Secondary components and ratio trimmers

A blend usually has one component at load and two or three at a fraction of it. The minor components are where selectivity comes from, and they are also where a specification quietly degrades — not because the material is impure, but because the ratio between them moves.

Why minor components are harder to hold

Three reasons, none of them about assay. First, a small absolute error is a large relative error: half a percent on a component dosed at two percent is a quarter of that component. Second, minor components are often the ones with the awkward chemistry — an aldehyde that oxidises, a conjugated diene that polymerises — so they age faster than the material carrying the load. Third, they are usually weighed in smaller portions, which multiplies handling error in the blending house.

What a supplier can and cannot control

We can hold the composition of each lot and report it on the certificate. We cannot hold the ratio of your blend: that is set when you weigh, and it depends on your balance, your clean-down and your operator. The useful division of labour is that the certificate defines what went into the drum, and your batch record defines what came out of the blend.

Practical controls

• Keep the minor components in their original containers until weighing; decanting into smaller unlabelled units is where identity is lost.
• Weigh minor components on the smallest balance that will take the container, not on the one that happens to be free.
• Record the lot number of every component on the blend batch record. Without it, a later comparison of catch has nothing to compare.
• Where a component is sensitive to air, weigh it last and close the container immediately.

When to re-specify rather than re-order

If a blend has been stable for several seasons and then stops working, the usual suspects in order are: dispenser ageing, a supplier change on a minor component, and a formulation change nobody wrote down. Re-specifying the minor components is cheaper than reformulating the blend, and it starts with the certificates rather than with a new trial.

Minor components are drawn from every class in the catalogue — alcohols as modifiers, aldehydes for early release, ketones and spiroacetals where a blend needs to differ from a straight alcohol lure.

Ask which components carry the risk in your blend