## 3 Results and Discussion  
The results of the contact angle tests provided information on the surface quality of the manufactured biocomposites before and after degradation. The contact angle results obtained are presented as a graph in Figure 2.  
The incorporation of natural fibres of both wool and flax has a significant effect on the wettability of the PLA-based composites. It was observed that the degradation of pure PLA under UV light and composting conditions causes a decrease in the contact angle. The presence of natural fibres increases the values of contact angles on the surface of samples of nondegraded composites (immediately after their production). However, after degradation,  
Figure 2: Contact angle of PLA/natural fibre composites before and after degradation process. The error bars represent the standard deviation of measurements made 6 times for each sample. the measured contact angles of the biocomposites are different, probably related to the uneven degradation of PLA and the presence of areas of exposed fibres. Although cellulose is strongly hydrophilic, there are studies that describe its influence on the wetting of the surfaces and thin layers. The high hydrophilicity of cellulose can be reduced with mineral additives such as TiO\({}_{2}\)[26]. Also, studies by [PERSON] and [PERSON] [27] confirmed an increase in contact angle value when composite samples containing cellulose are subjected to UV ageing processes. Despite the use of a HDPE matrix, significant changes in the surface of the investigated HDPE with wood flour composites were observed. In our studies, it was found, that there is a tendency for the contact angle to decrease after UV degradation and increase under simulated composting degradation for PLA/natural fibre composites with 20 wt.% fibre content. Roughness measurements were the second test performed to assess the surface quality of the composite samples. The results obtained in the study are presented in Figures 3 and 4. The evidence of strong UV degradation on the PLA surface was confirmed by the significant increase in roughness after ageing under UV radiation. The presence of natural fibres causes an increased surface roughness in the resulting composite after exposure to ultraviolet (UV) radiation; however, compared to pure PLA, flax fibres slow down degradation, while wool fibres accelerate it. Both linen and wool accelerated degradation in the composer compared to the degradation of pure PLA. In the case of the addition of wool, an increased roughness was observed compared to pure PLA after both irradiation and composting, while linen delayed the degradation under UV light but accelerated it in the soil, as seen in Figure 4. Other scientists in their research observed similar changes in roughness after ageing processes. The presence of flax fibres in the composite significantly increases the R\({}_{\text{a}}\) values [18], and the sisal fibre in a PLA matrix, after 15 days in compost, doubles its roughness (from a value of 1.2 \(\upmu\)m to values ranging from 2 to 3.5 \(\upmu\)m of the R\({}_{\text{a}}\) index). The pure PLA matrix itself increases its roughness from a value of 0.5 \(\upmu\)m to a value of 1 \(\upmu\)m. In all studies, it was observed that, with an increase in the content of natural fibres in the composite, the rate of surface roughening also increases [28]. The increase in roughness can be correlated with an increase in the rate of biodegradation because the greater surface area allows easier transport of water deep into the material and the anchoring of fungi and microorganisms in the pores and defects of the composite. The right combination of fibres in the composite will allow the life of the biomaterial to be regulated.