Self-bonded natural fiber product with high hydrophobic and EMI shielding performance via magnetron sputtering Cu film

To obtain the natural fiber products with high electromagnetic interference (EMI) shielding effectiveness (SE), magnetron sputtering Cu film was firstly applied to the surface of an eco-friendly self-bonded natural fiber product (SNFP) (0.8 mm in thickness). For a better combination of Cu film onto the SNFP surface, the chemical etching using sodium chlorite was newly used to treat the SNFP for obtaining an improved surface roughness. The surface morphology and chemical compositions were studied by the scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). A rougher fiber surface was successfully obtained due to the shedding of surface lignin with decreased lignin content from 62% to 52% after the etching treatment. When sputtering Cu film for 1 h, 2 h, 3 h, and 4 h, the EMI SE values were increased to be 22 dB, 22.7 dB, 24.6 dB, and 25.5 dB, respectively, which all indicated that more than 99.4% incident signals were blocked. SEM observations revealed that an increased surface roughness could be achieved with the sputtering time increased from 1 h to 3 h. The water contact angle increased from 76.4 degrees to 105.9 degrees for 1 h sputtering, indicating that the sputtering Cu film could obviously improve the hydrophobic property of SNFP. When the sputtering time increased to be 3 h, this product exhibited the best hydrophobic performance with a maximum water contact angle of 131.5 degrees.