title: Development of biomaterials from sustainably produced macroalgae feedstocks

authors: Jayasooriya, Nethmie

subjects: cellulose

abstract: Upgrading and maintaining large-scale wastewater treatment plants (WWTPs) is notably expensive, particularly in rural areas of New Zealand. Freshwater macroalgae ponds may offer a cost-effective alternative for wastewater treatment in these areas. These ponds produce significant amounts of residual macroalgae biomass as a by-product of the bioremediation process, which is nutrient-rich and contains valuable biopolymers like cellulose. Utilizing this residual biomass as a substrate for high-value cellulose production is yet to be demonstrated. Therefore, this thesis investigated the potential of utilizing this residual freshwater macroalgae biomass to develop bioproducts (cellulose and biostimulants) aligning with the principles of a circular economy and waste recovery.

The first chapter investigated the dual extraction process of biostimulants and high-purity cellulose from Oedogonium calcareum grown in primary effluent. It introduces an economical and effective extraction method utilizing a hot alkali, which also provides disinfection, ensuring that the biomass is free from pathogens, making it safe for further use. The biostimulant extract was found to be comprised of several plant-promoting substances. Subsequently, the residual biomass was used to extract cellulose, and the quality of this Oedogonium-derived cellulose was assessed to determine its characteristics for potential future use in biocomposites.

In the second chapter, a comparative analysis was conducted on cellulose extracted from four macroalgae species, namely Rhizoclonium sp., Zygnema sp., Oedogonium sp., and Stigeoclonium sp. This research filled a significant gap by providing a detailed characterization of cellulose derived from freshwater macroalgae, which has been less studied compared to cellulose from marine macroalgae. This chapter makes a significant contribution by fully characterizing the physicochemical properties of freshwater macroalgae cellulose, which as a by-product of wastewater treatment, provides an alternative and sustainable source of cellulose with potential future applications in biocomposites.

The final chapter details the development of biocomposite films using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) reinforced with cellulose nanofibers derived from a naturally co-existing mixed algae culture of Cladophora sp. and Rhizoclonium sp. The production and characterization of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-oxidized Cellulose NanoFibre (CNF) from these macroalgae was accessed. Additionally, PHBV polymer biocomposite films incorporating either commercially available plant-derived CNF, unmodified algae cellulose, or TEMPO-oxidized CNF were compared. The films were comprehensively characterized, with a focus on their mechanical and thermal properties. The results demonstrated the potential of these biocomposite films for use in applications such as packaging materials, highlighting their environmental and functional benefits.

Overall, this thesis demonstrates significant advancements in the utilization of algae grown in wastewater for the successful extraction of bioproducts. It investigated the efficient recovery and application of macroalgae-derived cellulose and also highlighted the potential of these bio-based materials in enhancing the properties of the PHBV polymer, thus contributing to the development of sustainable biocomposite materials.

text: Development of biomaterials from sustainably produced macroalgae feedstocks Upgrading and maintaining large-scale wastewater treatment plants (WWTPs) is notably expensive, particularly in rural areas of New Zealand. Freshwater macroalgae ponds may offer a cost-effective alternative for wastewater treatment in these areas. These ponds produce significant amounts of residual macroalgae biomass as a by-product of the bioremediation process, which is nutrient-rich and contains valuable biopolymers like cellulose. Utilizing this residual biomass as a substrate for high-value cellulose production is yet to be demonstrated. Therefore, this thesis investigated the potential of utilizing this residual freshwater macroalgae biomass to develop bioproducts (cellulose and biostimulants) aligning with the principles of a circular economy and waste recovery.

The first chapter investigated the dual extraction process of biostimulants and high-purity cellulose from Oedogonium calcareum grown in primary effluent. It introduces an economical and effective extraction method utilizing a hot alkali, which also provides disinfection, ensuring that the biomass is free from pathogens, making it safe for further use. The biostimulant extract was found to be comprised of several plant-promoting substances. Subsequently, the residual biomass was used to extract cellulose, and the quality of this Oedogonium-derived cellulose was assessed to determine its characteristics for potential future use in biocomposites.

In the second chapter, a comparative analysis was conducted on cellulose extracted from four macroalgae species, namely Rhizoclonium sp., Zygnema sp., Oedogonium sp., and Stigeoclonium sp. This research filled a significant gap by providing a detailed characterization of cellulose derived from freshwater macroalgae, which has been less studied compared to cellulose from marine macroalgae. This chapter makes a significant contribution by fully characterizing the physicochemical properties of freshwater macroalgae cellulose, which as a by-product of wastewater treatment, provides an alternative and sustainable source of cellulose with potential future applications in biocomposites.

The final chapter details the development of biocomposite films using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) reinforced with cellulose nanofibers derived from a naturally co-existing mixed algae culture of Cladophora sp. and Rhizoclonium sp. The production and characterization of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-oxidized Cellulose NanoFibre (CNF) from these macroalgae was accessed. Additionally, PHBV polymer biocomposite films incorporating either commercially available plant-derived CNF, unmodified algae cellulose, or TEMPO-oxidized CNF were compared. The films were comprehensively characterized, with a focus on their mechanical and thermal properties. The results demonstrated the potential of these biocomposite films for use in applications such as packaging materials, highlighting their environmental and functional benefits.

Overall, this thesis demonstrates significant advancements in the utilization of algae grown in wastewater for the successful extraction of bioproducts. It investigated the efficient recovery and application of macroalgae-derived cellulose and also highlighted the potential of these bio-based materials in enhancing the properties of the PHBV polymer, thus contributing to the development of sustainable biocomposite materials.

year: 2024-07-17

title: Experimental investigation of timber-to-steel connection using self-drilling wing screws

authors: Mohanswamy, Gowrava

abstract: Self-drilling wing screws are well-suited for hardwood and pressed material boards and are explored as an alternative connector to traditional bolts for connecting thick hot-rolled steel with timber. The wing avoids force-feeding of the screw into the timber which prevents the timber from cracking. However, limited studies were found on the timber-to-steel connection using self-drilling wing screws under shear loading. This paper investigates the shear behaviour and capacity of self-drilling winged screw connections between radiata pine timber and hot rolled steel plate through the experimental test. In addition, tensile coupon tests, screw bending tests, moisture content tests, screw pullout tests, and screw bearing tests were performed to determine the material properties of the steel, timber, and screws. A total of 70 experimental tests were conducted on the timber to steel connection connections with different steel thicknesses (8mm-20mm), timber thickness (15mm-45mm), numbers of screws (1-3), and screw axis angle (45°-90°). The failure mode is theoretically analyzed using Johansen yield theory. The resulting data from Eurocode 5 [24] was compared with experimental results as current AS/NZ standards lack adequate guidance in addressing timber-to-steel connections. From the above comparison, it was found that the Eurocode 5 [24] was under-conservative by 90%. Based on the experimental results, new design equations for calculating the shear capacity of self-drilling winged screws are proposed.

text: Experimental investigation of timber-to-steel connection using self-drilling wing screws Self-drilling wing screws are well-suited for hardwood and pressed material boards and are explored as an alternative connector to traditional bolts for connecting thick hot-rolled steel with timber. The wing avoids force-feeding of the screw into the timber which prevents the timber from cracking. However, limited studies were found on the timber-to-steel connection using self-drilling wing screws under shear loading. This paper investigates the shear behaviour and capacity of self-drilling winged screw connections between radiata pine timber and hot rolled steel plate through the experimental test. In addition, tensile coupon tests, screw bending tests, moisture content tests, screw pullout tests, and screw bearing tests were performed to determine the material properties of the steel, timber, and screws. A total of 70 experimental tests were conducted on the timber to steel connection connections with different steel thicknesses (8mm-20mm), timber thickness (15mm-45mm), numbers of screws (1-3), and screw axis angle (45°-90°). The failure mode is theoretically analyzed using Johansen yield theory. The resulting data from Eurocode 5 [24] was compared with experimental results as current AS/NZ standards lack adequate guidance in addressing timber-to-steel connections. From the above comparison, it was found that the Eurocode 5 [24] was under-conservative by 90%. Based on the experimental results, new design equations for calculating the shear capacity of self-drilling winged screws are proposed.

year: 2024

title: Strawmen and the decolonisation of the academy

authors: Tauri, Juan Marcellus

subjects: Social justice

abstract: For this piece I take as my point of departure Biko Agozino’s response to a series of questions posed by a member of the audience, to a panel he was a member of during this time in New Zealand. The panel in question was part of the launch of a new journal, Decolonisation of Criminology and Justice, at AUT University, Auckland in June 2018. Biko was invited to give a speech at the launch of the journal, and participate in a panel discussion on the broad theme of ‘decolonising criminology and criminal justice’.

text: Strawmen and the decolonisation of the academy For this piece I take as my point of departure Biko Agozino’s response to a series of questions posed by a member of the audience, to a panel he was a member of during this time in New Zealand. The panel in question was part of the launch of a new journal, Decolonisation of Criminology and Justice, at AUT University, Auckland in June 2018. Biko was invited to give a speech at the launch of the journal, and participate in a panel discussion on the broad theme of ‘decolonising criminology and criminal justice’.

year: 2019-07-10