Resumen de Constructive applications of totora (schoenoplectus californicus) in binderless boards
Although the productive cycle of wood has demonstrated to generate less impacts than other materials such as cement or steel, the increasing pressure on land and forests, uneven distribution of forest resources, pests, and unstable wood markets has encouraged the research on alternative sources such as non-wood forest products for producing biomass-based materials such as particleboards that can be applicable in the construction field. Considering that many of the particleboards produced nowadays use adhesives that may pose some health and environmental concerns, several studies have been conducted about the ability of lignocellulosic materials to achieve self-bonding under certain heat and pressure conditions to produce binderless boards with potential environmental benefits. However, the self-bonding effect and final properties of the boards depend on the biomass type, time, temperature, pretreatments, among other parameters.
One non-wood forest product of interest is totora (Schoenoplectus californicus (C.A. Mey.) Soják). Totora is a sedge from the Cyperaceae family that grows mainly in the Americas from California to Tierra del Fuego and some of the Pacific Islands such as the Eastern Island, Hawaii, and Cook Islands. This plant has been traditionally used by many cultures in the past such as the Moche in Peru, the Incas in Los Andes, or the Ohlone in California. In some places the use of this plant has persisted to the present such as in the Uros Islands in Lake Titicaca where totora is used for making handicrafts, huts, boats, and even the artificial floating islands where their inhabitants live. Despite the long traditional use of this plant, the adaptability to different climate zones, fast-growth rate, and potential social and environmental benefits, the use of totora in the contemporary context is limited.
Although currently totora is not an industrial scale crop, the fast-growth rate of the plant, existing knowledge of traditional communities about how to harvest and manage it, and the potential synergies that can be achieved with natural and constructed wetlands for water treatments and carbon capturing facilities that at the same time could serve as convenient raw material sources, suggest the possibility of using this biomass for sustaining a competitive productive cycle with potential environmental benefits. In this scenario, the investigation tackles the feasibility of using totora for producing binderless boards applicable in the contemporary construction field by studying how each tissue of the plant behaves under different hot-pressing conditions, and how these production parameters influence the boards’ properties. It was demonstrated that boards produced with pith tissue made at 150°C after two hot-pressing cycles showed good mechanical properties and could be classified as boards of type P1 in accordance with the European standard EN 312. Although boards made at 180°C and 200°C showed internal fractures due to internal vapor pressures, in a case study of boards made with rind tissue using metallic mesh screens to allow a continuous vapor discharge during the hot-pressing process, no blisters and increase of internal bonding strength values were observed. The physical and chemical analyses of the raw plant tissues showed that the pith and rind have different characteristics. The main chemical differences of interest to the studied application are the softer consistency of pith particles and their lower solvent extractives content, which influenced the mechanical properties of binderless boards. Additionally, the chemical changes induced on the plant tissues by the hot-pressing process, which consisted mainly on the hydrolyzation reactions of lignocellulosic polymers, and their correlation with the boards’ mechanical properties and resistance against wood decaying organisms were studied. These data may help understand the mechanisms trough which this biomass achieve self-bonding, which could lead to the optimization of binderless boards production process and enhancement of desirable properties.
In conclusion, the use of totora in the construction field may have potential benefits from a sustainable point of view. The rind and pith of totora stems have different physical and chemical characteristics. Totora tissues can achieve self-bonding under hot-pressing conditions to produce binderless boards. The different characteristics of the rind and pith of totora stems influence the physical and mechanical properties of binderless boards produced with each tissue. The hot-pressing production process induce chemical changes in the material that may help elucidate the self-bonding mechanisms of this kind of biomass. The hot-pressing production process influence the resistance of totora binderless boards against wood decaying organisms. Totora binderless boards made with the pith tissue at 150°C showed good mechanical properties that can classify them as particleboards intended for general uses in dry conditions with reduced emissions but lower moisture resistance. The potential of using metallic mesh screens to produce boards with higher temperatures and better mechanical properties has been identified. Boards produced with all tissues may have potential applications in the thermal and acoustic insulation fields, which along with the absence of harmful adhesives, and more sustainable of end-of-life scenarios management can make totora binderless boards a competitive option in these construction materials’ markets.
