碳纤维/木质素基酚醛树脂复合材料的电磁屏蔽性能研究

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目的：为了扩大木质素应用领域，本文采用模压方法制出碳纤维/木质素基酚醛树脂复合材料，并对复合材料的力学性能，体积电阻率，电磁屏蔽效应进行详细研究，获得结果期望为木质素在电磁屏蔽领域提供有利借鉴。方法：本文以木质素基酚醛树脂(木质素质量分数为10 wt%)为基体树脂，填充20 wt%，30 wt%，40 wt%，50 wt%质量分数的碳纤维，混合均匀后使用平板硫化机制备不同碳纤维含量的碳纤维/木质素基酚醛树脂复合材料标样。采用微机控制电子万能试验机，金属四探头电阻率方阻测试仪和电磁屏蔽效能测试仪对复合材料进行表征。结果：碳纤维/木质素基酚醛树脂复合材料的力学性能随着碳纤维含量增加而增加，并在40 wt%达到最大值，此后力学性能开始下降。复合材料的体积电阻率则随着碳纤维含量增加而逐渐下降，复合材料的电磁屏蔽效能则随着碳纤维含量增加而增加，并在40 wt%碳纤维时，导电性和电磁屏蔽效能达到最大值。此时复合材料弯曲模量高达9203 MPa，弯曲强度达到82 MPa，体积电阻率达到0.003 Ω∙cm，电磁屏蔽效能最高能达到75 dB (30 MHz~1500 MHz)。结论：碳纤维/木质素基酚醛树脂复合材料的力学性能，体积电阻率，电磁屏蔽效应都与碳纤维的含量有关。当碳纤维含量达到40 wt%时，碳纤维分散在木质素基酚醛树脂中，连接不同木质素基酚醛树脂分子，形成立体交联网络结构，从而增强复合材料的力学性能和导电性能。但是过多的碳纤维填充量会降低体系的润湿性，带来许多物理缺陷从而降低力学性能。当体系的碳纤维填充量为 40 wt%时，碳纤维形成较完整的导电网络，可强烈反射电磁波并且消耗电磁能量，提高了复合材料的电磁屏蔽效能。 Objective: In order to improve the application fields of lignin, carbon fiber (CF)/lignin-based phe-nolic resin composites were prepared by lignin-modified phenolic resin and thermosetting tech-nology. The effects of CF content on the resistivity, mechanical properties and electromagnetic shielding effectiveness (EMI SE) of composites were studied in detail. In addition, these results would provide a useful reference for lignin in the field of electromagnetic shielding. Method: In the experiment, 20 wt%, 30 wt%, 40 wt% and 50 wt% of CF were filled with lignin-based phenolic resin (10 wt% of lignin), and the system was mixed and homogenized using a flat vulcanizer CF mass fraction of CF/lignin based phenolic resin composite material samples, and the composite materials were characterized by microcomputer control electronic universal testing machine, metal four probe resistivity square resistance tester and electromagnetic shielding performance tester. Results: The results showed that the mechanical properties of the composites increased with the increase of CF content, and reached the maximum value at 40 wt% CF. But the volume resistivity decreased with the increase of the CF content. The EMI SE also increased as CF content increased and got to the maximum value at 40 wt% CF. It can be seen that the composite with 40 wt% CF had excellent physical properties: Electrical resistivity was 0.003 Ω∙cm, flexural modulus was up to 9202.93 MPa, and the EMI SE reached 75 dB. Conclusion: The mechanical properties, volume resistivity and EMI SE of CF/lignin-based phenolic composites are related to the mass fraction of CF. 40% CF, acting as physical crosslinking point, dispersed in the lignin-based phenolic resin, which connected different lignin-based phenolic resin molecules to form a cross-linked network structure, thereby enhancing the mechanical properties of composite materials. However, excessive CF leads to the poor wettability, bringing a lot of physical defects and thus reduces the mechanical properties. When CF is 40%, the CF web with good conductivity is filled into the lignin-based phenolic resin so that the probability of forming the conductive network between the fillers is greatly increased. The complete network structure can strongly reflect the electromagnetic wave and consume electromagnetic energy and reduce its resistivity and improve the shielding effectiveness.