Study on the Durability of E-Glass Fiber/Vinylester resin Composites in Various Environment. Seung Yul Lee, Byung Hyun Ahn and Chang Kwon Moon a

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1 Solid State Phenomena Vols (2007) pp Online: (2007) Trans Tech Publications, Switzerland doi: / Study on the Durability of E-Glass Fiber/Vinylester resin Composites in Various Environment. Seung Yul Lee, Byung Hyun Ahn and Chang Kwon Moon a Division of Materials Science and Engineering, Pukyong National University, Busan , Korea. a Corresponding author: moonck@pknu.ac.kr Keywords: environmental condition, durability, composites, degradation, interface Abstract. The effect of various environmental conditions on durability of E-glass fiber/vinylester resin composites has been investigated with tensile test specimen of strand type. The durability test method performed by strand type specimen was more convenient and reliable than other conventional test method. The weight gain of E-glass fiber reinforced composites increased with the immersion time in both water and alkali solutions, and the weight gains at 80 were a little greater than ones at 20. The tensile strength decreased with the immersion time in all aqueous solution, and the tensile strength in 80 of alkaline solution decreased most rapidly. The decrement of tensile strength in various environmental conditions was mainly caused by the degradation of interface and damage of glass fiber surface. Introduction In recent years, fiber reinforced composite materials have been extensively used in industry whole because they have superior specific strength, modulus, and durability compared with existent metal and ceramic materials. Specially, application of fiber reinforced composite materials in construction is active because of light weight and long-life. The corrosion resistance of glass fiber reinforced plastic (GFRP) rebar is better than that of steel rod for general concrete reinforcement. Recently, using of GFRP rebar in concrete construction is expected [1]. This induces to improve the limit of size by heavy weight of existent reinforcing rod, and to gain economical profit ratio for construction as improved corrosion life [2]. In Fact, composite materials is prone to be degraded by surrounding heat, moisture, ultraviolet (UV) radiation and high ph environments [3]. The recent researches about durability of fiber reinforcement composite materials have dealt with the effects of time and temperature on the strength and life time of GFRP laminates [4-5], and about durability GFRP rebar in various environments [1]. However, while length of tensile test specimen is about 900mm at existent examination process, there is shortcoming of serious data deflection due to large size of specimen and test machine [6]. And experimental data in this area is rather scarce. In this paper, E-glass fiber/vinylester resin composites with strand type have been prepared and the effect of various environment conditions on durability of the composites has been experimentally investigated. Experimental Procedure Materials and Specimen Preparation. The materials used in this study are as follows. The fiber used was E-glass fiber (ER270FW, Hankuk Fiber Glass Co. Ltd.). The matrix resin used was vinylester(rf1001, Cray valley ) containing 44~48% styrene, 1phr of methyl ethyl ketone peroxide (MEKPO, Cray valley) and 0.4 phr of cobalt- naphthenate(conap) solution ( Cray valley). For the preparation of tensile test specimen with strand type, the glass fiber bundle was passed through the resin bath to impregnate. Impregnated glass fiber bundle was cured at room temperature for 24hrs, then followed at 80 for 2hrs and at 120 for 2hrs. Tensile test specimen having gauge length of 100mm was prepared by attaching paper tab[6]. 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-21/09/15,14:37:17)

2 836 Advances in Nanomaterials and Processing Durability test. In order to investigate the durability in the various environmental conditions, specimens were exposed to the following 2 sets of environmental conditions up to 150 days. (a) Set A: Immersion in deionized water (ph 7~8), at 20 and 80 (b) Set B: Immersion in alkaline solution formed by using 0.16% Ca(OH) 2, 1.0% NaOH, and 1.4% KOH, to simulate the high ph level(ph 13), at 20 and 80 Weight gain. Specimens of strand type composites for tensile test were immersed for certain period of time in deinoized water and alkaline solution at 20 and 80, then the weight gain was measured according to the given immersion time using an analytical balance(at400, Mettler) and three standard specimens were used at each condition. Tensile test. Tensile test was carried out using tensile test machine (Micro 350, Testometric Materials Testing Machines) equipped with load cell of 500kgf. Ten specimens were tested at each condition with crosshead speed of 2 mm/min at room temperature. Tensile strength was calculated by dividing maximum tensile load by cross section of fiber only, because tensile strength of matrix is much smaller than one of the fiber. Results and Discussion Weight gain. Fig. 2 represents the weight gains of the E-glass fiber/vinylester resin composites as a function of immersion time in various water environments. It can be seen that the weight gains are similar between the deionized water and alkaline solution conditions at same temperature. Weight gain in deionized water is a little bigger than one in alkaline solution condition. This is due to increase of water viscosity by such as Ca and Na in alkaline solution. It is also observed that weight gain at 80 appeared much higher than weight gain at 20 through the whole immersion time. It is also thought that high water absorption resulted in reduction of water viscosity itself in high temperature. Weight gain (wt.%) Alkaline solution 20'C Alkaline solution 80'C Deionized water 20'C Deionized water 80'C Fig. 2. Weight gains of the glass fiber/vinylester resin composites as a function of immersion time in various water environments. 0.2 Tensile test. Fig. 3 shows the change of the tensile strength of the glass fiber/vinylester resin composites as 0.1 a function of immersion time in various water environments. We can see that the tensile strength Immersion time (days) decreased with the immersion time in the all environmental conditions. In both water and alkaline solution, decrease of tensile strength was more serious at 80. Especially, tensile strength in alkaline solution decreased drastically. Comparing with other conditions, in deionized water at 20, tensile strength did not differ so much through the whole immersion time. In deionized water at 80, tensile strength decreased rapidly up to 10 days, and then decreased slowly. On the other hand, in alkaline solution at 20, tensile strength decreased rapidly through the whole immersion time. In alkaline solution at 80, tensile strength decreased sharply up to 10 days and then decreased very smoothly up to 30 days, then the change was little up to 150 days. From these results, we can induce that this composite system is very weak in the alkaline solution. This is probably that the damage of matrix resin, interface and fiber itself were occurred by alkaline attack at same time. Generally, E-glass fibers are susceptible to degradation when in contact with water, as an alkaline component on the glass fiber was eluted to moisture by the exchange reaction with hydrogen ion in

3 Solid State Phenomena Vols Tensile strength (GPa) Alkaline solution 20'C Alkaline solution 80'C Deionized water 20'C Deionized water 80'C Fig. 3. Tensile strength of the glass fiber/vinylester resin composites as a function of immersion time in various water environments. 1.0 water. So the serious decline of tensile strength of specimen in alkaline solution at 80 is considered that 0.0 damage of glass fiber itself by alkaline ion was more Immersion time (days) effective than interface damage between matrix and glass fiber. Although vinylester resin known as good corrosion resistance was used in this composite system, we can see that degradation effect of alkaline solution environment on tensile strength of strand composites was much bigger than one of deionized water environment. Observation of fracture surface. Fig. 4 shows a SEM photograph of tensile fracture surface of the strand composites before the immersion. It can be seen that there were hackles that made by resin attached keenly to fiber when interfacial adhesion of fiber and matrix resin is strong. Fig. 4. SEM photograph of tensile fracture surface of E-glass fiber/vinylester resin composites (no aging). Fig. 5 shows tensile fracture surfaces of the strand composites after the immersion of 150 days in various water environments. We can see that the hackle is attached weakly in Fig. 5(a). It is shown that interface between the fiber and resin did not much degrade according to aging in deionized water at 20, and it is also thought the reason of supporting of tensile strength did not much decrease with the immersion time as presented Fig. 3. In Fig. 5(b), debonding of fiber and matrix was remarkably presented and hackle could not be observed. From this, we could see serious degradation of interface. We could guess that the degradation of interface and fiber itself was serious due to the length of fiber pulled out was very short in Fig. 5(c). In Fig. 5(d), we could observe that surface resin of specimen was degraded seriously and fibers were not pulled out. Through this, it can be speculated that fiber itself was severely damaged as well as the degradation of resin and interface. Fig. 6 shows fracture surface of composite after the immersion of 150 days in alkaline solution at 80. Transverse cracks on the fiber are observed. The tensile strength of strand composites should be significantly affected by these transverse cracks as shown in Fig. 3. From above mentioned, we could realize that the tensile strength is reduced by damage of matrix resin, interface and fiber itself when the E-glass fiber exposed to alkaline and high temperature. Conclusions The effect of various environmental conditions on durability in E-glass fiber/vinylester resin composites has been investigated using tensile test specimen of strand type. Durability test in various environmental conditions using the tensile specimen of strand type was more convenient and reliable than conventional test method. The weight gains increased with immersion time in both water and alkaline environment. It is also observed that the weight gains at 80 were bigger than at 20.

4 838 Advances in Nanomaterials and Processing (a) Deionized water at 20 (b) Deionized water at 80 (c) Alkaline solution at 20 (d) Alkaline solution at 80 Fig. 5. SEM photographs of tensile fracture surface of E-glass fiber/vinylester resin composites after the immersion of 150 days in various water environments. Fig. 6. Fracture surface of composites after the immersion of 150 days in alkaline solution at 80 The tensile strength decreased with the immersion time in all environment conditions. The decrement of tensile strength did not differed through the whole immersion time at 20, but tensile strength decreased rapidly up to 10 days of immersion in alkaline solution at 80. The decrement of tensile strength during immersion in various environment conditions was mainly caused by the degradation of interface and damage of glass fiber surface. References [1] A. Abbasi, P. J. Hogg: Composites, Vol. 36(2005), pp [2] D. H. Kim: Polymer Sci. & Tech(Korea), Vol. 10(1999), pp [3] J. W. Chin, T. Nguyen, and K. Aouadi: J. Comp. Tec., Res., Vol. 19(1997), pp [4] K. Liao, C. R. Schultheisz, D. L. Hunston: Composites: Part(B), Vol. 30(1998), pp [5] Y. Miyano, M. Nakada, N. Sekine: Composites: Part(B), Vol. 35(2004), pp [6] C. K. Moon, Y. H. Kim, and Y. H. Park: J. Kor. Soi. for Power System Eng., Vol. 9(2005), pp [7] D. Sagi-Mana, M. Narkis, A. Siegmann, R. Joseph, and H. Dodirk: J. Appl. Polym., Sci., Vol. 69(1998), pp

5 Advances in Nanomaterials and Processing / Study on the Durability of E-Glass Fiber/Vinylester Resin Composites in Various Environment /