Case study - Synergic Chemical Analysis:'There's no smoke without fire — or is there?'

A series of case studies illustrating how access to Sophisticated Evolved Gas Analysis can provide manufacturers with information about the gases evolved when materials are heated.

The thermal oxidation of a printed circuit board

Printed circuit boards (PCB's) are used in virtually everything we take for granted in modern life, for example cars, Phones, televisions, radios and computers. They are cheap to produce and offer speed and compactness that was not previously possible. Printed circuit boards are generally constructed from a resin (e.g. epoxy, polyimide and cyanate esters) reinforced by a fabric cloth, usually fibre glass. In domestic fires, commercial incinerators, or processing where high temperatures can be achieved such as
cutting, it is important for manufacturers to be aware of the type and identity of the gases evolved.

Synergic Chemical Analysis facility

The sophisticated evolved gas analysis facility has been used to identify the major gases evolved during the catalysed and uncatalysed degradation of polyethylene (PE) when it is heated under controlled conditions. The heart of the system is a sensitive balance which records the weight lost as a asample is heated at a fixed rate. The gases evolved from the sample are passed through two transfer lines. The first takes the sample directly to a mass spectrometer, which smashes the gas molecules apart and looks at the resulting characteristics breakdown pattern. The second takes the gases to a trap where they are collected and then seperated, identified and quantified using a gas chromatograph linked to a second mass spectrometer.

Both detection systems, which are very powerful in their own right, become awesome when used in combination.

Results

Figure 1 shows the weight loss curve for the thermal oxidation of a printed circuit board. Some information about the weight of material lost can be derived from this curve.

Usually, from this data alone it is not possible to obtain any information about the type of molecules being produced. However by using mass spectroscopic techniques we have been able to what compounds are evolved during each weight loss.

The chromatographic separation of the mixture of gases evolved from the printed circuit board is shown in Figure 2.

Each peak in Figure 2 represents a single component of the mixture evolved during the high temperature oxidation of a printed circuit board, the main products of which are brominated phenols and aromatics and other non-brominated aromatics.

Each component can be identified by its characteristic mass spectrum.

For example, the starred peak has been identified as 4-bromophenol and the mass spectrum for this compound is shown in Figure 3.

Full analysis of the numerous gases evolved when the printed circuit board was heated up to 1100 degrees celsius identified a number of molecules of varying toxicity including carbon dioxide, carbon monoxide, xylene, alkyl and brominated phenols, brominated benzenes and other brominated hydrocarbons. Figure 4.

Potential uses of the evolved gas analysis facility

The combinaton of chemical analysis techniques represents a powerful analytical facility which will benefit a wide range of companies, large and small, whether they are involved in routine quality assurance, failure analysis or the development of new products and materials.

The synergy system is a unique state-of-the-art facility which has enormous potential in a wide range of market sectors including:

• environmental pollutants and contaminants
• oils and petrochemicals
• paints, coatings and adhesives
• catalysts
• polymers and plastic/resins
• ceramics and composites
• fibres, fabrics, rubbers and foams
• packaging laminates
• aqueous solutions and dispersions
• soaps and surfactants
• body fluids
• food analysis