Masters Degrees (Chemical Engineering)

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Biorefining of tuber crop residues to recover phytochemicals for the formulation of composite films and coatings
(Stellenbosch : Stellenbosch University, 2023-12) Chaima, Catherine Tasankha; Chimphango, Annie Fabian Abel; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
ENGLISH ABSTRACT: The increased demand for processed sweet potatoes has promoted waste generation, mainly of the peels (15-40%), contributing to environmental pollution. Correspondingly, pollution from plastic packaging waste is increasing. Sweet potato peels (SPP) are rich in starch and bioactive compounds (polyphenols and anthocyanins) that can enable the formulation of films and coatings to reduce the use of plastic packaging. However, extracting starch and bioactive compounds from the peels can be challenging due to overlapping extraction conditions and incompatible extraction solvents. Thus, an optimised "green" sequential two-stage SPP biorefinery process (based on wet milling and ultrasound deep eutectic extraction) was developed to recover starch, then polyphenols, and anthocyanins. Additionally, a comparative environmental impact assessment between DES (green solvent) and methanol (conventional solvent) extraction methods was performed through a life cycle assessment (LCA). The wet milling starch extraction conditions: sodium bisulfite concentration (0.1-0.3%), liquid-solid ratio (2-4 mL/g), and extraction time (2-10 min)] using Box Behnken experimental design were optimised first for starch yield and purity. The extracted SPP starch was crosslinked with citric acid to enhance starch’s physiochemical properties (morphology, thermal stability, amylose content, and crystallinity) suitable for film and coating development. The bioactive compounds’ recovery using an ultrasound-assisted DES (UA-DES) from starch-extracted sweet potato peels (SSPP) was optimised next by varying DES concentration (0-90% v/v water), liquid-solid ratio (10-50 mL/g), and extraction time (2-120 min). Subsequently, the developed films and coatings were formed using the modified starch (5% w/v) and bioactive compounds in DES (2.75% v/v through solvent-casting. Under the optimal wet milling conditions of 2 min, 0.1% w/v bisulfite concentration, and a liquidsolid ratio of 3 mL/g, the starch yield achieved were 36.45-39.81%, surpassing the control (water), which yielded 34.40-35.46%. The citric-acid starch modification increased the amylose content from 20% to 29%. The UA-DES extraction efficiency at the optimal extraction conditions (22.5% v/v water/ DES, liquid: solid ratio of 20 mL/g, and 10 min processing time, was higher than UAmethanol’s. The UA-DES yield based on neochlorogenic acid, total phenolic content (TPC), and total anthocyanin content (TAC) were about 75 µg/g dw, 10.54 mg gallic acid equivalent (GAE)/g dw, and 17.83 g/g dw, respectively, compared to UA-methanol’s, 40.24 µg/g dw, 7.90 mg GAE/g dw, and 13.78 g/g dw. In addition, the DES’s environmental impacts were lower than methanol’s (global warming: 0.025 vs 19.6 kg CO2 eq, acidification potential: 1.295 x10-4 vs 9.16 kg SO2 eq, water consumption: 4.79 x10-4 vs 16.9 m3 , and human carcinogenic toxicity: 2.84 x10-4 vs 669 kg 1.4- Dibenzo[def,p]chrysene). The optimal composite film and solution (5% starch and 2.75% phenolic compounds) had a higher modulus of elasticity (6.97±1.3 MPa) and elongation at break (15.75±2.6%) Stellenbosch University https://scholar.sun.ac.za iii in comparison to the starch-only films (control). These improvements were attributed to the influence of the SSPP extracts in DES. Therefore, the two-stage biorefinery successfully extracted starch and bioactive compounds to develop eco-friendly films and coatings. Ultimately, the study's findings offer a greener extraction strategy for SPP that can reduce waste and add value. Furthermore, the SSPP fractionation in a biorefinery provides an opportunity for more value addition to sweet potato peels beyond starch production.
Cellulose nanoparticles as reinforcement and fillers in LDPE nanocomposites for production of low density packaging material
(Stellenbosch : Stellenbosch University, 2022-12) Mdungazi, Sean; Chimphango, Annie Fabian Abel; Greyling, Guilaume; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT: Cellulose nanocrystals (CNC) have the potential to be used as reinforcement in petroleum-based polymers such as low-density polyethylene (LDPE) in the synthesis of LDPE nanocomposites. One of the challenges is the addition of the CNC in the LDPE form agglomerates. Therefore, surface modifications of the CNC such as acetylation and polyethylene adsorption may be utilized to reduce the agglomeration. However, these modifications have the potential to impact the cumulative energy demand (CED) and global warming potential (GWP) of the overall synthesis process. The study aimed to investigate the effect of acetylation and polyethylene adsorption of the CNC on the dispersion in LDPE, and on Young’s modulus, tensile strength, stress at break, water contact angle (WCA), moisture absorption, CED and GWP of the LDPE nanocomposites. The LDPE nanocomposites reinforced with acetylated cellulose nanocrystals (ACNC) were prepared by mixing LDPE with ACNC. The degree of substitution (DS) of the ACNC was varied (DS 1.19, 1.62, and 1.94) with CNC loading (1, 3, and 5 wt. %). Subsequently, the LDPE nanocomposites reinforced with polyethylene oxide (PEO) adsorbed cellulose nanocrystals (PEO-CNC) were developed by mixing the LDPE with PEO-CNC. The PEO:CNC dosage was varied (0.5:1, 1.5:1, and 2.5:1) with CNC loading (1, 3, and 5 wt. %). The nanocomposites were solvent cast (140 °C) and injection moulded (130 °C, 350 bar). The dispersion was described using Free-path spacing and characterization was done using field emission scanning electron microscopy (FE – SEM). The functional (mechanical and physical) properties were investigated using stress-strain curves, the sessile drop method, and a precision balance. The CED and GWP were estimated using a life cycle assessment conducted using OpenLCA software. The results showed that only CNC loading had a significant effect (p<0.05) on the dispersion (D0.1 %) of the LDPE nanocomposites reinforced with ACNC and PEO-CNC. The dispersion (D0.1 %) of the ACNC and PEO-CNC decreased from 8.81 - 4.19 % and from 7.97 – 6.96 % respectively with an increase in CNC loading (1 – 5 wt. %). DS had a significant effect (p<0.05) on Young’s modulus of the LDPE nanocomposites reinforced with ACNC. Young’s modulus increased from 181.95 – 217.2 MPa with an increase in DS (DS 1.19 – 1.94). The CNC loading had a significant effect (p<0.05) on the tensile strength of both nanocomposites. The tensile strength decreased from 26.2 – 25.9 MPa and 32.98 – 9.11 MPa with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The stress at break decreased from 50 - 14.75 % with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with PEO-CNC. The DS, PEO dosage, and CNC loading had no significant effect (p>0.05) on the WCA. The WCA decreased numerically from 89.7 – 88.5° and 76.3 – 71.5 ° with an increase in CNC loading (1 – 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The PEO dosage, DS, and CNC loading had no significant effect on moisture absorption (p>0.05). The moisture absorption increased numerically from 1.10 – 8.83 % and from 3.29 – 6.93 % with an increase in CNC loading (1- 5 wt. %) for the LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The PEO dosage, DS, and CNC loading had no significant effect (p>0.05) on the CED and the GWP. The cumulative energy demand (CED) increased numerically from 3119 - 4032 MJ and 3040 - 4304 MJ with an increase in CNC loading (1 – 5 wt. %) for LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The GWP increased numerically from 331 - 482 kg·CO2 and from 328 - 470 kg·CO2 with an increase in CNC loading (1 – 5 wt. %) for LDPE nanocomposites reinforced with ACNC and PEO-CNC, respectively. The findings of the study show that acetylation increased Young’s modulus of the LDPE nanocomposites while PEO adsorption decreased the functional properties of the LDPE nanocomposites. Both acetylation and PEO adsorption had no impact on the environmental impact of the LDPE nanocomposites. The functional properties and environmental impact were mainly dependent on the CNC loading.
Development of a tier 3 method for calculating greenhouse gas emissions from pulp and paper mills in South Africa
(Stellenbosch : Stellenbosch University, 2023-03) Chikande, Adriano Quondie Persuade; Chimphango, Annie Fabian Abel; Van Rensburg, Eugene; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering.
ENGLISH ABSTRACT: The increasing threat of climate change caused by greenhouse gas (GHG) emissions has resulted in strict government emission regulations as a control measure toward emissions mitigation. These regulations and associated emission taxes have increased the cost of operations for large GHG-emitting industries, including the pulp and paper industry. The South African government requires pulp and paper mills (PPMs) to report emissions at the highest level (Tier 3) of the three-tiered IPCC GHG reporting method, which requires facility-level emission data. However, obtaining this type of data is challenging for PPMs due to the lack of continuous measuring systems at key points such as steam boilers and recovery furnaces. Therefore, there is a need to develop a method for Tier 3 reporting without a need for continuous measurements. This study investigated the feasibility of using a mass balance approach based on the principle of conservation of mass to develop a Tier 3 reporting method for the PPMs. The study involved analysing carbon flow from the entry gates to the exit gates of thirteen South African PPMs. This carbon was quantified using composition-based mathematical models developed for each carbon-containing input and output stream. These models were combined into a single mass balance model that calculates the emitted carbon as the difference between the input and output carbon using an Excel-based tool. In addition, this tool was used for sensitivity analyses to determine how emissions vary with changes in independent variables like the carbon content of input and output streams. The approach accounts for variations in the fuel quality and combustion efficiencies in PPMs using different technologies; hence, it is reliable. Sankey diagrams were used to report the carbon flow through the specified mill boundaries, and the total GHG emissions were calculated as the sum of CO2, CH4, and N2O emissions in tCO2-eq. Results showed that in 2020, 51% of the carbon leaving the PPMs was emitted as GHGs. 39% and 10% left the mills as pulp and paper products and as byproducts and wastes, respectively. The sector emitted 5 602 671 tCO2-eq (53% biogenic and 47% fossil) from activities under IPCC Codes 1A1a, 1A2d, 1A2f, 2A2, and 2A4d. Results also showed that virgin fibre-based mills produce 2.8 times more GHG emissions than recycled fibre-based mills, which suggested that recycled fibre usage should be promoted. Moreover, the models indicated that replacing coal with natural gas can halve emissions. Therefore, using natural gas could be the next step to environmental sustainability for South African PPMs. Sensitivity analyses revealed that the higher a process stream’s carbon flow rate, the larger the extent by which emissions will change with stream properties like carbon and moisture content variations. This study is the first to provide a Tier 3 reporting method for South African PPMs. A Tier 3 methodology results in improved GHG accounting accuracy which is crucial in developing climate change mitigation strategies in line with South African environmental legislations.
Development of processing schemes for high-value utilization of pumpkin by-products
(Stellenbosch : Stellenbosch University, 2023-12) Chifomboti, Lindah Phambala; Chimphango, Annie Fabian Abel; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
ENGLISH ABSTRACT: Pumpkin use for production of high-value products including pre-processed cuts, has increased due to consumers’ preference for healthy lifestyles. This trend is generating substantial amounts of residues, mainly peels (rich in β-carotene and protein) and seeds (rich in oil and protein), without a proper disposal strategy. Thus, value can be added to the seeds and the peels by co-production of high-quality edible oils, β-carotene, and protein through an integrated multi-feedstock biorefinery concept. Edible oils are often recovered by cold pressing extraction (CPE) to preserve bioactive compounds. However, CPE has a low extraction efficiency (< 85%), and the edible oils produced lack oxidative stability, requiring the addition of synthetic antioxidants (β-carotene), which also serve as a pigmentation agent. Notably, vegetable oils are the preferred solvents for β-carotene extraction from plant biomass. In this study, novel processing schemes were developed and assessed for co-extraction of pumpkin seed oil (PSO) and β-carotene from pumpkin seeds and peels. Residues from the oil/β-carotene extraction (rich in protein) became feedstock for protein extraction (PE) through an enzyme (protease or viscozyme-L)-assisted hydrolysis. The objective was to increase PSO yields and oxidative stability through in-situ β-carotene extraction and enrichment, and to obtain protein as an additional high-value product in a sequential process with minimal processing steps. Microwave pre-treatment (MP) of the seeds and peels was employed to enhance PSO, βcarotene, and protein extraction. Three schemes were developed by the sequential integration of CPE and PE: (1) using microwaved seeds, (2) microwaved seed-peel mixture, and (3) untreated seed-peel mixture. Process conditions for CPE and in-situ enrichment with βcarotene (seed-to-peel ratio, 50 – 90 % w/w; microwave power, 200 – 600 Watts (𝑔. 𝑚2 103 𝑠𝑒𝑐3 ⁄ ); irradiation time, 120 – 240 sec; cold pressing pressure, 10 – 20 MPa), and PE from the press residue (liquid-to-solid ratio, 10 – 30 mL/g; enzyme dose, 1 – 3 % w/w; extraction time 2 – 5 h) were optimized for maximum yields in a three-level Box Behnken Design response surface methodology. The seed composition was ~54% crude oil and 35 % protein, and that of the peel ~11% protein and ~15 mg/ 100 g β-carotene. The CPE residues from mixed feedstock had 60.92 % protein. Microwave pre-treatment increased β-carotene, and protein extraction by 7.3-fold, and 38.65 % (protease-assisted extraction), respectively. The optimized CPE conditions were 80 % w/w seeds, 600 Watts (𝑔. 𝑚2 103 𝑠𝑒𝑐3 ⁄ ), 240 sec, and 20 MPa, providing 73.58 % recovery yield, and those of PE were 26.71 mL/g, 3 % w/w enzyme dose (viscozyme-L (5.0 pH, 55 °C)), 5 h; and 20.83 mL/g, 3 % w/w enzyme dose (protease (8.0 pH, 40 °C)), 4.24 h with 74.70% and 61.76% protein recoveries, respectively. Stellenbosch University https://scholar.sun.ac.za v PSOs extracted from the mixed feedstock were pigmented with β-carotene (~5.50 mg/ 100 g oil), and had higher oxidative stability at elevated temperatures (180 °C, 6 h) than unpigmented oils (2.01 mg/ 100 g oil), making them a suitable replacement for synthetic antioxidants in fortified-vegetable oils. Furthermore, protease (4.9 – 116.6 ± 1.18 mg/L) produced essential amino acids in higher concentrations than viscozyme-L (1.2 – 47.1 ± 2.47 mg/L). Thus, the microwave-assisted processing CPO scheme with pumpkin seed-peel mixture provides a potential multi-product pathway for obtaining maximum value from pumpkin residues.
Maize (Zea mays) bran as a biorefinery feedstock for the co-extraction of nutraceuticals and functional food compounds
(Stellenbosch : Stellenbosch University, 2024-03) Nkhoma, Mcphancio; Chimphango, Annie Fabian Abel; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
ENGLISH ABSTRACT: The interest in extracting functional food compounds such as prebiotics, antioxidants, and nutraceuticals from renewable resources has increased as they offer several health benefits. Functional compounds such as ferulic acid (FA), xylooligosaccharides (XOS), and proteins have been extracted mainly from lignocellulosic material such as wheat bran. This study investigated the feasibility of biorefining three types of maize bran (white, yellow, and purple) using green methods based on green chemistry principle (such as enzymes, organic acids, and emerging technologies such as microwave treatment) to co-produce xylooligosaccharides, proteins, and phenolic acids. The main objective was to compare the selective extraction of protein, ferulic acid, and xylooligosaccharides based on yields and functional properties. The protein was extracted from the maize brans under mild alkaline conditions, while the xylooligosaccharides and ferulic acid were extracted using microwave-assisted-lemon juice extraction and microwave-assisted enzymatic extraction, respectively. The target was to extract the xylooligosaccharides with a degree of polymerization of at least 2, phenolic compounds with high antioxidant activity (at least 80%), and protein with increased solubility. The profiling showed that yellow maize bran has more hemicellulose (51.89 ± 0.48 %), followed by white maize bran (44.44 ± 0.27 %) and purple maize bran (38.37 ± 0.44) with the least hemicellulose content. The extraction conditions were optimised using Box-Behnken statistical design based on yield for protein and XOS. In addition to yield, the FA optimization included total phenolic content and antioxidant activity. In the mild alkaline extraction of protein, sodium bicarbonate concentration was varied from 0.5 – 1.5 M, time from 1–3 h, and temperature from 30 – 50 °C). The optimisation of ferulic acid recovery from destarched maize bran was conducted by varying the extraction time from 2 to 6 h, solid loading from 5 to 15% w/v, and enzyme dosage from 40 to 80 U). Furthermore, the optimisation of XOS extraction conditions varied temperature (110 – 130 °C), time (2 – 6 h) and lemon juice concentrations (50 –100 v/v%). The optimised conditions for the protein extraction were: time, 2 h; concentration, 1 M; and temperature 40 °C with a protein yield of 5.48 and 7 %w/w in yellow maize bran and purple maize bran, respectively. The application of microwave treatment increased the production of FA by more than 20 %. Specifically, the yield of FA increased from 0.81 to 3.84 mg/g in purple maize bran, from 0.4 to 3.98 mg/g in yellow maize bran, and from 0.28 to https://scholar.sun.ac.za iii 4.25 mg/g in white maize bran. The XOS yields obtained from purple maize bran, yellow maize bran, and white maize bran were 24.41, 23.41, and 23.53%, respectively, with degrees of polymerization of 15.82, 15.85, and 15.93 for XOS from white, yellow, and purple maize bran, respectively. These results demonstrate the potential application of the extracted xylooligosaccharides as prebiotics in the food industry. The findings of the present study suggest that yellow and purple maize bran are suitable sources of protein, ferulic acid, and xylooligosaccharides, while white maize bran is well-suited for ferulic acid and xylooligosaccharides.
Recovery and functionalization of cellulosic fibers from pulp and paper mill waste streams
(Stellenbosch : Stellenbosch University, 2022-04) van der Watt, Liezl Carien; Chimphango, Annie Fabian Abel; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH SUMMARY: Pulp and paper mills lose between 1 to 3% of their production to waste effluent. The effluent contains cellulosic fibre which is normally discarded as sludge to landfills or is incinerated. This is a waste of valuable resources. The objectives of the current project were: (i) identify waste streams in Kraft pulp and paper mills, (ii) develop and validate a method to recover these fibres and (iii) to develop and validate a method to functionalize the recovered fibres to nanocellulose. The recovery method was developed based on fibre size distribution and validated based on flotation efficiency (> 55%) while the functionalization method was based on forming nanocellulose gel-like suspensions within 5 min of mechanical treatment. The waste sources were categorized into continuous and batch losses. The largest source of continuous waste is from the paper machine whitewater not treated by save-all devices (a unit installed to recover fiber internally) whereas, the greatest batch losses occur during grade changes. Sludge samples were collected from various sampling points in the Kraft mill bleaching plant as well as from paper machine broke systems and paper machine cut-offs or trimmings. The fibres from these locations are normally sprayed into paper machine, alkaline and acid effluent drains. Fibres from the effluent streams were recovered by flotation with colloidal gas aphrons (CGAs) generated using two types of non-ionic surfactants (synthetic and green-based). The average size of fibres collected were 93±3.1, 72±3.9 and 93±5.3 𝜇𝑚 for paper machine, alkaline and acid effluent streams. The synthetic surfactant used was Triton X-100 and the alternative, green-based surfactant tested was N-Dodecyl 𝛽-D-maltoside (DDM). The average recovery efficiencies achieved by both surfactants were between 50 and 78%. DDM is a promising alternative to Triton X-100 and achieved similar efficiencies. Functionalization of nanocellulose fibres was achieved by phosphorylation pre-treatment using ammonium dihydrogen orthophosphate and urea in the ratio 1:1.2:19.6, which gave nanocellulose gel-like suspensions within 5 min of blending using a high speed blender (900 W nutribullet). The suspensions obtained were highly heterogeneous by being both in the microscale (1.0 to 2.0 𝜇m) and nanoscale ranges (50 to 800 nm). Alcohol insoluble (95% ethanol) films were made from these recovered fibres. The results obtained after validating the fibre recovery and functionalization methods formed a basis for evaluating the feasibility of using soft sensors to predict the quality of nanocellulose produced. The properties of the fibres collected along the different stages in the bleaching sequence produced nanocellulose materials with varying quality as determined by particle size distribution and other measured properties of the recovered fibres like zeta potential (between -31 and -58 mV ) and crystallinity indices (between 13 to 27%). By using index quality models combined with near-infrared spectroscopy results a soft sensor can be developed that can accurately predicted the quality of the nanocellulose material produced. Based on the results of this study it was concluded that all effluent streams can be combined into a single waste source from which fibres can be recovered and functionalized to high-value products like nanocellulose.
The simultaneous extraction and depolymerisation of lignin, from vine shoots using one-pot microwave-assisted deep eutectic solvent systems
(Stellenbosch : Stellenbosch University, 2024-03) Scholtz, Nicholas Edward; Chimphango, Annie Fabian Abel; Pfukwa, Helen; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
ENGLISH ABSTRACT: The growing concern stemming from the use of fossil fuel-based materials has become prominent over -time. The environmental pollution it causes, together with the rapid decline of their reserves has demanded for more sustainable alternatives. One such material is lignin. Its aromaticity makes it unique from other constituents which together with its high carbon content makes it a suitable material for the synthesis of carbonaceous materials, such as phenol, which is mostly derived from fossil fuels. Currently, the largest commercial supplier of lignin is waste effluents from pulp and paper mills, but lignin obtained from these mills has altered chemical structures resulting from the numerous, intense processing conditions and harsh chemicals used and currently has no significant commercial value. Alternative sources of lignin are biomass materials. It is difficult to selectively obtain lignin from biomass because of the complex and irregular structure of lignin. Therefore, severe, and multiple processing steps are required to obtain adequate yields of pure lignin. Large amounts of biomass (organic waste) such as vine shoots that contain lignin, are generated from vineyards for vinification (winemaking), and currently, they have limited uses. Therefore, the aim of this study entailed the development of a one-pot process, using green chemicals and processes, to extract lignin whilst simultaneously depolymerising it from vine shoot powder (VSP). The solvents used were two deep eutectic solvents (DESs) namely, ChCl: LA and AlCl3: ChCl: BDO and to minimise processing times and temperatures the use of microwave-assisted extraction (MAE) was employed as a heating system. A Box-Behnken experimental design (BBD) was used to optimise the molar ratio (between the HBA and HBD), reaction temperature, and reaction time to maximise the lignin yield and purity from VSP. The lignin content of the VSP was estimated to be 26.3%. Under optimised conditions using ChCl: LA, a yield and purity of 92.5% and 99.6% were obtained and using AlCl3: ChCl: BDO a yield and purity of 88.0% and 91.4% were obtained. The degree of depolymerisation was gauged through molecular weight analysis using size-exclusion chromatography (SEC). The two optimised lignin samples measured weight average- (Mw) and number average- (Mn) molecular weights of 12580 and 5090 g/mol, respectively using a microwave-assisted ChCl: LA system and 10490 and 4830 g/mol, respectively using a microwave-assisted AlCl3: ChCl: BDO system. The degree of depolymerisation was compared to a reference lignin sample obtained using organosolv process. The reference sample had Mw and Mn values of 16080 and 9400 g/mol, respectively. Under optimised conditions, DESs were recycled and reused for lignin extraction and obtained lignin yields of 32.1% and 26.8% using ChCl: LA and AlCl3: ChCl: BDO, respectively. The purities were 81.3% and 67.6%, respectively. Hence, high- quality lignin could be obtained using recycled DESs. Furthermore, a one-pot process for the simultaneous extraction and depolymerisation of lignin from vine shoots was successful and has shown that less energy intensive processes can be used to do so, whilst using green chemicals. The findings of this study showed that vine shoots were a suitable source of lignin and could be extracted in high yields and of high quality using green procedures and chemicals in a one-pot process.
UV degradation of bioplastics and conventional plastics in the marine environment
(Stellenbosch : Stellenbosch University, 2023-03) Mzabane, Ondela; Akdogan, Guven; Chimphango, Annie Fabian Abel; Dorfling, Christie; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
ENGLISH ABSTRACT:In the modern era, there has been a significant increase in the production of and demand for conventional plastics. Increased plastic use is a serious concern for the world. This is because of the accumulation of plastic in the marine environment, which leads to negative impacts on the marine ecosystem. In the marine environment, plastics are exposed to ultraviolet (UV) radiation, temperature changes, physical stress, salinity, and oxidation. Therefore, a key strategy to address this issue is to actively promote and develop biodegradable plastics in efforts to address and alleviate plastic pollution in the marine environment. The study aimed to investigate and compare physical and chemical degradation between bioplastics and conventional plastics to micro-plastics in the marine environment, with little or no microorganism effects. Three different plastics were investigated: polypropylene (PP), polyethylene terephthalate (PET), and polylactic acid (PLA). All plastics were 4 cm × 10 cm in size. Plastics were exposed to two treatments in different environments: (i) a dry UV pretreatment (in air) of neat plastics at two UV irradiances (65 and 130 W/m2 ), and (ii) artificial seawater tests under the same UV conditions. Each run commenced for four weeks, during which UV radiation was cycled for a total of 24 hours: 12 hours on, and 12 hours off. Sampling took place every seven days for further analysis. For signs of degradation, changes in mass loss, carbonyl index, percentage crystallinity, hardness, and morphology were tracked. Results from UV pre-treatment tests showed that in air, high UV irradiation (130 W/m2 ) resulted in more degradation compared to low UV irradiation (65 W/m2 ). Polypropylene was more susceptible to degradation than polyesters (PET and PLA). Degradation in seawater was slow for all plastics. There was a decrease in most properties of seawater compared to the pretreatment tests. This is because, in seawater, the degraded surfaces from the pre-treatment may have been washed away, exposing new surfaces. This investigation showed that the degradation rate is temperature-dependent, and processes in the ocean are slowed down because seawater is a good heat sink. Polylactic acid was the least responsive plastic to UV degradation in both environments.

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