Hayley Smith

Topic

Greener Extraction and Structure-Property Relationships of Alginate for Biodegradable Plastic Applications

Department of Civil Engineering

Date & location

• Tuesday, July 14, 2026

• 11:00 A.M.

• Elliott Building, Room 230

• & Virtual Defence

Reviewers

Supervisory Committee

• Dr. Heather Buckley, Department of Civil Engineering, University of Victoria (Supervisor)

• Dr. Kristian Dubrawski, Department of Civil Engineering, UVic (Member)

• Dr. Karolina Valente, Department of Mechanical Engineering, UVic (Outside Member) 

External Examiner

• Dr. Michael Cunningham, Department of Chemical Engineering, Queen’s University 

Chair of Oral Examination

• Dr. Andrea McKenzie, Department of History, UVic

   

Abstract

Alginate is a kelp-derived biopolymer with growing potential for bio-based plastics, films, coatings, and packaging materials. To advance utilization, scalable use of alginate requires extraction processes that reduce chemical hazard and environmental impact while producing polymers with physicochemical properties suitable for material fabrication. First, alginate extraction methods were screened for human and environmental hazard, and three lower hazard protocols were tested. Extraction chemistry strongly affected alginate properties and process impacts. Two of the three methods evaluated had higher greenhouse gas emissions of 987 and 389 kg CO2-eq. In contrast, an ambient temperature sodium citrate chelation protocol produced higher yield of 26.7% and lower emissions of 177 kg CO2-eq, but lower molecular weight of 59.5 kDa. To improve polymer quality, the citrate process was optimized using Response Surface Methodology. Optimum conditions of 49.5°C, 1 h, and 0.125 M sodium citrate produced alginate with 21.0% yield and molecular weight of 508 kDa, a ninefold increase over non-optimized citrate extraction. The optimized method was reproducible at 20-fold scale and reduced total energy use by 62% and global warming potential by 17%. Films prepared from the optimized alginate showed greater flexibility, with tensile strain of 11%, and lower stiffness, with a Young’s modulus of 2091 ± 236 MPa, than films from lower molecular weight commercial alginate. The optimized citrate process was then applied to cultivated northeast Pacific kelps to establish feedstock benchmarks. Ten blade biomass samples spanning five species from British Columbia and Alaska were screened. Two samples failed phase separation. For the remaining eight feedstocks, yields ranged from 12.0 to 26.1% dry weight, molar mass ranged from 36.6 to 623 kDa, and seven samples exceeded 400 kDa. M/G ratios ranged from 0.14 to 1.38, demonstrating broad compositional variation relevant to crosslinking and material performance. Finally, calcium alginate films were used to evaluate how uronic acid composition (M/G ratios from 0.25 to 1.98) and glycerol concentration govern film properties. Both factors influenced the films’ physical and mechanical properties. Notably, FTIR showed that changes in Ca2+ carboxylate coordination were largely associated with glycerol content and corresponded with differences in network structure, thermal stability, and mechanical performance.