Amine-Functionalized Lignin as an Eco-Friendly Antioxidant for Rubber Compounds

Abstract

Although the typical antioxidant, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), ensures high durability and long lifespan for rubber compounds, it generates a highly toxic quinone in water, causing serious environmental pollution. Herein, as an alternative material of 6PPD, we newly introduce ecofriendly amine-functionalized lignin (AL) to be incorporated in rubber, which can provide excellent combinatorial antiaging properties of thermal stability and ozone/fatigue resistances through radical scavenging effect. The heterolytic ring-opening reaction of AL and sulfur can accelerate curing and improve the cross-link density by 28% (v, 4.107 × 10 −4 mol/cm 3 ), consequently reducing the ozone vulnerable areas of the matrix and further improving the aging resistance. Notably, AL allows its rubber compound to exhibit superior anti-ozone performance after ozone aging, with the arithmetic surface roughness (Sa) of 2.077 μm, which should be compared to that of 6PPD (4.737 μm). The developed chemically modified lignin and the methodology have enormous potential as a promising additive for future eco-friendly rubber compounds. The eco-friendly lignin-based antioxidant manufactured by amination reaction has the potential to reduce environmental pollution for the future rubber industry.

Recent Advances of Lignin Functionalization for High-Performance and Advanced Functional Rubber Composites

“…While the simultaneous use of amines and hindered phenols may produce synergistic effect with superior antioxidation effect. Chung et al 106 functionalized lignin with diethylenetriamine (DETA) via Mannich reaction, resulting in grafted primary and secondary amine groups onto lignin molecules, which exhibits improved radical scavenging performance. The resultant aminefunctionalized lignin (AL) provided superior resistance to thermal and ozone aging on NR composites, which is comparable to 6PPD.…”

Investigation of novel polyanilines as new antioxidants for ethylene propylene diene monomer rubber composites

“…This can lead to an increase in the curing rate and crosslink density of rubber. 25 The ts 2 and tc 90 are the scorch and cure times while cure rate index (CRI) is a cure rate index, which measures the rate of vulcanization depending on the difference between optimum vulcanization and incipient scorch time. 26 It is observed from the results that rubber composites containing 3b, 3c, and 3d compounds showed lower cure time (tc 90 ) and higher CRI than the other composites indicating that these compounds (3b, 3c, and 3d) had an accelerating effect on the curing process.…”

Antioxidative Behavior of an Eco-Friendly Chitosan-Based Biomass Macromolecular Antioxidant for Styrene–Butadiene Rubber (SBR)/Silica Composites

“…1,2 However, due to the presence of plenty of unsaturated double bonds in the rubber matrix, the rubber molecule chains are prone to crosslinking or breaking induced by light or thermal oxygen, or ozone during processing and application, resulting in the deterioration of their performance and appearance, consequently shortening the lifetime of rubber products. 3,4 Generally, the addition of antioxidants during rubber compounding can delay the aging process of rubber materials and extend their service life. 5,6 But most of the traditional rubber antioxidants are small molecular organic compounds, which are easily prone to migration from the polymer matrix during the process and usage.…”

“…Rubber products are widely applied in many fields because of their outstanding high elasticity, such as tires, medical gloves, pipes, wires and cables, adhesives, etc. , However, due to the presence of plenty of unsaturated double bonds in the rubber matrix, the rubber molecule chains are prone to crosslinking or breaking induced by light or thermal oxygen, or ozone during processing and application, resulting in the deterioration of their performance and appearance, consequently shortening the lifetime of rubber products. , …”