No abstract

The goal of this study is to examine how the extrusion process affects the dispersion, length, and thermal degradation of cellulose fibers (CF) in polypropylene (PP) composites. Bleached sulfite CF are pelletized and then compounded (20 and 30wt%) in a co-rotating twin screw extruder. The pelletizing process of CF is found to cause extensive fiber breakage. The fiber length is decreased from an initial 1.7 to 0.8 mm. The results show that higher screw speed, higher fiber content, and two extrusions not only increase the shear energy, resulting in improved fiber dispersion but also cause fiber breakage and thermal degradation. The composite's mechanical properties are not improved with better fiber dispersion and the reason for this might be the extensive fiber breakage and thermal degradation. Moreover, it is found that the PP polymer is also slightly degraded during the compounding process.

Cushion foam sheets, made from different blends of wheat starch, were developed with a co-rotating twin-screw extruder machine and compared to commercial plastic foam cushions. An experimental study was developed to identify the effect of three ingredients: glycerol, gluten, and sodium bicarbonate on the bulk expansion, the cellular structure and the mechanical properties of the resulted foams. The experiments showed that the properties of the resulted foams were affected by the formulation. Foams with high level of glycerol and gluten content had lower densities and higher expansion ratio, cell size area, and cell wall thickness than blends with high level of sodium bicarbonate, which had better mechanical strength but less elasticity and shock absorption. The extruded materials had shown their suitability for cushioning use by having comparable physical properties with the commercial plastic foams. The dynamic cushion curve test indicated that the starch-based foam sheets provided good shock absorption properties. They had lower and larger deceleration peak than the expandable polyethylene foams we tested.

Cellulose fibers are rarely used for the extrusion of composites because of the problems in feeding them into the extruder and in dispersing them properly. Pelletization made it possible to feed cellulose fibers into extruder, but it reduced dramatically the fiber length. The goal of this study was to optimize the pelletization process for extrusion applications. Bleached sulfite cellulose fibers were pelletized at different moisture contents and with the optional addition of carboxymethyl cellulose (CMC). The pellets were subsequently extruded with polypropylene matrix without compatibilizer. Fiber dispersion and fiber breakage during extrusion were investigated. Pre‐blending of polymer and fiber pellets and introduction of the fibers through a side extruder were compared. CMC acted as a processing aid during pelletization, resulting in lower fiber breakage but in compact and stiff pellets. Lower moisture content also increased the compactness of the pellets. The dispersability of the fibers during extrusion decreased with increased pellets' compactness. CMC created inter‐fiber bonds, decreasing further the fibers' dispersability. The fiber length in the composites was the same regardless of the pelletization parameters. Early introduction of the fibers improved fiber dispersion. Feeding through side extruder was more stable and more reliable than pre‐blending. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Nowadays, product protection during transportation has become essential as import-export is increasing drastically. As a result, wrapping is used to stabilize and protect the goods and must be performed properly. The most commonly used wrapping material is the linear low-density polyethylene (LLDPE), either manually or through a mechanical equipment. This study will focus on the adequation of stretch film standard to wrapping and transport applications. Both manual and mechanical films were analysed. The anisotropy of the materials was investigated. Characterization of the material was focused on tensile properties, elastic recovery, permanent deformation and stress retention in order to correspond to pallet wrapping applications. It was found that both materials showed anisotropic behaviours. Standard testing conditions were found to not be described properly transport wrapping applications. Relaxation time and extension speed were found to significantly affect hysteresis properties.