UTILIZING OF B CLASS CARBON FIBER IN COMPOSITE MATERIALS

Transcription

1 UTILIZING OF B CLASS CARBON FIBER IN COMPOSITE MATERIALS Hiromishi So, Taiei Kusuhara SJJ Co., Ltd., Osaka, Japan Hiroyuki Inoya, Supaphorn Thumsorn, Hiroyuki Hamada Kyoto Institute of Technology, Kyoto, Japan Abstract Carbon fiber (CF) reinfoced polymer composites were fabricated by direct fiber feeding injection molding (DFFIM) process. Three polymer matrices were used including polyamide 66 (PA66), polypropylene (PP) and polycarbonate (PC). Two types of commercial treated CF with called a standard CF (CF-A) and a non-standard CF (CF-K) were applied in this research. Additionally, the CF-K was desizing to remove its surface treatment. The reinforcing fibers were fed into vented hole of the vented barrel injection molding of DFFIM process. The effect of fiber types and the desizing on tensile properties and morphology of the composites was investigated. The desizing of fiber promoted fiber dispersion, reduced fiber agglomeration and improved adhesion between fiber and the matrix. Hence, tensile modulus and tensile strength of the CF reinforced polymer composites. The DFFIM process would be an alternative fabrication for composites production in automotive industry. Introduction Fiber reinforced plastic (FRP) which made a contribution to the light weight process, was expected to replace the position of steel in automobile industry. Carbon fiber plays an important role as reinforcement in composite and achieved excellent properties [1-3]. Carbon fiber composites have very high mechanical properties and light weight, so that various application fields have been spread out to aerospace and aircraft industries. Not only contineous fiber reinforced composites but also short fiber composite fabricated by injection molding are important material system in automobile industry. However carbon fiber is expensive in short fiber composites. Research and developmet are needed to fully usage of carbon fiber performance; that means optimiation of fiber surface treatment, effective fiber length in products and so on. However, the high price obstructed the widely application of carbon fiber. On the other hand, the sub-quality products or the non-standard that called B-class carbon fiber were produced inevitably during the producing process or when the product type changes. At present, the electroconductibility of carbon fiber has been put into practical application as the raw material for IC tray to eliminate the effect of static electricity phenomenon. By this way, the B-class carbon fiber can be used widely as raw material of FRP, achieving a low cost as reinforcement. Regarding as far as the FRP products, fiber length, distribution, orientation and the interface between fiber and resin are the effecting aspects of the mechanical properties. By considering these four aspects during the injection molding process, the product made from B-class carbon fiber can be expected to achieve the comparable mechanical properties as A-class product or the standard fiber product. Normally in order to binding or treating carbon filaments, sizing agent is used, however the sizing agent prevent dispersion of the filaments in injection molding products. Poor dispersion state reduces strength of the composite because there is no resin adhered with bind ing Page 1

2 filaments so that crack can be generated from the unimpregnated part easily. If desized carbon fiber can be put into injection molding machine directly, good dispersion state is expected. In this research the adapted injection technique as called direct fiber feeding injection molding (DFFIM) was carried out. DFFIM technique is that reinforced fiber is directly fed into venting hole of vented injection molding as shown in Figure 1 [4-5]. According to this method, the compounding processes can be ignored, which it leads to the fiber breakage during the process. In this paper the standard and the non-starndard carbon fiber were used. Three polymer matrices were used; PA66, PP and PC. After that, the mechanical property of FRP was tested and discussed. Carbon filaments were usually surface treated by sizing agent in order to form a fiber bundle. Thus in this research, the sizing agent was removed before fed into the screw with the good distribution and orientation as well as good statue of interface of carbon fiber bundle ensured. Plastic supply CF roving Matrix control feeding unit Plastic supply monitor Vented hole Figure 1: Direct fiber feeding injection moldong (DFFIM) [4-5]. Materials Experimental Polyamide 66 (PA66), polypropylene (PP) and polycarbonate (PC) were used as matrix resins. Two types of 3% carbon fiber reinforced PA66 (CF/PA66) including standard CF (CF3-A/PA66) and non-standard CF (CF-K/PA66). Standard-CF (CF-A) and non-standard-cf (CF-K) were used as reinforcing fiber in DFFIM process. Both A and K were commercial surface treatment. The non-standard-cf-k was desizing of the surface treatment and referred as (D- CF-K). Sample Preparation The matrix and reinforcing CF were injection molded by DFFIM process with 3 ton injection molding machine (TI-3F6, Nihon Yuki Co., Ltd., Japan). The reinforcing fiber was fed into vented hole of injection molding barrel. The barrel temperatures at nozzel were set at 29 C, 23 C and 3 C for matrix resin of PA66, PP and PC, respectively. Characterization Tensile testing was performed with ASTM D638 by Instron universal testing machine (Instron426, USA). The testing speed was 1 mm/min. Page 2

3 Morphology of tensile fractured surface was observed by scanning electron microscope (JSM52, JEOL, Japan). Results and Discussion Mechanical Properties of the Composites Figure 2 shows the comparison in tensile properties of CF/PA66 in commercial grade and DFFIM process. Tensile moduli of the commercial CF/PA66 were higher than the composites from DFFIM process. However, in DFFIM, tensile modulus of the composites increased when CF was desizing in the non-standard CF-K (D-CF-K). On the other hand, tensile strength of the D-CF-K composites significantly improved. It was considered that a rough surface of the desizing fiber would be better in matrix resin impregnation. In addition, the desizing was promoted fiber dispersion on the polymer matrix. 12 PA66 3 PA66 Tensile modulus (GPa) Tensile strength (MPa) CF-A/PA66 CF-K/PA66 CF-A/PA66 CF-K/PA66 D-CF-K/PA66 CF-A/PA66 CF-K/PA66 CF-A/PA66 CF-K/PA66 D-CF-K/PA66 Figure 2: Tensile modulus and Tensile strength of CF/PA66 composites with DFFIM. Tensile properties of the CF/PP composites by DFFIM are presented in Figure 3. Tensile modulus and tensile strength of the non-standard CF in CF-K/PP composite were higher than the standard CF (CF-A/PP) composite as shown in Figure 3. It can be indicated higher stiffness of in the composites with CF-K than CF-A with PP matrix. The similar tend was found in the CF/PA6 composites. Figure 3 shows tensile strength of the CF/PP composites, which tensile strength of the desizing CF-K was the highest value. It was confirm that desizing of CF-K improved the impregnation and yielded better adhesion in this composite resulted in higher tensile strength as depicted in Figure PP 3 25 PP Tensile modulus (GPa) Tensile strength (MPa) CF-A/PP CF-K/PP D-CF-K/PP CF-A/PP CF-K/PP D-CF-K/PP Figure 3: Tensile modulus and Tensile strength of CF/PP composites with DFFIM. Page 3

4 Figure 4 shows the effect of CF on tensile properties of the CF/PC composites. Tensile modulus of the composites with the non-standard CF was improved after desizing process. Tensile moduli of the CF/PC composites were similar tend as the values in the CF/PA66 and the CF/PP composites with DFFIM. However, tensile strength of the CF/PP was poor when compounded with the desizing CF-K. It might be due to low wetting perfomance of PC matrix with the desizing fiber. It can be noted that tensile strenght of the CF/polymer composites was related to the property of the inherent matrix. The maximum tensile strength was found in the CF/PA66 followed with the CF\PC and the CF/PP. On the contrary, tensile modulus of all composites with different matrix were similar, which CF proesented as the main stiffness in the composites PC 3 25 PC Tensile modulus (GPa) Tensile strength (MPa) CF-A/PC CF-K/PC D-CF-K/PC CF-A/PC CF-K/PC D-CF-K/PC Figure 4: Tensile modulus and Tensile strength of CF/PC composites with DFFIM. Morphology of the Composites Figure 5 and Figure 5 present SEM pohotographs of the CF-K/PA and the D-CF-K, respectively. Less of matrix resin was found on the fiber in Figure 5. On the other hand, it can be seen that fibers were more wetting and adhered after fiber desizing as shown in Figure 5. It would promote adhesion and interaction between fibers and polymer matrix, which improved tensile modulus and tensile strength of the CF/PA66 composites. Figure 5: SEM photographs of CF-K/PA66 composite and D-CF-K/PA66 composite by DFFIM. Page 4

5 Figure 6 depicts SEM photographs of the CF/PP composites with DFFIM. There was agglomeration of CF on the PP matrix in the CF-A/PP composite, which resulted in lower values of tensile modulus and tensile strength of this composite. It was found part of fiber was not well dispersed in the CF-K/PP composite while its tensile modulus was high. However, the desizing fibers were better dispersed and less agglomeration in the compsoites, which yielded higher values of tensile modulus and tensile strenth of the D-CF-K/PP composite. CF-A/PP (DFFIM) CF-K/PP (DFFIM) (c) D-CF-K/PP (DFFIM) Figure 6: SEM photographs of CF/PP composites by DFFIM. Page 5

6 SEM photographs of the CF/PC composites are presented in Figure 7. It can be seen that fibers were agglomerated on the PC matrix. It was considered that viscosity of PC was high so that the matrix resin was less wetting on the CF with or without desizing. Therefore, tensile strength of the CF/PC composites was almost unchanged in different types of CF. CF-A/PC (DFFIM) CF-K/PC (DFFIM) (c) D-CF-K/PC (DFFIM) Figure 7: SEM photographs of CF/PC composites by DFFIM. Conclusions DFFIM showed the advantage for fabricating carbon fiber reinforced polymer composites with discarding compounding step. Tensile strength of the CF/PA66 from DFFIM was significantly higher than the commercial grade CF/PA66. However, the contents of the fibers by DFFIM should be confirmed. The desizing of surface treatment improved dispersion and adhesion of the fiber on the polymer matrix with resulting in enhanced tensile modulus and tensile strength of the composite. It can be noted that viscosity of polymer influenced on the wetting of resin as well as the agglomeration of the fibers. The DFFIM process would be futher applied for composites production in automotive industry. Page 6

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