An Ionomeric Renewable Thermoplastic from Lignin‐Reinforced Rubber

Abstract

An ionomeric, leathery thermoplastic with high mechanical strength is prepared by a new thermal processing method from a soft, melt‐processable rubber. Compositions made by incorporation of equal‐mass lignin, a renewable oligomeric feedstock, in an acrylonitrile‐butadiene rubber often yield weak rubbers with large lignin domains (1–2 µm). The addition of zinc chloride (ZnCl2) in such a composition based on sinapyl alcohol‐rich lignin during a solvent‐free synthesis induces a strong interfacial crosslinking between lignin and rubber phases. This compositional modification results in finely interspersed lignin domains (<100 nm) that essentially reinforce the rubbery matrix with a 10–22 °C rise in the glassy‐to‐rubbery transition temperature. The ion‐modified polymer blends also show improved materials properties, like a 100% increase in ultimate tensile strength and an order of magnitude rise in Young's modulus. Coarse‐grained molecular dynamics (MD) simulations verify the morphology and dynamics of the ionomeric material. The computed result also confirms that the ionomers have glassy characteristics.

Lignin as Alternative Reinforcing Filler in the Rubber Industry: A Review

“…The distribution of different types of crosslinks is affected by the reversion time, and the inclusion of lignin showed that it actually takes part during the vulcanization process and that the mechanism is due to the thermal stability itself. Besides, the conventional vulcanization (CV) system delayed the optimum cure time, but the semi-efficient (semi-EV) and efficient vulcanization (EV) systems increased the cure rate (Nando and De, 1980;Shukla et al, 1998;Kakroodi and Sain, 2016). Nevertheless, some studies reported that the presence of lignin decreased the crosslink density and the number of polysulphidic crosslinks while maintaining the number of disulfidic and monosulfidic crosslinks (Kumaran and De, 1978;Kakroodi and Sain, 2016).…”

“…Besides, the conventional vulcanization (CV) system delayed the optimum cure time, but the semi-efficient (semi-EV) and efficient vulcanization (EV) systems increased the cure rate (Nando and De, 1980;Shukla et al, 1998;Kakroodi and Sain, 2016). Nevertheless, some studies reported that the presence of lignin decreased the crosslink density and the number of polysulphidic crosslinks while maintaining the number of disulfidic and monosulfidic crosslinks (Kumaran and De, 1978;Kakroodi and Sain, 2016). They suggested that the incorporation of lignin in the rubber matrix masked some of the cross-linking sites on the rubber molecules.…”

“…This was due to the protection given by lignin against degradation processes in the rubber matrix during mixing with high mechanical and thermo-oxidative stresses. However, flex crack resistance could sometimes be improved even at lower cross-link density of the rubber, and there was also an increase in crack growth resistance due to the higher percentage of disulfidic crosslinks (Kakroodi and Sain, 2016).…”

“…The thermal stability of rubber composites was investigated through thermal decomposition, as displayed in Table 3 (Jiang et al, 2013). Environmental stresses such as oxygen and heat led to undesirable chemical changes in polymers, such as loss of ductility, loss of surface quality, and changes in their molecular weights and structures Kakroodi and Sain, 2016). The changes to rubber molecular weights were due to chain scission followed by cross-linking of the produced macro-radicals with unsaturated C=C double bonds.…”

Lignin-Reinforced Nitrile Rubber/Poly(vinyl chloride) Composites via Metal Coordination Interactions

“…Lai et al reported that the polydimethylsiloxane (PDMS) cross-linked by abundant Zn 2+ –carboxylate interactions was very strong at room temperature and exhibited fast thermal-healing properties . Metal coordination bonds can also undergo reversible rupture and reconstruction under the tensile stress, which effectively dissipates mechanical energy and provides excellent mechanical properties. , Filippidi et al incorporated reversible Fe 3+ -catechol coordination interactions into a lightly cross-linked epoxy network . The tensile strength, toughness, and stiffness of the Fe 3+ -containing network were improved by 2–3 orders of magnitude compared with the Fe 3+ -free network .…”