ISO 2896 Rigid Cellular Plastics - Determination of Water Absorption

The ISO 2896 Rigid Cellular Plastics - Determination of Water Absorption standard, published by the International Organization for Standardization (ISO), describes a method for determining the water absorption of rigid cellular plastics by measuring the buoyancy force on a test sample after immersion in 50 mm of water for 4 days. This standard includes corrections to account for any changes in the sample volume, as well as the volume of water in the cut-face cells of the sample. Water absorption is expressed as the average of the percentage increase in volume relative to the original volume for several samples.

The method described is designed for use in quality control and product specification.

In principle, a material's water absorption capacity is determined by measuring the buoyant force acting on a sample immersed in distilled water for a specific period of time.

At least three samples must be tested. Samples must have a volume of at least 500 cm³ ^, a nominal length of 150 mm, and a nominal width of 150 mm. For materials produced and sold with natural or laminated surfaces, the thickness must be as manufactured. For materials thicker than 75 mm and without a surface coating, the material must be cut to a thickness of 75 mm for testing. The distance between two surfaces should not vary by more than 1% (parallelism tolerance). The surfaces of the samples must be smooth and dust-free. Samples should be dried in a dryer at room temperature until the average of two consecutive weighings, taken at least 12 hours apart, does not differ by more than 1%.

The testing process essentially follows these steps:

• The work is carried out in a room where the temperature is maintained in accordance with the ISO 291 standard. Unless otherwise specified, the conditions should be a temperature of 23 degrees plus/minus 2 degrees and a relative humidity of 50 percent plus/minus 5 percent.
• The sample is weighed to the nearest 0,1 g.
• The dimensions of the sample are measured according to the ISO 1923 standard.
• The cylindrical container is filled with distilled water at room temperature after the air has been removed.
• The assembled cage is submerged in water, bubbles are removed, it is placed on a scale, and the apparent mass is determined to the nearest 0,1 g.
• The sample is placed in the cage. The cage is then re-submerged in water so that the distance between the water surface and the top surface of the sample is approximately 50 mm. Any visible air bubbles in the sample are removed with a brush or by shaking.
• The cylindrical container is covered with a low-permeability plastic film.
• After 96 hours plus/minus 1 hour or another agreed-upon immersion time, the plastic film is removed, and the apparent mass of the submerged cage containing the sample is determined to the nearest 0,1 g.
• The sample is visually inspected for signs of swelling. To determine corrections for swelling and cut surfaces, Procedure A (even swelling) and Procedure B (uneven swelling) are monitored.
• This procedure is applied separately for each sample.

In short, the ISO 2896 standard includes a method for determining the water absorption properties of rigid cellular plastics. These materials are lightweight foams with a closed or partially closed cell structure, commonly used for thermal insulation, flotation, packaging, and structural applications. Examples include rigid polyurethane (PUR), polyisocyanurate (PIR), polystyrene (EPS/XPS), and phenolic foams.

Water absorption is a critical property, as moisture ingress can significantly affect a foam's thermal performance, dimensional stability, mechanical strength, and long-term durability.

The ISO 2896 standard defines laboratory procedures for measuring how much water a rigid cellular plastic absorbs when exposed to water under specific conditions. This standard generally covers the following:

• Preparation of test samples
• Immersion conditions
• Exposure time
• Surface drying procedures
• Mass measurement before and after exposure.
• Calculation of absorbed water.

The result is usually expressed as follows:

• Mass percentage increase (percent)
• Water absorbed per unit volume or area

Water absorption is calculated from the difference between dry and wet masses, according to the formula given in the standard.

The ISO 2896 standard is considered important for the following reasons:

• Thermal insulation performance: Rigid foams are commonly used as insulation materials. The water inside the foam cells increases thermal conductivity, reducing insulation efficiency. Examples of applications include:
  • Building insulation panels
  • Cooling systems
  • Cold storage facilities
  • HVAC insulation
• Durability assessment: Moisture can cause the following:
  • Cell wall disruption
  • Freeze-thaw damage
  • Reduced compressive strength
  • Premature aging

This standard helps predict long-term service behavior.

• Material comparison: Manufacturers and buyers use the results from this standard to objectively compare different foam materials. For example,
  • Extruded polystyrene (XPS) has a lower water absorption rate compared to expanded polystyrene (EPS).
  • Closed-cell polyurethane (PUR) generally performs better than open-cell foams.
• Compliance with building and product standards: Water absorption properties are often a mandatory requirement in the following areas:
  • Building regulations
  • Maritime applications
  • Automotive insulation systems
  • Cold chain packaging

The data from the ISO 2896 standard is frequently referenced by other standards and technical specifications.

This standard is widely used in the following areas:

• Construction (roof, wall and floor insulation)
• Automotive (acoustic and thermal insulation parts)
• Marine (floating equipment)
• Packaging (temperature-controlled transport)
• Manufacturing of household appliances (refrigerators, freezers)

The advantages of using the ISO 2896 standard are as follows:

• Standardized global testing method
• Reliable comparison among suppliers.
• Improved product quality control.
• Better durability estimation
• It supports certification and compliance.

In conclusion, the ISO 2896 standard provides a standardized method for evaluating the water absorption behavior of rigid cellular plastics, a crucial factor affecting insulation efficiency and service life. By measuring moisture absorption, manufacturers can optimize foam formulations, and end-users can select materials suitable for challenging environmental conditions.

In industries where moisture resistance is essential, the ISO 2896 standard is a fundamental quality and performance benchmark.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the ISO 2896 standard.