Wuhan university Journal of Natural Sciences 2014.Vol.19No.1.034-040 Article|D1007-1202(2014)1-003407 DOl10.1007/s11859-014-0975-7 Interface Enhancement of dass Fiber/Unsaturated Polyester Resin Composites with Nano-silica Treated Using Silane Coupling Agent o LUo Weicai, WANG Xiao 0 Introduction HUANG Ronghua, FANG Pengfei'T 1. School of Physics and Technology, Wuhan University Glass fiber reinforced unsaturated polyester resin Wuhan 430072 Hubei China (UPR)composite materials have become the alternatives 2. School of Power and Mechanical Engineering, Wuhan of conventional structural materials, such as wood and University, Wuhan 430072, Hubei, China steel in some applications, because of its good mechani o Wuhan University and Springer-Verlag Berlin Heidelberg 2014 cal properties. Mechanical properties of fiber-reinforced UPR composites depend on the properties of the con- Abstract: Nano-silica treated with different kinds of coupling stituent materials. the nature of the interfacial bonds. the agent(KH550, A-143, A-151)was used to modify the surface mechanisms of load transfer at the interphase, and the condition of glass fiber, and then, the modified glass fiber/ unsatu- adhesion strength between the fiber and the matrix 2) rated polyester resin(UPR)composites materials were prepared. The goal of this paper is to improve the adhesion Scanning electron microscopy(SEM), dynamic mechanical analy- strength between the fiber and the matrix of the compos- sis( DMA), and impact test were used to characterize the composite materials' structure and properties. The morphology of composite materials shows that the adhesion between nano-silica and glass Adhesion strength between the fiber and the matrix fiber is improved when silane coupling agent is added in. The can be attributed to some combination of the following DMA and impact test results show that silane coupling agent (es- phenomena: mechanical adhesion, adsorption and wet pecially KH550 and A-151)could effectively improve the com- ting, electrostatic attraction, and chemical bonding posite's mechanical properties. When the dose of KH550 was 0. 1% Then, several modification techniques are developed for (m m), the storage modulus and impact strength reached the improving the adhesion strength between the fiber and maximum Key words: silane coupling agent; unsaturated polyester resin the matrix. Surface treatment of reinforcement is a UPR); glass fiber; nano-silica common method to improve adhesion properties by in CLC number: TQ 323 creasing electrostatic interactions or facilitating chemical bonding between the reinforcement material and the ma- Received date: 2012-12-26 trix+ Silane coupling agents, which are generally Foundation item: Supported by the National Natural Science Foundation of considered as adhesion promotors between fillers and the of China(J1210061) matrix, are widely used in the surface treatment of the Biography: LUO Weicai, male, Master candidate, research direction: polymer materiale-Mail:Iwc210@126.com reinforcement process Towhomcorrespondenceshouldbeaddressed.E-mail:fangpf(@whu.edu.cn Nanometer-sized materials as a reinforcement also
2014, Vol.19 No.1, 034-040 Article ID 1007-1202(2014)01-0034-07 DOI 10.1007/s11859-014-0975-7 Interface Enhancement of Glass Fiber/Unsaturated Polyester Resin Composites with Nano-Silica Treated Using Silane Coupling Agent □ LUO Weicai1 , WANG Xiao1 , HUANG Ronghua2 , FANG Pengfei1† 1. School of Physics and Technology, Wuhan University, Wuhan 430072, Hubei, China; 2. School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, Hubei, China © Wuhan University and Springer-Verlag Berlin Heidelberg 2014 Abstract: Nano-silica treated with different kinds of coupling agent (KH550, A-143, A-151) was used to modify the surface condition of glass fiber, and then, the modified glass fiber/ unsaturated polyester resin (UPR) composites materials were prepared. Scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and impact test were used to characterize the composite materials’ structure and properties. The morphology of composite materials shows that the adhesion between nano-silica and glass fiber is improved when silane coupling agent is added in. The DMA and impact test results show that silane coupling agent (especially KH550 and A-151) could effectively improve the composite’s mechanical properties. When the dose of KH550 was 0.1% (m︰m), the storage modulus and impact strength reached the maximum. Key words: silane coupling agent; unsaturated polyester resin (UPR); glass fiber; nano-silica CLC number: TQ 323 Received date: 2012-12-26 Foundation item: Supported by the National Natural Science Foundation of of China (J1210061) Biography: LUO Weicai, male, Master candidate, research direction: polymer material. E-mail: lwc210@126.com † To whom correspondence should be addressed. E-mail: fangpf@whu.edu.cn 0 Introduction Glass fiber reinforced unsaturated polyester resin (UPR) composite materials have become the alternatives of conventional structural materials, such as wood and steel in some applications, because of its good mechanical properties. Mechanical properties of fiber-reinforced UPR composites depend on the properties of the constituent materials, the nature of the interfacial bonds, the mechanisms of load transfer at the interphase，and the adhesion strength between the fiber and the matrix[1,2]. The goal of this paper is to improve the adhesion strength between the fiber and the matrix of the composites. Adhesion strength between the fiber and the matrix can be attributed to some combination of the following phenomena: mechanical adhesion, adsorption and wetting, electrostatic attraction, and chemical bonding[3]. Then, several modification techniques are developed for improving the adhesion strength between the fiber and the matrix. Surface treatment of reinforcement is a common method to improve adhesion properties by increasing electrostatic interactions or facilitating chemical bonding between the reinforcement material and the matrix[4-10]. Silane coupling agents, which are generally considered as adhesion promotors between fillers and the matrix, are widely used in the surface treatment of the reinforcement process. Nanometer-sized materials as a reinforcement also
LUO Weicai et al; Interface Enhancement of Glass Fiber/Unsaturated Polyester improved the adhesion between the fiber and the matrix. fiber was not pretreated Wang et al found out that the glass fiber/vinyl ester composites containing multiwalled carbon nanotubes (MWCNTS) showed better bonding between the gl NH,-CH,-CH,-CH,-Si-OC,H, KH550 fiber and the resin matrix. Many researchers ana- lyzed the effect of the nano-silica on the performance of le composites. However, they did not discuss the influ- CHA ence of the nano-silica on the interface cohesiveness of Cl- CH,-CH2-CH,- Si -OCH, A-143 the composites. Although Zheng et al5 prepared the OCH SiO2-glass-fiber epoxy composites to study the influence of nano-silica on the mechanical properties, they did not consider the effect of the addition of coupling agents CH,=CH -Si-OC,H,A-151 In this study, different kinds and amount of coupling agents were used to modify nano-silica. Glass fiber wa DC,H. modified by the same amount of the modified nano-silica. Fig. 1 Molecular formula of 7-aminopropyl-triethoxysilane Then, the modified glass fiber/UPR composite material (KH550), Vinyl-triethoxysilane(A-151), and x-chloro-propyl tri- was prepared By comparing composite materials'mac- methoxy silane(A-143) roscopic properties and microstructure before and after Table 1 Dose of the reinforcement the addition of the nano-silica treated with coupling agents, we knew the relationship between the kind and nd Sample Coupling agent Dose of reinforcement/% control dose of coupling agent and composite materials'per KH550 0.10 KH550 KH550 1 Experimental A-143 6 A-143 1.1 Materials A-143 8 Unsaturated polyester resin(A407-901)was pro- vided by the Nanjing Jinling DSM Resins Co, Ltd. Glass fiber(the eCr 469L-2400) was purchased from Chong qing Polycomposites International Co, Ltd. The 1.3 Sample characterization nano-silica was purchased from Hubei wuhan University 1)Scanning electron microscopy(SEM)analysis Silicone New Material Co, Ltd. Methyl ethyl ketone The morphology of samples with cryogenically fractured peroxide and cobalt naphthenate were used in this ex- surface under liquid nitrogen was examined with FEI periment. The coupling agents used in this experiment Sirion-FEG were ?-aminopropyl-triethoxysilane (KH550), Vi- 2)The dynamic mechanical test. NETZSCH DMA l-triethoxysilane (A-151), and 7-chloro-propyl 242C was used for dynamic mechanical analysis. The methoxy silane (A-143). The molecular formula operation condition: heating rate 2 C/ min, the vibration shown in fig. 1 frequency 1Hz, and scan range from25℃tol80℃ 1.2 Sample Preparation 3)Impact test. The tests were performed according Nano-silica was pretreated with different kinds and to GB2571-81 at room temperature using with an impact amount of silane coupling agent. Then, the glass fiber tester(MZ-2054)made by Jiangdu Pearl Test Machinery was modified by means of the pretreated nano-silica and Factory then dried and pruned. A certain amount of A407-901 methyl ethyl ketone peroxide, and cobalt naphthenate 2 Results and Discussions were mixed with the modified glass fiber into the mold The mold was kept at 100 C for I h to prepare the sam- 2.1 The Morphology of Glass Fiber before and ples. Coupling agents' type and content relative to glass after Modification fiber (% m: m) are shown in Table 1. The sample of During the formation of the interface layer, the fiber No I was the composite materials, for which the glass and the matrix usually experience the process of contact
LUO Weicai et al: Interface Enhancement of Glass Fiber/Unsaturated Polyester … 35 improved the adhesion between the fiber and the matrix. Wang et al[11] found out that the glass fiber/vinyl ester composites containing multiwalled carbon nanotubes (MWCNTs) showed better bonding between the glass fiber and the resin matrix. Many researchers[12-14] analyzed the effect of the nano-silica on the performance of the composites. However, they did not discuss the influence of the nano-silica on the interface cohesiveness of the composites. Although Zheng et al[15] prepared the SiO2-glass-fiber epoxy composites to study the influence of nano-silica on the mechanical properties, they did not consider the effect of the addition of coupling agents. In this study, different kinds and amount of coupling agents were used to modify nano-silica. Glass fiber was modified by the same amount of the modified nano-silica. Then, the modified glass fiber/UPR composite material was prepared. By comparing composite materials’ macroscopic properties and microstructure before and after the addition of the nano-silica treated with coupling agents, we knew the relationship between the kind and dose of coupling agent and composite materials’ performance. 1 Experimental 1.1 Materials Unsaturated polyester resin (A407-901) was provided by the Nanjing Jinling DSM Resins Co., Ltd. Glass fiber (the ECR 469L-2400) was purchased from Chongqing Polycomposites International Co., Ltd. The nano-silica was purchased from Hubei Wuhan University Silicone New Material Co., Ltd. Methyl ethyl ketone peroxide and cobalt naphthenate were used in this experiment. The coupling agents used in this experiment were γ-aminopropyl-triethoxysilane (KH550), Vinyl-triethoxysilane (A-151), and γ-chloro-propyl trimethoxy silane (A-143). The molecular formula is shown in Fig.1. 1.2 Sample Preparation Nano-silica was pretreated with different kinds and amount of siliane coupling agent. Then, the glass fiber was modified by means of the pretreated nano-silica and then dried and pruned. A certain amount of A407-901, methyl ethyl ketone peroxide, and cobalt naphthenate were mixed with the modified glass fiber into the mold. The mold was kept at 100 ℃ for 1 h to prepare the samples. Coupling agents’ type and content relative to glass fiber (%, m︰m) are shown in Table 1. The sample of No.1 was the composite materials, for which the glass fiber was not pretreated. Fig. 1 Molecular formula of γ-aminopropyl-triethoxysilane (KH550), Vinyl-triethoxysilane (A-151), and γ-chloro-propyl trimethoxy silane (A-143) Table 1 Dose of the reinforcement Sample Coupling agent Dose of reinforcement/% 1 control — 2 KH550 0.10 3 KH550 0.25 4 KH550 0.50 5 A-143 0.10 6 A-143 0.25 7 A-143 0.50 8 A-151 0.10 9 A-151 0.25 10 A-151 0.50 1.3 Sample Characterization 1) Scanning electron microscopy (SEM) analysis. The morphology of samples with cryogenically fractured surface under liquid nitrogen was examined with FEI Sirion-FEG. 2) The dynamic mechanical test. NETZSCH DMA 242C was used for dynamic mechanical analysis. The operation condition: heating rate 2 ℃/ min, the vibration frequency 1Hz, and scan range from 25 ℃ to 180 ℃. 3) Impact test. The tests were performed according to GB2571-81 at room temperature using with an impact tester (MZ-2054) made by Jiangdu Pearl Test Machinery Factory. 2 Results and Discussions 2.1 The Morphology of Glass Fiber before and after Modification During the formation of the interface layer, the fiber and the matrix usually experience the process of contact
Wuhan University Journal of Natural Sciences 2014, Vol 19 No. 1 and wetting. The wetting performance of the interface glass fiber surface is smooth without the nano-silica depends on the size of the area where the fiber and the treated with coupling agent. There are a lot of attach- matrix attract from each other!6]. The fiber always at- ments when the glass fiber was pretreated with tracts these components, which reduce their surface en- nano-silica and coupling agent( Fig. 2(b)-(d). The results ergy, and the maximum is preferential show that the adhesion between the fiber and the The sem photographs for glass fiber surface mor- nano-silica is improved when the nano-silica is pre phology are shown in Fig. 2. Figure 2(a)shows that the treated with silane coupling agent Fig 2 SEM images for glass fiber surface morphology (a) without nano-silica and coupling agent (2 000x);(b) glass fiber/nano-silica treated with KH550(500X); (c) glassfiber/nano-silica treated with A-143(500x )(d) glass fiber/nano-silica treated with A-151(5 000x) 2.2 Effect of the Nano-silica and Coupling 1 tan S A Agent on the Composites Properties It has been found that the storage modulus (E) of tan s and tan 8 are the loss factors for composite and the composite increases with the addition of nano-silica matrix, respectively, v is the volume fraction of fiber treated with coupling agents( Figs. 3 and 4). Compared The smaller the value A, the stronger the interface cohe- with the composites without the addition of the nano- siveness Ashida et all proposed the following formula silica and the coupling agent, the peak of the composites loss factor(tan d)value is shifting to higher temperature (tan )=(tan8)m-alt Interface cohesiveness(A) is according to Luis (tan Smax)e and(tan Smax )m are the maximum values of Ibrarra's formula tan8 for the composite and the matrix, respectively 14000 15000 Sample 5 b)1600 ample 2 49000F Sample 4 8000 Sample 6 6000 3000 4000 Sample I Sample I 2 000 Sample 1 4060801001201401601 255075100125150175 255075100125150175 T/C Fig 3 Relationship between the composite storage modulus(E) and the dose of the silane coupling agent (a)KH550,(b)A-143,(c)A-l5l
36 Wuhan University Journal of Natural Sciences 2014, Vol.19 No.1 and wetting. The wetting performance of the interface depends on the size of the area where the fiber and the matrix attract from each other[16]. The fiber always attracts these components, which reduce their surface energy, and the maximum is preferential. The SEM photographs for glass fiber surface morphology are shown in Fig. 2. Figure 2(a) shows that the glass fiber surface is smooth without the nano-silica treated with coupling agent. There are a lot of attachments when the glass fiber was pretreated with nano-silica and coupling agent (Fig.2(b)-(d)). The results show that the adhesion between the fiber and the nano-silica is improved when the nano-silica is pretreated with silane coupling agent. Fig. 2 SEM images for glass fiber surface morphology (a) without nano-silica and coupling agent (2 000 × ); (b) glass fiber/nano-silica treated with KH550 (500 × ); (c) glassfiber/nano-silica treated with A-143 (500 × ); (d) glass fiber/nano-silica treated with A-151 (5 000 × ) 2.2 Effect of the Nano-Silica and Coupling Agent on the Composites Properties It has been found that the storage modulus ( ) E′ of the composite increases with the addition of nano-silica treated with coupling agents (Figs. 3 and 4). Compared with the composites without the addition of the nanosilica and the coupling agent, the peak of the composite’s loss factor (tan δ) value is shifting to higher temperature. Interface cohesiveness (A) is according to Luis Ibrarra’s formula[17]: c f m 1 tan 1 1 tan A V δ δ =× − − tan c δ and tan m δ are the loss factors for composite and matrix, respectively, Vf is the volume fraction of fiber. The smaller the value A, the stronger the interface cohesiveness. Ashida et al [18] proposed the following formula: f max c max m (tan ) (tan ) δ δα = − V (tan max δ )c and (tan max δ )m are the maximum values of tanδ for the composite and the matrix, respectively. Fig. 3 Relationship between the composite storage modulus ( ) E′ and the dose of the silane coupling agent (a) KH550; (b) A-143; (c) A-151
LUO Weicai et al; Interface Enhancement of Glass Fiber/Unsaturated Polyester 0.36 Sample I 0.30 0.30 e2g024 0. 18F Sample 0.18 Sample 7 0 55075100125150175 255075100125150175 55075100125150175 Fig4 Relationship between the loss factor(tano) and the dose of the silane coupling agent (a)KH550,(b)A-143;(c)A-l5l The parameter a is the characterization of the interfa- Table 2 Glass fiber surface treatment methods on the cial adhesion. It reveals that the relationship between the material properties of the interface composite mechanical internal friction peak(tan dmas) e tanδ the pure basic internal friction peak(tan Smax )m, and the 0.40222 0.79 -0.136 interfacial bond strength. The greater the value a, the 0.16875 better the adhesion capacity of the interface. Table 2 234567 0.17044 0.24 0.173 0.18233 0.157 shows that the tan Smax value of the glass fiber decrease 0.18046 with the addition of the treatment (nano-silica treated 0.1909 0.145 with the coupling agent ) It indicates that the compatibil- 0.1810 0.159 ity and the adhesion strength between the matrix and 0.1804 -020 0.159 glass fiber increase with the addition of the assistant The three kinds of silane coupling agent have a bet 0.17144 er modification effect on improving the performance of all have good mechanical properties(as shown in Fig. 5) the glass fiber/UPR composites. The composite materials The storage modulus (E) of the composite is E20 19.5 17.5 317.5 17.0 00.10.20.3040.5 00.10.20.3040.5 00.10.20.3040.5 Dose of reinforcement /% Dose of reinforcement /% Dose of reinforcement /% Fig 5 Relationship between the composite impact strength and the dose of the silane coupling agent (a)KHs50,(b)A-143,(c)A-l5l about 16 000 MPa with the 0. 1%(m: m)KH550 at highest storage modulus of composite is 13 000 MPa(as room temperature, while the glass-transition temperature shown in Fig 3(b)). The maximum impact strength is (Tg)also reaches up to be 140 C. When the dose of the 19.4 J/cm(as shown in Fig. 5(b). Moreover, the impact KH550 increases to 0. 25%(m: m)and 0.5%(m: m), strength of the composite at the dose of 0. 25%(m: m)is the peak of the loss factor(tan o)value has a little change, the same as the nontreated one Meanwhile, E and TR value decrease significantly(as The storage modulus (E of the composite treated shown in Figs. 3-5). Fig. 5(a)shows that the impact with 0.5%(m : m)A-151 reaches 16 000 MPa at room strength of the composites is higher than that of the temperature, and Tg value also reaches up to 137 C(as composite without the treatment. The impact strength is shown in Fig 4(c). Figure 5(c)shows that the highest best when the dose of KH550 is 0. 1%(m:m). This re- impact strength is 20.2 J/cm", which increases by cult is as same as the dma results 17.44%, as compared with the nontreated one When the glass fiber is treated with A-143, the It has been reported that there is no relationshi
LUO Weicai et al: Interface Enhancement of Glass Fiber/Unsaturated Polyester … 37 Fig. 4 Relationship between the loss factor (tanδ) and the dose of the silane coupling agent (a) KH550; (b) A-143; (c) A-151 The parameter α is the characterization of the interfacial adhesion. It reveals that the relationship between the composite mechanical internal friction peak (tan max δ )c , the pure basic internal friction peak (tan max δ )m, and the interfacial bond strength. The greater the value α , the better the adhesion capacity of the interface. Table 2 shows that the tan max δ value of the glass fiber decrease with the addition of the treatment (nano-silica treated with the coupling agent). It indicates that the compatibility and the adhesion strength between the matrix and glass fiber increase with the addition of the assistant. The three kinds of silane coupling agent have a better modification effect on improving the performance of the glass fiber/UPR composites. The composite materials Table 2 Glass fiber surface treatment methods on the material properties of the interface Sample tan δ max A α 1 0.402 22 0.79 −0.136 2 0.168 75 −0.25 0.175 3 0.170 44 −0.24 0.173 4 0.182 33 −0.19 0.157 5 0.180 46 −0.20 0.159 6 0.190 97 −0.15 0.145 7 0.181 01 −0.19 0.159 8 0.180 43 −0.20 0.159 9 0.191 38 −0.15 0.145 10 0.171 44 −0.24 0.171 all have good mechanical properties (as shown in Fig. 5). The storage modulus ( ) E′ of the composite is Fig. 5 Relationship between the composite impact strength and the dose of the silane coupling agent (a) KH550; (b) A-143; (c) A-151 about 16 000 MPa with the 0.1% (m︰m) KH550 at room temperature, while the glass-transition temperature (Tg) also reaches up to be 140 ℃. When the dose of the KH550 increases to 0.25% (m︰m) and 0.5% (m︰m), the peak of the loss factor (tan δ) value has a little change; Meanwhile, E′ and Tg value decrease significantly (as shown in Figs. 3-5). Fig. 5(a) shows that the impact strength of the composites is higher than that of the composite without the treatment. The impact strength is best when the dose of KH550 is 0.1% (m︰m). This result is as same as the DMA results. When the glass fiber is treated with A-143, the highest storage modulus of composite is 13 000 MPa (as shown in Fig.3(b)). The maximum impact strength is 19.4 J/cm2 (as shown in Fig.5(b)). Moreover, the impact strength of the composite at the dose of 0.25% (m︰m) is the same as the nontreated one. The storage modulus ( ) E′ of the composite treated with 0.5% (m︰m) A-151 reaches 16 000 MPa at room temperature, and Tg value also reaches up to 137 ℃ (as shown in Fig.4(c)). Figure 5(c) shows that the highest impact strength is 20.2 J/cm2 , which increases by 17.44%, as compared with the nontreated one. It has been reported that there is no relationship
Wuhan University Journal of Natural Sciences 2014, Vol 19 No. 1 between the effect of the coupling agent on the polyester growth. The kinetic energy and strain potential energy composite and the polarity of the organic functional concentrated at the crack tip is converted into the non- groups of the coupling agent!' The glass fiber treated continuity boundary deformation energy with chlorine propyl silane coupling agent has a very 2.3 Glass Fiber/Unsaturated Polyester Resin high surface energy. Therefore, the glass fiber can easily Composites Fracture Morphology and Analysis be infiltrated by resin solution. Vinyl in the vinyl silane Through the observation of the SEM photograph of coupling agent can react with the unsaturated bond of the the fracture surface of the samples(as shown in Fig. 6) UPR. The amino in the Kh550 can react with the stem the effect of the surface treatment on the adhesion be grafting anhydride functional groups and then enhance tween glass fiber and the matrix and the relationship be- the interface bonding strength, thus further improving the tween the treatment and the performance is discussed performance of the composite. However, the three cou- Figure 6(a)shows that the fracture surface of the pling agent can improve the dispersion effect glass fiber is smooth when the glass fiber is not pretreated nano-silica. For this phenomenon, there are two reasons: with silane coupling agent and nano-silica. SEM photo- 1)With the addition of coupling agent, the surface en- graphs of the fracture surface of the glass fiber treated ergy of nano-silica is lowered, the reunion of nano-silica with nano-silica(treated with 0.25%(m: m)KH550) in the matrix is decreased, and nano-silica can disperse /unsaturated polyester composites are shown in Fig. 6(b) easily. The surface energy of the polymer is low. Low It can be seen from the figure that the surface is not surface energy of nano-silica can be more easily com- smooth and wrapped by the colloid layer. It explains that patible with polymer matrix. 2)The surface of nano-sil- the combination of the fiber and the matrix is good. When ica treated with the coupling agent can form a soft inter- the glass fiber is treated with A-143 and A-151(as shown facial layer. When the materials are subjected to stress, in Fig. 6(c)and(d), the phenomenon of the glass fiber the layer can play a role as an inhibitor against crack being pulled out do not exist ow3o"6磁8 Fig 6 SEM images of the fracture surface of the samples a)the untreated glass fiber composites(1 000x )(b)glass fiber treated with nano-silica /0. 25%(m: m)KH550 (2 000X )(c)glass fiber treated th nano-silica /0.25%(mm)A143(1 000x )(d)glass fiber treated with nano-silica/0. 25%(m: m)A151 (500X)
38 Wuhan University Journal of Natural Sciences 2014, Vol.19 No.1 between the effect of the coupling agent on the polyester composite and the polarity of the organic functional groups of the coupling agent[9]. The glass fiber treated with chlorine propyl silane coupling agent has a very high surface energy. Therefore, the glass fiber can easily be infiltrated by resin solution. Vinyl in the vinyl silane coupling agent can react with the unsaturated bond of the UPR. The amino in the KH550 can react with the stem grafting anhydride functional groups and then enhance the interface bonding strength, thus further improving the performance of the composite. However, the three coupling agent can improve the dispersion effect of nano-silica. For this phenomenon, there are two reasons: 1) With the addition of coupling agent, the surface energy of nano-silica is lowered, the reunion of nano-silica in the matrix is decreased, and nano-silica can disperse easily. The surface energy of the polymer is low. Low surface energy of nano-silica can be more easily compatible with polymer matrix. 2) The surface of nano-silica treated with the coupling agent can form a soft interfacial layer. When the materials are subjected to stress, the layer can play a role as an inhibitor against crack growth. The kinetic energy and strain potential energy concentrated at the crack tip is converted into the noncontinuity boundary deformation energy. 2.3 Glass Fiber/Unsaturated Polyester Resin Composites Fracture Morphology and Analysis Through the observation of the SEM photograph of the fracture surface of the samples (as shown in Fig. 6), the effect of the surface treatment on the adhesion between glass fiber and the matrix and the relationship between the treatment and the performance is discussed. Figure 6(a) shows that the fracture surface of the glass fiber is smooth when the glass fiber is not pretreated with silane coupling agent and nano-silica. SEM photographs of the fracture surface of the glass fiber treated with nano-silica (treated with 0.25% (m︰m) KH550) /unsaturated polyester composites are shown in Fig.6 (b). It can be seen from the figure that the surface is not smooth and wrapped by the colloid layer. It explains that the combination of the fiber and the matrix is good. When the glass fiber is treated with A-143 and A-151 (as shown in Fig.6 (c) and (d)), the phenomenon of the glass fiber being pulled out do not exist. Fig. 6 SEM images of the fracture surface of the samples (a) the untreated glass fiber composites (1 000 × ); (b) glass fiber treated with nano-silica /0.25%(m:m) KH550 (2 000 × ); (c) glass fiber treated with nano-silica /0.25% (m:m) A143 (1 000 × ); (d) glass fiber treated with nano-silica/0.25% (m:m) A151 (500 × )