83 CHAPTER 4 INFLUENCE OF LYOCELL FIBER BLENDS ON THE COMFORT CHARACTREISTICS OF HOSPITAL TEXTILES This chapter deals with the production of blended yarns, analysis of the yarn characteristics, selection of cover factor for fabric production, production of woven fabric samples with different weave structures and analysis of their properties. It also deals with optimization of blend composition, specification of fabrics suitable for Hospital Textiles. This chapter contains two parts in which the first part deals with the influence of lyocell/polyester blends on the development of hospital textile products and the second part deals with the influence of micro lyocell/ micro polyester blends on hospital textiles. 4.1 PART I: INFLUENCE OF LYOCELL / POLYESTER BLENDS ON THE COMFORT CHARACTREISTICS OF HOSPITAL TEXTILES 4.1.1 Production of Lyocell /Polyester Blended Yarns Lyocell and polyester staple fibers of 1.8 denier and 32 mm fiber length were blended in the fiber stage in the advanced micro processor based spinning plant and 30 s count ring spun yarns were produced. The blend proportions used are as follows:
84 100% Lyocell 85:15 Lyocell/Polyester 70:30 Lyocell/Polyester Higher proportion of polyester leads to poor comfort characteristics of the fabric, which is not suitable for hospital textiles. Hence polyester blend ratio is restricted to 15% and 30%. The yarn samples were tested for yarn properties and are listed in the Table 4.1. Table 4.1 Lyocell and Polyester Yarn Parameters Parameters Lyocell 100:0 Lyocell/polyester 85:15 Lyocell/polyester 70:30 Count (Ne) 30.4 29.3 30.7 Breaking Elongation (%) 7.01 6.58 7.76 Tenacity (N/Tex) 16.36 14.7 21.31 Twist per cm 7.0 7.0 7.0 RKM Value 24.97 22.53 32.48 From the yarn parameters, it is found that lyocell/polyester blend of 70:30 blend proportion has comparatively higher strength and elongation due to the presence of polyester fiber which has higher strength than lyocell fiber. 4.1.2 Influence of Fabric cover factor on the suitability of Hospital Textiles Since some of the comfort and surface properties like air permeability, water vapour permeability, thermal conductivity and frictional coefficient of a fabric depend on the fabric cover factor, selection of fabric cover factor was carried out by weaving fabrics with four different cover
85 factors and analyzing their comfort properties. As lyocell is the major component of all the fabrics developed, selection of cover factor was carried out using fabrics produced using lyocell yarns. Fabric samples were produced with cover factors such as 20, 22, 24 and 26 by varying the ends per inch and picks per inch and the fabrics produced were analyzed for their parameters and comfort properties. The test results are shown in the Table 4.2 and Table 4.3. Table 4.2 Fabric Parameters of lyocell fabrics with different cover factors Cover Ends/cm Thickness Strength(kgf) Elongation Frictional factor x picks/cm (mm) (%) Factor Warp weft Warp weft Static Dynamic 26 50x35 0.25 100 95 23.95 15.41 1.24 0.92 24 40x35 0.21 110 90 18.75 13.54 1.28 0.92 22 35x28 0.20 110 75 10.4 13.54 1.37 0.87 20 30x25 0.19 65 80 9.34 10.41 1.47 0.97 Table 4.3 Comfort Properties of lyocell fabrics with different cover factors Cover factor Air Thermal Water Absorption Spreading permeability conductivity vapour (sec) area (c 3 /cm 2 /s) (w/m/k) permeability (g/m 2 /day) (cm 2 ) 26 28.30 0.0096 1777.88 0.70 3.90 24 41.50 0.0153 1866.67 0.76 4.38 22 95.80 0.0082 1866.67 0.80 4.91 20 155.6 0.0147 2044.44 0.85 5.25
86 From the test results it was observed that, warp and weft density of a fabric has an influence on the comfort properties of the fabric. Thickness, strength and elongation of the fabric increases with the increase in cover factor. Strength and elongation increase may be due to the contribution of more number of yarns for the fabric strength and elongation of the fabric. The frictional coefficient of the fabric reduces with increase in cover factor which may be attributed to the increase in packing density resulting in lower number of crests and troughs leading to a smoother fabric surface. The time taken to absorb water also decreases with decrease in cover factor. The porous structure of the fabric with lower cover factor allows water to permeate through the fabric rapidly. Similarly presence of pores acts as a channel for distribution of water drop let, hence the spreading area of the fabric increases with decreasing cover factor. Air permeability and water vapour permeability of the fabrics show a decreasing trend with increase in cover factor. The open structure of the fabric with lower cover factor allows more air to pass through thereby increasing the air permeability. Similarly, water vapour permeability also increases with openness of the fabric. Thermal conductivity has a varying trend and is high for fabric with cover factor 24. From the test results it is observed that fabric with cover factor 24 has the required strength, elongation, air permeability, water vapour permeability and at the same time has better water absorbing and frictional characteristics. Since water management and frictional properties are important for hospital textiles, cover factor 24 was selected as the suitable cover factor for all the fabrics to be developed for hospital textiles.
87 4.1.3 Preparation of Lyocell / Polyester Blended Fabric Samples The objectives of the research are to ensure appropriate heat transfer, moisture management and air transport between the human body and the environment. Since the type of weave structure affects the water absorption and frictional characteristics of a fabric, three types of weaves were considered for fabric production. The plain weave is compact weave with higher tensile strength and twill weaves have higher float length which gives good absorption and elongation characteristics. Based on the literature survey, it was planned to produce fabrics with plain weave, 2/2 twill weave and 1/3 twill weave. From each of the blended yarns produced, three fabric samples with plain weave, 2/2 twill weave and 1/3 twill weave were produced with a cover factor of 24. Hence nine different samples were produced using 100% lyocell, 85:15 and 70:30 lyocell / polyester blended yarns.the list of fabric samples produced are given in the Table 4.4. Table 4.4 List of lyocell / polyester Fabric Samples Sample Yarn count (Ne) Yarn type Weave L(1) Plain L(2) 30.4 100% Lyocell 2/2 Twill L(3) L/P 85:15 (1) L/P 85:15 (2) L/P 85:15 (3) L/P 70:30 (1) L/P 70:30 (2) L/P 70:30 (3) 29.3 85:15 Lyocell/ Polyester 30.7 70:30 Lyocell/ Polyester 1/3 Twill Plain 2/2 Twill 1/3 Twill Plain 2/2 Twill 1/3 Twill
88 4.1.4 Testing of Lyocell / Polyester Fabric Samples Strength, elongation and fabric parameters of the nine fabric samples produced are listed in the Table 4.5. Table 4. 5 Lyocell / Polyester Fabric Parameters S.No Ends /cm Picks /cm Fabric weight (g/m 2 ) Fabric thickness (mm) Warp strength (kgf) Warp elongation (%) Weft strength (kgf) Weft elongation L(1) 37 30 152 0.37 60.50 13.92 60.82 13.67 L(2) 36 30 149 0.39 73.02 11.08 59.96 12.58 L(3) 37 27 151 0.40 67.26 10.83 60.24 13.92 L/P 85:15 (1) 36 25 170 0.41 68.81 16.42 42.59 10.67 L/P 85:15 (2) 37 30 175 0.46 74.64 11.92 61.45 14.83 L/P 85:15 (3) 38 34 173 0.50 67.81 11.50 66.84 15.58 L/P 70:30 (1) 37 26 188 0.50 71.83 17.00 74.60 14.67 L/P 70:30 (2) 37 34 198 0.53 74.69 13.00 65.33 18.42 L/P 70:30 (3) 37 34 195 0.55 72.79 14.33 69.58 16.08 (%) 4.1.5 Results and Discussion The nine fabric samples produced were desized, scoured, tested and analysed for the following properties using standard testing procedure under standard atmospheric conditions. Air Permeability Thermal Conductivity Water vapour Permeability Water Absorbency Water spreading area Wickability - Vertical Wicking In-plane Wicking Drying time
89 The test results are plotted in the form of charts with error bar; the error bar representing the standard error of the mean. 4.1.5.1 Strength of lyocell / polyester Blended Fabrics The fabric strength increases in proportion to the polyester fiber content in the fabric. The 85:15 and 70:30 lyocell: polyester blended fabrics have higher strength compared to 100% lyocell fabric. This may be attributed to the higher tenacity of polyester yarn when compared to 100% lyocell yarn. All fabric samples show higher strength in warp way than weft way. 4.1.5.2 Elongation of lyocell / polyester blended Fabrics It is observed that for the fabric with higher polyester content, the extensibility is higher owing to the high extensibility of polyester fiber. The twill woven fabrics have higher elongation values as compared to plain fabrics. This is because of higher mobility of the yarns due to less crossover points in a twill fabric. Most of the fabric samples exhibit higher weft way elongation than warp way elongation. The higher weft way elongation is the basic requirement of a bed linen to ensure contour matching of the body in the cross wise direction. The comfort properties of the nine fabric samples produced are given in the Table 4.6.
90 Table 4.6 Comfort Properties of the Lyocell/ Polyester Blended Fabrics Sample No Air permeability (cm 3 /cm 2 /s) Thermal conductivity (w/m/k) Water vapour permeability (g/m 2 /day) Absorption (sec) Spreading area(cm 2 ) Vertical wicking -Warp (cm) Vertical wicking -Weft (cm) L(1) 83.03 0.017 4523.8 8 4.38 2.50 2.14 L(2) 124.55 0.019 4967.3 7 4.13 2.72 4.2 L(3) 138.38 0.022 6564.0 6 3.90 4.20 5.45 L/P 85:15 (1) 62.275 0.006 2661.1 7 7.00 3.33 3.00 L/P 85:15 (2) 83.03 0.007 4789.9 5 6.63 4.00 6.00 L/P 85:15 (3) 95.80 0.013 5056.0 4 6.50 7.50 6.70 L/P 70:30 (1) 46.12 0.005 2572.3 6 8.18 5.45 4.20 L/P 70:30 (2) 77.84 0.007 3814.2 5 7.75 6.00 10 L/P 70:30 (3) 95.80 0.011 4435.1 4 7.45 6.70 10 4.1.5.3 Air Permeability of Lyocell / Polyester Blended Fabrics Air permeability is a measure of the amount of air passing through the fabric per unit area. The air permeability results of the lyocell / polyester blended fabrics, as shown in the Figure 4.1 reveals that the fabrics made from lyocell fibers have higher air permeability. Figure 4.1 Air Permeability of Lyocell / Polyester Blended Fabrics
91 Lyocell fibers, being smoother, circular with more number of micro fibrils, assists easy passage of air through the yarn cross-section, which results in higher air permeability. The result also shows that the air permeability decreases with higher polyester content in the respective blended fabrics. This may be attributed to the compact structure of the fabric having higher polyester content, and hence lesser number of pores of lower cross-sectional area available for air passage. Considering the influence of the type of weave, the highest value was observed for fabrics with twill weave, and the lowest, for those with plain weave. 100% lyocell fabric with 1/3 twill weave has the highest value of air permeability and 70:30 lyocell / polyester fabric with plain weave has the lowest air permeability value. A significant difference exists between the air permeability of these fabrics with respect to blend proportions because p-value (0.0025)< 0.05 and F 2,8 values (37.45) are greater than F critical (6.94) at 95% confidence level. Similarly, there is a significant difference between the air permeability of these fabrics with respect to weave because p-value (0.0025) < 0.05 and F 2,8 values (41.06) are greater than F critical (6.94) at 95% confidence level. A negative correlation between the air permeability against the increasing blend proportion of polyester in the blended fabric has also been identified. The regression equations are given in the Table 4.7. Table 4.7 Correlation Coefficient between Air Permeability and Blend Fabric Plain Woven Fabric Proportion of Lyocell / Polyester Blended Fabric Regression Equation between Air permeability and Blend Proportion R 2 Value Y 1 = -18.455x 1 + 100.72 R 2 = 0.9948 2/2 Twill Fabric Y 2 = -23.355x 2 + 141.85 R 2 = 0.8322 1/3 Twill Fabric Y 3 = -21.29x 3 + 152.57 R 2 = 0.75
92 Among the plain woven fabrics, a strong correlation exists between the blend proportion and air permeability which is proved by the R 2 value of 0.9948. Among the twill fabrics similar correlation is observed but the R 2 value is comparatively less. 4.1.5.4 Thermal Conductivity of Lyocell / Polyester Blended Fabrics The thermal conductivity of lyocell and polyester blended fabrics measured using the Lee s Disc is shown in Figure 4.2. Figure 4.2 Thermal Conductivity of Lyocell / Polyester Blended Fabrics It is observed from the figure that the thermal conductivity of the fabric seems to have a direct correlation with lyocell fiber content. As the lyocell content increases thermal conductivity of the fabric also increases, on contrary, as the proportion of polyester fiber content increases, the thermal conductivity decreases, which may be attributed to the lower conductivity of polyester fiber. The thermal conductivity values of the twill woven fabrics were noticed to be higher than the plain woven fabrics due to the increased float length leading to more area of contact. A significant difference exists between the thermal conductivity of these fabrics with respect to blend proportions because p-value (9.31 x 10-5 )<
93 0.05 and F 2,8 value (205.2) is greater than F critical (6.94) at 95% confidence level. Similarly, there is a significant difference between the air permeability of these fabrics with respect to weave because p-value (0.0025)< 0.0016 and F 2,8 values (47.01) are greater than F critical (6.94) at 95% confidence level. A negative correlation between the thermal conductivity against the increasing blend proportion of polyester in the blended fabric has also been noticed. The regression equations are given in the Table 4.8. Table 4. 8 Correlation Coefficient between Thermal Conductivity and blend proportion of Lyocell / Polyester Blended Fabrics Fabric Regression Equation between Thermal R 2 Value conductivity and Blend Proportion Plain Woven Fabric Y 1 = -0.006x + 0.0213 R 2 = 0.812 2/2 Twill Fabric Y 2 = -0.006x + 0.023 R 2 = 0.75 1/3 Twill Fabric Y 3 = -0.0055x + 0.0263 R 2 = 0.8811 4.1.5.5 Water Vapour Permeability of Lyocell / Polyester Blended Fabrics Moisture vapour transfer is the ability of a fabric to transfer perspiration in the form of moisture vapour through it and is measured in terms of g/m 2 /day. It is observed from Figure 4.3 that as the polyester % in lyocell/ polyester blended fabrics increases, water vapour permeability of the fabric reduces. An ideal fabric should allow water vapour on skin (perspiration) to pass through its pores, irrespective of the fiber material s natural absorbency. If the water vapour cannot escape at a faster rate than it is released by the skin, it leads to sweat accumulation and hence discomfort. From the air permeability test it has been observed that as the polyester
94 component in lyocell/polyester blended fabrics increases, the air permeability decreases, which interprets that these fabrics are having lower porosity which results in lower moisture vapour transmission. Figure 4.3 Water Vapour Premeability of Lyocell / Polyester Blended Fabrics This behavior can also be explained by the moisture vapour transmission mechanism. As the lyocell proportion in the fabric increases, moisture regain of the material will be increased causing higher diffusivity. A hygroscopic fabric absorbs water vapour from the humid air close to the sweating skin and releases it in dry air. This enhances the flow of water vapour from the skin to the environment comparatively higher than a fabric which does not absorb and reduces the moisture built up in the microclimate. Whereas fabric with less hygroscopicity will provide higher resistance to the water vapour transfer. The moisture vapour transfer is higher for twill woven fabrics as compared to that of plain woven fabrics due to higher porosity. A significant difference exists between the water vapour permeability of these fabrics with respect to blend proportions because p-value (9.31 x 10-5 ) < 0.05 and F 2,8 values (205.2) are greater than F critical
95 (6.94) at 95% confidence level. Similarly, a significant difference exists between the water vapour permeability of these fabrics with respect to weave because p-value (0.0025)< 0.05 and F 2,8 values (47.01) greater than F critical (6.94) at 95% confidence level. A negative correlation between the water vapour permeability against the increasing blend proportion of polyester in the blended fabric has also been noticed. The regression equations are given in the Table 4.9. Table 4.9 Correlation Coefficient between Water Vapour Permeability and blend proportion of Lyocell / Polyester blended Fabrics Regression Equation between Water Fabric vapour Permeability and Blend R 2 Value Proportion Plain Woven Fabric Y 1 = -975.75x + 5203.9 R 2 = 0.7841 2/2 Twill Fabric Y 2 = -576.55x + 5676.9 R 2 = 0.8622 1/3 Twill Fabric Y 3 = -1064.5x + 7480.6 R 2 = 0.9453 4.1.5.6 Water Absorbency of Lyocell / Polyester Blended Fabrics From the Figure 4.4, showing the water absorbency of lyocell / polyester blended fabrics, it can be observed that the lyocell/ polyester blended fabrics have excellent water absorbency. There is a strong polar attraction between fiber molecules and water due to the highly hydrophilic nature of lyocell. Its higher water retention and liquid holding capacity may be due to the strong hydrophilic attraction between water and lyocell fibers and water retention in the inter fibrillar spaces of the fibers, whereas being hydrophobic in nature polyester does not form bonds with water molecules, but due to its positive contact angle (75 o ), liquid surface is dragged very
96 smoothly, which offers high transfer in case of polyester. So, when a small proportion of polyester is added in the system, it acts as a channel to the water and forms capillary and enhances the transfer phenomena. Figure 4.4 Water Absorbency of Lyocell / Polyester Blended Fabrics Hence the blended fabrics exhibit very good water absorbency resulting in immediate transfer of moisture to the outer layers and gives a dry feel. This property is essential to keep the patient dry and avoids problem created due to wet skin. The 85:15 and 70:30 lyocell: polyester blended fabric immediately absorbs water to its maximum capacity, within 5 seconds. This shows that addition of small amount of polyester enhances absorbency. A negative correlation exists between the time taken to absorb a drop of water against the increasing blend proportion of polyester in the blended fabric. The regression equations are given in the Table 4.10. All the three woven fabrics show a negative correlation between the blend proportion and water absorbency and the R 2 values are more than nine.
97 But there is no significant difference between the water absorbency of these fabrics with respect to blend proportions because F 2,8 values are lower than F critical at 95% confidence level. Table 4.10 Correlation Coefficient between Water Absorbency and Blend Proportion of Lyocell / Polyester Blended Fabrics Fabric Regression Equation between water R 2 Value absorbency and Blend Proportion Plain Woven Fabric Y 1 = -1.105x + 7.93 R 2 = 0.93 2/2 Twill Fabric Y 2 = -1.13x + 8.47 R 2 = 0.9433 1/3 Twill Fabric Y 3 = -1.19x + 9.1367 R 2 = 0.994 4.1.5.7 Water Spreading area of Lyocell / Polyester Blended Fabrics blended fabrics. Figure 4.5 shows the water spreading ability of lyocell / polyester Figure 4.5 Spreading area of Lyocell / Polyester Blended Fabrics
98 Spreading area is a measure of the extent to which a drop of water spreads on the surface of the fabric. 70:30 lyocell/ polyester blended fabric spreads water to the maximum extent when compared to the other two proportions. Presence of small amount polyester increases the spreading area and enhances the dryability. Due to hydrophobic nature of polyester, it fails to form bonds with water molecules and allows them to easily move along the channels, attracted by the lyocell fiber content of the yarn, water spreads to the maximum extent. Table 4.11 Correlation Coefficient between water spreading area and Blend Proportion of Lyocell / Polyester Blended Fabrics Regression Equation between Water Fabric spreading area and Blend Proportion R 2 Value Plain Woven Fabric Y 1 = -0.25x + 2.2333 R 2 = 0.9868 2/2 Twill Fabric Y 2 = -0.2x + 1.8333 R 2 = 0.9231 1/3 Twill Fabric Y 3 = -0.25x + 1.7667 R 2 = 0.9868 A negative correlation exists between the water spreading area against the increasing blend proportion of polyester in the blended fabric. The regression equations are given in the Table 4.11. 4.1.5.8 Vertical Wickability of Lyocell / Polyester Blended Fabrics Vertical wicking is a measure of the ability of the fabric to wick away moisture along the vertical direction. The vertical wicking ability of lyocell / polyester blended fabrics in warp and weft directions are given in the Figure 4.6 and 4.7 respectively. By analyzing the curves it is observed that the distance traveled by water is very short in the case of the 100% lyocell fabric but it increases markedly with the addition of small percentage of polyester. Addition of a small portion of polyester increases the water wicking height to a great extent, in comparison to that of 100% lyocell fabric.
99 This behavior can be explained by absorption and wicking phenomena. Lyocell is a highly hydrophilic fiber; it has a good absorbency but due to its high affinity to water, when water molecule reaches in the capillary, it forms bond with the absorbing group of the fiber molecules, which inhibits the capillary flow along the channel formed by the fiber surfaces, so in case of 100% lyocell the movement of water is mainly governed by the absorption of water by the fibers and its movement along the fiber, which results in very less movement of water along the fabric. Figure 4.6 Vertical wicking (warp way) of Lyocell / Polyester Blended Fabrics Figure 4.7 Vertical Wicking (Weft Way) of Lyocell / Polyester Blended Fabrics
100 Whereas being hydrophobic in nature polyester does not form bonds with water molecules, and also due to its positive contact angle (75 o ), drags the liquid surface very smoothly, which offers high wicking in case of polyester. So, when a small proportion of polyester is added in the system, it acts as a channel to the water which comes through the capillary and enhances the wicking phenomena. From the figure 4.6 and 4.7, it can be observed that vertical wicking along both warp and weft directions increases with the addition of polyester and 70:30 lyocell: polyester blended fabric has higher wickability. Wickability along weft direction is higher than warp direction which may be due to the lower tension in weft yarn resulting in increased capillary radius.the higher tension in warp yarn reduces the capillary size and since wicking rate is proportional to (capillary radius) ½, wicking along weft way is higher than warp way. Twill woven fabrics show higher wickability than plain woven fabrics due to higher float length. 4.1.5.9 Inplane Wicking of Lyocell / Polyester Blended Fabrics Water uptake by the fabric samples at different time period is measured in g/cm 2 by inplane wicking test. The water uptake by the lyocell / polyester blended fabrics with different blend proportions, during 5 and 10 seconds has been plotted in Figure 4.8. Water uptake has been found to increase with the increase in polyester proportion. The simple empirical equation clearly shows that as the polyester proportion (x) increases, the water uptake value by the fabric (y) increases. It is observed that blending has an important role in moisture related comfort properties of clothing. The rapidity or rates of absorption here
101 greatly influence the thermo physiological comfort, but hydrophilic proportion has an adverse effect on the liquid moisture transmission behavior. Figure 4.8 Inplane Wicking of Lyocell / Polyester Blended Fabrics The vertical as well as horizontal wicking of the material increases with the increase in polyester proportion in the lyocell/ polyester blended fabrics. The lyocell component of the fabric will act for the quick absorption of the perspiration from the skin and smaller polyester proportion will help to spread the absorbed liquid to the outer surface of the fabric, due to its high wicking property. The lyocell/polyester blended fabrics show very good inplane wicking than the 100% lyocell fabrics. Among all the combinations, the twill weaves show better inplane wicking and 1/3 twill has higher wickability due to higher float length. All the fabric samples are capable of holding more than 0.04 mg of water per square cm of the fabric.
102 4.1.5.10 Frictional Behavior of Lyocell/ Polyester Blended Fabrics Fabric friction, which is defined as the resistance to motion, can be detected when a fabric is rubbed mechanically against itself or tactually between the finger and thumb. Friction is considered to be one property of cloth which has considerable importance, when skin is in close contact with the fabric. The ratio of frictional force (F) to normal load (N) is calculated and denoted as (F/N). From the tables, it can be seen that the static frictional ratio value is represented as (F/N)s and the kinetic frictional ratio value as (F/N)d. Static friction is the force which opposes the tendency of a body at rest to start to move over another surface, and kinetic friction is the force which opposes the motion of two surfaces moving on each other. When two fabrics are in contact, they may interact structurally, which contributes to high friction. When the fabric is in contact with another fabric, the surface fibers penetrate into the domain of the other fibers of the contacting fabric, and form a loose inter-fabric structure. Figure 4.9 Frictional Behavior of Lyocell / Polyester Blended Fabrics
103 The (F/N) ratio represents the energy lost in breaking this loose structure, while resistance comes from the adhesion at contact points of fibers and the bending of fibers in moving fabric surface. From the figure 4.9 showing the frictional behavior of lyocell / polyester blended fabrics, it can be observed that the lyocell rich fabrics have lower frictional factor. As the surface of the 100% lyocell fabrics have very smooth surface, the resistance due to the formation of the loose structure at the interface of the two moving surfaces is less. When polyester is blended with lyocell, it offers higher friction which may be due the lower moisture content of polyester leading to dry feel and lack of lubrication for the movement of fabric. Twill fabrics offer less friction compared to plain woven fabrics and among the twill fabrics also 1/3 twill offers lower friction. 4.1.5.11 Drying Ability of Lyocell/ Polyester Blended Fabrics Drying time depicts the time taken by the fabric to dry completely and the drying rate of the lyocell/ polyester blended fabrics are shown in the Figure 4.10. Drying Rate of Lyocell/Polyester RWR% 70 60 50 40 30 20 10 0 10 min 20 min 30 min 100 L(P) 100 L(2/2) 100 L(1/3) 85/15 L:P(P) 85/15 L:P(2/2) 85/15 L:P(1/3) 70/30 L:P(P) 70/30 L:P(2/2) 70/30 L:P(1/3) Figure 4.10 Drying Rate of Lyocell/ Polyester blended Fabrics
104 Even though lyocell gives a dry feel, it takes longer duration to dry. Presence of polyester hastens the drying rate. The 70:30 lyocell/polyester blended fabrics dry quickly than 85:15 blends. This faster drying property may be attributed to the presence of polyester which dries faster. 4.2 PART II: INFLUENCE OF MICRO LYOCELL AND MICRO POLYESTER BLENDS ON THE CHARACTERISTICS OF HOSPITAL TEXTILES 4.2.1 Introduction This part of the research work aims at analyzing the suitability of micro fibers of lyocell and polyester for hospital textile applications. This chapter deals with production of blended yarns from micro lyocell and micro polyester fibers in two different blend proportions and production of woven fabrics from each blended yarn with different weave structures and analysis of their comfort properties. 4.2.2 Production of Micro Lyocell and Micro Polyester Blended Yarns The fiber parameters of micro lyocell and micro polyester staple fibers are given in the Table 4.12. Table 4.12 Properties of Micro polyester and Micro Lyocell Fibers Property Micro polyester Micro Lyocell Linear density (denier) 0.8 0.9 Length, mm 32 34 Tenacity, cn/dtex 5.5 3.6 Elongation at break, % 19.5 12
105 Staple fibers of micro lyocell are blended with micro polyester in different proportions to produce 30s count yarns. The blend proportions used are as follows. Micro Lyocell - 100% Micro Lyocell : Micro Polyester - 85:15 Micro Lyocell : Micro Polyester - 70:30 Micro Polyester - 100% Since micro polyester rich fabrics lag in comfort properties and are not suitable for hospital textiles, only two blend proportions with lower micro polyester content such as 85:15 and 70:30 are selected for yarn production. Blending and spinning of micro lyocell and micro polyester fibers are carried out in advanced micro processor based spinning plant. The blended yarns were tested for yarn properties and are listed in the Table 4.13. Table 4.13 Micro Lyocell/ Micro Polyester Blended Yarn Parameters Micro Micro Lyocell/ Micro Lyocell/ Micro Parameters Lyocell Micro polyester Micro polyester Polyester 100% 85:15 70:30 100% Count (Ne) 30.20 29.80 29.60 29.7 Breaking elongation(%) 7.81 7.58 7.87 12.5 Twist per cm 6.90 7.10 7.00 7.20 RKM Value 24.97 22.53 23.48 28.25 4.2.3 Production of Micro Lyocell/ Micro polyester Blended Fabrics Three different fabrics with plain weave, 2/2 twill weave and 1/3 twill weave were produced from each of the blended yarns with a cover factor
106 of 24. Twelve different fabric samples were produced with 100% micro lyocell, 70:30 and 85:15 micro lyocell : micro polyester and 100% micro polyester blended yarns. The list of fabric samples are given in the Table 4.14. Table 4.14 List of Micro Lyocell/ Micro Polyester Fabric Samples Sample number Yarn Yarn type count(ne) ML (1) ML (2) 30.2 100% Micro Lyocell ML (3) ML/MP 85:15 (1) ML/MP 85:15 (2) 29.8 85:15 Micro Lyocell/ Micro Polyester ML/MP 85:15 (3) ML/MP 70:30 (1) ML/MP 70:30 (2) 29.6 70:30 Micro Lyocell/ Micro Polyester ML/MP 70:30 (3) MP (1) MP (2) 29.7 100% Micro Polyester MP (3) Weave Plain 2/2 Twill 1/3 Twill Plain 2/2 Twill 1/3 Twill Plain 2/2 Twill 1/3 Twill Plain 2/2 Twill 1/3 Twill 4.2.4 Analysis of the specifications of Micro Lyocell/ Micro polyester Blended Fabrics The fabric specifications, strength and elongation of the twelve samples are listed in the Table 4.15.
107 Table 4.15 Micro Lyocell/ Micro Polyester Blended Fabric Parameters Sample No Ends Picks Fabric Fabric Warp Warp Weft Weft /cm /cm weight thickness strength elongation strength elongation (g/m 2) mm) (kgf) (%) (kgf) (%) ML (1) 35 39 172 0.42 80.50 16.90 65.82 13.67 ML (2) 35 39 173 0.45 83.02 18.50 64.96 12.58 ML (3) 35 38 175 0.51 87.26 20.20 62.24 13.92 ML/MP 85:15 (1) 35 39 161 0.45 84.40 20.80 66.70 23.30 ML/MP 85:15 (2) 35 39 163 0.52 85.50 21.70 61.70 25.20 ML/MP 85:15 (3) 35 38 165 0.50 83.10 21.70 48.40 18.40 ML/MP 70:30 (1) 34 39 152 0.42 93.20 24.20 44.90 20.40 ML/MP 70:30 (2) 36 39 154 0.50 88.20 24.20 42.30 18.60 ML/MP 70:30 (3) 36 38 158 0.52 86.20 28.90 40.00 16.30 MP (1) 35 38 133 0.45 92.59 21.33 73.60 21.50 MP (2) 36 39 129 0.50 95.53 22.67 72.40 20.60 MP (3) 35 39 127 0.52 96.68 26.33 74.70 22.20 4.2.5 Results and Discussion 4.2.5.1 Strength of Micro Lyocell / Micro Polyester Blended Fabrics The micro fiber blended fabrics show higher strength and elongation when compared to normal denier fiber fabrics. Among the micro fiber blended fabrics, as the proportion of micro polyester fiber content increases, the fabric strength increases. The 100% micro polyester fabric has the highest strength among all fabric samples. This may be attributed to the higher tenacity of mico polyester yarn when compared to 100% micro lyocell yarn. All fabric samples show higher strength in warp way than weft way. 4.2.5.2 Elongation of Micro Lyocell /Micro Polyester Blended Fabrics It is observed that for the fabric with higher micro polyester content, the extensibility is higher. This may be attributed to the higher
108 inherent elongation (10.5%) of micro polyester yarn when compared to micro lyocell yarn with 7.01% elongation.the twill woven fabrics have higher elongation values as compared to plain fabrics. This is because of higher mobility of the yarns due to less crossover points in a twill fabric. Most of the fabric samples exhibit higher weft way elongation than warp way elongation. The twelve fabric samples produced were tested for their comfort properties and analyzed for their behavior. Test results are given in the Table 4.16. Table 4.16 Properties of Micro Lyocell/ Micro Polyester blended Fabrics S.No Air permeability (cm 3 /cm 2 /s) Thermal conductivity (w/m/k) Water vapour permeability (g/m 2 /day) Absorption (sec) Spreading areas (cm 2 ) Inplane wicking (g/cm 2 ) (5s) Inplane wicking (g/cm 2 ) (10 s) Frictional Factor - static Frictional factordynamic ML (1) 62.28 0.032 3991.7 0.02 4.78 0.044 0.051 0.74 0.60 ML (2) 68.50 0.088 4789.9 0.02 4.40 0.066 0.089 0.94 0.83 ML (3) 77.40 0.043 5133.2 0.02 4.00 0.069 0.098 0.78 0.57 ML/MP 85:15 (1) 73.26 0.024 3550.1 0.02 5.12 0.029 0.061 0.73 0.61 ML/MP 85:15 (2) 93.20 0.079 3814.2 0.02 4.70 0.059 0.072 0.91 0.79 ML/MP 85:15 (3) 103.00 0.034 4618.3 0.03 4.15 0.068 0.078 0.67 0.57 ML/MP 70:30 (1) 88.96 0.015 3081.1 0.02 6.10 0.058 0.055 0.66 0.55 ML/MP 70:30 (2) 108.20 0.056 3598.1 0.03 5.00 0.067 0.068 0.77 0.70 ML/MP 70:30 (3) 113.20 0.031 3912.4 0.05 4.45 0.067 0.073 0.63 0.55 MP (1) 98.20 0.012 2561.3 0.03 7.50 0.046 0.051 0.74 0.66 MP (2) 120.40 0.042 3254.1 0.04 5.50 0.049 0.061 0.76 0.64 MP (3) 130.30 0.028 3877.4 0.06 4.55 0.068 0.062 0.79 0.83
109 4.2.5.3 Air Permeability of Micro Lyocell/ Micro Polyester Blended Fabrics The air permeability characteristics of the twelve woven fabrics are given in the Figure 4.11. Figure 4.11 Air Permeability of Micro Lyocell/ Micro Polyester Blended Fabrics The air permeability results reveal that the fabrics made from micro polyester fibers have higher air permeability. Considering the influence of the kind of weave, highest value was observed for fabrics with twill weave, and the lowest for those with plain weave. Fabrics made of 100% micro polyester fabrics with 1/3 twill weave have the highest value of air permeability. A significant difference exists between the air permeability of these fabrics with respect to blend proportions because p-value (6.23E-05)< 0.05 and F 2,8 values (63.25) are greater than F critical (4.76) at 95% confidence level. Similarly there is a significant difference between the air permeability of these fabrics with respect to weave because p-value (0.0005)< 0.05 and F 2,8 values (34.79) are greater than F critical (5.14) at 95% confidence level. A positive correlation between the air permeability against the increasing blend proportion of micro polyester in the blended fabric has also been noticed. The regression equations are given in the Table 4.17.
110 Table 4.17 Correlation Coefficient between Air Permeability and Blend Fabric Plain Woven Fabric Proportion of Micro Lyocell/ Micro Polyester blended Fabrics Regression Equation between Air permeability and Blend Proportion R 2 Value Y 1 = 12.34x 1 + 49.81 R 2 = 0.990 2/2 Twill Fabric Y 2 = 17.07x 2 + 54.9 R 2 = 0.972 1/3 Twill Fabric Y 3 = 16.89x 3 + 63.75 R 2 = 0.970 Among the plain woven fabrics, a strong correlation exists between the blend proportion and air permeability. The R 2 value is 0.990. Among the twill fabrics similar correlation is observed but the R 2 value is comparatively less. 4.2.5.4 Thermal Conductivity of Micro Lyocell/ Micro Polyester Blended Fabrics The thermal conductivity of the twelve woven fabrics made out of micro lyocell and micro polyester blended yarns and three different structures are shown in Figure 4.12. It is observed that the thermal conductivity of the fabric seems to have a direct correlation with micro lyocell fiber content. As the micro lyocell content increases, thermal conductivity of the fabric also increases, on contrary, as the proportion of micro polyester fiber content increases, the thermal conductivity decreases, which may be attributed to the higher thermal conductivity of the micro lyocell fibers and lower thermal conductivity of micro polyester fibers.
111 Figure 4.12 Thermal conductivity of Micro Lyocell/ Micro Polyester blended Fabrics The thermal conductivity values of the twill woven fabrics were noticed to be higher than the plain woven fabrics due to the increased float length of the twill woven fabrics. There is a significant difference exists between the thermal conductivity of these fabrics with respect to blend proportions because p- value (0.02594)< 0.05 and F 2,8 values (6.49) are greater than F critical (4.76) at 95% confidence level. Similarly there is a significant difference between the thermal conductivity of these fabrics with respect to weave because p- value (0.000589)< 0.05 and F 2,8 values (32.8) are greater than F critical (5.14) at 95% confidence level. A negative correlation between the thermal conductivity against the increasing blend proportion of micro polyester in the blended fabric has also been noticed. The regression equations are given in the Table 4.18.
112 Table 4.18 Correlation Coefficient between Thermal Conductivity and Blend Proportion of Micro Lyocell/ Micro polyester Blended Fabrics Fabric Regression Equation between Thermal R 2 Value conductivity and Blend Proportion Plain Woven Fabric Y 1 = -0.006x + 0.038 R 2 = 0.964 2/2 Twill Fabric Y 2 = -0.016x + 0.106 R 2 = 0.975 1/3 Twill Fabric Y 3 = -0.004x + 0.046 R 2 = 0.914 4.2.5.5 Water Vapour Permeability of Micro Lyocell/ Micro polyester Blended Fabrics Moisture vapour transfer is the ability of a fabric to transfer perspiration in the form of moisture vapour through it. Figure 4.13 represents the water vapour permeability of microfiber blended woven fabrics. From the experimental result, it has been observed that water vapour permeability increases with increase in micro lyocell content of the fabric, due to the increase in the number of hydrophilic group in the material. As the micro lyocell proportion in the fabric increases, moisture regain of the material also increases causing higher diffusivity. In the same way moisture transfer through sorption-desorption process will increase with the hygroscopicity of the material. Hence micro polyester fabric with less hygroscopicity provides higher resistance to the water vapour transfer.
113 Figure 4.13 Water Vapour Permeability of Micro Lyocell/ Micro polyester Blended Fabrics There is a significant difference exists between the water vapour permeability of these fabrics with respect to blend proportions because p- value (0.000164) < 0.05 and F 2,11 values (45.14) are greater than F critical (4.76) at 95% confidence level. Similarly, there is a significant difference between the water vapour permeability of these fabrics with respect to weave because p-value (0.000209)< 0.05 and F 2,11 values (47.54) are greater than F critical (5.14) at 95% confidence level. A negative correlation between the water vapour permeability against the increasing blend proportion of micro polyester in the blended fabric has also been noticed. The regression equations are given in the Table 4.19. Table 4.19 Correlation Coefficient between Water Vapour Permeability and Blend Proportion of Micro Lyocell/ Micro Polyester blended fabrics Fabric Plain Woven Fabric Regression Equation between Thermal conductivity and Blend Proportion R 2 Value Y 1 = -0.476x + 4486 R 2 = 0.998 2/2 Twill Fabric Y 2 = - 482.3x + 5069 R 2 = 0.893 1/3 Twill Fabric Y 3 = -447.3x + 5503 R 2 = 0.913
114 4.2.5.6 Water absorbency of Micro Lyocell/ Micro Polyester blended Fabrics Water absorbency is a measure of the time taken to absorb one drop of water and is shown in the Figure 4.14. Sanjay S Chaudhari states that the smaller the diameter of the fiber or the greater the surface energy, the greater is the tendency of a liquid to get absorbed through the fabric. Owing to the high surface energy and excellent hydrophilic property of the micro lyocell, it picks up the moisture more readily than micro polyester which is a hydrophobic fiber. Micro lyocell rich fabrics take just a fraction of a second to absorb a drop of water. Figure 4.14 Water Absorption of Micro Lyocell/ Micro Polyester Blended Fabrics Brojeswari Das (2009), Dr Naresh M. Saraf explains that higher spreading rate is due to the decrease in contact angle between the fabric surface and water and increase in inter fiber and inter yarn pores and pore volumes of the material. The variation in contact angle of water with fabric and its effect on wetting and wicking is shown in Figure 4.15.
115 Figure 4.15 Contact Angle of Water As the micro lyocell proportion increases in the fabric, number of water absorbing group increases, leading to higher hydrophilicity and higher absorption rate. On the other hand the amount of water taken up by the pores will be dependent on the porosity of the material. Being highly porous in nature and due to its micro structure, micro lyocell exhibits higher water absorbency. A significant difference exists between the water absorbency of these fabrics with respect to blend proportions because p-value (0.034197)< 0.05 and F 2,11 values (5.71) greater than F critical (4.76) at 95% confidence level. Similarly a significant difference exists between the water absorbency of these fabrics with respect to weave structure because p-value (0.042875)< 0.05 and F 2,11 values (5.57) greater than F critical (5.14) at 95% confidence level. 4.2.5.7 Water Spreading area of Micro Lyocell/ Micro Polyester Blended Fabrics Spreading area is a measure of the extent to which a drop of water spreads on the surface of the fabric which is an indicator of its drying rate which is shown in the Figure 4.16. The micro polyester rich fabric spreads water to a maximum extent, when compared to micro lyocell rich fabrics. Presence of small amount of micro polyester increases the spreading area and enhances the dry ability.
116 Figure 4.16 Spreading area of Micro Lyocell/ Micro Polyester Blended Fabrics Due to the hydrophobic nature of micro polyester, water molecules do not form bonds with micro polyester, but the presence of more inter fibrillar spaces and high pore volume results in higher moisture spreading rate of micro polyester rich blends. On contrary, due to the formation of bonds between fiber and water molecules and higher moisture content of micro lyocell, it absorbs water and it restricts the spreading rate of water. A significant difference exists between the water absorbency of these fabrics with respect to blend proportions because p-value (0.034197)< 0.05 and F 2,11 values (5.71) are greater than F critical (4.76) at 95% confidence level. Similarly, there is a significant difference between the water absorbency of these fabrics with respect to weave because p-value (0.042875)< 0.05 and F 2,11 values (5.57) are greater than F critical (5.14) at 95% confidence level.
117 4.2.5.8 Vertical Wicking of Micro Lyocell/ Micro Polyester Blended Fabrics Wicking is the spontaneous flow of a liquid in a porous substance, driven by capillary forces. Liquid transfer mechanisms include water diffusion and capillary wicking, which are determined mainly by effective capillary pore distribution, pathways and surface tension. Figure 4.17and 4.18 represents the wicking behavior of micro fibers blended woven fabrics in warp and weft direction respectively. From Figure 4.17 & 4.18 it is evident that as the micro polyester content of the fabric increases, the time taken to wick water to a particular height of the fabric also increases. Tyagi (2009) states that the hydrophilic groups of manmade cellulosic component of the fiber mix governs the liquid moisture transport through capillary interstices in yarns, it may obviously be the contributing factor for high wickability of the micro lyocell rich fabrics. Lyocell is a highly hydrophilic fiber and it has good water absorbency. Due to its high affinity to water and more surface energy, water molecules are attracted by the fibers and hence exhibit higher absorbency. Micro lyocell fibers, due to its finer structure, form more inter fibrillary channels in the yarn which induces capillary action of the absorbed water leading to higher wicking of micro lyocell rich fabrics.
118 Figure 4.17 Vertical Wicking (warp way) of Micro Lyocell/ Micro Polyester Blended Fabrics Figure 4.18 Vertical Wicking (weft way) Polyester Blended Fabrics of Micro Lyocell/ Micro It can also be observed that as the fiber composition varies, there is a substantial variation in wicking behavior. Being hydrophobic in nature polyester has lesser affinity to water molecules, hence shows lower wickability. The effect of inter fibrillary spaces due to micro structure is the same for both micro lyocell and micro polyester fabrics, but the hydrophilicity has dominant effect on the wicking behavior. Further the higher wickability is
119 due to the decrease in contact angles and increased pore volumes of the micro lyocell rich fabrics. All fabric samples exhibit higher wickability in weft direction compared to warp direction. The regression equations are given in the Table 4.20. A positive correlation exists between the time taken to absorb water and the proportion of micro polyester in the fabric, both in warp and weft ways, which implies that the wickability decreases as the proportion of micro polyester increases. Table 4.20 Correlation Coefficient between Vertical Wicking and blend Proportion of Micro Lyocell/ Micro polyester blended fabrics Regression Equation between vertical Fabric wicking (warp way)and Blend R 2 Value Proportion Plain Woven Fabric y = 0.52x+2.25 R² = 0.9324 2/2 Twill Fabric y = 0.59x + 2.6 R² = 0.922 1/3 Twill Fabric y = 0.79x + 2.75 R² = 0.9978 Regression Equation between vertical wicking (weft way) and Blend Proportion Plain Woven Fabric y = 0.93x + 3.25 R² = 0.9637 2/2 Twill Fabric y = 0.51x + 6.7 R² = 0.8984 1/3 Twill Fabric y = 0.89x + 6.85 R² = 0.9368
120 4.2.5.9 Inplane Wicking of Micro Lyocell/ Micro Polyester Blended Fabrics Water uptake by the fabric samples at different time period measured by inplane wicking test is given in Figure 4.19. Figure 4.19 Inplane Wicking of Micro Lyocell/ Micro polyester Blended Fabrics Water uptake is found to increase with the decrease in micro polyester proportion. Due to hydrophilic nature and micro structure, the micro lyocell rich fabrics absorb more amount of water in a given time. Twill woven fabrics made of micro lyocell fabrics absorb around 0.07 grams of water per cm 2 of fabric proving its ability to absorb sweat and ensures moisture free micro climate near the skin. 4.2.5.10 Frictional Behavior of Micro Lyocell/ Micro Polyester Blended Fabrics The static and dynamic frictional characteristics of micro lyocell/micro polyester blended woven fabrics are given in the Figure 4.20.
121 Figure 4.20 Frictional Factor of Micro Lyocell/ Micro polyester Blended Fabrics From the figure 4.20 it is observed that as the micro polyester content in the fabric increases, the frictional factor decreases. This may be attributed to the lower specific density of micro polyester fibers. Due to lower specific density of these fbres, more number of fibers will be packed in a given count of yarn. Due to the higher packing density of fibers in the yarn, the yarn is more uniform and bulkier than micro lyocell yarn of equal count. Hence micro polyester fiber offers very less crests and troughs than micro lyocell fabrics leading to reduced frictional factor. 4.2.5.11 Drying Rate of Micro Lyocell/ Micro Polyester Blended Fabrics Liquid transporting and drying rate of fabrics are two vital factors affecting the physiological comfort of garments. The moisture transfer and quick dry behaviors of textiles depend mainly on the capillary capability and moisture absorbency of the fibers. These characteristics are especially important in garments worn next to the skin or in hot climates. In these situations, textiles are able to absorb large amounts of perspiration, draw
122 moisture to the outer surface and keep the body dry.the drying rate of the micro lyocell/micro polyester fabrics are shown in the Figure 4.21. Drying rate of Micro polyester/micro lyocell RWR% 80 70 60 50 40 30 20 10 0 10 MIN 20 MIN 30 MIN 40 MIN 100 MP(P) 100 MP(2/2) 100 MP(1/3) 85/15 ML:MP(P) 85/15 ML:MP (2/2) 85/15 ML:MP (1/3) 70/30 ML:MP (P) 70/30 ML:MP (2/2) 70/30 ML:MP (1/3) Figure 4.21 Drying Rate of Micro lyocell/ Micro polyester Blended Fabrics Based on the results of the drying rate as shown in Figure 4.21, the performance ranking is shown below: MP: 100 > ML/MP: 85/15 > ML/MP: 70/30 > ML: 100. From the test results, it can be inferred that, as the micro polyester component of the blended fabric increases, the drying rate also increases. Presence of micro polyester improves the drying rate and dry feel of the garment. Raul (2008) stated that the remaining water ratio (RWR) is lower for the skin conditions as the heat provided by the environment enables quicker evapouration. Initially the moisture releases from the fabric and then the moisture releases from fibers. Moreover the curve shows an inflection point at about 20min, corresponding to a lower evapouration. In fact, the first part of the behavior, represented by higher slope, corresponds to the moisture release from the fabric and the second part of the curve, with a lower slope, corresponds to the moisture release from fibers.
123 4.6 CONCLUSIONS Single layered hospital textiles were developed using lyocell/polyester blended yarns with two blend ratios such as 85:15 and 70:30. Since higher proportion of polyester reduces the air permeability, water vapour permeability and thermal conductivity of fabrics, which are the prime factors in maintaining thermophysiological comfort of human body, polyester-rich fabrics lag in comfort characteristics and are not suitable for hospital textile applications. Hence the proportion of polyester in the blend was limited to 30%. From the analysis of the comfort properties of lyocell blended fabrics, the following conclusions are arrived at: As the proportion of polyester fiber content in the fabric increases, the fabric strength shows an increasing trend but the elongation shows a decreasing trend. From the analysis of the comfort characteristics, it was found that the air permeability and water vapour permeability decreases with increase in polyester content. 100% lyocell fabric has higher air and water vapour permeability. On contrary, as the lyocell content in the blended fabric increases, the thermal conductivity of the fabric increases. 100% lyocell fabric has higher thermal conductivity. Presence of hydrophobic fiber increases the absorbency of the fabric by reducing the time taken to absorb a drop of water. 70:30 lyocell /polyester blended fabrics with 1/3 twill weave structure has better water absorbency. Vertical and inplane wicking ability of the blended fabric increases with increase in polyester content in the fabric. 70:30 lyocell /polyester blended fabrics with 1/3 twill weave structure has better wickability in both directions.