EU har som mål att år 2020 ha minskat utsläppen av växthusgaser med 20 % och ökat andelen förnyelsebar energi till 20 %. I Sverige är andelen fossilt bränsle som förbränns ca 30 %. Denna studie syftar till att utreda om termokemiskt behandlade biobränslen kan ersätta de kommersiella fossila bränslena. Resultatet har nåtts med simulering i programvaran Fuelsim och insamling av experimentella data.  En simulering ska påvisa om syreberikning gynnar bränslena och experimentella data används för att se vilka problem som finns för respektive bränsle. Den biomassa som analyserats kommer från ett vedslag liknande gran eller tall som har genomgått processen mellansnabb pyrolys, torrefiering eller steam explosion. Ingen ekonomisk aspekt har tagits i beaktande vid utvärderandet av bränslena. Pyrolysprocessens produkt pyrolysvätska har flera utmaningar framför sig innan den kan ersätta befintliga oljor. Den är väldigt korrosiv, har en hög fukthalt och en kort lagringstid på sex månader. Pyrolysvätskan tycks gynnas av en syreberikning på 0,5 till 2 %. Pyrolyskoksen har potentialen att ersätta eller samförbrännas med kol i kolpulvereldadepannor. Pyrolysgasen innehåller en stor mängd CO2 vilket ger den ett lågt energiinnehåll. Både pyrolyskoksen och pyrolysgasen bör i första hand förbrännas i en fluidbäddspanna som är integrerad med pyrolysreaktorn eftersom pannanläggningen behöver värmen. Torrefieringsgasen är en biprodukt från framställningen av torrefierad biomassa. Problem med filtrering och kondensering av gasen medför att den bör sameldas med något annat bränsle för att återföra värmen till reaktorn. När den torrefierade biomassan pelleterats förbränns den lämpligast i storskaliga pannor såsom bubblande fluidbädd(BFB)-, eller cirkulerande fluidbädd(CFB)- eller rostpannor men även mindre pelletspannor är möjligt. Intrimning av bl.a. luftflöden är nödvändig vid samförbränning och även vid konvertering från annat bränsle för att uppnå en erforderlig förbränning. Simuleringsresultaten av steam explosion (SE) pellets visar potential som ersättare till både träpelleten och stenkolet. Baserat på simuleringen förbränns SE pellets lämpligast i CFB-, BFB- eller rostpannor. Ett begränsat utbud av experimentella data medför dock att bränslet inte kan utvärderas fullständigt. Studien visar att det inte är helt problemfritt att konvertera från ett kommersiellt bränsle till ett termokemiskt behandlat bränsle och att fler experimentella data behövs för att utvärdera bränslenas förbränningsegenskaper. / A goal set by The European Union is to reduce the emissions from greenhouse gases by 20 % and increase renewable energy with 20 % until year 2020.  Fossil fuels account for about 30 % of Sweden’s combusted fuel. The purpose of this study is to investigate if thermochemically treated biofuels can replace or be co-fired with commercial fuels. The results are gathered from experimental data and from the simulations made with the software Fuelsim.  A simulation will be made to determine whether oxygen-enrichment favors the fuels and experimental data is used to investigate if any combustion problems exist with these fuels. The biomass that have been analyzed comes mainly from pine wood or spruce wood trees which have been processed through either a fast pyrolysis, torrefaction or a steam explosion reactor. No economic aspect has been taken into account in the evaluation of the fuels. One of the pyrolysis process products is pyrolysis liquid which has several challenges ahead before it can replace existing oils. It is very corrosive, has a high moisture content and the storage time is limited to short period of six months. The pyrolysis liquid seems favored by an oxygen-enrichment of 0,5 to 2 % according to the simulation results. The pyrolysis char has the potential to replace or be co-fired with coal in a pulverized coal burner. Pyrolysis gas contains a large amount of CO2, giving it a low energy content. Both char and gas should primarily be combusted in a fluid bed boiler that is integrated with the pyrolysis reactor as boiler plant requires heat. The torrefaction gas is a by-product from the processing of torrefied biomass. Current problems with filtration and condensation of the gas entails that it should be co-fired with another fuel to return the heat to the torrefaction reactor. When the torrefied biomass has been pelletized it is preferably combusted within a large scale boiler such as bubbling fluid bed- (BFB), circulating fluid bed- (CFB) or grate boilers also smaller pellet boilers is possible. Fine adjustments of airflow etc. are required when co-firing or when converting from another fuel to achieve required combustion of the torrefied pellets. The steam explosion pellet simulation results shows that the potential to replace both wood pellets and coal. Based on the results combustion of steam explosion pellets is preferable in either a CFB-, BFB- or grate boiler. This fuel cannot be fully evaluated because of the limited range of experimental data. This study shows that it is problematic to convert from commercial fuels to a thermochemically treated fuel and more experimental data is needed to evaluate the fuels combustion characteristics.

A novel biodegradable ammonia control material was developed from steam exploded corn cob and its adsorption capacity was studied by packed column and titration method. The packed column studies showed that the maximum absorption capacities of the raw corn cob (RCC) and the steam exploded corn cob (SECC) were 10.45 mg NHB3B/gRCC and 59.80 mg NHB3B/gSECC respectively. However, the titration of the water slurries with a NHB4BOH showed that the capacity of the SECC was 14.4 times that of RCC. The large difference between the packed column (SECC/RCC = 5.7) and the slurry titration (SECC/RCC = 14.4) was probably because: (1) the initial ammonia reaction products blocked the pores of the SECC and reduced diffusion into the pore structure; (2) the ammonia gas flow rates were too high and therefore the gas did not penetrate the pores; (3) the gas contact time was below the equilibrium value; and (4) since interior pore surface area is usually larger than the external surface area of a particle, it appears the low column SECC/RCC ratio is due to reactions on the SECC particle surface whereas the slurry result was a combination of both. Fourier Transform Infrared, FTIR spectroscopy was conducted on RCC, SECC, ammonia adsorbed on RCC and ammonia adsorbed on SECC in the range 4000–700 cmP-1P. The FTIR bands in the region between 1500 and 2000 cmPâ 1P showed a considerable difference between RCC and SECC. When SECC was treated with ammonia, the carboxylic functional group peak at 1700 cmP-1P was reduced and a new peak was observed at 1584 cmP-1P. The adsorption, desorption test and the heat of adsorption results suggested combined physisorption and chemisorption of ammonia on SECC but chemisorption was found to play an important role in ammonia removal. The BET specific surface area of RCC was 3.4 m2/g whilst that SECC was less than 1 m2/g. Although SECC had a low surface area compared with RCC its adsorption capacity was found to be greater than that of RCC meaning the adsorption process is chemically controlled. Also, the pore size distribution showed that RCC exhibited both macroporosity and mesoporosity whilst SECC showed only mesoporosity. It is interesting to note that upon steam exploding RCC, the macropores within RCC collapsed to form more mesopores in SECC. The high uptake of SECC was determined to be its small pore width compared to that RCC. Simultaneous Differential Scanning Calorimetry, DSC and Thermal Gravimetric Analyzer, TGA, was used to determine the heat of adsorption of ammonia on SECC. The heat of adsorption of ammonia on SECC was 33.00 kJ per mole of NHB3B. This study shows that SECC could be potentially used to remove NHB3B from various emission sources. / Master of Science

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21373号 / 工博第4532号 / 新制||工||1706(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 前 一廣, 教授 河瀬 元明, 教授 佐野 紀彰 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Dissolution of cellulose is an important but complicated step in biofuel production fromlignocellulosic materials. Steam and supercritical carbon dioxide (SC-CO2) explosion are two effective methods for dissolution of some lignocellulosic materials. Loading and explosion are the major processes of these methods. Studies of these processes were performed using grand canonical Monte Carlo and molecular dynamics simulations at different pressure/ temperature conditions on the crystalline structure of cellulose. The COMPASS force field was used for both methods.The validity of the COMPASS force field for these calculations was confirmed by comparingthe energies and structures obtained from this force field with first principles calculations.The structures that were studied are cellobiose (the repeat unit of cellulose), water–cellobiose, water-cellobiose pair and CO2-cellobiose pair systems. The first principles methods were preliminary based on B3LYP density functional theory with and without dispersion correction.A larger disruption of the cellulose crystal structure was seen during loading than that during the explosion process. This was seen by an increased separation of the cellulose chains from the centre of mass of the crystal during the initial stages of the loading, especially for chains in the outer shell of the crystalline structure. The ends of the cellulose crystal showed largerdisruption than the central core; this leads to increasing susceptibility to enzymatic attack in these end regions. There was also change from the syn to the anti torsion angle conformations during steam explosion, especially for chains in the outer cellulose shell. Increasing the temperature increased the disruption of the crystalline structure during loading and explosion. / Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 10 oktober 2014,klockan 13.00 i KS101-salen, Kemigården 4, Göteborg.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The need to mitigate the twin crises of peak oil and climate change has driven a headlong rush to biofuels. This study was aimed at the development of a process to efficiently convert steam explosion pretreated (STEX) sugarcane bagasse into ethanol by using combinations of commercial enzyme cocktails and recombinant Saccharomyces cerevisiae strains. Though enzymatic saccharification is promising in obtaining sugars from lignocellulosics, the low enzymatic accessibility of the cellulose and hemicellulose is a key impediment thus necessitating development of an effective pretreatment scheme and optimized enzyme mixtures with essential accessory activities. In this context, the effect of uncatalysed and SO2 catalysed STEX pretreatment of sugarcane bagasse on the composition of pretreated material, digestibility of the water insoluble solids (WIS) fraction and overall sugar recovery was investigated. STEX pretreatment with water impregnation was found to result in a higher glucose recovery (28.1 g/ 100 bagasse) and produced WIS with a higher enzymatic digestibility, thus was used in the optimization of saccharification and fermentation. Response surface methodology (RSM) based on the 33 factorial design was used to optimize the composition of the saccharolytic enzyme mixture so as to maximize glucose and xylose production from steam exploded bagasse. It was established that a combination of 20 FPU cellulase/ g WIS and 30 IU -glucosidases/ g WIS produced the highest desirability for glucose yield. Subsequently the optimal enzyme mixture was used to supplement enzyme activities of recombinant yeast strains co-expressing several cellulases and xylanases in simultaneous saccharification and fermentations SSFs. In the SSFs, ethanol yield was found to be inversely proportional to substrate concentration with the lowest ethanol yield of 70% being achieved in the SSF at a WIS concentration of 10% (w/v). The ultimate process would however be a one-step “consolidated” bio-processing (CBP) of lignocellulose to ethanol, where hydrolysis and fermentation of polysaccharides would be mediated by a single microorganism or microbial consortium without added saccharolytic enzymes. The cellulolytic yeast strains were able to autonomously multiply on sugarcane bagasse and concomitantly produce ethanol, though at very low titres (0.4 g/L). This study therefore confirms that saccharolytic enzymes exhibit synergism and that bagasse is a potential substrate for bioethanol production. Furthermore the concept of CBP was proven to be feasible. / AFRIKAANSE OPSOMMING: Die behoefte om die twee krisisse van piek-olie en klimaatsverandering te versag, het veroorsaak dat mense na biobrandstof as alternatiewe energiebron begin kyk het. Hierdie studie is gemik op die ontwikkeling van 'n proses om stoomontplofde voorafbehandelde (STEX) suikerriet bagasse doeltreffend te omskep in etanol deur die gebruik van kombinasies van kommersiële ensiem mengsels en rekombinante Saccharomyces cerevisiae stamme. Alhoewel ensiematiese versuikering belowend is vir die verkryging van suikers vanaf lignosellulose, skep die lae ensiematiese toeganklikheid van die sellulose en hemisellulose 'n hindernis en dus is die ontwikkeling van' n effektiewe behandelingskema en optimiseerde ensiemmengsels met essensiële bykomstige aktiwiteite noodsaaklik. In hierdie konteks, was die effek van ongekataliseerde en SO2 gekataliseerde stoomontploffing voorafbehandeling van suikerriet bagasse op die samestelling van voorafbehandelde materiaal, die verteerbaarheid van die (WIS) breuk van onoplosbare vastestowwe in water (WIS), en die algehele suikerherstel ondersoek. Daar was bevind dat stoomontploffing behandeling (STEX) met water versadiging lei tot 'n hoër suikerherstel (21.8 g/ 100g bagasse) en dit het WIS met ‘n hoër ensimatiese verteerbaarheid vervaardig en was dus gebruik in die optimalisering van versuikering en fermentasie. Reaksie oppervlak metodologie (RSM), gebasseer op die 33 faktoriële ontwerp, was gebruik om die samestelling van die ‘saccharolytic’ ensiemmengsel te optimaliseer om sodoende die maksimering van glukose en ‘xylose’ produksie van stoomontplofde bagasse te optimaliseer. Daar was bevestig dat ‘n kombinasie van 20 FPU sellulase/ g WIS en 30 IU ‘ -glucosidases/ g’ WIS die hoogste wenslikheid vir glukose-opbrengs produseer het. Daarna was die optimale ensiemmengsel gebruik om ensiemaktiwiteit van rekombinante gisstamme aan te vul, wat gelei het tot die medeuitdrukking van verskillende ‘cellulases’ en ‘xylanases’ in gelyktydige versuikering en fermentasie SSFs. In die SSFs was daar bevind dat die etanol-produksie omgekeerd proporsioneel is tot substraat konsentrasie, met die laagste etanolopbrengs van 70% wat bereik was in die SSF by ‘n WIS konsentrasie van 10% (w/v). Die uiteindelike proses sal egter 'n eenmalige "gekonsolideerde" bioprosessering (CBP) van lignosellulose na etanol behels, waar die hidrolise en fermentasie van polisakkariede deur' n enkele mikroorganisme of mikrobiese konsortium sonder bygevoegde ‘saccharolytic’ ensieme bemiddel sal word. Die ‘cellulolytic’ gisstamme was in staat om vanself te vermeerder op suikerriet bagasse en gelyktydig alkohol te produseer, al was dit by baie lae titres (0.4 g/L). Hierdie studie bevestig dus dat ‘saccharolytic’ ensieme sinergisme vertoon en dat bagasse 'n potensiële substraat is vir bio-etanol produksie. Daar was ook onder meer bewys dat die konsep van CBP uitvoerbaar is. / The National Research Foundation (NRF) for financial support

Densification of biomass is often necessary to combat the negative storage and handling characteristics of these low bulk density materials. A consistent, high-quality densified product is strongly desired, but not always delivered. Within the context of pelleting and briquetting, binding agents are commonly added to comminuted biomass feedstocks to improve the quality of the resulting pellets or briquettes. Many feedstocks naturally possess such binding agents; however, they may not be abundant enough or available in a form or state to significantly contribute to product binding. Also, process parameters (pressure and temperature) and material variables (particle size and moisture content) can be adjusted to improve the quality of the final densified product.<p>Densification of ground biomass materials is still not a science, as much work is still required to fully understand how the chemical composition and physical properties, along with the process variables, impact product quality. Generating densification and compression data, along with physical and mechanical properties of a variety of biomass materials will allow for a deeper understanding of the densification process. This in turn will result in the design of more efficient densification equipment, thus improving the feasibility of using biomass for chemical and energy production.<p>Experiments were carried out wherein process (pressure and temperature) and material (particle size and moisture content) variables were studied for their effect on the densification process (compression and relaxation characteristics) and the physical quality of the resulting products (pellets). Two feedstocks were selected for the investigation; namely, poplar wood and wheat straw, two prominent Canadian biomass resources. Steam explosion pretreatment was also investigated as a potential method of improving the densification characteristics and binding capacity of the two biomass feedstocks.<p> Compression/densification and relaxation testing was conducted in a closed-end cylindrical die at loads of 1000, 2000, 3000, and 4000 N (31.6, 63.2, 94.7, and 126.3 MPa) and die temperatures of 70 and 100°C. The raw poplar and wheat straw were first ground through a hammer mill fitted with 0.8 and 3.2 mm screens, while the particle size of the pretreated poplar and wheat straw was not adjusted. The four feedstocks (2 raw and 2 pretreated) were also conditioned to moisture contents of 9 and 15% wb prior to densification. <p> Previously developed empirical compression models fitted to the data elucidated that along with particle rearrangement and deformation, additional compression mechanisms were present during compression. Also, the compressibility and asymptotic modulus of the biomass grinds were increased by increasing the die temperature and decreasing product moisture content. While particle size did not have a significant effect on the compressibility, reducing it increased the resultant asymptotic modulus value. Steam explosion pretreatment served to decrease the compressibility and asymptotic modulus of the grinds.<p>In terms of physical quality of the resulting product, increasing the applied load naturally increased the initial density of the pellets (immediately after removal from the die). Increasing the die temperature served to increase the initial pellet density, decrease the dimensional (diametral and longitudinal) expansion (after 14 days), and increase the tensile strength of the pellets. Decreasing the raw feedstock particle size allowed for the increase in initial pellet density, decrease in diametral expansion (no effect on longitudinal expansion), and increase in tensile strength of the pellets. Decreasing the moisture content of the feedstocks allowed for higher initial pellet densities, but also an increased dimensional expansion. The pretreated feedstocks generally had higher initial pellet densities than the raw grinds. Also, the pretreated feedstocks shrank in diameter and length, and had higher tensile strengths than the raw feedstocks. The high performance of the pretreated poplar and wheat straw (as compared to their raw counterparts) was attributed to the disruption of the lignocellulosic structure, and removal/hydrolysis of hemicellulose, during the steam pretreatment process which was verified by chemical and Fourier transform infrared analysis. As a result, a higher relative amount of lignin was present. Also, the removal/hydrolysis of hemicellulose would indicate that this lignin was more readily available for binding, thus producing superior pellets.

Densification of biomass is often necessary to combat the negative storage and handling characteristics of these low bulk density materials. A consistent, high-quality densified product is strongly desired, but not always delivered. Within the context of pelleting and briquetting, binding agents are commonly added to comminuted biomass feedstocks to improve the quality of the resulting pellets or briquettes. Many feedstocks naturally possess such binding agents; however, they may not be abundant enough or available in a form or state to significantly contribute to product binding. Also, process parameters (pressure and temperature) and material variables (particle size and moisture content) can be adjusted to improve the quality of the final densified product.<p>Densification of ground biomass materials is still not a science, as much work is still required to fully understand how the chemical composition and physical properties, along with the process variables, impact product quality. Generating densification and compression data, along with physical and mechanical properties of a variety of biomass materials will allow for a deeper understanding of the densification process. This in turn will result in the design of more efficient densification equipment, thus improving the feasibility of using biomass for chemical and energy production.<p>Experiments were carried out wherein process (pressure and temperature) and material (particle size and moisture content) variables were studied for their effect on the densification process (compression and relaxation characteristics) and the physical quality of the resulting products (pellets). Two feedstocks were selected for the investigation; namely, poplar wood and wheat straw, two prominent Canadian biomass resources. Steam explosion pretreatment was also investigated as a potential method of improving the densification characteristics and binding capacity of the two biomass feedstocks.<p> Compression/densification and relaxation testing was conducted in a closed-end cylindrical die at loads of 1000, 2000, 3000, and 4000 N (31.6, 63.2, 94.7, and 126.3 MPa) and die temperatures of 70 and 100°C. The raw poplar and wheat straw were first ground through a hammer mill fitted with 0.8 and 3.2 mm screens, while the particle size of the pretreated poplar and wheat straw was not adjusted. The four feedstocks (2 raw and 2 pretreated) were also conditioned to moisture contents of 9 and 15% wb prior to densification. <p> Previously developed empirical compression models fitted to the data elucidated that along with particle rearrangement and deformation, additional compression mechanisms were present during compression. Also, the compressibility and asymptotic modulus of the biomass grinds were increased by increasing the die temperature and decreasing product moisture content. While particle size did not have a significant effect on the compressibility, reducing it increased the resultant asymptotic modulus value. Steam explosion pretreatment served to decrease the compressibility and asymptotic modulus of the grinds.<p>In terms of physical quality of the resulting product, increasing the applied load naturally increased the initial density of the pellets (immediately after removal from the die). Increasing the die temperature served to increase the initial pellet density, decrease the dimensional (diametral and longitudinal) expansion (after 14 days), and increase the tensile strength of the pellets. Decreasing the raw feedstock particle size allowed for the increase in initial pellet density, decrease in diametral expansion (no effect on longitudinal expansion), and increase in tensile strength of the pellets. Decreasing the moisture content of the feedstocks allowed for higher initial pellet densities, but also an increased dimensional expansion. The pretreated feedstocks generally had higher initial pellet densities than the raw grinds. Also, the pretreated feedstocks shrank in diameter and length, and had higher tensile strengths than the raw feedstocks. The high performance of the pretreated poplar and wheat straw (as compared to their raw counterparts) was attributed to the disruption of the lignocellulosic structure, and removal/hydrolysis of hemicellulose, during the steam pretreatment process which was verified by chemical and Fourier transform infrared analysis. As a result, a higher relative amount of lignin was present. Also, the removal/hydrolysis of hemicellulose would indicate that this lignin was more readily available for binding, thus producing superior pellets.

The current research investigates the utilization of cotton gin waste as a feedstock to produce a value-added product - fuel ethanol. Cotton gin waste consists of pieces of burs, stems, motes (immature seeds) and cotton fiber, and is considered to be a lignocellulosic material. The three main chemical constituents are cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are polysaccharides of primarily fermentable sugars, glucose and xylose respectively. Hemicellulose also includes small fractions of arabinose, galactose, and mannose, all of which are fermentable as well. The main issue in converting cotton gin waste to fuel ethanol is the accessibility of the polysaccharides for enzymatic breakdown into monosaccharides. This study focused on the use of steam explosion as the pretreatment method. Steam explosion treatment of biomass has been previously described to increase cellulose accessibility. The governing factors for the effectiveness of steam explosion are steam temperature and retention times. The two factors are combined into a single severity term, log(Ro). Following steam explosion pretreatment, cotton gin waste was subjected to enzyme hydrolysis using Primalco basic cellulase. The sugars released by enzyme hydrolysis were fermented by a genetically engineered Escherichia coli (Escherichia coli KO11). The effect of steam explosion pretreatment on ethanol production from cotton gin waste was studied using a statistically based experimental design. The results obtained from this study showed that steam exploded cotton gin waste is a heterogeneous material. Drying and milling of steam exploded cotton gin waste was necessary to reduce variability in compositional analysis. Raw cotton gin waste was found to have 52.3% fermentable sugars. The fiber loss during the steam explosion treatment was high, up to 24.1%. Xylan and glucan loss from the pretreatment was linear with respect to steam explosion severity. Steam explosion treatment on cotton gin waste increased the hydrolysis of cellulose by enzyme hydrolysis. Following 24 hours of enzyme hydrolysis, a maximum cellulose conversion of 66.9% was obtained at a severity of 4.68. Similarly, sugar to ethanol conversions were improved by steam explosion. Maximum sugar to ethanol conversion of 83.1% was observed at a severity of 3.56. The conclusions drawn from this study are the following: steam explosion was able to improve both glucose yields from enzyme hydrolysis and ethanol yields from fermentation. However, when analyzed on whole biomass, or starting material basis, it was found that the fiber loss incurred during steam explosion treatment negated the gain in ethanol yield. / Master of Science

Steam exploded fibers from Yellow Poplar (Liriodendron tulipifera) wood were assessed in terms of (a) their impact on torque during melt processing of a thermoplastic cellulose ester (plasticized CAB); (b) their fiber incorporation and dispersion characteristics in a CAB-based composite by SEM and image analysis, respectively; and (c) their impact on the mechanical properties (under tension) of CAB-based composites having fiber contents of between 10 and 40% by weight. The fibers included water-washed steam exploded fibers (WEF), alkali-extracted fibers (AEF), acetylated fibers (AAEF), all from Yellow poplar (log Ro = 4.23), and oat fillers (COF) as control. The stepwise increase in cellulose content by extraction, and especially the (surface) modification by acetylation, contributed to increased torque during melt processing, and to improved interfacial adhesion as well as fiber dispersion. As compared to pure CAB, AAEF generated the highest increase in torque (+ 421%) followed by AEF (+ 260%) and WEF (+ 190%) at 40% fiber content by weight. AAEF was also found to enhance the tensile properties of the resulting composites. SEM studies of the tensile fracture surfaces indicated significant interfacial delamination and also pull - out of fibers when WEF, AEF, and COF were used to reinforce the CAB matrix. Composites with AAEF, by contrast, revealed fracture surfaces with reduced interfacial delamination and with significant fiber fracturing during failure. Image analysis was used to determine fiber dispersion within the resulting composites quantitatively. Significant improvement in fiber dispersion was achieved when the matrix was reinforced with acetylated fibers (AAEF). Fiber addition to the matrix resulted in loss of strain at break (- 80 to - 93%) and slight or significant increases in modulus (+ 47 to + 103%) depending on fiber type at 40% fiber content. Maximum stress declined for all fibers except AAEF at all fiber contents. AAEF-based composites revealed a decline in maximum stress when fiber content rose to 10%, and this reversed when fiber content increased beyond 10%. This increase in strength is consistent with the rule of mixtures that stipulates reinforcement of the matrix by fibers that are capable of transferring stresses across the fiber-matrix interface. All fibers suffered length decreases during melt processing. / Master of Science

Thesis Abstract This thesis has been performed under co-tutelle supervision between Charles University in Prague (Czech Republic) and Strasbourg University (France). It also profited from the background and cooperation of Institute of Inorganic Chemistry Academy of Science of the Czech Republic and French Commission for Atomic and Alternative energies (CEA Cadarache, France). Results of the work contribute to the OECD/NEA project Serena 2 (Program on Steam Explosion Resolution for Nuclear Applications). Presented thesis can be classed in the scientific field of nuclear safety and material science. It is aimed on the so-called "molten nuclear Fuel - Coolant Interaction" (FCI) that belongs among the recent issues of the nuclear reactor severe accident R&D. During the nuclear reactor melt down accident the melted reactor load can interact with the coolant (light water). This interaction can be located inside the vessel or outside in the case of vessel break-up. These two scenarios are commonly called in- and ex-vessel FCI and they differ in the conditions such as initial pressure of the system, water sub-cooling etc. The Molten fuel - coolant interaction can progress into thermal detonation called also "steam explosion" that can challenge the reactor or containment integrity. Recent experiments have shown that...