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Accelerated Ageing Tests for Evaluations of a Durability Performance of Glass-fiber Reinforcement Polyester Composites
J. Mater. Sci. Technol., 2010, 26(6), 572-576.
Accelerated Ageing Tests for Evaluations of a Durability Performance of Glass-fiber Reinforcement Polyester Composites Yunying Wang1)† , Jiangyan Meng2) , Qing Zhao2) and Shuhua Qi1)
1) School of Science, Northwestern Polytechnical University, Xi an 710072, China 2) Department of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China [Manuscript received April 27, 2009, in revised form November 9, 2009]
The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin (191#) and its glass-fiber reinforcement polyester composites (GFRPC). The samples were exposed in an artificial xenon arc lamp ageing cell or a thermo-oxidative ageing cell. Morphology and gloss of the specimens were investigated by using a microscope and a gloss-meter, respectively. The tensile strength, bending strength and inter-laminar shear strength (ILSS) of GFRPC were tested before and after exposure, and were considered to evaluate the durability performance of this material. The polyester resin was analyzed by fourier transform infrared (FT-IR) spectroscopy. The results showed that the glossiness of the specimens got worse and some cracks appeared on their surface during the course of ageing, the tensile strength and bending strengths of the specimens first increased and then decreased. The ILSS of the composites decreased after they were aged in the xenon arc lamp cell, but increased while they were aged in the thermo-oxidative cell. The changes of these trends become more obvious during ageing in the xenon arc lamp cell, so the main influencing factor leading to the failure of this material is UV irradiation. KEY WORDS: Ortho-phthalic; Artificial thermo-oxidation ageing; Artificial xenon arc lamp ageing; UV irradiation; Inter-laminar shear strength (ILSS)
1. Introduction Glass fiber reinforced unsaturated polyester composites (GFRPC) are widely used in the applications such as blades for wind turbines, construction structures, boat hulls etc. Studies on the exposure of such materials to the environmental conditions for example varying temperature, humidity, ultraviolet radiation etc., are of outmost importance in order to assess the impact of these important ageing factors on their mechanical behavior[1] . Studies on GFRPC in China are less than that in developed countries[2–4] . The morphological and chemical evolutions of tubular glass-epoxy composites after artificially or naturally photo-ageing were studied to determine the durability of the composites[5–7] . † Corresponding author. Tel.: +86 791 3863145; E-mail address: [email protected] (Y.Y. Wang).
Those would lead to some major results that whether in a natural or artificial environment, the thickness of the organic matrix decreases linearly with cumulative global exposure energy. The comparisons between natural and artificial evolutions proved that rainfall was a major parameter in amplifying the erosion phenomenon. The ageing behavior of glass fiber reinforced 191# unsaturated polyester resin has been studied in literature [8–10], and it is indicated that this material is more sensitive to UV irradiation than other environment factors, for example, temperature and O2 . The purpose of this work is to establish an ageing database for the polymer material exposed on China western exposure region and to research the relationship between the natural exposure ageing and the artificial accelerating ageing for the polymer material. We describe herein a study on the ageing behavior of the GFRPC subjected to the laboratory artificial
Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
573
ageing cell. 2. Experimental 2.1 Preparation of specimens The 191# polyester was prepared by mixing 100 g resin, 1–2 g cyclohexanone peroxide initiator, 0.5 g cobalt naphenate accelerator together, and pouring the mixture into rectangular moulds. The polyester samples were cured for about 24 h in the moulds at ambient temperature. Concerning GFRPC sample, two kinds of specimen were made, one of them possessed 10% (weight ratio of the resin) inorganic fillers Al(OH)3 , the other did not possess the filler. They were provided in ca. 800 mm×800 mm of 1 mm (for dynamic mechanical analysis (DMA) testing), 4 mm (for the tensile and bending strength testing), and 15 mm (for the ILSS). The fiber weight fraction of the composites was 50%±5%. All of the specimens were heat-treated for 48 h in the oven at 45◦ C. The surfaces of the two types of samples were smooth and glossy, and the polyester specimens were semi-transparent. 2.2 Instrumentation and ageing parameters An SN-900 artificial xenon arc lamp aging cell (Shanghai Lin-Pin equipment Co., China) was used to evaluate the durability performance of the specimens. The ageing parameters were: exposure intensity 1000±200 W·m−2 (monitored by an exposure meter continuously), spraying/non-spraying cycle 18 min/102 min, temperature 63±3◦ C, and 12 h exposure/12 h non-exposure. An FQRLS-800 artificial thermo-oxidation ageing cell (Shanghai Fuqi equipment Co., China) was used to evaluate the durability performance of the material. Ageing parameters were: temperature 70±1◦ C, aeration rate 50 times/h, wind speed 0.5 m/s, and continuous exposure for 24 h. 2.3 Test methods 2.3.1 Fourier transform infrared (FT-IR) spectroscopy analysis The KBr pressed-sheet method was adopted, whereby the cured resin was ground to powder, and the powder was mixed with KBr (1:50, weight ratio), then the mixture was pressed into a sheet. A Nicolet 170X type FT-IR spectrometer (USA) was used for the analysis. The resolution ratio was 4 cm−1 and the frequency range was 4000–450 cm−1 . 2.3.2 Morphology tests The morphology of the samples was tested by XPV-203E optical microscope (Shanghai optical instrument Co., China). The glossiness of specimens
Fig. 1 Sketch of the ILSS
was investigated using a JKGZ-1 gloss-meter (Tianjin Jingke precision instrument factory, China). The angle of the measured light is 60 deg. 2.3.3 Mechanical tests In order to accurately determine the exact impact of the environmental ageing on the viscoelastic behavior of the material, thermal scans were performed on small bars of dimension 25 mm×15 mm×1 mm for the polymer material. The test machine was a Q800 type from TA instruments. Test mode used here was three-point bending under controlled strain. Testing span was 60 mm. Temperature was set between room temperature and 200◦ C with a constant frequency of 1 Hz. The preload was set at 0.125 N and the oscillation amplitude was 15 μm. All specimens were tested in pristine condition for different ageing time. Static tensile tests were performed on WDW-50 universal testing machine (Jinan Shijin Instrument Co., China) at 2 mm/min crosshead speed for the composites, and at 5 mm/min crosshead speed for the polymer material. Tensile strain was measured by strain gauges attached along the longitudinal axis of the specimen. The specimen dimensions were 180 mm×20 mm×4 mm. Three-point bending tests were performed on WDW-50 universal testing machine for the polymer materials. The specimen dimension was 80 mm×15 mm×4 mm. Testing span was 60 mm. The specimen s dimension and shape of the ILSS of the composites are shown in Fig. 1. ILSS tests were performed on WDW-50 universal testing machine at 10 mm/min crosshead speed. 3. Results and Discussion 3.1 Morphology of the composites Morphologies of the composites are shown in Fig. 2. The surfaces of the composites display some irregularities or/and cracks (Fig. 2(a)–(c)). The glass fiber exposes from the composites after the xenon
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Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
tificial ageing, the cell temperature was set at 70◦ C (higher than the ambient temperature), the polyester had fewer double bonds since they easily reacted with each other to form a cross-linked structure, and the anhydride and hydroxyl groups underwent dehydration to form carbonyl (–COO) in the molecular chain (–OH peak weakened, –COO enhanced). This is a post-cure reaction, and the change may lengthen the molecular chain and increase the molecular weight, and may partly alter the chemical constitution of the polyester, leading to internal stress. When this stress reaches a certain level, the small cracks will appear in the surface, which become more prevalent during the course of ageing. The plots of the glossiness of the specimens vs ageing time is shown in Fig. 3. The glossiness of the composites changes more badly with time, losing its glossy in the course of xenon arc lamp ageing. And this change becomes somewhat slowly after aged 1500 h (GFRPC with filler) and 2300 h (GFRPC). For thermo-oxidative ageing, the gloss of the sample hardly changes, and the gloss value is about 66–70 in the course of ageing. The color change occurs because of many reasons. However, in this work, the presence of metallic ions is the primary reason. Because cobalt naphthenate was used as a promoter, the cobalt ions took part in the reaction and the surfaces of the samples ultimately appeared yellow and lost the gloss. Figure 3 tells us that inorganic filler would affect the surface properties of the composites. The reason may be that the inorganic filler would absorb specific band UV to form the radical group. 3.2 Mechanical property Fig. 2 Morphology of the composites: (a) before ageing, (b) thermo-oxidative ageing for 240 d, (c) xenon arc lamp ageing for 240 d
Fig. 3 Relationship between the glossiness percent of the specimens and xenon arc lamp ageing time
lamp ageing for 240 d (Fig. 2(c)) and thermo-oxidative ageing for 240 d (Fig. 2(b)), because the resin is ablation from the surfaces of the composites. For ar-
The tensile strength, the bending strength and the ILSS of the composites are shown in Figs. 4– 6, respectively. The tensile strength and the bending strength of the composites are increasing at first ageing stage and decreasing gradually (Figs. 4 and 5). The strength of GFRPC is higher than that of GFRPC with filler by contrasting Fig. 4(a) with (b), Fig. 5(a) with (b), and the inorganic filler would influence the mechanical performance of the material. At early ageing period, the polyester took place during post-cure reaction and physical ageing, and this may lengthen the molecular chain and increase the molecular weight, leading to the increase of the strength of specimens. In the case that the remaining double bonds reacted completely, and the dehydration reaction finished, thus the strength of the material was no longer increased. Moreover, physical ageing of the polymer would alter the aggregation structure of the polymer, and increase the cross-linking density[11] . So the tensile strength and the bending strength of the composites were increasing at first ageing stage. After longer period ageing, the polyester resin might undergo some degree of degradation under the synergistic impact of UV, high temperature, and O2 , then the
Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
Fig. 4 Relationship between the tensile strength of GFRPC and thermo-oxidation (a) and xenon (b) ageing time
575
Fig. 6 Relationship of GFRPC s ILSS with thermooxidation (a) and xenon (b) ageing time
strength of the specimens decreased. The ILSS of the composites are increasing after aged in the thermo-oxidative ageing cell (Fig. 6(a)), and decreasing from the beginning of the xenon ageing (Fig. 6(b)). The post-cure reaction of the resin may be accelerated under the impact of higher temperature, and periodical spraying may influence the interface of the composites. The glass-fiber of the specimens is not treated, and the varying humidity of the ageing cell affects the interface binding of the fiber/resin. So the ILSS of the specimens are deceasing in the course of the xenon arc lamp ageing. In a word, this material is easier to be aged in the xenon arc lamp cell. 3.3 FT-IR spectra
Fig. 5 Relationship between the bending strength of GFRPC and thermo-oxidation (a) and xenon (b) ageing time
To investigate the microscopic structure change, the polymer was studied by FT-IR. The FT-IR spectra are shown in Figs. 7 and 8. The absorption peak (1725, 1289–1300, 1125 cm−1 ) of ester is enhanced obviously, and the absorption peak (3450 cm−1 ) of hydroxyl (–OH) is also changed. The absorption peak (705, 745 cm−1 ) of the duplet bond is enhanced, and the absorption peak (2926, 2853 cm−1 ) of the methane(–CH2 –) is also increased. All of the changes are to prove that the esterification of the hydroxyl and anhydride has occurred, the radical polymeriza-
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Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
Fig. 7 FT-IR spectra of the resin aged by xenon arc lamp for 0, 90 and 240 d
materials aged in the above conditions were 191# unsaturated polyester and its GFRPC. The experimental results revealed that some irregularities/cracks occur after artificial ageing. The exposed glass-fiber could be seen from the sample because of the ablation of the organic resin from the aged material. The tensile strength and the bending strength of the composites increased in shorter ageing period and then decreased at longer time (about ageing for 120 d). The ILSS of the composites increased after the sample was aged in the thermo-oxidative cell, while decreased after the sample was aged in the xenon arc lamp cell. The inorganic filler would influence the morphology and the mechanical performance of the material. And the main influencing factor leading to the failure of this material is UV irradiation.
Acknowledgement This work was supported by the National Natural Science Foundation of China (No. 50533060). REFERENCES
Fig. 8 FT-IR spectra of the resin aged by thermooxidative for 0, 90 and 240 d
tion of the duplet bond (post-cure reaction) and the main chain of the polymer have been lengthened, and the movement of the molecular chain becomes more difficult. So the strengths of the specimens increase. 4. Conclusion Two environmental chambers that can simulate accelerated ageing on polymers and composites were adopted: one of chambers was a thermo-oxidative ageing chamber, providing temperature and oxygen, the other was a xenon arc lamp ageing chamber, providing UV radiation, temperature and humidity. The
[1 ] D.E. Mouzakis, H. Zoga and C. Galiotis: Compos. Part B-Eng., 2006, 10, 1. [2 ] Z.Y. Xue: Shanghai Build. Mater., 2002, 6, 34. (in Chinese) [3 ] V. Oteino-Alego: in 1st Int. Conf. on Ageing Studies and Lifetime Extension of Materials, Oxford, UK, 1999, 113. [4 ] D. Leveque, A. Schieffer, A. Mavel and J.F. Maire: Compos. Sci. Technol., 2005, 65, 395. [5 ] L. Monney, C. Dubois, D. Perreux, A. Burtheret and A. Chambaudet: Polym. Degrad. Stabil., 1999, 63(2), 219. [6 ] L. Monney, R. Belali, J. Vebrel, C. Dubois and A. Chambaudet: Polym. Degrad. Stabil., 1997, 56(3), 357. [7 ] C. Dubois, L. Monney, N. Bonnet and A. Chambaudet: Compos. Part A–Appl. Sci. Manuf., 1999, 30(3), 361. [8 ] C.Y. Zhu, Q. Zhao and J.Y. Meng: Fail. Anal. Prev., 2008, 3(3), 12. (in Chinese) [9 ] Y.Y. Wang, J.Y. Meng and Q. Zhao: China Adhesives, 2008, 17(8), 34. (in Chinese) [10] Y.Z. Xiao, Q. Zhao, Y.Y. Wang and W.Q. Du: Surf. Technol., 2009, 39(1), 5. (in Chinese) [11] D.Y. Shen and R.Y. Qian: Polym. Bull., 1993, 20(4), 193.
Accelerated Ageing Tests for Evaluations of a Durability Performance of Glass-fiber Reinforcement Polyester Composites Yunying Wang1)† , Jiangyan Meng2) , Qing Zhao2) and Shuhua Qi1)
1) School of Science, Northwestern Polytechnical University, Xi an 710072, China 2) Department of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China [Manuscript received April 27, 2009, in revised form November 9, 2009]
The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin (191#) and its glass-fiber reinforcement polyester composites (GFRPC). The samples were exposed in an artificial xenon arc lamp ageing cell or a thermo-oxidative ageing cell. Morphology and gloss of the specimens were investigated by using a microscope and a gloss-meter, respectively. The tensile strength, bending strength and inter-laminar shear strength (ILSS) of GFRPC were tested before and after exposure, and were considered to evaluate the durability performance of this material. The polyester resin was analyzed by fourier transform infrared (FT-IR) spectroscopy. The results showed that the glossiness of the specimens got worse and some cracks appeared on their surface during the course of ageing, the tensile strength and bending strengths of the specimens first increased and then decreased. The ILSS of the composites decreased after they were aged in the xenon arc lamp cell, but increased while they were aged in the thermo-oxidative cell. The changes of these trends become more obvious during ageing in the xenon arc lamp cell, so the main influencing factor leading to the failure of this material is UV irradiation. KEY WORDS: Ortho-phthalic; Artificial thermo-oxidation ageing; Artificial xenon arc lamp ageing; UV irradiation; Inter-laminar shear strength (ILSS)
1. Introduction Glass fiber reinforced unsaturated polyester composites (GFRPC) are widely used in the applications such as blades for wind turbines, construction structures, boat hulls etc. Studies on the exposure of such materials to the environmental conditions for example varying temperature, humidity, ultraviolet radiation etc., are of outmost importance in order to assess the impact of these important ageing factors on their mechanical behavior[1] . Studies on GFRPC in China are less than that in developed countries[2–4] . The morphological and chemical evolutions of tubular glass-epoxy composites after artificially or naturally photo-ageing were studied to determine the durability of the composites[5–7] . † Corresponding author. Tel.: +86 791 3863145; E-mail address: [email protected] (Y.Y. Wang).
Those would lead to some major results that whether in a natural or artificial environment, the thickness of the organic matrix decreases linearly with cumulative global exposure energy. The comparisons between natural and artificial evolutions proved that rainfall was a major parameter in amplifying the erosion phenomenon. The ageing behavior of glass fiber reinforced 191# unsaturated polyester resin has been studied in literature [8–10], and it is indicated that this material is more sensitive to UV irradiation than other environment factors, for example, temperature and O2 . The purpose of this work is to establish an ageing database for the polymer material exposed on China western exposure region and to research the relationship between the natural exposure ageing and the artificial accelerating ageing for the polymer material. We describe herein a study on the ageing behavior of the GFRPC subjected to the laboratory artificial
Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
573
ageing cell. 2. Experimental 2.1 Preparation of specimens The 191# polyester was prepared by mixing 100 g resin, 1–2 g cyclohexanone peroxide initiator, 0.5 g cobalt naphenate accelerator together, and pouring the mixture into rectangular moulds. The polyester samples were cured for about 24 h in the moulds at ambient temperature. Concerning GFRPC sample, two kinds of specimen were made, one of them possessed 10% (weight ratio of the resin) inorganic fillers Al(OH)3 , the other did not possess the filler. They were provided in ca. 800 mm×800 mm of 1 mm (for dynamic mechanical analysis (DMA) testing), 4 mm (for the tensile and bending strength testing), and 15 mm (for the ILSS). The fiber weight fraction of the composites was 50%±5%. All of the specimens were heat-treated for 48 h in the oven at 45◦ C. The surfaces of the two types of samples were smooth and glossy, and the polyester specimens were semi-transparent. 2.2 Instrumentation and ageing parameters An SN-900 artificial xenon arc lamp aging cell (Shanghai Lin-Pin equipment Co., China) was used to evaluate the durability performance of the specimens. The ageing parameters were: exposure intensity 1000±200 W·m−2 (monitored by an exposure meter continuously), spraying/non-spraying cycle 18 min/102 min, temperature 63±3◦ C, and 12 h exposure/12 h non-exposure. An FQRLS-800 artificial thermo-oxidation ageing cell (Shanghai Fuqi equipment Co., China) was used to evaluate the durability performance of the material. Ageing parameters were: temperature 70±1◦ C, aeration rate 50 times/h, wind speed 0.5 m/s, and continuous exposure for 24 h. 2.3 Test methods 2.3.1 Fourier transform infrared (FT-IR) spectroscopy analysis The KBr pressed-sheet method was adopted, whereby the cured resin was ground to powder, and the powder was mixed with KBr (1:50, weight ratio), then the mixture was pressed into a sheet. A Nicolet 170X type FT-IR spectrometer (USA) was used for the analysis. The resolution ratio was 4 cm−1 and the frequency range was 4000–450 cm−1 . 2.3.2 Morphology tests The morphology of the samples was tested by XPV-203E optical microscope (Shanghai optical instrument Co., China). The glossiness of specimens
Fig. 1 Sketch of the ILSS
was investigated using a JKGZ-1 gloss-meter (Tianjin Jingke precision instrument factory, China). The angle of the measured light is 60 deg. 2.3.3 Mechanical tests In order to accurately determine the exact impact of the environmental ageing on the viscoelastic behavior of the material, thermal scans were performed on small bars of dimension 25 mm×15 mm×1 mm for the polymer material. The test machine was a Q800 type from TA instruments. Test mode used here was three-point bending under controlled strain. Testing span was 60 mm. Temperature was set between room temperature and 200◦ C with a constant frequency of 1 Hz. The preload was set at 0.125 N and the oscillation amplitude was 15 μm. All specimens were tested in pristine condition for different ageing time. Static tensile tests were performed on WDW-50 universal testing machine (Jinan Shijin Instrument Co., China) at 2 mm/min crosshead speed for the composites, and at 5 mm/min crosshead speed for the polymer material. Tensile strain was measured by strain gauges attached along the longitudinal axis of the specimen. The specimen dimensions were 180 mm×20 mm×4 mm. Three-point bending tests were performed on WDW-50 universal testing machine for the polymer materials. The specimen dimension was 80 mm×15 mm×4 mm. Testing span was 60 mm. The specimen s dimension and shape of the ILSS of the composites are shown in Fig. 1. ILSS tests were performed on WDW-50 universal testing machine at 10 mm/min crosshead speed. 3. Results and Discussion 3.1 Morphology of the composites Morphologies of the composites are shown in Fig. 2. The surfaces of the composites display some irregularities or/and cracks (Fig. 2(a)–(c)). The glass fiber exposes from the composites after the xenon
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Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
tificial ageing, the cell temperature was set at 70◦ C (higher than the ambient temperature), the polyester had fewer double bonds since they easily reacted with each other to form a cross-linked structure, and the anhydride and hydroxyl groups underwent dehydration to form carbonyl (–COO) in the molecular chain (–OH peak weakened, –COO enhanced). This is a post-cure reaction, and the change may lengthen the molecular chain and increase the molecular weight, and may partly alter the chemical constitution of the polyester, leading to internal stress. When this stress reaches a certain level, the small cracks will appear in the surface, which become more prevalent during the course of ageing. The plots of the glossiness of the specimens vs ageing time is shown in Fig. 3. The glossiness of the composites changes more badly with time, losing its glossy in the course of xenon arc lamp ageing. And this change becomes somewhat slowly after aged 1500 h (GFRPC with filler) and 2300 h (GFRPC). For thermo-oxidative ageing, the gloss of the sample hardly changes, and the gloss value is about 66–70 in the course of ageing. The color change occurs because of many reasons. However, in this work, the presence of metallic ions is the primary reason. Because cobalt naphthenate was used as a promoter, the cobalt ions took part in the reaction and the surfaces of the samples ultimately appeared yellow and lost the gloss. Figure 3 tells us that inorganic filler would affect the surface properties of the composites. The reason may be that the inorganic filler would absorb specific band UV to form the radical group. 3.2 Mechanical property Fig. 2 Morphology of the composites: (a) before ageing, (b) thermo-oxidative ageing for 240 d, (c) xenon arc lamp ageing for 240 d
Fig. 3 Relationship between the glossiness percent of the specimens and xenon arc lamp ageing time
lamp ageing for 240 d (Fig. 2(c)) and thermo-oxidative ageing for 240 d (Fig. 2(b)), because the resin is ablation from the surfaces of the composites. For ar-
The tensile strength, the bending strength and the ILSS of the composites are shown in Figs. 4– 6, respectively. The tensile strength and the bending strength of the composites are increasing at first ageing stage and decreasing gradually (Figs. 4 and 5). The strength of GFRPC is higher than that of GFRPC with filler by contrasting Fig. 4(a) with (b), Fig. 5(a) with (b), and the inorganic filler would influence the mechanical performance of the material. At early ageing period, the polyester took place during post-cure reaction and physical ageing, and this may lengthen the molecular chain and increase the molecular weight, leading to the increase of the strength of specimens. In the case that the remaining double bonds reacted completely, and the dehydration reaction finished, thus the strength of the material was no longer increased. Moreover, physical ageing of the polymer would alter the aggregation structure of the polymer, and increase the cross-linking density[11] . So the tensile strength and the bending strength of the composites were increasing at first ageing stage. After longer period ageing, the polyester resin might undergo some degree of degradation under the synergistic impact of UV, high temperature, and O2 , then the
Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
Fig. 4 Relationship between the tensile strength of GFRPC and thermo-oxidation (a) and xenon (b) ageing time
575
Fig. 6 Relationship of GFRPC s ILSS with thermooxidation (a) and xenon (b) ageing time
strength of the specimens decreased. The ILSS of the composites are increasing after aged in the thermo-oxidative ageing cell (Fig. 6(a)), and decreasing from the beginning of the xenon ageing (Fig. 6(b)). The post-cure reaction of the resin may be accelerated under the impact of higher temperature, and periodical spraying may influence the interface of the composites. The glass-fiber of the specimens is not treated, and the varying humidity of the ageing cell affects the interface binding of the fiber/resin. So the ILSS of the specimens are deceasing in the course of the xenon arc lamp ageing. In a word, this material is easier to be aged in the xenon arc lamp cell. 3.3 FT-IR spectra
Fig. 5 Relationship between the bending strength of GFRPC and thermo-oxidation (a) and xenon (b) ageing time
To investigate the microscopic structure change, the polymer was studied by FT-IR. The FT-IR spectra are shown in Figs. 7 and 8. The absorption peak (1725, 1289–1300, 1125 cm−1 ) of ester is enhanced obviously, and the absorption peak (3450 cm−1 ) of hydroxyl (–OH) is also changed. The absorption peak (705, 745 cm−1 ) of the duplet bond is enhanced, and the absorption peak (2926, 2853 cm−1 ) of the methane(–CH2 –) is also increased. All of the changes are to prove that the esterification of the hydroxyl and anhydride has occurred, the radical polymeriza-
576
Y.Y. Wang et al.: J. Mater. Sci. Technol., 2010, 26(6), 572–576
Fig. 7 FT-IR spectra of the resin aged by xenon arc lamp for 0, 90 and 240 d
materials aged in the above conditions were 191# unsaturated polyester and its GFRPC. The experimental results revealed that some irregularities/cracks occur after artificial ageing. The exposed glass-fiber could be seen from the sample because of the ablation of the organic resin from the aged material. The tensile strength and the bending strength of the composites increased in shorter ageing period and then decreased at longer time (about ageing for 120 d). The ILSS of the composites increased after the sample was aged in the thermo-oxidative cell, while decreased after the sample was aged in the xenon arc lamp cell. The inorganic filler would influence the morphology and the mechanical performance of the material. And the main influencing factor leading to the failure of this material is UV irradiation.
Acknowledgement This work was supported by the National Natural Science Foundation of China (No. 50533060). REFERENCES
Fig. 8 FT-IR spectra of the resin aged by thermooxidative for 0, 90 and 240 d
tion of the duplet bond (post-cure reaction) and the main chain of the polymer have been lengthened, and the movement of the molecular chain becomes more difficult. So the strengths of the specimens increase. 4. Conclusion Two environmental chambers that can simulate accelerated ageing on polymers and composites were adopted: one of chambers was a thermo-oxidative ageing chamber, providing temperature and oxygen, the other was a xenon arc lamp ageing chamber, providing UV radiation, temperature and humidity. The
[1 ] D.E. Mouzakis, H. Zoga and C. Galiotis: Compos. Part B-Eng., 2006, 10, 1. [2 ] Z.Y. Xue: Shanghai Build. Mater., 2002, 6, 34. (in Chinese) [3 ] V. Oteino-Alego: in 1st Int. Conf. on Ageing Studies and Lifetime Extension of Materials, Oxford, UK, 1999, 113. [4 ] D. Leveque, A. Schieffer, A. Mavel and J.F. Maire: Compos. Sci. Technol., 2005, 65, 395. [5 ] L. Monney, C. Dubois, D. Perreux, A. Burtheret and A. Chambaudet: Polym. Degrad. Stabil., 1999, 63(2), 219. [6 ] L. Monney, R. Belali, J. Vebrel, C. Dubois and A. Chambaudet: Polym. Degrad. Stabil., 1997, 56(3), 357. [7 ] C. Dubois, L. Monney, N. Bonnet and A. Chambaudet: Compos. Part A–Appl. Sci. Manuf., 1999, 30(3), 361. [8 ] C.Y. Zhu, Q. Zhao and J.Y. Meng: Fail. Anal. Prev., 2008, 3(3), 12. (in Chinese) [9 ] Y.Y. Wang, J.Y. Meng and Q. Zhao: China Adhesives, 2008, 17(8), 34. (in Chinese) [10] Y.Z. Xiao, Q. Zhao, Y.Y. Wang and W.Q. Du: Surf. Technol., 2009, 39(1), 5. (in Chinese) [11] D.Y. Shen and R.Y. Qian: Polym. Bull., 1993, 20(4), 193.