Five kinds of polyimide (PI) foams were prepared from dianhydride and diamine by esterification process. The microstructure of foam was characterized by SEM and visualization methods, and many properties of material were measured, including heat resistance, fire resistance, compressive strength, heat insulation and acoustic absorption. It was shown that the cell size of foam was from 1 to 1.5 mm. The cell edge of PI BM and PI BO foam was obscure, and the cell wall was thinner than the PI BD , PI OD and PI BO-DM foam with thicker cell edge and poor cell size homogeneity. Five types of PI foams presented the trait of flexible foam plastics. All of them possess high decompose temperature, and their limiting oxygen index surpassed 40 percent, and thermal diffusion coefficients were less than 0.030 W/m·°C. In addition, PI BO , PI OD , and PI BO-DM foam had excellent acoustic absorption.

This paper presents an experimental study on manufacture and characterization of an insulating foam coating in the coaxial cables where a physical blowing agent (butane) is used. Coaxial cables with foam insulator are widely used in communication industries. The insulating foam plays a key role in the attenuation properties of the coaxial cables. In this research work, an extrusion setup was prepared to produce foam insulated coaxial cable using butane as the physical foaming agent. The effect of die geometry (die gap and die outlet diameter) on foam morphology and loss-attenuation were investigated using a blend of LDPE (90%)-HDPE (10%) as the main material. The results show that an acceptable low loss-attenuation is achievable via using a polyethylene compound and adjusting processing parameters.

The compression behaviour of carbon foams derived from synthetic naphthalene based and coal tar based mesophase pitch is studied. After carbonization and graphitization, the structure of carbon foam is modified obviously and compression behaviour decreased dramatically due to the transition of foam from two-dimensional turbostratic structures to graphite structures. The SEM, X-Ray diffraction and compression behaviour are used in the study of modification of mechanical properties. The results show that the compressive strength of carbon foam obtained from synthetic mesophase pitch is only 30% of the foam obtained from coal tar based mesophase pitch. The SEM shows that the length of micro-cracking of foam derived from synthetic mesophase pitch is as high as 5 μm and that of foam derived from coal tar based mesophase pitch is less than 2 μm. The causes of the differences in properties focused on rod structure of naphthalene based pitch transformed easier to three-dimensional sandwich structure.

Rigid thermoplastic foams, also known as structural foams, have been produced since decades to enhance specific properties, reduce material consumption and avoid shrinkage of thermoplastic injection molded parts. A good understanding of their behaviour is needed to properly design and predict their performance for a given set of functional requirements. While the variation of mechanical properties in dependence of the density reduction has been the traditional approach to characterise the mechanical performance of this type of materials, little attention has been paid to the variation of properties depending on the foam morphology. As the second part of a research where the effects of the injection molding parameters on the foam morphology are analyzed, mechanical tests were conducted to study the variation of the properties along an injection molded plate. The correlations between the foam morphology and the tensile and flexural modulus of elasticity are studied.

The foaming behaviour of polymer blends was systematically investigated using carbon dioxide as a blowing agent. Two batch-processing techniques were used to prepare specimens of different size. Various binary mixtures over a wide compositional range were selected as reference materials, in particular including immiscible (poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) blends. Moreover, the influence of a compatibilization with block copolymers was investigated for PPE/SAN blends. The resulting foam morphology was characterised by evaluating the density, the cell size distribution, the cell wall morphology and the compression behaviour. Besides the commonly accepted key criteria for foaming neat polymers, our study identified significant factors determining the foamability of blends such as the blend morphology, the rheological and the thermal properties. Interestingly, the compatibilization of these PPE/SAN blends by block copolymers was identified as a technique to establish micro- and submicrocellular foam morphologies with nanostructured cell walls. In view of these results, new pathways for the tailoring of cellular materials are derived.

This paper presents a characterization of the PLA-CO 2 system for solid-state foaming process with a particular goal of producing low density foams. The diffusivity of CO 2 in PLA increases with increasing saturation pressures. The results show that low relatively density (lower than 10%) can be achieved in a wide processing window. The cell size can vary from tens of microns to several hundreds of microns depending on the solid-state foaming process parameters. There are significant differences in relative density and cell size for 2 and 3 MPa saturation cases, which are likely due to the much higher crystallinity at 3 MPa (26.4%) compared to 2 MPa (9.7%). Foams with cell size of around 300 μm and relative density of 3% were produced at 2 MPa saturation. It was observed that the higher the gas pressure, the higher the rate of gas-induced crystallization. Further, the gas-induced crystallization as well as the gas concentration in PLA during sorption reach their respective maximum values at approximately the same time for all gas pressures explored. For specimens saturated at 2 MPa, there is a substantial jump in crystallinity (from 5.2% to 23.4%) after foaming.

This paper discusses the control of the foaming process for production of variable microcellular structures and morphologies for novel acoustical foams under investigation. For that purpose, the foaming process was controlled for production of foam samples with various microcellular structures. Crosslinked LDPE was used as a base material for the produced foams. Very high open-cell content (ranging between 43 – 95%), high microcellular cell densities (9×10 8 – 1.6×10 9 cells/cm 3 ) and desired expansion ratios (3 – 9 folds) were successfully obtained. While the material is overly porous, it is noted that the unfoamed skins on the outer surfaces of the samples have prevented sound waves from penetrating the samples. Manual skin removal resulted in slight improvement in sound absorption testing. However, in order to get more reliable data, skinless samples need to be produced.

In this paper, the equivalency between the foaming time and foaming temperature of the cell density, the number of cells per unit volume remaining in the foamed plastics, will be discussed. The foaming was carried out by the following method. The blowing agent was soaked into the solid resin at high pressure under temperature lower than the glass transition temperature of the resin. After the blowing agent reached its saturation state, cell nucleation and cell growth were induced by heating various foaming temperatures higher than glass transition temperature and various foaming times after decompression. Finally, cell growth was halted by cooling. Concretely, using a device that can accurately control temperature and the decompression rate, polystyrene (PS) and polycarbonate (PC) resins which are amorphous resins were foamed under various the foaming temperatures and the foaming times by the above-mentioned method. The following results were obtained. (1) Cell density of foamed PS and PC plastics shows time and temperature dependence as the cell density becomes large when foaming temperature is low and foaming time is short. (2) Equivalency is maintained between the foaming time and foaming temperature dependence of the cell density of PS and PC foamed plastics, and they can be expressed with one master curve respectively. That is, the time-temperature equivalent law is held about cell density. (3) These results seem to become one technique to select the foaming condition of foamed plastics having required cell densities.

The thickness of a skin layer on the parts made by a microcellular injection moulding process may influence its properties, including impact and tensile strength, density and sound transmission. Therefore it is necessary to study the variations in skin layer thickness with processing parameters. In this paper, the influences of temperatures in the mould cavity on the skin layer's thickness are addressed. In addition, the relationship between the temperature distributions across the cavity of the mould, with impact strength on parts made using a microcellular injection moulding process, was addressed. * T SL , the temperature at which the skin layer forms, was proposed. According to previous studies, T SL is expected to be similar to the polymer melting point for semi-crystalline polymer and the glass transition temperature for amorphous materials. In addition, a method to predict variations in skin layer thickness with mould temperature is discussed.