Preparation of EPDM Flame-resistant Cable Materials Weili Wu 1, a, * and Lei Tian 1,b

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vol. 151, pp doi: / Trans Tech Publications, Switzerland Preparation of EPDM Flame-resistant Cable Materials Weili Wu 1, a, * and Lei Tian 1,b 1 College of Materials Science and Engineering, Qiqihar University, Qiqihar , Heilongjiang, China a, * wuweili2001@163.com, b skyrock007@163.com Keywords: Cable materials; EPDM; Mechanical properties; Thermal properties; Preparation Abstract. EPDM cable materials were prepared, in which EPDM was used as raw materials, silica as a reinforcement, sulfur and dicumyl peroxide (DCP) as the curing agent, aluminum hydroxide (ATH) and magnesium hydroxide (MH) as the flame retardants. The best content and cure parameters of EPDM cable materials were determined by testing hardness, tensile strength, elongation at break, thermal properties and oxygen index, as well as analyzing SEM. The results showed that the properties of EPDM cable materials with DCP were better than those with sulfur or sulfur / DCP blend. The flame retardance of EPDM cable materials with ATH / MH blend was better than that with ATH or MH. The ideal formula of EPDM flame-resistant cable material was EPDM 100 phr, silica 45 phr, DCP 3.5 phr, ATH 90 phr and MH 10 phr. The best curing conditions were at 170 o C under 1.2 MPa for 10 min. Introduction Wire and cable is featured with conveying energy and information functions, known as the national economy blood vessel and nerve. Therefore, the wire and cable hold in the important position in the commercial field [1]. The wire and cable products have insulating layer except bare wire product. The insulating materials are widely applied in the wire and cable field. The influence of wire and cable on the environment has paid more and more attention in their used process. The developed countries such as Europe, America and Japan are strictly prohibited to use the environmental protection cables [2-7]. At present, expensive low-smoking flame retardant cable materials are mainly depended on import in China, so its application is restricted in some extent. As the rapid development of economic construction, the improvement of safety requirements and great demand of low smoking flame retardant cable, a lot of manufacture has studied low-smoking flame retardant cable [8-10]. The halogen-free flame retardant environment friendly insulating cable materials were investigated in the work, in which EPDM was used as main raw material, and is of ozone resistance, flame resistance, weather resistance, thermal properties and so on [11,12]. Experimental Materials. As industry products, EPDM (Z3080P) and ZnO were produced by Jilin Chemical Industrial Co.,Ltd. and China National Brother Chemical Group Corporation respectively. Dicumyl peroxide (DCP) a chemical pure was supplied by Shanghai Chemical Reagents Company of Chinese Medicine Group. The other ingredients such as sulfur, stearic acid (SA) and so on, were all common commercially avail materials on the market. Sample prepare. The details of the formulation of the mixes are EPDM 100 phr, ZnO 5 phr, SA 1, Silica Variable, Accelerator M 0.5 phr, Antioxidant D 1.5 phr, and Sulfur 1.5 phr, which phr is parts per hundred rubbers (part by mass, g). First, EPDM was plasticated on two-roll mill (SK-160 Tianjin Electrotechnical Mechanical plant), in which roll temperature was controlled o C and nip gap 1mm, then the mixed rubber was prepared by adding various ingredients on XK-160 two-roll mill for 15 min at o C, while the nip gap was about 4.0 mm. The mixtures of different compositions were molded into the vulcanized rubber in an electrically heated hydraulic press (XLB-D ) at 170 o C under 1.0 MPa for 8 min. At last, the vulcanized rubbers were cut the adaptable samples. 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-05/03/16,17:14:07)

2 Applied Mechanics and Materials Vol Result and Discussion Effect of silica content on EPDM properties. EPDM needs to be reinforced because of bad mechanical properties of raw rubber. The silica was chosen as reinforcement in this work. The effect of silica content on EPDM properties is shown in Table 1. Table 1 Effect of silica content on EPDM properties Silica (phr) Shore A hardness Tensile strength (MPa) Elongation at break (%) a /67 b 5.3/ / /77 6.1/ / /84 6.6/ / /88 6.8/ / /94 7.8/ / /93 5.8/ / /92 5.1/ /571 a Before heat aging, b After heat aging. Hardness is gradually increasing with adding silica in Table 1. When silica content is 55 phr, hardness and tensile strength appear to the peak value, but elongation at break and thermal properties are inferior. In Fig.1a, silica diffuses into EPDM, mix uniformity, and encapsulate compactly, it proves that the compatibility of EPDM with 45phr silica is good. In Fig.1b, silica generates accumulation phenomena because it is too much, it results in high hardness, bad compatibility, holes in fractured section, and the decrease of mechanical properties. It proves that 55phr silica is over capacity. Therefore, 45phr silica is suitable. (a) (b) Figure. 1 SEM photos of silica reinforced EPDM composites (a) silica 45phr; (b) silica 55phr Effect of sulfur and DCP on EPDM properties. There are not cross-linking bonds between the rubber molecules before the rubber is not cured, and the macromolecule chains happen to slip and difficultly keep a regular shape under external force. So the rubber must be vulcanized. The sulfur and dicumyl peroxide (DCP) were chosen as the curing agent in this work. The effect of sulfur and DCP on EPDM properties is shown in Table 2. Table 2 Effect of sulfur and DCP on EPDM properties Sulfur / DCP a Shore A hardness Tensile strength (MPa) Elongation at break (%) 1.0 / 0 72/73 5.5/ / / 0 75/84 6.6/ / / 0 83/94 6.5/ / / 0 84/94 7.9/ / / 0 84/94 7.3/ /815 0 / /91 6.5/ /859 0 / /90 7.7/ /841 0 / /93 9.0/ /835 0 / / / /850 0 / / / /867 0 / / / /885

3 242 New Trends in Mechatronics and Materials Engineering 0 / / / /740 0 / / / /736 0 / / / / / / / / / / / / / / / /817 a silica 45phr. As sulfur adding, hardness, elongation at break, tensile strength and thermal properties gradually increase, and up to peak value when sulfur content is 2.5phr. The addition of the DCP has no significant effect on the hardness, but the tensile strength and elongation at break gradually increase, and mechanical properties appear to excellence at 3.5phr. It can be seen that DCP as the curing agent is much better than sulfur, but DCP/sulfur blend as the curing agent is worse. In addition, when use the same content curing agent, the effect of DCP on the EPDM properties is better than that of sulfur. Therefore, DCP is chosen as curing agent, and the optimal content is 3.5phr. This can be explained that EPDM is a saturate rubber, the sulfur as curing agent is improper, but DCP is suitable. Effect of Al (OH) 3 and Mg (OH) 2 on EPDM properties. The combustion of rubber and other polymer compounds in the air will happen to be very intense oxidation reaction. So the flame retardant was added into the rubber cable materials to increase flame resistance. In the rubber materials, inorganic flame retardant is widespread used, such as aluminum hydroxide (ATH) and magnesium hydroxide (MH). Oxygen index is considered to be balanced standard of flame resistance. The effect of the aluminum hydroxide and magnesium hydroxide on EPDM performances is given in Table 3. Table 3 Effect of Al(OH) 3 and Mg(OH) 2 on EPDM performances Al(OH) 3 / Mg(OH) 2 a Shore A hardness Tensile strength (MPa) Elongation at break (%) OI 0 / / / / / / / / / / / / / / / / / / / / / a Silica 45phr, DCP 3.5phr. With increasing amounts of ATH, hardness and oxygen index gradually increase, but tensile strength and elongation at break is in downturn. The addition of MH makes hardness and oxygen present uptrend, tensile strength is excellent in 10 phr, and elongation at break shows irregular change. The effect of ATH flame retardant on EPDM is better than MH, the effect of MH / ATH blend is also better than ATH. It can be seen that the function of ATH and MH flame retardant is based on

4 Applied Mechanics and Materials Vol dehydrated and endothermic reaction. Because a lot of heat is absorbed in the loss of crystal water, the temperature of EPDM body is decreased, at the same time, the loss of crystal water forms steam, dilute oxygen concentration around EPDM, and result in combusting difficultly. ATH dehydration endothermic (1.97 KJ/g) is greater than MH (0.77 KJ/g), so ATH more timely and efficiently controls EPDM temperature rise, thus show better fire retardant effect, and makes the combustion performance of EPDM material further reduce. In addition, the flame retardant efficiency of ATH and MH blend is outstanding, it can be seen that ATH appear to endothermic peak (peak value 583K) in the range of K, then MH appear to the endothermic peak (peak value 688K) in the range of K, their endothermic temperature ranges are mutual complementation in burning to make the EPDM combusting capability to further reduce. When ATH / MH mass ratio is 90/10, hardness, tensile strength and elongation at break give maximum values. In brief, the optimum amount of flame retardant is aluminum hydroxide 90 phr and magnesium hydroxide 10 phr. (a) Figure. 2 SEM photo of flame retardant modified EPDM (a) Al(OH) 3 / Mg(OH) 2 =90/10 (b) pure Al(OH) 3 (b) The fracture section of EPDM with 90 phr Al (OH) 3 and 10 phr Mg (OH) 2 blend (Figure. 2a) is more homogeneous, smooth surface, but the fracture section with pure Al (OH) 3 flame retardant (Figure. 2b) is rough, a lot of particle can not be filled into EPDM, and further proves that the efficiency with 90 phr ATH and 10 phr MH blend is better than that with 100 phr ATH. Effect of curing condition on the EPDM performances. According to cable processing characteristics, the vulcanization for insulating rubber cable sheath is formed in a pipeline, and need to be under the lower pressure (less than 1.2 MPa). On the condition of the lower pressure, the effects of curing temperature and time on EPDM performance are shown in Table 4. Table 4 Effect of curing condition on the EPDM performances Cure conditions a Shore A hardness Tensile strength (MPa) Elongation at break (%) OI Temperature ( o C,1.2 MPa 8 min) /90 7.8/ / /89 7.7/ / /89 9.7/ / /90 8.9/ / /91 8.7/ / Time (min,170 o C 1.2 MPa) 6 82/93 8.2/ / /89 9.7/ / /89 9.8/ / /91 9.2/ / /91 9.1/ / a Silica 45phr, DCP 3.5phr, Al(OH) 3 90phr, Mg(OH) 2 10phr. In Table 4, with the temperature rising, the changes of hardness and oxygen index change aren t obvious, tensile strength, elongation at break and thermal properties show drop down a trend after rising, and reach to the maximum at the 170 o C, so determine the optimum curing temperature of 170 o C. As time flowing, hardness, tensile strength, elongation at break and oxygen index are gradually increasing, and reach to the maximum in 10 minutes, then appear to drop. It can be seen that cable is

5 244 New Trends in Mechatronics and Materials Engineering cured in the pipeline, in which the curing pressure by vapor control is generally lower. In lower pressure case, the higher curing temperature is need, so curing temperature takes the 170 o C. Below this temperature, EPDM would not be fully cured, but EPDM would be oxidation fracture above 170 o C. Similarly, it is the same explanation for the curing time. Therefore, the optimum curing condition is at 170 o C under 1.2MPa for 10min. Summary EPDM cable materials have flame resistance, excellent mechanical and thermal properties, and were successfully prepared, in which EPDM is used as main raw material. When 45phr silica is added, EPDM mechanical and thermal properties are good. The properties of EPDM cable materials with DCP are better than those with sulfur/dcp blend, and the best content of DCP is 3.5phr. The flame resistance and mechanical and thermal properties of EPDM cable materials with 90 phr Al (OH) 3 /10 phr Mg (OH) 2 blend is best. The optimum curing condition is at 170 o C under 1.2MPa for 10 min. References [1] J. van der Geer, J.A.J. Hanraads, R.A. Lupton, The art of writing a scientific article, J. Sci. Commun. 163 (2000) [1] Sun X, Zhang J Y, Gui W W., Development Trend and Market Demand of Electrical Cable Materials Industry in China, Plast. Sci. Techn. 6 (2009) [2] Goto T, Yamashita M, Sakamaki M., Development of Y-branch joint for 275-kV XLPE and fluid-filled cable, Elect. Eng. Japan.164 (2008) [3] Naskar K, Mohanty S, Nando G B., Development of thin-walled halogen-free cable insulation and halogen-free fire-resistant low-smoke cable-sheathing compounds based on polyolefin elastomer and ethylene vinyl acetate blends, J. Appl. Polym. Sci., 104 (2007) [4] Hsu Y T, Chang-Liao K S, Wang T K, Kuo C T., Monitoring the moisture-related degradation of ethylene propylene rubber cable by electrical and SEM methods, Polym. Degra. Stab., 91 (2006) [5] Hwang I, Lee J S, Spencer B F., Isolation System for Vibration Control of Stay Cables, J. Eng. Mech., 135 (2009) [6] Milani G, Milani F., Genetic algorithm for the optimization of rubber insulated high voltage power cables production lines, Compu. Chem. Eng., 32 (2008) [7] Anandakumaran K., IEEE Aging and Condition Monitoring Studies of Composite Insulation Cables Used in Nuclear Power Plants, Trans. Dielect. Electr. Insulation, 14 (2007) [8] Yang Y Q, Wei G, Duan H J, Feng Y C., Research Progress on Halegen-free Flame-retardant PE Cable Materials, Plast. Sci. Techn., 36 (2008) [9] Li Z A., Ethylene-propylene Copolymer based Compound for Electric Cable Insulation:A Rheological and Processability Study, Rubb. Plast. Resour. Utili., (2009) [10] Wang Y S., The prepared method of EPR cable materials with radiation resistant, low smoking and halogen-free flame retardant, China Rubber Science and Technology Market, (2009)17. [11] Li T, Zhang L Q., Study on Application of EPDM and prepared of novel blend, Beijing Uni. Chem. Technol., (2006) [12] Xiong L M, Li L., Study on The Formulation Design and Applied Properties of EPDM/CPE Blends, Nanchang Hangkong University, (2008)

6 New Trends in Mechatronics and Materials Engineering / Preparation of EPDM Flame-Resistant Cable Materials / DOI References [2] Goto T, Yamashita M, Sakamaki M., Development of Y-branch joint for 275-kV XLPE and fluid-filled cable, Elect. Eng. Japan. 164 (2008) /eej.20514