Mirta I. Aranguren

Modified woodflour as thermoset fillersPart I. Effect of the chemical modification and percentage of filler on the mechanical properties

Composites made from an unsaturated polyester/styrene thermoset matrix and esterified woodflour have been prepared and tested. Different degrees of esterification of the wood particles with maleic anhydride were obtained by using different times of reaction, which lead to materials with varied final properties. Water absorption performed on treated particles indicates that they are more hydrophobic than the untreated ones. Flexural, compression and dynamic-mechanical tests were performed on composites to find out an optimum level of chemical modification of the woodflour. Moreover, the relationship between the filler content and the composite final properties was also studied for a selected filler treatment. An important increment in particle dispersion was obtained by modifying the woodflour with maleic anhydride.

Crystallization of polydimethylsiloxane : effect of silica filler and curing

Previous publications on the low temperature behavior of polydimethylsiloxane (PDMS) described semiquantitatively or in an incomplete way the different features appearing during the heating cycle of previously cooled PDMS. The main deficiency of these descriptions is in the quantitative measurement of the heat of fusion. This value was reported per mole of chain atom, which has been misunderstood by other researchers as being per mole of structural units. The object of the present work is to give a systematic view of the low temperature behavior of PDMS with special attention to the melting behavior of the polymer. The effects of the previous cooling rate, molecular weight of the polymer, filler addition and crosslinking on the characteristics of d.s.c. thermograms of PDMS are reported and discussed. A simplified view of the different effects is presented, which allows the calculation of the heat of fusion of the different samples from the corresponding value of a completely crystalline polydimethylsiloxane.

Modified woodflour as thermoset fillers: II. Thermal degradation of woodflours and composites

Abstract Composites made from an unsaturated polyester/styrene thermoset matrix and maleic anhydride esterified woodflour have been prepared and tested. Different degrees of esterification of the wood particles with maleic anhydride (MAN) were obtained by using different times of reaction, which led to materials with varied final properties. X-ray diffraction studies have been carried out on raw and chemically treated woodflours. The degree of crystallinity of modified woodflours is lower than that of the untreated one and decreases as the MAN content of the samples increases. The thermal degradation of the woodflours, matrix, and derived composites was estimated by thermogravimetry (TG) in nitrogen environment. Thermogravimetry was shown to be sensitive enough to detect differences between woodflour samples with different treatments and degrees of esterification and between composites with different woodflour contents.

Moisture diffusion in polyester-woodflour composites

Abstract The understanding of water–polymer interactions in polymeric composite materials is critical to the prediction of their behavior in applications where they are exposed to water or humid environment. Moisture diffusion in unsaturated polyester–woodflour composites exposed to environments kept at room temperature and different relative humidities was investigated. Equations obtained from microscopic mass balances for vapor diffusion in solids were used to determine the effective diffusion coefficients of the different woodflours, neat resin and composites. The effect of the size and shape of the composite specimens used in the experimental work on the final moisture content was also evaluated. Different models were used to predict the composite effective diffusion coefficients as a function of filler concentrations.

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.

Polyurethane Foams Obtained from Castor Oil-based Polyol and Filled with Wood Flour:

A natural polyol was prepared from castor oil by alcoholysis with triethanolamine. The oil and the oil-based polyol were characterized by infrared spectroscopy and through the analytical determination of their functional groups, both techniques indicating that the hydroxyl content increased significantly after the alcoholysis reaction. The modified oil was subsequently used as the polyol component in the formulation of rigid polyurethane foams. Wood flour was chosen to be incorporated as filler in these materials. Physical, thermal, and mechanical properties of the neat and reinforced foams were measured, analyzed, and compared to a reference commercial system. The chemical reaction between wood flour and isocyanate strongly affected the composites’ response to thermo-gravimetric tests. Compression modulus and yield strength decreased as wood flour content increased. The effect of the foam density on the compression properties was also investigated.

Polyelectrolyte films based on chitosan/olive oil and reinforced with cellulose nanocrystals

Composite films designed as potentially edible food packaging were prepared by casting film-forming emulsions based on chitosan/glycerol/olive oil containing dispersed cellulose nanocrystals (CNs). The combined use of cellulose nanoparticles and olive oil proved to be an efficient method to reduce the inherently high water vapor permeability of plasticized chitosan films, improving at the same time their tensile behavior. At the same time, it was found that the water solubility slightly decreased as the cellulose content increased, and further decreased with oil addition. Unexpectedly, opacity decreased as cellulose content increased, which balanced the reduced transparency due to lipid addition. Contact angle decreased with CN addition, but increased when olive oil was incorporated. Results from dynamic mechanical tests revealed that all films present two main relaxations that could be ascribed to the glycerol- and chitosan-rich phases, respectively. The response of plasticized chitosan-nanocellulose films (without lipid addition) was also investigated, in order to facilitate the understanding of the effect of both additives.

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.

Liquid rubber modified vinyl ester resins: fracture and mechanical behavior

Abstract The fracture and mechanical behavior of vinyl ester resins (DVER) cured with styrene (S) and modified with two different liquid rubbers has been determined and related to the microstructure of the resulting modified thermosets. Carboxyl terminated poly(butadiene-co-acrylonitrile) (CTBN), a common toughening agent for epoxy resins, is an almost unreactive rubber with the DVER and S comonomers. During crosslinking the system undergoes a phase separation mechanism similar to that occurring in unsaturated polyester resins (UPE) modified with a low profile additive (LPA), such as polyvinyl acetate (PVAc). This process leads to materials, which exhibit a sharp drop in density at high CTBN concentrations (≥10% by weight) and to the development of a co-continuous microstructure in these materials. This feature is consistent with a maximum in fracture toughness as a function of the additive (CTBN) content, followed by a rapid deterioration in toughness at higher concentrations. On the other hand, the use of a reactive rubber, vinyl terminated poly(butadiene-co-acrylonitrile, VTBN, as the additive leads to a different morphology consisting on rubber inclusions in the thermoset matrix. This structure gradually reduces the fracture and mechanical performance of the resins modified with increasing concentration of reactive elastomer.

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.