Stabilization of Hybrid Adhesives and Sealants by Thermodynamic Tuning of Molecularly Optimized Lignin Bio-Additives: Small Changes, Big Effects

Abstract

The use of lignin as a functional additive has long been a promising topic in both industry and academia, but the development of such systems is still limited by the considerable challenges posed by the incompatibility of lignin with common polymers. Herein, we designed modified silicone (MS) sealants with enhanced UV and thermal stability by incorporating molecularly engineered lignin bio-additives while establishing robust design principles to finely adjust the morphology of such blends by tailoring the molecular structures of lignin fractions. To that end, we first constructed a library of lignin fractions with various molecular weights (obtained by fractionating Kraft lignin and by using a lignin model compound) and with several chemical modifications (acetylation, butyrylation, and silylation). The lignin bio-additives were then melt-blended with MS polyethers. The experimental phase diagrams of the resulting blends were established and rationalized with a thermodynamic framework combining Hansen solubility parameters and Flory−Huggins theory, unraveling fascinating insights into the complex solubility behavior of lignin fractions and notably, for the first time, the subtle interplay between molecular weight (entropic effects) and chemical modifications (enthalpic effects). A molecularly optimized lignin additive was then selected to achieve full solubility while providing better thermal stability and UV-blocking properties to the resulting MS material. Overall, this article provides robust design principles for the elaboration of functional biomaterials with optimized morphologies based on rationally engineered lignin fractions.

One‐Pot Reversible Complexation‐Mediated Polymerization (RCMP) from Benzylic Alcohols for Facile Access to Polymer‐Grafted Lignin

“…Lignin absorbs UV light encompassing all of UV‐A (315–400 nm), UV‐B (280–315 nm) and UV‐C (200–280 nm) and serves as natural broad‐spectrum sunscreens and anti‐aging agents of organic plastics and films owing to the abundance of aromatic rings present in lignin [29,30] . However, mere physical blending of lignin with synthetic polymers causes phase‐separation and gives opacity or limited UV‐shielding properties due to their immiscibility [31] …”

“…[29,30] However, mere physical blending of lignin with synthetic polymers causes phase-separation and gives opacity or limited UV-shielding properties due to their immiscibility. [31] The immiscibility problem can be solved by using polymer-grafted lignin. We prepared an approximately 100 μm thick film by mixing pure PMMA (94 wt %) with 7d), lignin formed large aggregates in the PMMA matrix because of the immiscibility, making the film less transparent.…”

One‐Pot Reversible Complexation‐Mediated Polymerization (RCMP) from Benzylic Alcohols for Facile Access to Polymer‐Grafted Lignin

“…[29,30] However, mere physical blending of lignin with synthetic polymers causes phase-separation and gives opacity or limited UV-shielding properties due to their immiscibility. [31] The immiscibility problem can be solved by using polymer-grafted lignin. We prepared an approximately 100 μm thick film by mixing pure PMMA (94 wt %) with 4, entry 1 for 72 h).…”