The aims of the study were (a) the determination of the physicochemical characteristics of properties of pellets made of shredded residue from hay, wheat straw, and their blend at a ratio of 50:50, and (b) the determination of a mathematical model of pellet durability, using a response surface method. Tests were conducted according to applicable standards. As a result of thermal changes during the pressure agglomeration process, the material moisture content of pellets had slightly decreased versus raw three biomasses by 0.50% w.b. (wet basis) to a final value within the range of 5.56–5.87% w.b. The pellet properties of the blend were not adequately represented by the arithmetic mean of their components. Pellets made of hay, straw, and their blend, had DM (DM—dry matter) specific densities of 1034, 974, and 1102 kg m⁻³, respectively. The densities showed correlation with calorific values (r = 0.637), which were in the range of 16.07–17.00 MJ kg⁻¹. The pellet durability coefficient correlated negatively with particle size and biomass moisture content. On the basis of previous conclusions, a non-linear mathematical model was formulated to account for the pellet durability coefficient relative to pellet moisture, and the relation of particle sizes and specific density to pellet bulk density.

Fractional composition, as well as the temperature of the agglomeration process, affect the quality and mechanical properties of briquettes. In this research, shredded forest logging residues were investigated. Compaction tests were carried out for several specially prepared mixtures made of shares of fractions with different particle sizes. The moisture content, density of briquettes, specific work of compaction, mechanical durability, and biomass susceptibility to compaction were analyzed. Studies have confirmed the significant impact of the fractional composition of compacted biomass on its susceptibility to process parameters and the quality of the final product. Statistical analysis confirmed that the density of the briquette, its durability, the specific work of compaction, and the susceptibility of the tested biomass to compaction strongly depend on the particle size of the compacted biomass. An increase in temperature to 73 °C increased specific work by 40% and contributed to the high quality of briquettes in the range from 0.768 to 1.14 g·cm⁻³.