Agro-Industrial Biowaste Valorisation by Engineering Controlled-Release Polyphenol Products for Applications in Sustainable Agriculture

Electrospinning and electrospraying nanotechnologies were used to valorise agro-industrial residues into biohybrid controlled-release polyphenol (CRP) scaffolds. Four polyhydroxybutyrate ± polycaprolactone (PHB±PCL) architectures were fabricated that differed in polymer phase, Klason lignin from hazelnut shell (HS-KL) presence vs. absence, and co-location with grape-pomace polyphenols (GP-PPs), as well as in distribution between fibres and bead-like depots. Scaffolds were characterised using optical microscopy/stereomicroscopy/SEM, FTIR, UV-Vis spectroscopy, and dynamic water contact angle (absorption). GP-PP release was monitored for 14 days at ~25 °C and 37 °C, the latter representing shallow-soil hot-spell conditions in Mediterranean zones. All matrices exhibited multimodal release, with modest initial bursts and three phases (<i>burst</i>, <i>mid</i>, and <i>late tail</i>), analogous to controlled-release fertiliser profiles. At ~25 °C, the PHB/PCL matrix with HS-KL confined to PHB fibres and GP-PP in large PCL beads showed the highest <i>total</i> GP-PP release, whereas the architecture with HS-KL and GP-PP co-located in both PHB and PCL fibres and in PCL depots combined high <i>total</i> release with a smoother, well-metered late phase. At 37 °C, this HS-KL-GP-PP co-located scaffold was the most robust, retaining the highest <i>total</i> and <i>late tail</i> release. These results identify HS-KL-GP-PP co-located PHB/PCL architectures as promising carriers for temperature-resilient delivery of bioactive polyphenols in Mediterranean agrosystems.