Proper blending rate improving mechanical and rheological properties of low density polyethylene/bamboo composites

Abstract: In fact, the ultimate properties of wood-plastics composites (WPCs) not only rely on the structure, composition and morphology, but also depend on the processing conditions, such as processing temperature, pressure (blending rate ) and time. Due to the degradation of bamboo powder under high processing temperature or long processing time, this paper studied mainly the effects of blending rate on the mechanical and rheological properties of low density polyethylene (LDPE)/bamboo powder composites, which were fabricated by the melt compounding method with the compounding temperature of 170 ℃and 10 min, by using the rotational rheometer, material testing machine and scanning electron microscope (SEM). The maleic anhydride grafted polyethylene (MAPE) was selected as the compatibilizer for LDPE and bamboo powder. The mass proportion of LDPE, MAPE and bamboo powder was set to 65:5:30. The mechanical properties, water absorption and morphology of LDPE/bamboo composites were investigated in detail by changing the blending rate (40, 75 and 100 r/min). Before experiments, all the materials were dried in vacuum oven at 70 ℃for 24 h. The addition of bamboo powder improved the tensile strength and flexural strength of LDPE, which were increased by 28% and 115% respectively compared to neat LDPE, but reduced the impact strength of LDPE. The tensile strength and flexural strength of the LDPE/bamboo composites decreased as the rotation rate increased from 40 to 100 r/min. The flexural modulus of LDPE/bamboo composites decreased from 48.45 to 40.75 MPa as blending rate increased from 40 to 100 r/min, and the highest flexural modulus increased by 238% compared to neat LDPE (14.35 MPa); however, the notched impact strength of LDPE/bamboo composites increased from 12.8 (40 r/min) to 18.27 kJ/m2 (100 r/min), lower than that of neat LDPE (29.19 kJ/m2). For rheological experiments, the LDPE/bamboo composites exhibited shearing thinning behaviors, and at the same frequency, the complex viscosity of LDPE/bamboo composites decreased as blending rate increased, indicative of the improvement in processing performance; the storage modulus of LDPE/bamboo composites also reduced as blending rate increased, indicating the rigidness reduction, and this result was consistent with the results from mechanical properties. Also, the water absorption of LDPE/bamboo composites decreased from 0.89% (40 r/min) to 0.59 % (100 r/min). The reason was that the high blending rate caused the LDPE and bamboo powder to compound more evenly and the interfacial performance between LDPE and bamboo power was improved. The SEM results showed that at low blending rate (40 r/min), the bamboo powder surface was only coated with a thin layer of resin, and the interface between LDPE and bamboo powder was very clear, indicative of poor interfacial properties, and no plastic deformation was observed; at high rotation rate (100 r/min), bamboo powder was coated with a thick layer of polymer resin, exhibiting good interface performance with LDPE, and what's more, the big plastic deformation was observed in matrix, suggesting LDPE/bamboo composite (100 r/min) exhibited a good toughness. The above results confirmed that elevating blending rate could improve the toughness and reduce the water absorption of LDPE/bamboo composites, and in our experiments, the LDPE/bamboo composites, produced by blending rate (100 r/min), exhibited the better impact strength and water absorption.