Date of Award
Doctor of Philosophy (PhD)
William Scott Whiteside
This research studied is about development of seaweed biodegradable nanocomposite films reinforced with cellulose nanocrystals (CNCs) from seaweed biomass and investigating the properties of the films. Study was conducted to isolate CNCs from seaweed biomass and these isolated CNCs are applied to developed seaweed biopolymer films. At last, degradability of these films was evaluated with a weight loss method in soil burial and lake water immersion systems.
CNCs were extracted from seaweed biomass of brown, red, and green by four steps process of depolymerization, bleaching, acid hydrolysis, and mechanical dispersion. Physicochemical and thermal properties were determined for each seaweed group and compared. Among the seaweeds, Sargassum fluitans (brown seaweed) was used to isolate CNCs and applied to alginate nanocomposite (Alg/CNCs) films. Alg/CNCs films showed gradual decreasing of water absorption/solubility, water vapor permeability (WVP), oxygen permeability (OP), and light transmittance with increasing addition of CNCs. Also, addition of CNCs enhanced the tensile strength but elongation of Alg/CNCs films did not show the tendency due to its shrinkage. Scanning electron microscopy (SEM) results indicated that CNCs layers can be formed in the alginate polymer matrix, and the Fourier-transform infrared spectroscopy (FTIR) spectra showed the chemical interaction between alginate polymer matrix and CNCs. Thermal stability test with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) data suggested the addition of CNCs can improve the thermal properties of Alg/CNCs films.
Seaweed nanocomposite films were also developed with brown seaweeds crude extracts; kombu (Laminaria japonica) and sargassum (Sargassum natans). Obtained supernatant after acid-base pretreatment was used for film forming solution. Seaweed biopolymer films were formed by casting-evaporation method. CNCs were isolated from residues with acid-base pretreatment and applied to seaweed biopolymer film for developing bionanocomposite film. Kombu nanocomposite film was prepared with 5% CNCs (KNF-5), and sargassum nanocomposite film was formed with 5% and 25% CNCs (SNF-5 and SNF-25, respectively). Without addition of CNCs, kombu film (KF) appeared as a dark brown color and sargassum film (SF) as a light brown color. CNCs did not affect the color of the films. Through the SEM observation, holes and cracks were found in surface and cross section of KF and SF but they were covered up with CNCs. Chemical structure changes indicated the molecular strength was increased when CNCs were added to the KF and SF. Also, higher crystallinity index was obtained after CNCs addition. These changings led to improving not only the physicochemical characteristics but also mechanical, barrier, and thermal properties. Total phenolic contents, DPPH radical scavenging effect, and reducing power assay indicated that kombu film showed higher antioxidant properties than sargassum film but not significantly related to the CNCs addition.
Developed bionanocomposite films were conducted to degradation test for evaluating their biodegradability. It was performed under indoor soil burial and lake water immersion systems for 35 days and degradation rate was determined by weight loss. In both conditions, degradation results varied in the order as followed: Alginate nanocomposite film (ANF-5) > alginate film (AF) > KNF-5 > SNF-25, SNF-5 > KF > SF. Alginate-based films degraded up to 35% in soil and 53% in lake water for 35 days. In the case of seaweed films, they were eliminated by soil in 28 days and lake water in 7 days. Morphological observation showed wrinkles, pores, and cracks on their surface in the later days of the experiment. Besides, chemical structure changes revealed molecular bonding in polymer matrix diminished at the last stage of the process compared to before the test. Thermal stabilities also decreased due to reduction of the bonding strength after a certain period of days in both soil burial and lake water immersion systems.
Doh, Hansol, "Development of Seaweed Biodegradable Nanocomposite Films Reinforced with Cellulose Nanocrystals for Food Packaging" (2020). All Dissertations. 2663.