Effect of the surface enrichment of coupling agent on the interfacial properties and interlaminar fracture toughness of GFRPs
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摘要: 浸润剂是形成复合材料界面的关键组成，理解浸润剂特性对复合材料界面和宏观力学的影响机制，对发展高性能复合材料有着重要的科学价值。本文研究了采用两种不同浸润剂体系的高强玻璃纤维织物的表面、界面和层间断裂韧性等性能，发现其中一种浸润剂体系的纤维表面发生了更显著的偶联剂表面富集，偶联剂表面富集导致纤维/树脂之间具有较高的动态接触角，同时纤维/树脂的界面剪切强度下降。作为对比，偶联剂较少表面富集的浸润剂体系，纤维/树脂之间的动态接触角较小，同时界面剪切强度较高。两种复合材料的I型、II型层间断裂韧性均基于纤维/树脂之间的界面脱粘机制，较多偶联剂表面富集的浸润剂降低了复合材料的界面连续性，而较少偶联剂表面富集的浸润剂则与树脂形成了连续的界面相，界面粘结良好，并诱导了层间断裂时的织物拔出机制，I型和II型层间断裂韧性分别比前者高56.5%和62.2%。Abstract: Sizing agents are the key component to form the composite interface. Understanding the influence of sizing agents on the interfacial and mechanical properties of composites has important scientific value for the development of high-performance composites. The surface structures, interfacial properties and interlaminar fracture toughness of two high strength glass fiber fabric reinforced epoxy resin composites (GFRPs) with two different sizing agents were studied. The results show that one of the sizing agent has significant surface enrichment of the silane coupling agent, resulting in the increase in dynamic contact angle and the decrease in interfacial shear strength between fiber and resin. Contrarily, another sizing agent has less surface enrichment of silane coupling agent. The corresponding fiber has smaller dynamic contact angle and higher interfacial shear strength with the epoxy resin. The mode I and mode II fracture of the composites with these two sizing agents are based on the same mechanism, i.e., the interfacial debonding between resin and fiber. The interfacial continuity is reduced for the composite with the sizing agent existing higher surface enrichment of silane coupling agent. While for the composite with the sizing agent with less silane coupling agent surface enrichment, a continuous interface formed between the interphase and resin, resulting in good interfacial adhesion. The mode I and mode II interlaminar fracture toughness increased by 56.5% and 62.2% compared with these of the former composite, respectively.
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Key words:
- GFRPs /
- interface structure /
- sizing agent /
- coupling agent /
- interlaminar fracture toughness /
- contact angle
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图 1 测试试样的结构和加载方式
Figure 1. Sketch map of the structures and loading modes of the samples
PTFE—Polytetrafluoroethylene
图 2 典型的织物A (FA)或织物B (FB)的SEM图像
Figure 2. SEM image of the typical fabric A (FA) or fabric B (FB)
图 3 FA和FB纤维使用DMF去除浸润剂前后的AFM图像，其中FA去除前(a)和去除后(b)，FB去除前(c)和去除后(d)
Figure 3. AFM images of the surfaces of the original FA fiber (a), desized FA fiber (b), original FB fiber (c) and desized FB fiber (d)
图 4 复合材料截面的SEM图像：(a) FA/环氧树脂AC318；(b) FB/AC318
Figure 4. SEM images of the cross sections of composites: (a) FA/epoxy resin AC318; (b) FB/AC318
图 5 I型层间断面照片：(a) FA/AC318；(b) FB/AC318；(c) 两者的GIC载荷-位移曲线；I型层间断面的SEM图像：(d) FA/AC318；(e) FB/AC318
Figure 5. Photographs of the mode I fracture surfaces: (a) FA/AC318; (b) FB/AC318; (c) GIC load-displacement curves; SEM images of the mode I fracture surfaces: (d) FA/AC318; (e) FB/AC318
图 6 II型层间断面照片：(a) FA/AC318；(b) FB/AC318；(c) 两者的GIIC载荷-位移曲线；II型层间断面的SEM图像：(d) FA/AC318；(e) FB/AC318
Figure 6. Photographs of the mode II fracture surfaces: (a) FA/AC318; (b) FB/AC318; (c) GIIC load-displacement curves; SEM images of the mode II fracture surfaces: (d) FA/AC318; (e) FB/AC318
图 7 复合材料断面纤维-树脂界面区域的高倍SEM图像：(a) FA/AC318；(b) FB/AC318
Figure 7. High magnification SEM images of the fractured fiber/resin interfaces: (a) FA/AC318; (b) FB/AC318
表 1 原始纤维和N, N-二甲基甲酰胺(DMF)处理纤维的表面元素组成
Table 1. Surface element compositions of original fibers and N, N-dimethylformamide (DMF) treated fibers
Fiber Si/at% C/at% N/at% O/at% FA untreated 7.73 56.88 9.89 25.51 FA treated 14.48 33.04 14.56 37.93 FB untreated 4.24 71.32 1.86 22.58 FB treated 7.93 61.27 3.30 27.52 
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表 2 纤维浸入树脂中的动态接触角
Table 2. Dynamic contact angles between fiber and resin
Fiber First
advancing
angle/(º)First
receding
angle/(º)Secondary advancing angle/(º) Secondary receding angle/(º) FA 68.4±1.8 0 28.7±5.9 0 FB 55.5±0.5 0 18.9±2.5 0
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表 3 两种纤维去浸前后的微界面剪切强度
Table 3. Interfacial shear strength of the original and desized fibers
Fiber Original fiber/MPa Desized fiber/MPa FA 42.9±5.9 34.7±6.0 FB 47.1±4.7 42.6±4.3
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表 4 复合材料的层间断裂韧性
Table 4. Interlaminar fracture toughness of the composites
Composite GIC/(J·m−2) GIIC/(J·m−2) FA/AC318 550.8±57.5 1062±215 FB/AC318 862.0±133.5 1723±325
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