One of nonwoven fabric manufacturing aims is reproducing textile- like fabrics in terms of their mechanical properties. The ability of nonwovens to be made in apparel products is judged according to their physical and mechanical properties. Nonwoven mechanical properties have been long studied to detect their similarity to traditional textiles.
The low drape of nonwoven fabrics has precluded their usage in the apparel industry. However there has been substantial progress in nonwoven fabric properties since the studies showed poor drapeability of nonwovens compared to traditional fabrics. Studies concerned with nonwovens drape are now reviewed.
Cusick in 1962 investigated subjectively the drape amount and preference of a group of six fabrics including two nonwoven (bonded-fibre) fabrics. Half skirts were tied on a model and assessed by a panel of judges. The nonwoven fabrics were the lowest drapeable fabrics. However one of them was preferred to one skirt made of woven fabric. Six nonwoven fabrics were tested objectively using the drape coefficient, number of nodes and bending and shearing stiffness. These fabrics were random webs and bonded chemically using a nitrile rubber binder and had different fibre contents. The drape coefficient values ranged between 94.3- 96.3% and none of them draped well or generated nodes on the darpemeter. Nonwoven fabrics measured were found with bending length and shear stiffness higher than apparel fabrics (Cusick 1962).
Cusick et al. in 1963 measured selected physical properties of a range of commercially available nonwoven fabrics at that time, including parallel-laid, cross-laid, random laid, composite, and perforated fabrics. Two woven fabrics were also examined for comparison. They found that the nonwovens lacked the attractive appearance and aesthetic appeal of the woven fabrics. Parallel laid fabrics were preferred over random and cross laid fabrics. Fibre and binder properties and the nature of the association between them and the web structure characterised the nonwovens’ mechanical behaviour. The nonwovens and wovens measured had significantly different behaviour. The woven fabric strength was higher than nonwovens except parallel-laid nonwoven fabrics. Generally, the initial modulus which was dependant on fibre type, increased with the fabric nonwoven density. Rupture, bursting and tear strength were higher for woven fabrics than nonwovens. The tear strength had the least difference between the two types of fabrics. Nonwovens had higher crease resistance than woven fabrics. The bending length of the nonwovens were higher than the woven fabrics’ with ranges 10- 4 cm and 1-4 cm respectively. The nonwovens had higher shear moduli than the wovens. The nonwovens had lower drape than woven fabrics, the nonwoven DC was around 96% and the woven fabrics had DC between 71
and 39%. One of the woven fabrics (rayon sailcloth) had drape behaviour similar to the nonwovens. They found that the drapemeter was insensitive to differentiate between fabrics of high DC including nonwovens. The drapemeter dimensions were developed for measuring woven fabrics and were not suitable for nonwoven fabrics (Cusick et al. 1963). This could support this current research study’s objective to develop an alternative drape measurement system for measuring nonwovens drape.
Hearle et al. studied the impact of fibre, binder and weight on nonwoven fabrics’ properties. Fabric initial modulus was correlated with drape coefficient. Fabric initial modulus is related directly to its components’ (fibre and binder) moduli. They found that fibre modulus had a significantly higher impact on nonwovens’ modulus than the binder modulus. Also, they found that nonwovens with similar drapeability to traditional textiles (DC around 70%) could be made by employing fibre content with initial modulus around 30 g/tex. Increasing the nonwovens weight threefold was found to improve the nonwoven’s drapeability (Hearle, Michie and Stevenson 1964).
In 1965, Cusick tested a group of fabrics including 124 woven fabrics and 6 nonwovens for drape coefficient. The woven fabrics’ drape coefficient ranged between 26.4 and 97.2. The nonwovens’ DC ranged between 96.3 and 97.7. This means that the nonwoven fabrics had low drapeability and there were woven fabrics with similar drapeability to them (Cusick 1965). In 1965, Freeston and Platt stated that nonwovens at that time had high stiffness due to their constituent fibres having restricted movement which was due to the type of bonding between them. The existence of binder increased the tensile strength and decreased the flexibility. However, the flexibility could be improved by adjusting the manufacturing processes. It was found that increased fibre length at bond areas between fibres, fibre density and the distance between bonding points and using binders with improved mechanical properties (lower moduli with maintenance of elastic recovery and strength) were able to enhance the flexibility (Freeston and Platt 1965).
Michie and Stevenson studied improving the aesthetic characteristics of nonwoven fabrics while retaining the initial fabric strength. They studied the effect of stretching on the mechanical properties of the nonwoven fabrics. They determined that stretching beyond a threshold value of 3% decreased the initial modulus, shear modulus, bending length, and drape coefficient. Slight change was found for the rupture stress. However, no effect was found for the breaking strain and the elastic recovery. The drape coefficient showed significant relationship with bending length, but this was not true with shear modulus. The drape behaviour was improved significantly for the more extensible fabrics, in the best case, DC changed from 96% to 91%. It was determined that the improvement in drape is, therefore, greater than
might be gauged from the rather small decrease in drape coefficient and is certainly significant. At the same time, the fabrics cannot be claimed to have reached the stage of reasonable drape in the textile sense (80% highest) (Michie and Stevenson 1966).
Zeronian and Wilkinson related nonwoven bending length and modulus to the draping quality of fabrics. However, they stated that initial modulus is not easily related to nonwoven drape if it differs inconstantly with the bending modulus. The heat-bonded nonwovens acted more similarly to elastic homogenous materials than the saturated-bonded fabric. Uniform distribution of binder and thickness were required if equality between bending modulus and initial modulus which provides moduli similar to homogeneous elastic material, was to be achieved. Moreover, they stated that nonwovens of viscose rayon fibres grafted with poly- n butyl acrylate had the highest moduli due to its high adhesion effect. Low bending modulus was required for improved drape. Therefore, strong saturation-bonded fabrics which had high initial modulus subsequently had poor drape behaviour unless the high initial modulus is coupled with low bending modulus. This impact would be achieved by increasing the binder content in the inner side of the nonwovens than the outer sides which would be able to enhance the draping quality (Zeronian and Wilkinson 1966).
Sengupta and Majumdar found that drape and handle of parallel-laid nonwoven fabrics of xanthate-binder and cotton fibres improved with the addition of a wetting agent, as inferred from the values of initial moduli (Sengupta and Majumdar 1971).
Newton and Ford in 1973 stated that nonwoven stiffness and strength have been long linked to each other. Stiff undrapable nonwovens had always high strength. This means that there had to be a choice between engineered fabric stiffness or strength which prevents nonwovens from being used in apparel manufacture. However, recently, nonwoven properties were improved and became more textile like with good drape and strength properties (Newton and Ford 1973).
The performance characteristics of seven fusible interfacings (woven, knitted and nonwoven) including drape in terms of their effect on face fabric were investigated by Koenig and Kadolph in 1983. The drape coefficients of all interfaced specimens were higher than face fabric with no interfacing. A similar drape profile was found for specimens with interfacings within the same physical structure group, however different drape profiles were found for each interfacing group from different groups. Interfaced specimens draped parallel to their least rigid direction (the bias direction) when interfacings had similar rigidity in lengthwise and crosswise directions. However, they draped parallel to the lengthwise direction when the interface fabric’s lengthwise rigidity was greater than its cross direction ( oriented
web). Interfacing structures with the least rigidity had the least effect on the drape configuration of the fabric with no interfacing (Koenig and Kadolph 1983).
Amirbayat and Hearle’s point of view was that nonwovens had properties midway between textiles and paper properties, this could enable them to be more employable for textile products due to their increased resemblance to textile properties (Amirbayat and Hearle 1989a).
Patel and Warner developed a new model to predict the bending behaviour of point bonded nonwoven fabrics. The bending performance of nonwoven fabric was estimated from the basic fibre and fabric properties i.e. fibre diameter and modulus, fabric and bond thicknesses, as well as unit cell and bond dimensions. This could assist fabric designers to determine its drapeability (Patel and Warner 1994).
These bonding processes using binders, however, seriously limit the relative freedom of movement between fibres, and the most limiting property of nonwovens was their poor drape. Termonia showed that nonwovens with a three-dimensional fibre orientation distribution have a much lower bending stiffness than those with a planar distribution. Variations in fibre density across the fabric thickness are also of great importance. Random variations due to inconsistency in the laydown process increased the bending stiffness. Whereas the latter can be considerably decreased by concentrating most of the fibre weight within the neutral (or mid-) plane of a fabric. This study agrees with Freeston and Platt’s results (Termonia 2003).
Saleh in 2003 investigated the capability of using nonwovens in the apparel field – especially as shirting fabrics in terms of their mechanical properties. The FAST properties of nonwoven fabrics including different bonding methods (i.e. hydroentangled, chemically bonded, thermal bonded and hydroentangled + chemically bonded) and fibre content (i.e. Viscose rayon, polyester, cotton and Nylon) were compared with woven fabrics (already used in apparel production. The four types of mechanical properties’ curves/ trends on polar plot, generally, showed similar silhouette (behaviour/trend). However, the hydroentangled fabrics had the lowest values of bending length, bending rigidity and shear rigidity and the highest extensibility values. So, she found that the hydroentangled nonwovens could show good handle properties compared to other nonwovens. Saleh referred this ability to the free fibres in the cross section due to their twist and migration within the fabric structure.
Saleh also found that the mechanical properties of the hydroentangled nonwovens lie between the maximum and the minimum values of the woven shirting fabrics except the extension at 5, 20 and 100g/cm in the crosswise direction. This was considered probably to the low weight of the tested
hydroentangled nonwovens, as there was a reverse relationship between fabric weight (area density) and extensibility.
She has concluded that the potentiality for the presence of nonwovens- as light weight fabrics- in the apparel industry was dependent on hydroentangled fabrics (based on their low stress mechanical properties) (Saleh 2003).