Metals Associated with Anaerobic Adhesives

Anaerobic adhesives are designed to be metal-sensitive, especially with respect to the mono- or divalent transition metals, e.g. Cu, Fe, Co, Ni, Mn, etc. these elements function by homolysing the hydroperoxide compound into free radicals which initiate polymerisation. It is important to be able to measure trace concentrations (ppb levels) of these metals as such levels may cause instability in these products. Contamination can be caused by raw materials or metal from the plant components used in the manufacturing process. 

Sample preparation of anaerobic adhesives for metal content is an important step, be it by destructive or non-destructive methods. Inactive metal salts are added directly to anaerobic formulations as fillers or for thixotropic reasons. Generally, active transition metals are not added directly to anaerobic adhesives but are prepared as activators in aerosol solvents to be applied to inactive surfaces as part B of an adhesive formulation. In the majority of cases trace metal analysis of anaerobic adhesives is only required for batches with problematic stability and is best done using destructive methods. 

To study methods of sample preparation for metal analysis of anaerobic adhesives the following laboratory-prepared adhesives containing the usual additives and spiked with and without metals were used for comparison  

Note Type of monomer used can vary from basic ethylene glycol mono- or di-methacrylates to complex structures that are beyond the scope of this book. Type of stabilisers, initiators, promoters, colorants, fillers, rubbers and thixotropic agents are propriety to adhesive manufacturing companies. 

10 Destructive Methods of Sample Preparation for Metals Content in 

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Newer adhesives of the acrylic, anaerobic or radiation-curable types must, if they are structural, have a relatively high degree of toughness and durability if they are to compete with or challenge epoxy adhesive systems. Likewise, newer radiation-curable, pressure-sensitive adhesive systems must exhibit the properties of permanence largely associated with cross-linked adhesive masses deposited from an acrylic solution polymer base. Epoxy resin structural adhesives largely define the existing area on the one hand the cross-linked acrylics deposited on plastic or metallic films the other. 

Because they are metal catalysed and polymerise spontaneously in the absence of oxygen, anaerobic materials are ideally suited to the sealing of porosities. Unlike traditional sealing media, there are no volumetric changes associated with solvent loss, nor is heating needed to harden the adhesive. Low viscosity, high-strength products should be used. 

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