Composites made from acetylated lignocellulosic fibers of different origin

Abstract

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.

Effect of Pretreatment of Raw Material on Properties of Particleboard Panels Made from Wheat Straw

“…However, recent studies have revealed that bonding quality can be improved by treating straw with different chemicals and enzymatic methods that enhance surface wettability and increase the surface free radical concentration (Rowell et al 1997;Loxton and Hague 1996;Gomez-Bueso et al 2000;Karr and Sun 2000;Han et al 2001;Schmidt et al 2002;Zhang et al 2003;Li et al 2011).…”

Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials

“…Acetylation has proved to reduce swelling of natural-fiber composites, but stiffness and strength have been reported to decrease when acetylation is used [3][4][5][6][7]. This drawback can, however, be avoided if certain types of matrix systems are used, according to Gomez-Bueso et al [8]. Steaming has been reported to give similar effects, with reduced swelling, stiffness, and strength [4,9].…”

Chemical Modification of Wood by Polyglycerol/Maleic Anhydride Treatment

“…However, while much reports have been done on the application and uses of glycerol (Jungerman and Sonntag 1991 and references cited within), much less has been described on the use of polyglycerol (PG), which appears in the literature essentially as patents. They involved the bulking of wood cell walls with various chemicals like polyethyleneglycols (PEGs), phenol/formaldehyde resins (Meyer 1984), anhydrides (Hill and Jones 1999;Gomes-Bueso et al 1999) or isocyanates (Baird 1969;Ellis and Rowell 1984) which prevent shrinkage or swelling. A number of chemical treatments have been investigated to improve the dimensional stability of wood (Wallström and Lindberg 1999).…”