What is Mercerized Cotton?

by Tom Beaudet

Why Mercerization?

Mercerized cotton is sometimes referred to in the crafts as pearl or pearle cotton. It is cotton yarn or fabric which has been put through a series of processes, primarily to increase luster. The added desirable water handling properties gained are a secondary bonus.

Cotton fiber grows in a boll; each fiber is produced from an individual seed (about 5,000 altogether) in the base. The fiber starts out as a projecting hollow sheath and each night a new layer of cellulose is laid down on the inside of the sheath until about thirty layers are built up. At this point the fiber is like a solid cylindrical rod having a central lumen or canal pointing to the tip consisting entirely of cellulose. When the boll bursts and exposes these fibers to sun and air they dry up and collapse, becoming flatter and ribbon like with alternating left and right spiral twist every two or three turns. This is cotton fiber in its original state.

Through the ages countless attempts have been made to alter the fiber, sometimes with a specific end use in mind and other times just as pure research. In 1851, John Mercer was granted a British Patent for work he had done pertaining to cotton, linen and other vegetable fibrous materials that in effect caused certain changes in the character of the fiber when subjected to caustic soda, sulfuric acid, and/or other chemicals, etc. He went on to list a number of these changes, one of which was that caustic soda caused the fiber to swell, become round and straighten out (but it did not impart any change in luster). At the time Mercer introduced these processes, the British cotton trade showed no interest in any of it and it all sat in obscurity for about forty years. In 1890 Horace Lowe was granted a British patent in which he claimed that by applying Mercer's caustic soda process to cotton yarn or fabric under tension a resultant high luster (a result of the light reflection off the smooth, round surface) was imparted to the fiber. It became an overnight success and revolutionized the cotton industry. The rest is history.

Mercerization and Luster

We must keep in mind when making comparisons between the water absorbency quality of mercerized and unmercerized cotton that the primary reason for mercerizing cotton is to gain luster. Like virtually all other chemical applications to affect change in fiber, concentration alone is not as important as the combination of time, temperature and concentration. In this case cotton held under specified tension for ten minutes with an application of between 21%-23% caustic soda (NaOH), at room temperature results in the desired luster and increased tensile strength. Without the tension there is no increased luster. It has been established that luster is a result of light reflection off the surface of the selected product. The more glass like the surface, the better the luster. Yarn in its spun, treated state still has a very fine covering of tiny fiber ends (fuzz). This fuzz is removed by passing the yarn (or fabric) through a controlled heated atmosphere termed singeing (gas fired in the past, electric more currently) resulting in a cleaner surface.

Absorbancy and Twist

In order to gain luster we must apply the mercerizing treatment while the yarn or fabric is under tension, (Lowe's findings). Cotton mercerized in a relaxed state gains no luster, (Mercers's findings). Since fine, long stapled fiber will give us the best adhesion with the lowest twist, (required for treating under tension to gain luster) it is usually those types of cotton (Sea Island, Egyptian, Pima) that are selected for yarn to be mercerized. Consequently when we are comparing the water absorption qualities of a skein of mercerized cotton against a skein of unmercerized cotton in our dye bath or for other treatment purposes we may also be comparing long staple cotton against short staple cotton, which have entirely different fiber characteristics. Therefore, any discussion concerning the water absorbency quality must also consider the effect of twist on the ability of that cotton fiber to absorb moisture. In addition we must recognize that we may be talking about moisture content and moisture regain which is another variable. That said, let us take a look at the two kinds of cotton by reducing the variables.

First, Mercer's and subsequent testing showed a dramatic increase in absorption of dyestuffs (up to 25% NaOH, then leveling off) for the mercerized sample of cotton spun yarn, with all other variables constant. There is an increase in water absorption (7.5% to 8.5% regain) as well.

Secondly, when Mercer conducted his studies and recognized the increased affinity treated fiber had for direct dyes, water, and iodine (iodine being important element in qualitative testing), he concluded this affinity was a result of the amount of NaOH absorbed by the fiber during treating. Further testing proved that cotton fiber in its roving state (no twist) would absorb more NaOH than fiber in a twisted state and as a result absorb more water or dye. The amount of absorbed NaOH was proportionate to the amount and type of twist, singles, and ply.

Industry Studies and Published Results

In my personal experience, the ability to control and predetermine the water absorption properties of a given yarn through its twist factor, rather than through mercerization, are far greater, and therefore have been more extensively studied by engineers (including myself), than that of mercerizing. The problem here is that the studies that were conducted were done for proprietary reasons and the results to support the numbers are not published.

As an example, the three primary functions of a papermaker's felt are water removal, finish, and power transmission. Water removal is a very important factor because the better the water removal, the faster the machine will run. The finish is equally important because the felt must be absolutely defect free; the slightest imperfection in the surface would leave a mark in the paper. The biggest factor is power transmission. The entire press section is run off of one drive roll. Some of these press sections are three stories high and pull tons of pulp in an aqueous state through its cycle. Some require an endless felt 25 feet wide and 110 feet long. If the felt tears off under load at startup you never get to test the water removal or the finish. Extensive studies were conducted to determine optimum operating results for water removal and formulas were developed for pounds per inch stress through fiber selection, yarn size, twist in singles and plied twist in both Z and S, chemical treatments, etc. The problem is the results are guarded like the gold in Fort Knox. Therefore, we cannot print out numbers in an objective fashion. We can say in a subjective manner that in fact twist in yarn can affect over a wide range of permeability the ability of that yarn to absorb and give up water.

Conclusion

Looking at the information presented so far, we can conclude that mercerized cotton absorbs more water and dye than unmercerized cotton, and that the twist in yarn will affect the water handling properties of that yarn proportionate to the amount of twist.

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Tom Beaudet has worked with three major textile companies in his career (Milliken, Albany International, and Tetko) and loved every minute of it. He has and will continue to be involved with handweaving since college, more so since he retired.

"Keep those Beaters moving, its good for your health." - Tom Beaudet

Copyright © 1999 by Tom Beaudet under the GFDL and/or Creative Commons licenses.

Tom Beaudet

49 Western Ave.

Westfield, MA 01085

Thankx Tom Beaudet.

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About ozone part 3

Figure 3. Data obtained during 16-min test on water that contained C. difficile spores at 75/C (Microsearch Laboratories Ltd., May 15, 2004).

Test #2. Testing of Four OTEX Laundering Cycles – Microsearch Labs - Nov. 8, 2004

Four ozone laundering cycle studies (Test Codes) of various garments were conducted and the challenge organisms (S. aureus MRSA strain and C. difficile) recovered and analyzed post-washing. Cycle 1 (Test Code 1) is a heavy washing for foul and infected, heavily soiled clothing. This cycle also has a sluice cycle (high wastewater level flush). The machine fills up with cold water, does a wash action, and continuously drains through an overflow. This sluice cycle is followed by a normal wash cycle. Cycle 2 (Test Code 2) is for lightly soiled sheets and towels.

Cycle 3 (Test Code 3) is for delicate items, such as personal clothing and woolens. Cycle 4 (Test Code 4) is a rewash cycle used for oil/grease stained articles. With this cycle, 50/C water is used to emulsify the oils and aid washability.

Figure 4. EU Suspension Test conducted on OTEX ozone laundry water with C. difficile spores (Microsearch Laboratories Ltd., May 15, 2004).

The amount of ozone is constant for each washing programme. The difference between cycles is that the more heavily soiled items require more detergent, which destroys some of the ozone. It is important to know that satisfactory microorganism kills can be attained by the four washing cycles, regardless of the degree of soil.

A control untreated batch also was tested for these microorganisms in duplicate. Results are listed in Table 1. All ozone launderings resulted in > 5-logs kill (>99.999%), whereas washing without ozone (Controls) gave <99.999 % kill.

Test #3. – Microsearch Labs – MRSA Contamination of Nurses Uniforms Test – 2004

Microsearch Laboratories carried out comparative tests on nurses’ uniforms impregnated with a strain of the superbug MRSA (methicillin-resistant Staphylococcus aureus). This microorganism is being detected with increasing frequency in USA hospitals and care homes (TIME Magazine Archive, 2006).

The care labels of nurses’ uniforms commonly carry the recommendation that they should be washed at 40ºC (104°F). Therefore, one test was carried out using a conventional 40ºC wash cycle (without ozone). A second test was carried out with an OTEX (cold water) cycle.

Figure 5 is a photograph showing the MRSA microorganism which had been impregnated onto a membrane. The membranes were implanted into the garments prior to the uniforms undergoing any laundry process.

Figure 5. MRSA impregnated onto membrane. Microsearch Labs, 2004.

Figure 6 shows the residual MRSA culture on the recovered membrane after having been washed at 40ºC (104°F). Figure 7 shows the absence of residual MRSA culture on the recovered membrane after an OTEX ozone-laundering cycle.

Figure 6. MRSA on membrane after 40°C wash.

Figure 7. Absence of MRSA after OTEX.

Results – These results indicate that a greater than log-8.0 reduction (99.999999%) in MRSA was obtained on populations of garments washed by the OTEX process. The average log reduction achieved by the 40ºC (104°F) wash was only 3.3 (99.93%). To clarify, the reduction of MRSA achieved by the OTEX procedure was greater than log-8.0. Microsearch personnel were unable to isolate any survivors from the OTEX treated garments. (Microsearch Laboratories, 2004).

Test #4. Antimicrobial Efficacy of the OTEX Process at 60% Ozone Output Against

Escherichia Coli - Microsearch Labs, April 29, 2005

A validation trial was conducted to determine the antimicrobial activity of an OTEX treatment at 60% of the maximum ozone output of the OTEX system against Escherichia coli. In this trial, E. coli was added as liquid culture directly to the input flow of a JLA washing machine. This culture was added in sufficient volume to produce a contamination level of the order of log-7 cells/mL.

This work and the reconsideration of the optimum operating ozone level was prompted by confounding adverse evidence produced during a third party evaluation during which poor log kill data was obtained for E. coli. The initial aim in this trial was to produce evidence of a baseline

log kill potential with E. coli as a direct contaminant of wash waters with no additives running at ambient temperature, then to demonstrate the effect of ozone under identical conditions.

An ambient temperature wash trial was conducted which contained no additives and which was of 20 minutes duration. Estimates of the E. coli levels in the wash water were obtained by the analysis of samples collected at 3, 10 and 20-minute intervals. In an identical wash program after the first sample was recovered (i.e., 3 minutes) the OTEX device was activated and thereafter produced a continuous charge of ozone at 60% of the maximum available ozone output. Subsequent sampling occurred as described above.

Each trial was preceded by a hot sanitizing wash and rinse cycle. Data obtained are reported in Table 2 and Figure 8.

Table 2.	OTEX Revalidation Trial 60% Ozone Output Treatment
		T = 3 min		T = 10 min	T = 20 min
		E. coli		E. coli	E. coli
Treatment		Cfu/mL		Cfu/mL	Cfu/mL
Ambient Wash
No Ozone No		9.30E+07		8.40E+07	6.20E+06
Additives
Ambient OTEX
Only 60%
Ozone Output		7.80E+07		< 1	< 1
Wash

Figure 8. E. coli kill data for OTEX at 60% of the available ozone output vs ambient wash treatments. Microsearch Labs, April 29, 2005.

In the control experiment with no additives or ozone treatment, these data show an E. coli log-reduction of approximately 1 log cycle during the 20-minute wash period. During the treatment with ozone E. coli could not be recovered after the initial dosing period. In fact by the ten-minute

mark, these data indicate that a 7-log reduction was obtained corresponding to 7 minutes of

ozone dosing at 60% of the maximum available output.

Test #5. OTEX Bacteriological and Viral Investigation: OTEX Laundry System

Solution Test (OTEX Report Sept. 2005)

A laboratory investigation was carried out with the objective of providing documentary evidence of the bactericidal and virucidal activity of the OTEX system at ambient temperature against thermal disinfection (75°C = 167°F)) wash processes. The work was carried out on 1 July 2005 at JLA’s R & D Technical Laboratory, Ripponden, West Yorkshire, UK. The microorganisms and viruses employed (Table 3) were independently prepared by Microsearch Laboratories Ltd. for testing.

Table 3. Solution Challenge Test Organisms

Microorganism		cfu/mL
Staphylococcus aureus		1.3E+08
Pseudomonas aeruginosa		3.1E+09
Candida Albicans		3.1E+08
Escherichia coli		5.2E+08
Streptococcus faecalis		5.0E+08
Aspergillus niger		3.1E+08
Clostridium difficile		4.2E+08
Clostridium perfringens		9.2E+08
Campylobacter jejuni		6.0E+08
Aeromonas mixed species		8.2E+08
Actinobacter sps		4.3E+08
Lactobacilli sps		3.9E+08
Virus particle	Particles/mL
Lambda phage	3.8E+24
FCoVA	2.6E+24
Saccharomyces virus ScV-L-BC	3.1E+23
Vibrio phage fs1	2.6E+28

The four virus particles selected for testing represent both single and double strand RNA and DNA, which is the structure of the vast majority of all virus types.

Program Details and Test Conditions – Tests were carried out using an extended sluice program in a JLA model HW164 (16 k dry weight) washing machine. No detergent was employed during this series of tests. Details are tabulated below.

Tests were conducted with water temperatures at both ambient, i.e., as supplied, and at 75°C (167°F), which is above the recommended thermal disinfection temperature of 71°C (160°F). Domestic supply water was employed with a water hardness of 60 ppm CaCO₃ for all tests.

Program Details:	Cycle Time (mins)		Temp		Wash Action
			(°C)
Program 1: Cold	30		Ambient
Sluice					12 sec wash/3
Program 2: Thermal	30		75°C		sec stop time
Sluice
Detergent Volumes		No Detergent in use.

A single unit OTEX system was employed and was maintained at the following settings throughout the trial with the exception of the control test with no ozone:

Ozone Concentration Setting	8 (highest)
Pressure	5 psi
Flow Rate	3.5 cfh

Test samples were taken from the wash drum throughout the wash cycle to determine the concentration of dissolved ozone in the water. This was measured by using the Chemets method, which employs DPD chemistry. Dissolved ozone levels increased from 0.2 ppm at the start to 0.6 ppm after 15 minutes, with samples being taken at 3, 7, 11, and 15 minutes of washing.

Data obtained are presented in Figures 9-14. Figures 9, 10 and 11 show results of bacterial sampling at ambient temperature - no ozone (control), 75°C (167°F = thermal washing), and ambient temperature with ozone (OTEX), respectively. Note that without ozone and at ambient temperature (Figure 9), only small amounts of bacterial kills were obtained. With thermal washing (Figure 10), three strains of bacteria remained at significant levels even after 15 minutes. But with ozone at ambient temperature (Figure 11), no bacteria were present after 3 minutes of washing.

Figure 9. Test results - control @ ambient temperature - no ozone – bacteria.

Figure 10. Test results - Thermal @ 75°C - no ozone – bacteria.

Figure 11. OTEX System - Ambient Water Temperature - bacteria.

Figures 12, 13 and 14 show similar results of virus and phage sampling at ambient temperature - no ozone (control), 75°C (167°F = thermal washing), and ambient temperature with ozone (OTEX), respectively. Note that without ozone and at ambient temperature (Figure 12), only small amounts of viral inactivations were obtained. With thermal washing (Figure 13), viral

inactivations were obtained after 5 minutes., and the same results were obtained with ozone at ambient temperature (Figure 14) after 5 minutes (but at lower costs).