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Aesthetics

Aluminum hydroxides can be used to give desirable translucent effects, similar to marble and onyx in some solid surface applications and are widely used for this. The information on formulations is largely proprietary, but dispersants and coupling agents are widely used to maximize performance.

Abrasion Resistance

Thermoset polymers such as PMMA are widely used in solid surface applications and, where these need good wear resistance, such as in kitchen sinks and worktops, then hard fillers such as quartz and cristobalite are used. In other instances (e.g., vanity basins), the ability to polish out scratches means that relatively soft fillers, such as aluminum hydroxide, are employed. As described above, these also have aesthetic advantages.

Toughness

Thermoset polymers are quite brittle materials and this is one reason for the prevalence of glass fibers in their composites. Although not generally one of their main functions, rigid, particulate fillers may also increase fracture toughness. This is a complex topic, well covered by Jackson et al. (2003). In general the improvement is thought to originate from crack pinning by the particles and is most noticeable with smaller particle size and with good particle to matrix adhesion. The strength of the particulate additive also appears to be important in determining whether significant toughening is achievable. Weak particles, especially those that can be readily cleaved, such as talc, aluminum hydroxide and mica, can actually act as the loci for failure.

Fatigue strength can also be important in some thermoset applications (such as the solid surface applications referred to under abrasion resistance). Again it is a complex topic, with both static and dynamic fatigue and environmental factors (e.g., wet or dry) to be considered. It is not frequently addressed in the literature, although the work by Jackson et al. (2003) referred to above gives a good introduction. Environmental factors, especially water, can have a profound effect and lead to accelerated failure, with good interfacial adhesion, such as provided by coupling agents, playing an important stabilizing role.

 
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