## 3 Results and Discussion
The results of the flexural strength test are summarised in Table 2, and the selected flexural curves are shown in Figure 5. In Figure 5a, it can be seen that the mechanical properties of PLA after composing are slightly altered, while a significantly broken and degraded structure of the material with very poor properties can be seen after UV irradiation. In Figure 5b, flax is observed to have slowed the loss of mechanical properties during UV degradation of the sample, while it significantly accelerated the composting process. For the addition of wool (Figure 5c), there are also similar relationships to those for the addition of flax. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **E (GPa)** & **Tensile Strength (MPa)** \\ \hline PLA & 2.39 \(\pm\) 0.08 & 47.61 \(\pm\) 0.08 \\ L10 & 3.22 \(\pm\) 0.09 & 60.57 \(\pm\) 9.73 \\ L20 & 3.73 \(\pm\) 0.37 & 63.59 \(\pm\) 8.76 \\ W10 & 2.20 \(\pm\) 0.28 & 33.82 \(\pm\) 6.77 \\ W20 & 2.04 \(\pm\) 0.05 & 23.86 \(\pm\) 0.82 \\ PLA\_UV & 1.09 \(\pm\) 0.12 & 3.13 \(\pm\) 1.13 \\ L10\_UV & 2.68 \(\pm\) 0.21 & 28.22 \(\pm\) 5.94 \\ L20\_UV & 3.37 \(\pm\) 0.50 & 19.71 \(\pm\) 9.23 \\ W10\_UV & 1.24 \(\pm\) 0.17 & 7.64 \(\pm\) 3.59 \\ W20\_UV & 1.08 \(\pm\) 0.01 & 13.35 \(\pm\) 3.35 \\ PLA\_CO & 2.59 \(\pm\) 0.07 & 51.28 \(\pm\) 5.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Young modulus and tensile strength for PLA and PLA/natural fibre composites before and after degradation. Figure 4: Surface roughness measured for different composites: (**a**) Ra and (**b**) Rz. The error bars represent the standard deviation of measurements made 3 times for each sample. PLA has poor resistance to UV radiation (PLA_UV--a 92% drop in transmitted force during testing). Radiative degradation leads to the almost-complete destruction of PLA samples. PLA in damp soil, on the other hand, does not change as much (PLA_CO--a 10% drop in transmitted force during testing). The use of flax as a filler in the PLA matrix reduced the destructive impact of UV radiation on the PLA matrix in the investigated biocomposites. However, it was observed that, in this case, degradation in moist soil (L20_CO) has a more significant effect. However, this degradation is at a level of 63% compared to a sample containing flax and not exposed to degradative factors. Wool as an additive, similar to the addition of flax, slows UV degradation. However, the addition of wool fibre results in a significant decrease in the transmitted force values when exposed to moist soil (compared to a similar sample with flax). PLA undergoes hydrolytic degradation that involves several steps, including the diffusion of water into the amorphous phase of PLA, macromolecules chain scission by hydrolysis of the ester bonds, and the formation of the oligomers and monomers; and, in the next step, we see partial hydrolysis of the crystalline fractions [29]. Since washed wool fibre is hygroscopic and hydrophilic, it facilitates the transport of water deep into the material, leading to the hydrolysis of the PLA matrix and its degradation, thus accelerating the degradation of the entire material. UV degradation was slowed down by each type of fibre, and more force had to be applied to destroy the composite. The more fibres, the greater the difference in destructive forces, and the addition of flax slowed UV degradation significantly more than the addition of wool. For the degradation caused by composting, an acceleration of the degradation rate can be seen under the influence of fibre addition, since the force used to destroy the composite is, in each case, lower than that used with pure PLA. For L10 samples, the difference is very small compared to PLA. In this case, the greater the addition, the faster the degradation, and the wool fibres accelerated the degradation more. It can be seen (Table 2) that the mechanical properties of the composite increased after the addition of flax fibre in both cases compared to pure PLA. For small amounts of wool fibre, the properties are comparable to those of PLA, but with the large addition