María M. Reboredo

Dependence of the mechanical properties of woodflour–polymer composites on the moisture content

Woodflour of Eucaliptus saligna with two different chemical treatments (mercerization and esterification with maleic anhydride) was used as filler of an unsaturated polyester matrix. Woodflour was treated to increase the interfacial adhesion with the matrix, to improve the dispersion of the particles, and to decrease the water sorption properties of the final composite. The objective of this study was to determine the influence of the moisture content and the woodflour chemical modification on the physical and mechanical properties of the different composites. Results indicated that mechanical properties (compression and bending tests) were severely affected by moisture and chemical modifications. In wet conditions, the composites made from treated woodflour had the lowest flexural modulus and ultimate stress. It was found that this was a reversible effect, because the original values of the compression properties were recovered after drying. Temperature scans in dynamic mechanical tests showed that an irreversible change occurred during exposure to humid environments, probably due to the hydrolysis of the polyester matrix. Essentially, the same behavior was observed for matrix and composites; however, a wood-related transition overlapped the main transition in the case of wet composites.

Mechanical properties of woodflour unsaturated polyester composites

Agrowastes and woodflour are a potential and attractive alternative of cheap reinforcement for brittle polymeric materials because they can reduce costs and, at the same time, improve certain properties. On the other hand, their high moisture sorption and low microbial resistance are disadvantages that need to be considered and, as far as possible, corrected. Polyester resins are widely used throughout the world, and can be processed with reinforcing agents very easily. In this work, the effect of the addition of chemically modified woodflour on the final properties of unsaturated polyester composites was studied. The filler was treated with an alkaline solution to increase its interfacial area and then modified with maleic anhydride (MAN) under severe reaction conditions (140°C, 24 h). No improvement in the mechanical behavior of polyester–woodflour composites was found when particles were only alkali treated, while the composites prepared with MAN-treated woodflour offered better performance under compressive loads. Simple mechanical models used to fit the experimental flexural behavior indicated that a good compatibility between filler and matrix was obtained regardless of the kind (treated or untreated) of reinforcement used.

Composites from sawdust and unsaturated polyester

Wood is an inexpensive filler that reduces the overall cost of polymer composites, with loss in some properties (e.g., ultimate strength, elongation, and water sorption often suffer with the addition of fillers) and a gain in others (e.g., Young modulus increment, reduced weight with respect to inorganic fillers, reduced wear of the processing equipment). Sawdust of Eucaliptus saligna or calcium carbonate have been used as reinforcing fillers of an unsaturated polyester matrix. The ultimate strength, elongation, and modulus are presented as a function of the filler concentration and surface treatment. The dynamic mechanical properties were used to determine the influence of the moisture content on the performance of the final material.

Integral-skin polyurethane foams

A model describing the expansion of a polyurethane (PU) foam in a closed mold is developed. An energy balance is stated, together with constitutive equations for the vaporization rate of the foaming agent and the polymerization kinetics. A numerical solution is obtained for an experimentally-characterized PU formulation. It is shown that in order to avoid premature gelling or undesirable density distributions, the wall temperature must be close to the initial one. The relative fraction of skin in the foam may be increased by decreasing the part thickness or by adding less catalyst or more blowing agent to the formulation. Factors affecting cream, rise, and process times are discussed.

Sawdust modification : maleic anhydride chemical treatment

The aim of this work was to modify the sawdust surface in order to obtain a compatible filler for unsaturated polyesters. Maleic anhydride (MAN) was used as sawdust modifier. The possible esterification of sawdust with MAN was investigated. The efficiency of the treatment was determined by using chemical analysis, infrared spectroscopy (FTIR) and water retention value (WRV) test. Even under mild conditions (room temperature, no catalyst), esterification was achieved. FTIR technique allowed to determine that maleic anhydride reacted by one acid group with the sawdust surface. WRV were analysed using a Langmuir type equation which fitted the experimental results well.ZusammenfassungDiese Arbeit beabsichtigt, die Oberfläche von Sägemehl zu modifizieren, um daraus einen geeigneten Füller für Polyesterkunststoffe zu gewinnen. Als Reagenz wurde Maleinsäureanhydrid (MAN) benutzt. Mögliche Veresterung von OH-Gruppen des Sägemehls wurde untersucht. Das Ausmaß der Reaktion wurde überprüft anhand von chemischen Analysen, Infrarotspektroskopie (FTIR) und Wasserrückhaltevermögen (WRV). Schon unter milden Bedingungen (Zimmertemperatur ohne Katalysator) erfolgte die Veresterung. Aus den FTIR-Spektren ergab sich, daß die Maleinsäure nur mit einer Säuregruppe mit dem Sägemehl reagiert. WRV-Werte wurden mit Hilfe einer Lamgmuir-Gleichung abgschätzt, die die experimentellen Daten gut wiedergibt.

Composites Made from Lignocellulosics and Thermoset Polymers

Abstract Composites made from a stryrene/unsaturated polyester thermoset matrix and woodflours from different wood species have been prepared and tested. Pine (Pino Eliottis), eucaliptus (Eucaliptus Saligna) and marmelero (Ruprechia Laxiflora), a softwood and two semihard woods respectively, were selected for this study because of the availability and local abundance. The particles were used untreated and chemically modified with maleic anhydride (MAN). Thermogravimetric analysis and analytical techniques were used in the characterization of untreated and treated flours. Dispersion of the fibrous particles, as well as maximum filler concentration (accompanied by complete wetting of the wood fibers) was dependent on the treatment and on the wood species utilized. Bending and compression tests indicated some improvement in the performance of the composites, if the woodflour was previously esterified. Scanning electron microscopy (SEM) allowed to observe changes in the fracture surfaces due to MAN treatment of the fibers.