ISO 2896:2001 pdf download

ISO 2896:2001 pdf download.Rigid cellular plastics – Determination of water absorption.
A.1 Principle
A specimen of less than monocellular thickness is cut from the material on a slicer and its shadowgraph projected onto a screen by means of a scale slide assembly and projector. The average cell chord length is determined by counting the cells or cell-wall intersections within a specified distance, and this length is then converted to the average cell diameter by a mathematical formula.
A.3 Procedure
A.3.1 For each direction in which it is intended to determine the average cell diameter, cut a piece measuring 50 mm x 50 mm, and of the thickness of the sample, from the sample in the area to be tested. Prepare the cell- viewing specimen(s) by cutting a thin slice (less than monocellular) from one of the cut surfaces of each such piece of material. The slice shall be as thin as practicable so that the shadowgraph will not be occluded by overlapping cell walls. The optimum slice thickness will vary with the average cell size of the material, with smaller cell diameters requiring thinner slices.
A.3.2 Insert the slice into the slide assembly (5.6). Position the scale zero on the grid line at the top of the area to be measured. Reassemble the slide.
A.3.3 Insert the slide assembly into the projector (5.7). Focus the projector on a wall or screen so that a sharp- image shadowgraph results.
A.3.4 Determine the average cell chord length t from the projected shadowgraph as follows:
First count the number of cells (or cell walls) that intersect the 3 cm straight line projected with the specimen. Then divide the length of the line by the number of cells counted to obtain the average chord length t. If the specimen is less than 3 cm long, count the cells on the maximum grid length usable.
A.3.5 When the cell structure is anisotropic, determine the average cell diameter in each of the three principal directions and use the average of the three results.
A.4 Calculation
Calculate the average cell diameter using the equation