Jeanette M. Cardamone

Digital Image Analysis for Fabric Assessment

Conventional methods of fabric inspection are tedious and require close association. In this work, digital image analysis for fabric assessment (DIAFA) is applied to modem and historic fabrics. Fabric images are divided into arrays of pixels with peak intensities distributed over gray scale ranges (histograms) and along constructed lines (line profiles). Fabric cover is measured by segmenting a histograms B/w pixels, yarn spacing, and yarn thickness from moving point averages by calculating the breadth of a peak corresponding to an individual yarn at half the maximum peak height for a given line profile. The results show very good agreement with known values (r = 0.919, n = 30, p < 0.01). Fourier power spectra provide facile measurements of yarn parameters in close agreement with the results from line profiling. With DIAFA, a small tool kit is developed to assist in the objective analysis of the structural integrity of fabrics in the museum environment, and it could be very useful in advancing automated fabric inspection.

DCCA Shrinkproofing of Wool Part I: Importance of Antichlorination

Dichlorodicyanuric acid (DCCA) is one of the oldest chlorination reagents for imparting shrinkage resistance to wool. It is commonly used in the Hercosett® shrink-proof process in which certain reactive and cationic polymeric resins are applied to wool. We further investigate the use of DCCA and the importance of the subsequent antichlorination step to document the ensuing changes in fiber morphology and fabric properties. We use DCCA alone in a range of concentrations from 5 to 40% owf. Treatments with 5% applied at 30°C for 60 minutes from a citric acid buffered system, pH 4, followed by antichlorination with hydrogen peroxide or hydrogen bisulfite show small increases in alkali solubility and in bursting strength. Less than 2% chlorine is detected in 5 and 20% DCCA/antichlorinated spent baths. The 5% DCCA/hydrogen peroxide treatment improves shrinkage resistance by 54% and whiteness by 63% when compared to untreated fabrics. Structural changes in the exocuticle increase with increasing DCCA concentrations to the point of complete scale smoothing. Following the extent of oxidation with a broad range of DCCA concentrations and the effect of antichorination on 5 and 20% DCCA treatments provides useful informa tion for designing alternative systems to control shrinkage.

Controlling Shrinkage in Wool Fabrics: Effective Hydrogen Peroxide Systems

Alkaline hydrogen peroxide (H2O2) systems, including dicyandiamide, gluconic acid, and Triton X surfactant, used alone or followed by enzyme treatments, are investigated for their effectiveness in imparting shrinkage resistance to wool fabrics. Fractional factorial analysis shows that H2O 2 is the most important factor and enzyme the second contributing factor in shrinkage control. An effective H2O2, nonenzymatic system with Triton X-114 limits structural changes to surface smoothing of the fibers and yields a relative area shrinkage of 2.95%. Another effective H2O2 system, using the same pretreatment but followed by an enzymatic treatment with additives—polyacrylamide to restrict enzyme activity to the fiber surface and sodium sulfite to reduce disulfide linkages—yields 1.16% area shrinkage. The most important factor in shrinkage control is replacing the hydro phobicity of the wools surface with an anionic charge through the formation of cysteic acid. This leads to the release of 18-methyleicosanoic (18-MEA) acid from the fiber surface and underlying cell membrane complex attached to the surface scales of wool through thioester linkages. TLC, FTIR, and EI-MS are used to prove the presence of fatty acids and 18-MEA in spent baths and in extracts of the treated fabrics. Imparting hydrophilicity to wool by conferring an anionic charge suggests new possibilities for wool reactivity.

Combined bleaching, shrinkage prevention, and biopolishing of wool fabrics

In earlier work, we established that alkaline hydrogen peroxide systems that include dicyandiamide, gluconic acid, and Triton X surfactant, used alone or followed by enzyme treatments, control shrinkage in wool fabrics to 3.0% and 1.2%, respectively. We have perfected this system for complete shrinkage control with no loss in mechanical properties by using the same pretreatment and enzyme applied from a buffered triethanolamine solution that incorporates sodium sulfite. Fabrics treated by this method are bright white and exhibit a soft handle with a smoothed surface. Digital image analysis is used to quantify fiber projections above the fabric surface for a measurement of smoothness. A statistical analysis with a central composite design reveals the optimum concentrations of enzyme, sodium sulfite, and exposure time that maximize shrinkage control while maintaining adequate levels of tensile strength and weight loss.

Activated Peroxide for Enzymatic Control of Wool Shrinkage Part I: Elucidation

The ARS process combines activated peroxide for pretreatment and enzyme for subsequent treatment to provide bleached, biopolished, and shrinkage-resistant wool. The pretreatment step is of particular interest because it combines dicyandiamide (DD) with alkaline peroxide to form peroxycarboximidic acid, a stable and powerful bleaching agent that is stabilized by gluconic acid (GA) when applied at pH 11.5 for 30 minutes at 30 ° C. Analytical methods of analysis provided information showing that the active bleaching component, peroxycarboximidic acid, is formed immediately upon the combination of DD with alkaline H2O2 and that cyanamide forms concomitantly as a co-product. The peroxide pretreatment bath was stable at room temperature for up to 4.5 hours with only 10% peroxide consumed. It should therefore be possible to reconstitute the bleaching bath for further utilization. The eventual alkaline hydrolysis of cyanamide to form urea and the recombination of urea with peroxycarboximidic acid formed the end-product, guanylurea, shown by high performance liquid chromatography associated with electron impact mass spectrometry (LC/EI-MS), Fourier transforminfrared (FT-IR), and 13C NMR. Differential scanning calorimetry and peroxide titration of pretreatment baths provided evidence that GA stabilizes the activated peroxide. Activated DD peroxide pretreatment is essential to the ARS process for it provides a high level of whiteness without loss in fabric properties and it prepares the wool fiber for enzymatic treatment designed to selectively modify the scales of wool to biopolish the fabric surface and provide itch-free, machine-washable wool.

Characterizing Wool Keratin

Keratin from wool is a reactive, biocompatible, and biodegradable material. As the biological structural component of skin (soft keratins) and of nails, claws, hair, horn, feathers, and scales (hard keratins) pure keratin comprises up to 90% by weight of wool. Wool was treated in alkaline solutions to extract from 68% to 82% keratin within 2 to 5 hours of exposure at 6 5 ∘ C . The keratin products were water-soluble and were confirmed to contain intermediate filament and microfibrillar component-proteins of fractured, residual cuticle, and cortical cells. Oxidation of wool by peroxycarboximidic acid in alkaline hydrogen peroxide produced keratin products with distinct microcrystalline structures: descaled fibers, fibrous matrices, and lyophilized powders. Morphology and confirmation of peptide functionality were documented by SEM, Amino Acid Analysis, SDS-PAGE gel electrophoresis, MALDI-TOF/TOF, and FTIR analyses. The reactivity of keratin from wool models the reactivity of keratin from low-value sources such as cattle hair.

Low-temperature Dyeing of Wool Processed for Shrinkage Control

Wool fabrics treated for shrinkage control by applying a novel two-step ARS process3 involving an activated peroxide bleach followed by enzyme treatment were dyed at lower temperatures within shorter dyeing times than conventional dyeing with acid dyes which require 90 ° C or higher for 60 minutes or longer. The shrinkage control process involved bleaching pretreatment with dicyandiamide in alkaline hydrogen peroxide and with gluconic acid additive at 30 ° C (86 ° F) for 30 minutes followed by sulfite-assisted serine protease treatment for biopolishing and shrinkage prevention at 45 ° C (113 ° F) for 40 minutes. Dye uptake with time over the temperature range of dyeing showed that untreated fabrics and pretreated fabrics exhibited sigmoidal dyeing behavior with exhaustion within 55–70 minutes at 55–60 ° C. Fabrics pretreated and subsequently treated with enzyme exhibited exponential dyeing behavior with exhaustion within 20–30 minutes at 30–55 ° C. We attributed low temperature dyeing with reduced dyeing times to changes in wool morphology and chemical structure as documented by both scanning electron and confocal fluorescent microscopy. The ARS process provides shrinkage control with greater ease of bleaching and dyeing.

Enzyme-mediated Crosslinking of Wool. Part II: Keratin and Transglutaminase

Keratin hydrolysates (KH) and their lyophilized powders (KP) were applied with transglutaminase (amine γ-glutamyltransferase EC 2.3.2.13; TG) to fine jersey wool fabric bleached by peroxycarboximidic acid in the first step of the ARS process. The full ARS process involving treatment with proteolytic enzyme (Esperase 8.0L™) after pretreatment by bleaching can result in up to 18% fabric strength loss in fine-gage jersey knits, yet the ARS process has met with industry acceptance. To alleviate strength loss we applied solutions of KH and KP in combination with TG as a transferase enzyme to catalyze transamidation reactions involving keratin as KH and KP and keratinaceous wool fabric in order to provide crosslinking between and among these keratin constituents. Treatments of KH from 100% to 10% owb with TG showed that shrinkage could be controlled; application of 6% owf KP and 2% owf TG controlled shrinkage to 4.89%. Scanning electron micrographs showed that the keratin material coated the fibers to fill the raised scales of the wool. The results of statistical analysis predicted the optimum application conditions of 5% KP and 5% TG. These conditions minimized felting shrinkage to 5.21% and fabric weight change to 0.26% and maximized dry burst strength to 4.7% loss and increase in fabric whiteness to 17.8 whiteness index units. Wool material, including hydrolysates and powders crosslinked by TG enzyme mediation can provide a rich resource for the production of modified keratin-based biomaterials.

Activated Peroxide for Enzymatic Control of Wool Shrinkage Part II: Wool and Other Fiber-type Fabrics

In Part I we investigated the mechanism for bleaching wool with activated peroxide in the pretreatment step of the chemoenzymatic ARS process for whitening, biopolishing, and shrinkage prevention of wool. Here in Part II we report on applying the process to wool woven and knit fabrics of various constructions and fabric weights and to woven fabrics of other fiber compositions. The contribution of relaxation shrinkage to overall shrinkage that includes felting shrinkage is pronounced in wool fabrics, especially knits. The ARS process is specific for controlling felting shrinkage to provide dimensional stability in machine washing and drying. When applied to acetate, cotton, nylon, polyester, viscose, 62% wool/38% cotton, and a wool/Nomex blend the process was most effective for controlling the shrinkage of acetate, cotton, nylon, viscose, and wool/cotton blend. We treated wool, cotton, and viscose at pH 11.5, 30°C for 30 minutes with individual components used in ARS pretreatment: dicyandiamide (DD), gluconic acid (GA), alkali (NaOH), and hydrogen peroxide (H2O2), and subsequently applied the enzyme treatment. We found that NaOH imparted a mercerizing effect to cotton and viscose and shrinkage was limited to less than 1%. Only the combination of DD/GA/NaOH/H2O2 imparted highest whiteness to wool, cotton, and viscose. When pretreatment utilizing activated DD peroxide was followed by enzyme applied at pH 8–9, 45°C for 40 minutes, the wool fabrics became dimensionally stable and biopolished for itch-free comfort.

DCCA Shrinkproofing of Wool Part II: Improving Whiteness and Surface Properties

In Part I, 20% owf DCCA treatment of wool fabric provided complete shrinkage control, but yellowness and deterioration of fabric handle resulted. In Part II, a mod ified 20% owf DCCA treatment overcomes these limitations. This is an improvement over the conventional two-step process in which DCCA chlorination is followed by resin application to prevent shrinkage in wool fabrics. In step 1 of the treatment, gluconic acid (GA) is applied with DCCA. After neutralization and antichlorination, GA is applied with hydrogen peroxide (H2O2). The role of GA is to moderate the harsh effects of DCCA and H2O2 as documented by scanning electron micrographs of the fibers and improved surface properties of the fabrics. Although the level of DCCA is high, all released chlorine is consumed, and residual chlorine found in spent baths is less than 2%. This modified DCCA system can serve as a model for choosing components when designing alternative systems to chlorination for shrinkage control.