Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

O uso de recursos florestais e madeireiros como cargas em matrizes poliméricas pode originar novos materiais com forte apelo ecológico e econômico. Dentre os resíduos do processamento mecânico e químico da madeira, há uma série de materiais de fácil acesso que podem ser manipulados a partir de certas técnicas de biorrefinaria, tais como a madeira, a casca de madeira, as pinhas (frutos do pinus), as acículas (folhas do pinus), a lignina residual (processo kraft) e o lodo de papel derivadas do processo químico de polpação celulósica. Tais matérias primas foram incorporadas em espumas rígidas e semi-rígidas de poliuretano (PU) processadas pelo método da expansão livre, utilizando-se uma mistura de óleo de mamona e glicerina loira como biopoliol, com vistas a obtenção de espumas quimicamente estáveis e ecologicamente corretas. A compatibilidade de algumas dessas cargas no sistema PU foi testada mediante reações induzidas na presença de isocianato e catalisador. As espumas PU foram caracterizadas por meio de técnicas de microscopia e espectroscopia, além de ensaios mecânicos, térmicos, higroscópicos, óticos, de resistência a chamas e de resistência à radiação UV. Por fim, foi avaliado o efeito de expansões sob confinamento nas propriedades morfológicas, mecânicas e térmicas do PU puro e de uma espuma carregada PU/madeira As espumas apresentaram estabilidade química e a inserção das cargas no PU puro possibilitou a obtenção de espumas com células homogêneas, melhor desempenho higroscópico, níveis similares de condutividade térmica e flamabilidade, além de maior brilho e diferentes padrões de cor. A farinha de madeira apresentou a maior afinidade com o sistema PU, seguida pela lignina kraft, resultando em espumas carregadas com células menores, mais arredondadas e com maior teor de células fechadas, além de espumas com maiores estabilidades térmica e dimensional. Todas as espumas apresentaram fotodegradações similares, marcadas por uma cor alaranjada, acompanhada por uma acentuada perda de brilho. As espumas carregadas naturalmente mais escuras foram mais resistentes à fotodegradação por serem capazes de causar um efeito contrário ao da descoloração natural do PU quando sujeito aos raios UV. O confinamento diminuiu o diâmetro médio de células da espuma PU/madeira e a anisotropia do PU puro, levando a formação de células mais homogêneas, marcadas por números de arestas rompidas e de células abertas aparentemente menores, que resultaram em maiores densidades aparentes e melhores propriedades mecânicas para espumas preparadas a 50% de confinamento e menor condutividade térmica para as espumas confinadas a 70%. / The use of forestry and wood-based resources as fillers in polymer matrices may originate new materials with strong environmental and economic appeals. Among the wastes from chemical and mechanical processing of wood, there are many materials readily available, which can be handled through biorrefinary techniques, like wood flour, wood bark, pine cones (fruits), pine needles (leaves), residual lignin (e.g. from kraft process) and paper sludge, the last two from the chemical processing of cellulosic pulp. In this thesis, such raw materials were incorporated into rigid and semi-rigid polyurethane (PU) foams prepared by the free-rising pouring method, using a mixture of castor oil and crude glycerin as a bio-based polyol in order to achieve chemically stable and eco-friendly foams. Compatibility of the fillers with the PU system was evaluated using induced reactions in the presence of isocyanate and catalyst. The PU foams were characterized by microscopy and spectroscopy techniques, as well as mechanical, thermal, hygroscopic, optical, flame resistance and UV radiation resistance tests. And the effect of rising under confinement on the morphological, mechanical and thermal properties of neat PU and wood/PU foam composites was also investigated The foams presented chemical stability and the addition of fillers into PU yielded foams with more homogeneous cells, better hygroscopic performance, similar thermal conductivities and flammabilities, as well as higher specular glosses and different colorimetric patterns. The wood flour presented the highest affinity with the PU system, followed by kraft lignin, resulting in foam composites with smaller and more rounded cells, with higher closed-cells content, and increased thermal and dimensional stabilities. All foams presented similar photodegradation behavior characterized by an orange color and a significant loss in specular gloss. The foam composites, being naturally darker, were more resistant to photodegradation, since they had an opposite effect related to natural discoloration under UV radiation. The confinement decreased cell diameter for the wood filled PU foam and the anisotropy index for neat PU foam, yielding more homogeneous cells, with fewer broken edges and open-cells, with greater apparent densities and better mechanical properties for foams prepared at 50% confinement and lower thermal conductivity for foams confined at 70%.

O uso de recursos florestais e madeireiros como cargas em matrizes poliméricas pode originar novos materiais com forte apelo ecológico e econômico. Dentre os resíduos do processamento mecânico e químico da madeira, há uma série de materiais de fácil acesso que podem ser manipulados a partir de certas técnicas de biorrefinaria, tais como a madeira, a casca de madeira, as pinhas (frutos do pinus), as acículas (folhas do pinus), a lignina residual (processo kraft) e o lodo de papel derivadas do processo químico de polpação celulósica. Tais matérias primas foram incorporadas em espumas rígidas e semi-rígidas de poliuretano (PU) processadas pelo método da expansão livre, utilizando-se uma mistura de óleo de mamona e glicerina loira como biopoliol, com vistas a obtenção de espumas quimicamente estáveis e ecologicamente corretas. A compatibilidade de algumas dessas cargas no sistema PU foi testada mediante reações induzidas na presença de isocianato e catalisador. As espumas PU foram caracterizadas por meio de técnicas de microscopia e espectroscopia, além de ensaios mecânicos, térmicos, higroscópicos, óticos, de resistência a chamas e de resistência à radiação UV. Por fim, foi avaliado o efeito de expansões sob confinamento nas propriedades morfológicas, mecânicas e térmicas do PU puro e de uma espuma carregada PU/madeira As espumas apresentaram estabilidade química e a inserção das cargas no PU puro possibilitou a obtenção de espumas com células homogêneas, melhor desempenho higroscópico, níveis similares de condutividade térmica e flamabilidade, além de maior brilho e diferentes padrões de cor. A farinha de madeira apresentou a maior afinidade com o sistema PU, seguida pela lignina kraft, resultando em espumas carregadas com células menores, mais arredondadas e com maior teor de células fechadas, além de espumas com maiores estabilidades térmica e dimensional. Todas as espumas apresentaram fotodegradações similares, marcadas por uma cor alaranjada, acompanhada por uma acentuada perda de brilho. As espumas carregadas naturalmente mais escuras foram mais resistentes à fotodegradação por serem capazes de causar um efeito contrário ao da descoloração natural do PU quando sujeito aos raios UV. O confinamento diminuiu o diâmetro médio de células da espuma PU/madeira e a anisotropia do PU puro, levando a formação de células mais homogêneas, marcadas por números de arestas rompidas e de células abertas aparentemente menores, que resultaram em maiores densidades aparentes e melhores propriedades mecânicas para espumas preparadas a 50% de confinamento e menor condutividade térmica para as espumas confinadas a 70%. / The use of forestry and wood-based resources as fillers in polymer matrices may originate new materials with strong environmental and economic appeals. Among the wastes from chemical and mechanical processing of wood, there are many materials readily available, which can be handled through biorrefinary techniques, like wood flour, wood bark, pine cones (fruits), pine needles (leaves), residual lignin (e.g. from kraft process) and paper sludge, the last two from the chemical processing of cellulosic pulp. In this thesis, such raw materials were incorporated into rigid and semi-rigid polyurethane (PU) foams prepared by the free-rising pouring method, using a mixture of castor oil and crude glycerin as a bio-based polyol in order to achieve chemically stable and eco-friendly foams. Compatibility of the fillers with the PU system was evaluated using induced reactions in the presence of isocyanate and catalyst. The PU foams were characterized by microscopy and spectroscopy techniques, as well as mechanical, thermal, hygroscopic, optical, flame resistance and UV radiation resistance tests. And the effect of rising under confinement on the morphological, mechanical and thermal properties of neat PU and wood/PU foam composites was also investigated The foams presented chemical stability and the addition of fillers into PU yielded foams with more homogeneous cells, better hygroscopic performance, similar thermal conductivities and flammabilities, as well as higher specular glosses and different colorimetric patterns. The wood flour presented the highest affinity with the PU system, followed by kraft lignin, resulting in foam composites with smaller and more rounded cells, with higher closed-cells content, and increased thermal and dimensional stabilities. All foams presented similar photodegradation behavior characterized by an orange color and a significant loss in specular gloss. The foam composites, being naturally darker, were more resistant to photodegradation, since they had an opposite effect related to natural discoloration under UV radiation. The confinement decreased cell diameter for the wood filled PU foam and the anisotropy index for neat PU foam, yielding more homogeneous cells, with fewer broken edges and open-cells, with greater apparent densities and better mechanical properties for foams prepared at 50% confinement and lower thermal conductivity for foams confined at 70%.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

O presente trabalho tem como objetivo analisar as propriedades mecânicas, térmicas, termo dinâmico-mecânicas e morfológicas de compósitos preparados com poliestireno expandido reciclado e pó de madeira. Compósitos com diferentes teores de agente compatibilizante e diferentes teores de pó de madeira foram desenvolvidos em extrusora dupla rosca co-rotante e moldados por injeção. Os resultados obtidos demonstram que o compatibilizante com maior quantidade de anidrido maleico, menor massa molar ponderal média e utilizado em quantidade igual a 2% em massa gerou compósitos com melhores propriedades mecânicas. A melhora na adesão interfacial também foi observada através da análise termo dinâmico-mecânica. Verificou-se aumento no módulo de armazenamento, redução na altura do pico de tan δ e também menor valor do fator de adesão, associado com a maior adesão na região da interface. Para os compósitos desenvolvidos com diferentes teores de pó de madeira a densidade obtida foi semelhante a densidade teórica indicando estar de acordo com a regra das misturas. A utilização de compatibilizante reduziu o teor de vazios dos compósitos. Os resultados obtidos nos ensaios de flexão demonstraram que o módulo de flexão aumenta com a quantidade de carga e também se aproxima do comportamento previsto pela regra das misturas, entretanto os compósitos sem compatibilizante apresentaram redução na resistência a flexão com o aumento do teor de pó de madeira. No ensaio de impacto observou-se redução da resistência ao impacto com a adição de carga, porém os compósitos com compatibilizante apresentaram resultados superiores aos compósitos sem compatibilizante para todos os teores de pó de madeira. Observou-se aumento no módulo de armazenamento, no módulo de perda e também na efetividade do reforço com a adição de pó de madeira. Ocorreu redução na largura e também na altura do pico de tan δ conforme a adição das partículas de madeira, contudo os compósitos com compatibilizante apresentaram redução mais acentuada devido à melhora na adesão interfacial. O modelo teórico para predizer o comportamento do módulo de armazenamento demonstrou proximidade com os valores experimentais para baixos teores de carga. Para tan δ o modelo teórico se mostrou inadequado. As micrografias dos compósitos sem compatibilizante indicaram arrancamento e a presença de vazios entre o pó de madeira e a matriz, entretanto os compósitos com compatibilizante demonstraram maior recobrimento das partículas de madeira pela matriz. A estabilidade térmica dos compósitos com compatibilizante foi reduzida para todos os teores de pó de madeira quando comparada aos compósitos sem compatibilizante. / Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-05-29T19:17:12Z No. of bitstreams: 1 Dissertacao Matheus Poletto.pdf: 13891003 bytes, checksum: 55e82e4ccfc0e75de63aa030fd38a84e (MD5) / Made available in DSpace on 2014-05-29T19:17:12Z (GMT). No. of bitstreams: 1 Dissertacao Matheus Poletto.pdf: 13891003 bytes, checksum: 55e82e4ccfc0e75de63aa030fd38a84e (MD5) / The present work aims to analyze the mechanical, thermal, dynamicalmechanical thermal properties and morphology of composites based on recycled polystyrene and wood flour. Composites with different types and levels of coupling agent and also with different levels of wood flour were developed in a co-rotating twin-screw extruder and injection molded. The results show that the coupling agent with higher amount of maleic anhydride, lower weight average molecular weight and used in to 2% by weight produced composites with better mechanical properties. The improvement in interfacial adhesion was also observed by dynamical-mechanical thermal analysis. An increase in the storage modulus, decrease in peak height and also lower value of adhesion factor, was observed due to the improved on interfacial adhesion. For the composites developed with different levels of wood flour density obtained was similar to theoretical density indicating that in accordance with the rule of mixtures. The use of coupling agent reduced the concentration of voids in the composites. The flexural modulus increases with the amount of wood flour and also approaches the behavior predicted by the rule of mixtures, however the composites without coupling agent showed reduction in flexural strength. The impact strength decreases with the addition of wood flour, but the composites with coupling agent showed better results than the composite without coupling agent for all levels of wood flour. There was an increase in the storage modulus, loss modulus and also the efficiency of filler with the addition of wood flour. There was a reduction in width and also in peak height of tan δ as the addition of wood particles, composite with coupling agent demonstrated greater reduction due to improved on interfacial adhesion. The theoretical model to predict the behavior of the storage modulus showed proximity with the experimental values for low levels of filler. Theoretical model for tan δ proved inadequate. The micrographs of composites without coupling agent indicated the presence of pulled-out traces and gaps between the wood flour and matrix, however the composites with coupling agent show the strong bonding and good wetting of the fillers by the matrix. The thermal stability of composites with coupling agent was reduced for all levels of wood flour when compared to composites without coupling agent.

O presente trabalho tem como objetivo analisar as propriedades mecânicas, térmicas, termo dinâmico-mecânicas e morfológicas de compósitos preparados com poliestireno expandido reciclado e pó de madeira. Compósitos com diferentes teores de agente compatibilizante e diferentes teores de pó de madeira foram desenvolvidos em extrusora dupla rosca co-rotante e moldados por injeção. Os resultados obtidos demonstram que o compatibilizante com maior quantidade de anidrido maleico, menor massa molar ponderal média e utilizado em quantidade igual a 2% em massa gerou compósitos com melhores propriedades mecânicas. A melhora na adesão interfacial também foi observada através da análise termo dinâmico-mecânica. Verificou-se aumento no módulo de armazenamento, redução na altura do pico de tan δ e também menor valor do fator de adesão, associado com a maior adesão na região da interface. Para os compósitos desenvolvidos com diferentes teores de pó de madeira a densidade obtida foi semelhante a densidade teórica indicando estar de acordo com a regra das misturas. A utilização de compatibilizante reduziu o teor de vazios dos compósitos. Os resultados obtidos nos ensaios de flexão demonstraram que o módulo de flexão aumenta com a quantidade de carga e também se aproxima do comportamento previsto pela regra das misturas, entretanto os compósitos sem compatibilizante apresentaram redução na resistência a flexão com o aumento do teor de pó de madeira. No ensaio de impacto observou-se redução da resistência ao impacto com a adição de carga, porém os compósitos com compatibilizante apresentaram resultados superiores aos compósitos sem compatibilizante para todos os teores de pó de madeira. Observou-se aumento no módulo de armazenamento, no módulo de perda e também na efetividade do reforço com a adição de pó de madeira. Ocorreu redução na largura e também na altura do pico de tan δ conforme a adição das partículas de madeira, contudo os compósitos com compatibilizante apresentaram redução mais acentuada devido à melhora na adesão interfacial. O modelo teórico para predizer o comportamento do módulo de armazenamento demonstrou proximidade com os valores experimentais para baixos teores de carga. Para tan δ o modelo teórico se mostrou inadequado. As micrografias dos compósitos sem compatibilizante indicaram arrancamento e a presença de vazios entre o pó de madeira e a matriz, entretanto os compósitos com compatibilizante demonstraram maior recobrimento das partículas de madeira pela matriz. A estabilidade térmica dos compósitos com compatibilizante foi reduzida para todos os teores de pó de madeira quando comparada aos compósitos sem compatibilizante. / The present work aims to analyze the mechanical, thermal, dynamicalmechanical thermal properties and morphology of composites based on recycled polystyrene and wood flour. Composites with different types and levels of coupling agent and also with different levels of wood flour were developed in a co-rotating twin-screw extruder and injection molded. The results show that the coupling agent with higher amount of maleic anhydride, lower weight average molecular weight and used in to 2% by weight produced composites with better mechanical properties. The improvement in interfacial adhesion was also observed by dynamical-mechanical thermal analysis. An increase in the storage modulus, decrease in peak height and also lower value of adhesion factor, was observed due to the improved on interfacial adhesion. For the composites developed with different levels of wood flour density obtained was similar to theoretical density indicating that in accordance with the rule of mixtures. The use of coupling agent reduced the concentration of voids in the composites. The flexural modulus increases with the amount of wood flour and also approaches the behavior predicted by the rule of mixtures, however the composites without coupling agent showed reduction in flexural strength. The impact strength decreases with the addition of wood flour, but the composites with coupling agent showed better results than the composite without coupling agent for all levels of wood flour. There was an increase in the storage modulus, loss modulus and also the efficiency of filler with the addition of wood flour. There was a reduction in width and also in peak height of tan δ as the addition of wood particles, composite with coupling agent demonstrated greater reduction due to improved on interfacial adhesion. The theoretical model to predict the behavior of the storage modulus showed proximity with the experimental values for low levels of filler. Theoretical model for tan δ proved inadequate. The micrographs of composites without coupling agent indicated the presence of pulled-out traces and gaps between the wood flour and matrix, however the composites with coupling agent show the strong bonding and good wetting of the fillers by the matrix. The thermal stability of composites with coupling agent was reduced for all levels of wood flour when compared to composites without coupling agent.

Les travaux présentés dans ce manuscrit sont consacrés à l'élaboration et l’étude des propriétés physiques et thermiques d’une nouvelle génération de composites bois/polymère.Ils sont composés d’une matrice bio-sourcé le pebax®, qui est un thermoplastique élastomèreet de farine de bois de production locale, issue du pin maritime. La matrice pebax® a été choisie car elle présente plusieurs avantages, notamment, une élongation avant ruptureimportante, un point de fusion inférieur à 200°C pour éviter la dégradation du bois au coursde la mise en oeuvre et un caractère hydrophile améliorant l’affinité entre la matrice et lerenfort. Les composites ont été élaborés par extrusion bi-vis et injectés sous forme d’haltèresnormalisées pour les tests mécaniques. Au cours de ces travaux, nous avons montré la bonne qualité de l’interface entre le bois et la matrice, permettant de s'affranchir de l’utilisation d’agents compatibilisants. Nous avons aussi mis en évidence une forte amélioration de la stabilité thermique des composites sous atmosphère oxydante par rapport à celle de la matrice et du bois séparément. Les caractérisations mécaniques et rhéologiques effectuées sur les composites ont permis de montrer l’effet rigidifiant de la farine de bois avec un taux critique entre 20% et 30% de charges pour lequel le comportement des composites évolue d’un type élastomérique à celui de solide moins ductile. La dernière partie des travaux a été consacrée à l’évaluation de la prise en eau des composites. En accord avec les travaux de la littérature, nous avons montré une augmentation de la prise en eau avec le taux de bois. De plus, nous avons démontré que le début de l’absorption d’eau de nos composites suit un mécanisme de diffusion de type Fickien. / The physical properties and thermal stability of a new family of wood polymer composites (WPC) using a bio-based thermoplastic elastomer matrix (pebax® copolymers) were studied. The matrix is a polyether-b-amide thermoplastic elastomer which presents an important elongation at break, a melting point below 200°C which helps prevent degradation of wood fibres. The hydrophilic character of pebax® leads to a good interaction with wood fibres. We have chosen several types of wood flour as reinforcement agent, focusing on wood flour from maritime pine. Composites compounds were made using a laboratory twin screw extruder prior to injection molding to obtain tensile test samples. We have demonstrated the good quality of the interface between wood fibres and matrix, without using any specific compatibilizing agent. Most importantly, we have pointed out a strong improvement of thermal stability of composites under air atmosphere, compared with the behaviour of the matrix or wood separately. We have also characterized the mechanical properties of these composites. The resulting data show an improvement of the tensile modulus with increasing wood content and a decrease of elongation at break, with a behaviour change from elastomeric to less stretchable solid behaviour between 20% and 30% of wood content.The last part of our work was dedicated to the evaluation of water absorption of thecomposites at different wood content. We have shown an increase of water absorption withincreasing wood content and we demonstrated a Fickian diffusion process at the onset ofwater absorption.

Abstract Wood powders are used in numerous applications such as thermoplastics and filters, and a lot of research effort has been put into developing novel ways of utilising them. The mechanical processing of wood powders, especially at particle sizes below 100 µm, has been reported in several studies, but they lack information on the effect of fine grinding conditions on the particle morphology and cellulose crystallinity, both of which are important parameters in the further processing of wood powders and in their various applications. This makes it very difficult to design and optimise fine grinding processes with different applications in mind. The aim of this thesis was to study the dry fine grinding of wood in several impact-based fine grinding mills in order to find out their effect on the properties of the wood and to study the energy required for the mechanical processing of the resulting powders. The effect of the main operational parameters on the properties of dried Norway spruce wood and the energy consumption was studied using three impact-based fine grinding mills that were capable of pulverising the wood down to a median particle size of less than 25 µm. It was found that the impact events occurring in media mills can be used for the production of very fine wood powders with lower cellulose crystallinity and rounder shaped particles having more uniform shape distribution than powders pulverised to a similar size range by means of impact events in non-media mills. A practical estimate was obtained for the minimum specific energy consumption in fine grinding in mills involving grinding media that could be utilised as a target for optimisation. Impact-based media milling under cryogenic conditions can be used to obtain different Norway spruce wood powders from those produced under ambient grinding conditions, i.e. without the freezing effect of nitrogen liquid. The energy efficiency of fine grinding can be enhanced by choosing cryogenic rather than ambient conditions. The moisture content of the wood has greater influence on the size and shape of the particles when milling is accomplished under ambient conditions. Torrefaction can reduce the energy consumption in impact-based media mills for median particle sizes over 17.4 µm (± 0.2 µm), while the shape and cellulose crystallinity of the particles are not significantly affected by torrefaction pretreatment as a function of energy consumption. / Tiivistelmä Puujauheita käytetään laajalti erilaisissa sovelluksissa, kuten esimerkiksi biokomposiiteissa ja suodattimissa. Tämän lisäksi on olemassa paljon tutkimustietoa siitä, kuinka puujauheita voitaisiin hyödyntää laajemminkin. Puu voidaan mekaanisesti prosessoida alle 100 µm:n kokoluokkaan, mutta yksityiskohtaista tietoa kuivahienojauhatuksen olosuhteiden vaikutuksesta jauheiden morfologiaan ja selluloosan kiteisyyteen ei ole saatavilla. Puujauheen morfologialla ja selluloosan kiteisyydellä on kuitenkin merkittävä vaikutus sovelluksia ja jatkojalostusta ajatellen. Puun kuivahienojauhatuksen tiedon puute hankaloittaa merkittävästi prosessin suunnittelua ja optimointia erilaisia sovelluksia varten. Tämän väitöskirjan tavoitteena on selvittää iskuihin perustuvien hienojauhimien vaikutukset puun ominaisuuksiin ja tutkia mekaanisen prosessoinnin energiatehokkuutta hienojauhatuksessa. Tutkimuksessa selvitettiin kolmen erilaisen iskuun perustuvan hienojauhatusmyllyn pääasiallisten operointiparametrien vaikutusta kuivatun metsäkuusen ominaisuuksiin ja energiankulutukseen. Jokaisella hienojauhimella onnistuttiin tuottamaan puujauhoja, joiden mediaanikoko oli alle 25 µm. Iskuihin perustuvalla jauhinkappalemyllyllä saatiin tuotettua puujauhoa, jonka selluloosan kiteisyys on alhaisempi ja partikkelimuodot pyöreämpiä verrattuna samankokoisiin puujauhoihin, jotka on tuotettu iskuihin perustuvilla jauhinkappaleettomilla hienojauhatusmyllyillä. Työssä saatiin käytännöllinen arvio kuivatun metsäkuusen hienojauhatuksen minimienergiankulutukselle iskuihin perustuville jauhinkappalemyllyille, mitä voidaan käyttää kyseisten myllytyyppien optimoinnin tavoitteena. Työssä havaittiin lisäksi, että kryogeenisiä jauhatusolosuhteita käyttämällä voidaan tuottaa erilaisia puujauhoja verrattuna puujauhoihin, jotka prosessoidaan ilman nestetyppijäädytystä, kun jauhatus suoritetaan iskuihin perustuvalla jauhinkappalemyllyllä. Ilman nestetyppijäädytystä puun kosteuspitoisuudella on merkittävämpi vaikutus puujauhojen ominaisuuksiin kuin kryogeenisissä olosuhteissa jauhetuilla. Kryogeenisillä jauhatusolosuhteilla voidaan parantaa myös jauhatuksen energiatehokkuutta. Torrefioinnilla voidaan vähentää hienojauhatuksen energiankulutusta iskuihin perustuvilla jauhinkappalemyllyillä, kun tavoitekoon mediaani on yli 17,4 µm (± 0,2 µm). Torrefioinnilla ei ole vaikutusta selluloosan kiteisyyteen tai partikkeleiden muotoon energiankulutuksen funktiona.

Ce travail de thèse a pour objectif de comprendre la fragilité des composites à matrice polymère (PVC) contenant des particules de bois. Dans un premier temps, il s’agit d’examiner le rôle de chacun des constituants : matrice et charge, sur les propriétés mécaniques du composite. Cette étude a montré que l’influence des paramètres relatifs à la microstructure de la matrice PVC est minoritaire face à celle des paramètres de la farine de bois. Pour mettre en évidence le rôle des particules de bois, une méthode d’analyse de leur dispersion et leur orientation par une technique 3D non destructive, a été employée : la tomographie aux rayons X. Un traitement spécifique des données a permis de quantifier la taille, l’orientation et la connectivité des particules. Ainsi, on a montré que l’existence d’agglomérats et/ou d’un réseau percolant fragilise fortement le composite ce qui explique la chute de la résistance au choc lorsque le taux de farine de bois augmente. Pour optimiser le compromis fragilité/ductilité, différentes solutions ont été envisagées. Dans un deuxième temps, nos travaux s'intéressent à l'évolution de l'endommagement de matériaux composites possédant différents taux de farine de bois. Cette évolution est mesurée à l'aide de deux techniques : l'émission acoustique et la tomographie aux rayons X in-situ. La décohésion à l’interface entre la matrice PVC et les particules de bois est le mécanisme initiant l’endommagement. La transition ductile/fragile des composites s’explique par la coalescence de ces cavités. L’ajout de modifiant choc ne réduit pas suffisamment ce mécanisme. Les agents de couplage sont donc la voie à explorer afin d’améliorer l’interface matrice/particules et remédier au défaut d’adhésion qui pénalise ces composites. / The aim of the present study is to understand the origin of the brittleness of PVC/wood flour composites (WPC). The influence of the matrix and of the filler is investigated: fiber parameters are key factors that significantly affect the mechanical properties of WPC. Fiber dispersion, orientation and particles connectivity can be accurately assessed by using the non-destructive X-ray tomography technique. The qualitative and quantitative analysis of tomography experimental results allows a 3D visualisation of the composite. The brittleness of the composites is caused by agglomerates and/or the presence of a percolated network: it explains why impact resistance decreases when the wood flour content increase. To optimise the rigidity/ductility compromise, several solutions are considered. The other part of this work consists of combining acoustic emission and X-ray tomography to study the evolution of damaging in composite materials with different wood flour content. An original coupling of these two techniques is implemented. The main failure mechanism involved in such composites is the decohesion between the matrix and the wood particles. The ductile/brittle transition occurs when the cavities coalescence becomes the dominant process over the PVC matrix failure. Adding impact modifiers is not sufficient to improve the ductility of the composite. Coupling agents are the route to be explored so as to improve the interfacial adhesion between the matrix and the particles.