Overview - ISO 3387:2020 (rubber crystallization by hardness)
ISO 3387:2020 specifies a standardized test method to determine progressive stiffening of rubber caused by crystallization, using hardness measurements (IRHD). The method applies to raw, unvulcanized (compounded) and vulcanized rubber with an initial hardness at the test temperature between 10 IRHD and 85 IRHD. It is particularly relevant for polymers that show crystallization under cold‑climate conditions (for example chloroprene and natural rubber). The method is not suitable for materials that crystallize substantially within the 15‑minute conditioning interval used to establish initial hardness.
Key topics and technical requirements
- Principle: measure either the increase in hardness after specified storage times at test temperature, or the time required to reach a specified hardness increase.
- Test temperatures: options range from +23 °C down to −70 °C (±2 °C). When known, use the temperature nearest the material’s maximum crystallization rate.
- Typical crystallization maxima (approximate): chloroprene −10 °C; natural rubber −25 °C; dimethyl silicone rubber −55 °C.
- Duration and readings: common readings after 24 h and 168 h; intermediate readings (48 h, 96 h) recommended. If hardness rises >10 IRHD at 24 h, repeat with shorter intervals (1, 2, 4, 8 h).
- Apparatus: cold chamber (gaseous heat-transfer medium, ±2 °C), hardness gauges per ISO 48‑2, tweezers/tongs, heated press for moulding unvulcanized samples.
- Test pieces: standard thickness 8–10 mm. Minimum thicknesses: 4 mm (for 35–85 IRHD) or 6 mm (for 10–35 IRHD). Edge‑distance and surface flatness requirements apply for comparability.
- Conditioning: test pieces held >8 h after moulding must be decrystallized at 70 °C for 45 min, then conditioned at standard laboratory temperature 30–60 min before testing.
- Measurement practice: use method L, N or H per ISO 48‑2 based on initial IRHD; take median of 3 or 5 measurements spaced ≥4 mm apart.
Practical applications and users
- Who uses ISO 3387:2020: R&D laboratories, material scientists, rubber compound developers, quality control labs, and manufacturers of elastomer products intended for cold climates.
- Why use it: evaluate cold‑temperature aging and stiffness increase from crystallization; compare formulations; support material selection for seals, hoses, tires and outdoor rubber goods exposed to low temperatures.
- Value: provides repeatable, comparable hardness‑based metrics for crystallization tendency without requiring more complex structural analysis.
Related standards
Keywords: ISO 3387:2020, rubber crystallization, hardness measurements, IRHD, cold‑weather rubber testing, chloroprene, natural rubber, hardness gauge, cold chamber.