Agroindustrial waste can be used as material for housing and infrastructure
Guidelines for a research project about agroindustrial wastes and their potential use as appropriate materials for housing and infrastructure include converting waste into resources, substituting toxic raw materials for healthy inputs, and migrating from harmful to sustainable production processes.
The Agrowaste project is coordinated by Holmer Savastano Jr. at the University of São Paulo's Animal Science & Food Engineering School (FZEA-USP) in Pirassununga, Brazil.
"We developed two lines of research: one with inorganic matrix composites, exploring the addition of biomass fly ash and biomass fibers to the Portland cement matrix for the production of flat or corrugated fiber cement board; the other with organic matrix composites, exploring the use of plant resin-bound biomass fibers and particles for the production of board for packaging, pallets and furniture," said Savastano.
The inorganic product line will offer an alternative to asbestos cement, while the organic line will offer an alternative to phenolic resin-impregnated particleboard and chipboard. Asbestos and phenolic resins are widely held to be carcinogenic. Notably, asbestos cement is banned in a growing number of countries (currently 69) in compliance with the recommendations of the World Health Organization (WHO).
Phenolic resins are banned in several countries, but not in Brazil. However, their days are numbered. They are not only toxic, but also unsustainable because they are refined petroleum products. "Asbestos cement was used for decades, and during that time, industry adapted to it perfectly. It seemed an unbeatable technical solution, especially thanks to its low cost, but the impact on health means other less toxic reinforcing fibers must be found," Savastano said.
"Our project has already produced results with potential technology transfer to commercial firms. Fiber cement can be used in the manufacturing of corrugated roofing as well as board, siding and other components for the construction industry. We didn't just substitute the fiber; several adjustments had to be made to the production process, and we worked on this with firms that make fiber cement in Brazil. Specific cement curing methods were required, for example," he said.
A study led by Savastano to develop fiber cement curing technology produced fiber cement board using a mixture of cement, plastic fibers and plant pulps. "Our approach increasingly consists of using biomass fly ash as a substitute for conventional Portland cement and plant fibers instead of plastic fibers," Savastano said.
This would configure a third-generation product. The first generation consisted of cement reinforced with mineral fibers. The already viable second generation combines cement, plastic fibers and plant pulps. The third generation entails the progressive substitution of cement and plastic fibers with biomass fly ash and plant fibers, thereby reducing the impact of the material and making it more sustainable in accordance with the increasingly widespread environmental expectations of society.
"The more plant-based, the more sustainable," Savastano said. "Therefore, the next step after the current project, which is nearing completion, will be to precisely perform sustainability analyses and to calculate how the use of greater amounts of plant fibers would influence variables such as energy consumption in production and durability of the end product."
For now, the plant fibers used in research are still extracted from cellulose pulp owing to commercial availability. "In a country like Brazil, we can easily use various fibrous plants as sources of pulp," Savastano said. "For example, important alternatives in São Paulo State, which is the country's leading producer of sugarcane, could be sugarcane bagasse and straw as sources of both fiber and ash. If we consider the national territory as a whole, there are many other non-wood biomass alternatives, such as sisal, banana and bamboo, to cite only a few examples."
Substitution of sugarcane bagasse for cellulose pulp, for example, would comply with the requirement that waste should be converted into resources, contributing to the optimization of agroindustrial processes. "What we now call waste isn't waste at all, but improperly used raw materials," Savastano said. "One of the aims of our project is to offer this kind of approach to the business community."
Guadeloupe's location in the tropics, like much of Brazil, is an important factor in the synergy achieved by the teams of researchers from USP and UAG. Agriculture is the locomotive of Guadeloupe's economy, and the main crops are sugarcane and bananas.
Because Guadeloupe and Brazil have similar climates, certain building solutions, such as those that use biomass, are part of the traditional culture in both places. In addition, the interaction between the two groups has been enriched by their complementary skills. "They're stronger in chemistry and we're stronger in engineering," Savastano said.
For the organic line, involving the production of particleboard sheets or panels, the researchers depend on bought-in plant resin, in this case made from castor oil. "We're focusing mostly on biomass," Savastano said.
"There's a good reason for this: biomass accounts for at least 85 percent of the material mass, while resin accounts for only 15 percent. We've purchased a resin that meets all the technical specifications, but we haven't yet mastered its production. If our project is to have a future, the next step must be to acquire this competency by partnering with groups that have mastered this technology."
The researchers at USP were recently contacted by scientists at North Carolina A&T State University in the United States who are using pig manure to produce an organic binder or aggregate. This is only one example of the many possibilities to be explored with respect to resins.
The researchers at USP have worked with green coconut shells, sugarcane bagasse, sisal, and even empty cement bags that have been discarded after use. These materials constitute the mass bound by the resin. One potential application is in the furniture industry, which could use particleboard covered with thin sheets of wood veneer or waterproof laminate.
"These panels have huge potential," Savastano said. "They could have multiple layers with optimized mechanical, thermal, acoustic or aesthetic properties, and different types of panels could be designed for specific uses in construction, furniture, packaging, etc. This is where engineering has a major contribution to make by considering such factors as mechanical strength, waterproofing and durability. Production scale is key, but in any event, the switch to alternative materials won't happen overnight. Any adjustment to industrial processes has to be thoroughly researched to ensure consistency and reliability for both manufacturers and users."