WOOD REINFORCED TANNIN COMPOSITES MODIFIED WITH NATURAL RUBBER

M. A. MOSIEWICKI; J. BORRAJO; M. I. ARANGUREN

Buenos Aires, Argentina

Simposio; III Internacional Conference on Science and Technology of Composite Materials, COMAT2005; 2005

Universidad Nacional de Mar del Plata. Universitá degli Studi di Perugia

The development of polymeric materials prepared from natural products have gained increased importance in the last decade, due to threats of uncertain petroleum supply in the future and concerns about environmental pollution. Natural products present some advantages, which turn them interesting: they are abundant and available from renewable resources, show low cost and offer the possibility of biodegradation. In particular, some developments have been driven by environmental considerations, such as the reduction of emissions of volatile compounds. That is the case of tannin based polymers, used to reduce phenol emissions of phenolic type resins. Polyflavonoid tannins are natural polyphenolic materials that can be crosslinked by reaction with formaldehyde or hexamethylenetetramine crosslinking agents, the last one leading to cured products with low formaldehyde emissions .Most of the scientific and technological reports have focused on their use in the manufacture of adhesives (particleboards, plywood). Recently has been reported the use of these polymers in the manufacture of fiber composite materials and the results showed that these composite materials present very good mechanical properties in dry conditions, but in wet environments present a water absorption rate very high. The cured tannin matrix is more hygroscopic than the woodflour fibers and the mechanical properties are significatively deteriorated because of water absorption.  In order to improve the properties of this materials in wet conditions and following the tendency of using natural products, this work reports the effect of adding natural rubber to the composite materials formulated with commercial tannin adhesive, hexamethylentetramine as hardener and using woodflour as filler. Scanning electron microscopy of fractured samples was used to know the matrix morphology and to evaluate the interphase between filler and matrix. Flexural tests were performed on composites with different content of rubber and filler in dry and wet conditions.