Research on Friction and Wear Properties of MC Nylon/ Carbon Nano Tubes Composites Tiejun Ge 1,2,a, Jing Wang 1,b and Wei He 1,2,c

Transcription

1 Advanced Materials Research Vol. 662 (2013) pp (2013) Trans Tech Publications, Switzerland doi: / Research on Friction and Wear Properties of MC Nylon/ Carbon Nano Tubes Composites Tiejun Ge 1,2,a, Jing Wang 1,b and Wei He 1,2,c 1 Research Center of Plastics Engineering, Shenyang University of Chemical Technology, Shenyang State Key Laboratory of Robotics a ,getiejun@163.com; b , wangjing_00219@163.com; c , hwdut@126.com Keywords: MC nylon; Wear-resisting; Mechanism of abrasion Abstract. In this article, MC nylon/carbon nano tubes (CNTs) composites were prepared by in-situ polymerization method. The friction and wear properties were determined. The sample wear surface morphology carried out by scanning electron microscope (SEM) and the wear mechanism was investigated. It was found that the friction coefficient of composites has decreased with the amount of CNTs increasing in the composites. Addition amount of CNTs is up to 0.3% (weight percent), abrasion index decreased to minimum. The abrasion index of the sample of wearing a long time is smaller than that of the sample of wearing a short time. The sample with wearing less time mainly take place adhesive wear, however, mainly happen abrasive wear and adhesive wear for wearing time is longer. Further more, carbon nano tubes (CNTs) are not only improve the wear resistance of composites but also improve the mechanics performance. Introduction Monomer casting (MC) nylon is a kind of excellent performance engineering plastics, compared with other production methods this methods of nylon 6 production is simple, higher mechanical strength, lower polymerization temperature, high molecular weight and widely used etc. [1] However, due to water absorption, lower dimensional stability, lower heat distortion temperature and poor wear resistance of its use resulted in certain restrictions, modified of MC nylon become a hot research topic [2]. The CNTs have a very high toughness[3]. Which have a structure similar to graphite and C60, and its pipe wall having a hexagonal structure of the graphite layer, therefore CNTs have excellent self-lubricating properties[4]. When the CNTs to join other material to form a composite material, due to its tubular structure, high toughness, high strength, wear resistance is improved and the mechanical properties and other aspects have also made progress, due to its tubular structure, high toughness, high strength[5,6]. Experimental Raw materials. Caprolactam, Japan Ube company; Carbon nano tubes (CNTs), Shenzhen Nanotech Port Co., Ltd; Silane coupling agent(kh-570), Nanjing Xiangfei Chemical Research Institute; NaOH (analytically pure), Tianjin Damao Chemical Reagent Factory; Toluene diisocyanate(tdi), Tianjin Damao Chemical Reagent Factory; Concentrated sulfuric acid(h 2 SO 4 ), Tianjin Damao Chemical Reagent Factory; Concentrated nitric acid(hno 3 ) Tianjin Damao Chemical Reagent Factory. Equipments and instruments. Magnetic heating mixer, DF-101S, China Gongyi Instrument Co., Ltd; Flat vulcanizing machine, Third Qingdao Rubber Machinery Factory; Mould: made by self. Sample preparation. First of all, it was added CNTs 0.3g in the three-necked flask, and then the concentrated sulfuric acid 25ml was added and concentrated nitric acid 75ml. It is about 0.5 h for ultrasonic oscillation. Then the three-necked flask put into the water bath of 80 C heating for 6 h and cooling reflux. Then use distilled water washing to ph = 7 and centrifugal separation. The drying temperature is 60 C and last for 3 hours. 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 TTP,

2 Advanced Materials Research Vol It was added a certain amount of KH-570 with anhydrous ethanol solution, CNTs, and mixed liquor into another three-necked flask. The three-necked flask is heating and stirring for 0.5h. It is about 4 h for ultrasonic oscillation and takes out into an oven for drying last for 3 hours. A certain quantity of caprolactam monomer was added in the three-necked flask and heated to 90 C until it completely melted. Then it was slowly warming up to 130 C with vacuum pumping for 0.5h at this temperature. A proper amount of NaOH and CNTs was added. Slow warming up to 140 C and using vacuum pumping for 0.5h at 140 C. After vacuum pumping, added 0.35ml TDI into the three-necked flask. It is stirring for 2 minutes. And then pouring the melt into mold which was preheated to 180 C. Keep the mold at 180 C for 0.5h. Cool the mold down to room temperature and then demolded. Results and Discussion Friction coefficient CNTs percentage contents Fig. 1 Effect of CNTs contents on friction coefficient of MC nylon composites. Fig. 1 shows that with increasing the addition of different contents of CNTs in composites, friction coefficient of the sample surface is gradually reduced. The friction coefficient of pure MC nylon is When the added amount of the CNTs is up to 0.5%, the friction coefficient reaches the minimum value For the CNTs in the MC nylon system play a lubricating role, the friction coefficient will be reduced h 3.0h 4.5h Abrasion index CNTs percentage content Fig. 2 Effect of wear-time on abrasion index of MC nylon composites. From Fig. 2, it can be seen that at the same time, every curve first decreases with the increases of the CNTS and then increased. The abrasion index is lowest with the CNTs content of 0.3%. Comparing the three curves, curve of wearing for 1.5h is at top, abrasion index of wearing a relatively short period of time is larger than the sample of wearing a long time. Wearing curve for 4.5h is in the bottom. It is indicated that a longer wearing time the abrasion index decreases, however, the shorter time of wearing with the greater the abrasion index.

3 42 Nanotechnology and Precision Engineering Each curve first decreases and then increases, according to this phenomenon, we can speculate that it is physical adsorption between CNTs with silane coupling agent KH-570. The molecule of KH-570 is generally composed of a hydrophilic polar group and a lipophilic non-polar group. Its polar group is adsorbed on the surface of the CNTs, so that the non-polar groups are exposed. Such non-polar groups and the organic medium can affinity and thereby reduce surface tension and the CNTs particles will be separated from each other and to achieve the dispersing effect. Due to the physical adsorption and easily eluted when the CNTs contents increased there will be a certain degree of agglomeration. So the abrasion index of the entire system will rise. The results show that small amounts of CNTs were added in composites which can improve the abrasion resistance of the MC nylon composites. It is due to improve mechanical properties by CNTs. CNTs can be filled in pits of friction surface, serve to reduce the role of the surface roughness, and isolation role played in the friction process. And then CNTs can scroll and reduce wear and tear. This phenomenon is most apparently when CNTs content is up to 0.3%. When the addition contents are to continue to increase, due to the CNTs will produce weakened system again, wear resistance and abrasion index rise. There will be a certain shedding when the wear time is relative longer. It will be more CNTs that can roll on the surface, due to the self-lubricating effect of the CNTs, therefore reduce wearing. (a) abrasive surface of wear for 1.5h (b) abrasive surface of wear for 4.5h Figure 3. MC nylon / CNTs composites wearing surface morphology. Based on the Fig. 3 (a), it is visible that scratches and separated debris on specimen surface of wearing for 1.5h and there is also presence of traces of micro-cutting in these scratches and abrasion loss is greater. It mainly occur adhesive wear at this time. In Fig. 3 (b), it can be seen that significantly some wear mark and some scratches. When wearing for some time, the sample surface is uneven, and will generate some higher micro-protrusions point. These micro-protrusions points are to bear the entire load to cause many micro-bump undergoes plastic deformation and more closely contacting the surface of the sample. Therefore, wearing after a period of time there mainly is abrasive wear. When the abrasive wear occurs, the CNTs shedding played the "isolation" role and the abrasion loss will be reduced and thus will reduce the abrasion index. Table 1. Effect of CNTs contents on Mechanical Properties of MC nylon. CNTs contents Tensile strength Elongation at break Impact strength [%] [MPa] [%] [KJ m -2 ]

4 Advanced Materials Research Vol From Table 1, it can be seen that by adding CNTs, the mechanical properties of MC nylon composites are greatly improved. The tensile strength increases first and then decreases. When the content of CNTs is up to 0.3%, the tensile strength is up to 87.93MPa. It has 8.18% promoted compared with the pure MC nylon. With an increasing in the content of CNTs, the elongation at break decreases gradually. The impact strength is gradually increased with the increasing of the CNTs. When the content of CNTs is 0.5%, the impact strength is 47.01MPa which higher than pure MC nylon. Conclusions (1) Friction coefficient of MC nylon composites modified by the CNTs is much lower than that of pure MC nylon. When the amount of the CNTs is up to 0.5%, the smallest friction coefficient value is of It reduced 74.64% than pure MC nylon. (2) MC nylon composite abrasion index will increase with increasing wearing time. That is to say, the shorter time of wearing, the greater the abrasion index is. (3) Wearing less time mainly occur adhesive wear, however, wearing longer occurs mainly adhesive wear and abrasive wear. (4) The addition of CNTs not only makes the MC nylon abrasion resistance improved but also be able to improve the mechanical properties. Acknowledgement This work was supported by State Key Laboratory of Robotics.(No. RLO201016). References: [1] Fukumoto Shu Polyamide resin Handbook Z. P.Shi, W.R.Zhang, L.C.Tang, China Petrochemical Publications,China 1994).(In Chinese). [2] Z.J. Ren, R.C. Ning. Composite Materials Reported, Vol. 17 (2000) No.(2), pp (in Chinese). [3] H.C. Zhang, Y.C.Yu, S.Y. Liu, et al. Mechanical Science and Technology, Vol. 22 (2003) No.(3).pp (In Chinese). [4] W.M. Liu, Q.J. Xue, L. Gao, et al. Lubrication Engineering, Vol. 48 (1992) No.4. pp (In Chinese). [5] T. Noguchi, A. agario, S. ukazawa, et al. Materials Transactions, Vol. 45 (2004) No.2, pp [6] X.H. Chen, G Hang, C.S. Hen, et al. Journal of Inorganic Materials, Vol. 18 (2003) No.6, pp (In Chinese). [7] P. Yang, K.F. Yao, Journal of Tribology, Vol. 25 (2005) No.5, pp (In Chinese).

5 Nanotechnology and Precision Engineering / Research on Friction and Wear Properties of MC Nylon/ Carbon Nanotubes Composites /