## 3 Results and Discussion
### Color Fastness to Rubbing  
Color fastness to rubbing refers to the ability of a yarn-dyed fabric to maintain its original color under the influence of an external force. The test method is mainly to take a pure white fabric (dry or wet) and tie it to the friction head, then carry out the reciprocating friction movement on the fabric to be tested, and then finally take off the white fabric, compare the color which is stained on the upper surface with the standard color comparison card, and obtain the color fastness rating. For the color \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Permeability** & **Thickness** & **Permeability** & **Thickness** \\  & **(Fabric1) (mm/s)** & **(Fabric1) (mm)** & **(Fabric2) (mm/s)** & **(Fabric2) (mm)** \\ \hline Desized & 95.98 & 0.68 & 37.62 & 0.44 \\ Laser & 91.62 & 0.70 & 32.21 & 0.41 \\ Enzyme & 94.62 & 0.67 & 34.63 & 0.42 \\ NaClO & 95.93 & 0.69 & 36.92 & 0.44 \\ KMnO\({}_{4}\) & 90.92 & 0.68 & 34.11 & 0.46 \\ H\({}_{2}\)O\({}_{2}\) & 94.42 & 0.66 & 36.96 & 0.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Permeability and thickness of denim fabrics with different bleaching types. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Weight (Fabric1)** & **Weight (Fabric1) Loss (\%)** & **Weight (Fabric2)** & **Weight (Fabric2) Loss (\%)** \\ \hline Desized & 35.83 \(\pm\) 0.01 & 0 & 29.20 \(\pm\) 0.01 & 0 \\ Laser & 33.29 \(\pm\) 0.01 & 7.09 & 27.34 \(\pm\) 0.01 & 6.37 \\ Enzyme & 33.38 \(\pm\) 0.01 & 6.84 & 27.48 \(\pm\) 0.01 & 5.89 \\ NaCIO & 33.34 \(\pm\) 0.01 & 6.95 & 27.56 \(\pm\) 0.01 & 5.62 \\ KMnO\({}_{4}\) & 32.70 \(\pm\) 0.01 & 8.74 & 26.92 \(\pm\) 0.01 & 7.81 \\ H\({}_{2}\)O\({}_{2}\) & 33.49 \(\pm\) 0.01 & 6.53 & 27.44 \(\pm\) 0.01 & 6.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Weight of denim fabrics with different bleaching types. fastness to rubbing, grade 5 is the best and grade 1 is the worst. Compared with grades 4-5, grade 5 indicates that the color of white fabric (after rubbing) is lighter, and the color fastness to rubbing of denim fabric is better. The results of color fastness to rubbing of denim fabrics with different bleaching types are described in Table 7. It can be seen from Table 7 that the color fastness to dry and wet friction of four kinds of denim fabrics has declined to different degrees after being bleached in different ways. Generally speaking, the color fastness to wet friction has declined more significantly, because the chemical bonding energy of water-soluble dyes or hydrophilic dyes and fibers will decrease in the presence of water, accelerating the separation and transfer of dye molecules. From the perspective of the washing method, the color fastness to dry and wet rubbing of denim fabric treated by manganese bleaching is the most obvious decline, followed by laser washing. This is because the reaction mechanism of manganese bleaching is that KMnO4 generates reactive oxygen species [O] in acid condition, which has a special strong oxidation property. It can not only decompose the dye on the fiber surface, but also decompose the fiber to a certain extent. However, the acid solution is corrosive to the fiber, which causes the most serious damage to the fiber on the surface of the fabric. The dye directly falls off without the carrier, resulting in most of the reduction of the color fastness to dry and wet friction. Laser bleaching is used to etch the surface fiber of denim fabric at high temperature, which will decompose some fibers. However, due to the controllable parameters and short processing time, the degree of fiber damage is not large. The color fastness to dry and wet rubbing of denim fabric is much lower than that of manganese bleaching, and it is within the allowable range of production. Oxygen bleaching and chlorine bleaching only decompose the dye on the surface of the fabric, and there is no damage to the fiber, so the color fastness to dry and wet rubbing is not greatly reduced.