Master of Philosophy (M.Phil.)

Permanent URI for this collectionhttp://192.248.9.226/handle/123/18719

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item: Thesis-Full-text
Optimization of bio-chemical conversion of rice straw to 5-(hydroxymethyl) furfural
(2024) Wanninayake, PN; Gunawardena SHP; Subasinghe SADT; Rathnayake HHMP
Agricultural waste-based biorefinery merges waste and production sectors to develop a circular economy. One such biorefinery product, 5-(hydroxymethyl) furfural (5-HMF) has gained increasing interest as a versatile platform chemical to produce chemicals and fuels, and rice straw will be an ideal feedstock to produce 5-HMF. Limited studies on the direct conversion of rice straw to 5-HMF reveal the requirement of extensive research. This MPhil research study focuses to identify the most feasible conversion process to convert rice straw into 5-HMF, and optimize the required process parameters in laboratory-scale to be used in unit processes in scaled-up implementation. As the first objective, this thesis has proposed a roadmap, elucidating the existing methods for rice straw pretreatment to convert cellulose and cellulose conversion to 5-HMF processes. Then cellulose conversion to 5-HMF was evaluated, considering catalyst used, solvent system, process temperature, and process time. Eventually, an evaluation method, based on a generalized objective function with penalty scores, was developed and used its minimum value to find the optimal process configuration at the lowest cost for large-scale 5-HMF production. However, considering the feasibility of large-scale application of these processes in Sri Lankan context, combinatory acid/ alkaline pretreatment method and mineral acid-catalyzed cellulose to 5-HMF conversion process were selected for the optimization. The final objective was experimentally optimization of the process parameters of each, using an advanced optimization technique, response surface methodology. Central composite design-based experiments were used to develop statistical models for each process. Quantitative analyses were performed, using regression techniques, analysis of variance, and residual analysis, whereas qualitative analyses were carried out via Fourier Transform Infrared Spectroscopy. The pretreatment process was carried out to maximize the outcome of rice straw biorefinery. It included two steps: (1) dilute sulphuric acid treatment at reduced temperatures to optimize hemicellulose removal, and (11) dilute sodium hydroxide treatment at reduced temperatures to optimize lignin removal. The maximum hemicellulose removal (15.78%) was observed at optimal conditions of 0.26 moldm−3 acid concentration, 98.1 ∘C reaction temperature, and 30.48 min reaction time. The maximum removal of lignin (20.98%) was obtained at 2.55 moldm−3 sodium hydroxide concentration, 80.5 ∘C reaction temperature, 106.48 min reaction time. An optimized acid- catalyzed hydrothermal process for the in-situ production of 5-HMF from rice straw extracted cellulose was obtained, using a biphasic reaction system. The maximum yield of 5- HMF was 23.51% at optimal conditions of 0.046 moldm−3 dilute hydrochloric acid concentration, 180 ∘C process temperature, and 107 min process time. Finally, validation experiments were performed, and the observed optimum results showed close agreement with the predicted, confirming rice straw biorefinery process optimization. Keywords: Rice straw, Biorefinery, 5-(hydroxymethyl) furfural, Pretreatment, Cellulose, Catalytic conversion, Optimization, Respo
item: Thesis-Abstract
Investigation of the effect of pretreatment methods on lipid yield and fatty acid profile of locally isolated microalgae species
(2024) Sandani, WAP; Ariyadasa TU; Premachandra JK
The introduction of a novel chemical cell disruption method with economic and environmental feasibility to increase the lipid extraction yield is of paramount importance to enhance the commercialization drive of microalgae biofuels. Recently, researchers have suggested a novel chemical cell disruption method, electro-Fenton’s process (EFP), for microalgal biodiesel production. The present study demonstrates the feasibility of employing EFP incorporating a sacrificial steel anode as a novel approach for microalgal cell disruption. Primarily in the current research, Chlorella sp. has been selected after screening four locally available microalgal species and it was identified as Chlorella homosphaera using molecular identification. Moreover, the effect of chlorophyll removal on the FAME profile and quality of biodiesel produced using C. homosphaera were evaluated where chlorophyll removal significantly improved the biodiesel quality while reducing the resulted lipid yield. Selected process parameters of the electrolytic cell were optimized using the electro-generation of H2O2 prior to the EFP experiments. Subsequently, the electrolytic cell with the optimized reactor parameters was employed in microalgal cell disruption via EFP incorporating a sacrificial steel anode where two process parameters, namely reaction time and the biomass concentration, were optimized. Moreover, results were compared with wet (WT) and dry (DR) lipid extraction methods without cell disruption. The EFP showed a significant improvement in lipid yield over the WT method and comparatively higher biodiesel quality than WT and DR methods. Finally, the results obtained for optimized EFP were analyzed comparatively with four conventional mechanical methods. According to the results, EFP contributed to the production of biodiesel with comparatively improved quality than that of mechanical cell disruption methods. Thus, the results of the present study demonstrate that the EFP could be a promising method for industrial-scale applications owing to the ability to produce high-quality biodiesel compared to conventional mechanical methods. Keywords: microalgae, lipid yield, chlorophyll removal, electro-Fenton’s process, chemical cell disruption
item: Thesis-Full-text
Development of biopolymer filled natural rubber latex-based composite films to enhance biodegradation
(2021) Jayathilaka LPI; Ariyadasa TU; Egodage SM
Natural rubber latex (NRL) is the primary resource in developing thin film products including NRL gloves. These comprehensive applications of NRL are lead to the widespread formation of discarded solid material. Majority of these NRL-based product wastes are subjected to an incineration, landfill, or recycling. Recycling of NR waste is not usually effective owing to expensive and inadequate resources. Therefore the generation of heavy buildup of NR waste has become an immense social and environmental issue. Although NRL is biodegradable in nature, it has become more resistant to degradation, with the alteration of its properties to meet the processing requirements. To reduce the rising of NR waste problem, an attempt to enhance biodegradation process by coupling NR with degrading biomaterials has attracted more interest in research. Therefore this study is focused on evaluating applicability of corn-derivatives (cornstarch (CS), corn flour (CF), and corn grain (CG)) to develop a novel NRL-based biocomposite to enhance biodegradation as well as physico-mechanical, aging properties and compare with the conventional fillers. Corn-derivatives were employed to enhance the biodegradability and physico-mechanical properties of NRL-based composite films by changing filler content from 0 to 50 phr. Significant alteration in physico-mechanical properties were noticed with the type of the filler and NR-CG demonstrate improved adherence with NR matrix. Moreover addition of CG in NRL-based composite films increased degradation; with exceeding 70% mineralization detected for 50 phr CG loading after 15 weeks of soil burial. The agreement among physico-mechanical properties and biodegradation restrict the CG loading in the NRL-based composite films to 20 phr by obtaining the specifications of NRL-based products. The results showed that NRL-based composite films with CG loading of 20 phr support to the ASTM D3578, the specification for producing NRL gloves; with 50% mineralization after 15 weeks of soil burial. A glove material was successfully produced with NRL-based compounds including CG 20 phr loading and further improvements of composite films can be done by using it with industrial glove manufacturing process.
item: Thesis-Abstract
Optimization of influencing parameters for dry anaerobic co-digestion of lignocellulosic biomass
(2021) Lakshitha WAA; Rathnasiri PG
Anaerobic digestion offers an attractive solution for recovering energy from rice straw (RS) which is a lignocellulosic agricultural residue produced in huge quantities in Asia and Africa. Given the high solids content of this feedstock, high solids anaerobic co-digestion in batch mode is a process that can be applied. In this study, optimal operating conditions for the co-digestion of RS with cow dung (CD) in pure batch reactors and batch reactors with leachate recirculation are assessed. The preliminary experiments carried out in pure batch conditions showed that the initial concentration of RS in the mixture of substrates, i.e., S 0 , (g VS rice straw /kg of mixture) is an important parameter. Only the batch reactors with the lowest S 0 values (29g VS RS /kg) produced biogas after a long lag phase of 14 days. The use of digestate from a previous batch as an inoculum was investigated with S 0 values of 29 and 55 g VS RS /kg. Re-use of the digestate as an inoculum source drastically improved both the initial degradation kinetics and the methane yield measured after 60 days for the S 0 of 29 g VS RS /kg, as lag phase time period almost reached to zero and final methane yield of this reactor was 222 ml/g VS. This indicates a 104 % increase of specific methane yield increase compared to the reactor that only has the same S 0 concentration but the substrate mixture comprises only RS and CD. However, for 55 g VS RS /kg, the degradation kinetics were affected: after two months, 32% of the biodegradable organic matter was not eliminated. Leachate recirculation experiments were conducted in leach-bed reactors (LBRs) with S 0 between 30 and 65 g VS RS /kg, the highest methane yield was recorded at the lowest S 0 value, confirming that in batch mode during high solids anaerobic co-digestion (HSAcoD) conditions, an initial RS concentration around 30 g VS RS /kg is recommended for industrial applications. Then mathematical modeling was applied to estimate kinetic parameters related to HS-AcoD process using the modified Gompertz model. Results obtained from Batch experiment no.3 (i.e., the three consecutive batches) were considered for the mathematical modelling. Modified Gompertz model very closely predicted the ultimate methane yield (M max almost 0.99 in each scenario. Degradation kinetics improved drastically with the strategy of re-using digestate, as for the Batch-2 the lag phase period (λ) reduced from 14 days to almost zero. Ultimate methane yield increased by 104% through this approach. Degradation kinetics were negatively affected with the increase of TS% within the substrate mixture even though digestate was reused as an inoculum. In Batch-3 ultimate methane yield was 138 ml/g VS which was a 38% reduction compared to Batch-2, even though digestate was used as the main inoculum source for the both batches. But it was a 27% increase compared to Batch-1 which CD was used as the only inoculum.
item: Thesis-Full-text
Biological removal of sulfurous pollutants in skim latex wastewater
(2020) Samarathunga IR; Rathnasiri PG
Skim Latex Wastewater (SLW) contains high concentrations of sulfate, together with organic matter and nitrogenous compounds such as Ammonia and protein. High concentrated sulfuric acid is added in coagulation process to recover rubber particles and ammonia is used for preservation of rubber latex. Under anaerobic digestion, sulfate breakdown into hydrogen sulfide which is one of the highly toxic, corrosive and odorous gas which causes severe threat to the environment and health Nevertheless, it degrades the commercial value of biogas as a renewable energy source causing severe corrosion in connected components of equipment. Conventional biological process to treat sulfate rich wastewater consists of two processes, sulfate reduction to sulfide by Sulfate Reducing Bacteria (SRB) and Sulfide oxidation to elemental sulfur by Sulfide Oxidation Bacteria (SOB) in separate reactors. Major objectives of this research study are to investigate the effect of ammonia rich SLW on sulfate reduction and Hydrogen sulfide emission reduction under anaerobic condition and develop strategies for enhancement of sulfate reduction for subsequent elementary sulfur formation under different micro-aeration techniques. Optimum conditions for both sulfate reduction as well as elementary sulfur formation are also investigated. In previous studies, various reactor configurations have been developed by integrating both the SRB and SOB into a single reactor. In this study SRB and SOB integrated suspended growth reactor for SLW which is not only rich in sulfate, but also ammonia and protein which ultimately breakdown to produce more ammonia is introduced. This new reactor is termed as Single-stage Sulfate-removal Micro-aerated Anaerobic Digester (SSMAD). It is hypothesized that this SRB and SOB integrated micro-aerated anaerobic reactor approach can be applied to enhance removal of sulfurous pollutants from SLW. To achieve the research objectives, seven experiments were conducted. All experiments were conducted semi batch wise using 3 litres airtight completely mixed anaerobic reactors which were maintained at 35 ±1 ̊C. From the results, it can be concluded that, Single-stage Sulfate-removal Micro-aerated Anaerobic Digester (SSMAD) simultaneously reduced high concentrated influent sulfate of SLW, while hydrogen sulfide been transformed to reusable elemental sulfur. To achieve the optimum sulfate reduction as well as maximum elemental sulfur yield, bulk liquid of the SSMAD was micro-aerated with air at rate of 1.6 ml/hr for two hours following half an hour of feeding SLW. It was found that yield and the stability of the generated elemental sulfur improved at O2/S ratio 1.0-1.2, after 18-24 hours of feeding. At this range, specific H2S formation was less than 0.2 mmol/mmol while the sulfate reduction was 95.8%. The COD/SO4-2 ratio of SLW was nearly 3 and it was increased to 5 adding an external electron donor for efficient sulfate reduction but further increased up to 10, reduced the sulfate reduction as Methanogens dominate than SRB. Although ethanol enhances the sulfate reduction than acetate, excess ethanol adversely affected on the micro-aerobic systems degrading generated elemental sulfur back to gaseous H2S faster. Thus, the elemental sulfur yield reduced by 69% when the COD/SO4-2 ratio was increased from 5 to 10. However, sufficient precautions were taken to increase the C/N ratio from 3.8 to 6.9, by maintaining pH of the reactor at 7.5-8.0 and volumetric loading at 50 l/m3.d to minimize ammonia inhibition in the reactor. Developed novel approach through Single-stage Sulfate-removal Micro-aerated Anaerobic Digester (SSMAD) can be successively used to recover sulfurous pollutants from SLW
item: Thesis-Abstract
Natural rubber latex nanocomposites : effect of montmorillonite clay structure on reinforcement and extractable proteins
Amarasiri, MDSA; Walpolage, S; Rathnayake, U
Natural rubber (NR) latex-clay nanocomposite (NRLCN) prepared with montmorillonite (MMT) clay aqueous dispersion was evaluated for reinforcement, extractable proteins and barrier properties. Physio-mechanical properties of the NRLCN were compared with conventional NR latex composites containing CaCC>3. The NRLCN structure was characterized with X-ray diffraction and scanning electron microscope (SEM) techniques. X- ray diffraction data showed that, with a lower concentration of clay, highly exfoliated clay structure was achieved whilst clay aggregation gradually resulted with a higher concentration of clay. Crosslink density and volume fraction ofrubber in the swollen gel as computed based on the solvent absorption data ofthe latex nanocomposite films increased while molar mass between crosslink ofthe rubber decreased with the increase of clay concentration. As a result of nano scale dispersion of montmorillonite clay and higher crosslink density of the latex nanocomposite films, resistance to permeation of small molecules through the NRLCN is significantly enhanced in comparison to conventional NR latex-CaC03 composites. Solid state mechanical properties ofNRLCNs have shown a significant reinforcement effect of dispersed nanoclay platelets but without sacrificing the elastic properties. Results have been explained in terms of degree of clay dispersion/exfoliation, crosslink density and strain induced crystallization. The extractable protein content was analysed for the NRLCN samples using the Modified Lowry Method. It had shown a significant reduction ofthe extractable protein content in the NR latex films when montmorillonite clay is introduced. The NRLCNs were leached using typical industrial leaching conditions and also tested for the extractable protein content which dropped well below the allergenicity level of human skin. The extractable protein content of raw NR latex-clay un-vulcanized films had shown similar results as the NRLCN which confirms the attraction of protein cations with the nanoclay platelets. The entrapped protein has accelerated the vulcanization reaction of the NRLCN which caused higher crosslink density. Higher mechanical properties, very low extractable protein content and improved barrier resistance indicated that NR latex nanocomposite containing montmorillonite clay is a potential replacement for conventional NR latex composites containing CaCC>3.
item: Thesis-Abstract
Preparation and characterization of nutrient rich nanoparticles/composites for agricultural applications
Munaweera, MTIS; Karunarathne, V; Kottegoda, NS; Ismail, SM
The work describes a novel strategy for controlled and sustained release of plant nutrients nitrogen (N), phosphorous (P) and potassium (K) into soil. In the study two nano systems, (a) inorganic inner nano-core consisting of macronutrient nanoparticles (b) a natural cellulose based outer core containing micro / nano porous cavities were used in order to obtain slow and sustained release of nutrients. Hydroxyapatite (HA) nanoparticles were synthesized, surface modified using urea and characterized using PXRD, SEM / EDX, AFM, FTIR and TGA / DTA. Urea modified HA nanoparticles dispersion and saturated potassium chloride solution were separately pressurized into the cavities present in Gliricidia sepium, a soft wood stem, under a pressure of 9 bar. N, P and K release behavior ofthe nanofertilizer composition was studied using soil from three elevations in Sri Lanka (pH 4.2, 5.2 and 7) and the release properties were compared with that of a commercial fertilizer composition. The release properties ofthe nanofertilizer show a slow and sustained release. In general, at all pH values, even on day 32, the remaining N to be released in the nanofertilizer was about 20% and there was no more N to be released in the commercial fertilizer. A similar trend shows for K release and at all pH values the remaining K to be released in nanofertilizer after 40 days was about 15% while there was no more K to be released in the commercial fertilizer. The solubility of P of in the nanofertilizer system was higher than the P release of the commercial fertilizer. A model was developed for the solubility of bulk HA / HA nanoparticles. The solubility of HA in terms ofsoluble phosphate (P043') can be expressed by an equation, 3 4 7 10-if vjcw; p0*3"L 5 total 2.503Kfl2+fx0.509Xv7] 8 3 5*e From pH 3 to 4 and pH 4.5 to 6 the decrement of log value of total soluble phosphate concentration per unit pH is 11.8 and 3.03, respectively, when the ionic strength of the soil solution is between 12 to 110 mol kg'1 according to the Ostwald and Freundlich equation, the solubility of phosphate can be increased by reducing the size of HA, that is, by using HA nanoparticles.
item: Thesis-Full-text
Characterization of calcium carbonate filled natural rubber - low density polyethylene blends prepared with a titanate coupling agent
(2019) Sampath WDM; Egodage SM; Edirisinghe DG
The aim of this study was to develop reactive blends from natural rubber (NR) and low density polyethylene (LDPE) with acceptable physico-mechanical properties. NR and LDPE blends at different blend ratios were produced in a Brabender Plasticorder by melt mixing at a temperature of 150 oC, and rotor speed of 60 rpm. 20 parts per hundred parts of polymer (pphp) calcium carbonate was added as an inorganic filler. Physico-mechanical and chemical properties of the blends and composites were determined according to international standards. Thermal properties were determined using a differential scanning calorimeter. Morphology and structural characteristics were examined by a scanning electron microscope and fourier transform infrared analyzer, respectively. 50/50 NR/LDPE blends were prepared using three vulcanizing systems: sulphur, peroxide and mixture of sulphur and peroxide. NR/LDPE blend prepared with the mixed vulcanizing system showed the highest physicomechanical, chemical, and ageing properties with a fine morphology. A series of simple blends was formulated by varying the LDPE loading from 10 to 90 pphp at 20 pphp intervals. The tensile strength, tear strength, and hardness increased with the increase of LDPE loading, while elongation at break decreased. The continuous phase of blends changed from NR to LDPE above 30 pphp LDPE loading. The optimum tensile and ageing properties were obtained for the composite prepared with 20 pphp calcium carbonate with or without titanate coupling agent (titanate CA) at 30 pphp LDPE loading. Further, 70/30 NR/LDPE composite prepared with 0.7 pphp titanate CA presented the highest physicomechanical, chemical and ageing properties. Furthermore, the performance of the 70/30 NR/LDPE blends produced with 0.3 pphp peroxide was greater than that of the composites prepared without the peroxide and with a high amount of peroxide. Nevertheless, tensile properties, stress and strain of the 70/30 NR/LDPE composite improved with partial replacement of LDPE with recycled LDPE (rLDPE). The composite with 20 pphp rLDPE indicated the best improvement in all physico-mechanical properties.
item: Thesis-Full-text
Development of a national risk acceptance criteria for managing major industrial hazards
(2018) De Silva, KGVK; De Alwis, AAP; Gunasekera, MY
This work attempts to address the issue of managing risk to the safety of the public posed by Major Accident Hazards (MAH) from the Chemical Process Industry (CPI) in Sri Lanka. The research essentially focuses on the establishment of a suitable risk acceptance criteria as well as an appropriate framework that can be used in determining the level of safety offered by a particular MAH installation in Sri Lanka. The “level of safety” of an installation is then compared against the risk acceptance criteria to determine its acceptability in the Sri Lankan context. The history of process safety management as is understood at present was investigated and the different risk regulation regimes currently in practice globally were identified. The role of risk assessment in each risk regulatory regime was investigated and the need for risk informed decision making was firmly established. The thesis then focuses on the prevalent categories of approaches in risk assessment. The different risk assessment approaches are investigated further. Out of those approaches, the consequence assessment and probabilistic risk assessment approaches or methods were chosen for the development of the risk assessment framework. The different risk metrics used to express the risk for each approach and the respective risk acceptance criteria were identified. Then appropriate risk acceptance criteria were developed for the two approaches. The establishment of a safety distance corresponding to 1% fatality of the public was adopted for the consequence based assessment method whereas a FN criteria line with an anchor point of (10, 10-4) and slope -1 was chosen for the probabilistic risk assessment method. The applicability of the different risk acceptance criteria in the Sri Lankan context is carried out for the case of propane storage tank. Data gaps and constraints are identified. Both methods adopt a conservative decision making approach. A significant constraint is the lack of a nationally verified and validated set of failure rate data for process equipment and ignition probability data; these are essential for establishing conditional probabilities when calculating accident frequencies. The usage of generic data for failure rates is not recommended due to the wide variability in different data sources. Further, allowing room for choosing an arbitrary set of failure rate data could create an opportunity for biasing the risk acceptance decision. In this work, a framework is presented for applying the risk acceptance criteria developed. An FN curve based on upper bound data for the probabilistic risk assessment method and modified consequence assessment method are developed. The probabilistic risk assessment method is modified to accommodate the variability in generic failure rate data. The decision of acceptability is made by defining an FN curve using upper bound values of the FN curve and comparing it with the criterion line. A safety distance proportionate with the overall level of risk based on a relative risk reduction factor (RRRF) is introduced.
item: Thesis-Full-text
Methodology for comparison of chemical process routes based on environment, health and safety aspects at early stages of chemical process plant design
(2018) Anuradha HBB; Gunasekara MY; Gunapala O
The chemical process route selection is one of the important decisions that needs to be taken during initial stages of plant design and development. Although conventionally the economic factor has been considered in this selection process, presently the environmental, health and safety (EHS) issues have also become main concerns as hazards related to EHS can be largely reduced by avoiding them during initial stages of plant development. Therefore, in order to select a route, the assessment of alternate chemical process routes based on EHS aspects and their comparison need to be carried out. For this assessment, comparison and selection methodologies are needed. Most of the methodologies available for chemical process routes assessment and selection, consider mainly environmental or health or safety hazards individually or in combination of two of them. Although few methodologies are available that consider all three EHS aspects, those that consider EHS hazards posed by both types of releases namely daily plant operational and accidental are lacking. In this work fuzzy based inherent environmental, health and safety hazard index called EHS-Fuzzy Index is developed to compare chemical process routes based on integrated EHS hazards due to daily operational activities of the plant as well as accidental releases. The EHS-Fuzzy Index includes information of thirteen EHS related parameters which is available during routes selection stage. The lower the EHS-Fuzzy Index the more environmental friendly, occupational healthy and safer the chemical route. Further, this methodology can be used to compare and rank alternative chemical routes based on environmental hazard or health hazard and safety impact separately as well. The EHS-Fuzzy Index was applied in a case of six routes to manufacture methyl methacrylate (MMA). The Tertiary Butyl Alcohol (TBA) chemical route to manufacture MMA showed the least EHS-Fuzzy Index value. By applying the MMA case study in the radial polygon diagram method, the results obtained using the EHS-Fuzzy Index methodology were verified.
item: Thesis-Full-text
Application of nanoclay on polyester fabrics as a bio-inspired approach to improve moisture management
(2018) Abeywardena, SBY; Walpalage, S; Perera, WPSK; Somararatne, MCW
Bio-inspired and biomimetic surface modifications are identified as one of the fascinating areas of research. In this study, nature’s way of cooling elephants’ body temperature using mud bathing was mimicked to create moisture management in polyester fabric. For that, bentonite nanoclay (BNC) was covalently grafted on polyester fabric using (3-aminopropyl) triethoxysilane (APTES) as a coupling agent. The novel modification method was proved qualitatively and quantitatively using characterization techniques such as X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR), X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Xray fluorescence (XRF) and Thermo gravimetric analysis (TGA). Moisture management tests, and physical and mechanical properties of modified polyester fabric were used to analyse the accomplishment of the modification. Hydroxyl groups on edges of BNC played a vital role in grafting with APTES. Primary amine group in APTES reacted with ester groups in polyester fibres, while silanols reacted with BNC. XRD analysis confirmed grafting of APTES on the surface of BNC without intercalation. XPS and FTIR spectroscopies confirmed the new secondary amide bond formation, while surface morphology was observed from SEM images. The significant enhancement in wettability, absorptive capacity, drying rate and wicking length proved moisture management property of polyester fabric. This fabric coating strongly withstood more than 10 cycles of laundry and against 5000 abrasion cycles. Physical and mechanical properties of modified fabrics remained unchanged, while tensile strength and elongation showed a slight improvement due to fibre preserving aminolysis reaction between APTES and ester groups in polyester fabrics. It is expected that this bio-inspired BNC modified polyester fabric may break the barrier of using polyester in various hydrophilic textile applications.
item: Thesis-Full-text
Drying kinetics of coir pith and the performance in flash drying
Fernando, JAKM; Amarasinghe, ADUS; Jayasundara, JMMA
Drying and retting can be identified as the most important factors affecting the quality variations in dried coir pith which directly affects the final quality of compressed coir pith products. A pilot scale flash dryer was designed and fabricated to examine the effect of hot air temperature and velocity on the drying behavior of coir pith. Hot air drying was carried out to examine the drying kinetics by allowing the coir pith particles to fluidize and circulate inside the drying chamber. The physico-chemical properties of volume expansion ratio (VE), water retention capacity (WRC), bulk density, pH and electrical conductivity (EC) of compressed coir pith discs were measured. Scanning electron microscopy was used to analyze the microstructures of dried coir pith. The results were compared with the two other drying techniques namely sun drying and oven drying. The effect of time duration for retting and the method of retting the coconut husk were also examined. The optimum temperature for coir pith drying was found to be 140 C. The most suitable range of particle size and the range of moisture content in dried coir pith were identified as 0.5 – 6.3 mm and 12 - 23% (w/w, dry basis) respectively. The VE, WRC, pH and EC of coir pith dried in the flash dryer at the optimum temperature of 140 C was found to be 5.01 ± 0.21, 4.02 ± 0.10 (w/w), 5.95 ± 0.08 and 330 ± 16 μs/cm respectively. These values were comparable with those of the sundried coir pith. Oven drying caused rupturing the cells and case hardening of coir pith. Similar effect was observed with temperatures > 140 C for hot air drying and flash drying. VE and WRC of coco discs were found to increase significantly, pH to change marginally and EC to drop significantly with the increase of retting time. The effective moisture diffusivity was found to increase from 1.18 × 10-8 to 1.37 × 10-8 m2/s with the increase of hot air velocity from 1.4 to 2.5 m/s respectively. Correlation analysis and residual plots were used to determine the adequacy of existing mathematical models for describing the drying behavior of coir pith using hot air. A new mathematical model was proposed and it gave the best correlation between observed and predicted moisture ratio with high value of coefficient of determination (R2) and lower values of root mean square error (RMSE), reduced chi-square (χ2) and mean relative deviation (E %). Wang and Singh model and Linear model were also found to be adequate for accurate prediction of drying behavior of coir pith. Since the experimental setup of this study closely simulated the particle motion and heat and mass transfer in flash drying due to induced fluidization and circulation, the new model has a great potential in designing and modeling of the flash drying of coir pith.
item: Thesis-Abstract
Ultrasonic devulcanization of sulfur vulcanized natural rubber
Maduwage, S; Amarasinghe, ADUS; Munidradasa, DAI
The high-energy ultrasound could be used to devulcanize rubber as it can focus energy into localized sites for selective bond rupture. The research work reported to date suggests that the ultrasonic technology is more suited to convert rubber waste to a usable material efficiently, effectively and environmental friendly. The ultrasonic devulcanization reactor consisted of three main sections, namely a power source, ultrasonic transducer with sample holding unit, and a monitoring system to measure the amplitude, frequency and power. N-cyclohexyl-2-benzthiazyl sulfenamide (CBS) accelerated unfilled natural rubber vulcanized with conventional sulfur vulcanizing system and with efficient sulfur vulcanizing system were used as the model rubber compounds in these experiments. 2 mm thick vulcanized rubber sheets were directly kept on the vibrating diaphragm of the ultrasonic transducer. The frequency of ultrasonic wave was varied in a range of 20 to 50 kHz and the power level was varied up to 800 watt. The treatment time was limited to 10 minutes when treated at high power levels. The vibrating amplitudes were measured at different power levels with the variation of ultrasonic frequency. Curing behaviour, gel content and cross-link density were studied for rubber samples devulcanized at different process conditions. The increase in cross-link density and gel content of the samples treated at lower amplitudes indicated the formation of additional cross-links. However, the higher vibrational energies associated with high amplitudes resulted in lower cross-link densities and gel contents indicating a breakdown of bonds. Cure curves of virgin and devulcanized NR samples suggested that the fast initial curing of devulcanized NR was due to the presence of active sufidized rubber molecules formed due to break down of some cross-links during devulcanization. The lower maximum torque values observed in the devulcanized samples were due to the partial breakdown of C-C bonds in the main chain. The tensile properties of the revulcanized samples gave comparable results with that of virgin rubber. A theoretical process model was developed to express the extent of devulcanization in terms of cross-link density. It was based on the vibrational energy transfer mechanism. The model treated the vulcanized rubber as a pure elastic solid containing void regions. Experimental and theoretical values lied within ± 10% error limits. The model showed that the media effect on the nature of void excitation was significant and the viscoelasticity was also considerable. However, the effect due to surface tension was negligible.
item: Thesis-Abstract
Optimization of woody biomass torrefaction in inert and oxidative atmospheres using combined experimental and modelling approach
(2023) Devaraja, UMA; Gunarathne, RMDS
Torrefaction is a thermochemical pretreatment method to increase the energy density of biomass. The process is carried out at 200-300 ⁰C in an inert atmosphere. However, large-scale use of inert gas is neither realistic nor economical. More than 50% of industrial flue gas in Sri Lanka is greater than 200 oC and has less than 10% oxygen content which is suitable as a torrefaction medium. Lab-scale torrefaction experiments were conducted for Gliricidia and Rubberwood, at 250-300 oC temperature range and 30–60 minutes in nitrogen and 3%, 6%, 9% oxygen environments to understand the torrefaction behaviour. TGA and FTIR were used to characterize raw and torrefied biomass. In the lab-scale experiments in inert torrefaction, Gliricidia and Rubberwood showed more than 30% mass loss under the most severe conditions, resulting in a 22.8% and 11.6% volatile drop, respectively. The higher heating value of the torrefied product increased from 18.9 MJ/kg to 30.15 MJ/kg for Rubberwood and from 19.46 MJ/kg to 28.2 MJ/kg for Gliricidia under the most severe conditions. The severity factor was modified by finding the optimum fitted parameter ω, establishing a feedstock-specific relationship between torrefaction severity and operating conditions. The normalized severity factor shows a linear correlation with the properties of torrefied biomass, which could facilitate torrefaction modelling. Rubberwood shows its optimum oxidative torrefaction properties at 300 oC temperature and 31-min residence time and 9% oxygen, whereas Giricidia shows it at 286 oC temperature at a 60-min residence time and 9% of oxygen. A process model was developed for oxidative torrefaction, and results show that CO2 has the highest volume fraction, followed by CO and CH4 in the non-condensable product and water has the highest fraction in the condensable product. Acetic acid, formic acid, phenols and furfurals were other dominant components. Keywords: Gliricidia, Rubberwood, Torrefaction, Oxidative torrefaction, Process simulation, Aspen Plus

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