Linseed flax studies in vitro were carried out at the Laboratory of Genetic – Biotechnological, Department of Crop Science and Animal Husbandry of Lithuanian University of Agriculture in 2002-2005, photomorphogenetic processes were investigated at the Laboratory of Plant Physiology of the Lithuanian Institute of Horticulture in 2004-2005. Optimal conditions for the dedifferentiation of linseed flax stem segments and hypocotyls cells and those of secondary differentiation in vitro were ascertained. Light technology of a solid body was used for investigation and an optimal combination of light parameters has been selected, promoting photomorphogenesis in vitro. Factors determining androgenesis and gynogenesis processes in vitro were evaluated and potential androgenic and gynogenic genotypes for the development of initial selection material were selected.

Study aim is to study endogenic and exogenic factors preconditioning morphogenesis of linseed flax in vitro. Linseed flax studies in vitro were carried out at the Laboratory of Genetic – Biotechnological of Lithuanian University of Agriculture in 2004-2006. Factors which influence morphogenetic capability of linseed flax cultivars ‘Lirina’, ‘Barbara’ and ‘Szaphir’ in tissue culture were investigated. Two different types of explants – stem segments and hypocotyls – of the three genotypes were cultivated in nutrient media differing in their macro and micro salts concentration, vitamins and different levels of growth regulators. Our results showed that intensity of morphogenesis was affected not only by exogenous growth regulators, but also by the type of explant and genotype. Hypocotyls-derived callus gave the better results than that stem-segment-derived callus on all tested media. Four-weeks-old callus showed the maximum shoot regeneration frequency. The best morphogenetic capabilities were demonstrated for cultivar ‘Szaphir’. The largest number of shoots was produced by all the cultivars on MSB5 nutrient medium supplemented with cytokinin 2iP (2.0 mg 1-1). The master’s final work comprises 50 pages, including 3 tables, 10 figures and 66 literature references.

Three oil crops, chia (Salvia hispanica L.), flax (Linum usitatissimum L.), and castor (Ricinus communis L.), were studied because of their nutritional and industrial values. Chia and flax are rich in an ω3 fatty acid, α-linolenic acid, and castor is a very high oil producer and high in a hydroxy fatty acid. Ethyl methanesulfonate (EMS) and gamma rays were employed to mutagenize chia seeds to produce early flowering mutants. The M1 population was grown and induced to flower by short-day photoperiods. The M2 population was planted in the field in Lexington, KY in 2008. Early flowering plants were found 55 days after planting while non-mutagenized plants did not produce any flower buds until the 7th of October, 82 days after planting, at a daylength of 11 hours and 32 minutes. 0.012% of the EMS-treated M2 population and 0.024% of the gamma radiation-treated population flowered much earlier than the controls. M3 early flowering mutant lines were able to flower at photoperiods of 12-15 hours in a greenhouse. Selected lines produced flower buds on the 7th of July, 47 days after planting, at a daylength of 14 hours and 41 minutes in the field in Lexington, Kentucky. Different varieties of flax were evaluated for seed yield and field performance in Kentucky. Plant height and yield data were collected from three growing seasons. Yields from 2006 trial varied from 368-1,267 kg/ha. Yields from 2007 and 2008 were much lower due to drought. The variety ‘Carter’ gave the highest yield every season. Flax can be grown in Kentucky but yields are low. Two high-yield castor varieties, ‘Carmencita’ and ‘TTU-LRC’, were crossed in greenhouse. The F1 population was grown in the field. Inflorescences were covered to ensure self-pollination. The F2 population showed a high degree of segregation for plant height, stem color, capsule color and seed yield in the following growing season. Data on plant height, number of branches, color, and yield was collected from 89 F2 individuals. Fifteen lines with the highest yield were selected to plant in the field in spring of 2009. New high-yield castor varieties are being developed for production in Kentucky.

Previously seed coat color in flax has been used as a phenotypic marker for specialty quality traits and currently there is an increasing demand to use seed coat color in flax to market flax for human and animal nutrition uses. Seed coat color was studied to 1) understand the inheritance of seed coat color conditioned by the b1 locus, to 2) understand the relationship of other important flax traits with seed coat color as well as to 3) identify markers that are linked to seed coat color for future marker assisted selection of seed coat color. Spearman’s rank correlation and an allelism test was used to show the inheritance of the alleles at the b1 locus. Bulked segregant analysis (BSA) was used to identify putatively linked markers with the b1 locus, these were then screened on the CDC Bethune x M96006 recombinant inbred line population. Furthermore, the CDC Bethune x M96006 and CDC Bethune x USDA-ARS Crystal recombinant inbred line populations were used to identify any important flax traits that had a significant relationship with seed coat color. It was shown that seed coat color conditioned by the b1 locus was stably inherited and that b1vg and b1 are allelic to one another. The results of the BSA showed that there were 17 candidates for linkage but when these markers were screened on the population only the Lu456 from linkage group (LG) six was identified to have linkage (χ²=3.90; P<0.05) with the b1 locus. Additionally, it was shown that the b1 seed coat color allele of the b1 locus had a pleiotropic effect on flower color and flower shape and that seed coat color was associated with linolenic fatty acid content. None of the traits examined were found to be associated with the b1vg allele of this locus. These results show that the b1 locus is likely present on linkage group six, more marker coverage on linkage group six of markers that are polymorphic between the two seed coat color parents would increase the accuracy of detection. Lastly, this study showed that plant breeders should consider using the b1vg allele that conditions the variegated seed coat color to mark unique lines with important combinations of traits because it sorted independently for seed quality traits. Whereas, the yellow seed coat color conditioned by the b1 allele was found to be associated with higher linolenic fatty acid content and the semi-lethality of this allele would make it not suitable for use in parental lines.

Le lin cultivé (Linum usitatissimum L.) est l’une des principales sources de lignanes, faisant de cette plante un modèle d’étude de cette voie du métabolisme spécialisé. Les principaux lignanes de lin dérivent de composés optiquement actifs, en particuliers les stéréoisomères du sécoisolaricirésinol qui sont synthétisés à partir de pinorésinol via laricirésinol. Les principales enzymes impliquées dans la synthèse de ces stéréoisomères sont deux isoformes de pinorésinol-laricirésinol réductases (PLR) déjà caractérisées et possédant des énantiospécificitées opposées. Néanmoins l'action de ces deux réductases bifonctionnelles ne permet pas d'expliquer les profils d'accumulation complexes notamment de laricirésinol et ses dérivés observés dans les graines, tiges et suspensions cellulaires de lin. Afin de mieux comprendre les mécanismes mis en oeuvre menant à ces profils d’accumulation de lignanes chez cette plante, la recherche de nouvelles PLRs a révélé l’existence de deux nouvelles isoformes. L’analyse de l'expression des gènes ainsi que l'activité enzymatique in vitro de ces deux nouvelles PLR putatives, LuPLR3 et LuPLR4 ont été élucidées. LuPLR4, in vitro, présente une activité réductase uniquement du pinorésinol. Ce type d’activité est ici décrit pour la première fois en dehors de la famille Brassicées et permet d’expliquer en partie les profils d’accumulation complexes observés chez le lin. De par leurs propriétés biocides, les lignanes sont suspectés jouer un rôle dans les mécanismes de défense des plantes. Dans le cadre de ce travail, suite à une élicitation fongique à l’aide d’extraits de Fusarium oxysporum spp. linii, un agent pathogène commun du lin, l’analyse de l’expression des différents gènes codant les isoformes de PLRs a révélées une induction globale et coordonnée. En particulier, dans le cas de l’isoforme LuPLR1, des délétions et mutations dans la région promotrice de son gène ont permis de mettre en évidence une région impliquée dans la régulation de la réponse à l’élicitation par F. oxysporum. Cette région contient plusieurs boîtes W, sites de liaison putatifs pour des facteurs de transcription de type WRKY. Les facteurs de transcription WRKY jouent un rôle dans les réponses aux stress biotique et abiotique. Un facteur de transcription candidat LuWRKY36 a été isolé à partir de suspensions cellulaires traitées avec des éliciteurs de F. oxysporum ou de l'acide abscissique. En particulier, les expériences de gel-retard et DPI-ELISA ont montré la capacité de liaison de LuWRKY36 à la boîte W3 présente du promoteur du gène LuPLR1. Cette régulation a ensuite été confirmée in vivo. Nous rapportons également l'impact différentiel de l'élicitation par des extraits de F. oxysporum sur l’expression des gènes LuWRKY36 et LuPLR1 ainsi que la production de sécoisolaricirésinol dans les variétés de lin sensible (Barbara) et résistante (Baïkal) à la fusariose. Enfin, la pleine exploitation des nombreux effets bénéfiques (en santé humaine ou cosmétique notamment) du sécoisolaricirésinol et des autres composés phénoliques accumulés dans les graines de lin nécessitent la mise au point de procédés d’extraction “verts”, efficaces voir sélectifs. Nous rapportons ici que l’utilisation de solvants eutectiques de type NADES (Natural Deep Eutectic Solvent) qui couplée à une extraction assistée par ultrasons, dans le cadre d’un procédé de type cracking, utilisant comme matériel de départ un coproduit d’extraction de l’huile de lin produit de manière innovante, permet d’obtenir des rendements d’extraction élevés et sélectifs de ces différents composés d’intérêt dans le cadre d’une démarche d’éco-extraction. / L. usitatissimum is one of the richest sources of lignans. Main flax lignan is optically active secoisolariciresinol that is synthesized from pinoresinol via lariciresinol. Key enzymes involved in the synthesis of this lignans are two isoforms of pinoresinol-lariciresinol reductases with opposite enantiospecificity. The action of bifunctional reductase does not allow for an explanation for the accumulation of lariciresinol and its derivates in seeds, stem and cell suspension. To try and better understand complex lignan profile we report expression and activity of two new putative PLRs, LuPLR3 and LuPLR4. LuPLR4 in vitro acts only as pinoresinol reductase what has only been seen in Brassicaceae family until now. Lignans play a role in plant defense. All PLRs are upregulated following Fusarium oxysporum attack, a common flax pathogen. Promoter deletions and mutation evidenced region involved in regulation of LuPLR1 gene response to Fusarium. The region contains several W boxes, putative binding sites for WRKY transcription factors. WRKY transcription factors play a role in response to biotic and abiotic stress. We have isolated LuWRKY36 from two cell suspension treated with Fusarium oxysporum or abscisic acid. Gel-shift assay and DPI-ELISA showed binding of LuWRKY36 to W box present in the LuPLR1 gene promoter. This regulation was also confirmed in vivo. We also report the differential impact of F. oxysporum elicitation on LuWRKY36 and LuPLR1 gene expression and secoisolariciresinol production in flax cultivars Barbara (Fusarium sensitive) and Baikal (Fusarium tolerant). Many beneficial effects of secoisolariciresinol and other phenolic compounds found in flax require “green” extraction and sometimes targeted purification of a specific compound. We report here that natural deep eutectic solvents using ultrasound assisted extraction can extract phenolic compounds from flax seed coat and that results indicate that by tuning different parameters of extraction we can target purification of desired plant product.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Avaliamos o efeito do consumo materno de SDG (Diglicosídeo Secoisolariciresinol) e de óleo de Linhaça+SDG sobre parâmetros bioquímicos e hormonais das ratas e das proles machos e fêmeas na lactação. As ratas lactantes foram separadas em: controle (C), ração controle cuja proteína foi caseína; (SDG): ração C com 400mg de SDG/Kg de ração; OLSDG: ração C com 400mg de SDG/Kg de ração e 7% de óleo de linhaça. No 14 e 20 dias de lactação as ratas foram ordenhadas e no 21 dia foram sacrificadas por punção cardíaca. Leite e soro foram coletados para avaliação bioquímica e hormonal. Hormônios foram quantificados por radioimunoensaio. As proles machos e fêmeas foram sacrificadas aos 14 e 21 dias de idade. Os animais foram eviscerados para análise da composição corporal. Monitoramos a ingestão alimentar e a massa corporal (MC) durante o período experimental. As ratas SDG apresentaram maior gordura corporal (GC; +39%), enquanto as OLSDG menor conteúdo mineral (-20%) e trigliceridemia (TG) (-39%). As ratas SDG e OLSDG apresentaram hiperprolactinemia (+389% e 153%, respectivamente) sem alteração na concentração de estradiol. No 14 dia de lactação, o leite das ratas OLSDG apresentou menores teores de lactose(-17%) e de proteínas (-20%) e o das ratas SDG apenas menor teor de proteína (-21%). A partir do 13 dia de lactação tanto os machos quanto as fêmeas OLSDG apresentaram menor MC (-14%, -16%, respectivamente). No 14 dia de lactação os machos SDG e OLSDG apresentaram menor gordura corporal (-24%, -55%, respectivamente ) e a prole SDG maior massa de gordura visceral (+39%). Os machos SDG apresentaram maiores concentrações de TG (+105%) e hipoprolactinemia (-41%). Os machos OLSDG também apresentaram hipoprolactinemia (-41%). As fêmeas SDG e OLSDG apresentaram maior estradiol aos 14 dias (+86% e +176%) que se normalizou aos 21 dias, maior colesterolemia (+16%) e as SDG apresentaram maior trigliceridemia (+74%). Aos 21 dias os machos e as fêmeas SDG e OLSDG apresentaram menor trigliceridemia (-48%, -54%,42% e -59%, respectivamente). Os dois componentes principais da semente de linhaça produzem alterações bioquímicas e hormonais tanto nas mães, quanto nas proles, independente do sexo. Entretanto, as alterações observadas diferem entre mães e prole e de acordo com o gênero. Entre as alterações mais importantes ressaltamos a hiperprolactinemia materna que pode ser um dos motivos para a hipoprolactinemia da prole e a hipertrigliceridemia causada pela ingestão de SDG pelas mães. / We evaluated the mothers intake of SDG (Diglicoside secoisolariciresinol) and flaxseed oil + SDG upon biochemical and hormonal parameters of lactating female rats and the male and female offspring during lactation. The female lactating rats were divided into: Control (C): feeding a diet with casein; (SDG): feeding diet C added 400mg of SDG/Kg diet; (OLSDG): diet C added 400mg of SDG/Kg diet and 7% of flaxseed oil. Milk samples were obtained on the 14th and 20th days of lactation and the mothers were sacrificed and blood collected by cardiac puncture on the 21st day. Milk and serum were collected for biochemical and hormonal analysis. The male and female offsprings were sacrified on the 14th and 21st day. The hormonal dosages were measured by radioimunassay. The animals were completely eviscerated to analyze body composition. Body mass (BM) and food intake were monitored during all experimental period. The SDG rats showed higher fat mass (+39%) while the OLSDG rats showed lower mineral content (-20%) and triglycerides (TG) serum levels (-39%). The SDG and OLSDG rats showed higher prolactin levels (+339% and +153% respectively) without changes in serum estradiol. On the 14th day of lactation we observed lower lactose (-17%) and protein (-20%) content in the OLSDG rats milk while in the SDG only lower protein (-21%). From the 13th day of lactation both the males and females OLSDG showed lower BM ( - 14%, - 16%, respectively). On the 14th day the male SDG and OLSDG showed lower fat mass (-24%, -55%, respectively), and the SDG offspring showed higher visceral fat mass (+39%). The SDG male also showed higher TG levels (+105%) and lower prolactin levels (-41%). The OLSDG males also showed lower prolactin serum levels (-41%). The OLSDG female showed higher serum estradiol at 14 days (+86% e +176%), which normalized at 21 days and higher cholesterolemia (+16%) and the SDG female presented higher TG levels (+74%). On day 21th day the male and female SDG and OLSDG showed lower TG levels (-48%,-54%, -42% and 59% respectively). Thus, the two main component of flaxseed showed biochemical and hormonal changes in the mothers and offspring, independent of gender. However, the changes observed in mothers differ from the offspring, and differ accordingly with the sex of offspring. The most impressive changes were the maternal hyperprolactinemia that can be one of the cause for the observed hypoprolactinemia in the offspring and the other main finding was the hypertriglyceridemia in the SDG group.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Avaliamos o efeito do consumo materno de SDG (Diglicosídeo Secoisolariciresinol) e de óleo de Linhaça+SDG sobre parâmetros bioquímicos e hormonais das ratas e das proles machos e fêmeas na lactação. As ratas lactantes foram separadas em: controle (C), ração controle cuja proteína foi caseína; (SDG): ração C com 400mg de SDG/Kg de ração; OLSDG: ração C com 400mg de SDG/Kg de ração e 7% de óleo de linhaça. No 14 e 20 dias de lactação as ratas foram ordenhadas e no 21 dia foram sacrificadas por punção cardíaca. Leite e soro foram coletados para avaliação bioquímica e hormonal. Hormônios foram quantificados por radioimunoensaio. As proles machos e fêmeas foram sacrificadas aos 14 e 21 dias de idade. Os animais foram eviscerados para análise da composição corporal. Monitoramos a ingestão alimentar e a massa corporal (MC) durante o período experimental. As ratas SDG apresentaram maior gordura corporal (GC; +39%), enquanto as OLSDG menor conteúdo mineral (-20%) e trigliceridemia (TG) (-39%). As ratas SDG e OLSDG apresentaram hiperprolactinemia (+389% e 153%, respectivamente) sem alteração na concentração de estradiol. No 14 dia de lactação, o leite das ratas OLSDG apresentou menores teores de lactose(-17%) e de proteínas (-20%) e o das ratas SDG apenas menor teor de proteína (-21%). A partir do 13 dia de lactação tanto os machos quanto as fêmeas OLSDG apresentaram menor MC (-14%, -16%, respectivamente). No 14 dia de lactação os machos SDG e OLSDG apresentaram menor gordura corporal (-24%, -55%, respectivamente ) e a prole SDG maior massa de gordura visceral (+39%). Os machos SDG apresentaram maiores concentrações de TG (+105%) e hipoprolactinemia (-41%). Os machos OLSDG também apresentaram hipoprolactinemia (-41%). As fêmeas SDG e OLSDG apresentaram maior estradiol aos 14 dias (+86% e +176%) que se normalizou aos 21 dias, maior colesterolemia (+16%) e as SDG apresentaram maior trigliceridemia (+74%). Aos 21 dias os machos e as fêmeas SDG e OLSDG apresentaram menor trigliceridemia (-48%, -54%,42% e -59%, respectivamente). Os dois componentes principais da semente de linhaça produzem alterações bioquímicas e hormonais tanto nas mães, quanto nas proles, independente do sexo. Entretanto, as alterações observadas diferem entre mães e prole e de acordo com o gênero. Entre as alterações mais importantes ressaltamos a hiperprolactinemia materna que pode ser um dos motivos para a hipoprolactinemia da prole e a hipertrigliceridemia causada pela ingestão de SDG pelas mães. / We evaluated the mothers intake of SDG (Diglicoside secoisolariciresinol) and flaxseed oil + SDG upon biochemical and hormonal parameters of lactating female rats and the male and female offspring during lactation. The female lactating rats were divided into: Control (C): feeding a diet with casein; (SDG): feeding diet C added 400mg of SDG/Kg diet; (OLSDG): diet C added 400mg of SDG/Kg diet and 7% of flaxseed oil. Milk samples were obtained on the 14th and 20th days of lactation and the mothers were sacrificed and blood collected by cardiac puncture on the 21st day. Milk and serum were collected for biochemical and hormonal analysis. The male and female offsprings were sacrified on the 14th and 21st day. The hormonal dosages were measured by radioimunassay. The animals were completely eviscerated to analyze body composition. Body mass (BM) and food intake were monitored during all experimental period. The SDG rats showed higher fat mass (+39%) while the OLSDG rats showed lower mineral content (-20%) and triglycerides (TG) serum levels (-39%). The SDG and OLSDG rats showed higher prolactin levels (+339% and +153% respectively) without changes in serum estradiol. On the 14th day of lactation we observed lower lactose (-17%) and protein (-20%) content in the OLSDG rats milk while in the SDG only lower protein (-21%). From the 13th day of lactation both the males and females OLSDG showed lower BM ( - 14%, - 16%, respectively). On the 14th day the male SDG and OLSDG showed lower fat mass (-24%, -55%, respectively), and the SDG offspring showed higher visceral fat mass (+39%). The SDG male also showed higher TG levels (+105%) and lower prolactin levels (-41%). The OLSDG males also showed lower prolactin serum levels (-41%). The OLSDG female showed higher serum estradiol at 14 days (+86% e +176%), which normalized at 21 days and higher cholesterolemia (+16%) and the SDG female presented higher TG levels (+74%). On day 21th day the male and female SDG and OLSDG showed lower TG levels (-48%,-54%, -42% and 59% respectively). Thus, the two main component of flaxseed showed biochemical and hormonal changes in the mothers and offspring, independent of gender. However, the changes observed in mothers differ from the offspring, and differ accordingly with the sex of offspring. The most impressive changes were the maternal hyperprolactinemia that can be one of the cause for the observed hypoprolactinemia in the offspring and the other main finding was the hypertriglyceridemia in the SDG group.

O carcinoma hepatocelular (HCC) apresenta mau prognóstico o que torna importante sua quimioprevenção. Nesse sentido, a tributirina (TB), um inibidor de desacetilases de histonas (HDACi), mostrou-se um quimiopreventivo promissor da hepatocarcinogênese. Avaliaram-se aqui efeitos quimiopreventivos de lipídios estruturados (EST) obtidos por interesterificação enzimática a partir da TB com o óleo de linhaça (LIN). Ratos foram tratados com EST (grupo EST; 165 mg/100g peso corpóreo [p.c]), TB (grupo TB; 200 mg/100g p.c), LIN (grupo LIN; 133 mg/100g p.c), mistura de TB com LIN (grupo LIN; 165 mg/100g p.c) ou maltodextrina (MD) (grupo MD; controle isocalórico; 300 mg/100g p.c) diariamente durante 8 semanas consecutivas por gavagem. Duas semanas após início dos tratamentos, os animais foram submetidos ao modelo de hepatocarcinogênese do \"hepatócito resistente\" (RH). Os grupos EST e TB apresentaram atividade quimiopreventiva bloqueadora e supressora, respectivamente, da hepatocarcinogênese. TB induziu a apoptose, ao contrário dos EST. O tratamento com TB resultou na acetilação e trimetilação da H3K9 e H3K27, enquanto EST atuaram somente na trimetilação das mesmas. Quando analisada a expressão de genes envolvidos com modificações em histonas, EST e TB reduziram a expressão de Ezh2 e de Hdac4. Por outro lado, somente os EST aumentaram a expressão de Hdac6. Tal efeito por parte dos EST merece ser mais investigado, uma vez que esta desacetilase vem sendo sugerida como alvo potencial para o desenvolvimento de fármacos. Em conclusão, a atividade quimiopreventiva de EST e da TB envolve na hepatocarcinogênese experimental mecanismos epigenéticos que podem ou não ser distintos. / Hepatocellular carcinoma (HCC) has a poor prognosis, which makes its chemoprevention important. Tributyrin (TB), which is a histone deacetylase inhibitor (HDACi), is a promising chemopreventive agent of hepatocarcinogenesis. The chemopreventive effects of structured lipids (STLs) that were obtained by the enzymatic interesterification of TB with flaxseed oil (FSO) were evaluated in the present study. Rats were treated with STLs (STL group, 165 mg/100 g body weight (bw)), TB (TB group, 200 mg/100 g bw), FSO (FSO group, 133 mg/100 g bw), TB mixed with FSO (BLD group, 165 mg/100g bw) or maltodextrin (MD) (MD group; isocaloric control; 300 mg/100 g bw) daily for eight consecutive weeks by gavage. Two weeks after the initiation of treatment, the animals were subjected to the resistant hepatocyte hepatocarcinogenesis model (RH). The STL and TB groups developed blocker and suppressive chemopreventive activity against hepatocarcinogenesis, respectively. TB treatment induced apoptosis, unlike the STL treatment. Additionally, TB treatment resulted in the acetylation and trimethylation of H3K9 and H3K27, whereas the STLs acted only in the trimethylation of these histones. When analyzing the expression of genes involved in histone modifications, the STLs and TB reduced enhancer of zeste homolog 2 (Ezh2) and histone deacetylase 4 (Hdac4) gene expression. Conversely, only the STLs increased Hdac6 gene expression. This effect of the STLs warrants further investigation because this deacetylase has been suggested as a potential drug development target. In conclusion, the chemopreventive activities of the STLs and TB in experimental hepatocarcinogenesis involve epigenetic mechanisms that may be distinct.

Novel uses of wheat gluten (WG) proteins, obtained e.g. as a coproduct from bio-ethanol production, are presented in this thesis. A flame-retardant foam was prepared via in-situ polymerization of hydrolyzed tetraethyl orthosilicate (TEOS) in a denatured WG matrix (Paper I). The TEOS formed a well-dispersed silica phase in the walls of the foam. With silica contents ≥ 6.7 wt%, the foams showed excellent fire resistance. An aspect of the bio-based foams was their high sensitivity to fungi and bacterial growth. This was addressed in Paper II using a natural antimicrobial agent Lanasol. In the same paper, a swelling of 32 times its initial weight in water was observed for the pristine WG foam and both capillary effects and cell wall absorption contributed to the high uptake. In Paper III, conductive and flexible foams were obtained using carbon-based nanofillers and plasticizer. It was found that the electrical resistance of the carbon nanotubes and carbon black filled foams were strain-independent, which makes them suitable for applications in electromagnetic shielding (EMI) and electrostatic discharge protection (ESD). Paper IV describes a ‘water-welding’ method where larger pieces of WG foams were made by wetting the sides of the smaller cubes before being assembled together. The flexural strength of welded foams was ca. 7 times higher than that of the same size WG foam prepared in one piece. The technique provides a strategy for using freeze-dried WG foams in applications where larger foams are required. Despite the versatile functionalities of the WG-based materials, the mechanical properties are often limited due to the brittleness of the dry solid WG. WG/flax composites were developed for improved mechanical properties of WG (Paper V). The results revealed that WG, reinforced with 19 wt% flax fibres, had a strength that was ca. 8 times higher than that of the pure WG matrix. Furthermore, the crack-resistance was also significantly improved in the presence of the flax. / <p>QC 20170524</p>

Les éco-composites s'imposent progressivement comme une alternative à certains matériaux classiques. L'utilisation de fibres végétales en guise de renfort permet en effet d'améliorer les performances environnementales de ces matériaux ainsi que leurs propriétés spécifiques élevées. Dans ce contexte, cette étude propose d'élaborer un éco-composite sandwich dont les peaux sont constituées d'une résine thermoplastique innovante associée à des fibres de lin et à une âme en balsa. Tout d'abord, les comportements statiques de la résine et de l'âme sont analysés. Par la suite, le composite renforcé de fibres de lin constituant les peaux du sandwich est étudié. Les caractéristiques élastiques principales du pli UD en contraintes planes sont déterminées. De plus, une analyse des mécanismes d'endommagement est effectuée au moyen de la technique d'émission acoustique. Le comportement des poutres sandwiches sollicitées en flexion est ensuite étudié. Une attention particulière est portée à la compréhension des modes de rupture et à l'influence des variations locales des propriétés mécaniques de l'âme. Par ailleurs, certaines propriétés dynamiques de cette structure sont explorées, notamment son comportement en fatigue et sa réponse à l'impact afin de discuter de sa durabilité. Enfin, une étude expérimentale du comportement vibratoire des poutres composites et sandwiches est réalisée. Le rôle des différents constituants dans l'amortissement global des vibrations est discuté au moyen d'une modélisation par élément finis. L'ensemble des propriétés déterminées sont comparées à celles des matériaux non bio-sourcés, afin de situer ses performances. / Bio-based composites appear to be very promising alternatives to traditional composites. The use of natural fibres as reinforcement reduces the environmental impact of these materials and their specific properties are significantly increased. In this context, this work focuses on the manufacturing and the mechanical characterization of a bio-based sandwich structure. The skins are made of an innovative thermoplastic resin associated with flax fibres. The core is made of balsa wood. First, quasi-static analyses are performed on the different components. Then, the tensile properties of the composite skins are studied. Moreover, the main damage mechanisms are identified and described by means of the acoustic emission technique. Next, the flexural behavior of the whole sandwich structure is studied. Particular attention is paid to the detection and prediction of the main fracture modes. Moreover, the statistical spreads of the material properties of the balsa core are taken into account. In addition, cyclic fatigue and impact tests are performed to investigate the behavior of this structure under dynamic loads, and to discuss whether or not this material could be suitable for potential semi-structural applications. Finally, experimental analyses of the vibration behavior of composite and sandwich beams are performed. The contributions of the different components to the global damping properties of the sandwich structure are analyzed by means of a finite elements model. This work also compares the properties of this bio-based sandwich to those of traditional materials, in order to benchmark its mechanical performances with a view to further industrial usage.