The construction industry heavily consumes energy and plastic and emits high levels of emissions. Adopting eco-friendly materials holds the potential to reduce its carbon footprint.
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Recently, researchers examined a blend of rice husks and cellulose—typically destined for landfills or incineration—and evaluated its viability as a building material. Their findings revealed promising thermal and mechanical properties, rendering it suitable for various uses, notably as insulation for environmentally conscious structures.
The building industry ranks second in plastic usage and contributes over a third of global energy-related greenhouse gas emissions. Manufacturing construction materials results in pollution of air, land, and water. Thus, utilizing agro-industrial waste for construction materials gains appeal for their reduced environmental impact.
Presently, scientists in Panama have established a rice husk-based insulation material and evaluated its thermal and mechanical properties to contribute to a new generation of materials made from waste materials. They have published their outcomes in Frontiers in Built Environment.
Here we show that is possible to create alternative insulating material from recycled newspaper and rice husk. The developed material has competitive thermal conductivity compared to many natural and recycled insulation materials.
Dr. Nacarí Marín Calvo, First Author and Researcher, Universidad Tecnológica de Panamá, Centro Regional de Azuero
A Four-Ingredient Recipe
Rural Panama, the study's location, regards rice husk as agricultural waste typically discarded in landfills or incinerated, posing a substantial environmental issue. The husks were shredded to produce the mix. Then cellulose, acquired from recycled and shredded newspaper, is added, followed by borax, which makes the mix resistant to fungi and offers fire-retardant properties. All components are bonded with glue.
The scientists analyzed various material compositions to check the performance of the material when more or less rice husk is used. The initial mix is made from 14% newspaper, 9% rice husk, 15% borax, and 62% glue. In the remaining two compositions, the quantity of rice husk was raised, leading to a reduction in the amount of newspaper. However, the proportions of borax and glue stayed consistent.
Marín Calvo says, “We found that the results were similar in all three compositions in k-values, maximum stresses, and compressive strength values.”
Head-To-Head with Other Natural Materials
Thermal conductivity, also often called k-value, defines the capacity of a material to conduct heat. The material is more suitable for insulation when the k-value is low. The k-value ranged between 0.0409-0.04607 watts per meter Kelvin (W/mK) for the verified compositions. Other natural and recycled insulation materials have k-values ranging from 0.027 to 0.1 W/ m/K.
Tensile strength is the extreme stress that a material can withstand when stretched or pulled before breaking. Testing revealed that maximum stress in average tension ranged from 1.31 to 1.76 megapascals (MPa) for the three compositions. Pascal is the unit used to measure the force applied at a 90° angle on the surface of an object. Materials based on cardboard, cement, and sand have similar tensile strength values.
The compressive strength values obtained are between 20.19 and 21.23 MPa. Compressive strength defines a material’s ability to resist being pushed together. The acquired values allow the scientists to confirm the possibility of using the developed material in construction applications.
Beyond Building
The researchers highlighted the necessity for further studies to validate the material's insulation capabilities and its performance in climates differing from the high humidity experienced in Panama.
As a part of future research, we are evaluating the degradation of the developed material under ambient controlled conditions.
Dr. Nacarí Marín Calvo, First Author and Researcher, Universidad Tecnológica de Panamá, Centro Regional de Azuero
Additional research avenues could explore alternative configurations, like integrating long fibers oriented in a singular direction to enhance the material's behavior under tension. Marín Calvo concludes, “We can conclude that the material could also potentially be used in various engineering domains, including the production of lightweight components, construction panels, and sustainable packaging.”
Journal Reference
Marín-Calvo, N., et al. (2023). Thermal insulation material produced from recycled materials for building applications: cellulose and rice husk-based material.Frontiers in Built Environment. doi.org/10.3389/fbuil.2023.1271317