Properties Of Composites Made Of Pretreated-Corn Stalk Fibers And High-Density Polyethylene

This study aims to evaluate the potentials of corn stalk fibers used as reinforcement of corn stalk fibers/high density polyethylene (HDPE) composites prepared through extrusion. The effects of extrusion conditions, fibers size and loading levels on the mechanical properties of the composites were investigated. Chemical pre-treatments were conducted to improve the interfacial compatibility between the fibers and plastics. The performances of the composites reinforced with pre-treated fibers were also discussed.The effects of fibers size and loading level showed that the tensile strength and tensile modulus presented a trend of first increase and then decrease. The flexural modulus increased slightly with the increased loading of corn stalk fibers, while the impact strength decreased obviously. The comprehensive mechanical properties of corn stalk fibers/HDPE composites reached the maximum values at a fiber content of 50%. As the aspect ratio of corn stalk fibers increased, the mechanical performance of resultant composites was enhanced. The composites had the best mechanical strength when the aspect ratio of corn stalk fibers was 40-60 mesh. The scanning electron microscopy (SEM) results indicated that the composites containing 20-40 mesh corn stalk fibers had the worst fracture morphology due to non-uniform distribution of fibers in HDPE matrix, while the fracture surface of composites made of 40-60 mesh corn stalk fibers was the best.The corn stalk fibers were pretreated by NaOH solution (concentration used was 3%,6%, and 9%) and acetic anhydride (processing time was 1h,2 h,3 h) respectively. The corn stalk fibers pretreated by these two chemical methods exhibited more thermal stability than the control, and alkali treatment was more effective. Alkalization eliminated a number of lignin and part of ash on the fiber surface, which increased the crystallinity and made the fiber surface rougher. Acetylation could replace a part of hydroxide radical of corn stalk fibers through esterification and therefore reduced fibers polarity. It was observed that the fibers became more brittle and surface cracks appeared after acetylation.The composites were prepared with 50% pre-treated corn stalk fibers (the concentration of NaOH was 3% and acetylation time was 2h) in order to investigate the mechanical, thermal and chemical properties and interfacial properties of corn stalk fibers/HDPE composites. Compared with untreated corn stalk fibers-reinforced composites, the comprehensive mechanical properties of the composites reinforced with alkalization-treated fibers were improved. The tensile strength and flexural strength increased most obviously. The mechanical properties of the composites prepared with alkalization-treated fibers were close to that of the composite reinforced with poplar fibers. Fibers after acetylation became more brittle and cracks showed on surface, thus the mechanical strength decreased slightly. The FTIR result showed that ester bond characteristic peaks appeared at 1730 cm-1, indicating that hydroxyl radical of stalk fibers reacted with acetic anhydride. The thermal stability of the composites contained alkalization- and acetylation-treated corn stalk fibers were superior. Compared to acetylation, alkalization treatment was more effective to enhance thermal stability. The SEM revealed that alkalization contributed more in improving the interfacial adhesion between corn stalk fibers and HDPE matrix.The results of this study demonstrated the feasibility of using corn stalk fibers as reinforcement to produce corn stalk fiber/HDPE composites. The performances of composites can be designed and controlled by adjusting the addition ratio of corn stalk fibers to HDPE. The mechanical properties of composites prepared with pretreated corn stalk fibers were comparable to that of the composites reinforced with wood fibers, indicating that the utilization of corn stalk fibers can offer a practical approach to ease the intensive timber supply. This study also contributes in the reduction of resource waste and air pollution caused by burning corn stalks.