Dimensional and surface properties of plasma and silicone treated wool fabric

To improve the dimensional properties of wool fabric, two kinds of silicone polymers are applied to plasma pretreated wool. With this treatment, hygral expansion increases slightly but still remains smaller than that of silicone treated wool without the plasma pretreatment. The wrinkle recovery angles of wool increase with the treatment, and the values of fabric treated with plasma and silicone polymers are higher than those with no plasma pretreatment. In addition, the harsher handle imparted by plasma modification is improved with silicone treatment. The results show that the plasma pretreatment modifies the cuticle surface of the wool fibers and increases the reactivity of the wool fabric toward silicone polymers. Therefore, the combination of plasma and silicone treatments can improve the dimensional stability, wrinkle resistance, and performance properties of the wool. Surface smoothness of the treated fabrics as measured with a new evaluation system shows good correspondence with results from a KES-FBa surface tester.

For many years, dimensional instability of woven wool fabrics has been a problem for garment makers. Fabric dimensions can change during garment making or subsequently during wear as the fabric is subjected to different humidity conditions, including steaming. This is the major cause of seam puckering, poor pattern matching at seams, changes in the intended garment size, and other garment distortions such as waviness at edges and sagging.

The properties that are most important in the dimensional stability of a fabric are relaxation shrinkage and hygral expansion. Other measures of dimensional stability, such as locked-press shrinkage, tend to be complex mixtures of relaxation shrinkage and hygral expansion.

Hygral expansion is a reversible change in fabric dimensions brought about by moisture absorption by the wool fibers. The phenomenon is highly wool-specific, and its study has gained impetus with the recent trend of light-weight, all-season woolens [7].

The mechanism of hygral expansion has been extensively studied by several researchers, notably Baird, Cednas, and Olofsson, among others, and is now understood to originate from changes occurring in the yam crimp radius [1, 5, 15]. Radial swelling of individual fibers upon moisture absorption induces a crimped yarn to straighten within the weave structure [8, 9, 19]. However, because of the complexities involved and the subtle interactions of the various factors controlling the dimensional stability of wool fabrics, the topic is not easy to explain or discuss, nor can the subject be properly treated in a few papers.

In earlier papers, we reported that organofunctional silicone polymers were able to improve the dimensional properties of wool fabric [10]. Treatment with a mixture of aminofunctional and epoxyfunctional silicone polymers improves the performance properties of wool fabric as well as the dimensional stability.

In order to enhance the reactivity of silicone polymer with wool and to increase the uniformity of its distribution, it is good practice to increase the wettability and anionic character of the wool surface. Low temperature plasma treatment by glow discharge is of interest as an effective technique for modifying the polymer surfaces, particularly oxidative plasma treatments, which can create new anionic groups, such as sulphonate and carboxylate, and improve the wettability of wool fibers [4, 14]. Therefore, we expect that the reactivity of the wool fabric surface to chemicals will be enhanced with the plasma treatment.

In this study, we investigate plasma pretreatment of wool fabric to increase its reactivity with silicone polymers. The fabrics are pretreated with O^sub 2^ low temperature plasma and subsequently with silicone polymers. We evaluate changes in the mechanical and dimensional properties of the wool. In addition, we examine changes in performance properties, such as tear strength and breaking strength, fabric hand, and surface smoothness appearance with the application of plasma and silicone polymers.

Experimental

A scoured and crabbed plain weave worsted fabric (150 g/m^sup 2^) with 62 ends/inch and 64 picks/inch was used for the experiments. The silicone softeners selected for testing included Dow Corning(R) 108 emulsion as an aminofunctional silicone softener, and Dow Coming(R) 4592 and hydrophilic Dow Corning(R) 193 as epoxyfunctional silicone softeners. Triton X-100 was the wetting agent. All other chemicals were reagent grade and used without further purification.

FABRIC TREATMENTS

After air-cleaning, the wool fabric was oxygen plasma treated in plasma equipment manufactured by Vacuum Science Co., as shown in Figure 1. This apparatus consists of four main parts-a high vacuum pump, a gas-feeding part, a radio frequency generator, and a reaction chamber. With the radio frequency generator, the frequency of the electric field was held at 13.56 MHz and its maximum power was 600 W.

To process the wool fabric, the reactor chamber, 380 mm in diameter and 250 mm high, was first evacuated to less than 0.1 torr, then injected with 99.9% pure oxygen gas at a 50 cc/min flow rate. Samples were then treated by plasma discharge at different power levels of 50, 100, and 150 W for 60 seconds. Finally, the fabrics were conditioned prior to the pad-dry-cure process.

The wool samples were then impregnated in an aqueous bath (bath ratio = 1:10) containing silicone polymers (2% owf) for 2 minutes and padded to 80 +/- 3% through squeeze rollers under 1.5 kg/cm^sup 2^. The padded samples were dried at 100 deg C for 3 minutes, followed by curing at 130 deg C for 3 minutes, then rinsed with fresh water and air-dried. Samples were stored under standard conditions (21 deg C and 65%RH) before other properties were evaluated.

MEASUREMENTS

The KES-FB system was used to test the fabric mechanical properties of samples under standard conditions, and sixteen fabric mechanical properties were obtained for each sample. The fabric primary hand values for men's summer suitings were then evaluated [13]. Hygral expansion induced into the fabric during the process was evaluated by Shaw's test method [18]. The performance properties of treated samples were evaluated using standard procedures, including wrinkle recovery angle (WRA) (AATCC 66-1978), breaking strength (ASTM D-1682-64), and Elmendorf tearing strength (ASTM 13- 1424-81). All measurements were repeated for the five samples with the same treatment and averaged. Surface morphology of the wool fabrics was evaluated with a scanning electron microscope (Jeol Ltd., JSM-35) after coating with gold in a vacuum. Surface analysis by electron spectroscopy for the chemical analysis was carried out with an ESCA MK 11 (LVG Scientific Ltd.) by irradiating a sample with monoenergetic soft x-rays and analyzing the energy emitted by electrons.

Results and Discussion

SURFACE MODIFICATION BY PLASMA PRETREATMENT

The major changes brought about by the exposure of wool fibers to plasma are in surface wettability, molecular weight of the surface layer, and chemical composition of the surface. For the most part, the effects of the plasma treatment on wool fibers are confined to the surface layer 1-10 (mu)m deep. As a result, the bulk properties of the treated fibers remain unchanged [17, 20].

EscA has been used with wool fibers by a number of researchers, who directed most of their interest and attention to the changes in the S^sub 2p^ spectrum after various oxidative treatments [3]. Millard showed that the sulfur peak in untreated wool fibers occurred at a binding energy level of 164 eV, corresponding to cystine, but when wool was exposed to an oxidizing plasma or corona discharge, a second peak appeared at approximately 168 eV, corresponding to cysteic acid (R-SO^sub 3^H) groups [14]. In Figure 2, therefore, the second peak of sulfur observed at 168 eV corresponds to cysteic acid groups induced by 02 plasma treatment.

Peak deconvolutions of the C^sub 1s^ spectra of wool fabric are shown in Figure 3. Wave separation is divided into three components, assuming that peak I at 283.5 eV corresponds to --CH, peak 2 at 285.5 eV to --CO-- and --CN--, and peak 3 at 287.3 eV to --COO-- and --CON-_ [14]. It is clear from Figure 3 that 02 low-temperature plasma treatment of wool fibers increases peak 2 and peak 3 compositions considerably, and their relative intensities are summarized in Table I. Thus, the oxygen atoms induced on the wool surface might exist in the form of --C--O-- and --COO--, appearing to play an important role in increasing the hydrophilicity of the wool surface.

MECHANICAL PROPERTIES OF TREATED WOOL