ISO 498:1992

Overview

ISO 498:1992 specifies a controlled method to prepare dry, homogeneous, substantially bubble-free films from natural rubber latex concentrate (Hevea brasiliensis). The procedure covers required apparatus, sampling references and a stepwise casting and drying process to produce reproducible specimens for testing and quality control.

Key practical constraints noted in the standard:

• Not intended for compounded or vulcanized latices, artificial rubber dispersions, or latices from sources other than Hevea brasiliensis.
• Total solids content is critical for correct film formation (target ≈62% m/m).

Key Topics

Apparatus and materials

• Mould: prepared by cementing glass or rigid plastic strips (6 mm wide, 1.5 mm thick) on a flat glass plate; cavity size typically 100–150 mm sides. A mould so prepared will give dry films about 1 mm thick at 62% solids.
• Gauze: square-mesh (polyamide or stainless steel) with average aperture 180 µm ± 10 µm for straining.
• Straightedge (wood, plastic or stainless steel) for scraping excess latex at a single pass (up to 25 mm/s).
• Oven capable of 35 °C ± 2 °C; cabinet or covered dust-free area; thin clear cellulosic-film sheets; desiccator or airtight container; beaker (≈50 cm3).
• Adhesives (for fixing strips to glass): epoxide resin or poly(vinyl acetate) dissolved in methyl ethyl ketone.

Sampling and measurements

• Carry out sampling in accordance with ISO 123.
• Determine total solids in accordance with ISO 124. If the solids content is >62% m/m, dilute with distilled water to 61.5% m/m; if ≤62% no dilution is required.

Procedure highlights

• Mix sample gently, allow to stand 5 minutes, then strain 35–40 cm3 through gauze into beaker and let stand 5 minutes covered.
• Remove surface bubbles in the beaker, pour latex into the mould in a continuous stream while moving the beaker to avoid bubbles, allow 1 minute and scrape off the excess with a straightedge once only.
• Dry cast film in a dust-free atmosphere for at least 16 h; if required, complete drying in oven at 35 °C ± 2 °C. Handle dry film using cellulosic sheets and store in a desiccator in the dark and cool place.

Applications

• Producing standard test specimens for laboratory evaluation of natural rubber latex properties.
• Ensuring repeatable specimen preparation for comparative testing and quality control in latex processing and R&D.
• Useful reference for laboratories establishing sampling and casting workflows for latex film testing.

Related Standards

• ISO 123 - Rubber latex - Sampling (referenced for sampling methods).
• ISO 124 - Rubber latices - Determination of total solids content (referenced for solids measurement).

Keywords: ISO 498:1992, natural rubber latex, dry films, specimen preparation, sampling, total solids, latex casting, QC.