ISO 248-1:2021

Overview

ISO 248-1:2021 specifies two standardized laboratory methods for determining the volatile‑matter content of raw rubbers: the hot‑mill method and the oven method. The standard applies primarily to rubbers in the “R” group of ISO 1629 (rubbers with unsaturated carbon chains, e.g., natural rubber and di‑olefin‑derived synthetics). It also allows use on other raw rubbers only when it can be demonstrated that mass loss is due solely to volatiles and not to rubber degradation. Note: the two methods can give different results; oven method, procedure A, is the reference method in case of dispute.

Key topics and requirements

• Two test routes:
  • Hot‑mill method (procedures A and B) - material is sheeted/milled on a heated laboratory mill until mass stabilizes.
  • Oven method (procedures A and B) - material is dried in a ventilated oven to constant mass.
• Applicability limits:
  • Hot‑mill method is not applicable to natural rubber, to synthetics that are difficult to handle on a mill, or to powders/chips.
  • Oven method is suitable for natural rubber and many synthetic types.
• Apparatus & conditions:
  • Hot‑mill roll surface temperature typically maintained at 105 °C ± 5 °C with roll clearance 0.25 mm ± 0.05 mm.
  • Oven (ventilated, preferably air‑circulating) maintained at 105 °C ± 3 °C.
  • Balances: hot‑mill tests use balances to 0.1 g; oven method specifies balances to 0.1 mg for precise determinations.
• Sample handling:
  • Homogenization (Annex B) is required for some procedures; sample sizes and test‑portion masses are specified (e.g., ~250 g for homogenization, ~10 g oven test portion for natural rubber).
• Results & precision:
  • Mass loss is expressed as percent volatile‑matter; the standard provides the calculation formulae and precision data (see Annex C).
• Ancillary guidance:
  • Annex A summarizes method applicability; Annex B details homogenization; Annex C gives precision/ITP results.

Applications

• Quality control of incoming raw rubber and production batches.
• Supplier verification and acceptance testing.
• Research and development of rubber grades and processing conditions.
• Contract testing laboratories offering standardized volatile‑matter assays.
• Troubleshooting processing issues related to moisture and volatile residues.

Who uses this standard

• Rubber manufacturers and compounders
• Quality assurance and laboratory personnel in the rubber industry
• Independent testing laboratories
• Procurement and materials engineers specifying incoming raw materials

Related standards

• ISO 1629 (rubber classification)
• ISO 1795 (sampling and preparative procedures)
• ISO 2393 (mixing mill equipment and procedures)

Keywords: ISO 248-1:2021, volatile-matter content, raw rubber testing, hot-mill method, oven method, natural rubber, synthetic rubber, homogenization, laboratory mill, raw rubber quality control.