2. Methods
2.1. Materials
The black-liquor lignin was prepared from black-liquor which is a condensed byproduct from an alkali pulping company in Hunan Province, China. Chinese poplar and reed are used as the main feedstock paper production with the black-liquor as byproduct. All the solvents used in the study were purchased from Nanjing Reagent Co. Ltd. The lignin prepared method is listed below (Hu et al., 2013): (1) black liquor was acidified to a pH value of 2 with 50 wt.% H2SO4 and stirred for 1 h at 55 °C; (2) the acidified black liquor was filtrated under vacuum, and the filtrated cake was washed with deionized water to neutral; (3) after drying at 80 °C for 12 h, the isolated lignin was extracted with benzene/ethanol (1:2, v/v) for 12 h at 90 °C to remove some sugars with low molecular weight; (4) the extracted liquid was heated at 40 °C under 0.4 MPa to remove the benzene/ethanol solvent, and the remaining solid lignin was dried at 80 °C for 12 h; (5) further purification for benzene/ethanol extracted lignin was carried out according to the Lundquist purification method (Thring, 1994); (6) the solid lignin was obtained after being dried at 80 °C for 12 h.
Plastics including polyethylene (PE), polypropylene (PP) and polystyrene (PS) were provided by Li Ke Polymer Materials Company in Shanghai, China. The particle size of plastics is around 80–120 mesh. The black-liquor lignin was grounded and seized to produce particle size of 70–100 mesh. The ultimate analysis and proximate analysis of black-liquor lignin and different plastics are listed in Table 1.