Selection, pretreatment, and use of wheat bran for making thermoplastic composite

Abstract. Recently, the use of natural fibers as fillers or reinforcing agents in manufacturing biocomposites has received widespread attention because of the harmful effects of the petroleum derived synthetic polymer waste. In this study, wheat bran (WB), as a new source of natural fiber, has been investigated to be utilized in manufacturing biocomposites. Wheat bran samples of different cultivars, grown in varying environment, were collected, and the lignocellulosic compositions of these bran samples were analyzed to identify cultivars with the highest cellulose content. The selected bran sample was treated using several thermo-physical and chemical methods including dilute sodium hydroxide (NaOH), dilute sulfuric acid (H₂SO₄), liquid hot water (LHW), calcium hydroxide (CaOH), organosolv such as aqueous ethanol (EtOH), and methyl isobutyl ketone (MIBK). The bran cellulose content of the cultivar Mountrail was 10.9%, and it increased to 35.1% and 29.6% when treated with H₂SO₄ and NaOH, respectively. Hemicelluloses content decreased to 6.83% and 24.9% in H₂SO₄ and CaOH treated bran, respectively. Scanning Electron Microscopy (SEM) showed surface cleaning of treated bran while maintaining sufficient surface roughness when treated with H₂SO₄, NaOH, and MIBK. The treated and untreated wheat brans were compounded and molded with polypropylene (PP) using with and without compatibilizer, and the resulting composite specimens were tested for mechanical characterization. The flexural strength and modulus increased with the addition of NaOH treated fibers at the loading rate of 20% or more and by using maleic anhydride polypropylene (MAPP), implies that wheat bran as an agricultural grain by-product is a very promising to be used as reinforcement for polymer materials.