Densification of Wood—Influence on Mechanical and Chemical Properties when 11 Naturally Occurring Substances in Wood Are Mixed with Beech and Pine

Abstract

The need to increase the use of renewable biomasses for energy supply, such as fuel pellets is significant. However, different types of biomasses have different mechanical properties to be pelletized, which entails a limitation in available raw materials for pellet producers. Within this study eleven different pure substances from biomasses were separately mixed with European beech and Scots pine, to identify its impact on the densification process. Beech and pine pellets were used as control materials against their corresponding pellets mixed with substances representing: cellulose, hemicelluloses, other polysaccharides, lignin, protein, and extractives. The mechanical properties were investigated as well as FT-IR and SEM analyses on the pellets. The results showed that the addition of the substances xylan and galactan created the hardest pellets for both pine and beech and that adding extractives to wood affects pine more than beech in relation to hardness. The FT-IR data could not provide clear explanations as to the variation in hardness and springback behavior through the identification of major functional groups in each pellet. It can be concluded that biomass residues rich in xylan and galactan increase pellet quality in terms of strength and durability without affecting the production process.

Forest Industrial Waste Materials Upgraded to Fertilizer Pellets for Forest Soil

“…However, as seen in Table 4, bark's bulk density is lower than hydrochar and ash. As seen in Table 5, the power need and temperature during pelletization are lower for the mix with bark, meaning that bark is a lubricant in the pelleting process, which is consistent with other studies [33]. So, it is likely that the pellets with bark can increase their bulk density by increasing the presslength slightly.…”

“…When it comes to durability, it is clear that adding bark to hydrochar and ash creates a more durable pellet (see 6). Likely, the reason behind an increase in the mechanical quality of the bark-blended pellets can be attributed to lignin; however, these bondings are not tested, and extractives or carbohydrates have been found to generate even better bondings than lignin [33], so further studies are needed. The pellets produced based on this study using the two blends have met the ISO standards regarding moisture and bulk density, and for 45/10/45 also durability (BD800+ (>900 kg/m 3 ), DU95.0− (<90%), and DU95.0 (≥95%) and M08 (moisture ≤ 8%)) (See Figure 5).…”

“…Beyond that, a small amount of bark is added to pellet production to increase the pellets' durability [32]. Bark also contains a large amount of extractives [31], which can act as a lubricant within the die channel [33]. Studies of hydrochar pelleting have shown that by adding a lubricant binder, the pelletizing process is more energy-efficient [34], and hydrochar seems to need binders [7].…”

Biomass from Green Areas and Its Use for Energy Purposes

“…For the analyzed pellets, the destructive force oscillated in the range from 601.53 to 788.71 N. The addition of fir sawdust from coniferous trees during the production process of pellets from waste biomass of sunflower and tobacco improved the strength parameters of the tested pellets [33]. Analyzing the destructive force for pellets made of coniferous and deciduous sawdust and beech wood, it was found that 166 N to 654 N was needed to destroy different types of pellets [38]. The mechanical strength of pellets produced from straw increases as a result of the use of an additive in the form of coniferous sawdust during the production process [39].…”

“…The mechanical properties of pellets depend in particular on the type of materials used for their production, the water content, the chemical composition of raw materials, and the addition of an adhesive [37,38]. Pellets made of raw materials containing large amounts of starch are characterized by greater resistance to mechanical damage.…”