Rotational Molding of Linear Low-Density Polyethylene Composites Filled with Wheat Bran

Application of lignocellulosic fillers in the manufacturing of wood polymer composites (WPCs) is a very popular trend of research, however it is still rarely observed in the case of rotational molding. The present study aimed to analyze the impact of wheat bran content (from 2.5 wt.% to 20 wt.%) on the performance of rotationally-molded composites based on a linear low-density polyethylene (LLDPE) matrix. Microscopic structure (scanning electron microscopy), as well as physico-mechanical (density, porosity, tensile performance, hardness, rebound resilience, dynamic mechanical analysis), rheological (oscillatory rheometry) and thermo-mechanical (Vicat softening temperature) properties of composites were investigated. Incorporation of 2.5 wt.% and 5 wt.% of wheat bran did not cause significant deterioration of the mechanical performance of the material, despite the presence of ‘pin-holes’ at the surface. Values of tensile strength and rebound resilience were maintained at a very similar level, while hardness was slightly decreased, which was associated with the porosity of the structure. Higher loadings resulted in the deterioration of mechanical performance, which was also expressed by the noticeable rise of the adhesion factor. For lower loadings of filler did not affect the rheological properties. However, composites with 10wt.% and 20 wt.% also showed behavior suitable for rotational molding. The presented results indicate that the manufacturing of thin-walled products based on wood polymer composites via rotational molding should be considered a very interesting direction of research.

Polypropylene/polyethylene two-layered by one-step rotational molding

At present, a two-layered product can be molded through various processes. The rotational molding process is a thermoplastics process that can produce products with a two-layered structure; however, it requires special equipment or additional steps in the processing, which make the processing more complex. However, previous research has shown that, through the use of materials with different particle sizes and melting points, two-layered products can also be molded. Thus, this research uses an axial powder flow apparatus to determine the possibility of a two-layered molding between polypropylene (PP) and linear low-density polyethylene (LLDPE). The differences in the particle shapes of a PP homopolymer and copolymer have been considered. The particle sizes of both PPs were determined to be larger than that of LLDPE, and were mixed in a ratio of 50:50 (%wt) using a dry blending method. The results of this experiment show that the two-layered molding of PP and LLDPE using an uncomplicated technique for rotational molding has a high probability of success.