Biomass-Derived Humin-like Furanic Polymers as an Effective UV-Shielding Agent for Optically Transparent Thin-Film Composites

Synthesis of 5-hydroxymethylfurfural from saccharide biomass yields humin-like furanic polymers (BFPs) as a byproduct. As a maiden attempt, BFP was successfully separated and explored as an effective UV-shielding agent by blending with poly(vinyl alcohol) (PVA, 0.5–2.0 wt %). PVA/BFP composite films showed high stability and durability even under extreme conditions, such as intense UV irradiation, sunlight exposure, and thermal treatment, while retaining their UV-shielding efficiency. The PVA/BFP (0.5–2.0 wt %) composite film showed 63–99% UV-shielding capacity in the entire UV range with 48–89% optical transparency; in addition, the decolorized BFP composite film showed superior UV-shielding efficiency (98%) with >98% optical transparency. Thermal stability of the film witnessed significant improvement, exhibiting higher thermal degradation temperature (Td, by 57 °C) and glass transition temperature (by 7.3 °C). Further, the composite film exhibited an excellent mechanical strength of 71 MPa and 338% strain to break, compared to the PVA film (25 MPa mechanical strength and 177% strain), along with enhanced DMA storage modulus. Application of UV shielding was demonstrated through rhodamine B photodegradationstability, which showed that incorporation of BFP resulted in mere 0.4% degradation of rhodamine B, while neat PVA films showed 100% degradation. The enhanced photostability of rhodamine B while using PVA/BFP is attributed to the formation of BFP and PVA charge-transfer complexes.