## 2 Materials and Methods
### Research Methods  
Contact angle testing was performed on a Kruss DSA 10 MK2 goniometer to determine the changes in wettability of the samples before and after degradation. Roughness measurement was performed using the Hommelwerke T1000 profilometer. The software calculated R  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **PLA** & **Flax** & **Wool** & **UV** & **Soil** \\
**Name** & **(\% wt.)** & **(\% wt.)** & **(\% wt.)** & **Degradation** & **Degradation** \\  & & & & & **Process** & **Process** \\ \hline PLA & 100 & - & - & - & - \\ W10 & 90 & - & 10 & - & - \\ W20 & 80 & - & 20 & - & - \\ L10 & 90 & 10 & - & - & - \\ L20 & 80 & 20 & - & - & - \\ PLA\_UV & 100 & - & - & + & - \\ W10\_UV & 90 & - & 10 & + & - \\ W20\_UV & 80 & - & 20 & + & - \\ L10\_UV & 90 & 10 & - & + & - \\ L20\_UV & 80 & 20 & - & + & - \\ PLA\_CO & 100 & - & - & - & + \\ W10\_CO & 90 & - & 10 & - & + \\ W20\_CO & 80 & - & 20 & - & + \\ L10\_CO & 90 & 10 & - & - & + \\ L20\_CO & 80 & 20 & - & - & + \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of all the sample types tested, their composition, and the degradation process they were subjected to.  
Figure 1: **(a)** Granulate with PLA and flax fibres. **(b)** Specimens of PLA/wood composite after injection moulding.  
(average roughness of a surface) and R\({}_{\rm z}\) (difference between the tallest \"peak\" and the deepest \"valley\" in the surface) to characterise the roughness. Mechanical tests were carried out on a Zwick/Roell RetroLine 1445 test machine. The method used was the three-point bending of the specimens (PN-EN ISO 178). Each type of composite tested was subjected to DMA (dynamic mechanical analysis) tests on a DMA 850 (TA Instruments). The tests were carried out at a constant frequency of 10 Hz and in the temperature range of \(-60\div 100\)\({}^{\circ}\)C, with a heating rate of 5 \({}^{\circ}\)C/min, using three-point bending mode. PLA, L10, and W10 samples (before and after degradation processes) were subjected to thermogravimetric analysis (TG). Measurements were preformed using a TGA 550 (TA Instruments) thermal analyser, in platinum crucibles, under a nitrogen atmosphere. The heating rate was \(10\)\({}^{\circ}\)C/min. The study was conducted at the temperature range \(45\div 600\)\({}^{\circ}\)C. DSC analysis was performed on PLA, L10, and W10 samples (before and after degradation processes), using DSC 1 from Mettler Toledo with STARe software. The samples were subjected to a heating (\(10\)\({}^{\circ}\)C/min)/cooling (\(30\)\({}^{\circ}\)C/min)/heating (\(10\)\({}^{\circ}\)C/min) temperature program in the temperature range of 0-210\({}^{\circ}\)C, under nitrogen atmosphere, with a flow rate of 30 mL/min. The samples were placed in pierced and sealed aluminium pans. The reference sample was an empty crucible. Using data from the DSC analysis, the degree of crystallinity (X\({}_{\rm c}\)) was calculated using the following formula (Equation (1)):  
\[\rm X_{c}=\frac{\Delta H_{m}}{\Delta H_{m}^{0}(1-a)} \tag{1}\]  
where \(\Delta H_{m}\) is the heat of melting of studied PLA composite, \(\Delta H_{m}\)\({}^{0}\) is the heat of melting of 100% crystalline polymer (for PLA 93.7 J/g [25]), and a is the mass fraction of the additive (fibres). The microstructure of the composites was investigated using an FEI Nova NANO SEM 200 scanning electron microscope equipped with an EDS analyser from EDAX and using a Keyence VHX-900F digital microscope.