**1. Introduction**

Environmental friendliness and green alternatives have been a significant concern, to reduce carbon footprint and alleviate environmental toxicity problems [1, 2]. Lignocellulose is the most abundant renewable biopolymer ever existing [1, 3]. Cellulose, hemicellulose, and lignin count up to more than 90−95% of lignocellulosic texture [4]. Lignin is an organic polymer whose structure is highly dependent on its native source. In general, it is an amorphous, isotropic material, covered, for example, in the wooden stem of a plant. All plants and algae comprise lignin in different amounts, in addition to cellulose and hemicellulose [5, 6]. Lignin amount also differs according to the time of harvesting. The lignin content gets much higher, the older the plant gets. For instance, lignin presents about 12.4 ~ 29.4% of hemp [7] and 2.5 ~ 3.8% of flax [8]. Nevertheless, the highest lignin content can be found in woods, with a percentage of 20 ~ 30% [9]. Lignin leads to a so-called lignification of the stem (from Latin: *lignum*). This makes it more robust and stronger by gumming the cellulose part together [10]. This partly also

occurs in leaves. It is extracted from these natural sources via physical, chemical, or biological methods.

Physical processes include steam explosion and mechanical grinding. The physical route yields high-purity lignin. However, it is hard to be industrially upscaled. Chemical processes commonly used for pulp and paper, such as the kraft and sulfite process, utilize reagents that trigger reactions, yielding moderate-purity lignin, depending on the parameters. The harsher the reaction environment and chemicals utilized, the lower the quality of lignin will become. New processes such as organosolv process running on water and ethanol as main solvents with an optional acid catalyst will result in higher quality lignin due to the mild reaction conditions. However, to obtain high-purity lignin, the respective fraction will need to undergo further treatment. Finally, the biological option involves enzymes that break lignin bonds with cellulose and hemicellulose. Despite producing high-purity lignin, this technique is not favorable due to its low speed. The majority of industrial lignins are extracted chemically from their sources.

Extracted lignin has high molecular weight and poor reactivity with other polymeric materials. Hence, its uses are limited to combustion applications. Around 98% of lignin is burnt as a low-value fuel, while the rest is fabricated into commercial products [11]. In order to increase lignin utility, its structure has to be modified first. The purpose of the modification is to enhance lignin reactivity and homogeneity and lower the probability of infusible solids formation. Boosting lignin value is called "lignin valorization." **Table 1** summarizes different valorization processes, which are covered in the following section.

With a share of 4.3% of the European pulp production and total production of 5 million tonnes of paper in Austria, there is an approximate market demand of 116.3 billion tonnes of pulp only in Europe. Multiplying this with a mean value of the content of lignin in wood, taking 25%, there is a total yearly amount of 29 million tonnes of lignin. Adding further lignin sources as mentioned above as well, the value is significantly increasing. The following chapter addresses, how the velarization process takes place to not waste this amount of lignin. Afterward, Chapter 3 deals


#### **Table 1.** *Lignin valorization processes.*

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

with further processing of lignin-based epoxy resin synthesis. Concluding, a short chapter will summarize the findings.
