The effects of sodium sulfite (SS) content and injection molding temperature on the viscoelasticity of bloodmeal-based thermoplastics were assessed using creep, recovery, and stress relaxation. Both SS and processing temperature affected standard mechanical properties and time-dependent behavior. Increased SS content led to greater creep, greater strain at break, and reduced modulus and mechanical strength of the material. Furthermore, the use of a higher injection molding temperature also reduced modulus and strength. Higher molding temperature also caused an increase in the fraction of creep recovered in 20 min. These results confirmed that increased SS increased chain mobility and that injection molding at 140°C instead of 120°C did not cause excessive thermal cross-linking.