.5 0 G2 90.2 9.8 0 G3 90.7 9.3 0 H0 76.0 8.4 15.6 H1 61.0 6.4 32.6 H2 66.0 7.3 26.7 H3 64.6 6.6 28.8

Purpose

To see the effect of PA6 and MAPP on the fibermatrix interfacial bonding in composites. (a) Stress-strain relationship of GF/PP composites (G0: 10wt.%GFPP; G1:10wt.%GFPP+5wt.%PA6; G2:10wt.%GFPP+2wt.%MAPP; G3:10wt.%GFPP+2wt.%MAPP+5wt.%PA6)

Polyamide 6 (PA6, Toray Industries Inc., Japan) and Maleic anhydride-g-polypropylene (MAPP with 5 wt.% maleic anhydride, POLYTACK H-1000P, Idemitsu Kosan Co., Ltd.,

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G3 showed similar stress-strain behavior with the G0. It can be seen that the using of co-coupling agent of PA6 and MAPP (G3) greatly improved the compatibility between PA6 and PP matrix. The highly reactive maleic anhydride groups in MAPP can react with the amine terminal groups of polyamide, which is one of the effective compatibilizing agents for PP and PA6. Thus the using of the selected coupling agents had no significant effect on the interfacial bonding between GF and PP matrix. However, from the immiscibility of PA6 and PP, the interfacial bonding between CF and PP did not improve by the addition of PA6. The co-coupling agent system hybrid composite (H3) showed the best tensile properties. It can also be seen from SEM micrograph that the matrix remained on the carbon fiber surface after fiber pull out. This result confirmed the efficiency of cocoupling agent, which the MAPP bridging between PA6 and PP matrix improved the interfacial bonding between CF and PP matrix.

(b) Stress-strain relationship of CF/GF/PP composites with different coupling agents (H0: 10wt.% GFPP+ as-received CF; H1: 10wt.% GFPP+5wt.%PA6+as-received CF; H2: 10wt.% GFPP+2wt.%MAPP+as-received CF; H3: 10wt.% GFPP+2wt.%MAPP5wt.%PA6+as-received CF) Fig.2 Stress-strain relationship of GF/PP and CF/GF/PP composites with different coupling agents The fiber contents in hybrid composites is shown in Table 2. It can been seen that although the single carbon roving and the same matrix feeding were used in DFFIM process, the carbon fiber contents was affected by the addition of PA6 and MAPP. The addition of PA6 and MAPP at the feeding hopper resulted in the different PP feeding rates. To clarify the effect of coupling agents on tensile properties of GF/PP and CF/GF/PP composites, the stress-strain curve of different composites were presented in Figure 2. The coupling agent on the matrix-fiber interface of GFPP composites is limited. And for the hybrids composites, generally, the hydrophobic nature of polypropylene was incompatible with hydrophilic amine terminal groups of polyamide 6. The small reduction in tensile strength of G1 composite was caused by incompatibility of PA6 and PP matrix. Uncoupled hybrid composite (H0) showed plastic deformation of PP matrix after reaching a maximum stress. However, coupled hybrid composites (H1, H2, H3) showed brittle failure. The tensile modulus and strength of hybrid uncoupled and coupled hybrid composites were presented in Figure 3, respectively. Although the fiber loading content of H1 composite was higher than H0, there was no different in tensile modulus and tensile strength. The SEM micrographs of fracture surface in Figure 4 revealed that the small area of incompatible between PP and PA6 was found around glass fiber. On the other hand, G2 and

(a)

(b) Fig.3 Comparison of tensile modulus and tensile strength between GF/PP and CF/GF/PP composites with different coupling agents.(a) Tensile modulus; b) Tensile strength)

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The 30t-tons injection molding machine (TI-30F6, TOYO Machinery & Metal Co., Ltd) with a vented barrel was used for making the specimen to explain the effect of different contents of PA6 on the GF/CF reinforced PP composites. The barrel temperature is 240℃ while the mold temperature is 30℃. The speed of screw plasticization is 40% of max rotation and the max rotation speed is 450 rpm. The 25wt.% GF/PP pellets and other mixed pellets were fed at constant speed through the controllable feeding hopper and the feeding speed is 50 r/min and 75 r/min, respectively. Lower feeding speed leads higher carbon fiber contents in DFFIM process, thus the carbon fiber contents of in 75r/min would be less than that in the condition of 50r/min. Specimen’s detail information is also shown in Table 3.

Code C0 C1 C2 C3 C4 C5 C6 C7 Fig.4 SEM micrographs of fracture surface of GF/PP and CF/GF/PP composites with different coupling agents

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PART II EFFECT OF DIFFERENT CONTENT OF PA6 AND MAPP ON THE TENSILE PROPERTIES OF HYBRID COMPOSITES

Table 3 Specimen code Composition 25wt.% GFPP 25wt.% GFPP + CF 25wt.% GFPP + CF+ 1wt.%PA6 25wt.% GFPP + CF+ 3wt.%PA6 25wt.% GFPP + CF + 5wt.%PA6 25wt.% GFPP + CF + 5wt.%PA6 + 2wt.%MAPP 25wt.% GFPP + CF + 5wt.%PA6 + 4wt.%MAPP 25wt.% GFPP + CF + 5wt.%PA6 + 6wt.%MAPP 25wt.% GFPP + CF + 5wt.%PA6 + 6wt.%MAPP

Feeding speed

50r/min

75r/min

4.3 Method The tensile properties of the specimens were determined by using a universal testing machine (55R 4206, Instron Co., Ltd.) at a constant crosshead speed of 1 mm/min, using five samples for each measurement. An extensometer (Instron Co., Ltd) with gauge length of 50 mm was used for the strain measurements. Fracture surfaces of the specimens were observed by scanning electron microscopy (SEM, JSM-5200 JEOL Japan Electronics Co., Ltd.). Prior to the SEM observations, all fracture surfaces of the tensile specimens were sputter coated with gold to avoid electrical charging during examination. The fiber contents were tested by two kinds of methods: Thermo Gravimetric Analysis (TGA) and Ignition loss method, respectively. Firstly, the contents of glass fiber and carbon fiber in composites were tested by using Thermo Gravimetric Analysis (TGA, Discovery TGA) in air atmosphere with heating speed 10℃/min. The weight of test specimen is 5±2 mg. The temperature was set from 25℃ to 800 ℃. It can get the fiber content in the composites by analysis the weight losstemperature curve. Then ignition loss method also were used for test the composition of composites. The weight of test specimen is about 2g. The composites were treated in 800℃ for 6 hours

4. MATERIALS AND TESTING METHODS 4.1 Materials The pre-compounded glass fiber polypropylene pellet: GWH42 with 25 wt.% loading content given by Sumitomo Chemical Co., Ltd, Japan. The carbon fiber (Grade: TR50S12L, 1200 Tex, diameter=7um) from Mitsubishi Rayon Co, Ltd, Japan were used as hybrid fiber. Polyamide 6 (PA6) (Grade: A1030BRL, Unitika Co., Ltd, Japan) and Maleic anhydride-grafted polypropylene (MAPP with 5wt.% maleic anhydride, Polytack H-1000P, IDEMITSU Kosan Co., Ltd., Japan) were used as coupling agent for carbon fiber and PP. 4.2 Preparation of the specimen A single roving carbon fiber was guided into the vent of the devolatilizing unit of the barrel and fed into the melt by the shearing action of the screw during plasticization process also as shown in Figure 1. All specimens were injection molded into dumbbell-shaped tensile bars. The thickness and width of the specimens are 3 mm and 10 mm.

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method, and the results were presented in Table 4 and Table5, respectively. The TGA method is too accurate to test the composition of hybrid composites fabricated by DFFIM process due to the fiber orientation in hybrds composites is not uniform in the core layer and the skin layer, and it is difficult to use about 5mg specimen to representative the entire sample. The fiber orientaton of composites made by DFFIM process will discuss in the following paragraph. And Ignition loss method use about 2g which is much more than TGA method thus the infulence of fiber orientation could be very small. So the result gained from ignition loss method is closed to the real value.

under the air atmosphere according to ASTM D3171-15. After the composites burned at that condition, only glass fiber were remained, and it can get the composition of composites according the feeding ratio of each material in mixed pellets through the controllable feeding hopper. 5. RESULTS AND DISSCUSSION Table 4 Composition of GF/PP and GF/CF/PP hybrid composites tested by TGA methods Matrix Glass fiber Carbon fiber Code (wt.%) (wt.%) (wt.%) C0 74.23 25.77 0.00 C1 62.23 21.02 16.75 C2 63.36 21.04 15.60 C3 66.66 22.25 11.09 C4 61.48 18.07 20.45 C5 61.88 20.40 17.72 C6 65.67 20.53 13.80 C7 62.10 19.26 18.64 Table 5 Composition of GF/PP and GF/CF/PP hybrid composites tested by ignition loss method Matrix Glass fiber Carbon fiber Code (wt.%) (wt.%) (wt.%) C0 75.06 24.94 0 C1 63.14 19.59 17.27 C2 61.20 20.07 18.73 C3 65.31 20.85 13.84 C4 61.70 19.16 19.14 C5 60.32 18.22 21.46 C6 66.69 19.58 13.73 C7 59.85 17.08 23.07 C8 62.38 17.80 19.82

(a) Tensile Modulus

(b) Tensile Strength Fig.6 Tensile modulus and tensile strength of GF/PP and CF/GF/PP composites with different coupling agents: (a) Tensile Modulus;(b) Tensile Strength Tensile stress-stain relationship of different GF/PP and CF/GF/PP composites with different contents of coupling agents were shown in Figure 5. GF/PP (C0) composites has the biggest stain value, and the tensile modulus of GF/PP (C0) composites could be increased with the adding of carbon fiber through the DFFIM process. It is due to high modulus of carbon

Fig.5 Stress-strain relationship of GF/PP and CF/GF/PP composites with different contents of coupling agents The composition of GF/PP and GF/CF/PP hybrid composites were tested by TGA method and Ignition loss

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seen the same results from Figure 7 and Figure 8 that the tensile modulus and tensile strength of C7 is larger than that of C8. And the reason is C7 has more fiber contents compared with C8 especially carbon fiber contents.

fiber. And, it can be seen from the tensile modulus and tensile strength of different GF/PP and CF/GF/PP composites with different coupling agents which were presented in Figure 6. The tensile strength increased mainly due to the interfacial bonding in the hybrid composites has improved. When compared with C0 (GFPP), the increase rate of tensile strength and tensile modulus of composites after the addition of carbon fiber and different contents of coupling agents is illustrated in Table 6. The tensile modulus of composites greatly improved after feeding the carbon fiber. Table 6 Increasing rate of tensile modulus and tensile strength after feeding carbon fiber and different contents of coupling agents Code Modulus (%) Code Tensile Strength (%) C1 125.25 C1 -13.20 C2 156.28 C2 -9.61 C3 112.10 C3 -5.75 C4 92.86 C4 -0.01 C5 182.36 C5 5.71 C6 176.74 C6 11.94 C7 165.68 C7 18.70

Fig.8 Tensile modulus and tensile strength of hybrid composites with different pellet feeding speed Also, from the Figure 9, it can be seen that the fracture surface which is fabricated by DFFIM process shows the fiber aggregation in the core layer while the GF/PP composites has not happened the fiber aggregation phenomenon. In the place where has fiber aggregation, there is little matrix between the interface of fiber and the matrix. Thus the adhesion or interfacial bonding is so poor in the core of dumbbell specimen fabricated by DFFIM process. And it is the main reason that the tensile strength of GF/PP (C0) composites has not shown obviously difference with other specimen. And it also indicates the fiber orientation in the hybrid composites made by DFFIM process is not even and use the method of TGA to test the fiber contents is not accurate enough.

Fig.7 Stress-strain relationship of hybrid composites with different pellet feeding speed And with the increase of glass fiber contents, the tensile modulus of composites also has grew by comparing to using the different GF contents pellets. The adding of 1wt. % of PA6 could improve the tensile modulus of GF/CF reinforced PP composites made by DFFIM process while adding more PA6 could have be counterproductive. Also, the MAPP can great increase the tensile properties of hybrid composites. Uncoupled hybrid composite (H0) showed plastic deformation of PP matrix after reaching a maximum stress. That is maybe due to the low contains of fiber while hybrid composite (C1, in Part I) showed brittle failure. Hybrid composite C7 and C8 were made in the same condition while the pellet feeding speed is different. It can be

Fig.9 SEM micrographs of fracture surface of C1 and GF/CF/PP hybrid composites fabricated by DFFIM process (up: C1; down: GF/CF/PP hybrid composites-DFFIM) From SEM micrographs of fracture surface of GF/PP and CF/GF/PP composites with different contents of PA6 and MAPP which is shown in the Figure 10, we can clearly see that the interfacial bonding between the PP and GF is improved with

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agent significantly improved the interfacial bonding between CF and PP. 2) There is fiber aggregation occurs in the core layer of specimen which is fabricated by DFFIM process. While there is not obviously fiber aggregation phenomenon happened in the normal injection molding process. 3) PA6 has positive effect on the tensile properties in 1wt.% while it has played negative role when the amount of PA6 had improved. And MAPP shows positive effect on the tensile properties.

the addition of PA6 and MAPP in the condition of 25 wt.% of GF in the pellets. With increasing addition the amount of PA6, the interfacial bonding between the CF and matrix has not shown significant improved. While the addition of MAPP to the hybrid composites system, the interfacial bonding of both GF, CF with PP has great improved. And the surface of CF and GF remain a lot of matrix, relatively. Thus it is the main reason that the tensile properties has greatly improved with the addition of MAPP. Within a certain range condition of MAPP, the more MAPP, the better tensile properties.

ACKNOWLEDGMENTS The authors would like to thank the China Scholarship Council (CSC) which is an organization affiliated to the Ministry of Education of the People’s Republic of China for partly supporting this work by the Scholarship under the Grant CSC No.201506630020. REFERENCES [1] Tripathi, D. ,2001, “Practical guide to polypropylene. Shrewsbury: RAPRA Technology” [2] Fu S Y, Lauke B, Maeder E, Yue C Y and Hu X, 2000, “Tensile properties of short-glass-fiber- and short-carbon-fiberreinforced polypropylene composites”, Compos Part A – Appl Sci Manu, 31 (10), 1117–1125. [3] Moritomi S., Watanabe T. and Kanzaki S., 2010, “Polypropylene Compounds for Automotive Applications”. SUMITOMO KAGAKU, R&D Report, Vol.1, 1-16 [4] Hashemi S, Elmes P. and Sandford S., 1997, “Hybrid effects on mechanical properties of polyoxymethylene”, Polym Eng Sci, 37 (1), 45–58. [5] Shao-Yun Fu, Bernd Lauke and Yiu-Wing Mai, 2009, “Science and engineering of short fibre reinforced polymer composites”, Woodhead Publishing Limited and CRC Press LLC, Boca Raton Boston New York Washington, DC,149-159. [6] M.F. Ashby and Y.J.M. Bréchet, 2003, “Designing hybrid materials”, Acta Materialia, 51, 5801-5821. [7] Henning Wallentowitz, 2013, “Innovation in Automotive Engineering: A look into the future”, J Automotive Safety and Energy, 4(2):95-108. [8] Ding Sufang and Tuo Haifeng, 2012, “The stiffness study of automobile plastic front-end module frame”, Modern Manufacturing Engineering, 04, 35-39. [9] Rosato D V, 1998, “‘Injection molding’ in Guide to short fibre reinforced plastics”,ed. Jones R F, Carl Hanser Verlag, Munich, 104–137. [10] Rees H, 1994, “Injection molding technology”, Carl Hanser Verlag, Munich, 15. [11] Rosato D V, 1995, “Injection molding handbook”, 2nd edn, Chapman & Hall, New York. [12] Lauke B, Schultrich B and Pompe W, 1990, ‘Theoretical considerations of toughness of short-fibre reinforced thermoplastics’, Polymer – Plastics Technology andEngineering”, 29 (7–8), 607–832.

Fig.10 SEM micrographs of fracture surface of GF/PP and CF/GF/PP composites with different contents of PA6 and MAPP 6. CONCLUSION In this paper, by discussion the tensile properties of glass fiber/ carbon fiber reinforced polypropylene hybrid composites fabricated by the DFFIM process, the following conclusions were obtained. 1) The addition of PA6 as coupling agent did not improve the interfacial bonding but the using of MAPP showed small improvement of bonding between carbon fiber and polypropylene. The using of PA6 and MAPP as co-coupling

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