Development of sustainable polymeric shells for fragrance oil microencapsulation using biobased and biomass precursors

This doctoral thesis presents the synthesis of environmentally sustainable microcapsules for the encapsulation of fragrance oil, utilizing biobased and biomass-derived monomers and polymers as shell wall materials. The microcapsules were formed via free radical polymerization, utilizing vinylidene functionalities primarily derived from itaconic acid (IA) (chapters 2-4). Additionally, in chapter 2, biobased methacrylate monomers such as tetrahydrofurfuryl methacrylate (THFMA) and glycerol dimethacrylate (GDMA) were also used. This approach provides an advancement over commercially available microcapsules that rely on fossil-derived monomers and toxic precursors such as methyl methacrylate, formaldehyde and isocyanates. Chapter 1 outlines the fundamentals and importance of fragrance oil, concept of emulsion systems and their stability, the common synthesis methods of microcapsules, and the different types of wall materials used in synthesizing sustainable microcapsules. This chapter also defines the characterization method employed for microcapsules, which is used throughout the thesis. Encapsulation efficiency (EE), measured at 25 ℃, quantifies the proportion of fragrance oil successfully encapsulated within the polymeric shell relative to the initial oil content. Solid content (SC) yield, determined at elevated temperatures (100 ℃ and 120 ℃), serves as an indirect measurement of the shell crosslinking density. This is because thermal exposure can lead to the polymeric shell dilation and thus, potential diffusion of the encapsulated fragrance oil. The objective of this thesis and aims of each subsequent chapter were also presented. Chapter 2 reports the synthesis of fully biobased acrylate microcapsules using itaconic acid (IA) or its esters as the hydrophilic monomer, co-polymerized with a biobased hydrophobic monomer, tetrahydrofurfuryl methacrylate (THFMA), and a biobased crosslinkable monomer, glycerol dimethacrylate (GDMA). The IA-based microcapsules obtained EE and SC yield (120 ℃) approaching 100%. This result demonstrated a feasibility of replacing petroleum-based poly(methyl methacrylate) (PMMA) microcapsules with entirely biobased alternatives. The synthesis of the microcapsules was done via interfacial polymerization through “one-pot” synthesis, which offers scalable potential in industrial manufacturing. In chapter 3, we synthesized two unsaturated polyesters (UPEs) using IA as the diacid, with biobased ethylene glycol (EG) and renewable isosorbide (ISB) as the diols, generating UPE-EG and UPE-ISB, respectively. The UPEs were used as polymerizable emulsifier particles via Pickering emulsion template. The UPEs were located on the oil-water interface and subsequently, through radical polymerization of the available vinylidene moieties on UPE, polyester-based microcapsules were fabricated. Owing to the inherent degradability of polyesters, the resulting microcapsules present a promising mitigation of the microplastic persistence in environment that were originated from microcapsules used in laundry applications. Both UPE-EG and UPE-ISB yielded high EE of 99% and SC yields of approximately 92% at 120℃. In chapter 4, we explored the use of lignin, a natural biopolymer, to synthesize microcapsules. Owing to its abundance, renewability and status as a byproduct of the pulp and paper industry, lignin represents a good promising sustainable material for advancing the bioeconomy. Hydroxyethylated lignin was esterified with monomethyl itaconate (MMI) to produce esterified lignin (EHL-MMI), introducing polymerizable vinylidene groups. Microcapsules synthesized using solely EHL-MMI exhibited limited interfacial deposition and low shell density due to the large steric structure of lignin, as a result, yielding a 29% SC yield at 100 ℃. The introduction of IA, as a molecular filler, at a ratio of 80/20 wt% for EHL-MMI and IA, respectively, significantly improved the shell density and achieved an EE of 98% and SC yield of 69% at 100 ℃. The resulting microcapsules is fully sustainable and environmentally friendly.