Effects of Functionalized Kraft Lignin Incorporation on Polypropylene Surface Energy and Practical Adhesion

Abstract

Polypropylene (PP) is a multifunctional and widely applied polymer. Nevertheless, its low energy surface and poor adhesion are well-known and might impair some prospective applications. Aiming to overcome these limitations, PP composites can be applied as a tool to enhance PP surface energy and then increase its practical adhesion. In this work, Kraft lignin (KL) was chemically modified and blended with PP. In short, KL was hydroxypropylated and further reacted with acetic anhydride (A-oxi-KL) or maleic anhydride (M-oxi-KL). Lignin modifications were confirmed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). PP-composites with different lignin contents, as well as pristine PP, were characterized in terms of their thermal behavior, morphology, surface energy, and practical adhesion by DSC, scanning electron microscopy (SEM), contact angle measurement, and peeling tests, respectively. Lignin incorporation did not affect the PP degree of crystallization. The lignin modifications led to a better compatibility with the PP matrix and surface energies up to 86% higher than neat PP. Increases of up to 66% in the peel strength were verified. Composites with M-oxi-KL showed the best adhesion performance, confirming the lignin functionalization is an efficient approach to improve the practical adhesion of PP films.

Lignin beyond the status quo: recent and emerging composite applications

“…27 Modifying the lignin structure allows for tailoring the surface properties of lignin-based composites, resulting in improved water resistance, biodegradability, and surface energy. 28 These properties make composites attractive for advanced applications, including those in the biomedical field, drug delivery, and tissue engineering. 29 This review presents a comprehensive overview of recent advancements in the emerging field of lignin-based sustainable composites.…”

Lignin‐based materials for the detection and adsorption of metal ions

“…Therefore, continued efforts have been put to both apply available chemistries for lignin processing and seek novel applications 7 . Examples include covalent modification of lignin, 8–11 lignin as additives, 12–14 UV protecting films, 15,16 and lignin blending for reinforcement of materials 17,18 …”

“…Therefore, continued efforts have been put to both apply available chemistries for lignin processing and seek novel applications. 7 Examples include covalent modification of lignin, [8][9][10][11] lignin as additives, [12][13][14] UV protecting films, 15,16 and lignin blending for reinforcement of materials. 17,18 Sensing technologies play a key role in our daily lives, witnessing widespread uses over the past few decades such as glucose sensors, pregnancy test kits, and recent COVID-19 home testers.…”

“…However, in some cases, chemical modification of lignin can be executed to improve the sensitivity and adsorption capability of lignin toward toxic elements. For chemical modification, phenolic hydroxy groups are often targeted thanks to their low pKa (10), wherein several chemical reactions have been attempted for various applications. 6,8 Another common reaction is electrophilic aromatic substitution in which electron-rich aromatics in lignin such as methoxy phenyl act as a nucleophile.…”