Junna Xin

Partial depolymerization of enzymolysis lignin via mild hydrogenolysis over Raney Nickel

In this work, partial depolymerization of enzymolysis lignin collected from a woody biomass-to-ethanol process was studied via mild hydrogenolysis under the catalysis of Raney Ni. The depolymerized lignin products were low molecular weight oligomers with increased hydroxyl values. The solvent selected, use of base and various reaction parameters were all found to influence yield of depolymerization, the molecular weight and hydroxyl value of the hydrogenated product. The depolymerized lignins displayed greatly enhanced solubility in organic solvents, and therefore would have great potential to be used as feedstock for many valuable thermosetting polymer applications.

Study of green epoxy resins derived from renewable cinnamic acid and dipentene: synthesis, curing and properties

An epoxy based on cinnamic acid (Cin-epoxy) and an anhydride curing agent based on dipentene were prepared. Both products are liquids of low viscosity at room temperature. For the synthesis of the epoxy, cinnamic acid was first converted to a diacid by reacting with maleic anhydride via Friedel–Crafts reaction, followed by allylation of the carboxylic groups and subsequent epoxidation of the allyl double bonds. The curing agent was the Diels–Alder adduct of dipentene and maleic anhydride (DPMA). The chemical structures of Cin-epoxy and DPMA were confirmed by 1H NMR, 13C NMR, FT-IR and ESI-MS. Non-isothermal curing of Cin-epoxy was studied using differential scanning calorimetry (DSC). In addition to DPMA, two commercial anhydrides were also used to cure Cin-epoxy and the curing reactivity and properties of cured resins were compared. Thermal mechanical properties and thermal stability of the cured epoxy resins were studied using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. Results showed that Cin-epoxy was slightly more reactive than the bisphenol A type epoxy DER 332 and displayed good dynamic mechanical properties and thermal stability.

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.

Enhanced melt free radical grafting efficiency of polyethylene using a novel redox initiation method

In this work, for the first time, redox initiation was employed in the melt free radical grafting of glycidyl methacrylate (GMA) and maleic anhydride (MA) onto polyethylene (PE) by reactive extrusion. Since it is very challenging to obtain high grafting degrees of GMA and MA onto polymer backbones through conventional free radical initiation, especially in the extrusion process, the strategy of using a peroxide/reducing agent initiator was introduced. The redox initiation system was composed of dicumyl peroxide (DCP) and Tin(II) 2-ethylhexanoate (Sn(Oct)2). The grafting reaction was monitored by torque rheometry and graft products were analyzed by Fourier Transform Infrared Spectroscopy. Effects of monomer concentration and DCP/Sn(Oct)2 ratio on the degree of grafting were studied. The redox initiation proved to be very effective in improving the grafting degree of GMA and MA onto PE. It is reasoned that, in the presence of Sn(Oct)2, the free radicals produced were not subject to a cage effect, yielding high initiator efficiency.

Preparation and Properties of Hydrogels Based on PEGylated Lignosulfonate Amine

Sodium lignosulfonate (SLS) was aminated to obtain a lignin amine (LA) compound, which was subsequently crosslinked with poly(ethylene glycol) diglycidyl ether (PEGDGE) to obtain hydrogels. The chemical structure of the resulting LA-derived hydrogel (LAH) was characterized by Fourier transform infrared (FTIR) spectroscopy, solid-state 13C NMR spectroscopy, and elemental analysis, and the interior morphology of the freeze-dried hydrogel was examined by scanning electron microscopy. NMR and FTIR spectroscopy results indicated that the amino groups of LA reacted with PEGDGE in the crosslinking reaction. The lignin content in the resulting hydrogel increased with an increase in the LA/PEGDGE weight ratio in the reaction, approaching a maximum (∼71 wt %) and leveling off. The hydrogel with such a composition happened to be the same as the one prepared by reacting the primary amines of LA and epoxy groups of PEGDGE in equal stoichiometry. These results strongly suggest that the formation of the hydrogel network structure was largely dictated by the reactions between the primary amines and epoxy groups. The gels with lignin contents at this level exhibited a superior swelling capacity, viscoelasticity, and shear properties.

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.

H3PW12O40 catalyzed liquid phase nitration of aromatics - : a green process without using H2SO4

H 3 PW 12 O 40 with Keggin structure showed excellent activity for liquid phase nitration of various aromatic compounds, suggesting the possibility of a green nitration process by simply replacing H 2 SO 4 in current nitration unit. The H 3 PW 12 O 40 could be recycled to use with constant activity. Effects of various reaction parameters were investigated extensively.