Biodegradable and renewable UV-shielding films are highly demanded to meet the increasing sustainable requirement for the environment. Lignin as a natural broad UV blocker has gained considerable attention; however, the poor dispersibility within synthetic polymers limited its applications. Thus, a bioinspired melanin-like polydopamine thin layer was incorporated for the first time with lignin nanoparticle (LNP) in this effort, forming a UV-blocking core–shell lignin–melanin nanoparticle (LMNP) with higher compatibility and durability. Subsequently, LNP, LMNP, melanin nanoparticles (MNP), and a mix of LNP and MNP (MixNP) were compounded with poly­(butylene adipate-co-terephthalate) (PBAT), to enhance the UV-barrier capability and photostability of PBAT films. The incorporated LMNPs were well distributed into PBAT, leading to improved tensile properties and thermal stability of the resulting films. All these films possessed remarkable UV-blocking capacity at NP concentration ranging from 0.5 to 5 wt %, blocking almost all of UV-A and more than 80% of UV-B light, while an appreciable optical transmittance could also be achieved. The PBAT–LMNP films displayed a high UV-shielding stability and the best retention in mechanical properties after UV exposure for 40 h. This work provides a very promising approach for fabricating biodegradable PBAT-based UV-blocking films for potential applications in agricultural or food packaging materials where the UV resistance is highly required.

Soda lignin was functionalized with tert-butyldimethylsilyl groups by the reaction with tert-butyldimethylsilyl chloride. The reaction conditions leading to a quantitative derivatization of lignin, hydroxyl groups were determined by 31 P and 1 H NMR and compared with those of acetylation. The functionalization was also confirmed by FTIR and size exclusion chromatography. The silylation enhances the thermal stability and lowers the T g of lignin as compared to the acetylation. In addition, the silylated lignins are soluble in a wider range of organic solvents, including solvents of low polarity and show a clear hydrophobic character with a contact angle with water higher than 100°. Neat, acetylated, and silylated lignins were then blended with low density polyethylene, and injection molded materials were analyzed with tensile tests, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). This study reveals the higher compatibility of the silylated lignin with the polyolefin matrix and hence the great potential of the silylated lignin for a use as an additive in apolar polymer matrices.

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In the present report an environmentally friendly approach to transforming renewable feedstocks into value-added materials is proposed. This transformation pathway was conducted under green conditions, without the use of solvents or catalyst. First, controlled modification of lignin, a major biopolymer present in wood and plants, was achieved by esterification with 11-maleimidoundecylenic acid (11-MUA), a derivative from castor oil that contains maleimide groups, following its transformation into 11-maleimidoundecanoyl chloride (11-MUC). Different degrees of substitution were achieved by using various amounts of the 11-MUC, leading to an efficient conversion of lignin hydroxy groups, as demonstrated by H and P NMR analyses. These fully biobased maleimide-lignin derivatives were subjected to an extremely fast (ca. 1 min) thiol-ene "click" polymerization with thiol-containing linkers. Aliphatic and aromatic thiol linkers bearing two to four thiol groups were used to tune the reactivity and crosslink density. The properties of the resulting materials were evaluated by swelling tests and thermal and mechanical analyses, which showed that varying the degree of functionality of the linker and the linker structure allowed accurate tailoring of the thermal and mechanical properties of the final materials, thus providing interesting perspectives for lignin in functional aromatic polymers.

Lignin, tannins, and cashew nut shell liquid are considered the main sources of aromatic-based macromolecules. They represent an abundant alternative feedstock for the elaboration of aromatic chemicals and polymers, with a view to replacing some fossil-based fractions. Located in different tissues of plants, these compounds, with a large diversity and structural complexity, have, to date, been considered as byproducts derived from fractionation-separation industrial processes with low added value. In the last decade, the use of click chemistry as a tool for the synthesis of controlled macromolecular architectures has seen much development in fundamental and applied research for a wide range of applications. It could represent a valid solution to overcome the main limitations encountered in the chemical modification of natural sources of chemicals, with an environmentally friendly approach to create new substrates for the development of innovative polymers and materials. After a brief description of the main aromatic biopolymers, including the main extraction techniques, along with their structure and their properties, this Review describes chemical modifications that have mainly been focused on natural polyphenols, with the aim of introducing clickable groups, and their further use for the synthesis of biobased materials and additives. Special emphasis is given to several as-yet unexplored chemical features that could contribute to further fundamental and applied materials science research.