Silk fabrics

In contrast to wool, in silk the acid nature of the proteinic substance (fibrion) predominates, which can permit whitening with acid and basic type of brightening agents. However, for silk direct brightening agents are preferred. 

Polyester fibres have no affinity for the water soluble optical brightening agents and thus water insoluble compounds are applied to polyester from dispersion in the same manner as disperse dyes by the formation of a solid solution in the fibre. These brightener particles penetrate into the fibre in a state of molecular dispersion and they are held in the fibre by Van der Waal s forces. A part of the finely dis- 

In the thermofixation process the fabric is padded with 5-25 g/I dilute suspension of optical brightening agent at room temperature with a liquor pick-up of approximately 50%, dried at about 120°C in an open stenter and then heated for 30-60 sec at 190-200°C. Finally, the goods are washed and dried. This process makes possible higher thoroughput of material with superior dimensional stability. 

In the pad-steam process the goods after padding with a liquor pick-up of about 80% are steamed at 100-101 C for 2-3 h or under pressure (1-1.5 kg/cm-) for 25-30 min. Alternatively, the goods may be thermofixed by superheated steam at 150-170°C for 3-5 min. 

With acid dyeing type, the goods are treated on jiggers or winch beck with a solution containing high affinity type brighteners (0.05 to 0.5%) and acetic or formic acid (pH 3.8 to 4.5) at 40°C for 10 min and then the temperature is raised to boil in 15 min and the treatment is continued for 30 min. The goods are rinsed and 

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The feeling of a spider web may be unsettling, but a similar natural material has been used for centuries to make silk fabric that is prized for its smooth texture. Silkworms produce the silk fibers used to make clothing. They feast on mulberry leaves and convert the molecules from these leaves into silk, from which they spin cocoons. 

The discovery of silk in China occurred many centuries BC, and by the time of the Roman empire, silk fabric was a prized trade commodity. The caravan routes across Asia became known as the Silk Roads. It is estimated that nearly 90% of the imports into the Roman Empire consisted of silk goods. 

Silk. Silk, the only natural fiber that comes in filament form, has been and still is one of the most appreciated and valued textile fibers. Silk filaments are secreted by the larvae of several types of silk moths to make their cocoons. Most silk is derived, however, from the larvae of the Bombyx mori moth, which has been widely cultivated in China for over 5000 years. Fragments of silk fabric dated to the late fourth millennium b.c.e. were found at Qianshanyang, in the province of Zhejiang, in China. There are, however, even earlier indications of the use of silk silk remains were found together with an eleventh-century b.c.e. mummy in Egypt, probably also providing evidence of ancient trading routes between the Far and Middle East. 

A. Kurahashi, A. Itaya, H. Masuhara, M. Sato, T. Yamada, and C. Koto, Depth distribution of fluorescent species in silk fabrics as revealed by total internal reflection fluorescence microscopy, Chem. Lett. 1986, 1413-1416. 

The products most often prepared, sometimes with considerable quantities of dressing, are those of cotton. Silk fabrics are also heavily dressed, but in this case it is not a mere superficial layer of extraneous matter, since the substances constituting the so-called weighting of silk are, partially at least, incorporated in the fibre (sec later Weighting of Silk). 

Mixed cotton, wool and natural silk fabric. 

If this shortened method is employed, the following rules must be followed in cotton and wool fabrics, the cotton is determined for preference as in case 1 (6) and the wool calculated by difference. In cotton and silk or wool and silk fabrics, the silk is determined for preference in the manner described in case 2 (c) and the other component calculated by difference. In cotton, wool and natural silk fabrics, the silk (2,c) and cotton (1,6) are determined for preference and the wool calculated. 

The objective of this work is to screen stabilizers for their effectiveness in slowing or preventing the degradation of silk fabric. The treated fabrics were then subjected to accelerated aging... 

Fabric. The silk fabric used in this work was an unweighted plain woven Chinese silk habutae (Testfabrics, Inc., Middlesex, NJ, style 605) having 126 ends/in. (37.6 denier), 117 picks/in. (32.6 denier) and weighing 1.11 oz./yd. The fabric as received had been degummed [1]. All fabric samples were taken from the same bolt. 

Table VII. Ammonia Content ( lmol/g silk) After Artificial Aging of Fabrics in Sets A and B.(4 Days at 150°C or 8 Days Light Exposure, Control Silk Fabric - 9.6 )...

Materials. The modern silk fabric tested was Testfabrics style 607 broadcloth, degummed but undyed and unbleached. The fabric yarn was 140/2 cotton count and the warp and filling threads/0.01 m are 40 and 33, respectively. Fabric weight was approximately 56 gm/m. ... 

Humidity levels were maintained at <5%, 50%, 70% or 90% +2% RH and a constant temperature of 90°C for a fixed time of 17 days. Samples of historic silk fabric were exposed at 90 °C and 80% RH for either 10 or 30 d. ys to induce further deterioration of mechanical properties. These materials were then coated with 1 and 5 Jim of Parylene-C. Silk samples were loosely affixed by sewing to temperature-resistant coarse polyester mesh which allowed both free air flow and also avoided contact between the metal and the fabric surfaces during the thermal aging tests. 

Light Exposures. Silk fabric samples, 0.25 m x 0.17 m, were mounted in Atlas Electric Devices aluminum sample holders according to AATCC Test Method 16E-1982 (7). An Atlas Ci-35 Weather-Ometer xenon-arc was used on continuous light cycle. Exposures were conducted at an irradiance of 0.35 W/m2 measured at 340 nm and the irradiance was monitored and controlled automatically. Borosilicate inner and outer filters were used to simulate the solar spectrum. The relative humidity was maintained at 65% and the black panel temperature was 50°C. The actual fabric temperature during the irradiation was measured, using small thermocouples threaded into the fabric, and was found to be 35 C. Control samples for these tests were kept in the dark at 35°C and 65% RH for the same time period as the illuminated samples. 

Samples of coated and uncoated silk fabric were removed at various intervals up to an exposure of 605 kJ at 340 nm. Maximum exposure of coated cloth was 242 kJ (340 nm). In addition, for a fixed total energy of 86 kJ (340 nm), the irradiance was maintained at 0.42 W/m2, 0.35 W/m2, and 0.28 W/m2 to evaluate reciprocity effects. Samples of both types of historic silk were exposed to 100 kJ (340 nm) and 360 kJ (340 nm) to induce additional deterioration. These highly exposed samples were coated with both 1 and 5 im of Parylene-C. 

Fabric color was determined with a Diano Matchscan 2 spectrophotometer. The reflectance spectra from 380 to 700 nm were measured over three layers of unexposed silk fabric using a small area of view (SAV). CIELAB color coordinates (L, a, b ) were calculated with the Matchscan software. 

Calculations. The stress-strain curves for the silk fabric were plotted automatically from the data obtained with the Instron. The initial modulus was determined from a suitable straight line portion of the stress-strain curve. The strain-to-break was then calculated with an effective gauge length determined from extrapolation of the initial modulus. The energy-to-break was calculated from the integrated area under the corrected stress-strain curve to the break point. 

Table 1. Tensile Properties of Coated and Uncoated Modern Silk Fabric...

To determine the effect of coating thickness on tensile properties, coating thicknesses of 0.25, 0.5, 0.75, 0.85, 1.0, 1.25 and 1.5 im of Parylene-C were applied to modern silk fabric. In Table 2, the breaking-load and strain-to-break are shown as a function of coating thickness, and a linear dependence is evident. A similar effect was observed when paper was coated with Parylene-C (5). 

Thermal Exposures. The thermally Induced changes in tensile properties of coated and uncoated silk fabric, expressed as percent retained breaking-load, strain-to-break and energy-to-break in Figures 2,3, and 4, respectively, are shown with the lines representing the calculated exponential decline. 

Coated silk was not tested at 150 °C because Parylene-C undergoes a markedly increased degradation when heated above 135°C. Because initial observations on the discoloration of silk fabric indicated a change in the nature of the degradation reaction at temperatures above 110°C, calculations were performed both including and excluding the 150 C data. 

As can be seen in Table 4, the "activation energy" derived from the series of exposures that includes silk fabric heated at 150°C predicts a half-life for the strain-to-break of 85 years at 20°C. The half-life at 20°C calculated from the series of exposures that covers the 70°C to 110°C range is markedly different, only 32 years. Such a large effect produced by inclusion of only one data point indicates that results obtained at this temperature may be suspect. By definition, the activation energy must be independent of temperature over the range of extrapolation. 

Tensile data obtained on silk fabric as a function of relative humidity at a fixed temperature level and time interval are shown in Figure 5. Between 0% and 50% RH, very little measurable change in properties was observed. Above 50% RH the degradation rates increased rapidly with increasing RH. Parylene-C also had no effect on the degradation rates of silk exposed at these RH levels. 

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