Executive Summary
A review of the literature relating to flow aids, their application and their testing has been undertaken with the objective of improving both the speed and efficiency of the selection procedure.
The selection of a suitable flow aid is comparable to arranging a marriage and potentially just as difficult. Finding a legal and lasting coupling is always hard but in the case of flow aids it is traditionally complicated by being a last minute arrangement when the host powder can no longer flow on its own.
A dossier of commercially available aids and their properties has been compiled and successful instances of both historical and current liaisons delivered. Such a record is useful but cannot provide a guide to all future relationships.
A more fundamental selection procedure requires a careful knowledge of the tendency of the partners to form a stable bond together while at the same time moving freely within a powder society. The complex interplay of the forces between the flow aid and the bulk powder has been documented and needs to be understood if a correct choice of aid is to be made.
Current developments put an additional demand on the flow aid partner. When added to a multi-component mixture the aid has the potential to displace other active ingredients and damage mixture quality. Pre-mixing or sequential addition may then be necessary. 'Add-on' qualities are also in demand with the aid being asked not only to promote flow but also to add some colour, a perfume or some additional quality to the bulk mixture. Such demands add complexity to the selection procedure but give added value to the flow aids having the required flexibility of application.
The effectiveness of a flow aid addition to a process will almost certainly require practical assessment and suitable methods are reviewed as are methods of conditioning the bulk powder.
In the interests of better marriage guidance a logic structure is proposed which will sequentially pose questions about the host powder, the flow aid and the method of testing.