# An Overview on Management and Valorisation of Winery Wastes
## 6 Wine By-Products as Raw Materials for Biopolymers and Natural Reinforcing Fillers
Solaris grape pomace was applied as carbon source for production of PHAs [119]. The residual polysaccharides of the grape pomace were enzymatically transformed into fermentable monosaccharides (106 g/dm\({}^{3}\)) and _Pseudomonas resinovorans_ was added to result in 21.3 g/dm\({}^{3}\) PHA and 0.05 g/dm\({}^{3}\)h productivity. The dephenolized grape pomace from the red grape _Vitis vinifera L_. variety was used in a multi-purpose four-stage cascading bio-refinery in order to obtain volatile fatty acids and applying them as a carbon substrate for PHA production [120]. A wine lees-based bio-refinery was designed in order to obtain ethanol, antioxidants, tartrate, and poly-3-hydroxybutyrate [121]. In this investigation, wine lees were used as a nutrient-rich supplement medium, in order to replace commercial yeast extracts and crude glycerol as carbon sources [121]. Table 7 presents studies in which biocomposites were obtained from biodegradable (polylactic acid, polybutylene succinate, or PHAs) polymers and wine by-products as reinforcing fillers. Vine shoots and grape stalks have low apparent densities (approximately 0.03 g/cm\({}^{3}\)), affecting the cost of transportation when large-scale operations are required [129]. Regarding the average particle size, wine lees present lower values (D\({}_{50}\) of 25 \(\upmu\)m) [128]. Lignocellulosic fillers, such as vine shoot or grape stalks containing particles with sizes varying between 0.3 mm and 5 mm surrounded by extended split fibres, and grape stalks (containing high amounts of cellulose, up to 30% wt. ), have the ability to augment the elastic modulus of polylactic acid up to 65% with an intrinsic elastic modulus of 6-9 GPa [122]. Other studies have outlined the potential of wine lees to improve the elastic modulus of various biopolymers (for example polybutylene succinate or poly-3-hydroxybutyrate-co-3-hydroxyvalerate) and reported an intrinsic elastic modulus of 4-7 GPa [125; 128]. Vine shoot and grape pomace were used as reinforcing fillers for poly-3-hydroxybutyrate-co-3-hydroxyvalerate, with vine shoots increasing the elastic modulus while grape pomace had no effect on this characteristic [127]. The identified reason was that grape pomace cellulose and hemicellulose contents were low (10% and 6%, respectively), but it was rich in lignin (up to 42%, acting as a coupling instrument between cellulose and hemicellulose) [127]. Additionally, the stiffening effect was due to the rigid inorganic particles (for example alumina silicates or potassium tartrates) from the wine lees, which possess small diameter sizes, leading to particles dispersion and homogeneity [127]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Biodegradable** & **Wine Waste** & **Filler Percent** & **Filler Treatment** & **Reference** \\ \cline{2-5}
**Polylactic acid** & **Grape stalks** & **30–50** & **Untreated** & [122] \\ \cline{2-5}  & **Grape pomace** & **5–20** & **Untreated** & [123] \\ \hline \multirow{4}{*}{Polybutylene succinate} & \multirow{4}{*}{Grape pomace} & \multirow{4}{*}{40–50} & Reactive extrusion & \multirow{4}{*}{[124]} \\  & & & with maleic & \\ \cline{1-1} \cline{4-5} Polybutylene & & & anhydride-grafted & \\ \cline{1-1} \cline{4-5}  & & polybutylene succinate & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \cline{1-1} \cline{4-5}  & & & & \\ \hline \multirow{4}{*}{Poly-3-hydroxybutyrate-co-3-hydroxyvalerate} & \multirow{4}{*}{Vine shoots} & Reactive extrusion with & \multirow{4}{*}{[127]} \\  & & & silane (for the 20\% & \\ \cline{1-1} \cline{4-5}  & & & formulation) & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Biocomposites obtained from biopolymers and wine by-products as reinforcing fillers. Some researchers reported that the incorporation of grape pomace (40% wt.) to flexible polybutylene succinate induced a critical loss of ductility (around 90%) [124]. However, polybutylene succinate containing wine lees powder (20% wt.)