Ahmed Allal

PREPARATION AND MECHANICAL CHARACTERIZATION OF PARTICLEBOARD MADE FROM MARITIME PINE AND GLUED WITH BIO-ADHESIVES BASED ON CORNSTARCH AND TANNINS

In this presented work, we describe the development and characterization of a new,environmentally friendly adhesive derived from cornstarch and tannins. The production of woodcomposites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as ureaformaldehyde (UF), phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), which cangenerate under certain conditions, problems for health and environment. The aim of our work is toreplace totally these synthetic resins. In order to evaluate the quality of cornstarch-tannin adhesives,particleboards were produced and physical and mechanical properties were investigated. Thesephysical properties included rheological, thermogravimetric analysis and solid phase 13C NMR analysisof resins. Internal bond, surface soundness, modules of rupture and modulus of elasticity mechanicalproperties of particleboards bonded with cornstarch-tannin adhesives were also determined.Particleboards bonded with formaldehyde-free cornstarch-tannin adhesive showedcomparable mechanical properties to the panels made with the commercial UF resins and satisfiedthe exigencies of panels for interior fittings used in dry medium (P2) according to European normsEN 312 (2004). Beyond 4 hours, rheological characterization show excellent structural stability ofcornstarch-tannin adhesive.

Corn flour-mimosa tannin-based adhesives without formaldehyde for interior particleboard production

A formaldehyde-free adhesive consisting of a corn flour/NaOH adhesive mixture and a mimosa tannin/hexamine intermediate component was developed and evaluated for application to wood panels such as particleboards. The main ingredients of this adhesive include corn flour, NaOH, mimosa tannin and hexamine. This study investigated the physical properties (rheological and thermal analysis) of corn flour/NaOH and mimosa tannin/hexamine adhesives as well as mechanical properties of particleboards produced with these adhesives. Thermomechanical (TMA) experiments indicate the best performance of the adhesives to be around the relative mass proportions of 50:50 between corn flour/NaOH and mimosa tannin/hexamine. Former NMR measurements on corn starch and mimosa tannin proved that the two components behave as a polymer blend rather than co-reacting. The laboratory results show that particleboards bonded with the adhesive at this optimal ratio show good mechanical properties. Moreover, the formaldehyde emission levels obtained from boards bonded with the optimal adhesive were considerably lower to those obtained from boards made with control urea formaldehyde.

Evaluation of decay resistance of wood products made from borax-impregnated wood and bonded with a formaldehyde-free cornstarch and tannin adhesive

Abstract• At present, the production of wood composites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as phenol-formaldehyde (PF) resins and urea-formaldehyde (UF) resins, which are non-renewable and therefore ultimately limited in supply.• This paper concerns the decay resistance of wood products bonded with a new, environment-friendly adhesive derived from abundant and renewable cornstarch and tannin. To improve the total resistance of the composite against both Coriolus versicolor and Coniophora puteana rot fungi, borax (di-sodium tetraborate) was added in proportions of 0.5%, 1% and 2% (w/w) to the cornstarch-tannin adhesives.• The results show that increasing the concentration of borax in the adhesive decreased the mechanical properties of the composite. The best way to avoid this problem was to use wood impregnated with borax.• Biodegradation studies were conducted on new composites, first without any treatment, followed by borax at 0.5% aqueous solution treatment. The results show that wood impregnated with borax, in the presence of tannin and sodium hydroxide in the adhesive improves the total resistance of the wood composite against both Coriolus versicolor and Coniophora puteana rot fungi.Résumé• Actuellement, la production des composites à base de bois nécessite l’utilisation d’adhésifs d’origine pétrochimique et à base de formaldéhyde, tels que le phénol-formaldéhyde (PF) et l’uréeformaldéhyde (UF), qui sont non renouvelables et limités dans l’approvisionnement.• Ce travail a pour objectif d’étudier la durabilité du bois collé avec une nouvelle colle naturelle à base d’amidon et tannin. Pour améliorer la résistance des composites vis-à-vis des deux types principaux de dégradation fongique, Coriolus versicolor et Coniophora puteana, nous avons ajouté à l’adhésif, différentes concentrations de borax (di-sodium tetraborate) 0,5 %, 1 % et 2 % (m/m).• Les résultats obtenus montrent que l’augmentation de la concentration du borax dans l’adhésif diminue les performances mécaniques des composites. La meilleure façon d’éviter ce problème est de traiter le bois avec du borax, avant collage.• L’étude de la biodégradation a été réalisée sur les nouveaux composites, d’abord sans traitement, et après traitement à 0,5 % (m/m) avec du borax. Les résultats montrent que le bois traité au borax associé à la présence des tannins et de NaOH dans l’adhésif améliore la résistance totale des composites vis-à-vis de Coriolus versicolor et Coniophora puteana.

Shear refinement of formaldehyde-free corn starch and mimosa tannin (Acacia mearnsii) wood adhesives

The aim of this work was to reduce the viscosity of formaldehyde-free corn starch–mimosa tannin wood adhesives, without adversely affecting the mechanical properties of the product. The reduction of viscosity was achieved using shear refinement. The study focused on the physical phenomena before cross-linking of the wood adhesive. The physical (rheological characterization) and mechanical (bond strength) properties of formaldehyde-free corn starch and mimosa tannin wood adhesives were measured. The results showed that the shear refinement (290 rpm and 5 min, optimal conditions) reduced the viscosity of the corn starch–mimosa tannin wood adhesives (from 100 000 to 458 Pa s) with the advantage of being stable over time. Mechanical tests showed that the shear refinement did not influence the mechanical properties of corn starch–mimosa tannin wood adhesives.

Mechanical characterization of industrial particleboard panels glued with cornstarch–mimosa tannin–urea formaldehyde resins

The aim of this work was to validate the utility and performance of optimal laboratory cornstarch–mimosa tannin-based resins in the industrial particleboard production. In this way, the cornstarch and mimosa tannin was introduced in the classic adhesive formulation in order to supply a part of urea-formaldehyde (UF). Our results show that industrial particleboard panels (8.2 m × 1.85 m × 19 mm) bonded with optimal cornstarch–mimosa tannin–UF (10:4:86; mass ratio) resins exhibited comparable mechanical properties to those of boards bonded with commercial UF resins and largely satisfied the exigencies of European norms EN 312. The formaldehyde emission levels obtained from panels bonded with cornstarch–mimosa tannin–UF were lower to those obtained from panels bonded with control UF. Finally, the addition of cornstarch and mimosa tannin improves markedly the water resistance of UF resins.