Effects of chemical treatments on mechanical and physical properties of flax fiber-reinforced composites

Abstract

Flax fibers, can be used as ecological alternatives to conventional reinforcing fibers (e.g., glass) in composites. Flax fibers have some advantages over glass fiber, because they are less dense, renewable, combustible and are relatively low in price. This excellent price-performance ratio at low weight, in combination with the environmentally friendly character is very important for the acceptance of natural fibers in large volume engineering markets. A major restriction to the successful use of natural fibers in durable composite applications is their high moisture absorption and poor dimensional stability. In order to improve the above qualities, various surface treatments of fibers including silane treatment, benzoylation, and peroxide treatment were carried out, to improve mechanical performance of fiber composites. Also, composites consisting of high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE) or HDPE/LLDPE, chemically treated fibers and additives were prepared by extrusion process. The extruded samples were then ground and test samples were prepared by rotational molding. The chemical analysis showed that selective chemical treatments increased the α-cellulose content of flax fibers from 73% to 95%, but caused a decline in hemicellulose and lignin content. Derivative thermogravimetry (DTG) curves indicated that chemically treated fibers were thermally stable in the region below 250°C and chemcial treatments increased the onset thermal decomposition temperature of flax fibers. The mechanical properties demonstrated an increase in tensile strength from 17.56 MPa of untreated fiber (20 wt%) reinforced LLDPE to 25.86 MPa of peroxide treated fiber (20 wt%) reinforced LLDPE. The increased hardness of flax fiber-reinforced composites was also very promising; it was 22.1 of untreated fiber (20 wt%) reinforced HDPE compared to 25.1 of silane treated fiber (20%) reinforced HDPE. This increase in fiber content has a positive effect on the mechanical properties of composites. The water absorption of the chemically treated flax fiber-based composites was lower than that of the untreated fiber-based composites. © Freund Publishing House Ltd.