A completely green approach was adopted for the production of biocomposites of polylactic acid (PLA) and cellulosic fibers (CF) via functionalization of CF with an aqueous solution of poly(ethylene oxide) (PEO) followed by extrusion with PLA and injection molding. The treatment with PEO improved the interfacial interaction among the components as well as the CF dispersion and free flow upon extrusion, allowing loading up to 30 wt % of CF. Moreover, the synergistic effect of PEO and CF greatly enhanced the physical–chemical properties of the biocomposites. Their storage modulus was higher with respect to pure PLA in the rubbery region. The stiffness and mechanical strength were found to be higher than those of PLA/PEO and remained comparable to pure PLA, whereas the elongation at break was 73–143% higher owing to the effective plasticizing and reinforcing effect exerted by PEO and CF respectively. Addition of PEO and CF had a great influence on the thermal properties, particularly on the glass transition and cold crystallization temperatures. Overall, the appealing properties of the proposed biocomposites combined with the sustainability of the developed process render them ideal for several technological applications within the plastic industry including food and cosmetic packaging, disposable items, and toys.

The fabrication of spiropyran-doped poly(vinylidene fluoride-co-hexafluoropropylene) electrospun fibers and the investigation of their optochemosensing properties when exposed to organic acid vapors are reported. The system is first activated through the conversion of the spiropyran molecules dispersed within the polymer to their fluorescent merocyanine photoisomers upon UV irradiation. The latter undergo protonation in the presence of acid vapors, giving rise to an evident colorimetric transition of the composite from purple to yellow and to a concurrent quenching in the spectral emission. Upon gas depletion under ambient conditions, the reversible interactions with the acid molecules lead to a spontaneous recovery of the free merocyanine form and, thus, of the initial materials' color and emission signal. Consistent with their higher surface to volume ratio, the nanofibrous mats exhibit a reduction in the response and recovery times by 25% and by more than 90% compared to composite fibers and films of the same material. The efficient vapor permeation/desorption confers a fast optical detection, which is linear with the acid concentration, and an outstanding reusability for over 40 protonation/recovery cycles. Therefore, the photoswitchable acidochromism of spiropyrans combined with the high specific surface area of the nanofibrous polymeric support provides a photoactivated fast optical and visual acid recognition suitable for integration within portable and reusable platforms targeting the real-time detection of acidic vapors for industrial and environmental applications.

A photoresponsive microstructured composite is fabricated through the impregnation of cellulosic filter paper (FP) with a spiropyran-modified acrylic polymer. The polymer enwraps uniformly each individual cellulose fiber, increases the thermal stability of cellulose, and ensures the preservation of the composite functionalities even upon removal of the surface layers through mechanical scratching. The photochromic spiropyran moieties of the polymer, even while embedded in the cellulosic sheet, can reversibly interconvert between the colorless spiropyran and the pink merocyanine isomeric states upon irradiation with UV and visible light, respectively. Moreover, the photochromic polymer presents a faster photochromic response and a higher resistance to photodegradation, with an outstanding reusability for more than 100 switching cycles when it is incorporated in the cellulose network. Most importantly, the acidochromism of the modified FP, attributed to the spiropyran molecules after UV activation, allows the real-time optical and visual detection of acidity changes and spoilage in food products, such as wine and milk. Spoilage due to bacterial degradation and oxidation processes generates acidic vapors that induce the protonation of the merocyanine. This results in a visually detectable chromic transition from pink to white of the treated cellulose fibers, corresponding to a blue shift in the absorption spectrum. The developed photoresponsive cellulose composite can serve as cost-effective robust optical component in integrated functional platforms and consumer-friendly indicators for smart food packaging, as well as portable on demand acidoresponsive interfaces for gas monitoring in industrial and environmental applications.