Center for Environmental Research and Technology

Abstract

The construction material industry in the United States continues to be one of the largest construction markets worldwide. The selection of appropriate construction materials is crucial when designing infrastructure for the development of societies today. The four main challenges of developing new exterior construction materials are light weight, strength and durability, toxicity, and cost. Traditional construction materials such as steel and concrete, can be corrosive resistance and are composed of chemical substances that pose a threat to humans and the environment.

Hemp fibers offers a solution to all four when used as reinforcement for exterior construction materials. Hemp fibers, which come from the hemp plant species, are a light-weight material that exhibits high tensile strength. Hemp fibers come from the stalk of the plant--a part that usually ends up in landfills or as compost, making the stalks extremely cheap. 

The current issue with industrial application of hemp fibers lies in the processing of the hemp stalks. The current commercialized mechanism for processing hemp is the Kraft pulping process, a procedure most used for lignocellulosic materials. This chemical pulping process involves the delignification of hemp fibers by treating hemp stalks with hot water, sodium hydroxide, and sodium sulfide. This mixture breaks the bonds that link lignin, hemicellulose, and cellulose – all of which make up the chemical composition of hemp. 

Although the kraft pulping process allows for the large global production of wood from cellulosic pulp, it poses many environmental and economic challenges, as well as operational problems. One of the main environmental issues is the control of air emissions from the recovery cycle. The Kraft pulping process also expends large amounts of energy into the boiling of black liquor (a byproduct from the kraft process) to burn lignin for energy, leaving salts to be recycled back to the pulping process. 

Our proposed solvent recovery system, Co-solvent enhanced lignocellulosic fractionation (CELF) allows for a more ecologically efficient method for the pulping of hemp fibers. CELF is a carbon-neutral process that fractionates lignin from plant biomass at low temperatures. Tetrahydrofuran (THF) is used as a co-solvent to aid the breakdown of lignin, and can easily be recycled due to its lower boiling point compared to water. CELF also produces higher yields of cellulose fibers because of its shorter operation time (less than 30 minutes), while taking advantage of THF’s low boiling point (65℃). By using lower temperatures and less processing steps, we reduce energy and operation costs of hemp fiber processing to become a viable, non-toxic reinforcement material for construction. The liquid product of our hemp stalks have been analyzed using high-performance liquid chromatography (HPLC) to determine cellulose, lignin, and hemicellulose yields of hemp stalk after treatment.