Alkali lignin/HDPE composites were prepared respectively with dioctyl phthalate (DOP)

dibutyl phthalate (DBP) and epoxidised soybean oil (ESO). The influence of plasticizer on mechanical properties of composites was studied. The results showed that these plasticizers could increase the elongation at break of composites and DOP had the best effect. With adding 7.5 phr DOP

the elongation at break of composites was 146.28%

much higher than that(83.8%) of composites without DOP. Composites were prepared with different contents of DOP to study the influence of DOP on mechanical properties

fracture morphology and rheological properties of composites. The mechanical properties of composites showed that the increasing DOP content was beneficial to the increasing of elongation at break. The SEM showed that the fracture surfaces of composites became coarser with the addition of DOP

and the toughness of composites increased. The rheological properties showed that the addition of DOP can lower the apparent viscosity () and complex viscosity (*) of the composites

and the linear viscoelastic region turned narrow

the storage modulus (G') and the loss modulus (G) also gradually declined with the increasing DOP content. According to the analysis it was concluded that DOP can adsorb on the surface of lignin particles and suppress the agglomeration of lignin particles in HDPE

which may improve the dispersion of lignin particles in HDPE and reduce the interaction force between the lignin molecules and the molecular chains of PE

thus the mechanical properties and rheological properties of the composites were improved.