Abstract: A method of treating a porous material comprising establishing a pressure differential across the material and treating the higher pressure side with a suspension dispersion or aerosol of droplets of a liquid. The droplets enter at least some of the pores, with the treatment conditions being such that the aerodynamic forces within the pores exceed the surface tension forces maintaining the integrity of the droplets. The droplets thus spread to provide a surface coating within the pores.

Abstract: A nebulizer for liquids, particulate materials or liquids/solids suspensions, comprising, within a vessel (10) containing a reservoir (11), an upright duct (13) with a plurality of circumferentially spaced outlet apertures (20), enclosing a coaxial air line (14) feeding a plurality of jets (16) duly aligned with outlet apertures (20) in the upright duct (13) so that an annular column of material is drawn from reservoir (11) to be dispersed by entrainment in the air streams from the jets (16). Larger droplets may return to the reservoir (11) while the smaller fraction issues from the vessel through an outlet (12). The relatively large outlet apertures (20) and the large cross-sectional area of the column of the material prevent blockage at the nebulizer head.

Abstract: A porous material, e.g. a paper, has pores with a range of sizes. A pore modifying agent comprising particles of a narrow size range is selectively incorporated within the larger pores to provide zones of high surface area. These greatly reduce the penetrability of the material, e.g. by mirco-organisms, while having relatively little effect on its air-permeability. The modifying agent may be incorporated by creating a pressure difference across the material, and treating it with a dispersion, e.g. an aerosol, of the modifying agent, under conditions of low inertia, and incorporating only a small amount of the agent, e.g. not more than 1% w/w.