IMR Materials Testing Technical Blog

4 Chemistry Tests for Determining Non-Metallic Materials Properties

Determining the beneficial characteristics and potential limitations of your material in advance of production can be a crucial step toward the ultimate success of your design. The presence of unexpected trace elements occasionally occurs due to environmental exposure or other factors. The presence of trace constituents may alter the predicted properties and performance of a material.

These 4 basic tests reveal important data for evaluating your non-metallic material.

Density/Specific Gravity

Specific gravity is defined as the ratio of the density of the substance in question to the density of a reference substance at a specified condition of temperature and pressure. This is accomplished by measuring the mass of a unit volume of a composite or polymer in a standard lab atmosphere and again while the material is submerged in water. A substance with a specific gravity of <1 will float in water.

The specific gravity of a composite material is actually the specific gravity of the raw polymeric material used in fabrication. Because polyethylene and polypropylene have specific gravities in the range 0.90–0.96, they will float, which must be considered if the final product’s operating environment is exposed to water.

Acid Digestion

Digestion of samples in acid helps to remove impurities/interference, bring unwanted metals existing in nonmetallic materials into solution as ions and make the sample readable by the analytical instrument.

The general approach is to grind or cut any accessible component part of a sample into small pieces or a powder; digest an aliquot completely in nitric acid, or for siliceous products, in a combination of hot, concentrated nitric and hydrofluoric acids; and analyze by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Other analytical methods, such as Inductively Coupled Plasma – Mass Spectrometry (ICP-MS), Flame Atomic Absorption Spectroscopy (FLAA), and Graphite Furnace Atomic Absorption Spectroscopy (GFAA), maybe used, under appropriate conditions, as an alternative to ICP-OES, using applicable, recognized analytical techniques for the alternative analytical method. 

Melt Flow Testing

The melt flow index (MFI) or melt flow rate (MFR) is a measure for the ease of flow of melted plastics. It is often used in the plastic industry for quality control of thermoplastics. The method is described in the standards ASTM D1238 and ISO 1133.

In general, a higher MFI indicates a lower material viscosity.  A lower melt flow rate corresponds to a higher molecular weight and/or less branching when comparing polymers of the same class.

The melt flow indexer is the most popular device in the plastic industry to determine material viscosities and is often used to test batch-to-batch consistency. However, it is also the least accurate method. To obtain more accurate and meaningful viscosity data, a capillary or a cone and plate rheometer should be used. Some companies will also perform in-mold rheology tests using actual manufacturing molds.

Flammability Testing

Tests are designed to evaluate ignition susceptibility, burning propagation, or combustion characteristics of non-metallic materials under a range of pressure and temperature conditions. 

Analysis of test results will reveal the ignition temperature, time to reach ignition, the rate of flame spread, the rate of combustion or rate of material loss, rate of heat liberation, heat transfer from flames, the evaluation of smoke, the measurement of smoke density, and the evolution and toxicological effect of the products of combustion.

For more information on IMR’s Chemical Analysis of Non-Metallic Materials capabilities, click here.

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