New Reinforcing Approach for Biobased UV-Curing Resins: Hybrid Lignocellulose Fillers with Improved Synergy and Wood Structure Mimics

Abstract

Lignocellulosic fillers have been widely investigated for various polymer resin applications since they have great potential for using wood biomass and recycled plastics. However, besides cellulose nanocrystals (CNC) and nanofibrils (CNF), not much of the other lignocellulose has been used for UV-curing resins. Even more so, none has been used in hybrid lignocellulose combination compositions. In the present work, the effects of hybrid lignocellulose fillers such as lignin (LN)/CNC/CNF/hemicellulose (HC) with ratio-varying compositions on UV-curing biobased resins have been investigated for wood-mimic material coating applications. The hybrid filler effects on the macromolecular chain network, surface morphology, thermomechanical properties, and thermostability were carefully studied. A combination of scanning electron microscopy, DMA Cole–Cole plot, contact angle, etc., allowed getting a sense of hybrid filler distribution and interaction within the polymer matrix. It was identified that an increase in the HC content of up to 38% contributes to more even particle distribution and achieves a maximum double bond conversion rate of about 80%. HC also contributes to porous surface structure, while CNC smooths surface morphology, and, in turn, CNF increases defects. Thermomechanical testing revealed the unique benefit of hybrid reinforcement, showing higher results than single-filler compositions despite the general decrease after incorporation of 5 wt % LN. The storage modulus showed a fourfold increase for 5 wt % LN composition. The observed enormous property enhancement has been attributed to the benefits of hybrid fillers, which mitigate characteristic radical scavenging properties of LN and strongly reduce general filler aggregation, allowing more even filler dispersion while also improving filler–matrix interface synergy. Seventeen different compositions clearly, in comparison to single fillers, show the benefit of hybrid lignocellulosic reinforcement and testify to the ability to precisely tune up material performance and achieve wood structure-mimicking coating materials.