Fabrics for the twenty-first century - The Courtauld Institute of Art

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Young and Jardine Fabrics for the twenty-first century 14 Figure 12 Bar chart summary of maximum change in tension on wetting. This batch of sailcloth was found to have a different response to previously tested batches; the permanent change in tension results in a decrease in the warp of 8.0 N and an increase in the weft of 8.3 N, compared to previous data that found a permanent decrease in the weft and warp of 25 and 18 N, respectively (Young, 1999). Figs. 11A and B show the response curves for the two batches of P110 tested. Both show unusual behaviour for a 100% polyester material in that they do not recover tension after wetting and drying. P110 2004 (Fig. 11A) loses tension on wetting and subsequent drying down to a value of 5.9 N weft and 2.9 N warp, whereas P110 2008 (Fig. 11B) has values of 35.6 N weft and 34.0 N warp, respectively. P110 2008 also takes only 1.5 hours compared to 5 hours for the P110 2004, because it has absorbed less moisture. This difference may be a result of differences in the residual size in the fabric, the amount of twist in the yarn, or additional finishing processes. The PET from which the filaments are made may have different degrees of polymerization and crystallinity. Fig. 12 summarizes the Tmax data (see Table 7) which clearly demonstrates the relative moisture response of the fabrics. RH response Fig. 13A shows the response curve of Polyflax 1008, showing the change in tension as function of time at different RH values. The step drop in load corresponds to the step increase in RH. Assuming a typical relationship between equilibrium moisture content as a function of RH (high gradient at 10–40%, plateau around 40–75%, high gradient 75–95%), then the slope of the initial region, from 10 to 40% RH, measures how fast moisture was taken up by the fabric and it gives a maximum response rate for the fabric. The slope of the region from 40 to 85% RH measures the response rate for the fabric due to slow changes in typical RH conditions. Because the moisture diffusion processes are nonlinear, by applying step changes one can also identify which RH values result in large changes in tension. Table 7 summarizes the data, tabulating the slope for the 10–40% RH and the 40–85% RH changes. The response to RH is complicated by fast creep in some of the fabrics during the tests. This creep is probably because the water lubricates the yarn cross-over Figure 13 (A) Tension response curve for step changes in RH for Polyflax 1008. (B) Tension response curve for step changes in RH for 12 oz cotton duck. (C) Tension response curve for step changes in RH for Peektex 17–220/56. (D) Tension response curve for step changes in RH for Carbotex 03_82. Studies in Conservation 2012 VOL. 0 NO. 0
points and allows yarn slippage (Young, 1996a) or the water molecules acts as a plasticizer to allow filaments to slip past each other. The effect has been observed most in the continuous yarn synthetic materials. Figs. 13B and C show the response curves for 12 oz cotton duck and Peektex 17-220/56. In the initial 10–40% RH region the cotton duck increases in tension with a delay before the tension reaches equilibrium at 40%. The fabric tension then increases in steps with step changes in RH. Peektex 17-220/56 has a fast, but small drop in tension as the RH increases, then remains almost constant, until 85% RH where a small increase in tension occurs in the weft direction. Fig. 13D shows the response curve for Carbotex 03_82. It is clear that a different mechanism is occurring with the introduction of moisture to the fabric. The yarns are made of polyamide (moisture regain at 20°C, 65% RH is ∼4% (Sefar Ltd., 2009)) with a carbonized outer shell (not responsive to moisture). It is suggested that the outer shell prevents moisture from reaching the polyamide and thus it only acts as a lubricant allowing yarn slippage. The change in tension is not fully recovered on drying. Except for Kevlar ® , which behaves like cotton duck and linen, all other synthetic materials show a similar trend in moisture response to Polyflax 1008 but with different magnitudes. An attempt was made to correlate the measured moisture response from the wetting and RH tests with simple weave properties for each type of fabric; including weft and warp crimp amplitude, crimp ratio, weave count, and weave count ratio. No significant pattern emerged from these comparisons, probably because yarn diameter and twist also varied between the fabrics. Discussion and conclusions For artist canvas and fabrics for structural reinforcement of easel paintings on canvas, in the early twenty-first century, polyester (PET form) still offers the best starting point as a raw material. However, the exact geometry of the woven fabric plays a major role in determining its bulk properties. Thus, not all polyesters have the same response to moisture, nor the same balance of mechanical properties. Care also has to be taken in assuming the same properties from batch to batch for the same fabric, as variations in the manufacturing process occur that alter the fabric properties. The synthetic fabrics with the most even biaxial stiffness are monofilament 55/31 (1.21), Sailcloth 00169 (1.04), Polyflax 1008 (1.20), and Carbotex 03_120. (1.01). The most uneven were Kevlar ® Scenic (3.14) and P110 2008 (2.87). The fabrics with the least response to moisture are: Polyflax 1008, Sailcloth 00169, loom state 9.1 oz Clipper, and Peektex 17-220/56. Young and Jardine Fabrics for the twenty-first century Drape and lustre were found to be useful parameters with which to quantify aesthetic and kinaesthetic properties of fabrics in the context of conservation. DCs between 0.6 and 0.85 give the ‘feel’ similar to traditional medium weight linen. A ‘stiff’ lining would require a DC greater than 0.85. Future research will relate the measurement of drape to flexural stiffness because this property directly measures out-of-plane properties of the fabric, and hence the ability to keep tears and cupping in-plane. Values of gloss in the range of 2.1–2.5 give an aesthetic similar to linen. This is achieved primarily by using spun rather than continuous yarns, and is further enhanced by dyeing the yarns in at least one direction. The amount of yarn twist will also have an influence (not evaluated as part of this study). Decreasing the yarn twist has been shown to decrease gloss (Kim et al., 2004). Twisting binds the fibres together and gives the yarn strength. There is an optimum twist factor for any yarn type depending on the fibre content and staple length. These two parameters could be incorporated into the design of future fabrics (Backer et al, 1956; Taylor, 2002). Overall, if aesthetics are not important and a very stiff fabric is required for lining with low moisture response and even properties, Sailcloth 00169 performs best. If a fabric is required which has very good kinaesthetic properties and quite good aesthetic properties, low moisture response, and is isotropic, then the Polyflax 1008 performs best. If a heavier weight fabric is required the loom state 9.01 Clipper is an option. These two fabrics also offer the best options for synthetic artist canvas. Clearly, application of an adhesive to the fabric will alter its properties when used as a lining canvas; this will depend on the type and penetration of the adhesive (Young & Ackroyd, 2001). An initial investigation into the application of adhesive and handling properties while lining was undertaken; further interpretation and application of these data, together with lining case studies, is reported elsewhere (Young, 2010). Both twill and triaxial weave geometries potentially offer better physical stability and resistance to tearing. Therefore, they will be investigated as part of future research. Surface modifications by irradiation with an excimer laser have been shown to affect the lustre, wetability, dyeability, and stability of the microstructures of the fibre surface (Lau et al., 1998). Surface treated polyester filaments have been developed for performance clothing which wick away moisture. Vapour deposition techniques have also been employed to modify the surface (Ma et al., 2005). Modification to the filament cross section e.g. trilobal cross sections Studies in Conservation 2012 VOL. 0 NO. 0 15
Page 1 and 2: Original research or treatment pape
Page 3 and 4: point for an artist canvas. For com
Page 5 and 6: ate of moisture entering the chambe
Page 7 and 8: Table 2 Measured crimp properties o
Page 9 and 10: Table 5 Calculated uniaxial and bia
Page 11 and 12: Table 6 Calculated biaxial stress r
Page 13: Figure 9 (A) Tension response curve
Page 17: Pan, N. 2007. Quantification and Ev

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