## 2 Results and Discussion
### Thermal Properties  
TGA was used to determine the thermal stability and decomposition of the lignin samples (Figure 5). A bird lignin (Figure 5a) from the same process was used to compare the thermal properties between softwood and hardwood lignin (Table 4). According to the literature the degradation of the lignin structure starts at 230-260 \({}^{\circ}\)C with the degradation of the propanoid side chain and then continues to cleave the linkages bonded with C-C bonds at 275-350 \({}^{\circ}\)C [37]. The relatively high T\({}_{\text{dst 95\%}}\) values of 273-302 \({}^{\circ}\)C for the unmodified lignins indicated low amounts of phenylpropanol side chains and aryl ether linkages and that the lignin was bonded by more stable C-C bonds, which is in agreement with our structural analysis of the lignin. The methylation of the phenolic groups slightly increased the stability of all the lignin samples compared to the unmodified lignin, as seen from the T\({}_{\text{dst 95\%}}\) values (Table 4). The acetylation decreased the stability which is contradictory to other studies [38], this indicate that the acetyl groups were cleaved or that the decrease in mass is due to evaporation of less volatile compounds. The cleavage could be catalyzed by some impurity, such as minuscule amounts of acetic acid from the reaction. To study this phenomenon two samples, unmodified pine lignin and acetylated pine lignin, were dried extensively at elevated temperature prior to analysis. The results (see Supporting Data) showed an slight increase in the T\({}_{\text{dst 95\%}}\) value for the acetylated sample from the initial value of 233 to 264 \({}^{\circ}\)C, which can partially be explained by the more efficient removal of volatiles, however, the T\({}_{\text{dst 95\%}}\) value was still lower than the 284 \({}^{\circ}\)C of the unmodified lignin, which could be due to that the cleaved acetyl groups can act as catalyst for further deacetylation. The acetylated lignins still had high T\({}_{\text{dst 95\%}}\) values which make acetylation a viable option to increase the compatibility of lignin with other polymers. The thermal stability can also be increased by performing the same esterification procedure with esters with longer chains. By adjusting the chain of the esters the chemical properties of the lignin can be tailored to increase the compatibility  
Figure 4: Multiplicity edited HSQC of the MTBE soluble fraction from the process of **(a)** pine and **(b)** spruce. CH\(/\)CH\({}_{3}\) shown as positive (blue) and CH\({}_{2}\) as negative (red).  
with specific polymers [14]. The use of this lignin in polymer blends could be promising, based on the T\({}_{\text{dst 95\%}}\) values, as blend processing temperatures are considerable lower, however, it is clear that the lignin starts to lose mass at lower temperatures and as seen from _[PERSON]_ et al. [26] the processing stability of a lignin/PLA blend was considerably decreased at 190 \({}^{\circ}\)C compared to 170 \({}^{\circ}\)C. The DTG maxima of the different samples were between 386-411\({}^{\circ}\)C with the methylated lignin slightly higher. The unmodified lignin had a higher char residue at 600 \({}^{\circ}\)C (wt %) than the methylated lignin, which could be due to the formation of more stable condensed structures in the unmodified lignin with free phenolic groups, while the acetylated samples had a lower char residue.