Sound absorption properties of acrylic carpets

The Journal of The Textile Institute

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Sound absorption properties of acrylic carpets Merve Küçük & Yasemin Korkmaz To cite this article: Merve Küçük & Yasemin Korkmaz (2017) Sound absorption properties of acrylic carpets, The Journal of The Textile Institute, 108:8, 1398-1405, DOI: 10.1080/00405000.2016.1254582 To link to this article: https://doi.org/10.1080/00405000.2016.1254582

Published online: 08 Nov 2016.

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The Journal of The Textile Institute, 2017 VOL. 108, NO. 8, 1398–1405 http://dx.doi.org/10.1080/00405000.2016.1254582

Sound absorption properties of acrylic carpets Merve Küçüka and Yasemin Korkmazb a

Department of Materials Science and Engineering, Istanbul Technical University, Istanbul, Turkey; bDepartment of Textile Engineering, Kahramanmaraş Sütçü Imam University, Kahramanmaraş, Turkey

ABSTRACT

Development of functional carpet structures is vital to improve sound quality of human life in transportation vehicles, residential and occupational environments. In this research, pile length and loop density parameters of acrylic carpets were studied to examine the effect on sound absorption properties. Carpet samples, with two different pile densities and four different pile lengths were produced for experimental purposes. Carpets with longer piles and dense loops result in the best sound absorption rates. Acrylic carpets produced with medium length piles and low density loops, yield better results at higher frequencies. Carpet samples with shorter piles and dense loops provide better sound absorption properties at low-to-mid frequencies. It has been observed that loop density and pile length parameters affect sound absorption properties at all frequency ranges. Anova analysis revealed that the combined effect of loop density and pile length parameters is evident in the mid and high frequency ranges.

Introduction Today, improvement of sound quality in our neighborhood is gaining more importance than ever before. Comfort and durability expectations have motivated significant amount of research toward development of functional sound absorbing materials. Traditional use of woven or knitted structures for floor and wall covering motivated, the improvement of their acoustic properties. Studies on functional woven or knitted textiles, elicit the development of microfiber-based fabrics (Na, Lancaster, Casali, & Cho, 2007), multiple layers of nanofiber webs (Na, Agnhage, & Cho, 2012), stacked thicker fabrics with bigger fiber diameter and dense fiber structure, on a fiber-reinforced sandwich structure (Zheng, Li, & Yang, 2013), combinations of weft-knitted (Honarvar & Jeddi, 2010) and warp-knitted spacer fabrics (Liu & Hu, 2010), plain woven fabrics produced by rotor spinning of finer weft yarns, constitute some major contributions to the development of improved sound absorption properties (Soltani & Zerrebini, 2012). Another common woven or knitted structure used traditionally for esthetic measures is, carpets. On the other hand architecture of building as concert halls, have extensively utilized carpeting materials to improve acoustic properties of the structures. Therefore, the study of carpet sound absorption properties by changing their physical parameters has become crucial. The research on carpet structures has mainly focused on comfort and durability features. Study on firmness revealed that carpets are beneficial in regulating posture and sway under a visual confliction or interference (Wu, Pan, & Williams, 2008), while

CONTACT  Merve Küçük  © 2016 The Textile Institute

[email protected]

ARTICLE HISTORY

Received 3 April 2016 Accepted 26 October 2016 KEYWORDS

Sound absorption; acrylic; carpet; loop density; pile height

compliant carpets yield faster sway velocity and smaller sway range providing better perceived comfort particularly on feet and ankles parts of the body (Wu, Pan, & Williams, 2007). Carpet pile height, fiber type, yarn diameter, heat setting, and yarn twist parameters affect pile deformation (Dayiary, Najar, & Shamsi, 2009), resiliency and retention of appearance (Grover, Zhu, & Twilley, 1993). The use of polyester fibers (Wilding, Lomas, & Woodhouse, 1990), incorporated into single yarns and joined into a plied yarn (Grover et al., 1993), interply low-melt yarn (Balasubramanian et al., 2004), wool woven Kermanshahi carpet with lower knot density and tanned wool woven Sirjani with higher knot density (Mirjalili & Sharzehee, 2005), jute carpet waste and randomly oriented, double-ply yarn-reinforced with epoxy or polyester matrix fibers (Onal & Karaduman, 2009) improved compression, flexion, load carrying capacity and pile recovery of carpets. Free charged species produced by corona currents around conductive filament tips to reduce body voltage of people walking on the carpet (Maclaga & Fisher, 2001), Nylon 66 fibers degraded by a para-toluene sulfonic acid solution to obtain controlled degradation enabling a sculpturing effect on pile carpets (Cribbs & Ogale, 2003), fluoropolymer treatment of nylon to improve water, oil and soil repellency properties (Radhakrishnaiah, 2005), soiling and acetone extraction to remove fluorocarbons applied to nylon 66 carpets during either spin finish or milling (Petrick, Hild, & Obendorf, 2006), contributed to comfort and durability studies on carpet structures. In review of the literature a few studies on acoustic properties of carpets were found.

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Earliest studies on backing material, pile structure, fiber content, yarn weight, density, pile height and underlay revealed that, cut-pile carpet backed with latex improve low-frequency sound absorption while decreasing high-frequency sound absorption properties (Harris, 1955). Also starch and latex backing improve flow resistance. At low frequencies wool fiber provides better sound absorption whereas viscose improves mid frequency sound absorption rates. Dense piles of wool Axminster carpet improves low frequency sound absorption while loose piles improve mid frequency properties. Hair and foam underlay is better at low frequencies while foam is better at mid frequencies. Wilton is better at low frequencies while hardtwist frieze Velvet with a latex back is better at mid frequencies. Impact measurement of a tapping machine on a concrete floor covered with carpet and underlay floor covering resulted in better impact insulation measured from a below reverberant room (Ford & Bakker, 1984). One of the few prominent studies on sound absorption revealed that, level loop texture in acrylic and polyester carpets at low frequencies, wool carpet with plush shag, level loop in acrylic carpet, long shag texture in nylon and polyester and wool plush carpets at medium frequencies, level loop in acrylic carpets at high frequencies, acrylic-based level loop carpets at all frequencies were most effective (Coulter & Wolfe, 1975). Air gap placed behind tufted carpets used for wall covering, cut-pile wool carpets with open loops, higher and dense piles, (Shoshani & Wilding, 1991), granulated carpet tiles including fibrous and un-sieved granular waste material (Rushforth, Horoshenkov, Miraftab, & Swift, 2005), multilayer carpet of wool and polyamide mixture coupled with a felt layer (Ricciardi & Lenti, 2010) provided the best sound absorption properties. Increasing pile density while increasing or holding pile height constant resulted in low-mid frequency sound absorption improvement for nylon and wool carpets. Increasing pile height while holding pile weight constant in loop pile fabrics resulted in improvements in sound absorption in a wider range of frequencies (CRI, 2014). Sole Cotton carpet and carpet on hair felt or foam rubber resulted in better sound absorption properties at mid frequencies. Loop pile tufted carpet placed on hair pad, pile carpet bonded to open-cell foam underlay amd tufted pile carpet on felt underlay yielded better sound absorption rates in the mid-to-high frequency ranges (Vorländer, 2007). In the above mentioned literature there has not been a thorough study of the effect of density and pile height on sound absorption properties of acrylic carpets. In this research a parametric study of acrylic carpet acoustics was performed and the effect of pile height and pile density on sound absorption properties were investigated.

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Acrylic yarn was produced, by staple cut and lightly twist of three yarns. Nm 12/4 65/35% polyester/cotton mixture was used as the filler yarn. 13/1 LBS (2400/1 dtex) jute and 13/2 LBS (2400/2 dtex) jute weft insertions were used for 40 warp × 40 weft and 40 warp × 60 weft yarn woven carpets, respectively. Measurement of physical parameters Loop density and pile height parameters of the samples were verified by lab measurements. Loop density indicates the number of loops in a specific area. The number of loops and spacing are counted, within 100 and 150 mm section, by moving parallel to the edge of the carpet and measuring according to ISO 1763, TS 5285 (at least 100 mm section of the carpet is visually inspected to count at least 41 loops and if lesser amount of loops are present, inspected section is extended beyond 100 mm to count adequate number of loops). Loop density parameters for 40 warp × 40 weft yarn woven and 40 warp × 60 weft yarn woven per 10 cm2 region were measured as 1600 and 2400 loop/dm2 density, respectively. Pile height of the carpet samples was measured by International Wool Secretariat Carpet Pile Height Gauges (3−25 mm plates). For acrylic carpets woven at 1600 and 2400 loop/dm2 density, pile height parameters were measured, starting from the back surface by Micronaire with 0.01-mm accuracy and an illuminated magnifier. Pile density and height parameters are listed in Table 1 along with average weight parameters measured by a laboratory type precision scale. Sound absorption measurements Carpet samples were cut to 100 and 29 mm diameters for low and high frequency sound absorption measurements, respectively. The carpet samples were laid as back facing up. The measurement sample dimensions were drawn and band knife cutting machine with a straight knife was used for cutting the samples. Five different samples were prepared for each specific composition and sound absorption properties were measured and averaged using Brüel & Kjaer impedance tube kit according to ISO 10534-2 and ASTM 1050-98 standards. The testing apparatus is an acoustic material testing system, featuring power amplifier, signal conditioner, impedance tube kit, calibrator, PC and Brüel & Kjaer PULSE™ interface (Figure 1). Impedance tube kit includes a large tube for measurement of low frequencies between 0.05 and 1.6 kHz and a small tube for measurement of high frequencies between 0.5 and 6.4 kHz. The large and small tube measurements can then be combined to obtain sound absorption rates for the frequency range between 0.05 and 6.4 kHz. Due to possible distortion of the signal by filtering effects at the end of the frequency

Materials and methods Carpet samples of different physical parameters were prepared. Acrylic carpets, with two different pile densities as 40 warp × 40 weft and 40 warp × 60 weft yarn per dm2 and four different pile height as 9, 10, 12.5 and 14 mm were produced for experimental purposes. Four hundred centimeter wide carpet samples with two lengths as 33 and 60 cm were produced by Wilton face-to-face weaving method as flat cut (velur) on a Schörrein α 300 double hook (shot) machine at 125  rev/min speed. 2100 dtex twist of staple acrylic were used for pile yarn.

Table 1. Acrylic carpet production parameters. Pile density (piles/dm2) 1600 1600 1600 1600 2400 2400 2400 2400

Pile height (mm) 9 10 12.5 14 9 10 12.5 14

Acrylic average weight (g/m2) 2112.19 2183.69 2557.19 2650.50 2311.94 2382.06 2899.19 3007.06

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Figure 1. Test bench for sound absorption measurements (courtesy of Brüel & Kjaer).

Figure 2. Sound absorption of acrylic carpets with pile heights of 9 mm, and loop density of 1600 and 2400 loop/dm2.

range, sound absorption results are presented for 0.05–6.3 kHz range.

Results and discussion Figure 2 shows sound absorption properties of acrylic carpet with 9 mm pile height and 1600, 2400 loop/dm2 density properties. Sound absorption of the carpet with loop density of 1600 loop/dm2 exhibit a linear increase between 0.05 and 5 kHz frequencies with a slightly slow down between 5 and 6.3 kHz, yielding a maximum absorption value of 0.74 at 6.3 kHz. Increasing the number of stitches 50% from 1600 to 2400 loop/dm2 results in more than 17% increase in sound absorption in the mid-tohigh frequency ranges with a maximum rate of 0.83 at 6.3 kHz.

In Figure 3, sound absorption properties are shown for acrylic carpets with 10 mm pile height and with 1600 and 2400 loop/dm2 density. Pile height of 10 mm and loop density of 1600 loop/dm2 resulted in a steady increase in sound absorption with a maximum of 0.74 at 6.3 kHz. Although maximal sound absorption values do not change significantly compared to 9 mm pile height, the rates for 10 mm yield a steep increase in sound absorption attaining 0.5 at 3.5 kHz when compared to 0.44 rates at similar frequencies for 9 mm pile height. 2400 loop/dm2 density results in a 25% increase in sound absorption with an ultimate rate of 0.87 at 6.3 kHz. Figure 4 shows sound absorption results for acrylic carpet with 12.5 mm pile height, 1600 and 2400 loop/dm2 density. For 1600 loop/dm2, besides a slight drop in sound absorption rate,

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Figure 3. Sound absorption of acrylic carpets with pile heights of 10 mm, and loop density of 1600 and 2400 loop/dm2.

Figure 4. Sound absorption of acrylic carpets with pile heights of 12.5 mm, and loop density of 1600 and 2400 loop/dm2.

around 1.5 kHz, acrylic carpet exhibit a steady increase in sound absorption with a maximum rate of 0.88 at 6.3 kHz. Increasing the number of loops results in an increase in sound absorption rates with a maximum rate of 75% at 3 kHz. The considerable increase was observed in the mid-to-high frequencies. Sound absorption of acrylic carpet with 2400 loop/dm2 density attains its maximum rate at frequencies between 5 and 6.3 kHz. Pile height of 14 mm and 1600 loop/dm2 density results in sound absorption rates increasing steadily to a maximum rate

of 0.77 at 6.3 kHz (Figure 5). Increasing loop density results in a maximum of 40% increase in sound absorption yielding maximal values of 0.9 at frequencies between 4 and 6.3 kHz. Acrylic carpet with 1600 loop/dm2 density attains its higher rates at frequencies between 5.5 and 6.3 kHz. The acrylic carpet with 2400 loop/dm2 density attains its ultimate rates in a wider range of frequencies between 4 and 6.3 kHz. The decrease in spacing between piles due to higher number of piles per unit area results in higher sound absorption rates for denser carpet structures.

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Figure 5. Sound absorption of acrylic carpets with pile heights of 14 mm, and loop density of 1600 and 2400 loop/dm2.

Figure 6. Sound absorption of acrylic carpets with 1600 loop/dm2 density.

Considering the results for all pile heights (9, 10, 12.5, 14 mm) sound absorption of acrylic carpets with higher loop density exhibit better sound absorption rates, compared to 1600 loop/ dm2. Also for higher loop densities and 12.5 and 14 mm pile heights, sound absorption rates tend to increase rapidly in the mid-to-high frequency ranges. Acrylic carpet with a pile height of 9  mm yields a steady increase in sound absorption with a maximum rate of 0.75 at 6.3 kHz (Figure 6). Increasing the pile height to 10 mm results

in an increase in sound absorption at frequencies between 1.5 and 4.5 kHz with a maximum rate of 13%. Increasing the pile height 25% results in an increase in sound absorption at frequencies between 3 and 6.3 kHz with a maximum rate of 30%. Increasing the pile height to 14 mm results in a slight increase in sound absorption at frequencies between 1.2 and 3.7 kHz with a maximum rate of 17%. However at frequencies between 3.8 and 6.3 kHz, sound absorption rate decreases with a maximum rate of 15%. For 1600 loop/dm2 density, higher piles as for 12.5 mm

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Figure 7. Sound absorption of acrylic carpets with 2400 loop/dm2 density.

results in a slight increase in sound absorption properties at higher frequencies. However, increasing pile height to 14 mm, results in a slight increase in sound absorption rates at low-tomid frequency ranges whereas yielding a decrease in sound absorption properties at high frequencies. Measurements of acrylic with 2400 loop/dm2 density and 9 mm pile height revealed that sound absorption rate increases steadily with a maximum of 0.83 at 6.3 kHz (Figure 7). Increasing the thickness by 1 mm results in a 12% increase in sound absorption at all frequencies. Increasing the thickness by 2.5 mm results in an increase in sound absorption at frequencies between 0.05 and 5 kHz with a maximum rate of 33%. Increasing the thickness to 14 mm results in a 10% increase at frequencies between 0.05 and 1.5 kHz while the material sound absorption rate decreases by almost 10% at frequencies between 1.5 and 6.3 kHz. There is significant increase in sound absorption rates for acrylic carpet with 12.5 mm pile height. However, increasing the thickness beyond 12.5 mm does not contribute significantly to sound absorption rates. For acrylic carpets with higher loop density, significant increase in sound absorption is observed for piles 12.5 and 14 mm. Low frequency is associated with longer wave length, yielding better sound absorption for longer piles at lower frequencies (Nick, Becker, & Thoma, 2002). Higher loop density reveals better sound absorption rates for acrylic carpets. Acrylic carpets with dense loops and longer piles yield significant increase in sound absorption. Increasing loop density for carpets with shorter piles yield marginal improvement in sound absorption, whereas longer piles in acrylic carpets with dense loops pose a significant contribution to sound absorption properties. Optimum acoustic rates for acrylic carpets were obtained for 12.5 mm pile height and 2400 loop/dm2 density parameters.

Table 2. Anova results for the effect of loop density (LD) and pile height (PH) on sound absorption. Frequency (Hz) 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

LD 0.0214