Tuan Liu

Selective cleavage of ester linkages of anhydride-cured epoxy using a benign method and reuse of the decomposed polymer in new epoxy preparation

Thermosetting polymers possess high dimensional stability, chemical resistance and thermal stability, and they are indispensable for many applications. However, conventional thermosetting polymers cannot be reprocessed and reshaped due to their permanent cross-linked structure. Therefore, recycling of thermosetting polymers is a serious challenge. Degrading thermosetting polymers into soluble oligomers and reuse of the oligomers in new resin systems may provide a favorable way to solve this problem. In this work, we developed an efficient method for chemical degradation of anhydride-cured epoxy using environmentally benign phosphotungstic acid (HPW) aqueous solution as the catalyst system at a mild reaction temperature of 190 °C. During reaction, the ester bond in the cross-linked structure was selectively cleaved, and the thermosetting polymer was fully converted to oligomers that contain multifunctional reactive groups. When the decomposed matrix polymer (DMP) was used as a reactive ingredient and added up to 40 wt% in the preparation of a new anhydride-cured epoxy curing system, the resulting cross-linked polymers still retained the mechanical properties of the neat polymer.

Correction to A Catalyst-Free Epoxy Vitrimer System Based on Multifunctional Hyperbranched Polymer

The corrected Figure 4c is shown here. With this correction, the calculated activation energy (Ea) is 62.8 kJ/mol. This correction affects the originally calculated Ea of 29.5 kJ/mol, but it does not change the following conclusion remark on page 6795: “According to previously reported literatures, the Ea of most epoxy-based vitrimers is usually between 70 and 150 kJ/mol. In this work, the greatly lower Ea indicates a high rate of TER for the HBE/SA system”.

Preparation of a lignin-based vitrimer material and its potential use for recoverable adhesives

A fully biobased vitrimer material with high lignin content is demonstrated. Ozone treated Kraft lignin is cured with sebacic acid epoxy to form bond-exchangeable crosslinked networks. The biobased vitrimer shows excellent shape memory and repairing properties at elevated temperatures. By taking advantage of these features, a promising recoverable adhesive is also demonstrated.

Eco-Friendly Post-Consumer Cotton Waste Recycling for Regenerated Cellulose Fibers

In this study, post-consumer cotton waste was chemically recycled to produce regenerated fibers using eco-friendly alkaline/urea solvent systems. Both white and colored cotton waste was shredded and hydrolyzed using sulfuric acid to reduce the molecular weight of the cotton fibers. Two solvent systems, i.e., sodium hydroxide/urea and lithium hydroxide/urea, were used to dissolve the hydrolyzed cotton to prepare solutions for fiber regeneration by wet spinning. The diameter, morphology, thermal properties, crystallinity, and tensile properties of the regenerated fibers were characterized by SEM, TGA, XRD, and tensile testing. Results showed that, using this recycling method, fibers with tensile properties comparable to current commercial regular rayon fibers made from wood pulp could be produced, and dyes in the original cotton waste could be conserved to produce fibers with intrinsic colors, thus eliminating the need for dyeing processes. This study demonstrated an economical upcycling method for post-consumer cotton waste with environmentally friendly solvents.

Catalytic Conversion of Biomass-Derived 1,2-Propanediol to Propylene Oxide over Supported Solid-Base Catalysts

A series of supported alkali metal salts were investigated as catalysts to produce propylene oxide (PO) from biomass-derived 1,2-propanediol via dehydrative epoxidation in a solid–gas reaction system. The effects of supports, cations, and anions in the alkali metal salts and calcination temperature were investigated by X-ray diffraction and CO2-temperature-programmed desorption. The results indicate the catalysts with relative mild basicity having higher yields of PO. The highest yield of PO is 58.2% from reactions at 400 °C at an atmospheric pressure over KNO3/SiO2. In addition, the catalyst could be reused after calcination in air at 550 °C.