Reactive Extrusion of Nonmigratory Active and Intelligent Packaging.

The environmental and economic burden of food waste demands new preservation technologies to reduce the degradative actions of spoilage such as moisture, oxygen, and microorganisms. Direct food additives can help maintain product quality; however, the limited life span of these additives combined with consumer desire for "clean label" products has motivated research into new food manufacturing technologies like active and intelligent packaging that can prevent and detect food spoilage. In this work, curcumin was grafted to polypropylene (PP-g-Cur) via reactive extrusion to produce nonmigratory active and intelligent packaging through a solvent-free, efficient, and continuous method. Immobilization of curcumin was confirmed by a standard migration assay exhibiting a maximum of 0.011 mg/cm2 migration, significantly below the EU migratory limit for food contact materials (0.1 mg/cm2). Compared to native PP films, PP-g-Cur films blocked 93% of UV light while retaining 64% transparency in the visible region, allowing for desirable product visibility while inhibiting UV degradation of packaged goods. While the ability of PP-g-Cur to inhibit growth of E. coli and L. monocytogenes was insignificant compared to control PP, free curcumin exhibited poor bacterial inhibition as well, suggesting that without hydrophilic modification, native curcumin has limited antimicrobial efficacy. PP-g-Cur films displayed significant radical scavenging in both organic (11.71 ± 3.02 TroloxEq (nmol/cm2)) and aqueous (3.18 ± 1.04 TroloxEq (nmol/cm2)) matrices, exhibiting potential for antioxidant behavior in both lipophilic and hydrophilic applications. Finally, when PP-g-Cur films were exposed to ammonia, an indicator of microbial growth, the color visually and quantitatively changed from yellow to red, demonstrating potential to indicate spoilage. These findings demonstrate the potential of a scalable technology to produce active and intelligent packaging to limit food waste and advance the capabilities of functional materials in a variety of applications.

Elucidating CO2 Chemisorption in Diamine-Appended Metal-Organic Frameworks.

The widespread deployment of carbon capture and sequestration as a climate change mitigation strategy could be facilitated by the development of more energy-efficient adsorbents. Diamine-appended metal-organic frameworks of the type diamine-M2(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) have shown promise for carbon-capture applications, although questions remain regarding the molecular mechanisms of CO2 uptake in these materials. Here we leverage the crystallinity and tunability of this class of frameworks to perform a comprehensive study of CO2 chemisorption. Using multinuclear nuclear magnetic resonance (NMR) spectroscopy experiments and van-der-Waals-corrected density functional theory (DFT) calculations for 13 diamine-M2(dobpdc) variants, we demonstrate that the canonical CO2 chemisorption products, ammonium carbamate chains and carbamic acid pairs, can be readily distinguished and that ammonium carbamate chain formation dominates for diamine-Mg2(dobpdc) materials. In addition, we elucidate a new chemisorption mechanism in the material dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-diaminopropane), which involves the formation of a 1:1 mixture of ammonium carbamate and carbamic acid and accounts for the unusual adsorption properties of this material. Finally, we show that the presence of water plays an important role in directing the mechanisms for CO2 uptake in diamine-M2(dobpdc) materials. Overall, our combined NMR and DFT approach enables a thorough depiction and understanding of CO2 adsorption within diamine-M2(dobpdc) compounds, which may aid similar studies in other amine-functionalized adsorbents in the future.