Effect of low-temperature plasma surface modification on the adhesive performance of CFRP
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摘要: 采用低温等离子体处理技术对碳纤维增强树脂复合材料(CFRP)表面进行处理，以氩气(Ar)、N2和O2作为等离子体激发气体，通过接触角测量仪、AFM、SEM和XPS等测试分析手段，对CFRP表面的润湿性、粗糙度、微观形貌和化学组分进行表征，并结合拉伸剪切试验测试和失效形貌分析，研究了等离子体气体类型、放电功率P和处理时间t对CFRP表面理化特性和胶接性能的影响。结果表明：Ar、N2和O2等离子体处理可以显著改善CFRP胶接性能，当P=800 W，t=20 s时，与未处理相比，CFRP胶接强度分别提高了138%、172%和253%。表面测试分析可知，Ar等离子体处理后，CFRP胶接强度的增加主要是通过提高表面清洁度和增大界面粘接表面积，试样失效模式由界面失效转变为内聚失效为主的混合失效模式。与Ar相比，N2等离子体处理后，CFRP表面生成了较多—NH2极性基团，表面活性增加，进一步提高了CFRP和胶粘剂之间界面的结合力。与以上两种气体相比，O2等离子体刻蚀CFRP表面更为剧烈，并对表层基团进行重组，形成了极性较强—COOH官能团，试样胶接强度提高效果最佳，试样失效模式由界面失效转变为基板失效。此外，当活性粒子的密度和能量过高时，较大的等离子体刻蚀孔隙，在一定程度上会降低胶接性能。Abstract: Ar, N2 and O2 were used as low-temperature plasma excitation gases to treat the surface of carbon fiber reinforced plastics (CFRP). The effects of plasma gas, discharge power and treatment time on the physicochemical properties, including wettability, roughness, microscopic morphology and chemical components of CFRP surface, were characterized by contact angle measurement, AFM, SEM and XPS. The adhesive joint property was investigated through tensile shear experiment and failure morphology analysis. Compared with untreated, the tensile shear strength of CFRP adhesive joints after Ar, N2 and O2 plasma treatment can significantly improve the bonding performance of CFRP, and when the plasma discharge power is 800 W and treatment time is 20 s, the adhesive joint strength increases by 138%, 172% and 253%, respectively. The surface test analysis shows that the improvement of CFRP adhesive strength after argon plasma treatment is mainly induced by improving the surface cleanliness and increasing the surface area for interfacial adhesive, and the failure modes of samples changes from interfacial failure to mixed failure mode with cohesive failure as the main mode. Compared with Ar, a greater number of polar chemical groups (—NH2) are generated on the CFRP surface after N2 plasma treatment, which increase the surface activity and further improve the interfacial adhesive strength between CFRP and adhesive. Compared with the above two gases, O2 plasma etch the CFRP surface more vigorously, as well as reorganize the surface chemical groups, forming a more polar —COOH functional group, so that the specimen adhesive strength is improved most effectively, and the specimen failure mode changes from interface failure to substrate failure. In addition, under the excessively high density and energy of the active particles, the adhesive performance will be reduced to some extent with the expansion of the pores by plasma etching.
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Key words:
- CFRP /
- low temperature plasma /
- adhesive property /
- surface modification /
- wettability
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图 1 碳纤维增强树脂复合材料(CFRP)层合板制作工艺
Figure 1. Production process of carbon fiber reinforced plastics (CFRP) laminnates
图 2 低压等离子体处理原理示意图
Figure 2. Schematic diagram of low pressure plasma processing principle
MF—Middle frequency; RF—Radio frequency
图 6 不同等离子体处理条件下CFRP试样的单搭接剪切强度
Figure 6. Lap-shear strength of CFRP samples under different plasma treatment conditions
图 7 (a) 不同气体等离子体处理后CFRP试样的拉伸断裂形貌(放电功率P=800 W，处理时间t=20 s)；(b) 不同P和t下O2等离子体处理后CFRP的拉伸断裂形貌
Figure 7. (a) Effect of plasma treatment with different gases on the tensile fracture morphologies of the CFRP samples (Discharge power P=800 W, treatment time t=20 s); (b) Tensile fracture morphologies of the CFRP samples under O2 plasma treatment with different P and t
图 8 不同等离子体处理条件下CFRP试样的水接触角
Figure 8. Water contact angle of CFRP samples under different plasma treatment conditions
图 9 不同气体等离子体处理后CFRP试样的水接触角( P =800 W， t =20 s)：(a)未处理；(b) Ar；(c) N2；(d) O2
Figure 9. Effect of plasma treatment with different gases on the surface water contact angle of CFRP samples (P=800 W, t=20 s): (a) Untreated; (b) Ar; (c) N2; (d) O2
图 10 不同气体等离子体处理后CFRP试样表面的2D和3D AFM图像(P=800 W，t=20 s)：(a)未处理；(b) Ar；(c) N2；(d) O2
Figure 10. 2D and 3D AFM images of CFRP samples surface treated under plasma treatment with different gases (P =800 W, t =20 s): (a) Untreated; (b) Ar; (c) N2; (d) O2
图 11 不同放电功率和处理时间下O2等离子体处理后CFRP样品表面的SEM图像：(a)未处理；(b) P=200 W, t=30 s；(c) P=800 W, t=20 s；(d) P=800 W, t=30 s
Figure 11. SEM images of CFRP samples surface treated under O2 plasma treatment with different discharge powers and processing time: (a) Untreated; (b) P=200 W, t=30 s; (c) P=800 W, t=20 s; (d) P=800 W, t=30 s
图 12 不同气体等离子体处理后CFRP试样表面XPS图谱(P=800 W，t=20 s)
Figure 12. XPS spectra of CFRP samples by plasma treatment with different gases (P=800 W, t=20 s)
图 13 不同气体等离子体处理后CFRP试样表面XPS光谱(P=800 W，t=20 s)：(a) C1s；(b) O1s；(c) N1s；(d) Si2p
Figure 13. Narrow-scan XPS spectra of CFRP samples surface treated under plasma treatment with different gases (P=800 W, t=20 s): (a) C1s; (b) O1s; (c) N1s; (d) Si2p
表 1 CFRP复合材料主要性能参数
Table 1. Main performance parameters of CFRP composites
Mechanical property Value E11/GPa 121 E22/GPa 8.6 E33/GPa 8.6 G12/MPa 3450 G13/MPa 3450 G23/MPa 2800 Poisson’s ratio 0.3 Density/(kg·m−3) 1467 Notes: E—Young’s modulus; i (i=1, 2, 3)—Direction; G—Shear modulus. 
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表 2 Araldite 2015主要力学性能参数
Table 2. Main mechanical property parameters of the Araldite 2015
Araldite 2015 Value Tensile strength/MPa 21.63 Shear strength/MPa 17.90 Elongation/% 0.33
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表 3 低压等离子体处理工艺参数
Table 3. Process parameters of low pressure plasma treatment
Item Nominal parameter value Plasma frequency/MHz 13.56 Power input/W 0-1000 Process pressure/Pa 100 Speed/(mL·min−1) 150
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表 4 不同气体等离子体处理后CFRP试样表面化学元素组成及其所占比例(P=800 W，t=20 s)
Table 4. Surface chemical composition and proportion of CFRP samples under plasma treatment with different gases (P=800 W, t=20 s)
Surface treatment C/at% O/at% N/at% Si/at% O/C/% N/C/% Untreated 74.52 17.85 3.87 3.76 23.95 5.19 Ar 72.89 21.42 3.46 2.23 29.39 4.75 N2 66.54 19.61 11.48 2.37 29.47 17.25 O2 62.47 30.89 3.17 3.47 49.45 5.07
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表 5 不同气体等离子体处理后CFRP试样XPS的C1s、O1s、N1s和Si2p分峰表面基团相对含量拟合数据(P=800 W，t=20 s)
Table 5. C1s, O1s, N1s and Si2p peak-differentiating and imitating data of relative content of surface groups for XPS of CFRP samples surface under plasma treatment with different gases (P=800 W, t=20 s)
at% Element Surface group Surface treatment Untreated Ar N2 O2 C1s C—C/C—H 71.92 70.95 68.01 60.36 C—O/C—N 23.71 25.49 27.96 33.37 C=O 4.37 3.56 4.03 6.27 O1s C—O 79.57 86.13 81.28 61.76 C=O 20.43 13.87 18.72 25.96 O=C—O 0.00 0.00 0.00 12.28 N1s C—NH2 100.00 100.00 100.00 100.00 Si2p Si—C 69.21 66.32 67.17 45.47 Si—O 30.79 33.68 32.83 54.53
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