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Levulinic Acid: Versatile Building Block for Plasticizer Design

Time: Fri 2021-09-24 14.00

Location:, Stockholm (English)

Doctoral student: Wenxiang Xuan , Polymerteknologi

Opponent: Professor Rafael Auras, Michigan State University

Supervisor: Professor Minna Hakkarainen, Fiber- och polymerteknologi, Polymerteknologi, Wallenberg Wood Science Center, Polymerteknologi; Universitetslektor Karin Odelius, Polymerteknologi

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The utilization of renewable resources is a challenging and an importantaspect towards development of sustainable plastic products. Therefore,commercial biomass conversion to produce biobased chemicals isnecessary to replace current fossil-based chemicals. In this thesis, a libraryof plasticizers was designed utilizing the biobased platform chemical,levulinic acid (LeA), as the building-block. In combination with othercurrent or future biobased constituents, LeA esters and their derivativesserved as a versatile plasticizer library for the biobased and biodegradablethermoplastic polylactide (PLA).The successful syntheses of thirteen plasticizers were confirmed, includingnine monomeric plasticizers employing a classic Fischer-esterification andfour oligomeric plasticizers by means of polycondensation, or a two-stepprocedure with ring-opening polymerization (ROP) of L-lactide, followedby Fischer-esterification with LeA. Utilizing nuclear magnetic resonance(NMR) spectroscopy, as the primary method, the reaction process wasmonitored and the structures of the designed plasticizers were determined.The structural characterization was further supported by electrosprayionization mass spectrometry (ESI-MS). From a plasticizer designperspective, the structure of the plasticizer molecules in combination withthe polymer matrix determines the plasticizer performance. The designedplasticizers with linear and flexible cores, ethylene glycol (EG) or 1,4-butanediol, demonstrated great potential, lowering the glass transitiontemperature (Tg) of PLA from 59 °C to 15 °C and 16 °C respectively andincreasing the strain at break of PLA from 5% to 546% and 227%respectively at 20 wt% addition. The introduction of branching (utilizingglycerol as a core) or cyclic and rigid cores (isohexide and 1,2-cyclohexanediol) lowered the plasticization efficiency. A cis-/trans stereoisomerism of the rigid cores could, to some extent, tune theplasticizing effect and the thermal stability of the plasticizers. Furthermore,when the ketones of LeA were converted into ketals by EG, the thermalstability of the plasticizers and their migration resistances wereconsiderably increased, leading to a lower rate of mass loss and a higher retained molecular weight for the hydrolyzed PLA after hydrolytic agingtests. Similar improvements were mirrored for the oligomeric plasticizers.The utilization of eugenol in plasticizer design realized dual-functioningoligomeric PLA plasticizers with antibacterial properties.