Doctor of Philosophy
Chemical and Biochemical Engineering
Chunbao (Charles) Xu
Paul J. Ragogna
Fossil fuel resources are being used today for most of humankind’s energy and chemical/material needs. The inevitable demise of these resources has created significant interest in the field of biomass and particularly, lignin valorization. As the world’s second most abundant polymer, more than 98% of the annually produced lignin is under-utilized either as an on-site heat source, or as landfill. Thus, finding practical approaches to modifying this inexpensive sustainable resource into materials of high value can be the next leap in lessening the dependence on fossil fuel resources and thus, developing a sustainable future.
In this thesis, kraft lignin is modified into methacrylated lignin (ML), lignin grafted with methacrylate functionalities at its hydroxyl sites. ML was incorporated at loading percentages of 10-31 wt.% into UV-cured coatings and the developed coatings were characterized according to their different properties.
The methacrylation process was optimized via response surface methodology using a central composite design to determine the effect of different reaction variables on the process’ recovered mass yield and to obtain the maximum possible recovered ML. The ML obtained from the optimized reaction conditions was then incorporated at 30 wt.% into a siloxane-based UV-cured coating as a proof of concept for the practicality of the optimization process.
ML was afterwards converted into a primary polyphosphine (lignophine) by a phosphane-ene reaction. The primary lignophine was then capped into tertiary alkylated and fluorinated lignophines, respectively using corresponding alkenes. The ability of the tertiary alkylated lignophine to coordinate to transition metals and sequester transition metal containing catalysts was determined using silver triflate a ring closing metathesis (RCM) reaction using Grubbs I (GI) catalyst, respectively.
Finally, the tertiary alkylated lignophine was converted into a free-standing UV-cured polyphosphonium (lignophonium) network. The obtained films showed high cure percentages and water contact angles, along with a surface charge density value well over the necessary threshold for antimicrobial films and swelling degrees suitable for controlled drug release. The films were probed for their controlled drug release ability using diclofenac as the loaded drug and examining the release in PBS and showed a promising release profile.
Hajirahimkhan, Soheil, "Chemical Modification of Lignin into Advanced Materials" (2018). Electronic Thesis and Dissertation Repository. 5604.
Available for download on Sunday, September 01, 2019