## 4 Conclusions  
The effect of a non-reactive epoxy binder generally used to fix the preform of the product in the LCM process was investigated. First, the permeability of the preform in the in-plane and out-of-plane directions were measured respectively using the unsaturated and saturated permeability equation according to the binder treatment. All the cases of fabric preform exhibited the highest permeability in the 90\({}^{\circ}\) direction (K1) and the lowest permeability in the 0\({}^{\circ}\) direction (k2), and both K1 and K2 decreased by about 80% with binder treatment at fiber volume fractions of 55% and 60%. The permeability in the out-of-plane direction also decreased with the binder treatment. In this case, the permeability in the out-of-plane direction of the binder-treated fabric preform (without heat treatment during the preforming process) decreased by approximately 80% compared to the neat fabric preform, and the binder-treated fabric preform (with heat treatment during the preforming process) decreased by approximately 98%. The reduction in permeability was significant even considering the reduction in the porosity of the preform arising from the presence of the binder. Thus, in agreement with the measurement results of permeability, this reduction was due to the fact that the binder changed the permeability characteristics of the preform. In particular, the binder was flattened and impregnated within the fibers during the preforming process including heat treatment, as was observed through micro-optical observation, and this binder significantly hindered the flow in the out-of-plane direction, resulting in a 98% reduction in the permeability. This decrease in permeability lowered the impregnation rate of the resin, which was closely related to the rate of production in the LCM process, resulting in a higher production cost. Additionally, the change in the kinetic friction coefficient used as a variable in forming simulations for wrinkle prediction in the LCM process was investigated according to the binder treatment. The friction coefficient was high when the binder was on the friction surface, and the binder became viscous at 110 \({}^{\circ}\)C, resulting in an increase in the friction coefficient by 40-200% compared to room temperature (25 \({}^{\circ}\)C). Therefore, based on the results of this study, changes in the characteristics of carbon fabric used as a reinforcement for composite materials can be predicted when a binder is used in the LCM process.  
Figure 10: The change in friction coefficient of the carbon fabric as a function of temperature.  
**Author Contributions:** [PERSON] carried out the experimental design of this study and wrote the original draft. [PERSON] also carried out experimental design of this study. [PERSON] organized experimental data. [PERSON] supervised this study. All authors read and approved the final manuscript.  
**Funding:** This work was funded by the Development of a Skin Spar Integrated Wingtip Composite Structure for a Single Aisle Aircraft using High Temperature Resin Infusion Process (20005403), Development of Mass Production Technology for Trunk Lid based on Hybrid Wet Compression Molding (10083584), Civil-Military Technology Cooperation Program (No.15-CA-MA-13-MKE) and the Technology Innovation Program (No.10053841) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).  
**Conflicts of Interest:** The authors declare no conflict of interest.