The effect of thermal properties on the three-dimensional knitted spacer fabrics made from functional fibers (i.e. Outlast, Coolmax) with different fiber compositions was studied. The spacer fabrics were specifically designed for mattress ticking applications. Samples were manufactured with two fabric tightness and knit designs, and four Outlast fiber compositions. Thermal conductivity, thermal resistance, thermal absorptivity, thermal diffusivity, and relative water vapor permeability were considered as thermal comfort properties. Alambeta and Permetest devices were used for the measurement of thermal properties. Fabric design was the leading criteria on the thermal resistance and water vapor permeability, while fiber compositions became more important on the thermal absorptivity. The contribution of Outlast fiber on the thermoregulatory efficiency of spacer fabrics was analyzed using a differential scanning colorimeter. The thermoregulatory effect of Outlast fiber was slightly observed in the 33% Outlast fiber composition. Water vapor permeability of open-skin samples was higher than the closed-skin samples, which was due to the holed/meshed structure of the open-skin structure for the same fiber content and fabric construction. Statistical analysis was also performed and confirmed the contribution of each factor, including their interactions. In particular, the interaction became more significant than the main factors for thermal diffusion behavior of samples.
The principle function of clothing is to enable the human to remain in a good physiological state, which is accepted as comfort. This state should cover thermal balance between internal body temperature and the environment, and maintaining the perspiration rate at a balance level. At the level of comfort, the skin temperature should be in the range of 33–35C. Knitted fabrics are usually preferred next-to-skin wear due to their extensibility and soft touch, while such positioning leads fabric comfort to be more important than in woven or non-woven fabrics.
The early studies related to the thermal properties of textiles set up the theoretical background for the concept of thermal behavior fabric and its relation with the human body.1–6 Clothing comfort is composed of three main features: thermophysiological, sensorial, and physiological comfort. Thermal- and moisture-related properties of textiles deals with the thermophysiological comfort of fabrics. Dynamic surface wetness of fabrics was correlated with skin contact comfort in wear for a variety of fabric types in which mobility of thin films of condensed moisture is an important element of wearing comfort.7 The mathematical model of the principal thermal properties in functional knit structures was devised by Geraldes et al.8 Thermal comfort properties of functional polypropylene knitted fabric for active wear and socks were evaluated for efficiency of fiber structure to suck moisture from the skin.9,10 The effect of fabric knit on the thermal comfort properties was studied by Oglakcioglu and Marmarali.11 Uc¸ ar and Yilmaz12 focused on thermal properties of various rib knit structures. Ozdil et al.13 reported the thermal properties of rib knit fabrics using various yarns of different yarn properties. Ramachandran et al.14 studied thermal insulation, thermal conductivity, and thermal diffusion of single jersey, rib, and interlock knitted fabrics made from ring and compact spun yarns.
The thermal behavior of next-to-skin knitwear has been studied by several researchers.9,10,15 Armit16 brought some specific aspects of bedding textiles and their influence on thermal comfort and sleep. The relation between the cool sensation of pillows and their thermal transport properties was investigated with special attention to the padding material.17 However, no researcher paid attention to the thermal comfort properties of three-dimensional (3D) knitted spacer fabrics specifically designed for mattress fabrics. The present research focuses on the effects of different fabric manufacturing parameters on the thermal comfort properties of mattress fabrics made from 3D spacer fabrics, rather than made by the usual production techniques and applications of spacer fabrics, as reviewed by Bruer et al.18 Statistical analysis was also performed for revealing the contribution of interactions in addition to the main effects. Special attention was given to the contribution of functional fibers, such as Outlast and Coolmax, on the thermal behaviors.
Materials and methods
Three-dimensional knitted spacer fabric was manufactured using different fibers (Coolmax, cotton, polyester (PES), Outlast) at different layers of fabric. Yarn properties were given in the order on which sections of the 3D knitted spacer fabrics they actually used (Table 1). Samples were knitted with E20, a 38-inch diameter double jersey circular knitting machine equipped with a spacer attachment. The term ‘spacer fabric’ refers to 3D knitted spacer fabric in this paper.
Samples were manufactured with two fabric tightness and knit designs, and four Outlast fiber compositions, where fabrics coded with letters ‘A’ and ‘B’ indicated loosely and densely knitted closed-skin structures, respectively, and letter ‘C’ indicated loosely knitted open-skin structure (Figure 1). The samples coded with ‘A’ and ‘C’ were knitted with the same machine settings, whereas ‘B’ coded samples used different machine settings in order to knit them densely.
The plain knit was used on both sides (face layers) of the spacer fabric for the samples with the closed-skin structure (A and B coded samples). The design of the open-skin structure (Figure 2) (C coded samples) is different in that one side of the spacer fabric is meshed knit, while other side is plain knit, similar to the samples coded with ‘A’ and ‘B’. While coding the samples, the numbers beside the capital letters indicated the level of Outlast fiber composition. For example, sample code A1 means a loose closed-skin structure with the Outlast fiber level of one. The positioning of yarns within each layer of spacer fabric, including the sample codes, is shown in Table 2. Front face layer refers to the side of the spacer fabric that is in touch with the human skin lying on the mattress, while the reverse face layer refers to the side of the spacer fabric that is in touch with the foam of the mattress, namely the lining side of the spacer fabric.
Multifilament PES yarn was used at the reverse face layer of all samples. On the front face layer of the spacer fabric, the ring spun yarn made from staple PES fiber and Outlast viscose fiber was used, with the percentage was given in Table 1. Monofilament PES yarn was always used at the binding layer (pile section) of all samples for generating the resilience property of the spacer fabric. The pile yarn density remained constant at all spacer fabrics. Fiber type and fiber composition were varied only at the front face layer of the spacer fabric; fabric design was also varied at this layer. Fiber composition of the sample was determined depending on the number of the yarns unraveled for loop length measurements. The fiber compositions given in Table 3 are the weight percentage of individual fibers within the fabric. The percentage of silver and carbon fibers within the given spacer samples are 0.3% and 1%, respectively; hence, these negligible percentages were not given in Table 3.
Fabrics were relaxed at a stenter, which is adjusted for spacer fabric finishing reaching final dimensional stability. The samples were laid on a flat surface in a standard atmospheric environment (20 2C and 65 2% RH) for a day, before the measurements were performed. Loop densities were measured using a magnifier. Loop density was measured at the front face layer of the spacer fabric. Ten measurements were made at different places of fabrics and the average was recorded. Fabric thickness was measured using a J. H. Heal & Co. Ltd fabric thickness meter according to the BS 2544 standard. The EN12127 standard was used for fabric weight measurements.