Study on mechanical properties of PEEK composites

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Study on mechanical properties of PEEK composites Lanzhu Zhang 1, a, Min Li 1,b and Hui Hu 1,c 1 130Meilong Road, Shanghai, VR China a lzzhang@ecust.edu.cn, b limin6688@126.com, c huihu@ecust.edu.cn Keywords: PEEK, Polymer composite, Tensile performance, Microstructure, SEM Abstract. The tensile properties of polyetheretherketone (PEEK) composites, which were reinforced with short fibers, such as short carbon fiber (SCF), short glass fiber (SGF), or filled with polytetrafluoroethylene (PTEF), expanded graphite and nano material TiO 2 were examined and studied. The weight content of short fibers, PTFE and expanded graphite was varied from 0-15%, and of TiO 2 was varied from 0-8%. The results showed, with increasing of the weight content of short fibers, the tensile performance (tensile strength and modulus) of PEEK composites was increased rapidly. If the weight percent of short fibers was more than 10%, this increasing tendency became slowly. With the increasing of PTFE content, the tensile strength was increased at first and then decreased rapidly. However, the tensile modulus kept constant during the change of PTFE content. The influence of expanded graphite and nano particles TiO 2 on mechanical properties of PEEK composites was also be studied here. Meanwhile, the reasons of different influence of these fillers were analyzed during microstructure changes of PEEK composites with SEM photographs. Foreword Polyetheretherketone (PEEK) is a typical high performance semicrystalline thermoplastic polymer with very good combination of thermal (Tg=143, Tm=338, continuous service temperature 250, heat distortion temperature often in excess of 300 ) and mechanical properties, chemical inertness, high toughness, high wear resistance and friction coefficient [1-3]. PEEK and its composites can be used in the situation of oil-free lubrication, low velocity and high loaded or polluted by liquid, dust or other medium with solid particles. PEEK is also a polymer of engineering with easy processibility by injection and extrusion. So it is applied in most varied fields, such as biomechanics, aeronautical, mechanical, electronics and automobile industry [4-6]. It is known that pure resin can hardly be directly used in some cases with high performance. Better is to be filled with some reinforce materials or some auxiliary agents. Here, PEEK with SCF, SGF, PTFE, expanded graphite and nano-material TiO 2 was studied and its tensile performance was compared and analyzed. Experiment process materials All test sampls here were injection molded with raw materials as follows. PEEK: manufactured by JUESP. PTFE: KT-300M from Japan. TiO 2 : CAS (R). SCF: TC36S-12K, Formosa Petrochemical (TAIWAN). SGF: EC W JA, Hangzhou. Expanded Graphite: purity>99%, Shanghai. Major equipments and instruments Twin-screw-extruders: ZSK 30P9P from Germany. Electron universal testing machine: DNS 100, Changchun Testing machine Institute. Scanning electron microscope (SEM): JSM-6360LV from Japan. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,03:07:52)

2 520 New Materials and Processes Preparing of test samples PEEK power was dried at 150 for at least 4 hours. The mixture of PEEK and fillers was achieved by twin-screw-extruders according to 16 recipes in Tab.1. The composites were finally manufactured using an injection molding machine at a barrel temperature of The injection pressure was kept constant at 11 MPa, and the mould temperature was fixed at 60. Besides, constant injection speed was applied at all the process. Test procedure Table 1. The mass fraction of filler [wt %] Filler CF GF PTFE EG TiO Sample Tensile performance was tested according to the GB/T During the test the tensile constant speed was kept at 3 mm/min. SEM examination: After tensile test, the fracture section was sprayed with metal, and then examined by SEM. 2 Results and Discussion Tensile Performance In this study, 16 receptions in Tab. 1 were divided into 5 groups according to different fillers, showed in Tab. 2. So the influence of different fillers on PEEK composites could be studied. Table 2. Group of Experiments Group Object Component 1 CF 1, 2, 3, 4 2 GF 1, 5, 6, 7 3 PTFE 8, 9, 3, 10 4 EG 11, 12, 3, 13 5 TiO 2 3, 14, 15, 16 The tensile test with different contents of SCF in PEEK composites was showed in Fig. 1. The data were based upon the average of five test specimens. From Fig. 1, it was found that the tensile performance of PEEK/SCF depended on the weight content of SCF. The tensile strength and modulus tended to increase as the weight content of SCF increased from 0 to 15%. When the weight percent of SCF reached 15%, the tensile strength of PEEK/SCF was Mpa, which was raised by 66% than

3 Advanced Materials Research Vols pure PEEK. From Fig.1 we could also see that the tensile strength increased slowly when the content of SCF was more than 10%. The change trend of tensile modulus was very similar to that of tensile strength from Fig.1. It could be imaged that SCF was the main component to bear tensile stress when the weight percent of SCF was less than 10%. At that time, the base material (PEEK) was the main part to transmit the tensile stress. With the increasing of content of SCF, more SCF could bear more tensile strength. If the weight percent of SCF was more than a certain value (e.g. 10% here), resin content was decreased so much that clad around the all surface of SCF. It leaded more defects and points with stress concentration came into being and then tensile performance of PEEK composite increased slowly [7]. /MPa The mass fraction of SCF/% /MPa Fig. 1 Effects of SCF content on tensile properties of PEEK/SCF composite The influence of the SGF content on performance of PEEK/SGF was showed in Fig. 2. The reinforce mechanism of SGF was very similar to that of SCF. We could see from Fig. 2, with the filling of SGF, the tensile strength of PEEK/SGF was increased rapidly. If the weight percent of SGF was 15%, the tensile strength of PEEK/SGF reached 101.5Mpa, which was raised by 18.3% than that without SGF. But this enhancement was less than that of SCF. The reason laid in that the contact surface between SGF and the base PEEK was not as good as that between SCF and PEEK. From Fig. 2 we could also see that while the content of SGF reached 10%, the tensile strength increased very slowly. And also the tensile modulus stayed nearly constant once the content of SGF is more than 5%. /MPa The mass fraction of SGF/% Fig. 2 Effects of SGF content on tensile properties of PEEK/SGF composites /MPa Fig. 3 showed the influence of PTFE on the performance of PEEK composite. When the filling content of PTFE was low, for example less than 5%, the tensile performance PEEK composites was better. The reason was that with some small particles of PTFE, heterogeneous nucleation is created

4 522 New Materials and Processes during crystallization of PEEK. It helps to refine the crystallized particles of PEEK. Because of the worse compatibleness between PTFE and PEEK [8], the defects in PEEK composites grow with the increasing of PTFE content in PEEK composites. So the tensile strength decreases rapidly. We could see from Fig. 2, with 15% weight percent of PTFE the tensile strength was MPa, which went down 15% than that without PTFE. While the tensile modulus kept nearly constant with the filling of PTFE. /MPa /MPa The mass fraction of PTFE/% Fig. 3 Effects of PTFE content on tensile properties of PEEK composites It showed the influence of the EG content on performance of PEEK composites in Fig. 4. With the increasing of weight percent of EG in PEEK composites, the tensile strength decreased clearly. With 15% weight percent of EG the tensile strength was MPa, which decreased by 14% than that without EG. One reason was the compatibleness between EG and PEEK is not good, so the defects in PEEK composites grew in number with increasing of EG. The other laid in that the uninformed distribution of EG in PEEK composites leaded to stress concentration, and decreased the tensile performance of PEEK composites [9]. We could also see from Fig. 4, while the weight percent of EG was less than 10%, the tensile modulus kept nearly constant. And it increased rapidly with more than 10% EG /MPa /MPa The mass fraction of EG/% 4000 Fig. 4 Effects of EG content on tensile properties of PEEK composites Fig. 5 showed the influence of Nano particles TiO 2 on the performance of PEEK composite. From it we could see, when the filling content of PTFE was relatively small, the tensile performance PEEK composites raised rapidly. And when the weight percent of Nano TiO 2 was 3%, the tensile strength of PEEK composites reached 136.2Mpa, which was raised by 9% than that without Nano TiO 2. While

5 Advanced Materials Research Vols increasing of Nano TiO 2 content, the influence of Nano TiO 2 was no more monotonous. The tensile modulus trended very similar to that of tensile strength. The first reason [10] laid in that some small particles of Nano TiO 2 create heterogeneous nucleation during crystallization of PEEK. It helped to refine the crystallized particles of PEEK. The second reason was that there many active groups on the surface of Nano TiO 2. It helped to form good interfaces between Nano TiO 2 and base material PEEK. While increasing Nano TiO 2, auto-agglutination of Nano TiO 2 particles occured on the base material PEEK. It leaded to form more defects in PEEK composites. So the tensile performance of PEEK composites went down with the increasing of Nano TiO 2 continuously. /MPa /MPa The mass fraction of TiO 2 /% Fig.5 Effects of TiO content on tensile properties of PEEK composites 2 Micro Structure Fig. 6 showed the SEM photograph of sample No.3 s transverse cross section. In sample No.3 the weight percent of SCF was 10%. We could see from Fig. 6, there was no air hole in the base material and the interface. Moreover, the interaction between base material PEEK and SCF was good because of PEEK. It showed that SCF could be good connected with PEEK base material, and the filling with SCF could raise the tensile performance of PEEK composites. Fig. 6 SEM photographs of fracture surfaces of sample No.3 It showed the SEM photograph of sample No.6 s transverse cross section in Fig 7. In sample No.6 the base material PEEK was filled with SGF with the weight percent 10%. We could see from Fig. 7, the surface of glass fiber was also cladded with same PEEK resin. But it was not so much good as that in Fig.6. It showed that SGF coould be connected with PEEK base material not as good as SCF, and the tensile performance of PEEK composites with SGF was also not good enough as that with SCF.

6 524 New Materials and Processes Fig.7 SEM photograph of fracture surfaces of sample No. 6 Fig.8 SEM photograph of fracture surfaces of sample No.9 Fig. 8 showed the SEM photograph of sample No.9 s transverse cross section. In sample No.9 the weight percent of PTFE was 5%. Sample No. 3 was also filled with PTFE and the content was 10%. From Fig.8 and Fig 6(b) we could find that the surface of PTFE particles was relatively smooth. And the surface of base material, where PTFE particles were failed out because of tensile break, was also smooth. Moreover, there were small gaps between PTFE particles and base material PEEK. It indicated that the compatibility between PTFE and PEEK was not good. It was tendency to come into defects with filling of PFTE in PEEK composites. And with the increasing of content of PTFE, the tensile performance of PEEK composites could be decreased. From SEM photographs of PEEK composites those showed above, we could also see many small fragments in the fracture section because of the filling of expanded graphite. It showed the interface between expanded graphite and PEEK was not good. So filling with expanded graphite could also decrease the tensile performance PEEK composites. Conclusions (1) Filling of SCF, SGF and Nano material TiO could evidently increase the tensile performance of 2 PEEK composites, especially SCF. However, both the filling of PTFE and expanded graphite could decrease the tensile performance of PEEK composites. (2) While the weight percent of SCF or SGF was more than 10%, or the weight percent of TiO 2 was more than 3% in PEEK composites, the increasing rate of tensile performance became slow. (3) The results could also be certified with SEM photographs of fracture section of PEEK composites, the bond performance between SCF and PEEK was better than that between SGF and PEEK. And the later was better than that between PTFE and expanded graphite with PEEK. It was difficult to display PTFE and expanded graphite particles in base material PEEK. This would also affect the tensile performance of PEEK composites. Acknowledgements This work was financially supported by Shanghai Leading academic discipline project(b503), Ministry of Education of Doctoral Young Teachers Fund.

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