Journal of Cellular Plastics

In microcellular plastics, produced by the solid-state batch method, an integral solid skin and a core with graded porosity can be created by allowing absorbed gas to diffuse from the surface of a saturated specimen prior to foaming. In this article a semi-empirical model is proposed to predict the local density of microcellular foam as a function of dissolved gas concentration. To this end, Henry’s law is applied on available experimental data for polystyrene—nitrogen system. The resultant spatial variation of mass density would be interesting for analyzing engineering structures made of microcellular plastics.

Due to the well-defined mechanical properties and high service temperature, considerable efforts have been devoted to the development of expanded polypropylene bead foams nowadays. A pilot scale batch foaming equipment with volume of 50 L was carried out to produce polypropylene and polypropylene/poly(lactic acid) bead foams with using n-pentane as the physical blowing agent. The resultant bead foams exhibited high expansion ratio up to 44.4, nice ellipse bead foam shape, well-defined cell structure and quite high cell density. Neat PP exhibited a narrow foaming temperature window around 4—5°C. Poly(lactic acid) possessed high n-pentane solubility, and the presence of 20% poly(lactic acid) was verified to obviously broaden the foaming temperature window to 10—15°C and facilitated the foam expansion. In this study, the fundamental issues such as pressure building in autoclave, n-pentane solubility, and various parameters to control bead foams’ expansion and cell morphology are presented.

Flexible polyurethane foam is widely used in numerous comfort applications such as automotive seat cushions and mattresses. It would be interesting to design a mechanical model which describes the behavior of this material in a series of test conditions. This study is devoted to the modeling of the quasi-static behavior of polyurethane foam using a memory integer model. Polyurethane foam undergoing large compressive deformation exhibits highly nonlinear elasticity and a viscoelastic behavior. The memory integer model describes the nonlinearity in a polynomial function and the viscoelasticity through a convolution function. Uniaxial compression tests help to identify the mechanical parameters of the model. The difference between the force responses of foam in load and unload phases constitute the base element of the method used in this article. Numerous precautions are taken into account to obtain accurate results which verify the thermodynamic conditions. Finally, the reliability as well as the limits of the memory integer model are discussed.

A series of aromatic polyester polyols (APP) were synthesized by transesterification of industrial poly(ethylene terephthalate) (PET) waste using di(ethylene glycol) in the presence or absence of glycerol, adipic acid, poly(propylene glycol), or hexanediol as functional additives. PET-waste-derived modified APP was used for the synthesis of polyurethane—polyisocyanurate (PU-PIR) foams. The isocyanurate yield of the PU-PIR foams determined by the temperature method was high (67—90%) and correlated well with the data of Fourier transform infrared measurements. The effect of chemical structure of the APP and its properties (viscosity, acid number, and hydroxyl number) on technological characteristics of the PU-PIR foams at equal/similar formulations was studied. PU-PIR foams prepared using PET-waste-derived APP were characterized by high closed cell content (more than 94%). The presence of the fragments of glycerol in the structure of APP decreased the core density and tensile strength and increased elongation at break of the resulting PU-PIR foams while the presence of the fragments of adipic acid acted vice versa.

Foaming of rubber profiles offers savings potential with respect to component weight, material consumption, and costs. Physical blowing agents are superior to chemical blowing agents in terms of economy, ecology, and efficient processing. The application of gear pumps in foam extrusion of ethylene propylene diene rubber compounds using nitrogen as blowing agent significantly improves the process stability due to minimized variations of process pressures. Experimental investigations show that the amount of blowing agent injected has a significant influence on density, foam structure, and surface roughness. Besides, the foam structure depends on die pressure and used materials. In addition to nitrogen, carbon dioxide and water are suited as well for the use as physical blowing agents.