The time needed from maximum torque to reach stabilization zone, that is the homogenous molten state of the
samples and the end torque were reduced, more observably as the content of the plasticizers increased till 15 wt.%.
Both of these bio-sourced plasticizers provided lubricating effect and increased the chain mobility of polymer,
which reduced the friction energy and shearing force needed (Ghosh et al., 2010). The reduction in shearing force
resulted in lowered torque. Less heat energy were converted from the friction resulted in reduced end stock
temperature as reported in Table 1. Nevertheless, marked reduction of end stock temperature close to the pre-set
temperature at 170 ºC was noticed when 10 wt.% of EPO and 15 wt.% of ESO were added into PLA. For all
plasticized PLA, after the rapid reduction of the maximum torque, there was a slight increase in torque until it
reached another point of gelation before it reduced to torque equilibrium. Piszczek (2005) reported a similar trend
with PVC plasticized with dioctyl phthalate (DOP). Accordingly, the addition of plasticizer lowered the gelation
temperature of plastic.