Dualistic effect of Kraft lignin on the viscoelastic behavior of biodegradable biobased PBSA

Abstract

Lignin is an abundant and low-cost renewable feedstock. In this investigation Kraft lignin was incorporated into the biodegradable poly(butylene succinate-co-adipate), PBSA, using a co-rotating twin-screw extruder to produce films. Lignin content varied from 2.5 to 15 wt% and two extrusion conditions were investigated. The influence of processing conditions and lignin content on PBSA degradation, mechanical and viscoelastic properties were assessed by size exclusion chromatography (SEC), tensile tests, parallel plate rheometry (steady state and oscillatory) and dynamic mechanical thermal analysis (DMTA). The thermal behavior of neat Kraft lignin was assessed by differential scanning calorimetry (DSC). The results suggest that lignin influenced the viscoelastic properties of PBSA differently as a function of temperature and lignin dispersion. Lignin may behave as a rigid particle and have a reinforcing effect on PBSA when significantly below the glass transition temperature (Tg), but gradually transition to a lubricant as the temperature is increased and molecular relaxation occurs.