Biobased materials made from renewable resources, such as wood, play an important role in the sustainable development of society. One main challenge of biobased building materials is their inherent moisture sensitivity, a major cause for fungal decay, mold growth and dimensional instability, resulting in decreased service life as well as costly maintenance. A new building material known as wood-plastic composites (WPCs) has emerged. WPCs are a combination of a thermoplastic matrix and a wood component, the former is usually recycled polyethylene or polypropylene, and the latter a wood processing residual, e.g. sawdust and wood shavings. The objective of this thesis was to gain more insight about characteristics of WPCs containing a modified wood component. The hypothesis was that a modified wood component in WPCs would increase the moisture resistance and durability in outdoor applications. The study comprises both injection molded and extruded WPC samples made with an unmodified, acetylated, thermally modified or furfurylated wood component in a polypropylene (PP), high density polyethylene (HDPE), cellulose ester (CAP, a cellulose ester containing both acetate and propionate substituents) or polylactate (PLA) matrix. The WPCs were prepared with 50-70 weight-% wood. The emphasis was on studying the moisture sorption, fungal resistance and micromorphological features of these new types of composites. Water sorption in both liquid and vapor phases was studied, and the biological performance was studied both in laboratory and in long term outdoor field tests. Micromorphological features were assessed by analyzing of the wood component prior to and after processing, and by studying the composite microstructure by means of a new sample preparation technique based on UV excimer laser ablation combined with scanning electron microscopy (SEM). Results showed that the WPCs with a modified wood component had a distinctly lower hygroscopicity than the WPCs with unmodified wood, which resulted in less wood-plastic interfacial cracks when subjected to a moisture soaking-drying cycle. Durability assessments in field and marine tests showed that WPCs with PP or CAP as a matrix and 70 weight-% unmodified wood degraded severely within a few years, whereas the corresponding WPCs with a modified wood component were sound after 7 years in field tests and 6 years in marine tests. Accelerated durability tests of WPCs with PLA as a matrix showed only low mass losses due to decay. However, strength losses due to moisture sorption suggest that the compatibility between the PLA and the different wood components must be improved. The micromorphological studies showed that WPC processing distinctly reduces the size and changes the shape of the wood component. The change was most pronounced in the thermally modified wood component which became significantly reduced in size. The disintegration of the modified wood components during processing also creates a more homogeneous micromorphology of the WPCs, which may be beneficial from a mechanical performance perspective. Future studies are suggested to include analyses of the surface composition, the surface energy and the surface energy heterogeneity of both wood and polymer components in order to tailor new compatible wood-polymer combinations in WPCs and biocomposites. / <p>QC 20121119</p>

Currently, soil termiticides are the primary termite defense mechanism used under and around living spaces in the continental United States. While this form of treatment has been effective for many years, the creation of a new, more environmentally friendly termite management system could reduce the amount of termiticides introduced annually into the environment around structures. A natural barrier containing soil amendments and mulches amended with insect-repellent plant tissues discourages termite foraging and directs the termites away from the structure. The proposed integrated management system developed during this project, divides a structure into three zones. Each zone has particular responsibilities to the overall biological durability of the structure. This study concentrates on the inner-detritus zone, which extends 24” (0.61m) from the outer wall of the structure, an area that can harbor potential hazards such as moisture traps, conducive termite food, water and protection sources, and other factors that could put undue biological pressures on the structure. Altering this zone, more specifically the pH of the soil and the mixture of products used as mulch, creates an environment unsuitable for termite foraging. This integration of several termite repelling strategies should obviate or significantly reduce the need for termiticidal soil barriers under and around houses.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study investigated the effect of thermal treatment technique, used in two treatment conditions: treated wood in an autoclave and after conditioning, subject to the treatment under electric heater (combination), and treated wood by using only electric kiln (oven) on mechanical, hygroscopic and biological properties of Pinus taeda L. and Eucalyptus grandis W. Hill ex Maiden woods, comparing them with the results obtained for the untreated wood. For that three trees with 25 years, were deployed for each species from which it drew the first two logs for making the samples used in the evaluations. In the combination treatment these parts were subjected to thermo treatment by autoclaving at 130°C/ ± 3°C and pressure of 2 kgf/ cm² for 3 hours and after a conditioning period, subjected to electric heat in an oven at 160°C/ ± 1°C for the same period, already parts for just treatment in oven were exposed the last condition. The physical properties consisted in the evaluation of weight loss and specific weight assigned to treatment, equilibrium moisture content, rate of water absorption, effectiveness of water repellency, anti swelling efficiency, tangential, radial, and volumetric swelling and coefficient of anisotropy, the mechanical properties consisted in evaluating the modulus of elasticity and rupture in bending, maximum resistance to compression parallel, Janka hardness, impact resistance, and finally to the biological was employed accelerated decay test in the laboratory using white rot fungi and brown. The effect of heat treatment employed in the two methodologies resulted in different effects than expected with regard to the mechanical and biological. The results indicated that heat treatments used were effective in reducing the hygroscopicity and increased dimensional stability of both species, the best results for the combination method. To provide the mechanical properties of different effects, reaching an increase of resistance to certain properties and for durability of biological parts, treatments favored decay fungi employees, more pronounced effect for the combined method. / A presente pesquisa objetivou investigar o efeito da técnica de retificação térmica, empregada sob duas condições de tratamento: madeira tratada em autoclave e após condicionamento, submetida ao tratamento em estufa (combinação), e madeira tratada pelo uso de estufa elétrica apenas (estufa), nas propriedades mecânicas, higroscópicas e biológicas das madeiras de Pinus taeda L. e Eucalyptus grandis W. Hill ex Maiden, comparando-as com os resultados obtidos para a madeira sem tratamento. Para tanto, foram amostradas três árvores com 25 anos, para cada espécie, de onde se extraíram as duas primeiras toras, para confecção dos corpos de prova utilizados nas avaliações. No tratamento de combinação, as peças foram submetidas a termorretificação em autoclave a 130ºC/±3°C e pressão de 2 kgf/cm², por 3 horas e, após um período de condicionamento, submetidas ao calor em estufa elétrica a 160°C/±1°C, pelo mesmo período; já as peças destinadas apenas ao tratamento em estufa foram submetidas a última condição. As propriedades físicas consistiram na avaliação da perda de peso e massa específica, atribuída ao tratamento, umidade de equilíbrio, taxa de absorção de água, efetividade de repelência à água, eficiência anti inchamento, inchamento tangencial, radial, volumétrico e coeficiente de anisotropia; as propriedades mecânicas consistiram na avaliação do módulo de elasticidade e ruptura em flexão estática, resistência máxima à compressão paralela, dureza de Janka, resistência ao impacto; por fim, para as propriedades biológicas, empregou-se o ensaio de apodrecimento acelerado em laboratório, utilizando fungos de podridão branca e parda. O efeito do tratamento térmico empregado sob as duas metodologias, provocaram resultados diferentes do esperado, no que se refere as propriedades mecânicas e biológicas. Os resultados obtidos indicaram que os tratamentos térmicos empregados, foram eficientes na redução da higroscopicidade e aumento da estabilidade dimensional de ambas as espécies, com os melhores resultados obtidos pelo método de combinação. Para as propriedades mecânicas, os tratamentos térmicos promoveram efeitos diversos, chegando a um incremento da resistência para certas propriedades e, em relação à durabilidade biológica das peças, os tratamentos favoreceram o apodrecimento aos fungos empregados, efeito mais pronunciado para o método combinado.