Catherine Lacoste

This article concerns the elaboration and the characterization of a novel biobased potato starch-beet pulp composite for packaging applications as cushion foams. A twin-screw extruder was used to elaborate composite foams. SEM observations of these materials were conducted, and thermomechanical properties were studied in terms of thermal transitions (TGA, DSC) and viscoelastic properties (DMA). The effect of relative humidity content on viscoelastic properties was analyzed as a function of frequency. The different test results show that the composite structures are homogeneously mixed. The sponge-like structure of the beet-pulp disappears indicating a good compatibility between the two mixed constituents. The DSC curve of starch-beet pulp foam shows a single thermal transition at 153.6 °C, indicating the thermal homogeneity of the obtained composite material. The density value of starch-beet pulp foam is higher than conventional foams, but this can be optimized by adjusting the technological parameters of the extruder. The viscoelastic properties of the developed materials depend on the relative humidity.

The objective of this study was to build a model that can predict the yellowing of styrene-stat-acrylonitrile (SAN) and acrylonitrile-butadiene-styrene (ABS) during processing in an internal mixer. Considering the change of color of SAN and ABS as they degrade, we correlate the yellowing of SAN and ABS to process parameters. We propose a method to represent the energy of mixing of polymer blends in an internal mixer to understand the complex mixing process of materials under different mixing conditions. Indeed, during processing, the properties of polymers could be affected by both thermal and mechanical degradation leading to several mechanisms of degradation. We presented a simplified model “h” taking into account the contribution of each process parameters applied in the internal mixer. Three process parameters were studied: the temperature T, the rotation speed of the blades V, and the residence time t. Thanks to this method of approach, a good correlation between the yellowing of styrenics and the mixing energy in the internal mixer was described. We validated this equation with two polymers: SAN and ABS, and this model can now predict the yellowing of SAN and ABS as a function of the process parameters in an internal mixer.

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.

Polymer melts can be mixed with many monomers, plasticizers, antistatics or foaming additives. Properties of such mixtures can change during blending because of chemical reactions like polymerization or crosslinking. The process may be carried out either in stirred tanks, extruders or in motionless mixers. In this paper we focused on the mixing time and the diffusion time of reagent, plasticizer and polymer thanks to rheological tools, and on the way how rheological properties can be studied during chemical reaction in polymer blending. The concept of rheoreactor and Couette analogy were introduced since we have a reactor on our disposal that can mix solution and measure rheological properties without taking sample. This apparatus appears to be an appreciable tool in complement of internal mixers that are specific to polymer blending. For example, we show the importance of the competition between mixing time and reaction time for reactive systems.