IMPROVEMENT OF THE MECANICAL PROPERTIES OF RECYCLED CFRP

Transcription

1 10th Japan International SAMPE Symposium & Exhibition (JISSE-10) November 27-30, 2007, Tokyo Big Sight, Tokyo, Japan IMPROVEMENT OF THE MECANICAL PROPERTIES OF RECYCLED CFRP Tetsuya Okazumi, Isamu Ohsawa, Kiyoshi Uzawa and Jun Takahashi, Department of Environmental and Ocean Engineering, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo , JAPAN ABSTRACT Thermosetting resin has been mainly used for CFRP (carbon fiber reinforced plastics) since their high specific strength and specific rigidity open the new frontier of airplane, space, military affairs and sports. However, it is still difficult to apply CFRP to mass produced productions although the price of carbon fiber is getting down. One of the big barriers is that mechanical properties, in especially impact energy absorption ability, of CFRP decrease extremely after recycling. The reason is well known that the fiber length of recycled CFRP becomes shorter than that of fresh CFRP. In this paper we investigate an effect on the properties of recycled CFRP of the addition of aramid fiber which has high impact energy absorption ability. KEYWORDS: CFRP, Recycle, Aramid 1 INTRODUCTION CFRP (carbon fiber reinforced thermosetting plastics), such as CF/Epoxy, has been used for aerospace fields as high strength and light weight material. It is said that the next stage of CFRP is wide spread use to many other general industrial field. Then, key points are cost, processability and recyclability. From such viewpoints, recycling of CFRP is one of the most practical and effective way as an inclusive solution [1-5]. However it is known that the fiber length of recycled CFRP becomes shorter than that of fresh CFRP, and it leads lower impact energy absorption ability (Fig. 1). That is impediment to the growth of recycled CFRP. Therefore, in this paper, the improvement of impact energy absorption ability by using aramid fiber is mainly discussed. The reason of the usage of the aramid fiber is its characteristic mechanical properties [6, 7]. Therefore aramid fiber is expected to support the poor impact energy absorption ability of recycled CFRP when aramid fiber is compounded with recycled CFRP. (Poster Session-13)-1 Copyright 2007 by SAMPE

2 Izod impact energy absorption (kj/m 2 ) F L F T 1 st L 1 st T 2 nd L 2 nd T 3 rd L 3 rd T 4 th L 4 th T Fig. 1 Influence of the repetition of recycling on the flexural properties of the CF/PP. 2 THE STUDY ON THE LENGTH OF ARAMID FIBER This chapter describes the difference among three kinds length of aramid fiber. 2.1 Test piece making PP (Y6005GM), produced by Idemitsu Co. Ltd., Japan, was used as matrix resin. And, following three kinds length of aramid fiber was examined. Aramid fiber was supplied by Teijin Techno Products Ltd., Japan. 1) PP: polypropylene pellet (Fig. 2) 2) A1: chopped aramid fiber, 1 mm of length (Fig. 3) 3) A3: chopped aramid fiber, 3 mm of length (Fig. 4) 4) A7: chopped aramid fiber, 7 mm of length (Fig. 5) Fig. 2 The pellet of polypropylene. Fig. 3 Chopped aramid fiber in 1mm. Fig. 4 Chopped aramid fiber in 3mm. Fig. 5 Chopped aramid fiber in 7mm. (Poster Session-13)-2

3 First of all, these fibers and resin were dried well, and each fiber was mixed with PP to make fiber volume fraction be 15%. Laboprastomil (Toyo Seiki Seisaku-Sho, Ltd., 10C100 R60) was used for the mixing. The mixing condition was 200 degree Celsius, 10 rpm, and 5 minutes. Next, the press molding was done by using hot press machine (Toyo Seiki Seisaku- Sho, Ltd., MP-S). The molding temperature was 200 degree Celsius, and the size of the molded board was 130mm 100mm 4mm. Finally, the molded boards were cut out for test pieces with a diamond cutter. The size of the test pieces of three points bending test were 70mm 15mm 4mm and those of Izod impact test were 90mm 10mm 4mm. 2.2 Experimental result Three points bending test was performed under the condition that load cell was 50kgf and cross head speed was 2mm/min. The support span was 64mm. Izod impact energy absorption test was performed under the condition that hammer load was 26.8kgf and span was 395mm. The test was done 5 times for A1, A3, and A7 respectively. The result is summarized in Table 1. Figs. 6 to 8 show the flexural modulus, the flexural strength and the Izod impact energy absorption of each material respectively. Table 1 Results of three points bending test and Izod impact energy absorption test. notation aramid fiber flexural flexural failure Izot impact volume fraction modulus strength strain energy absorption (%) (GPa) (MPa) (%) (kj/m 2 ) PP A A A Young's modulus (GPa) PP A1 A3 A7 Fig. 6 Flexural modulus of AF/PP. Strength (MPa) PP A1 A3 A7 Fig. 7 Flexural strength of AF/PP. Izod impact energy absorption (kj/m^2) PP A1 A3 A7 Fig. 8 Izod impact energy absorption of AF/PP (Poster Session-13)-3

4 2.3 Discussion Table 1 shows that fiber volume fraction of A7 was the highest though the value of flexural modulus and flexural strength was not so high. The reason can be that 7mm is so long that mixing cannot be done uniformly. The values of Izod impact energy absorption were almost the same between A3 and A7. However, the value of A1 was about half of that of A3 and A7. The reason can be that 1mm is too short to tolerate impact. From these results, we will use A3 in the following experiment. 3 RECYCLING OF CFRP WITH ARAMID FIBER This chapter describes the recycling of CFRP with aramid fiber A3. In this study, crushed CFRP was used as waste CFRP. 3.1 Test piece making PP (Y6005GM), produced by Idemitsu Co. Ltd., Japan, was used as matrix resin. And, following four kinds of composite was examined. Aramid fiber was supplied by Teijin Techno Products Ltd., Japan. Crushed CFRP made by T700SC-24K was supplied by Toray Industries, Inc., Japan. 1) C: crushed CFRP (CF/Epoxy, carbon fiber volume fraction is 60%) (Fig. 9) 2) C1: carbon fiber volume fraction from Crushed CFRP is 15% and aramid fiber volume fraction is 5% 3) C2: carbon fiber volume fraction from Crushed CFRP is 15% and aramid fiber volume fraction is 10% 4) C3: carbon fiber volume fraction from Crushed CFRP is 15% and aramid fiber volume fraction is 15% Fig. 9 Crushed CFRP First of all, these fibers and resin were dried well, and each fiber was mixed with PP to make carbon fiber volume fraction be 15%. Laboprastomil (Toyo Seiki Seisaku-Sho., Ltd., 10C100 R60) was used for the mixing. The mixing condition was 200 degree Celsius, 10 rpm, and 5 minutes. Next, the press molding was done by using hot press machine (Toyo Seiki Seisaku-Sho., Ltd., MP-S). The molding temperature was 200 degree Celsius, and the size of (Poster Session-13)-4

5 the molded board was 130mm 100mm 4mm. Finally, the molded boards were cut out for test pieces with a diamond cutter. The size of the test pieces of three points bending test were 70mm 15mm 4mm and those of Izod impact test were 90mm 10mm 4mm. 3.2 Experimental result The method was similar to Chapter 2. The result is summarized in Table 2. Vf in this table is not an actual value but just the target value. Figs. 10 to 12 show the flexural modulus, the flexural strength and the Izod impact energy absorption of each material respectively. Table 2 Results of three points bending test and Izod impact energy absorption test. notation fiber volume fraction (carbon/aramid) flexural modulus flexural strength failure strain Izot impact energy absorption (%) (GPa) (MPa) (%) (kj/m 2 ) C 15/ C1 15/ C2 15/ C3 15/ Young's Modulus (GPa) Strength (MPa) C C1 C2 C3 C C1 C2 C3 Fig. 10 Flexural modulus of recycled CFRP. Fig. 11 Flexural strength of recycled CFRP. 7 Izot impact energy (kj/m^2) C C1 C2 C3 Fig. 12 Izod impact energy absorption of recycled CFRP. (Poster Session-13)-5

6 3.3 Discussion The values of flexural modulus and strength were almost the same among three samples which contain aramid fiber. The reason can be that these values are mainly depending on carbon fiber because flexural modulus and strength of carbon fiber is much higher than those of aramid fiber. On the other hand, the value of Izod impact energy absorption is increase apparently when test pieces contain more aramid fiber. Carbon fiber has poor adhesiveness with thermoplastic, and the length of carbon fiber is not sufficient in both short carbon fiber reinforced thermoplastics and recycled CFRP, hence the impact energy absorption ability of these materials is not good. However, this study showed a possibility that such poor impact energy absorption ability will be improved by the addition of proper amount of aramid fiber. Especially, in case of the repetition of recycling as shown in Fig.1, carbon fiber will become shorter, but length of the aramid fiber is expected to be maintained. Furthermore carbon fiber and the aramid fiber are dispersed more uniformly during the repetition of molding. Then although mixture may generally be the opposite concept of recycling, this kind of mixture will contribute to be spreading application fields of recycled CFRP and consequently extend total life of carbon fiber. 4 CONCLUSIONS To improve the poor impact energy absorption ability of recycled CFRP, we tried to find a possibility of the usage of aramid fiber. Then we confirmed that the addition of aramid fiber improve the impact energy absorption ability of recycled CFRP. Of course, there are a lot of parameters to study for a practical application, we showed that there are proper length and volume fraction of aramid fiber in this study. We should also investigate the influence of surface treatment of aramid fiber to show a further potential of recycled CFRP and contribute to spread an application field of it. REFERENCES 1. H. Zushi, T. Odai, I. Ohsawa, K. Uzawa and J. Takahashi, Mechanical properties of CFRP and CFRTP after recycling, Proceedings of 15th international conference on composite materials (ICCM-15), (2005-6), pp H. Zushi, I. Ohsawa, M. Kanai, K. Uzawa and J. Takahashi, Fatigue behavior of unidirectional carbon fiber reinforced polypropylene, Proceedings of 9th Japan international SAMPE symposium, ( ), pp R. Fukui, T. Odai, H. Zushi, I. Ohsawa, K. Uzawa and J. Takahashi, Recycle of carbon fiber reinforced plastics for automotive application, Proceedings of 9th Japan international SAMPE symposium, ( ), pp K. Shibata, K. Maekawa and M. Kitajima, Composites recycling using depolymerizing thermoses under ordinary pressure, Proceedings of 9th Japan International SAMPE Symposium, ( ), pp J. Takahashi, K. Uzawa, I. Ohsawa, N. Matsutsuka, A. Kitano and K. Nagata, Applicability of recycled CFRP to secondary parts of automobile, Proceedings of the 12th US-Japan conference on composite materials, (2006-9), pp D. Hull, T. W. Clyne, translated by I. Kimpara, et. al., An introduction to composite materials First edition, Bayfu-kan, pp.8-65 (1983). (Poster Session-13)-6