The reorganization of cellulose fibers by swelling treatments in alkali solutions results in numerous changes to fiber structure, causing changes of chemical reactivity in the fiber‐solution heterogeneous system. An important part of the change in chemical reactivity is the change of fiber accessibility because it results in exclusion of chemicals such as reagents or catalysts from the fiber. In the second of a two‐part series of papers, we examine the influence of changes in fiber accessibility and/or reactivity due to treatment in swelling solutions on the performance or behavior of substrates during and after chemical finishing treatments. Changes in fiber accessibility due to alkali treatments are visualized with fluorescence microscopy. The effect of alkali treatments on enzymatic hydrolysis and pad‐dry‐cure crosslinking treatments of cellulose substrates are discussed as representative examples to demonstrate the effects of swelling processes on fiber reactivity and accessibility. Model calculations indicate that a considerable redistribution of chemicals in substrates occurs during dry‐cure operations resulting from molecule‐specific exclusion effects. Pilling tests on lyocell knit‐fabrics show the impact of preceding alkali processes on the final physical performance of textile fabric highlighting the importance of correct selection of alkali processes to achieve desired behavior.

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Lyocell fabrics were pretreated with NaOH, KOH and LiOH and subsequently crosslinked with three urea-formaldehyde based crosslinkers DMDHEU, DMeDHEU and DMU. The mechanical properties varied with the alkali concentration in fabrics crosslinked after pretreatment with 2-8 mol/l NaOH and 4 mol/l LiOH. In fabrics crosslinked after pretreatment with 2-8 mol/l KOH and 1-3 mol/l LiOH, in contrast, the mechanical properties were relatively insensitive to the alkali concentration. The difference in effects is attributed to the alkali influence on the accessibility of crosslinker in fiber structures. The NaOH and 4 mol/l LiOH pretreatments increase the accessibility of crosslinker but the KOH and 1-3 mol/l LiOH pretreatments do not appear to change accessibilities to the same extent. The results underscore the importance of alkali choice and process control in the pretreatments of lyocell. Both NaOH and KOH may be used to good effect. However, lyocell is more sensitive to changes of alkali concentration in NaOH treatments as compared to KOH pretreatments. Thus, the use of NaOH in pretreatments of lyocell will require a greater degree of monitoring and control of alkali concentrations as compared to when KOH is used.

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Lyocell fabric samples were pretreated with 2-8 mol/L sodium hydroxide (NaOH) and then resin-finished with dimethyloldihydroxyethylene urea, dimethyl dihydroxyethylene urea, and dimethylol urea based products. The resin-finishing treatments caused changes in the substrate properties, such as reduced accessibility, improved crease recovery, and reduced work of rupture and abrasion resistance. Differences were observed between resin-finished substrates as a function of the crosslinker type, and they were attributed to the influence of the crosslinker content and crosslink length in the substrates. The alkali pretreatments influenced the effects of resin finishing. A significant enhancement of the crosslinker penetration appeared within the substrates pretreated with 4 mol/L NaOH. Pretreatments with 6 and 8 mol/L NaOH also enhanced the crosslinker penetration, but the depth of catalyst penetration appeared to exceed that of the crosslinker; leading to demixing between the two components within the substrates. The penetration depth of a direct dye, C.I. Direct Red 81, appeared lower than that of the crosslinker in the alkali-pretreated substrates. Pretreatments with NaOH in the range of 4-8 mol/L appeared to create gradients of accessibility within fibers and yarns of lyocell fabrics, with the depth of reagent penetration increasing in the following order: C.I. Direct Red 81 < crosslinker < catalyst.

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