The conversion of lignocellulosic biomass into platform chemicals is the key step in the valorization of agricultural waste. Of the biomass-derived platform chemicals currently produced, lactic acid plays a particularly pivotal role in modern biorefineries as it is a versatile commodity chemical and building block for the synthesis of biodegradable polymers. Microwave-assisted processes that furnish lactic acid avoid harsh depolymerization conditions while cutting down reaction time and energy consumption. We herein report a flash catalytic conversion (2 min) of lignocellulosic biomass into lactic and glycolic acids under microwave irradiation. The batch procedure was successfully adapted to a microwave-assisted flow process (35 mL min(-1) ), with the aim of designing a scalable process with higher productivity. The C2 and C4 units recovered from the depolymerization were directly used as the starting material for a solvent and catalyst-free microwave-assisted polycondensation that afforded oligomers in good yields.
A new method of preparation of solid
epoxy resins (SER) with desired
epoxy-group content via an advanced process under microwave irradiation
is presented together with the results of molecular weight measurements
for narrow oligomeric fractions obtained from chromatographic separation
of SER. All the measurements were performed using gel permeation chromatography
(GPC) and matrix-assisted laser desorption ionization spectrometry–time
of flight mass spectrometry (MALDI-TOF/MS). In the GPC analysis, two
types of calibration were used: the first was a standard calibration
based on polystyrene standards, while the second was done on the basis
of a chromatograms of epoxy resins synthesized from bisphenol A (BPA)
and diglycidyl ether of bisphenol A (EDBPA). On the basis of the MALDI-TOF
analysis, it was assumed that the purity of starting materials, i.e.,
low molecular weight epoxy resin, clearly determined the structure
of the SER. In order to obtain an SER with linear chain structures
and an even number of polymerization degrees, the low molecular weight
epoxy needs to be characterized by a high content of diglycidyl ether
of bisphenol A (EDBPA) as it was observed for Rutapox 0162. In the
case of low molecular weight epoxy resins that contained a higher
oligomeric fraction of diglycidyl ether of bisphenol A (EDBPA) like
Epikote 828, one can observe an even and odd polymerization degree
which resulted in the branching of chain structures. Eventually, the
procedure of chromatographic separation of SER allowed a better correlation
of results from MALDI-TOF/MS and the GPC.
The Inside Cover picture shows the complementary action of different microwave reactors in destroying the polymer chains of lignocellulosic biomass and rebuilding oligomers from the recovered building blocks. We designed a “microwave factory in the lab” for a flash catalytic conversion of biomass to selective platform chemicals—a sustainable protocol carried out in a microwave flow reactor. Lactic and glycolic acids were efficiently reacted to synthesize oligomers via a solvent‐ and catalyst‐free microwave‐assisted process under vacuum. Enabling technologies play a important role in biomass valorization, from agricultural wastes to value‐added products in agreement with modern biorefinery. More details can be found in the Full Paper by Carnaroglio et al. on page 1342 (DOI: ).
All the monomers used in ring opening metathesis polymerization ( ROMP) were synthesized by two step reactions. The first step of the synthesis was the Diels-Alder reaction between furan and maleic anhydride to produce exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride. The second step was to prepared 7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, dimethyl ester by Fischer estrification of exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3dicarboxylic anhydride in refluxing methanol. 7-Oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, dimethyl ester was polymerized by ROMP catalyzed by commercially available ruthenium catalyst Ru(PPh3)2(Cl)2(CHPh) at defined concentrations relative to the monomer. Depending on the molar ratio of the monomer to the catalyst polymers with different large molecular weight were obtained. Molecular weights and polydispersities were confirmed by gel permeation chromatography. Monomers and polymers were also analyzed by FT-IR. Polyanions of poly (7-oxanorbornene-2,3-dicarboxylate) were prepared by hydrolysis of poly (dimethyl-7-oxabicyclo (2.2.1) hept-5-ene-2,3-dicarboxylic acid). It is worth noting that the polyanions in aqueous solution form hydrogels. The properties of the prepared polymers will be discussed in full paper.
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