ABSTRACT:Composites based entirely on renewable materials with flax fibers as reinforcement and cellulose acetate butyrate (CAB) as the matrix were prepared by compression molding. Scanning electron microscopy of the fracture surfaces showed insufficient penetration of the matrix into the fiber mat. Rheological measurements indicated that this was caused by the high melt viscosity of CAB. Various amounts of furfuryl alcohol (FA) were added to the matrix to control the melt viscosity of CAB. The melt viscosity was decreased dramatically by the introduction of FA, which acted as a CAB solvent and facilitated the impregnation of the flax fiber mats. The mechanical and dynamic thermal properties of composites based on flax mats and various amounts of CAB and FA were investigated. The addition of FA to CAB and the polymerization of FA resulted in a linearly increased modulus and an increase in the maximum fiber stress (strength) of flax composites but a decreased toughness.Dynamic mechanical thermal analysis (DMTA) showed that CAB/poly(furfuryl alcohol) (PFA) matrices were miscible because the glass-transition temperature (T g ) in the resulting blends occurred between the T g of the homopolymers. DMTA also showed that increasing the amount of FA in the matrix substantially increased the storage modulus of the composites at temperatures lower than 80°C. It was possible to tune the storage properties of the composites through the addition of appropriate amounts of FA to the matrices. The CAB/PFA matrix showed behavior between that of thermoplastics and thermosets because of the miscibility and affinity of its components.

Kraft lignin wood fiberboards ± The effect of kraft lignin addition to wood chips or board pulp prior to fiberboard production M. Westin, R. Simonson, B. O È stman Kraft lignin is a by-product of kraft pulping with great potential as an additive for wood composites. Kraft lignin was added to wood chips prior to de®bration and alternatively to ®bers to improve the properties of ®berboards. Lignin-wood ®berboards were produced on both laboratory and semi-industrial scale using different methods of adding the lignin and ®xing it with metal salt solutions. Both wet-formed (hardboards) and dry-formed (MDF) boards were produced. The properties of lignin hardboards without a post-heat-treatment were slightly better than heat-treated control hardboards. This indicates that addition of kraft lignin in combination with a di-or trivalent metal salt can be an economic alternative to heattreatment of boards. Results for MDFs indicate that boards with improved dimensional stability could be produced at relatively low cost without need of major investments in equipment.

Lignocellulosic ®bers of different origins were acetylated in large batches. The ®bers used were of commercial, medium density ®berboard (MDF) pulp quality produced from softwood, beech, waste wood (low quality residue from an intermediate forest cutting) and wheat straw, respectively. Fiber from de-inked, semi-bleached, recycled paper was also included in the study. Laboratory ®ber-boards were produced from the acetylated ®bers by using powdered phenolic resin of the novolak type as a binding agent. Control boards made from unmodi®ed ®ber were also produced. The ®berboards were subjected to mechanical and dimensional stability testing. The acetylation of the ®ber, regardless of the source of the lignocellulosic material, has a very positive impact on the performance of ®ber composite products. For instance, the thickness swelling for softwood ®berboard in water is reduced by approximately 90%, and the mechanical properties are slightly improved. Results from cyclic testing according to EN 321, (three cycles, each comprising 72 h water immersion, 24 h freezing at )18°C and 72 h drying at 70°C) show that more than 90% of the internal bond strength, IBS, remained after the testing. This value can be compared with the corresponding value of 30±40% obtained for ®berboards made from unmodi®ed ®bers. The remaining thickness swelling of ®berboards made from acetylated ®bers was independent of ®ber source and resin content. The results obtained showed that acetylation can improve the mechanical properties of ®berboards provided that a proper resin is chosen. Werkstoffe aus acetylierten Lignocellulosefasern verschiedener Herkunft. Teil 1: Eigenschaften der trockengeformten Faserplatten Lignocellulosefasern verschiedener Herkunft wurden in groûen Ansa Ètzen acetyliert. Verwendet wurden handelsu Èbliche, fu Èr die MDF-Herstellung aufgeschlossene Fasern aus Nadel-, Buchen-und Durchforstungsholz geringer Qualita Èt, sowie Weizenstroh. Fasern aus de-inktem, halbgebleichtem Altpapier kamen ebenfalls zum Einsatz. Aus den acetylierten Fasern wurden Laborplatten hergestellt unter Verwendung eines Phenolharzes vom Novolacktyp. Kontrollplatten wurden aus unbehandelten Fasern hergestellt. Die Acetylierung hatte, unabha Èngig von der Herkunft der Fasern, einen positiven Ein¯uû auf die Platteneigenschaften. Z.B. wurde die Dickenquellung der Platten aus Nadelholzfasern um 90% verringert und die mechanischen Eigenschaften leicht verbessert. Nach dem zyklischen Test (EN 321) blieben mehr als 90% der Querzugfestigkeit erhalten; bei Platten aus unmodi®zierten Fasern waren es dagegen nur 30±40%. Die Dickenquellung nach dem zyklischen Test war unabha Èngig von der Herkunft der Fasern und vom Harzgehalt. Die Ergebnisse zeigen, daû die mechanischen Eigenschaften von Faserplatten durch Acetylierung verbessert werden ko Ènnen, wenn ein geeignetes Harz verwendet wird.

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