journal homepage: www.elsevier.com/locate/jmatprotec
`
`Study of three-dimensional spacer fabrics:
`Physical and mechanical properties
`
`Joanne Yip∗, Sun-Pui Ng
`ACE Style Institute of Intimate Apparel, Institute of Textiles & Clothing, The Hong Kong Polytechnic University, Hong Kong
`
`a r t i c l e
`
`i n f o
`
`a b s t r a c t
`
`Article history:
`Received 27 June 2007
`Received in revised form
`25 October 2007
`Accepted 14 December 2007
`
`Keywords:
`Spacer fabrics
`Physical properties
`Mechanical properties
`
`Spacer is a three-dimensional knitted fabric consisting of two outer textile substrates which
`are joined together and kept apart by spacer yarns. Spacer fabrics are used for environmen-
`tal reasons, which can be used in different product groups such as mobile textiles (car seat
`covers, dashboard cover), industrial textiles (composites), medical textiles (anti-decubitus
`blankets), sports textiles and foundation garments (bra cups, pads for swimwear). In this
`study, the characteristics of different spacer fabrics including low-stress mechanical prop-
`erties, air permeability and thermal conductivity were investigated. Low-stress mechanical
`properties obtained by the KES-fabric evaluation system revealed that all tensile, bending
`and compression properties of spacer fabrics are greatly depending on the type of spacer
`fabric (warp knit or weft knit), the type of spacer yarn used (monofilament or multifilament),
`the yarn count of the spacer yarn, the stitch density and the spacer yarn configuration. Air
`permeability and thermal conductivity of spacer fabric are closely related to the fabric den-
`sity. This experimental work suggests that carefully selecting the spacer fabric according to
`the envisaged application is of primary importance.
`
`© 2007 Elsevier B.V. All rights reserved.
`
`1.
`
`Introduction
`
`Spacer fabric is a three-dimensional knitted fabric consisting
`of two separate knitted substrates which are joined together or
`kept apart by spacer yarns (New patterning possibilities, 2001;
`Wilkens, 1993; Lehmann, 1994). There are two types of spacer
`fabrics: warp-knitted spacer fabric and weft-knitted spacer
`fabric. The first type is knitted on a rib raschel machine having
`two needle bars (McCartney et al., 1999; Donaghy and Azuero,
`1999), while the second is knitted on a double jersey circular
`machine having a rotatable needle cylinder and needle dial
`(Shepherd, 2004; Sytz, 2004; Willmer, 2005).
`Spacer fabrics are widely used in different products such as
`mobile textiles (car seat covers, dashboard cover), industrial
`textiles (composites), medical textiles (anti-decubitus blan-
`kets), sports textiles and foundation garments (bra cups, pads
`
`for swimwear) (Heide, 2001; Spacer fabrics in medicine, 1999;
`Bras cups made from a new spacer fabric, 2001). Spacer fabric
`as a component material is highly breathable, thus creating a
`moisture free environment, which in turn reduces the chances
`of skin maceration. These lead to an increased level of comfort
`when compared to materials such as foam, neoprene and lam-
`inate fabrics. Spacer fabrics are regarded as environmentally
`friendly textile materials (unlike polyurethane foam), since
`they can be recycled (Wilkens, 1993; Heide, 2001).
`Spacer fabrics have been studied globally for many years
`(Wilkens, 1993; Lehmann, 1994). However, very little research
`work has been done on the effect of fabric characteristics
`on its physical and mechanical properties of spacer fabrics.
`In part I, the influence of several fabric structures on the
`physical and mechanical properties of spacer fabric will be
`discussed.
`
`∗ Corresponding author. Tel.: +852 2766 4848; fax: +852 2334 9607.
`E-mail address: tcjyip@inet.polyu.edu.hk (J. Yip).
`0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
`doi:10.1016/j.jmatprotec.2007.12.073
`
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`
`by Eq. (1):
`
`Thermal conductivity (k) =
`
`Heat flow rate × distance
`area × temperature difference
`
`(1)
`
`×
`
`Q t
`
`k =
`
`L
`A × T
`where, Q = the quantity of heat, t = time, L = thickness of the
`sample, A = surface area of the sample and T = temperature
`difference.
`
`Fig. 1 – Air resistance of different spacer fabrics.
`
`2.
`
`Experimental methods
`
`2.4.
`
`Bending and compression tests
`
`The KES-F (Kawabata Evaluation System) was used for mea-
`suring spacer samples’
`low-stress mechanical properties,
`including the response to bending and compression. The
`parameters obtained from these hysteresis curves are defined
`(Kawabata and Niwa, 1996) and shown in Table 1.
`
`2.1.
`
`Spacer fabric characteristics
`
`2.5.
`
`Stretchability and recovery tests
`
`Five different spacer fabrics were used in the present study.
`Sample 1 was a warp-knitted spacer fabric, while samples 2–5
`were weft-knitted spacer fabrics. The fabric characteristics of
`interest include the fabric density, spacer yarn type, thickness
`of the spacer fabric, spacer yarn diameter and arrangement.
`All the experiments were carried out under standard condi-
`tions, BS1051, at 20 ◦C and 65% relative humidity.
`
`2.2.
`
`Air permeability test
`
`The air permeability of the samples was studied with the KES-
`F8-AP1 air permeability tester (Yip et al., 2002). The results of
`the measurements on the air resistance (R), reported in Fig. 1,
`are averages from the values of 10 readings.
`
`2.3.
`
`Thermal conductivity test
`
`The thermal property was studied by KES-F Thermo Labo II
`(Kawabata and Niwa, 1996). This test is used to measure the
`power loss from BT-Box (Watt) to the Water Box through the
`spacer samples. The sample was put on the Water Box which
`is in the room temperature (20 ◦C). The temperatures of the
`BT-Box and Guard were set to a temperature of 30 ◦C. The
`amount of heat passing through the sample (in watts per
`square meter) was measured from the power consumption of
`the test plate heater. The thermal conductivity value (k) hav-
`ing a unit of W/mK of different spacer fabrics can be calculated
`
`The stretch and recovery properties of the spacer samples
`were tested by INSTRON 4411 according to the British standard
`4294. The specimen of standard dimensions was stretched
`under a specified load. The length of the specimen should
`be sufficient to allow a distance of 7.5 cm (L1) between the
`inner edges of the clamps to hold the specimen. The load
`was gradually increased on the specimen to 6 kg within 7.5 s.
`The load was maintained constant for 10 s and then reduced
`gradually until the clamps were returned to their original posi-
`tion. The loading conditions were reapplied immediately to
`the specimen and the length (L2) of the specimen was mea-
`sured after 1 min, following which the specimen was removed
`from the clamps and placed on a flat and smooth surface. Its
`dimension (L3) was measured before and after 1 min of fab-
`ric relaxation time. After 30 min, the distance was measured
`again (L4). The same procedures were applied to both warp
`and weft directions. The percentage values of elongation (E),
`recovery after 1 min (R1) and 30 min (R30) of different spacer
`fabrics were calculated by Eqs. (2)–(4), respectively as shown
`below:
`
`100(L2 − L1)
`L1
`
`E =
`
`R1 =
`
`100(L3 − L1)
`L1
`
`R30 =
`
`100(L4 − L1)
`L1
`
`(2)
`
`(3)
`
`(4)
`
`Table 1 – Definitions of bending and compression properties obtained by KES-F system (Kawabata and Niwa, 1996)
`Properties
`Symbol
`Definition
`
`Unit
`
`Bending properties
`Bending rigidity
`
`Compression properties
`Compressional resilience
`Fabric thickness at 50 gf/cm2 pressure
`
`B
`
`RC
`Tm
`
`Average slope of the linear regions of the bending hysteresis curve to 1.5 cm−1
`
`uN m
`
`Percentage energy recovery from lateral compression deformation
`Fabric thickness at 50 gf/cm2 pressure
`
`%
`mm
`
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`Table 2 – Fabric characteristics of different spacer fabrics
`Sample 1 (WA-MO)
`
`Sample 2
`(WE-MO-1)
`
`Sample 3
`(WE-MU-1)
`
`Sample 4
`(WE-MU-2)
`
`Sample 5
`(WE-MO-2)
`
`Fabric type
`
`Composition
`
`Density (kg/m3)
`
`Thickness (mm)
`
`Spacer yarn type
`
`Warp-knitted
`
`Weft-knitted
`
`Weft-knitted
`
`Weft-knitted
`
`Weft-knitted
`
`52% Polyester
`48% Polybutylene
`terephthalate (PBT)
`
`56% Polyester
`38% Nylon
`6% Spandex
`
`92% Polyester
`8% Spandex
`
`93% Polyester
`7% Spandex
`
`91% Polyester
`9% Spandex
`
`54.866
`
`4
`
`117.858
`
`3.3
`
`204.269
`
`2.87
`
`146.289
`
`2.91
`
`125.387
`
`3.54
`
`Monofilament
`
`Monofilament
`
`Multifilament
`
`Multifilament
`
`Monofilament
`
`Spacer yarn composition
`
`Spacer yarn diameter
`
`Spacer yarn arrangement ()
`
`100% Polybutylene
`terephthalate (PBT)
`0.046 mm
`
` = tan−1 t/w
` = 52.33◦
`
`100% Polyester
`
`100% Polyester
`
`100% Polyester
`
`100% Polyester
`
`0.057 mm
`
` = tan−1 t/w
` = 79.49◦
`
`0.701 mm/32
`filaments
` = tan−1 t/w
` = 78.07◦
`
`0.534 mm/32
`filaments
` = tan−1 t/w
` = 63.43◦
`
`0.058 mm
`
` = tan−1 t/w
` = 61.08◦
`
`3.
`
`Results and discussion
`
`3.1.
`
`Spacer fabric characteristics
`
`The fabric characteristics of five different spacer samples are
`shown in Table 2, while the sample fabrics’ structures (front,
`
`back and side views, for both warp-wise and weft-wise) are
`shown in Table 3. Generally, the thickness of spacer fabrics
`can range from 1.5 mm to 60 mm (New patterning possibilities,
`2001). The samples thickness used in this study range from
`2.8 mm to 4 mm which are the most commonly used values
`in the sports textile and foundation garment market. The
`compression resistance of the spacer fabric can be varied
`
`Table 3 – Fabric structure and microscopic view of different spacer fabrics
`
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`
`depending on the thickness of the structure and the type of
`joining yarns. Both monofilament and multifilament joining
`yarns of various diameters were used in this study. The spacer
`yarns were originally arranged perpendicular to the two outer
`fabrics, however, there was always a risk that when pressure
`was applied, the yarns would simply be pushed sideways,
`thus reducing the compression resistance (Lehmann, 1994).
`Therefore, the spacer yarns were later arranged in a v-shaped
`configuration (see the fabric structure shown in Table 3). The
`spacer yarn arrangement angle () can be calculated with Eq.
`(5) shown below:
`
` = tan−1 L
`
`W
`
`(5)
`
`Fig. 3 – Compressed thickness of spacer samples at
`50 gf/cm2 pressure.
`
`where L = thickness of the spacer fabric; W = segment width.
`
`3.2.
`
`Air permeability and thermal conductivity
`
`In this study, the air resistance (R) of different spacer fabrics
`was recorded and Fig. 1 shows the results (a higher number of
`kPa s/m indicates a higher air resistance of the fabric (Yip et
`al., 2002)). The thermal conductivity of different spacer fabrics
`was also recorded. Since a higher value of thermal conductiv-
`ity indicates a faster heat transfer from the skin to the fabric
`surface, this is usually associated with a cooler feeling (Yip et
`al., 2002). Fig. 2 shows the thermal conductivity of different
`spacer fabrics.
`An analysis of Figs. 1 and 2 shows that sample 1 (WA-MO)
`has the lowest air resistance and thermal conductivity, while
`sample 3 (WE-MU-1) has the highest values for these same
`properties.
`The air permeability of a fabric is closely related to the con-
`struction characteristics of the yarns it is made of, in which
`large volumes are occupied by air. There are several factors
`affecting the air permeability of the fabric, such as fabric’s
`structure, thickness, surface characteristics, etc. (Zhang et al.,
`2002). In this study, it is suggested that the fabric density
`shows the most significant effect on the air permeability and
`thermal property of the spacer fabric. A higher fabric density
`will hinder the air flows through the fabric, thus resulting in
`a poor air permeability of the fabrics. A higher fabric density
`will however have a better thermal conductivity, as there will
`be less space to trap air inside. A denser fabric therefore has
`better thermal ventilation.
`
`Fig. 2 – Thermal conductivity values of different spacer
`fabrics.
`
`3.3.
`
`Compression properties
`
`The compression resistance of different spacer fabrics under
`50 gf/cm2 pressure in terms of the percentage change in thick-
`ness, is shown in Fig. 3. A higher percentage of thickness
`compressed indicates a lower compression resistance. It is
`found that samples 3 (WE-MU-1) and 4 (WE-MU-2) have lower
`compression resistance than samples 1 (WA-MO), 2 (WE-
`MO-1) and 5 (WE-MO-2). It is apparent that fabrics using
`monofilament as spacer yarn generally have higher compres-
`sion resistance than those using multifilament yarn. When the
`results for spacer fabrics using the same type of spacer yarn
`were compared, it was found that the compression resistance
`of a sample is closely related to the spacer yarn arrangement.
`The resistance force of a spacer yarn is F sin . The sample
`which has a larger angle  will therefore have a higher com-
`pression resistance, assuming that the material and diameter
`of the spacer yarn used are the same.
`Table 4 shows the compressive resilience RC of differ-
`ent spacer fabrics (RC is the percentage energy recovery
`from deformation due to lateral compression). A higher per-
`centage indicates a better recovery property. The results
`indicate that samples 1, 2 and 5 recover better than sam-
`ples 3 and 4. We observed that the recovery properties after
`compression greatly depend on the spacer yarn type: spacer
`samples using monofilament as their spacer yarns have bet-
`ter recovery properties than those using multifilament spacer
`yarns.
`
`3.4.
`
`Bending properties
`
`In this study, the bending rigidity of different spacer fabrics
`was investigated, and Fig. 4 shows results for both warp-wise
`
`Table 4 – Compressional resilience of different kind of
`spacer fabrics
`Sample
`
`RC (%)
`
`1
`2
`3
`4
`5
`
`75.417
`52.247
`37.02
`35.15
`51.317
`
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`
`Fig. 4 – Bending rigidity of spacer samples.
`
`Fig. 5 – Elongation of different spacer samples.
`
`Table 5 – Elongation and recovery of the warp-wise
`spacer fabrics
`Sample
`Elongation,
`E (%)
`
`Recovery after
`1 min, R1 (%)
`
`Recovery after
`30 min, R30 (%)
`
`1
`2
`3
`4
`5
`
`49.17
`67.96
`93.28
`47.32
`114.03
`
`86.90
`95.74
`97.38
`94.36
`91.61
`
`96.83
`98.69
`99.53
`98.59
`96.88
`
`and weft-wise spacer fabrics. It appears that the bending rigid-
`ity of a spacer fabric is greatly related to the fabric type. Thus,
`a weft-knitted spacer fabric has a higher bending rigidity in
`the weft-wise direction, while a warp-knitted spacer fabric
`has a higher bending rigidity in the warp-wise direction. This
`behaviour is mainly due to the directionality of the incorpo-
`rated yarn (Machova et al., 2006; Reisfeld, 1996). When the
`samples are of the same fabric type (weft-knitted spacer fabric
`for example), we can further conclude that the bending rigid-
`ity is closely related to the fabric’s density, spacer structure
`and spacer type (Raz, 1993). We also found that weft-knitted
`spacer fabrics using interlock structure, monofilament spacer
`yarn and a higher fabric density have a higher bending rigidity.
`
`3.5.
`
`Stretch and recovery
`
`The stretch and recovery properties of different spacer fabrics
`were also studied, and results are reported in Tables 5 and 6 (a
`higher percentage indicates better stretch and recovery prop-
`erties). These results indicate that sample 1 (WA-MO) has the
`
`Table 6 – Elongation and recovery of the weft-wise
`spacer fabrics
`Sample
`Elongation, E
`(%)
`
`Recovery after
`1 min, R1 (%)
`
`Recovery after
`30 min, R30 (%)
`
`1
`2
`3
`4
`5
`
`159.68
`101.77
`129.80
`119.51
`86.73
`
`78.01
`90.83
`94.86
`85.31
`89.31
`
`94.30
`96.73
`97.09
`94.79
`96.16
`
`best stretchability in the weft-wise configuration and the poor-
`est stretchability in warp-wise. Sample 3 (WE-MU-1) has the
`best recovery property in both the warp-wise and weft-wise
`fabric configurations while sample 1 (WA-MO) has the poorest
`recovery property in both directions.
`These findings suggest that the stretchability of the spacer
`fabrics is closely related to their fabric type. The results shown
`in Fig. 5 reveal that the stretchability of a warp-knitted spacer
`fabric has a high stretchability only in the weft-wise direction,
`while the stretchability in the warp-wise direction is very low
`(below 50%). On the other hand, weft-knitted spacer fabrics
`have similar and high stretchability in both the weft-wise and
`warp-wise directions. As the spacer fabric is composed of two
`separate surface fabrics and linked together by a spacer yarn, it
`can therefore be concluded that spacer fabrics carry the same
`fabric stretchability as their fabric types (i.e. warp-knitted or
`weft-knitted).
`When the results of the weft-knitted spacer samples were
`compared, the stretchabilities of the weft-wise direction of
`samples 3 and 4 were found to be higher than those of samples
`2 and 5. This is due to samples 3 and 4 using multifilament
`spacer yarns, which have higher stretchability than those
`corresponding to samples using monofilament spacer yarns
`(King, 1985).
`
`4.
`
`Conclusion
`
`This study performs a quantitative investigation of various
`fabric characteristics, such as air permeability, thermal con-
`ductivity and low-stress mechanical properties (the latter
`including the stretchability, recovery, bending and compres-
`sion) of spacer fabrics. It is found that both air permeability
`and thermal conductivity are closely related to the fabric den-
`sity. The compression properties depend very much on the
`spacer yarn type and the spacer yarn arrangement. Bend-
`ing properties are closely related to the fabric type, structure,
`spacer yarn type and density while stretch and recovery prop-
`erties depend very much on fabric type and spacer yarn type.
`It is believed that the fabric characteristics of spacer fabric
`show a very significant effect on the air permeability, ther-
`mal conductivity and mechanical properties of spacer fabric.
`
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`
`Therefore, a careful selection of spacer fabric according to its
`envisaged application is of primary importance.
`
`r e f e r e n c e s
`
`Bras cups made from a new spacer fabric, 2001.
`Kettenwirk-praxis 2, E2–E3.
`Donaghy, J.G., Azuero, I.M., 1999. Moldable warp-knitted fabric
`and method of forming a seamless molded fabric portion
`therefrom. USPTO Patent Full Text and Image Database, US
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`Heide, M., 2001. Spacer fabrics: trends. Kettenwirk-praxis 1,
`E17–E20.
`Kawabata, S., Niwa, M., 1996. Modern Textile Characterization
`Methods. Marcel Dekker, New York, pp. 329–354, (Chapter 10).
`King, R.R., 1985. Textile Identification, Conservation, and
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`Lehmann, W., 1994. Elastic, moulded spacer fabric.
`Kettenwirk-praxis 3, E19–E20.
`Machova, K., Klug, P., Waldmann, M., Hoftmann, G., Cherif, C.,
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`McCartney, P.D., Allen, H.E., Donaghy, J.G., 1999. Underwire
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`
`same, and method of warp knitting such fabric. USPTO Patent
`Full Text and Image Database, US Patent No. 5669247.
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`Reisfeld, A., 1996. Warp Knit Engineering. National Knitted
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`Shepherd, A.M., 2004. Weft-knitted spacer fabrics. USPTO Patent
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`Wilkens, C., 1993. Raschel knitting spacer fabrics.
`Kettenwirk-praxis 3, E18–E20.
`Willmer, R., 2005. Circular knitting machine, especially for the
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`Zhang, P., Gong, R.H., Yanai, Y., Tokura, H., 2002. Effects of
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