Performance of Straw/Linear Low Density Polyethylene Composite Prepared with Film-Roll Hot Pressing

Thermoplastic composites are usually prepared with the extrusion method, and straw reinforcement material must be processed to fiber or powder. In this study, film-roll hot pressing was developed to reinforce linear low density polyethylene (LLDPE) with long continuous straw stems. The long straw stems were wrapped with LLDPE film and then hot pressed and cooled to prepare straw/LLDPE composite. Extruded straw fiber/LLDPE composite was prepared as a control. The mechanical properties of these LLDPE-based composites were evaluated. The hot pressed straw/LLDPE composite provided higher tensile strength, tensile modulus, flexural strength, flexural modulus, and impact strength than the traditional extruded straw/LLDPE composite, by 335%, 107%, 68%, 57%, and 181%, respectively, reaching 35.1 MPa, 2.65 GPa, 3.8 MPa, 2.15 GPa, and 25.1 KJ/m². The density of the hot pressed straw/LLDPE composite (0.83 g/cm³) was lower than that of the extruded straw/LLDPE composite (1.31 g/cm³), and the former had a higher ratio of strength-to-weight. Scanning electron microscopy indicated that the orientation of the straws in the composite was better with the new method. Differential scanning calorimetry tests revealed that in hot pressed straw/LLDPE composite, straw fibers have a greater resistance to the melting of LLDPE than extruded composite. Rotary rheometer tests showed that the storage modulus of the hot pressed straw/LLDPE was less affected by frequency than that of the extruded composite, and the better elastic characteristics were pronounced at 150 °C. The hot pressed straw/LLDPE composite absorbed more water than the extruded composite and showed a potential ability to regulate the surrounding relative humidity. Our results showed that straw from renewable sources can be used to produce composites with good performance.