Method for pore sealing a porous substrate, comprising: forming a continuous monolayer of a polyimide precursor on a liquid surface, transferring said polyimide precursor monolayer onto the porous substrate with the Langmuir-Blodgett technique, and imidization of the transferred polyimide precursor monolayers, thereby forming a polyimide sealing layer on the porous substrate. Porous substrate having at least one surface on which a sealing layer is provided to seal pores of the substrate, wherein the sealing layer is a polyimide having a thickness of a few monolayers and wherein there is no penetration of the polyimide into the pores.

Methods for reducing the density of thermoplastic materials and the articles made therefrom having similar or improved mechanical properties to the solid or noncellular material. Also disclosed are improvements to foaming methods and the cellular structures of the foams made therefrom, and methods for altering the impact strength of solid or noncellular thermoplastic materials and the shaping of the materials into useful articles.

A multilayer foam film with an enhanced perceived surface whiteness comprising for light-blocking, signage, and general packaging application is disclosed. In an embodiment, the film has a bulk density of less than 0.962 gr/cm.sup.3 wherein more than 50% of the cells in the foam layer are closed cells. In an embodiment, the multilayer foam film has a thickness greater than 1 mil and one of the solid skin layers contains white pigment. In another embodiment the white skin layer has a skin whiteness value of greater than 80 according to ASTM E313-73, and a skin layer tint value of less than 1 according to ASTM E313-73, and The lightness value (L*) of the white skin layer of greater than 90 in CIE L*a*b* dimension according to ASTM E308. In an embodiment, the film has a very smooth surface with a smoothness value of less than 25 in Sheffield smoothness unit configuration according to TAPPI T 538.

Provided are a thermoplastic elastomer (TPE) physically-foamed roll and a semi-continuous preparation method thereof. In the preparation method, the desorption of a high-pressure fluid is inhibited by controlling a solubility of the high-pressure fluid in a TPE roll and then subjecting the material to a quick freezing and gas-locking treatment at a specific temperature, and an impregnated roll can be stored at a low temperature for a long time or subjected to long-distance transportation, and can be stably subjected to continuous heating and foaming, which allows large-scale continuous production and is safe and environmentally-friendly. The present disclosure also provides a TPE physically-foamed roll prepared by the preparation method, and the TPE physically-foamed roll has a thickness of 0.1 mm to 3 mm, a density of 0.1 g/cm.sup.3 to 0.6 g/cm.sup.3, a foam cell size of 1 m to 200 m, and a Shore hardness of 20 C to 60 C.