A welding process may be configured to convert a substrate into a welded substrate by applying a process solvent to the substrate, wherein the process solvent interrupts one or more intermolecular force between one or more component in the substrate. The substrate may be configured as a natural fiber, such as cellulose, hemicelluloses, and silk. The process solvent may be configured as an ionic-liquid based solvent and the welded substrate may be a congealed network after the process solvent has been adequately swollen and/or mobilized the substrate. A welding process may be configured such that individual fibers of a substrate are not fully dissolved such that material in the fiber core may be left in the native state by controlling process variables. The welding process fibers may have a tenacity 10% or 20% greater or a diameter 25% less than that of a cellulosic-based yarn substrate.