**3.2 Epoxidation of lignin after pretreatment**

Large molecular weight and poor dispersity lower lignin compatibility with polymeric compounds. Better reactivity can be realized via chemical modification, for example, phenolation, hydroxymethylation, and demethylation. For instance, *Zhang et al.* [36] synthesized phenolated lignin, hydroxymethylated lignin, and demethylated lignin from native lignin through chemical modification. The modified lignin types were reacted with epichlorohydrin to obtain lignin-based epoxy resins, which were then utilized as feedstocks for new grouting materials. The newly prepared lignin-epoxy grouts outperformed the commercial ones, displaying great potential in replacing petroleum-based materials.

*Zhen et al.* [28] proposed a novel strategy (see **Figure 4**) to produce lignin-based epoxy resin from phenolated lignin. They demonstrated in their work the superiority of their new approach over the traditional one. They noticed a slight deterioration

*Perspective Chapter: Potential of Lignin Valorization with Emphasis on Bioepoxy Production DOI: http://dx.doi.org/10.5772/intechopen.108263*

**Figure 4.** *Aminated lignin structure.*

in thermal-mechanical performance when the lignin amount exceeded 20% (80% phenol). However, the values were still better than lignin-free resins (**Figure 5**).

Similar to the first approach, the steric-hindrance effect of lignin is still inevitable. However, its impact is not as bad as in the simple blending approach. With the technique discussed herein, the complete substitution of petroleum-based materials is achievable, which is a major step in the right direction toward the production of petroleum-free thermosets.

## **3.3 Epoxidation of unmodified lignin**

Unmodified, or technical, lignins refer to a large group of lignin by-products whose properties are very different from their native form [37]. Kraft lignin, lignosulfonate lignin, and organosolv lignin are some good examples of unmodified lignins [38].

**Figure 5.** *PLIEN production process as proposed by Zhen et al. [28].*

Like the previous method, BPA can be completely replaced with unmodified lignins in epoxy resin formulation. The main difference between the two techniques is the cost. Since technical lignins are already available as industrial wastes, no additional processing cost is added, which qualifies the current method for large-scale production [32].