Minimising Stabiliser Loss

Because process heating is expensive, lagging is invariably applied to heated process vessels to minimise heat loss, particularly during long-term hot storage. Such adiabatic or near-adiabatic systems are potentially hazardous if materials of limited thermal stability, or which possess self-heating capability, are used in them. Insufficiently stabilised bulk-stored monomers come into the latter category. 

Another concern underlying some of the newer products has been to minimise the loss of stabiliser (and hence loss of durability under outdoor conditions), whether caused by extraction by solvents in pipes carrying fluids, or by chemical decomposition or volatility. One new Cytec UV light absorber, Cyasorb THT, combines a HALS additive with triazine chemistry. The combination was tried partly to reduce loss of additive by migration, but it was foimd to maintain the strength of polyethylene for more than twice as long as some of its competitors. 

In addition, minimising the heat loss over the whole stabilisation zone results in a displacement of the extinction line in the left direction (towards lower fuel mass fractions). Since cooling causes the heat loss to be minimised, cooling efficiency opposes flame stability. 

Ideally, bone substitute materials should be replaced by mature bone without transient loss of mechanical support. Unfortunately, at present there is no material available fulfilling these requirements. Consequently, mechanically unstable bone defects ought to be stabilised with a non-resorbable metallic fixation made from stainless steel or titanium and the bone defect filled with a bone graft substitute. While the mechanical properties of the bone graft substitute are of minor importance, much more important it is to optimise the resorption rate of the bone graft substitute to minimise the time required for bone healing (Bohner, 2010). To control the resorption rate several strategies such as modification of the... 

Diffusion of additives through the polymer bulk and subsequent loss by volatilisation can be reduced in the above examples by incorporating the stabiliser function in a large molecule which is soluble in the substrate. The shape and size of an additive affects its rate of diffusion and rate of volatilisation and in the case of the large compact molecules, both of these are minimised compared with lower molecular weight compounds (e.g. IV, BHT, 1076, etc.). 

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