Investigation of the Tensile and Bending Properties of a Biomaterial Composed of Agave Fibers and Castor Resin ^†

The manipulation of materials is a task that man has performed for centuries, to be later applied in the design of artifacts.

The area of materials design, driven by knowledge in materials science and technology, enabled the manipulation and creation of new materials with better properties for specific applications, with biomimetics contributing to the development of more sustainable solutions [1].

Interest in bioinspired composites, which use natural and biodegradable materials, is also growing. Composites formed by polymeric matrices and plant fibers are currently one of the main areas of interest in the investigation of more ecological alternative materials, designed to preserve the environment and natural resources. The use of vegetable fibers to reinforce resins derived from vegetable oils allows the production of biodegradable composites formed by materials derived from renewable sources. Sisal fiber is promising for the development of this type of composite material due to its low cost, good mechanical properties, easy processing and availability in the market [2].

In this way, bioutilization (the use of biological raw material) is viable, as long as it contributes to the project’s sustainability objective and with benefits (or harm reduction) to the ecosystem and incorporates biologically inspired principles. This approach is successful when it relates the characteristics of the biological structure to the properties of the biological material [3].

This work explores the mechanical properties of a material under development in a doctoral thesis in the field of biodesign, which seeks to identify application potentialities with the desired properties in the search for a balance between lightness and resistance. Two types of castor resin and crushed agave fibers of different sizes were selected in order to obtain biodegradation, lightness and resistance. The central idea is not to develop the lightest material or the strongest material, but to identify a balance between lightness and strength that can be applied in the design of sustainable artifacts. Samples were produced that were tested in traction and bending to characterize their resistance in order to compare the properties obtained with other materials, such as Paulownia wood and marine plywood.

For the initial stages of development and manipulation of the bioinspired composite with different compositions, two types of resin derived from castor oil were used: rigid expansive polyurethane and rigid elastomer, with the incorporation of crushed and sieved agave fibers of different dimensions. Tensile (ISO 527) and bending (ISO D790) specimens were produced to determine their mechanical properties. The agave fibers were crushed and then separated, obtaining fibers of varying sizes. The fibers with the most suitable dimensions were selected for research purposes and for the production of composites. Silicone molds were made to produce the specimens by casting the mixtures. Samples of agave (in its natural form), paulownia and birch plywood were also manually produced for comparison, as they have different densities. Five samples were produced for each composition, with a total of 100 specimens being developed (50 for bending and 50 for traction).

In the process of separating the fibers, seven different sizes were obtained: 45 µm; 75 µm; 106 µm; 250 µm; 425 µm; 600 µm; and 850 µm, which were analyzed, and we selected the most suitable for performing the mechanical tests. The selected fibers were 106 µm and 600 µm, which can have different applications according to their configuration in powder or microfibers. A combination of four fiber sizes was also tested (106 µm; 250 µm; 425 µm; and 600 µm), in equal proportions of 5%, for performance comparison. Samples were prepared with 20% by weight fiber and 80% resin. All samples produced were analyzed for compliance with the requirements, having been measured with a caliper and visually observing straight edges and flatness. For the flexural tests, the samples were tested by three-point bending.

The results obtained with the tactile and sensorial experience through the manipulation of materials, and the mechanical properties obtained, are promising, highlighting the potential for its application in the design of biomimetically inspired artifacts.