Effect of CO2 Laser Treatment on the Fabric Hand of Cotton and Cotton/Polyester Blended Fabric

polymers

Article Effect of CO2 Laser Treatment on the Fabric Hand of Cotton and Cotton/Polyester Blended Fabric

On-na Hung and Chi-wai Kan *

Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; [email protected] * Correspondence: [email protected]; Tel.: +852-2766-6531

Received: 20 October 2017; Accepted: 8 November 2017; Published: 13 November 2017

Abstract: This paper compares the impact of laser treatment on cotton and cotton/polyester blended fabric hand properties, using the PhabrOmeter system. Five fabric hand properties, namely, stiffness, smoothness, softness, wrinkle recovery rate, and drapability, were obtained, and it was proven that laser treatment could be successfully used to change the fabric hand. In the case of pure cotton woven fabrics, the fabrics were found to have better drapability and wrinkle recovery after laser treatment. In cotton/polyester blended fabrics, stiffness was found to be relatively higher after laser irradiation.

Keywords: fabric hand; PhabrOmeter; CO2 laser; cotton; polyester; woven; blended fabric

1. Introduction The aim of this study was to evaluate the impact of laser treatment on fabric hand properties of plain pure cotton and cotton/polyester blended fabrics. Carbon dioxide (CO2) laser was used with different intensities in terms of resolution and treatment time. Due to the increasing concerns about pollution and protection of the environment, the need for environmentally friendly methods for surface treatments is established. Laser treatment, based on physical principles, offers advantages over conventional chemical methods. It enables precise surface modification in a short time. It is easy to apply and control and is totally environmentally clean with no consumption of water or chemicals [1–5]. Fabric hand has been recognized as one of the most important performance attributes of apparel textiles. It is defined as “perceived overall fabric aesthetic quality” [6]. The quality of the textile material is mainly perceived by touching and has a direct impact on the product’s appeal. Fabric hand not only affects the perception of consumers towards the products, but also development from the stage of design to manufacturing and merchandising through to the final consumer. Research works on fabric hand have used mainly two measurement approaches: subjective and objective assessments. Fabric hand obtained by subjective assessment is a traditional procedure in which trained handle experts describe the fabric quality. However, according to Pan [7], fabric hand is defined as the human tactile sensory response towards fabric, which involves not only physical but also physiological, perceptional, and social factors, which largely influence the accuracy and repetitive nature of the result. Since the subjective assessment is easily influenced by many factors, objective assessment methods like the Kawabata Evaluation System for Fabric (KES-F), the Fabric Assurance by Simple Testing (FAST), and PhabrOmeter systems have been developed. These systems quantify the fabric hand in terms of low-stress mechanical properties, including bending, shear, tensile, and surface properties [8–10]. Unlike the complex and lengthy KES-F and FAST measurement processes, the newly developed PhabrOmeter system has overcome these limitations as it can rapidly evaluate fabric hand properties [11]. A PhabrOmeter instrument is a fabric sensory quality evaluation system developed by Nu Cybertek, Inc. in Davis, CA, USA, and has become a designated machine by American Association

Polymers 2017, 9, 609; doi:10.3390/polym9110609 www.mdpi.com/journal/polymers Polymers 2017, 9, 609 2 of 12 of Textile Chemists and Colorist (AATCC) standard for fabric hand evaluation [12]. The PhabrOmeter system measures the “feels and looks”, or so called “sensory perceptions”, of such sheet type fibrous products. The PhabrOmeter system consists of an instrument and a software package. The system is based on the pattern recognition theory, by extracting the quality characteristics of the product, and connecting them to the human sense, so as to provide fast and reliable quality evaluation results. It fills a very important blank [12]. This system can measure both woven and knitted fabrics, and is capable of testing fabric hand objectively and obtaining the data in terms of five handle features, namely, stiffness (a higher value of stiffness refers to a stiffer fabric), smoothness (the larger the smoothness value, the smoother the fabric is), softness (the smaller the softness value, the softer the fabric is), drape (the smaller the drape value, the better the draping or shape of the fabric will be), and wrinkle recovery rate (a larger value of wrinkle recovery rate value implies higher resistance to wrinkling of the fabric) in one-time testing [13]. In order to study the effect of laser treatment on fabric hand, the PhabrOmeter fabric evaluation system is used for measurements in this study. By understanding the alteration of different properties of fabrics through laser treatment, better choice can be made between pre- and post-laser treatment in order to obtain the most desired fabric hand effect.

2. Experimental

2.1. Materials Two types of ready-for-dyeing woven fabrics were purchased from Lai Tak Enterprises Limited, Hong Kong, China. The fabric speciﬁcations are as shown in Table1.

Table 1. Fabric speciﬁcations of two woven samples.

Fabric code Cotton Cotton/polyester blended fabric Fabric Structure 3/1 Twill 3/1 Twill Composition 100% Cotton 60% Cotton/40% Polyester * Fabric Weight (g/m2) 240 229 Warp Density (end/cm) 57 48 Weft Density (pick/cm) 23 24 Warp Count (Tex) 34 29 Weft Count (Tex) 30 38 Yarn Twist Z twist Z twist * Percentage was obtained by solubility test based on BS4407: 1988 with 2% tolerance.

2.2. Sample Preparation The fabric samples were soaked with 30 mL/L acetone (Sigma-Aldrich, Hong Kong, China) for 10 min to remove any grease and dirt on the surface. After washing, the samples were rinsed with water and hydro-extracted in a Nyborg C290R Hydro-extractor for 5 min. Lastly, the samples were dried in a Nyborg T4350 tumble dryer (Electrolux, Stockholm, Sweden) for 15 min. All cleaned samples were conditioned under standard conditions of 65 ± 2% relative humidity and 21 ± 1 ◦C temperature for at least 24 h prior to all experimental and evaluation tests.

2.3. Laser Irradiation

A commercial pulsed CO2 source laser engraving machine (GFK Marcatex FLEXI-150, Jeanologia S.L., Valencia, Spain) was used under atmospheric conditions, coupled to an Easymark 2009 laser system (Roﬁn, Hamburg, Germany). The fabric samples were treated at different combinations of processing variables (resolution and pixel time), resolutions 52, 60, and 68 (dpi) and pixel time of 110, 120, 130, and 140 (µs), i.e., 12 combinations in total. Polymers 2017, 9, 609 3 of 12

2.4. Fabric Thickness Fabric thickness was measured by a thickness tester (Hans Baer AG, CH-Zurich telex 57767, Zurich, Switzerland) according to the ASTM D1777-96. Three specimens were used and the thickness of each specimen was measured at 10 different positions. Finally, the averaged thickness of each specimen was calculated. The change of fabric thickness was calculated based on Equation (1):

T − T Thickness change (%) = o × 100% (1) To where T (mm) refers to the thickness of the sample after treatment and To (mm) refers to the original thickness of the sample.

2.5. Fabric Hand Measurement Fabric hand properties were measured by the PhabrOmeter Model 3 fabric evaluation system (Nu Cybertek Inc., Davis, CA, USA) with software 3.7.1 according to the standard AATCC test method 202-2012. Three circular specimens with a diameter of 113 ± 2 mm were randomly cut from each fabric sample followed by testing, and were then averaged. Quantified data including stiffness, smoothness, softness, wrinkle recovery rate, and drape index were obtained with the following definitions. Stiffness—Any material that is easily bent may be described as flexible, limp, or pliable. Smoothness—Surface friction is resistance of surface to slipping. It can be thought of as how hard you have to push your fingertip to move it across a fabric. Softness—Compressibility may be judged by squeezing a crumpled piece of fabric in your hand. Wrinkle Recovery Rate—After the first measurement of a given fabric sample, the sample is allowed to recover for 5 min (ASTM) and is tested again. Drape Index—The extraction test is in fact a forced drape, and so it should be able to describe the fabric dynamic drape behavior. The test results can be used for drape test and comparison.

2.6. Scanning Electron Microscopy (SEM) Surface morphology of the fabric was investigated by SEM (Lecia Stereoscan 440, Cambridge Instruments, Cambridge, UK) with a resolution of 3 nm at 40 kV.

3. Results and Discussion

3.1. Cotton Fabric

3.1.1. Stiffness The stiffness of the control and the laser-treated fabrics is presented in Figure1. According to the PhabrOmeter system, the higher the value of stiffness, the stiffer the sample will be. Stiffness refers to the resistance offered by a material to a force tending to bend it [14]. Bending of the fabrics is affected by the mobility of warp and weft yarn, which is influenced by the fiber-fiber friction. With a greater fiber-fiber friction, the ability of the fibers to slide past each other during yarn and fabric deformation diminishes. This leads to a better resistance to deformation and consequently greater stiffness. The control fabric had stiffness value of 41.55. The control fabric had a lower stiffness value than most of the laser-treated fabrics, which demonstrates that the fabrics become stiffer after laser treatment [11]. Rigidity is affected by the friction coefficient between fibers forming the yarns and yarn diameter [15]. The higher rigidity is due to the etching effect caused by the laser treatment, as different sizes of pores are formed on the fiber surface leading to higher surface friction [16–18]. This is proven by the SEM image of laser-treated cotton shown in Figure2. The increase in the coefficient of friction between fibers results in the lower mobility of yarns. The increase in stiffness after laser treatment means the fabric becomes more difficult to sew and less comfortable to wear. Polymers 2017, 9, 609 4 of 12

44 Polymers 2017, 9, 609 4 of 12

Polymers 2017, 9, 609Stiffness 42 4 of 12

40 50 38 48

44 Laser processing variables (resolution/pixel time)

Stiffness 42 Figure 1. Relationship between the laser processing variables and stiffness of cotton fabric. 40 The control fabric had stiffness value of 41.55. The control fabric had a lower stiffness value than most of the laser-treated38 fabrics, which demonstrates that the fabrics become stiffer after laser treatment [11]. Rigidity is affected by the friction coefficient between fibers forming the yarns and yarn diameter [15]. The higher rigidity is due to the etching effect caused by the laser treatment, as different sizes of pores are formedLaser on the processing fiber surfac variablese leading (resolution/pixel to higher surface time) friction [16–18]. This is proven by the SEM image of laser-treated cotton shown in Figure 2. The increase in the coefficient of friction between fibers results in the lower mobility of yarns. The increase in stiffness after laser Figure 1. Relationship between the laser processing variables and stiffness of cotton fabric. treatmentFigure means 1. Relationship the fabric becomes between more the laser difficult processing to sew variables and less and comfortable stiffness of to cotton wear. fabric. The control fabric had stiffness value of 41.55. The control fabric had a lower stiffness value than most of the laser-treated fabrics, which demonstrates that the fabrics become stiffer after laser treatment [11]. Rigidity is affected by the friction coefficient between fibers forming the yarns and yarn diameter [15]. The higher rigidity is due to the etching effect caused by the laser treatment, as different sizes of pores are formed on the fiber surface leading to higher surface friction [16–18]. This is proven by the SEM image of laser-treated cotton shown in Figure 2. The increase in the coefficient of friction between fibers results in the lower mobility of yarns. The increase in stiffness after laser treatment means the fabric becomes more difficult to sew and less comfortable to wear.

Figure 2. Morphological feature (200×) of control cotton fabric (left) and laser-treated cotton fabric Figure 2. Morphological feature (200×) of control cotton fabric (left) and laser-treated cotton fabric with variables of 52 dpi/120 µs (right). with variables of 52 dpi/120 µs (right). As far as the laser processing variables are concerned, stiffness values of laser-treated fabrics are enhancedAs far asgradually the laser when processing the resolution variables and are pixel concerned, time are stiffnessincreased. values It is also of laser-treatedproved from the fabrics SEM are enhancedimages that gradually when the when resolution the resolution was increased and pixel and time pixel are time increased. was prolonged, It is also the proved density from and the sizes SEM imagesof pores that formed when on the the resolution fiber surface was were increased enhanced and [1 pixel8]. The time reason was prolonged,for this is that the with density the increase and sizes ofin pores resolution formed (dpi), on the more ﬁber laser surface spots wereare produced enhanced in [one18]. inch. The reasonThis leads for thisto continuous is that with dehydration the increase inand resolution oxidization,Figure (dpi), 2. Morphological resulting more laser in thefeature spots formation (200×) are produced of of control more incottonpores one fabric[18]. inch. This (left This )consequently and leads laser-treated to continuous increases cotton fabric the dehydration surface andfriction oxidization,with and variables thus resulting the of stiffness52 dpi/120 in the value µs formation (right [10].). Among of more all pores the laser-treated [18]. This consequently samples, the increases sample treated the surface at friction68 dpi/140 and thusµs has the the stiffness highest valuestiffness [10 value,]. Among which all means the laser-treated that this fabric samples, is the stiffest. the sample treated at As far as the laser processing variables are concerned, stiffness values of laser-treated fabrics are 68 dpi/140enhancedµ sgradually has the highest when the stiffness resolution value, and whichpixel time means are increased. that this fabricIt is also is theproved stiffest. from the SEM images that when the resolution was increased and pixel time was prolonged, the density and sizes 3.1.2. Smoothness of pores formed on the fiber surface were enhanced [18]. The reason for this is that with the increase inSmoothness resolution (dpi), describes more surfacelaser spots friction are produced or resistance in one to inch. slipping. This leads The to larger continuous the smoothness dehydration value, the smootherand oxidization, the fabric resulting is. Figure in the3 formationshows the of smoothness more pores [18]. value This of consequently the control and increases laser-treated the surface fabrics. Thefriction control and fabric thus has the the stiffness lowest value smoothness [10]. Among value all but,the laser-treated after laser treatment,samples, the the sample smoothness treated at value increases.68 dpi/140 This µs indicates has the highest that laser stiffness treatment value, which enhances means the that smoothness this fabric is of the the stiffest. cotton fabric surface.

As laser treatment has an etching effect on fabric surfaces, all ﬁbers protruding from the fabric surface are etched away (Figure2)[ 18]. With the increment of resolution (dpi), more laser spots are produced in one inch which would result in dehydration and oxidization for removing surface protruding fibers [18]. Therefore, the smoothness of fabric surface was enhanced, making the surface of the fabric more even. Polymers 2017, 9, 609 5 of 12

3.1.2. Smoothness Smoothness describes surface friction or resistance to slipping. The larger the smoothness value, the smoother the fabric is. Figure 3 shows the smoothness value of the control and laser-treated fabrics. The control fabric has the lowest smoothness value but, after laser treatment, the smoothness value increases. This indicates that laser treatment enhances the smoothness of the cotton fabric surface. As laser treatment has an etching effect on fabric surfaces, all fibers protruding from the fabric surface are etched away (Figure 2) [18]. With the increment of resolution (dpi), more laser spots are produced in one inch which would result in dehydration and oxidization for removing surface Polymersprotruding2017, 9, 609 fibers [18]. Therefore, the smoothness of fabric surface was enhanced, making the surface5 of 12 of the fabric more even.

Smoothness 72

Laser processing variables (resolution/pixel time)

Figure 3. Relationship between laser processing variables and the smoothness of cotton fabric. Figure 3. Relationship between laser processing variables and the smoothness of cotton fabric. When the effect of laser processing variables is considered, resolutions of 52 dpi, 60 dpi, and 68 dpiWhen show the similar effect effects of laser when processing the pixel variables time is altered is considered, from 110 resolutionsµs to 140 µs. of The 52 dpi,smoothness 60 dpi, andis thus 68 dpi showenhanced. similar As effects a result, when the the increase pixel of time laser is processi alteredng from variables 110 µ withins to 140 theµ ranges. The of smoothness52 dpi/110 µs is to thus enhanced.68 dpi/140 As µs a result, improves the the increase smoothness of laser of processingcotton fabric. variables within the range of 52 dpi/110 µs to 68 dpi/140 µs improves the smoothness of cotton fabric. 3.1.3. Softness 3.1.3. SoftnessSoftness is the flexural property of the fabric and is one of the factors related to the determination ofSoftness the wear is comfort the flexural of clothing. property It is of defined the fabric as compressibility, and is one of the i.e., factors the smaller related the to value, the determination the softer the fabric will be. All laser-treated fabrics have a larger value than the control fabrics (Figure 4), of the wear comfort of clothing. It is defined as compressibility, i.e., the smaller the value, the softer the implying that the fabrics have a slightly harsher surface after laser treatment, which reduces the fabric will be. All laser-treated fabrics have a larger value than the control fabrics (Figure4), implying softness during physical touching [13]. This decrease in softness may be due to the etching effect of thatfibers the fabrics caused have by laser a slightly treatment. harsher The softness surface value after laserof fabrics treatment, is found which to have reduces further theincreased softness when during physicalthe laser touching processing [13]. variables This decrease are enhanced, in softness implying may bethat due the tosoftness the etching of fabrics effect decreases. of fibers Since caused by laserthickness treatment. is one of The the softnessfactors affecting value ofthe fabrics softness is, laser found treatment to have with further high increased energy causes when a larger the laser processingreduction variables in thickness are (the enhanced, thickness implying may change that fr theom softness0.52 mm to of 0.44–0.47 fabrics decreases. mm after laser Since treatment) thickness is one[10] of the and factors hence lowers affecting the thesoftness softness, of the laser fabric treatment [17]. with high energy causes a larger reduction in thickness (the thickness may change from 0.52 mm to 0.44–0.47 mm after laser treatment) [10] and hencePolymers lowers 2017 the, 9, 609 softness of the fabric [17]. 6 of 12

82 80 78 76 74

Softness 72 70 68 66

Laser processing variables (resolution/pixel time)

Figure 4. Relationship between laser processing variables and the softness of cotton fabric. Figure 4. Relationship between laser processing variables and the softness of cotton fabric. 3.1.4. Wrinkle Recovery Rate Creasing/wrinkles of a fabric during wear do not constitute a desirable change in appearance. Cellulosic materials like cotton have poor resistance to creasing. The wrinkle recovery value measures the wrinkle resistance of the fabric. A larger wrinkle recovery rate implies higher resistance to the wrinkling of the fabric. This value is determined by measuring the fabric hand and drape of the fabric twice with a given time interval between measurements. During the test, the fabric is subjected to a pulling force and experiences complex wrinkles. After it is given a recovery time, the differences in terms of the defined fabric hand variables are measured again when it is tested for the second time. As shown in Figure 5, the control cotton fabric has a lower wrinkle recovery value than laser-treated fabrics. Therefore, the control cotton fabric tended to wrinkle more than the laser-treated fabrics. The larger values of the laser-treated cotton fabrics imply better recovery from the deformation during the test. After laser treatment, the fiber surface becomes rougher and thus the inter-fiber frictional force is increased, which will better withstand wrinkling. Therefore, laser treatment improves the wrinkle recovery of cotton fabrics. The improvement in the wrinkle recovery of cotton fabrics after laser treatment may help to reduce the conventional methods of anti-wrinkle finishing, which involve chemicals.

Wrinkle recovery rate Wrinkle recovery 0

Laser processing variables (resolution/pixel time)

Figure 5. Relationship between laser processing variables and the wrinkle recovery rate of cotton fabric.

Polymers 2017, 9, 609 6 of 12

82 80 78 76 74

Softness 72 70 68 66

Laser processing variables (resolution/pixel time) Polymers 2017, 9, 609 6 of 12 Figure 4. Relationship between laser processing variables and the softness of cotton fabric.

3.1.4. Wrinkle Recovery Rate Creasing/wrinkles of of a a fabric fabric during during wear wear do do not not constitute constitute a a desirable change change in in appearance. Cellulosic materials like cotton have poor resistance toto creasing.creasing. The wrinkle recovery value measures thethe wrinklewrinkle resistanceresistance ofof thethe fabric.fabric. A larger wrinkle recovery rate implies implies higher higher resistance resistance to to the the wrinkling wrinkling of of the the fabric. fabric. This This value value is determined is determined by bymeasuring measuring the thefabric fabric hand hand and and drape drape of ofthe the fabric fabric twice twice with with a a given given time time interval between measurements. During During the the test, test, the the fabric fabric is is subj subjectedected to a pulling force and experiences complex wrinkles. After it is given a recovery recovery time, the differe differencesnces in terms of the defined defined fabric hand variables are measured again when it is tested for the secondsecond time. As shown in Figure 55,, thethe controlcontrol cottoncotton fabric has a lowerlower wrinklewrinkle recoveryrecovery valuevalue thanthan laser-treatedlaser-treated fabrics.fabrics. Therefore, the control cotton fabric tended to wrinkle more thanthan thethe laser-treatedlaser-treated fabrics.fabrics. The larger values of the laser-treated cotton fabrics fabrics imply imply better better recovery recovery from from the the deform deformationation during during the the test. test. After After laser laser treatment, treatment, the thefiber fiber surface surface becomes becomes rougher rougher and thus and thusthe inter-fiber the inter-fiber frictional frictional force forceis increased, is increased, which whichwill better will betterwithstand withstand wrinkling. wrinkling. Therefore, Therefore, laser treatment laser treatment improves improves the wrinkle the wrinkle recovery recovery of cotton of cotton fabrics. fabrics. The Theimprovement improvement in the in thewrinkle wrinkle recovery recovery of ofcotton cotton fabr fabricsics after after laser laser treatment treatment may may help help to to reduce reduce the conventional methods of anti-wrinkle finishing,finishing, whichwhich involveinvolve chemicals.chemicals.

Wrinkle recovery rate Wrinkle recovery 0

Laser processing variables (resolution/pixel time)

Figure 5. Relationship between laser processing variables and the wrinkle recovery rate of cotton Figure 5. Relationship between laser processing variables and the wrinkle recovery rate of cotton fabric. fabric.

3.1.5. Drapability The fabric drape coefficient represents the fabric dynamic drape behavior and the fabric shape when the fabric is held at the edge. In simple terms, it is the response of the fabric towards gravity due to its own weight. The smaller the drape value, the better the draping or shape of the fabric will be. Comparison of the control fabric with laser-treated fabrics (Figure6) shows that laser-treated fabrics have lower drape coefficients than the control fabric. This illustrates that laser treatment affects the fabric drape of cotton fabrics. Since the fiber surface is roughened after laser treatment, the inter-fiber frictional force is increased, which will better withstand draping. Polymers 2017, 9, 609 7 of 12

3.1.5. Drapability The fabric drape coefficient represents the fabric dynamic drape behavior and the fabric shape when the fabric is held at the edge. In simple terms, it is the response of the fabric towards gravity due to its own weight. The smaller the drape value, the better the draping or shape of the fabric will be. Comparison of the control fabric with laser-treated fabrics (Figure 6) shows that laser-treated fabrics have lower drape coefficients than the control fabric. This illustrates that laser treatment Polymersaffects2017 ,the9, 609fabric drape of cotton fabrics. Since the fiber surface is roughened after laser treatment, the7 of 12 inter-fiber frictional force is increased, which will better withstand draping.

18 16 14 12 10 8 6 4 2 Drape coefficient 0

Laser processing variables (resolution/pixel time)

Figure 6. Relationship between laser processing variables and the drape coefficient of cotton fabric. Figure 6. Relationship between laser processing variables and the drape coefficient of cotton fabric. 3.2. Cotton/Polyester Blended Fabric 3.2. Cotton/Polyester Blended Fabric 3.2.1. Stiffness 3.2.1. Stiffness Bending properties are expressed in terms of stiffness values of the control and laser-treated cotton/polyesterBending properties blended are fabrics, expressed treated in under terms diff oferent stiffness combinations values of of the laser control processing and variables laser-treated cotton/polyester(Figure 7). A higher blended value fabrics, of stiffness treated refers under to a st differentiffer fabric. combinations All the other la ofser-treated laser processing fabrics reveal variables (Figurea larger7). A stiffness higher value value than of stiffnessthe control refers fabrics, to awhich stiffer demonstrate fabric. All that the laser other treatment laser-treated causes fabricsan revealincrease a larger in stiffness of value the cotton/polyester than the control blended fabrics, fabrics. which In demonstrateaddition, the enhancement that laser treatment in stiffness causes an increasevalue grows in stiffness when the of laser the processing cotton/polyester variables, blended resolution fabrics. and pixel In time, addition, are increased, the enhancement meaning in that the fabrics become stiffer after treatment with high laser power density. In general, stiffness is stiffness value grows when the laser processing variables, resolution and pixel time, are increased, affected by yarn mobility. Owing to melting and re-solidification, polyester fibers encase the meaning that the fabrics become stiffer after treatment with high laser power density. In general, neighboring cotton fibers (Figure 8) [17,18], which restricts the movement of yarns during bending. stiffnessThe degree is affected of polyester by yarn melting mobility. is enlarged Owing from to melting a partial and melting re-solidification, to the whole surface polyester melting fibers when encase the neighboringthe resolution cotton and pixel fibers time (Figure are increased,8)[ 17,18 ],as whichshown restricts in Table the2 [18]. movement As a consequence, of yarns during this further bending. The degreeintensifies of polyesterthe yarn restriction. melting is As enlarged a result, from the bo anding partial of melting fibers and to theyarns whole together surface by the melting melted when the resolutionpolyester enhances and pixel the time stiffness are increased,of the fabrics. as shownBending in properties Table2[ 18have]. As an aimportant consequence, effect on this both further intensifiesthe handle the and yarn tailoring restriction. performa As ance result, of textile the materials bonding [16]. of fibers and yarns together by the melted polyester enhances the stiffness of the fabrics. Bending properties have an important effect on both the handlePolymers and 2017 tailoring, 9, 609 performance of textile materials [16]. 8 of 12

80 70 60 50 40 30 Stiffness 20 10 0

Laser processing variables (resolution/pixel time)

Figure 7. Relationship between laser processing variables and the stiffness of cotton/polyester Figure 7. Relationship between laser processing variables and the stiffness of cotton/polyester blended fabric. blended fabric.

Figure 8. Morphological feature (200×) of control cotton/polyester blended fabric (left) and laser- treated cotton polyester blended fabric with variables of 52 dpi/120 µs (right).

Table 2. Percentage of polyester melted in the fabric.

Dpi/µs Percentage of polyester melted in the fabric (data extracted and calculated from Reference [17]) 52/110 12.26 52/120 12.45 52/130 13.26 52/140 13.61 60/110 13.61 60/120 13.78 60/130 16.76 60/140 17.86 68/110 20.44 68/120 20.53 68/130 22.29 68/140 22.73

Although too high rigidity can resist buckling and may not cause problems in garment creation generally, the comfort of wearing is lower. On the other hand, too low rigidity of the fabric gives rise to difficulties in the tailoring process. Cutting the fabrics becomes more difficult as they distort easily. In addition, it causes seam puckers more easily during the sewing operation. Therefore, with

Polymers 2017, 9, 609 8 of 12

80 70 60 50 40 30 Stiffness 20 10 0

Laser processing variables (resolution/pixel time)

PolymersFigure2017, 97., 609Relationship between laser processing variables and the stiffness of cotton/polyester8 of 12 blended fabric.

Figure 8. Morphological feature (200×) of control cotton/polyester blended fabric (left) and laser- Figure 8. Morphological feature (200×) of control cotton/polyester blended fabric (left) and treated cotton polyester blended fabric with variables of 52 dpi/120 µs (right). laser-treated cotton polyester blended fabric with variables of 52 dpi/120 µs (right).

Table 2. Percentage of polyester melted in the fabric. Table 2. Percentage of polyester melted in the fabric. Dpi/µs Percentage of polyester melted in the fabric (data extracted and calculated from Reference [17]) 52/110Dpi/µ s Percentage of polyester melted in the fabric12.26 (data extracted and calculated from Reference [17]) 52/12052/110 12.45 12.26 52/13052/120 13.26 12.45 52/14052/130 13.61 13.26 60/11052/140 13.61 13.61 60/110 13.61 60/120 13.78 60/120 13.78 60/13060/130 16.76 16.76 60/14060/140 17.86 17.86 68/11068/110 20.44 20.44 68/12068/120 20.53 20.53 68/13068/130 22.29 22.29 68/140 22.73 68/140 22.73

Although too high rigidity can resist buckling and may not cause problems in garment creation generally, the comfort comfort of of wearing wearing is is lower. lower. On On the the other other hand, hand, too too low low rigidity rigidity of the of thefabric fabric gives gives rise riseto difficulties to difﬁculties in the in tailoring the tailoring process. process. Cutting Cutting the fabrics the fabrics becomes becomes more difficult more difﬁcult as they as distort they distorteasily. easily.In addition, In addition, it causes it causesseam puck seamers puckers more easily more easilyduring during the sewi theng sewing operation. operation. Therefore, Therefore, with with appropriate control of laser processing variables, laser treatment may resolve the problems found in some pliable fabrics during the production stage [10].

3.2.2. Smoothness Smoothness refers to how hard one’s fingertip can push across a fabric surface. It is the surface friction and surface resistance to slipping. The smoothness of the fabrics declines after treatment with laser under different combinations of variables (Figure9). The reduction in smoothness may be due to the formation of pores and cracks by the etching effect on the cotton fiber surface with the partial melting of polyester after laser treatment, as shown in Table2[ 10,18]. This leads to an uneven fabric surface and a relatively high surface roughness. According to the SEM images shown in our previous work [10,18] as well as Figure8, when the laser power density is increased, more and more polyester fibers are melted. The melted polyester fibers cover the neighboring cotton fibers, in addition to the pores and cracks formed on them due to etching [10,18]. Some cotton fibers become encased under the re-solidified polyester but some may not, which leads to inconsistent surface smoothness; thus, the smoothness values are varied when the laser processing variables are changed. Polymers 2017, 9, 609 9 of 12

appropriate control of laser processing variables, laser treatment may resolve the problems found in some pliable fabrics during the production stage [10].

3.2.2. Smoothness Smoothness refers to how hard one’s fingertip can push across a fabric surface. It is the surface friction and surface resistance to slipping. The smoothness of the fabrics declines after treatment with laser under different combinations of variables (Figure 9). The reduction in smoothness may be due to the formation of pores and cracks by the etching effect on the cotton fiber surface with the partial melting of polyester after laser treatment, as shown in Table 2 [10,18]. This leads to an uneven fabric surface and a relatively high surface roughness. According to the SEM images shown in our previous work [10,18] as well as Figure 8, when the laser power density is increased, more and more polyester fibers are melted. The melted polyester fibers cover the neighboring cotton fibers, in addition to the pores and cracks formed on them due to etching [10,18]. Some cotton fibers become encased under Polymersthe re-solidified2017, 9, 609 polyester but some may not, which leads to inconsistent surface smoothness; thus,9 of 12 the smoothness values are varied when the laser processing variables are changed.

90 80 70 60 50 40 30 20 Smoothness 10 0

Laser processing variables (resolution/pixel time)

Figure 9. Relationship between laser processing variables and the smoothness of cotton/polyester Figure 9. Relationship between laser processing variables and the smoothness of cotton/polyester blended fabric. blended fabric. 3.2.3. Softness 3.2.3. Softness The smaller the softness value, the softer the fabric will be. The softness of the laser-treated cotton/polyesterThe smaller the blended softness fabrics value, is improved the softer compared the fabric with will the be. control The softnessfabrics, as of shown the laser-treated in Figure cotton/polyester10. As softness blendedis related fabrics to the isbulkiness improved of the compared fabrics, withthe increase the control in softness fabrics, after as shown laser intreatment Figure 10 . Asimplies softness that is related the fullness to the bulkinessof fabricsof isthe enhanced fabrics, the[16]. increase Due to inthe softness melting after and laser re-solidification treatment implies of thatpolyester the fullness fibers, of the fabrics cotton isfibers enhanced are encased [16]. inside Due to the the polyester melting fibers, and thereby re-solidification adding bulkiness of polyester to fibers,the fabrics the cotton (Figure fibers 8) are[18]. encased This would inside increase the polyester the fullness fibers, when thereby fabric adding thickness bulkiness is increased to the from fabrics (Figurethe merging8)[ 18]. of This cotton would and increase polyester the fibers. fullness when fabric thickness is increased from the merging of cottonPolymers and 2017 polyester, 9, 609 fibers. 10 of 12

80 70 60 50 40

30 Softness 20 10 0

Laser processing variables (resolution/pixel time)

Figure 10. Relationship between laser processing variables and the softness of cotton/polyester Figure 10. Relationship between laser processing variables and the softness of cotton/polyester blended fabric. blended fabric. 3.2.4. Wrinkle Recovery Rate 3.2.4. Wrinkle Recovery Rate Wrinkles are defined as fabric deformation based on its viscoelastic properties [19]. A lower wrinkleWrinkles recovery are deﬁned rate of aslaser-treated fabric deformation fabrics su basedggests on that its the viscoelastic ability to properties recover from [19]. folding A lower wrinkledeformation recovery decreases rate ofwhen laser-treated compared with fabrics the control suggests fabrics that (Figure the ability 11). The to wrinkle recover recovery from folding rate is affected by the elasticity of fabrics, particularly whether it is sufficient to overcome the friction that resists the movement of the yarns and fibers. With the cotton fibers being etched and the melting of polyester fibers which encase the surrounding fibers and yarns (Figure 8), the elastic recovery power of the fabrics declines, as does its power to resist and recover from creasing.

80 70 60 50 40 30 20 10 0 Wrinkle recovery rate Wrinkle recovery

Laser processing variables (resolution/pixel time)

Figure 11. Relationship between laser processing variables and the wrinkle recovery rate of cotton/polyester blended fabric.

3.2.5. Drapability The draping coefficient of laser-treated fabrics is found to be larger (Figure 12), meaning that the drapability of the fabrics decreases after laser treatment. As stiffness is one of the factors affecting the draping quality, fabrics that are more flexible and are easier to drape well [20]. However, the stiffness

Polymers 2017, 9, 609 10 of 12

80 70 60 50 40 30 Softness 20 10 0

Laser processing variables (resolution/pixel time)

Figure 10. Relationship between laser processing variables and the softness of cotton/polyester blended fabric.

Polymers3.2.4.2017 Wrinkle, 9, 609 Recovery Rate 10 of 12 Wrinkles are defined as fabric deformation based on its viscoelastic properties [19]. A lower wrinkle recovery rate of laser-treated fabrics suggests that the ability to recover from folding deformation decreases when compared with the control fabrics (Figure 11). The wrinkle recovery rate deformation decreases when compared with the control fabrics (Figure 11). The wrinkle recovery rate is affected by the elasticity of fabrics, particularly whether it is sufficient to overcome the friction that is affected by the elasticity of fabrics, particularly whether it is sufficient to overcome the friction that resistsresists the the movement movement of of the the yarns yarns andand fibers.fibers. With the cotton cotton fibers fibers being being etched etched and and the the melting melting of of polyesterpolyester fibers fibers which which encase encase the the surrounding surrounding fibersfibers and yarns yarns (Figure (Figure 8),8), the the elastic elastic recovery recovery power power ofof the the fabrics fabrics declines, declines, as as does does its its power power toto resistresist andand recover from from creasing. creasing.

80 70 60 50 40 30 20 10 0 Wrinkle recovery rate Wrinkle recovery

Laser processing variables (resolution/pixel time)

Figure 11. Relationship between laser processing variables and the wrinkle recovery rate of Figure 11. Relationship between laser processing variables and the wrinkle recovery rate of cotton/ cotton/polyester blended fabric. polyester blended fabric. 3.2.5. Drapability 3.2.5. Drapability The draping coefficient of laser-treated fabrics is found to be larger (Figure 12), meaning that the drapabilityThe draping of the coefficient fabrics decreases of laser-treated after laser fabrics treatmen is foundt. As stiffness to be larger is one (Figure of the factors12), meaning affecting that the the drapability of the fabrics decreases after laser treatment. As stiffness is one of the factors affecting the Polymersdraping 2017 quality,, 9, 609 fabrics that are more flexible and are easier to drape well [20]. However, the stiffness11 of 12 draping quality, fabrics that are more flexible and are easier to drape well [20]. However, the stiffness ofof the the laser-treated laser-treated cotton/polyester cotton/polyester blended fabric fabricss is is enhanced, enhanced, indicating indicating that that these these fabrics fabrics are are stifferstiffer and and more more difficult difficult to to drape. drape.

Draping coefficient 0

Laser processing variables (resolution/pixel time)

Figure 12. Relationship between laser processing variables and the draping coefficient of Figure 12. Relationship between laser processing variables and the draping coefﬁcient of cotton/ cotton/polyester blended fabric. polyester blended fabric. 4. Conclusions Results obtained for the fabric hand properties demonstrate that laser treatment can be successfully used to change different aspects of the fabrics including stiffness, smoothness, softness, drapability, and wrinkle recovery. Since the aesthetic performance of a garment is governed by the quality of fabric used, the silhouette of the garment can be altered according to the change in fashion trends through the application of laser treatment on fabrics. In the case of 100% cotton woven fabrics, the fabrics were found to have a better drapability and wrinkle recovery after laser treatment. One major disadvantage of cotton as a textile fiber is its tendency to crease and wrinkle. Hence, they are treated with wrinkle-free finishing. However, these finishing treatments are usually associated with resins that release formaldehyde, which is hazardous to human health. The treatment of fabrics with laser may help reduce the use of hazardous chemicals in finishing treatments. This not only can reduce the chemicals and derivatives used, but also reduce the consumption of water and help eliminate the potential possibility of causing harmful effects to human health. As for the cotton/polyester blended fabrics, the stiffness of the fabrics was found to be relatively higher after laser irradiation. Too low rigidity of the fabric gives rise to difficulties in the tailoring process. As a result, cutting the fabrics becomes more difficult as they distort easily, and it causes seam puckers more easily during the sewing operation. Therefore, with the appropriate control of laser processing variables, laser treatment may resolve such problems in some pliable fabrics during the production stage.

Acknowledgments: This work is part of unpublished PhD project submitted by On-na Hung in partial fulfilment of the requirements for PhD degree in the Institute of Textiles and Clothing, The Hong Kong Polytechnic University. Authors would like to express grateful thanks to The Hong Kong Polytechnic University for the financial support.

Author Contributions: Chi-wai Kan (C.K.) and On-na Hung (O.H.) conceived and designed the experiments; O.H. performed the experiments; C.K. and O.H. analyzed the data; O.H. wrote the paper and C.K. proofread the technical content.

Conflicts of Interest: The authors declare no conflict of interest.

Polymers 2017, 9, 609 11 of 12

4. Conclusions Results obtained for the fabric hand properties demonstrate that laser treatment can be successfully used to change different aspects of the fabrics including stiffness, smoothness, softness, drapability, and wrinkle recovery. Since the aesthetic performance of a garment is governed by the quality of fabric used, the silhouette of the garment can be altered according to the change in fashion trends through the application of laser treatment on fabrics. In the case of 100% cotton woven fabrics, the fabrics were found to have a better drapability and wrinkle recovery after laser treatment. One major disadvantage of cotton as a textile fiber is its tendency to crease and wrinkle. Hence, they are treated with wrinkle-free finishing. However, these finishing treatments are usually associated with resins that release formaldehyde, which is hazardous to human health. The treatment of fabrics with laser may help reduce the use of hazardous chemicals in finishing treatments. This not only can reduce the chemicals and derivatives used, but also reduce the consumption of water and help eliminate the potential possibility of causing harmful effects to human health. As for the cotton/polyester blended fabrics, the stiffness of the fabrics was found to be relatively higher after laser irradiation. Too low rigidity of the fabric gives rise to difficulties in the tailoring process. As a result, cutting the fabrics becomes more difficult as they distort easily, and it causes seam puckers more easily during the sewing operation. Therefore, with the appropriate control of laser processing variables, laser treatment may resolve such problems in some pliable fabrics during the production stage.

Acknowledgments: This work is part of unpublished PhD project submitted by On-na Hung in partial fulfilment of the requirements for PhD degree in the Institute of Textiles and Clothing, The Hong Kong Polytechnic University. Authors would like to express grateful thanks to The Hong Kong Polytechnic University for the financial support. Author Contributions: Chi-wai Kan (C.K.) and On-na Hung (O.H.) conceived and designed the experiments; O.H. performed the experiments; C.K. and O.H. analyzed the data; O.H. wrote the paper and C.K. proofread the technical content. Conflicts of Interest: The authors declare no conflict of interest.

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