## 3 Results and Discussion
### Biocomposites Production Process  
Research was also carried out on the possibility of using tall fescue biomass obtained from areas with different salinity levels in the plastics processing industry, developing biodegradable polymer composites in which some plastics were replaced with natural fillers. Natural fillers were prepared from tall fescue biomass with particles of less than 1 mm. Moisture analysis and sieve analysis of the obtained natural fillers were performed. The detailed share of the individual fractions is presented in Table 3.  
The bulk density of tall fescue fillers (average 0.215 kg\(\cdot\)L\({}^{-1}\)) was also determined.  
The effect of various tall fescue fillers on the tensile and flexural properties of PLA composites are shown in Table 4.  
The use of 20% by weight of _F. arundinacea_ biomass fillers in PLA-based composites reduced tensile strength by an average of 24%. However, it can be observed that these changes depend on the type of biomass used and range from 21% for sample FA_2 (soil salinity: 6.24 g NaCl\(\cdot\)L\({}^{-1}\) and Na\({}^{+}\) content in biomass: 2.45 mg\(\cdot\)g\({}^{-1}\)) to 28% for sample FA_6 (soil salinity: 2.82 g NaCl\(\cdot\)L\({}^{-1}\) and Na\({}^{+}\) content in biomass: 7.71 mg\(\cdot\)g\({}^{-1}\)). The use of tall fescue biomass natural fillers increased the modulus of elasticity of composites in relation to pure PLA--by an average of 28%. The best results were obtained for the FA_2 filler (about 34%), and the smallest increase in the module was recorded for the FA_6 filler (about 22%). The flexural strength of the composites at 20% by weight of the filler content decreased by about 22%. The modulus of elasticity determined during bending increased by an average of 26% compared to pure PLA.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Plant Biomass**} & \multirow{2}{*}{**Humidity (\%)**} & \multicolumn{6}{c}{**Particle Size Distribution (\%)**} \\ \cline{3-8}  & & **1 mm** & **0.5 mm** & **0.4 mm** & **0.25 mm** & **0.2 mm** & **0.1 mm** & **Below 0.1 mm** \\ \hline FA\_1 & 6.73 & 1.2 & 8.3 & 48.3 & 30.5 & 2.5 & 2.7 & 6.5 \\ FA\_2 & 7.65 & 0.8 & 3.5 & 51.3 & 29.3 & 4.7 & 3.2 & 7.2 \\ FA\_3 & 6.57 & 1.1 & 2.8 & 50.6 & 31.2 & 3.7 & 2.8 & 7.8 \\ FA\_4 & 6.33 & 0.8 & 3.1 & 49.5 & 30.6 & 4.2 & 2.9 & 8.9 \\ FA\_5 & 7.25 & 1.2 & 2.6 & 51.2 & 32.3 & 2.5 & 3.2 & 7.0 \\ FA\_6 & 6.84 & 1.1 & 3.6 & 40.9 & 40.2 & 3.4 & 3.6 & 7.2 \\ FA\_7 & 6.20 & 1.7 & 1.6 & 52.3 & 33.9 & 2.1 & 2.6 & 5.8 \\ FA\_8 & 6.54 & 1.5 & 2.1 & 49.2 & 35.4 & 2.1 & 2.4 & 7.3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Particle size distribution and humidity of fillers from _F. arundinacea_ biomass.  
It was found that PLA composites with fillers from tall fescue biomass did not show effective interfacial adhesion [50]. The lack of full adhesion at the interface of individual components may result from the chemical composition of lignocellulosic biomass [51, 52]. In SEM images, this phenomenon is visible in the form of a gap between the polymer matrix and the filler (Figure 6).  
The interfacial bonding forces of natural fillers with the polymer matrix were low, and even when low force was acting on the samples, the fillers detached from the matrix [53]. After exceeding this value, all the force acted only on the polymer matrix of the composite sample [54]. In addition, the value of the decrease in tensile and bending strength can be correlated with the type of reed fescue biomass used. It was observed that the FA_2 filler has the smallest effect on reducing the tensile and flexural strength of composites and the most favorable effect on increasing the modulus of elasticity. It should be added that this filler, despite being obtained from a crop with one of the highest salinities, was characterized using the lowest Na\({}^{+}\) content in biomass.