Natural Composites: Polymeric Matrices Based on Vegetable Resources

MIRTA I. ARANGUREN; MIRNA A. MOSIEWICKI; JULIO BORRAJO

Cancún, México

Conferencia; VIIIth International Conference on Frontiers of Polymers and Advanced Materials (VIIIth ICFPAM); 2005

Instituto de Investigaciones en Materiales, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México y CEA-DRT/LITTEN, Francia

The use of products from renewable resources to obtain composite materials has been increasing, in both scientific studies and commercial applications, during the last decade, mainly because it presents environmental and economic advantages. 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. Although most scientific and technological reports have focused on their use in the manufacture of adhesives (particleboards, plywood), the use of these polymers in the manufacture of molding powders or fiber composite materials has not been fully developed. Polyflavonoid tannins are natural polyphenolic materials that can be crosslinked by reaction with formaldehyde or hexamethylenetetramine (HEXA) crosslinking agents, the last one leading to cured products with low formaldehyde emissions. In the present study, this system was used as the polymer matrix of a pine woodflour composite. Perhaps more rich in possibilities as a source of different polymers is the use of plant oils as natural source of different resins. There are many reports on natural fiber composites using commercial thermosetting resins or thermoplastic polymers, but the use of a polymeric matrix from natural sources such as plant oils is relatively new. Linseed oil consists of triglyceride molecules, which are composed of three unsaturated fatty acid chains. An unsaturated polyester-like resin can be obtained by functionalizing the triglyceride molecules in two basic steps: glycerolisis to produce a monoglyceride and then reaction with maleic anhydride to produce a maleinated monoglyceride. The product is further blended with styrene, the reactive comonomer, and cured via a free radical polymerization to give a crosslinked thermosetting polymer. The produced polymer has carboxylic groups that can interact with the hydroxyl groups on the woodflour (filler).  The matrix has a relatively low modulus, but the addition of rigid particles increases the material stiffness. The wood particles have high strength and modulus, so they can impart better mechanical properties to the material improving its performance. In this presentation, the brief report on the synthesis of these natural based polymers and the study of their use as polymeric matrices in woodflour composites will be discussed.  The thermal and mechanical properties of these materials will be presented, as well as a discussion on the water absorption effect.