New composite based on brewery waste to improve the production of fiberboards

Environmental Impact of Agroindustrial Waste 

Globally, the food industry generates around 1.3 billion tons of waste per year, which has caused environmental problems such as habitat loss, greenhouse gas emissions, climate change, and pollution. The National Institute of Statistics and Census (INEC) has estimated that in Ecuador, approximately 14.4 thousand tons of waste are generated despite regulated legislation, and the brewing industry accounts for a significant portion of this. 

Brewer's Spent Grain Composition 

Brewer's spent grain (BSG) is a byproduct of the separation and filtration of barley after undergoing soaking, germination, and mashing processes. According to Ikram, the peripheral layers of barley (husk, pericarp, and bran) constitute BSG, and depending on the mashing phase, empty aleurone cells and endosperm may be present. BSG is mainly composed of cellulose (16.8–25.4%), hemicellulose (21.8–28.4%), and lignin (11.9–27.8%). However, harvesting and processing conditions, including time and location, affect the lignocellulosic composition. 

Use of Natural Fibers and Resins in the Manufacture of Particleboards 

Fiberboards or particleboards are construction materials typically produced by agglomerating wood-like fibers using thermosetting resins. Their characteristics depend on factors such as the type of fiber, orientation, size/shape, and mechanical properties inherent to the particleboard. A disadvantage of particleboards is their susceptibility to moisture, which can lead to swelling or warping when exposed to excessive humidity or water. However, they can be easily painted, laminated, or veneered to improve appearance and durability. 

In Ecuador, the particleboard industry mainly uses wood chips from reforested pine and some eucalyptus species, resulting in higher-quality products due to better control of the raw material. However, given their chemical similarity to wood, these panels can also be made from other lignocellulosic materials with high strength and a predetermined specific weight. In the search for more sustainable manufacturing processes and reducing the carbon footprint, some studies have proposed alternatives to reincorporate agricultural waste into industrial processes by producing particulate composites using agricultural byproducts such as barley husk/hybrid coconut husk, coconut fiber, rice husk, and brewer's spent grain. 

There is a growing trend to incorporate natural fibers from agricultural waste into urethane resins as a possible replacement for wood materials in the production of fiberboards. The feasibility of incorporating coconut fiber as filler material to produce particleboards with a polyurethane matrix based on castor oil and urea-formaldehyde has been studied, following the Brazilian standard NBR 14.810:2006. It is worth noting that this agricultural waste is abundant, as Brazil is the largest exporter of coconut in Latin America and the fourth largest in the world. The results showed an increase in the elastic modulus of coconut fiber panels with polyurethane resin compared to coconut fiber and urea-formaldehyde resin panels. One of the goals of this work was to reduce the toxicity of the synthetic adhesive by using castor oil in its composition. However, the adhesive still maintained some degree of toxicity due to the presence of urea-formaldehyde in its formulation. 

Challenges of Formaldehyde-Based Adhesives 

Fiberboards use phenol or urea-formaldehyde-based adhesives, which are characterized by notable homogeneity. In addition to their extensive use in wood composites, researchers have reported promising results in their use as binding agents for brewer's spent grain particleboards. However, a significant disadvantage is that melamine urea-formaldehyde (MUF) can release formaldehyde, which is classified as a carcinogen by the International Agency for Research on Cancer (IARC). Some researchers have made efforts to reduce formaldehyde emissions in fiberboard manufacturing or have developed rice husk particleboards with soy protein-based adhesives while comparing them with formaldehyde adhesives. Therefore, a global trend toward biodegradable, non-toxic, and renewable products has driven research to focus on bio-based adhesives. 

Feasibility of Brewer’s Spent Grain Fiberboards with Sorbitol Adhesives 

Bio-based resins have been developed in the past century to replace petroleum-based thermosetting resins and have also been used as an alternative to conventional resins in fiberboard applications. Sorbitol glycidyl ether (SGE) is an aliphatic epoxy, free of bisphenol A, a compound shown to be an endocrine disruptor used in other epoxy resins, such as synthetic bisphenol A diglycidyl ether (DGEBA), typically used in thermosetting applications. SGE resin is a promising material to replace traditional resins with toxic components in solvent-free applications, reducing the volatile component during manufacturing. This study demonstrate the feasibility of producing brewer's spent grain fiberboards with sorbitol-based adhesive and comparing them to the Ecuadorian wood fiberboard standard (NTE INEN 3110) to validate the potential application of the biocomposite.