International audienceAn experimental and theoretical analysis of the polypropylene foaming process using three different chemical blowing agents (CBA) was performed. A simple experiment was designed to analyze the foaming process of polypropylene (PP)/CO2 system under two different pressure conditions. The expansion ratio and final foam structure was measured both by direct observation and from optical measurements and image analysis, showing a good agreement. A single bubble simulation based on relevant differential scanning calorimetry and thermo-gravimetrical analysis experiments, assuming each CBA particles as a nucleation site and accounting for gas diffusion in the surrounding polymer matrix has been built. The sensitivity of the model to physical and processing parameters has been tested. The calculation results are compared to the experiments and open the route to a simplified method for evaluating the efficiency of CBA

International audienceRelationships for the prediction of various linear mechanical properties of polymeric sandwich foams obtained in injection processes were studied in comparison with shear, tensile, and flexural tests. The samples were obtained by a core-back foam injection molding process that enables one to obtain sandwich materials with dense skins and a foamed core as revealed by the morphological analysis. Tensile, shear, and flexural moduli were investigated for the skin, the core, and the overall foamed structure. In addition, the Poisson’s ratio of the skin was also determined. The core properties were specifically analyzed by machining the samples and removing the skins. Tensile and shear properties of the core can be well described by the Moore equation. The tensile modulus can be calculated by a linear mixing rule with the moduli of the skin and of the core in relation to the thickness of the layers. Shear and flexural moduli are described by a linear mixing rule on the rigidity in agreement with the mechanics of beams. Tensile modulus, out-of-plane shear modulus, and flexural modulus can finally be predicted by the knowledge of only very few data, namely the tensile modulus and Poisson’s ratio of the matrix, the void fraction, and thickness of the core. The equations were proved to be physically meaningful and consistent with each other

Polypropylene/poly(3-hydroxybutyrate-co-hydroxyvalerate) blend (PHBV) and polyethylene/PHBV blend were prepared by twin screw extruder using preformed copolymer (EVOH-g-PHBV) as compatibilizer or with functional polyolefins that can react in situ with the PHBV phase to form POs-g-PHBV. Scanning electron microscopy shows that by using either EVOH-g-PHBV preformed copolymer or formed copolymers in situ both emulsify the phase interface and reduce the interfacial tension, which result in an enhancement on the mechanical properties of compatibilized blends. Enhancement is more or less pronounced depending on the used PO matrix.

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Polypropylene (PP) was functionalized in the melt by grafting polar monomers using an internal mixer and a corotating twin-screw extruder. 2,5-Bis(tertbutylperoxy)-2,5-dimethylhexane (Luperox 101) and dicumyl peroxide (DP) were the used radical initiators. The polar monomers were itaconic acid (IAc), 2-octen-1-ylsuccinic anhydride (OY), 2-hydroxyethyl methacrylate (HEMA), and 3-allyloxy-1,2-propanediol (AP). Grafting was quantified by FTIR combined to Elemental Analysis. Grafting degree depends mainly on monomer and initiator natures and concentrations. Grafting degree maxima were 3.9, 2, 9.5, and 3.9 wt %, respectively, for IAc, OY, HEMA, and AP. Some properties of the modified PP were evaluated. Thermal analysis indicated that the polarity of PP increased by grafting reaction and size-exclusion chromatography showed that the grafting was not accompanied by a significant M w and viscosity decrease.

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