A multilayer material was produced by rotational molding to study the effect of composition on the mechanical behavior of a cylindrical liquid container. The first (outer) layer was a composite of linear medium density polyethylene (LMDPE) with 5, 10, or 15 wt% agave fiber (AF). The core (middle) layer was foamed LMDPE with different amount of foaming agent (0, 0.15, 0.25, 0.5, and 0.75 wt%). Finally, the third (internal) layer was neat LMDPE. This structure was produced to optimize the mechanical properties of the molded parts while decreasing weight with good surface properties. From the morphological analysis, it was observed that the layers are not always well defined because of gas migration, especially from the foamed core to the composite layer. As expected, density increased with fiber content while decreasing with foaming agent concentration. In general, impact strength (Charpy and Gardner) was directly related to the overall density of the part. POLYM. ENG. SCI., 56:278–286, 2016. © 2015 Society of Plastics Engineers

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Foamed linear medium density polyethylene parts were prepared by rotational molding in biaxial mode, using different amounts of chemical-blowing agent (azodicarbonamide). Morphological and mechanical properties are presented and discussed in terms of foam density, cell density, average cell diameter, and open cell content. Internal air temperature of the mold was measured as a function of time. Significant differences were observed between unfoamed and foamed parts. The use of an exothermic chemical-blowing agent increased the peak internal air temperature and part cooling was slower due to the presence of gas bubbles acting as insulating material. The most important changes were observed for foam density: adding 1 phr of azodicarbonamide the density decreased from 0.931 g/cm3 (0 phr azodicarbonamide) to 0.295 g/cm3. Finally, the mechanical properties were highly influenced by azodicarbonamide content. Tensile and impact properties were correlated with part density using a simple power–law equation.

Self-hybrid thermoplastic composites (combination of two fiber sizes) were obtained by injection molding using pine or agave fibers with polypropylene (PP). The effect of self-hybridization was determined through mechanical properties and water absorption for different total fiber contents between 10 and 30% wt. The results showed that impact strength (30% of fiber) and tensile modulus (20% of fiber) were improved by selfhybridization compared with composites formulated with only one fiber size. Flexural properties were not improved by self-hybridization. On the other hand, the combination of two fiber sizes had no effect on the water absorption behavior of these composites. Overall, the total fiber content was found to be an important parameter with 20% being the optimum condition where self-hybridization provides the best mechanical properties.

This paper reports the use of polysaccharides extracted from seed of Persea americana var. Hass in the synthesis of acrylic hydrogels. The effects of the chemical composition (acrylamide/acrylic acid), the concentration of crosslinking agent (glycerol diacrylate) and the type of initiation (redox, photoinitiation) of the hydrogels were evaluated with and without polysaccharides. Xerogels were characterized by FTIR spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), while for the swollen hydrogels the swelling kinetic and mechanical properties were evaluated. The kinetic parameters were obtained using the second order equation proposed by Schott, where it is reported that by increasing the concentration of the crosslinking agent, the degree of swelling is reduced because of the greater structural level. The increase of the amount of acrylamide and the amount of polysaccharides causes also a decrease in the swelling degree. The type of initiation also affected the hydrogels swelling kinetic, the photoinitiated hydrogels were the ones that captured less water. Moreover, the increasing of the glass transition temperature and the compression modulus with the crosslinking agent concentration and molar ratio AAm/AAc are observed for hydrogels with and without polysaccharides. The results demonstrate a successful incorporation of polysaccharides into the polymeric network.