Utilization of wheat-bran cellulosic fibers as reinforcement in bio-based polypropylene composite

Polymer composites reinforced with natural fibers have received widespread attention due to 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 in manufacturing bio-based composites. Wheat bran was pretreated with sodium hydroxide (NaOH) and the compositions were analyzed. Pretreatment removed fat, starch, and crude protein significantly and resulted in an increase of cellulose content from 10.9% to 29.6%. Polypropylene (PP) was melt-blended with bran in a screw-extruder with and without using a chemical compatibilizer, and test specimens were produced by an injection molder. Composite specimens tested for characterization of different thermophysical properties. A 16.3 % increase in flexural strength was obtained at fiber loading of 20 % or more, while tensile strength was comparable to neat PP using compatibilizer. Moduli increased and impact strength decreased with fiber addition. The highest tensile and flexural moduli were 2838 and 1702 MPa, respectively for WB/PP composite. The highest impact strength reduction was 66 % with WB/PP composite at 30 % loading rate. Thermal expansion coefficient of the WB/PP biocomposites decreased with a highest reduction of 64 %; meaning that WB, a grain by-product, is very promising as functional fibers for polymer materials. The interactions of WB fiber in bio-based polymer matrix for failure mechanism and composite strength were also studied by manufacturing WB/polylactic acid (PLA) composites using fiber loading optimized for WB/PP composite. Inferior mechanical performance of WB/PLA composites was observed compared to neat PLA. Poor adhesion, debonding, and fiber fracture were the dominating micromechanical deformation processes in WB/PP composites, whereas debonding, cavity, and crack formation due to fiber orientation resulted in poor performance of WB/PLA composites. Prospects of WB-based composites present opportunities for growers having beneficial uses of bran and compensating reduced profit margins.