CHAPTER 6 DESIGN AND DEVELOPMENT OF HOSPITAL BED LINEN

Transcription

1 186 CHAPTER 6 DESGN AND DEVELOPMENT OF HOSPTAL BED LNEN 6.1 NTRODUCTON The bed sheets used in hospitals are made of cotton or polyester cotton blended fabrics, which seems to date from the past centuries. But these hospital textiles need to ensure the comfort and hygienic level of the patient and needs to be engineered with specific comfort properties. But no effort has been made to make new textile materials that could help in reducing the discomfort experienced by the patients. This part of the research work aims at analyzing the comfort characteristics of existing hospital bed linen and analyzing the biomechanics of human body so as to understand the amount of heat and sweat to be transferred by the clothing next to the skin. This chapter also analyses the suitability of the lyocell fiber based single layered hospital textiles developed and their effectiveness in ensuring the thermo physiological comfort characteristics for the selected end use. 6.2 ANALYSS OF EXSTNG HOSPTAL BED LNEN A questionnaire was prepared and survey carried out in various hospitals to analyze about the type of mattresses and bed linen used in hospitals. The existing hospital bed linens used in hospitals were collected and analyzed for their comfort and hygienic properties.

2 187 Commercially used hospital bed linen, collected from various hospitals were found to be made of 100% cotton yarn with count in the range of 16 s, 20 s, 30 s and 40 s Ne which are bleached or vat dyed in blue or green color. The yarn and fabric parameters are given in the Table 6.1. Table 6.1 Yarn and Fabric parameters of hospital bed linen S.No Fabric type Yarn Ends Picks Fabric Fabric count /cm /cm weight g/m 2 thickness (mm) 1 Cotton Bleached 2 Cotton Bleached Plain 3 Cotton Bleached Twill 4 Cotton Vat dyed -Blue 5 Cotton Vat dyed -Green The Hospital bed linen fabrics were analyzed for their comfort and moisture management properties using standard test methods and are listed in the Table 6.2.

3 188 Table 6. 2 Comfort properties of hospital bed linen S.No Air Permeability (cm 3 /cm 2 /s) Thermal conductivity (w/m/k) Water vapourpermeability (g/m 2 /24 hrs) Absorption (sec) Spreading area (cm 2 ) Frictional Factor (F/N) static dynamic Vertical wicking- (warp) (cm) Vertical wicking- (Weft) (cm) Air Permeability of Hospital bed linen Figure 6.1 shows the air permeability values of the five commercially available hospital bed linen samples. Fabrics made of courser count yarn have higher air permeability when compared to finer fabrics with higher ends and picks per inch. This may be due to the lower porosity of fabrics with higher cover factor. Twill woven cotton fabrics made of 40 s count yarn has least air permeability whereas the coarser fabric made of 16 s count yarn has higher air permeability. Air Permeability cm3/cm2/s s 30s 40s 40s(b) 16s Figure 6.1 Air Permeability of hospital bed linen

4 Thermal conductivity of Hospital bed linen Thermal properties of textile materials especially thermal conductivity have always been the major concern, when the comfort properties of hospital textiles are concerned. Figure 6.2 shows the test results of thermal conductivity, which is a measure of the amount of heat transferred through fabric in w/m 2 /k for the five different hospital bed linen fabrics. Among the hospital bed linens, thermal conductivity is high for 16 s count hospital bed linen and least for 40 s twill woven fabrics. Fabrics with courser count conduct heat effectively when compared to finer fabrics. This may be due to the higher porosity of courser fabrics. Thermal conductivity w/m/k s 30s 40s 40s(b) 16s Figure 6.2 Thermal conductivity of hospital bed linen Water Absorbency of Hospital bed linen Figure 6.3 shows the water absorbing capability of hospital bed linen fabrics in terms of the time taken to completely absorb one drop of water by the surface of the fabric. The courser fabric made of 16 s count yarn absorbes water very fast compared to other fabrics and the vat dyed blue fabric made of 40 s count yarn takes maximum time for absorbing water. Other hospital bed linens exhibited moderately slower water absorbing property.

5 190 Water absorption Sec s 30s 40s 40s(b) 16s Figure 6.3 Water absorbency of hospital bed linen Water spreading area of Hospital bed linen Figure 6.4 shows the extent to which a water drop spreads on the fabric which is an indicator of its drying rate. Amongst the hospital bed linen fabrics, bed linen made of 20 s, 30 s and 40 s cotton fabrics showed maximum spreading area compared to other fabrics. Figure 6.4 Water spreading behavior of hospital bed linen

6 Frictional Factor of Hospital bed linen The static and dynamic frictional factor is measured for all hospital bed linen and is shown in Figure.6.5. Among the hospital bed linen fabrics, 40 s count cotton bed linen has less friction due to its finer yarn count and smooth fabric surface because of twill weave structure. Figure 6.5 Frictional factor of hospital bed linen Water vapour Permeability of Hospital bed linen Moisture vapour transfer is the ability of the fabric to transfer perspiration in the form of moisture vapour through it. t is measured in terms of the amount of water vapour passing through a square meter of fabric per day. A fabric with low moisture vapour transfer is unable to transfer sufficient moisture, leading to sweat accumulation and hence discomfort.the moisture vapour transfer ability of the existing hospital bed linen is shown in the figure 6.6. The vat dyed blue fabric made of 40 s count yarn has maximum water vapour permeability and other fabrics exhibit comparatively equal water vapour permeability.

7 192 Water vapor permeability g/m2/day s 30s 40s 40s(b) 16s Figure 6.6 Water vapour permeability of hospital bed linen As far as wickability is concerned, the finer fabrics have maximum wicking tendency both in warp and weft direction. 6.3 ANALYSS ON THE PHYSOLOGY OF HUMAN BODY The heat and moisture transmission behavior of a fabric plays a very important role in maintaining thermo-physiological comfort of the body. The human body continuously generates heat by its metabolic processes. The heat is lost from the surface of the body by convection, radiation, evaporation and perspiration. n a steady-state situation, the heat produced by the body is balanced by the heat lost to the environment by maintaining the body core temperature around 37ºC. A person can live comfortably only in a very narrow thermal environment from 26 C to 30 C without wearing clothing. With clothing, human beings can live and perform various physical activities comfortably in a wide range of thermal environments from -40 ºC to 40ºC. So clothing plays an important role in providing thermal protection for the human body and creates a comfortable thermal microclimate. The amount of heat and sweat generated by a sleeping person and a person confined to wheel chair is given in the Table 6.3.

8 193 Table 6.3 Range of metabolic heat generation for various activities Activities Sleeping 35 W/m 2 Seated Quietly W/m 2 Standing W/m 2 Normal activities 80 W/m 2 Heat generation Body temperature at rest 37 ºC Energy required for basic activity 40 kcal/hr/m 2 Metabolic rate of a sleeping person Metabolic heat generation 0.7 met(1 met is W/m² or 50 k cal/m 2.h) Heat disscipated through evapouration k cal/m 2.h Heat disscipated through clothing 38 k cal/m 2.h nsulation of air nsulation of clothing Total energy radiated by an adult male Total surface area of female thermal manikin. Sweat generation Perspiration in unstressed condition for resting person 0.14 m 2 Ch/k cal 0.18 m 2 Ch/k cal 2000k cal/day 1.8 m² 15g/m 2 /h (or) 360g/m 2 /day (or) 720 g/day/person Perspiration in hot condition 100 g/m 2.h Heat disscipated through evapouration The heat loss for every ml of water evapourated The maximum rate of sweating in an acclimatized adult. The transversal moisture diffusion Sweat generation for low activity Sweat generation for high activity k cal/m2.h 0.58 kcal 5 ml/min or 2000ml/hr 100 to 150 ml per day per m² of skin 500 ml/day 2 l /day 1 clo 0.18 m 2 Ch/k cal = 0.155m 2 C/w

9 Heat loss from human body Heat is generated within the human body by the combustion of food. The heat is lost from the body by Conduction and convection - about 16% Radiation - about 60% Evapouration of moisture - about 12% Exhaled air - about 12% Evapouration prevails at high ambient temperatures. Conduction and convection prevails at low ambient temperatures. Heat is liberated in a rate maintaining the internal body temperature at 37 o C.The total heat loss from an adult at normal activity is approximately 118 W (2 Met) in a room with temperatures between 19 o C and 34 o C. The metabolic heat generated and the amount of heat transferred from a person to surrounding by conduction, convection, radiation, evapouration and through exhaled air is listed for a person under the conditions of sleeping, sitting idle and normal activity below. Table 6.4 Heat transferred from a person to the surrounding Activity Sleeping Resting in bed Seated Normal activity Metabolic Heat transferred from a person to the surrounding rate Conduction Radiation Evapouration Exhaled or convection (60%) of Moisture (12%) (16%) (12%) w/m w/m w/m w/m w/m 2 73 w w 43.8 w 8.76 w 8.76 w 0.7 met 0.11 met 0.42 met 0.08 met 0.08 met 46 w/m w/m w/m w/m w/m 2 85 w 13.6 w 51 w 10.2 w 10.2 w 0.8 met 0.13 met 0.48 met 0.10 met 0.10 met 58 w/m w/m w/m w/m w/m w w 62.4 w w w 1 met 0.16 met 0.6 met 0.12 met 0.12 met w/m w/m w/m w/m w/m w 18.88w 70.80w 14.16w 14.16w 2 met 0.32met 1.20met 0.12met 0.12met air

10 195 n estimating the effect of convection on the cooling of the body, it is combined with conduction Heat loss by Conduction The basic heat transfer equation for conduction is Q ka(thot Tcold ) (6.1) t d Where, in this case, A would be the area of the human body (1.8 m 2 )and k the thermal conductivity of the air surrounding the body(5.7 x 10-5 cal/s/cmºc). Under normal conditions the heat conducted by a human body is 10.5 watts which is not sufficient to transfer the entire heat from the body Heat loss by Radiation The basic heat transfer equation for radiation is Q 4 hot cold t 4 e A(T T ) (6.2) where A is the area of the human body(1.8 m 2 ) and e is the emissivity of the skin. n this case the human skin is near ideal radiator in the infra red range and has an emissivity value of = 5.67 x 10-8 watts/m 2 /k 4 (Stephen Boltzmann constant) T hot = 307 K, T cold = 296 K, Under normal conditions the heat radiated by a human body is 133 watts, which is more than adequate to cool the body.

11 Heat loss by Evapouration At higher ambient temperature (>37ºC), the heat transfer mechanisms like radiation, conduction and convection transfers heat into the body rather than out. Since there must be a net outward heat transfer, the only mechanisms left under those conditions are the evapouration of perspiration from the skin and the evapourative cooling from exhaled moisture. Even when one is unaware of perspiration, physiology texts quote an amount of about 600 grams per day of "insensate loss" of moisture from the skin. The cooling effect of perspiration evapouration makes use of the very large heat of vapourization of water. This heat of vapourization is 540 calories/gm at the boiling point, but is even larger, 580 cal/gm, at the normal skin temperature. q T gm cal J 1 day 1 hr (600 ) (580 ) (4.186 ) ( ) ( ) 17 watts day gm cal 24 hr 3600 S (6.3) As part of the physiological regulation of body temperature, the skin will begin to sweat almost precisely at 37 C and the perspiration will increase rapidly with increasing skin temperature. Guyton reports that a normal maximum perspiration rate is about 1.5 liters/hour, but after 4 to 6 weeks of acclimatization in a tropical climate, it can reach 3.5 liters/hr. The maximum rate corresponds to a maximum cooling power of almost 2.4 kilowatts. The general energy balance equation is as follows, M W =C + R + E +C res +E res + S (6.4) Where M metabolic rate, W/m 2 W mechanical power, W/m 2

12 197 C convective heat loss from skin, W/m 2 R radiation heat loss from skin, W/m 2 E evapourative heat loss from skin, W/m 2 C res E res Convective heat loss from respiration evapourative heat loss from respiration S rate of body heat storage The left side of this equation is internal heat production and the right side describes the sum of heat exchanges from the human body. For normal activities, the mechanical power is negligible and can be made equal to zero. Under thermal equilibrium conditions, body heat production is equal to body heat loss. There is neither heat storage in the body, nor dissipation of stored heat from the body. Hence all the heat generated has to be dissipated through conduction, convection and radiation Heat transfer through clothing The basic metabolic heat generated in a body is to be transferred through clothing. Heat transfer through evapouration of sweat is governed by the water vapour permeability of fabric. For a body covered with clothing, the amount of heat transferred by convection, conduction and radiation are to be dissipated by thermal conductivity of the fabric worn next to skin assisted by heat transfer through air. Hence thermal conductivity, air permeability and moisture vapour permeability of a fabric determines the ability of a fabric to ensure thermal comfort. Clothing convective and radiative heat exchanges R and C can be determined in various ways. 1. Clothing convective and radiative heat exchanges R and C in W m 2 are determined principaly by:

13 198 Where, r R C (6.5) is the thermal insulation of clothing (m 2 C W 1 ), t is the temperature gradient across the clothing layer ( C) (normally skin to clothing surface) 2. For static conditions with no air motion, R+C is determined by: Where R C(Wm C ) 2 o 1 sk cl cl o sk o (6.6) cl a / f cl T f cl t cl t o cl a is the clothing area factor (the ratio in surface area between the outer clothing surface and the nude person s surface area; dimensionless), the clothing surface temperature, the ambient operative temperature ( C). intrinsic clothing insulation insulation of surface air layer T insulation of clothing with surface air layer (m 2 C W 1 ). 3. R+C can also be determined, as in ASHRAE standard by: Where, R+C (Wm 2 C 1 )= F cl (h c +h r ) (t sk t o ) (6.7) F cl h c h r - the dimensionless clothing efficiency factor - convective heat transfer coefficient (both in W m 2 C): - radiative heat transfer coefficient (both in W m 2 C): The dimension less clothing efficiency factor F cl can be determined by using the formula, F 1/(h h ) a a c r cl (6.8) cl a / fcl T T

14 199 The amount of heat radiated is likely to change with air movement and body motion due to the increased convection in and on the surface of clothing layers. Heat transfer through evapouration of sweat is governed by the water vapour permeability of fabric. Hence thermal conductivity, air permeability and moisture vapour permeability of a fabric determines the ability of a fabric to ensure thermal comfort. The amount of heat to be transferred by the fabric through thermal conductivity and moisture vapour permeability is given in the Table 6.5. Table 6.5 Amount of heat to be transferred Amount of heat Amount of moisture Activity conducted through vapour through fabric fabric Sleeping 30.94w/m g/ m 2 / day Resting in bed w/m g/ m 2 / day Seated w/m g/ m 2 / day Normal activity w/m g/ m 2 / day From the above Table it can be observed that the amount of moisture vapour to be transferred through the fabric ranges from173 to 280 g/ m 2 / day where as the water vapour permeability of the single layered and multi layered fabrics developed are more than 1600 g/ m 2 / day which is more than sufficient to transfer the moisture vapour. Hence all the fabrics developed are capable of transferring the moisture. To ensure thermal comfort, the metabolic heat generated must be dissipated through the cloth by conduction, convection or radiation. The regression equations for the convective heat transfer coefficients

15 200 (h c [W/ (m 2 K)]) for natural convection, driven by the difference between the mean skin temperatures corrected using the convective heat transfer area and the air temperature, and the convective heat transfer coefficient for a human in three different posture, when the difference in body and ambient temperature is around 5 C, are given in the Table 6.6. Table 6.6 Convective heat transfer coeffeicent of human body S.No Activity Formula for Convective heat transfer h c [W/ (m 2 K)] coefficient W/(m 2 K) 1 Standing (exposed to atmosphere) h c = T 0: ( ) Chair Sitting (contact with seat, chair back h c = T 0: ( ) and floor) 3 Sleeping (floor contact) h c = 0:881 T 0: ( ) The heat to be transferred for a sleeping person is W/ (m 2 K) whereas the heat transfer through all single and multi layered fabrics (annexure 1) are not sufficient to transfer the heat. f supplemented with an air circulation the amount of heat transferred could be improved. 6.4 COMPARSON OF THE COMFORT LEVEL OF THE SNGLE LAYERED HOSPTAL TEXTLES DEVELOPED Single layered hospital textiles were developed from Lyocell and its blends with polyester Micro lyocell and its blends with Micro polyester Bamboo yarns with Cotton and lyocell Bamboo charcoal yarn with lyocell

16 201 n all of the above mentioned fiber combinations, blended yarns and fabrics were produced by varying the blend proportion and weave structures. Among each set of fabrics, the fabrics having maximum comfort properties are analyzed for their ability to fulfill the performance requirement of hospital textiles. The following fabrics were found to have maximum comfort properties and they are compared in terms of the essential properties such as air permeability, thermal conductivity, water vapour permeability, water absorption and water spreading ability. Table 6.7 Comfort properties of selected single layered fabrics developed Lyocell Lyocell/ Microlyocell/ Micro Bamboo/ Bamboo Bamboo Fabric (100%) Polyester (70:30) Micro polyester (85:15) lyocell (100%) Lyocell (25:75) : Cotton Charcoal/ /Lyocell Lyocell (25:75) (50:50) Air permeability cm 3 /cm 2 /s Thermal conductivity, w/m/k Water vapour permeability g/m 2 /day Water absorption, sec Spreading area, cm Analysis of the air permeability of hospital textiles developed Figure 6.7 shows the air permeability of the few selected hospital textiles developed. t is observed from the figure that the bamboo and bamboo

17 202 charcoal fiber based blended fabrics show higher air permeability than the lyocell, micro lyocell blended fabrics. This trend may be attributed to the fine micro pores present in the bamboo fiber. Blending of polyester with lyocell reduces the air permeability. The air permeability value ranges from 77.4 to 178. Bamboo charcoal fabric has the maximum air permeability. Figure 6.7 Air permeability characteristics of single layered bed linen developed Analysis of the Thermal conductivity of hospital textiles developed Figure 6.8 shows the thermal conductivity characteristics of the selected single layered medical textile fabrics. Thermal conductivity is maximum in the case of bamboo: cotton /lyocell, which may be due to the best combination of the thermal conductive fabrics such as bamboo cotton and lyocell.

18 203 Figure 6.8 Thermal conductivity characteristics of single layered bed linen developed Lyocell/polyester blended fabrics have the least thermal conductivity due to the presence of polyester followed by micro lyocell and micro polyester blended fabrics. Bamboo and bamboo charcoal blended fabrics have higher thermal conductivity Analysis of the Water vapour permeability of hospital textiles developed Figure 6.9 shows the comparison of water vapour permeability of the selected hospital textile fabrics. t shows an interesting trend of higher water vapour permeability for the lyocell and micro lyocell blended fabrics which may be attributed to the fine and smooth structure of lyocell fiber and presence of polyester which reduces the formation of bonds between the water molecules and hydrophilic fiber there by increasing water vapour

19 204 permeability. The bamboo fibers due to their higher attraction towards water have lower water vapour permeability. Figure 6.9 Water vapour permeability characteristics of single layered bed linen developed Analysis of the Water absorption of hospital textiles developed Figure 6.10 Water absorption characteristics of single layered bed linen developed

20 205 From the figure 6.10 it is observed that the lyocell, blends of lyocell: polyester and bamboo charcoal fabrics have lower water absorbency. The bamboo rich fabrics and the micro fiber fabrics have excellent water management properties Analysis of the Water spreading area of hospital textiles developed From Figure 6.11, it is clear that water management ability of the micro fibers and lyocell/polyester fabrics are better than other fibers. Presence of polyester and polyester micro fibres influences the water spreading ability of micro fiber and lyocell/polyester blended fabrics. Figure 6.11 Water spreading characteristics of single layered bed linen developed Hence it can be concluded the hospital textile fabrics made of lyocell/polyester and microlyocel/micro polyester blended fabrics have better performance when compared to other fabrics.

21 COST ANALYSS OF HOSPTAL TEXTLES The cost of widely used hospital textiles made of cotton is given in the Table 6.8. Depending on the count and fabric specification, the cost of fabric per meter ranges from Rs.44 to Rs.72. The cost of hospital textiles developed from the new generation fibres is given in the Table 6.9. The Fabric cost /m 2 ranges from Rs. 95 to Rs. 100 for single layered fabrics and the single and multi layered fabrics made of Bamboo charcoal yarn costs around Rs. 160 to Rs.450. Since the bamboo charcoal yarn is imported from china and the yarn cost is high, compared to other fabrics, the bamboo charcoal fabric cost is high. The multi layered fabric made of bamboo and lyocell combination costs around Rs.110 to Rs The cost of newly developed hospital textiles are 1.5 to 2 times costlier than the existing fabrics made of cotton. Table 6.8 Cost analysis of Existing bed linen Cost of Existing Bed linen S.No EP x PP Warp count x Size(cm) Weft count Cost per piece(rs.) Cost/meter 2 (Rs.) x S x 30 S 145 x x S x 34 S 102 x x S x 40 S 160 x x /40 S x 2/40 S 145 x x S x 10 S 145 x

22 207 Table 6.9 Cost analysis of Hospital textiles developed S.No Fibre type Yarn cost (Rs) GSM Grey Fabric Cost/ m (Rs.) Bleached fabric Cost/ m (Rs.) Dyed fabric Cost/ m (Rs.) 1 Lyocell Lyocell: Polyester Bamboo Bamboo:cotton/ Lyocell Bamboo charcoal % : Micro polyester: Micro lyocell 7 Bamboo charcoal/ Lyocell Multi layered Knitted fabrics 8 Bamboo/ Lyocell Multi layered Knitted fabric Bamboo charcoal/ Lyocell Multi layered Woven fabrics Bamboo/ Lyocell Multi layered Woven fabric 50: : BC-3000 MP- 500 L- 360 B-340 L-360 MP-500 BC-3000 MP- 500 L- 360 B-340 L-360 MP PU foam Cost of mattress with Air circulation device Hollow fibre Air circulation device Total cost Non woven and fabric cover Mattress with air circulation device and air permeable water impermeable cover: 6000

23 CONCLUSONS From the analysis of the comfort and moisture management properties of existing hospital bed linen fabrics, it was found that fabrics made of courser count yarn have higher air permeability when compared to finer fabrics. The thermal conductivity is high for 16 S count hospital bed linen and least for 40 S twill woven fabrics. All hospital bed linens exhibited moderately good water absorbing property except the vat dyed blue fabric made of 40 s count fabric. The hospital bed linen fabrics made of 20 S, 30 S and 40 S cotton fabrics showed maximum spreading area compared to other fabrics. Coarser fabrics have high frictional coefficient and 40 S count cotton bed linen has less friction due to its finer yarn count and twill weave structure. All the bed linens have equal water vapour permeability of around 1500 to 2000 g/m 2 /day. From the analysis of the selected hospital textiles developed from each category, it is observed that the bamboo and bamboo charcoal fibre based blended fabrics have higher air permeability than the lyocell, micro lyocell blended fabrics. Lyocell /polyester blended fabric have the least thermal conductivity and bamboo, bamboo charcoal blended fabrics have higher thermal conductivity. Higher water vapour permeability is noted for lyocell and micro lyocell blended fabrics and the bamboo fibre fabrics have lower water vapour permeability. The bamboo rich fabrics and the micro fiber fabrics have excellent water management properties. Presence of polyester and micro polyester influences the water spreading ability of micro fibre and lyocell/polyester blended fibre fabrics.