1. Introduction
Environmental protection and methods to analyse the impact of textiles on quality and human health have been mandatory for many years and are now legal norms that need to be clarified through extensive product monitoring, such as circular economy principles. The choice of fibre is significant for the appearance of garments [
1] and the environmental impact in the dry state and after washes. Previous research described textile dust released into the atmosphere as a result of the production and use of various types of textiles. Exposure to textile dust occurs during the production process, finishing, use, textile care and textile recycling. A major problem with the presence of textile dust is the possibility of various diseases arising from daily exposure. Despite the focus on cotton dust, the same challenges exist in the processing, finishing, and application of a variety of natural and synthetic materials. Particles shed from synthetic textiles represent a bigger problem, as they are deposited and cannot be broken down for the most part, which further pollutes the environment and people [
2].
During the washing process, textiles are exposed to chemicals and mechanical agitation, which can create changes after repeated cycles. The extent of changes depends on textile characteristics (construction parameters, polymerisation degree, swelling capacity) as well as Sinner factors (chemicals, temperature, time, mechanical agitation) [
3].
Detergent formulations are often alkaline and contain bleach as oxidising agents, which can trigger the chemical damage of cellulose when combined with other elements. The loss of tensile properties in cotton textiles is strongly linked to the depolymerisation of cellulose [
4,
5]. Lower washing temperatures, high efficiency detergents, and low bath ratios are required for the washing process to be sustainable, resulting in external fibrillation and pigment particle migration [
6]. Cotton textile fibrillation may be associated with hydrophilicity, swelling, and construction features, namely the presence of shorter fibres in the yarn. This can be due to abrasion of the textile material in a wet (washing baths) or dry environment (tumble drying) [
7,
8]. Friction and deformation are two of the most common causes of clothing damage caused by washing machines [
9,
10]. The drying process at high temperature may affect the formation of cracks, and increased fibrillation.
Polyester fibres are characterised by high strength, crease resistance and fast drying, while cotton fibres are characterised by high strength, hydrophilicity and comfort [
11]. These two fibre groups account for more than 75% of global production, and thus the largest share of textile waste [
12]. Polyester fibres are semi-crystalline [
13], hydrophobic, do not swell in water and are not prone to certain degradation and fibrillation. The influence of abrasion under wet and dry conditions is related to the generation of pilling [
14,
15]. Cotton and polyester textiles have different dimensional stability in wet and dry environments, in addition to significant variances in characteristics.
Cotton fibres in the alkaline medium can swell radially and longitudinally during finishing, causing shrinkage and increasing the take-up and yarn cross-section. In fibres where the orientation of the cellulose chains is in the direction of the fibres, swelling is greater in the transverse direction than in the longitudinal direction [
16]. Increasing the crimp of washed cotton fabrics increases the elongation [
17].
Polyester materials may shrink or become damaged if exposed to a temperature higher than the temperature of thermal transition. It was found that recycled polyester sheds almost 2.3 times more microplastics in washing compared to virgin polyester, as the strength of the fibre is reduced due to thermal exposure and shear degradation during the recycling process [
18].
Cotton and polyester blends can meet special requirements for functional products, such as feel, appearance, dimensional stability, easy care and sufficient comfort [
14]. The blends offer a number of advantages over pure cotton materials, including the ability to wash at lower temperatures, to reduce deposit content and are less damaged after multiple wash cycles.
On the other hand, the presence of microplastic particles (MP) in natural and wastewater, sediment, soil, aquatic organisms, and air has been linked to textile sources [
19,
20,
21,
22,
23,
24].
According to [
25], “microplastic means particles containing solid polymer, to which additives or other substances may have been added, and where 1%
w/
w of particles have all dimensions 0.1 nm–5 mm, or a length of 0.3 mm–15 mm and length to diameter ratio of >3”.
The fragmentation [
26], degradation [
27], ageing [
28], washing [
29], and drying [
30] of synthetic textile products are all possible sources of MP particles in environment [
24]. Such products used for wet and dry cleaning of surfaces (mops), isolated synthetic fibres from vacuuming and drying, and fibres that come loose from clothing during home washing are the most common sources of MP in the environment [
31,
32]. Washing is thought to be responsible for around 35% of synthetic fibres in the environment [
15,
33].
The qualitative and quantitative determination of MP emissions and other released substances is difficult due to the variability and complexity of sources, as well as the fact that particulate matter is a vector for the dispersion of other emissions with varying degrees of risk in a real system. Numerous methods for determining particles were applied, either directly for the characterisation of dispersed systems [
20] or after separation methods [
34]. The choice of one or more methods of particle identification and/or separation in wet and dry environments is determined by knowledge of the system in which the particles originate. Total suspended solids (TSS) were found to be one of the best parameters for assessing the degree of particle loading in effluents and their separation [
31]. Various filters with different pore sizes can be used to determine this parameter, such as glass fibre filters [
35], polyethersulphonic filters [
36], cellulosic filters [
37,
38], polyamide, polycarbonate, metallic and aluminosilicate filters [
39,
40].
The purpose of this research was to examine cotton fabrics and cotton-polyester blends after three, ten, and fifty cycles by measuring the released particles in the dry state and in washes. Particles in the dry state were released by cyclic bending, so the particle sizes of the washed fabrics were measured separately. The distribution of particles released from cotton fabrics and fabrics made of a blend of cotton and polyester was observed both individually and as a combined system. The effluents of the washing process of the aforementioned fabrics were analysed by determining the physico-chemical parameters, TSS, TS (total solids), pH and conductivity to determine the degree of particle load.
At the same time, the effect of 3, 10 and 50 washing cycles on the thickness and strength, which are the structural properties of the investigated fabrics, were monitored. It is well known that Fourier transform infrared spectroscopy (FTIR) provides information about changes in the chemical structure and environment of polymeric materials, such as: the presence or absence of certain functional groups: shifts in the frequency of absorption bands and changes in the relative intensity of the bands; the appearance of new peaks due to modifications; and the monitoring of changes during the life cycle of the material [
41]. In addition, attenuated total reflectance Fourier’ transform infrared spectroscopy (FTIR-ATR) is a non-destructive analytical method that does not require lengthy sample preparation and has an exceptional wave number accuracy of 0.01 cm
−1, which allows for the determination of low concentrations of individual groups of compounds [
42]. For this reason, FTIR-ATR was applied in this study to evaluate the influence of 3, 10, and 50 washing cycles on the physicochemical changes of the cellulose polymer and polyethylene terephthalate that make up the cotton and cotton-polyester fabrics.
The originality of the research carried out can be seen in the connection between the amount of particles released from the fabrics in the dry state and and after the washing process.
2. Materials and Methods
2.1. Materials
Fabrics of 100% cotton and cotton-polyester (50:50) fabric in plain weave were produced on a Picanol OMNIplus 800 loom (air-jet loom, width 190 cm) at the Čateks d.o.o. textile mill, Čakovec, Croatia. The fabrics prepared in this way were scoured and, bleached according to the factory’s recipes and purchased for research purposes.The mass per unit area of cotton-polyester fabric is 158.6 gm−2, while the cotton fabric has a mass per unit area of 160.8 gm−2. Cotton and cotton-polyester fabrics have a warp and weft density of 20 picks per cm, and the fineness of two-ply yarn 14.2 tex.
The washing of the 3.6 kg fabrics, which contain 2.7 kg of cotton and 0.9 kg of polyester (3:1), was carried out in accordance with HRN EN ISO 15797:2002 using a standard detergent with fluorescent whitening agent, the composition of which is shown in
Table 1, to which 2 g/L peracetic acid (PAA) was added as a bleach in the washing process.
2.2. Washing Process
The cotton and cotton-polyester blend fabrics were washed in the laboratory washing machine Wascator FOM71 CLS by Electrolux at 75 °C using programme 2 with 3, 10, and 50 washing cycles. All process parameters comply with the standard, but due to the importance of the influence of the process conditions, a detailed description of programme 2 is included in
Table 2.
After washing, the samples were air-dried.
Table 3 shows the designations applied to samples before and after washing.
2.3. Methods
In order to monitor the influence of washing on the structural properties of fabrics before and after the washing cycle, the thickness was tested according to HRN EN ISO 5084:2003 Textiles -- Determination of thickness of textiles and textile products at ten different places using a thickness gauge DM 2000—Wolf, Germany with a precision of 0.001 mm. The thickness gauge is made up of two parts: a support to hold the material in place and a device called a pressure plate, which is a 25 cm2 circular plate that presses down on the material at a specific pressure (preload of 0.5 kPa). Tensile properties were measured on the samples in the weft direction before and after the washing cycles according to EN ISO 13934-1:1999 Textiles—Tensile properties of fabrics—Part 1: Determination of maximum force and elongation at maximum force using the strip method on a TensoLab Strength Tester (Mesdan S.p.A., Puegnago del Garda, Italy), distance between clamps 100 mm, bursting speed 100 mm/min and pretension 2 N.
Determination of overall decrease in breaking strength (total wear) was calculated according to ISO 4312:1989: Surface active agents—Evaluation of certain effects of laundering—Methods of analysis and test for unsoiled cotton control cloth.
The total wear,
Ut of the fabrics was calculated according to Equation (1):
where
Ut is total wear (%),
F0 is breaking force of unwashed fabric (N), and
F is breaking force of washed fabric (N).
Cotton and cotton-polyester fabric before and after 3, 10 and 50 washing cycles were analysed using Fourier transform infrared spectroscopy (FTIR, PerkinElmer, Spectrum 100, Shelton, CT, USA) with the attenuated total reflection (ATR) measurement technique obtained spectral curves were processed in Spectrum 100. Four scans were performed for each sample with a resolution of 4 cm−1 between 4000 cm−1 and 380 cm−1
The generation lint and other particles was measured on LasAir III (Particle Measuring Systems) laser particle counter connected to a particle generator in a laminar airflow booth. Samples were prepared according to EN ISO 9073-10 and mounted on the particle generator and subjected to controlled bending. The number of particles released during the test was measured in the following size categories: 0.3 µm for particle sizes of 0.3–0.5 µm; 0.5 µm for particle sizes of 0.5–1 µm; 1 µm for particle sizes of 1–5 µm; 5 µm for particle sizes of 5–10 µm; 10 µm for particle sizes of 10–25 µm; 25 µm for particle sizes larger than 25 µm. For each sample, the measurements were performed on 5 test tubes. This method was adopted from EN ISO 9073-10 Textiles—Test methods for nonwovens—Part 10: Lint and other particles generation in the dry state, with the test time adjusted to 30 min [
2].
The entire effluent (hence referred to as effluent) collected from the washing procedure and three rinse cycles was analysed as part of the research. Methods for characterising effluent after 3, 10 and 50 washing cycles include selected physicochemical parameters such as TSS, TS, pH, and conductivity.
The total suspended solids (TSS) of effluents were determined by the standard gravimetric method. After membrane filtration of effluent using 0.7 µm fibre glass filter (GF), mass of GF with filter cake as residue after drying at 100 °C was determined.
The total solids (TS) of effluents were determined by the standard gravimetric method in evaporating dish at 105 °C until constant mass was achieved.
pH and conductivity of effluents were determined using pH meter, Schott, ProLab 3000 and conductometer, CG 853, Schott, respectively.
To determine the similarity of the observed wash cycles and similar properties of all processed samples, hierarchical cluster analysis (HCA) was performed using a Minitab software, and graphs in the form of Ward’s dendrograms showed the homogeneous groups or clusters whose variables are connected by a certain similarity [
43].
4. Conclusions
This research examines the chemical, mechanical, and thermal impacts of 3 washing cycles, 10 washing cycles, and 50 washing cycles on 100% cotton and a 50/50 cotton-polyester blend in plain weave with no soiling in the dry state and after washes utilising fabric and effluent characteristics. Tensile properties, thickness and generated particles in the dry state depend on the number of washing cycles. Increased strength of cotton-polyesteru fabric after 3 and 10 washing cycles in the weft direction is the result of fibrillation and shrinkage. Changes in fabric properties, expressed as total wear in the warp direction after 50 washing cycles compared to unwashed amounting to 41.2% for cotton and 30.9% for cotton-polyester blend, can be attributed to the synergy of process parameters, fabric structure and raw material composition.
The number of particles released in the dry state > 25 µm is significantly lower than the number of particles released in the size of 0.3 to 5 µm. In all size categories, the quantity of particles released in the dry state is much larger from washed cotton fabric than from washed cotton-polyester fabric. Because the detergent contains water-soluble components, the TSS values obtained confirm the degree of contamination of the effluent with particles from the tested textile materials.
From the spectral bands of CO and CO /PES samples before and after 3, 10 and 50 washing cycles, no significant changes at the physicochemical level within the polymers of the tested samples were identified.
According to HCA dendrograms, particle release in early wash cycles is mostly regulated by material structure. Future wash cycles are influenced by chemical, mechanical, and thermal interactions. The findings of the research highlight the need for the use of an analytical approach to categorise and quantify particles released from textiles in both the dry state and washes in order to decrease the potential for detrimental impacts on humans and the environment.