# Synthesis and Processing of Melt Spun Materials from Esterified Lignin with Lactic Acid
## 2 Materials and Methods
### Synthesis of Fibers  
In a 1000 mL three-neck round bottom flask, 100 mL of LA was dissolved in 230 mL of CHCl\({}_{3}\), under vigorous stirring at room temperature for 1 h. Then, 100 mL of SOCl\({}_{2}\) was added to the mixture, dripping slowly and in small amounts in order to perform the chlorination reaction. As the SOCl\({}_{2}\) was added to the flask, vapors of SO2 were released from the chemical system according to the reaction in Figure 1[25]. According to this reaction, a nucleophilic substitution pathway occurs, in which the carboxylic acid is first converted into a chlorosulfite intermediate. Then, the chlorosulfite reacts with a nucleophilic chloride ion in order lactic acid chloride (LCI) to be synthesized. The released vapors indicate that the chlorination reaction has progressed. After partial evaporation of the solvent (CHCl3), the solution was added to 250 mL of pyridine. Then, 100 g of washed SKL was added to the mixture, and the blend was left under vigorous stirring at room temperature for 1 h. The temperature was then elevated at 120 \({}^{\circ}\)C, and a reflux condenser was adapted onto the flask. The esterification reaction duration was 5 h at the aforementioned conditions; the mechanism of the corresponding esterification reaction (alcoholysis) between the hydroxyl groups of SKL and lactic chloride is depicted in Figure 2[26]. According to the esterification process, an addition of oxygen (nucleophile) to the carbonyl group occurs, yielding a tetrahedral intermediate. Then, an electron pair from oxygen displaces the chloride (leaving group), generating a new carbonyl compound as a product. After the completion of the reaction, the solvent (pyridine) was evaporated. The solid product (SKL esterified with lactic chloride, SKL-LA) was oven-dried overnight at 70 \({}^{\circ}\)C.  
In a 1000 mL glass beaker, 45 g of poly(lactic acid) (PLA) was dissolved in 600 mL of chloroform under vigorous mechanical stirring. The blend was left under stirring overnight in order to ensure complete dissolution. Afterwards, 100 mL of SOCl2 was added dripping in the solution under mechanical stirring. The SOCl2 reacted with the hydroxyl groups of PLA and produced poly(lactic acid) chloride (PLCI) according to the reaction in Figure 3[25]. During the SOCl2 addition, there was a release of SO2 vapors that indicated the reaction progress. After completion of the reaction, the obtained product (PLCI) was dried and pulverized. Then, 25 g of the synthesized PLCI was dissolved in 270 mL of pyridine in a 500 mL three-neck round bottom spherical flask and was left  
Figure 1: Chemical reaction of the chlorination process. Figure 2: Esterification reaction between Softwood Kraft Lignin (SKL) and lactic acid chloride (LCI). under vigorous stirring overnight at room temperature. In the next step, 40 g of SKL was added, and the mixture was left to react at 120 \({}^{\circ}\)C for 5 h under vigorous stirring. After that, the solvent was evaporated, and the solid collected product of SKL-PLA (SKL esterified with PLA) was dried at 80 \({}^{\circ}\)C. The chemical reaction of the esterification process (alcoholysis) is illustrated in Figure 4 [26]. The abovementioned materials were mixed with HDPE, and the resulting blends were loaded in an extruder line, optimizing spinning parameters of extruder temperature, roller distance from the extruder, and extrusion speed for each precursor blend. The parameters and conditions for the optimization process for the HDPE spinning for the production of HDPE/SKL-LA (80:20) and HDPE/SKL-PLA (80:20) fibers are tabulated in Tables 1 and 2. The best results concerning the spinning ability of the blends were obtained for the conditions that are presented in Table 1. The blend mass ratio of the HDPE/esterified lignin was 80/20 by weight (HDPE/SKL-LA (80:20), HDPE/SKL-PLA (80:20)). The extruded precursor HDPE/SKL-PLA fibers were fixed in bundles and were thermally treated following four different thermal stages.