Effects of sacrificial coordination bonds on the mechanical performance of lignin-based thermoplastic elastomer composites

High performance plant-derived thermoplastic polyester elastomer foams achieved by manipulating charging order of mixed blowing agents

Plant-derived thermoplastic polyester elastomer (TPEE) is an environment friendly polymer known for its exceptional tear strength and mechanical properties, whose monomers are generated from crops. To prepare high-performance TPEE foams is still challenging due to the intrinsic shrinkage behavior. Herein, two microcellular foaming routes with different charging orders of mixed blowing agents, namely "CO2 firstly charging process (CO2-F-process)" and "N2 firstly charging process (N2-F-process)", were developed to elucidate the effects of mixed blowing agents on foaming behavior. Compared with the case in N2-F-process, more carbon dioxide and less nitrogen were adsorbed in CO2-F-process. Thus, TPEE foams prepared by N2-F-process show less shrinkage and higher creep recovery ratio than those prepared by CO2-F-process. Thanks to better structural stability and smaller shrinkage, TPEE foams prepared by N2-F-process exhibited enhanced strength and resilience. For the foams with similar density, compression strength can be increased by 52 %, and energy loss coefficient can be reduced to 50 %, by using N2-F-process. Thus, not only biomass TPEE foams with enhanced mechanical performance shows promising prospects in those areas that needs lightweight, insulation and high resilience, but also novel microcellular foaming technique with mixed blowing agents opens a new way for developing high-performance polymeric foams.

High-Performance, Light-Stimulation Healable, and Closed-Loop Recyclable Lignin-Based Covalent Adaptable Networks

In this work, high-performance, light-stimulation healable, and closed-loop recyclable covalent adaptable networks are successfully synthesized from natural lignin-based polyurethane (LPU) Zn2+ coordination structures (LPUxZy). Using an optimized LPU (LPU-20 with a tensile strength of 28.4 ± 3.5 MPa) as the matrix for Zn2+ coordination, LPUs with covalent adaptable coordination networks are obtained that have different amounts of Zn. When the feed amount of ZnCl2 is 9 wt%, the strength of LPU-20Z9 reaches 37.3 ± 3.1 MPa with a toughness of 175.4 ± 4.6 MJ m-3 , which is 1.7 times of that of LPU-20. In addition, Zn2+ has a crucial catalytic effect on "dissociation mechanism" in the exchange reaction of LPU. Moreover, the Zn2+ -based coordination bonds significantly enhance the photothermal conversion capability of lignin. The maximum surface temperature of LPU-20Z9 reaches 118 °C under the near-infrared illumination of 0.8 W m-2 . This allows the LPU-20Z9 to self-heal within 10 min. Due to the catalytic effect of Zn2+ , LPU-20Z9 can be degraded and recovered in ethanol completely. Through the investigation of the mechanisms for exchange reaction and the design of the closed-loop recycling method, this work is expected to provide insight into the development of novel LPUs with high-performance, light-stimulated heal ability, and closed-loop recyclability; which can be applied toward the expanded development of intelligent elastomers.

Organosolv Lignin Improved Thermoplastic Elastomeric Behavior of Polyethylene/Polyisoprene Blend

Thermoplastic elastomers are considered the fastest-growing elastomers in recent years because of their thermomechanical recyclability, in contrast to traditional thermoset rubbers. Polyolefins such as low-density polyethylene (LDPE) show low mechanical properties, particularly poor elongation when compared with an elastomer or rubber. In this study, LDPE resin is converted to highly ductile rubber-like materials with high elongation and low modulus properties on blending with polyisoprene rubber (IR), followed by treating with dicumyl peroxide as a curing agent and organosolv lignin as an additive. The technique of high shear melt-mixing, in conjunction with vulcanization or crosslinking using organic peroxide, is used to develop hybrid materials based on the LDPE/IR blend at a 70/30 mass ratio, where LDPE is replaced partly with lignin. Various characteristics such as tensile, viscoelasticity, melt flow, crystallinity, and phase morphology of the materials are analyzed. As expected, vulcanization with peroxide can improve the mechanical performance of the LDPE/IR blends, which is further improved with the application of lignin (2 to 5 wt. %), particularly tensile strain is profoundly increased. For example, the average values of the tensile strength, the modulus, and the ultimate elongation of neat LDPE resin are 7.8 MPa, 177 MPa, and 62%, respectively, and those of LDPE/IR/lignin/DCP 65/30/05/2 are 8.1 MPa, 95 MPa, and 238%, respectively. It indicates that the application of lignin/DCP has a profound effect on improving the ductility and elastomeric characteristics of the materials; thus, this material can have the potential to replace traditional rubber products.