Moisture Sorption And Anti-Biological Performances Of Corn Stalk Fiber/High-density Polyethylene Composites

Agricultural fiber plastic composites (APPC) can be extensively used for decking, railings, siding, windows and doors, garden architecture, and fencing. The outdoor application of AFPC has led to increased exposure of the materials to wetting. AFPC are susceptive to bio-deterioration under prolonged exposure to high humidity or liquid water, which can severely affect the economic value and usefulness of the product. This study aims to explore the feasibility of using alkaline copper quaternary (ACQ)-treated or zinc borate (ZB)-treated corn stalk fibers as reinforcement for corn stalk fiber/high density polyethylene (CSF/HDPE) composites prepared by extrusion. The mechanical properties, moisture absorption, anti-biological performances of CSF/HDPE composites were investigated.The effects of preservative types and concentration, and fiber loading levels on the mechanical properties of the composites were discussed. The composites were characterized by SEM and FTIR. The results indicated that with the increase of CSF application content and ACQ concentration, the mechanical properties of the composites were decreased. The mechanical property of CSF/HDPE composites reached the best level at CSF content of 50% and ACQ concentration of 1%.The flexural strength, flexural modulus and impact strength presented a trend of first increase and then decrease with increasing ZB loading level, while the tensile strength increased slightly. The composites had the best mechanical strength at 50% CSF addition and 2% ZB concentration.The moisture absorption properties of preservative-treated CSF/HDPE composites were studied. With the increase of ACQ level or ZB level, the equilibrium moisture contents (EMCs) of the composites were increased, while the thickness swelling presented a trend of first decrease and than increase. The EMC and the thickness swelling were increased with increasing the CSF application. The results indicated that the water absorption of ACQ-treated CSF-HDPE samples were much better than that of ZB-treated composites.The effects of different durability treatments on sorption and desorption isotherms of CSF/HDPE composites were investigated. The results indicated that EMCs of the composites increased with the increased of the amount of relative humidity (RH). With the increase of CSF applied content, EMCs of the composites increased. It was observed that the EMCs of the composites with incorporation of ACQ or ZB was slightly higher than that of the untreated composites. This result indicated that the preservatives had a small effect on the sorption and desorption performances of the composites.The experimental data of EMCs at various RHs fit to the Nelson’s sorption isotherm model well. The Nelson’s model can be used to predicate EMCs of CSF/HDPE composites under different RH environmental conditions.The performances of ACQ-treated or ZB-treated CSF reinforced HDPE composites against mold, decay, and termites were examined. Compared with untreated CSF/HDPE composites, the mass losses of composite with ACQ or ZB treatment reduced significantly. The mass losses of all composites were increased with the increase of CSF application, indicating that CSF in the composites were easily attacked by fungal. The incorporation of ACQ or ZB significantly reduced the mass losses and mold severity of CSF/HDPE composites, indicating that the biocide used was effective against termites and mold fungi even at higher CSF content (60%) formulations. Termite test showed that the mass losses of ACQ-treated samples at 3.0% level were significantly reduced compared to the untreated composites. This proved the superior performance of ACQ-treated CSF/HDPE against termites. It was also observed that no mold growth in the ACQ-treated CSF/HDPE samples, which demonstrated the enhanced mold resistant performances of the polymer composites from ACQ-treated CSF. The untreated CSF/HDPE had inferior mold resistance compared to untreated poplar-HDPE composite due to the chemical features of corn stalk and incomplete removal of pith.The results demonstrated that ACQ-treated or ZB-treated CSF/HDPE composites had superior performances against mold fungi, decay fungi, and termites. The mechanical properties, water absorption, and moisture absorption of the composites prepared with preservative-treated CSF were comparable to those of the composites reinforced with untreated CSF. This study can offer a practical way of conversion agricultural waste into value-added composites.