J. R. Cook

2—PERMANENT-PRESS EFFECTS IN WOOL: PART V: METHODS OF STABILIZING SET

Shrink-resist wool set in the normal way can lose wanted set or acquire unwanted set during machine-washing and tumble-drying because the molecular-bond rearrangements responsible for setting can still occur during the laundering cycle. The set can be stabilized to withstand such laundering by any of the following methods: the inhibition of thiol-disulphide interchange by: removing ionized thiol groups, or converting disulphide bonds to non-interchangeable links, such as —S—, —SCH2S—; the introduction of new cross-links; or denaturation to form structures that are slow to rearrange during washing. The stability of set is enhanced by a combination of the methods because these operate by different mechanisms. Prevention of thiol-disulphide interchange appears to be more important during washing, whereas the presence of cross-links appears to be more important to aid recovery during tumble-drying.

Dimensional Changes Resulting from Pressure-decatizing of Wool Fabric

An investigation is reported of the dimensional changes that occur in wool fabrics as a result of pressure-decatizing. Two ways in which these changes can arise are discussed, both of which depend on the hygral-expansion properties of the fabrics. The way in which dimensional changes can lead to set fabrics with substantial relaxation shrinkage is also considered.

6—SHRINK-RESISTING WOOL FABRIC WITH SILICONE POLYMERS: THE EFFECT OF POLYMER DISTRIBUTION

An investigation of the shrink-resistance that can be obtained with silicone polymers with different initial viscosities is reported. At treatment levels at which shrink-resistance depends on inter-fibre bonding, rather than encapsulation of fibres, the effectiveness of silicone polymers decreases as the initial viscosity of the polymer decreases. The low surface tension of silicone polymers allows them to spread spontaneously on wool fibres, which thereby depletes the amount of polymer available for inter-fibre bonding. This effect is more pronounced with polymers of low viscosity, which can spread more rapidly, and accounts for the relatively poor shrink-resistance obtained with the low-viscosity polymers.

22—SHRINK-RESISTING WOOL WITH SILICONE POLYMERS: THE EFFECT OF ADDED POLYBUTADIENE

Experiments are described which show that the level of shrink-resistance conferred on wool by a silicone polymer can be improved by adding a small amount of polybutadiene and cobalt naphthenate catalyst to the formulation. The presence of the polybutadiene increases the adhesion between the polymer and the wool fibres, and this is thought to be responsible for the improved shrink-resistance. Thermal oxidation and cross-linking of polybutadiene occur readily in the presence of cobalt ions via free-radical reactions, which may well lead to grafting between the polymer and the wool. Such grafting would increase the adhesion of the polymer to the fibres.

19—SHRINK-RESISTING WOOL WITH AQUEOUS SILICONE POLYMERS: THE EFFECT OF ADDED SYNTHAPPRET BAP

The level of shrink-resistance conferred on wool by an aqueous silicone-polymer emulsion (Ultratex ESC/EW) is dramatically improved by adding a small amount of the reactive prepolymer, Synthappret BAP, to the formulation. After high-temperature curing in the presence of catalytic amounts of dibutyltin dilaurate, the treated fabric withstood 20 cotton cycles in a domestic washing machine without felting. The polymer treatment increased the softness and smoothness ratings of the fabric, primarily owing to a pronounced reduction in the variability of surface friction.