How does the melting temperature affect semicrystalline plastics?

For semicrystalline plastics, the melting temperature ($T_m$) represents the critical threshold at which the material transitions from a solid state to a liquid or flowable state.12

In semicrystalline polymers, molecules are organized into ordered regions known as crystallites embedded within an amorphous matrix. While these materials may enter a rubbery state above their glass transition temperature, they remain structurally stable due to the presence of these crystalline regions.12

The melting temperature is the point at which the crystalline regions are no longer stable and begin to break down. Once the temperature exceeds $T_m$, the molecules gain sufficient mobility to flow past one another, allowing the polymer to be molded, extruded, or spun into fibers. Until this temperature is reached, the crystalline structure maintains the material's integrity, distinguishing it from noncrystalline polymers that transition directly from a rubbery state to a liquid state.12