Having worked for several years in the field of plastics, we’ve noticed that the technical data sheets provided by manufacturers often lack information or don’t follow a model that facilitates the comparability of characteristics among various materials.

This situation becomes even more critical when performing a failure analysis, where it’s necessary to accurately define the material’s performance under real-world conditions.

Let’s understand the reasons behind this problem and how to recognize the reliability of material characteristics reported in a technical data sheet.

Why are data sheets often lacking?

The main reasons we encounter difficulties when analysing data sheets are methodological, commercial, scientific, and economic in nature. Let’s detail them below.

Intrinsic complexity of polymers. The viscoelastic nature of polymers means that their properties depend heavily on temperature, load application time, and deformation rate. Presenting a complete set of data covering all these dependencies would be extremely complex and voluminous. Additionally, the presence of additives, compounds, and variability between production batches induced by small variations in the manufacturing process or raw materials can lead to substantial differences in final properties. Each formulation is unique, and data sheet values are often average, not guaranteed.

Costs of tests and certifications. Performing a wide range of tests, especially long-term ones (e.g., aging, creep), is costly and time-consuming. Manufacturers must balance the cost of testing with the perceived value to the customer.

Technical or commercial document? The data sheet is often seen as a sales/marketing document as much as a technical document. Its primary purpose might be to facilitate an initial selection rather than to provide all the data necessary for detailed design.

Aspects to include in a data sheet

Chemical composition of plastics

The very first factor to look for in a plastic material is its chemical composition. ISO 11469 and ISO 1043-1 standards provide a uniform marking system that allows us to identify single-constituent products (homopolymers or copolymers), polymer blends, and any recycled content present in the material.

Examples:

Single constituent: polyethylene >PE<

Single constituent with 20% recycled content: >PE(REC20)<

Blend of polyethylene and polypropylene: >PE+PP<

Blend of polyethylene with 20% recycled content and polypropylene: >PE(REC20)+PP<

The presence of additives transforms a polymer into a plastic material, drastically modifying its properties. To get information on the type and quantity of additives, other standards in the ISO 1043 series propose a method for identifying fillers or reinforcing agents, plasticizers, and flame retardants.

Examples:

Polypropylene with 30% glass fiber: >PP-GF30<

Polyvinyl chloride containing dibutyl phthalate as a plasticizer: >PVC-P(DBP)<

Polyamide 66 containing aluminum hydroxide as a flame retardant: >PA66-FR(60)<

Warning! The standards do not completely cover the myriad of additives we can find within plastics: pigments and colourants, nucleating agents, antioxidants, lubricants, antistatic agents, etc., can be added to improve material performance and processability, but they are not always free of side effects (consider, for example, potential migration in products intended for contact with food) and are rarely declared in technical documentation.

Technological properties of plastics

Beyond chemical composition, it’s essential to consider the technological properties of materials during selection. Each property category will be more or less important depending on the product’s intended use. ISO 10350-1 identifies a series of test procedures based on international standards for characterising plastics.

The property categories considered are:

Rheological properties: while these don’t include a complete rheological characterisation, measuring the Melt Flow Index (MFI) and shrinkage for moulded components provides a solid starting point for understanding melt behaviour during the production process. Some granule manufacturers also include graphs of viscosity as a function of shear rate and temperature, along with processing recommendations, in their data sheets.

Mechanical properties: this involves measuring short-term mechanical characteristics (tensile, flexural, and impact) as well as long-term properties (viscoelastic creep). The latter is often overlooked but is fundamental for preventing premature failure of plastics subjected to continuous loads. Although not covered by ISO 10350-1, many applications require information on how a plastic behaves under dynamic loads: in this case, knowing the loss factor (tan δ) is also very important.

Thermal properties: when discussing thermal properties, it’s common to only consider a material’s ability to transmit heat or insulate. However, a plastic’s behaviour is strongly influenced by temperature, so it’s important to know the maximum temperatures at which a given load can be applied (Vicat and deflection temperature under load), the coefficient of expansion, and flammability. Finally, Differential Scanning Calorimetry (DSC) allows us to measure the melting range, glass transition temperature, and, for a careful observer, the degree of crystallinity and other characteristics related to the material’s structure.

Electrical properties: many plastics are used as electrical insulators. For such applications, relative permittivity, dissipation factor, resistivity, and dielectric strength are crucial.

Physical properties: density and water absorption are other physical properties of practical importance that are normally evaluated.

Treeing in an electrical insulation. Ref. Plastics Failure Guide Cause and Prevention 2nd Ed., Hanser.

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