NATURAL POLYMERIC MATRICES / NATURAL FIBRES COMPOSITES – NATMAT

Biocomposites materials are and have been an area of growing interest and a subject of active researches. This is due to both environmental concerns as well as to the foreseen future scarcity of oil and oil-derived products. Biocomposites using natural fibers and oil-derived polymer matrices have exist and have been available commercially for quite sometimes. Thus, composites from natural fibers plus polypropylene and other oil-derived thermoplastic matrices for car doors interiors and other applications are well known and are used, although not as extensively as could be wished. However, for the same type of applications, composites using also natural matrices while still presenting high performance are talked about but in reality have not been developed or commercialized. This is due to the difficulty in finding matrices of natural origin capable of imparting all the required performance to the resulting composites. Conversely, considerable industrial interest in developing natural, or ‘Green’ wood adhesives to substitute synthetic thermosetting resins as adhesives for wood panels has been shown lately due to the variability in the cost of oil and to the mounting environmental pressure worldwide. A number of different approaches have been taken to investigate the use of soy protein adhesives, to upgrade adhesives from vegetable tannin free of aldehyde or, even formulations free of hardeners, etc. Some of these resins are already in industrial use and perform well, however the supply of these is still reasonably limited due to raw materials limitations. This translates into an increasing interest in the use of alternative materials or to co-react them with other, more abundant and widely available natural materials. The lignins are natural renewable polymers obtained from lignocelulosic materials. They are very abundant, non toxic, and can be produced at low production costs. Their use as adhesives for wood composites such as particleboard, MDF, OSB, plywood, etc., can be a reality. This evidence can be demonstrated to some big specialized laboratories in adhesives as the researches unit about wood materials as LERMAB (Epinal-France) and other research institutions as UDT (Concepción-Chile) with the same world prestige on composite materials from wood. The present proposal offers the possibility and one opportunity for taking advantage of the abundance of different types of lignin that can be found as a waste product in pulp mills. These kinds of lignin come from industrial processes, for example, Kraft lignin, lignosulfonate, organosolv, and lignin from pulp and paper mills. All of these lignins can be analysed and their management should be improved because it represents a high potential use. Another interesting raw material is the wheat straw which is a lignocellulosic material; this condition made it a good candidate as a lignin source promoting new uses, for instance, biocomposite thermoplastic material for car doors interiors, and other applications as a wood adhesive. While this project is being developed, it will be possible to study the lignin’s modification reactions, to increase its reactivity by introducing reactive groups as methylol in the polycondensation and with other natural composites as tannin extract. Such materials represent an attractive proposal for the preparation of biocomposites materials adhesive resins. The literature on the use of lignin to prepare wood adhesives is very extensive and good reviews of it exist. However the record of their industrial use is still poor. This research then deals first with the optimization of lignin-based adhesives for wood by attempting to eliminate the addition of a synthetic phenol-formaldehyde resin, substituting it with a natural vegetable tannin extract. The aim was then (i) to eliminate completely formaldehyde from the thermosetting resins, and (ii) to increase the proportion of natural, environment friendly materials in these new formulations.