Rotomolding and polyethylene composites with rotomolded lignocellulosic materials: A review

Abstract

Rotomolding is a versatile process used in the manufacture of thermoplastic polymeric materials to produce large hollow plastic parts. The aim of this review article was to discuss the rotomolding process and show the properties of the polyethylene composite and rotomolded lignocellulosic fibers, which are processed for prolonged periods under temperature. The main process parameters studied are the shaft speed of the equipment, molding temperature, polymer particle size, polymer melt flow index, and amount of material, which must be well controlled to achieve a non-degraded product with homogeneous thickness and no porosity. Rotomolded composites containing sisal, pine, coir, banana, flax, and maple wood fibers, among others, have been evaluated primarily for their mechanical (impact, flexural, and tensile strength) and morphological properties. The type, content, and treatment of lignocellulosic fillers are the most widely studied variables in polyethylene-based rotomolded composites. Fiber content was the variable that most influenced mechanical properties, particularly impact strength and hardness due to the voids formed by the hydrodynamic volume between the polymer matrix and lignocellulosic filler. Chemical treatment of the fiber by mercerization with NaOH made it more hydrophobic and the addition of maleic anhydride-grafted polyethylene as a coupling agent improved the interfacial adhesion between the non-polar polymer matrix and polar filler. However, the best mechanical property results were obtained with the use of maleic anhydride-grafted polyethylene.

Valorization of Invasive Plants from Macaronesia as Filler Materials in the Production of Natural Fiber Composites by Rotational Molding

“…Torres made similar observations (unchanged tensile properties and very significant losses in impact energy absorption) with lower amounts of cabuya and sisal fibers [ 23 ]. The incorporation of grafted polyethylene with maleic anhydride was found to allow one to increase the tensile elastic modulus by 50% for 20% agave or coir composites (compared to a PE matrix) [ 29 ], while impact properties were not improved and decreased by around 30%. On the other hand, the pre-impregnation of fibers with maleated polymer (maleic anhydride grafted PE [ 31 ] or PLA [ 39 ]) has been proven to increase fiber distribution and enable the obtaining of composites with lower amounts of voids (thus with lesser porosity), with significant improvements in both tensile and flexural elastic modulus, as well as reductions in tensile and flexural strength, for up to 20% agave fibers—although these properties were worse than those of untreated fibers.…”

“…The presence of voids and defects in a composite prevents good contact between the fiber and matrix, thus reducing nucleating effect (and thus leading to lower crystallinity values), which also explains the worse mechanical properties that are usually found in rotomolded composites, especially for those with high fiber contents [ 28 ]. In this context, we present a novel research work that studied the use of fibers from invasive plant species in rotational molding, as well as the influence of their size on the mechanical properties of the composites, by incorporating up to 20% of these fibers into a polyethylene (PE) matrix, which is the most common material in rotomolding [ 29 ].…”

New Method for Optimization of Polymer Powder Plasma Treatment for Composite Materials

“…Nowadays, polyethylene (PE) accounts 90% of materials processed by the rotational molding industry [ 5 ]. It is a polymer with low surface energy and generally poor adhesion properties [ 6 ]. It is not compatible with hydrophilic fibers (natural, glass, metal) without a suitable surface treatment [ 6 , 7 , 8 , 9 , 10 ].…”

“…It is a polymer with low surface energy and generally poor adhesion properties [ 6 ]. It is not compatible with hydrophilic fibers (natural, glass, metal) without a suitable surface treatment [ 6 , 7 , 8 , 9 , 10 ]. Problems with low adhesion between the matrix and the reinforcement can be solved by chemical treatment of fibers such as, e.g., silanization or plasma treatment or application of maleic anhydride-grafted polyethylene [ 5 , 7 , 11 , 12 ].…”

Morphological, thermal and mechanical properties of polypropylene foams via rotational molding

“…This technology is a low-stress/shear process aiming at producing stress-free and seamless hollow plastic articles such as containers, tanks, toys, medical equipment and several similar products over a very wide range of dimensions and shapes. [22][23][24][25][26][27][28][29] More recently, rotational molding was developed to process foamed parts. But very few works have been published on PP foams produced by rotational molding.…”