POLYURETHANE SURFACE TREATMENT ON TWO KINDS OF BASALT FIBER COMPOSITE AND MECHANICAL PROPERTIES COMPARISON Ting YANG 1, Zhenjin CUI 1,Jiahui YANG 2, Yuqiu YANG 2, Hiroyuki HAMADA 1 1 Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585 JAPAN 2 Donghua University, 2999 North Renmin Road, Songjiang District, Shanghai 201620 CHINA ABSTRACT Basalt fiber is a kind of fiber that has excellent mechanical properties and outstanding chemistry stability. So this fiber can be used as the reinforcement of composites. Basalt fiber s cost is much lower than carbon fiber, but its tensile strength is close to carbon fiber. Furthermore, China is rich in basalt mineral resources. In general, basalt fiber has promising development prospect. Nowadays, Basalt fiber is obtained increasing attention worldwide as a kind of promising reinforced fiber in composite field, which has the excellent mechanical properties, chemical resistance, comparative low cost, easily processing and abundance resource. In this paper, two kinds of basalt fabric, bulked yarn woven fabric and normal basalt fiber-woven fabric were used to fabricate composites. In specially, polyurethane dispersion (PUD) was used as the surface modification in composites. Two kinds of treated BFRP and virgins were tested by tensile test and scanning electron microscope (SEM) respectively. Comparison and analysis have been carried out in order to discuss the different influence by PUD surface treatment between two kinds of basalt fabric composites and the change of mechanical property by changing the PUD treatment s pick-up ratio and improved mechanical and thermal properties compared with virgins. 1 INTRODUCTION Fiber can improve composite s mechanical properties because it is strength is higher than resin, but only when fiber and resin have a good combination, composite s mechanical properties can be sufficiently improved, so the interface/interphase in fiber reinforced composites plays a very important role in determining the composite mechanical properties[1-3]. In order to achieve the best composite mechanical properties, many efforts have been made to improve interfacial properties. Fiber surface treatments are often used to create a fiber/matrix interface possessing different characteristics so that the fiber strength is utilized effectively under an optimum bonding. Therefore, it s critical to investigate the influences of surface treatment on composites mechanical properties. There are many surface treatment methods can be used in composites, including silane coupling agent and chemical sizing agent. In this paper, we used one of the chemical sizing agents---the polyurethane (PUD) surface treatment on the basalt fiber-woven fabric. It is considered that polyurethane have a good compatibility with epoxy matrix resin. However, there were few reports focused on its effect as surface treatment. In this research, polyurethane was applied as the surface treatment for basalt fiber reinforced epoxy matrix. The effects on composite s physical and mechanical properties were investigated and analyzed. 1
2 FABRICATION OF COMPOSITE 2.1 Material Polyurethane was used as surface treatment agent. Thermosetting bisphenol-a epoxy (JER828) and amine-system harder (JER-W) was applied as the matrix system in a ratio of 100:24. There are two kinds of basalt cloth were used in this study for composite reinforcement. One kind is bulked yarn woven fabric and another is normal basalt fiber woven fabric. Before surface treatment the basalt fiber-woven fabric was wiped out through acetone, and one type of each kind of basalt cloth didn t use PUD treatment wasn t wiped out through acetone. 2.2 Surface treatment of basalt fiber cloth These two kinds of composite reinforcement are used for PUD surface treatment. Prior to molding, the weight of pre-cut basalt cloth was measured as M0 followed by soaking into the different PUD solutions completely for 10 seconds. Clean tissue was used to wipe out the redundant solution on treated basalt cloth surface after taking out from the bath. Subsequently, the treated basalt cloth were put in convection oven for solvent s evaporation for 1.5 hour at 140 C. Finally, the weight of treated basalt cloth Mp was measured again for reference. Evaluation equation for polyurethane particle s pick- up ratio (P%) at unit basalt cloth weight was defined as Eq.1 In this formula, Mp corresponded treated-weight of basalt fiber-woven fabric after drying in oven, M0 corresponded to non-treat weight. The dilution ratio and pick-up ratio was summarized and provided in Table 1 and Table 2. 2.3 Fabrication of basalt/epoxy composites Hand layup and hot press molding technical was used for the preparation of basalt-cloth reinforced thermosetting epoxy resin matrix composites. Firstly, mixed epoxy and harder were put into the vacuum oven for 20 minutes at 70 in order to increase the liquidity for better mixing, impregnation and getting rid of the entrapped air-bubble. Afterwards, one layer of treated or non-treat fabric with the size of 250mm x 250mm was impregnated into matrix resin within 2-3 minutes to keep the matrix resin s fluidity. And then impregnated composite sheets were cured by hot press machine with applied force of 170 Newton. After being initially cured at 100 for 2 hours, molded panels were post-curved at 175 for 4 hours. The fiber content of composites was provided in Table 3 and Table 4. 2
Table 1 Surface treatment dilution ratio (normal basalt fiber woven fabric) Dilution ratio (PUD : Pick-up ratio Distilled) --- (no acetone wash) Untreated 1:7 (acetone wash) 0.31% 1:3 (acetone wash) 0.93% 1:0 (acetone wash) 9.09% Table 2 Surface treatment dilution ratio (bulked yarn basalt fiber woven fabric) Dilution ratio (PUD : Distilled) Pick-up ratio --- (no acetone wash) Untreated --- ( acetone wash) Only wash 1:7 (acetone wash) 1.16% 1:0 (acetone wash) 10.34% 1:3 (no acetone wash) 2.27% Table 3 Fiber volume content of composites (normal basalt fiber woven fabric) Sample Untreated PUD 0.31% PUD 0.93% PUD 9.09% V f 62.4% 69.9% 71.2% 45.7% Table 4 Fiber volume content of composites (bulked yarn basalt fiber woven fabric) Sample Untreated Only wash PUD PUD No wash+pud 1.16% 10.34% 2.27% V f 47.2% 55.2% 49.3% 45.0% 43.2% 3
3 EXPERIMENTAL 3.1 Measurement of composites tensile test For each type, 3 pieces of specimens with the geometry of 20mm x 200mm (width X length) were tested and the mean value of the data obtained was taken as the measured result (Gauge length is 100mm). And strain gauges were attached on the center of sample in order to obtain comparative accurate strain data. Tensile test was carried out on an Instron universal testing machine at a speed of 1 mm/min and the test room temperature is 22. 3.2 Fracture section observation After tensile test, the fracture surface of the tested samples was sputtered with gold for electron conductivity before observation. The cross sectional observations of molded sample after tensile test were carried out by using a field emission scanning electron microscope. The observations were focused on matrix fusion, state of resin impregnation, fiber/matrix interfacial interactions, and fracture morphologies to characterize interfacial bonding properties. 4 RESULTS AND DISCUSSIONS 4.1 Normal basalt fiber woven fabric composites The 4 types tensile stress-strain (S-S) curves for normal basalt fiber woven fabric composites were gathered in the Fig.1. From these curves, it s easily to find that with increasing of PUD pick-up ratio, the mechanical properties of materials achieved significantly improved. According to the Fig.2, it s worthwhile to note that the PUD surface treatment lead to higher Young modulus, but the modulus of 9.09wt% type dropped dramatically. The main reason was considered to the fiber volume content of this material is lower than other three materials. Nevertheless, the modulus is still higher than the sample without a surface treatment. As shown in Fig.3 is the tensile strength comparison among different PUD pick-up ratio, strength become higher when PUD pick-up ratio rose. However, though lower fiber volume content of 9.09wt% type, its tensile strength still enhanced a lot. Fig.1 Tensile stress-strain curves of normal basalts woven fabric composite with different PU treatment 4
Fig.2 tensile modulus comparison of normal basalts woven fabric composite with different PU treatment Fig.3 tensile strength comparison of normal basalts woven fabric composite with different PU treatment 4.2 Bulked yarn basalt fiber woven fabric composites The tensile stress-strain (S-S) curves of bulked yarn basalt fiber woven fabric composites were gathered in the Fig.4. From these curves, it s easily to find that with a low PUD pick-up ratio, the mechanical properties of materials is better than washed one, but when PUD pick-up ratio is too high, the strength began to down. The no washed and directly treated by PUD sample s called silane + PUD, and from curves it is showed that with two kinds of surface treatment agent treated, the mechanical properties is not good. As shown in Fig.5 and Fig.6 is the tensile modulus and strength comparison among different PUD pick-up ratio and washed sample, no washed sample, it s worthwhile to note that strength and modulus become higher than no washed sample s with low PUD pick-up ratio, but when PUD pick-up ratio continued to rise, the strength and modulus began to down. 5
Fig.4 Tensile stress-strain curves of bulked yarn basalts woven fabric composite with different PU treatment Fig.5 tensile modulus comparison of bulked yarn basalts woven fabric composite with different PU treatment Fig.6 tensile strength comparison of bulked yarn basalts woven fabric composite with different PU treatment 6
4.3 The mechanical properties comparison of two kinds of basalt fiber woven fabric composites From these figures, it is easily to find that, for normal basalt fiber woven fabric composites, PUD surface treatment has a great influence for materials mechanical properties, but for bulked yarn basalt fiber woven fabric composites, a good influence is very small. When PUD pick-up ratio is two high, the mechanical properties even become worse than no treatment. The reason lead to this is after PUD surface treatment, cloth will become harder than before, it s not good for fabrication by hand layup. Because a harder surface will lead to more bubbles. For normal basalt cloth, the influence is very small, but for bulked yarn, because it has a loose structure, so if the cloth becomes hard, it is difficult to make bubbles out from composite when fabrication. 4.4 Morphologies of BF/Epoxy composites tensile fracture The SEM images in Fig.7 shows that the surface morphologies of untreated and 0.39wt%, 0.93wt% and 9.09wt% PUD pick-up ratio treated basalt reinforced composites. It was easy to find after surface treatment, the resin on the fiber become more and the adhesion between fiber and resin is better as PUD pick-up ratio rising. And the SEM images in Fig.8 shows that the interface is becoming better with PUD surface treatment than washed by acetone sample. Fig.7 SEM observation of normal basalts woven fabric composite 7
Fig.8 SEM observation of bulked yarn basalts woven fabric composite 5 CONCLUSIONS In this research,through the tensile test, the basic mechanics property of two kinds basalt with different PUD pick-up ratio reinforced thermosetting epoxy were investigated. From the analysis of this paper, the following conclusions could be obtained. (1) For normal basalt cloth composite, it s easily to find that with increasing of PUD pick-up ratio, the mechanical properties of materials achieved significantly improved. (2) For bulked yarn basalt cloth composite, it is shows that that with a low PUD pick-up ratio the mechanical properties of materials is better than washed one, but when PUD pick-up ratio is too high, the strength began to down. And from curves it is showed that with two kinds of surface treatment agent treated, the mechanical property is not good. (3) For normal basalt fiber woven fabric composites, PUD surface treatment has a great influence for materials mechanical properties, but for bulked yarn basalt fiber woven fabric composites, a good influence is very small. The reason is bulked yarn cloth has a loose structure, and PUD surface treatment lead the cloth becomes hard, so it is difficult to make bubbles out from composite when fabrication. REFERENCES 1) Wacker G, Bledzki A K, Chate A. Effect of interphase on the transverse Young's modulus of glass/epoxy composites[j]. Composites Part A: Applied Science and Manufacturing, 1998, 29(5): 619-626. 2) James L.Thomason, Glass Fibre Sizings (A Review of the Scientific Literature), August 22 2012 3) J.G. Iglesias, J. Gonzalez-Benito, A.J. Aznar, J. Bravo, and J. Baselga, Journal of Colloid and Interface Science 250, 251-260 (2002) 4) F.M. Zhao, N. Takeda, Composites: Part A 31 (2000) 1203-1214 8