35 Testing of Woven Fabrics for Special Purpose Properties

M. Saravanan

Introduction:

The module discusses on testing of woven fabric properties namely special properties which is assessed on particular modified woven fabric. The woven fabric mainly characterized on their response against extreme factors which makes them unique in certain applications. The value addition properties such as fire resistant, resistance to bacteria, chemical resistance, water resistance, etc are covered here in this module exclusively test methods adopted for woven fabric. Woven fabric against various factors such as impact, ballistic, UV, etc and their test methods are discussed in this module.

Objective:

Module aims to discusses the following three points and elaborate them in detail inside the module.

1. Characterization techniques such as SEM, FTIR for woven fabric when they are subjected to unique chemical addition for special purpose.
2. Resistance to various parameters of woven fabric is touch upon in this module.
3. Test methods for fabric characterize and their efficiency against specific factors are elaborated in this module.

Scanning Electron Microscopy (SEM):

A normal SEM instrument, demonstrating the electron section, test chamber, EDS indicator, electronics console, and visual display monitors. SEM utilizes a focused beam of high-energy electrons to create a variety of signals at the surface of solid samples. The signals that derive from electron-sample interactions demonstrate data about the specimen including outside morphology (surface), chemical composition, and crystalline structure and orientation of materials making up the sample. In many applications, information are gathered over a chosen zone of the surface of the specimen, and a 2-dimensional picture is created that presents spatial varieties in these properties. Areas going from roughly 1 cm to 5 microns in width can be imaged in a scanning mode using regular SEM technique (amplification going from 20X to around 30,000X, spatial resolution of 50 to 100 nm). The SEM also capable of performing investigations of chose point areas on the specimen; this approach is particularly helpful in subjectively or semi-quantitatively deciding chemical compositions (utilizing EDS), crystalline structure, and crystal orientations (utilizing EBSD).

Fourier Transform Infrared Spectroscopy (FTIR):

FTIR is a technique which is utilized to get the spectrum of absorption of dye in the fabric. A FTIR spectrometer simultaneously gathers spectral data in a wide spectral range. This presents a huge preferred standpoint over a dispersive spectrometer which measures intensity over a narrow range of wavelengths at once.

FTIR is for the most part valuable for distinguishing chemicals that are natural or inorganic. It can be used to quantities some components of an unknown mixture. It can be applied to the investigation of solid, fluid and gasses.

FTIR is the most utilized for distinguishing sorts of chemical bonds (that is functional group). The wavelength of light absorbed is characteristic of the chemical bonds as can be found in this annotated spectrum. Utilizing FTIR chemical group are estimated for colored specimen. Also used as confirmatory test for functional group of a specifies chemical applied fabric samples.

Air Permeability:

Principle

Air permeability tester works based on the measurement of the rate of flow of air through a given area of fabric by a given pressure drop across the fabric.

Procedure

1.Take the conditioned specimen and mount a portion between the clamp and circular orifice with sufficient tension to eliminate wrinkles, if any, taking can to see that the fabric is not distorted in its own place.

2.Start the suction fan (or) other means to force air through the fabric and adjust the rate of flow of air till pressure drop off one centimeter water head across the fabric is indicated.

3.Note the rate of flow of air in cm3/s

4.Repeat the test at other different places. In all at least 10 test shall be carried out.

5.Calculate the rate at flow of air per cm2 of fabric in cm3/s by the following formula.

Water vapour permeability:

Pour around 20 ml of water into each cylindrical box and cover the opening with the specimen to be evaluated totally and seal them with the lid top. The width of the material must be at least 5 mm greater than the corresponding dimension of the aperture. Weigh the tightened boxes and place them in the cabinet and run for 6 hours. Expel the containers from the cabinet, and note the final weight. From the mean loss in weight and the area of the opening in the top of each box, compute the water vapor permeability in g/m2 per 24 hours utilizing the formula.

WVP = 24 x (M / A x T) g/m2/day

Fabric Impact Strength:

1. The given samples of fabric are prepared.
2. Before testing, the instrument is to be first adjusted without any sample on the pendulum.
3. The pendulum is dropped from the catch by keeping the pointer in vertical position. If the pointer shows zero on the scale, when moved by pendulum to the other side of the machine, it is said to be adjusting. If not, the catch which catches the pendulum has to be raised or lowered till the pointer shows zero, when the pendulum is released from that position.
4. The pendulum is raised to the catch on the right hand of the quadrant and kept in position and the pointer is placed near to the anticipated breaking position. The lea to be tested is secured to the base grip and the grip on the pendulum bob in the proper way without any twist in the lea.
5. The catch is then released and the pendulum swings to the other side pulling the sample and also the pointer and rises to a height and ruptures the yarn. The position of the pointer reads the energy spent in rupturing the sample in inch.lb. The experiment is repeated for 5 samples and the mean is calculated.

Water repellency:

1. Fasten the test specimen securely in the 152 mm metal hoop so that it presents a smooth wrinkle-free surface. Place the hoop on the stand of the tester with the fabric uppermost in such a position that the center of the spray pattern coincides with the center of the hoop.
2. In the case of twills, gabardines, piques or fabrics of similar ribbed construction, place the hoop on the stand in such a way that the ribs are diagonal to the flow of water running off the fabric specimen.
3. Pour 250 mL of distilled water at 27 ± 1°C (80 ± 2°F) into the funnel of the tester and allow it to spray onto the test specimen in 25-30 s. Avoid touching the funnel with the beaker while pouring the distilled water. Movement of the funnel will alter the spray disposition on the specimen. The spray time must be between 25-30 s, otherwise the nozzle should be checked to see if the holes are enlarged or blocked. Take the hoop by one edge and tap the opposite edge smartly once against a solid object, with the fabric facing the object, then rotate the hoop 180° and tap once more on the point previously held. Repeat the above steps for all three specimens.

Water Resistance:

The water in contact with the test specimen is regulated at 21 ± 2°C (70 ± 5°F). Dry the clamping surface. Clamp the specimen with the surface to be tested facing the water. Turn on the motor, press the lever to raise the overflow device at the rate of 10 mm/s, and close the air vent as soon as water flows from it. Disregarding water droplets that appear within approximately 3 mm adjacent to the edge of the specimen clamping ring, record the hydrostatic pressure at the moment water droplets penetrate the fabric in three different places.

Water Absorbency:

Absorbency in sec: This test method is designed to measure the water absorbency of textiles by measuring the time it takes a drop of water placed on the fabric surface (wound dressings) to be completely absorbed into the sample. Sample is placed over the top of a beaker so that the center is unsupported. A measured drop of water is placed on the fabric 1 cm from the  surface Time is recorded until the water drop absorbs completely. The amount of water absorbed in percentage is also calculated

Ballistic limit (V50) testing:

Ballistic Limit, Protection (V50 BL [P]) testing is expected to assess armor material by testing either a single sample or numerous apparently identical armor samples. The test depends on the Bruceton method for assessing a non-quantifiable response to a variable stimulus, e.g. a match ignites or does not, a light flashes or does not, and so on. These ‘go/no-go’ comes about are utilized to build up a a 50 percent probability of penetration only. The full penetration curve is not investigated.

V50 values depend on the average of equivalent quantities of velocities related with complete penetration (witness panel penetrated) and partial entrance (witness panel not penetrated). The quantity of velocities required to decide the V50 esteem value is required to be specified. So as to counteract skewing of the outcomes, the most minimal velocity related a complete penetration, and the most elevated velocity associated. V50 testing strategies for helmets regularly require that the protective divided in five segments – crown, front, back, left, and right sides – and that the fair impacts used to compute the V50 value be similarly appropriated among those areas.

Residual velocity testing:

Residual velocity testing is not expected to decide the resistance of a protective layer test to penetration, yet rather the potential lethality of a projectile after it has entered the defensive layer. Residual velocity (Vs – Vr) testing is usually conducted in conjunction with V50 testing, provided the V50 testing is led with an unbacked armor sample. Velocity computing instrumentation, situated behind the armor sample, is added to the V50 test and the residual velocity (Vr) is compared with the striking velocity (Vs) for each piercing shot. The distinction (Vs − Vr) is utilized to survey the level of lethality to be expected from ballistic dangers whose speeds surpass the level of protection of the material.

Flame Resistance:

• standard vertical flammability test
• durability of FR is important to washing
• fire fighters- less permeability due to heat stress , maximum time of wearing should be given to person
• furnishing no such worry but comfort is so important curtain material – no such worry It is important to test fabrics to ascertain if they are likely to be suitable for the application for which they are required. ASTM and BSI methods are available for such tests, in some cases, ISO standards also exist.

The first group of tests answer the question ‘does the fabric burn when a flame is applied to it?’ Both ASTM and BSI have a vertical specimen test for fabrics for thermal protection. ASTM D3659 resembles BS 3119, which has been virtually replaced by BS 5438. If the fabric ignites, these tests can determine the spread of flame and the burning rate. Fabrics for thermal protection should not ignite, so the other aspects are not needed. Tests to determine the critical oxygen content of textiles or LOI are ASTM D2863, which is identical to Method 141 of BS 2782.

The second group of tests answer the question ‘how well will fabric protect a person wearing it?’ ASTM D4108 and BS 3791 deal with this aspect. ISO6942 test has been drafted for gas-heated radiant panels. The ASTM test uses convective heat while the ISO test uses purely radiant heat.

Limited Oxygen Index tester:

Limiting Oxygen Index (LOI) is the percent concentration of oxygen at which a small sample will just burn downwards in a candle like manner. The test is likely the most surely understood of the standard fire tests. The device holds a little sample of material which is griped vertically in a tube in an environment where the relative concentration of oxygen and nitrogen can be changed. The point is to test the flammability of the sample with a little pilot fire to determine the minimum oxygen concentration required to simply manage burning of the specimen.

The specimen is placed vertically in a glass chimney, and an oxygen/nitrogen condition is set up with a flow from base of the chimney. The top edge of the sample is ignited, and the oxygen concentration in the flow is diminished until the point when the fire no longer supported.

Oxygen Index, in percent, is computed from the final oxygen concentrations tested. The test results relate just to the behavior of the test samples under the conditions of this test method and the outcomes must not be utilized to infer the fire risks of the material in different forms or under other fire conditions.

Vertical strip test:

The vertical strip test has accomplished the most extensive acceptance for deciding flammability. British Standard BS 5438:1989 depicts the test technique for measuring ease of ignition and rate of fire spread of vertically mounted test specimen. A predefined small butane flame is applied to the bottom edge of a vertical sample (200mm long \ 80mm wide) for prescribed times and the minimum start time is noted. In another set of experiments, a little lighting fire is given for 10 s to the bottom edge of a vertical mount sample and fire spread times are measured by recording the severance of marker threads in seconds.

Chemical Protective Cloth:

Assessment of chemical barrier properties

• various types of tests can be classified to 3

1. tests for assessing degradation resistance
2. tests for assessing penetration resistance
3. tests for assessing permeation resistance

Degradation resistance

DEGRADATION RESISTANCE MEASUREMENTS BY FOLLOWING METHODS:

a) degradation tests by immersion technique

b) degradation tests using one side exposure technique

c) degradation tests using solubility based evolution

Immersion based

1) ASTM D471-immesion for 22 to 760 hrs ( 5 different immersion periods) and temperature – 72deg.c to 250 deg.c(17 range)

2) ASTM D543 – immersed up to 7 days temperature – 50 to 70deg.c

3) ASTM D5- immersed for 24 hrs

Usually change in weight, volume & others measured

One sided

Ø  ASTM F1407 – weight change after exposure measured

Depending on weight loss fabrics are graded. Weight loss of 0-10% is Excellent, 11-20% is Good, while Moderate will be 21-30% and 31-40% rated as Poor.

Weight loss may occur due to degradation but a gain also occur, this may be due to absorption (or) adsorption of chemical

Solubility parameters

1. ASTM D3132 describes this method,
2. Material is immersed in different chemicals
3. Damage is assessed
4. Solvents with nearly solubility parameter will only affect fabric (or) coating
5. Once unknown solvent’s solubility parameter is know we can judge its effect on fabric
6. Draw back- works only with homogeneous substance.

Penetration resistance

ASTM defines flow of chemical through closure, porous materials, seams & pin holes, other imperfections in a protective clothing material as a non molecular basis

RUN- OFF BASED METHOD: Specimen kept at inclined position & chemical made to run off. Using AATCC 42, AATCC 118 & ISO 6530 chemicals can pass through membrane (plastic film)

HYDROSTATIC BASED: Liquid under pressure is made to come in contact with fabric.

AATCC 127, ASTM F903 follows it.

UV Protection:

UPF estimation by AATCC  test method 183-1999.

UV Protection Factor Value (UPF)

In-vita method is used to assess UV protection of cotton fabric as per the AATCC-183(2004) test method. It measures the transmission or UV blocking of UV radiation through fabrics by UV-VIS spectrophotometer (VARIAN, CARY 5000) .The UV profiles of the untreated samples are compared with spectra collected from the same fabric treated with extracted solution and effectiveness in shielding UV radiation is evaluated by measuring the UV protection, transmission and reflection. Each measurement is average of four scans obtained by rotating the sample by 900. The transmission data is used to calculate the UPF value, according to standard procedures.

Self – Cleaning action:

The self-cleaning activity is assessed for the treated textile fabric is by exposing the samples containing adsorbed coffee stain to visible irradiation. The measured quality of 6% coffee solution is introduced on the fabric and is allowed to spread. One half of each stain on the fabric is exposed to sunlight for 12-48 h, while the other half is covered with a black paper to prevent its irradiation from sun light. The exposed part of the stain is compared with that of covered part for self-cleaning action. Premier Color scan SS5100 Spectrophotometer is used to measure the change in K/S value. Where K is the absorption; and S is scattering. The self-cleaning property of treated cotton fabric is analyzed and reported in graphical form shown as fig. The K/S value of coffee stained cotton fabrics are measured in various treated cotton fabric structures in different duration of 12.24 and 48h.The percentage of decrease in K/S value for the exposed samples in higher concentration of Egg albumin coating.

Antimicrobial testing:

Testing for antibacterial action of treated fabric specimens is carried out using a qualitative method according to the standard AATCC test method 147 (Disk diffusion method). Mueller Hinton agar solution is prepared by dissolving Mueller Hinton agar (38 g/l) and nutrient broth (13 g/l) in distilled water (1000 ml) taken in a funnel shaped flask. At that point the flask subject to autoclave at 121ºC for 20 min. Sterilized petri plates are prepared with an equivalent thickness of Mueller Hinton agar medium. The hatched culture is swabbed on the agar plates utilizing swab stick. Disc shaped treated samples of diameter 1.8 cm are kept on the seeded agar plate. After incubation the antimicrobial action is assessed by measuring the inhibition zone diameter observed. Each test is performed twice and the average results are noted down.

Drug Release Test through UV Spectroscopy:

Drug release tests using basket (USP Apparatus) as per conventional dissolution procedures recommended for single – entity products at 75 and 100 rpm. Sampling aliquots of 5.0 ml are taken at 0, 5, 10, 15, 30 and 60 minutes will be toppled with equal volume of the fresh medium to maintain a constant total volume. At end of each test time, samples aliquots  filtered, diluted in dissolution medium, when necessary, and quantified. The liquid validated by spectrophotometric method, and the contents results were used to calculate the percentage release on each time of dissolution profile. The UV spectrophotometric analyze the samples in phosphate buffer pH 7.0 with 0.75 % of sodium lauryl sulphate (SLS) dissolution medium mainly for specificity, linearity, precision and accuracy as per ICH guideline. All absorbance were determined at 460 nm.

Acoustic Protection:

Standing wave apparatus used to choose the coefficient of assimilation of the given acoustic sample, plot the ingestion coefficient as a component of recurrence. Mechanical assembly chips away at the standard “accomplishing how much the wave looks like either an unadulterated standing wave or an impeccable voyaging wave” and the ensuing parameter named as Standing Wave Ratio (SWR). SWR is the proportion of the plentifulness of a halfway standing wave at an unfriendly to center point (most noteworthy) to the abundance at a neighboring center (minimum). SWR constantly has a regard more significant than or identical to solidarity. It is used to choose the reflection co-beneficial abundance (R), assimilation co-proficient (α) and impedance (Z) of any acoustic specimen.

Thermal Protection

Thermal Conductivity by Lee’s Disk Method is used for the fabric specimen. Fabric sample of unknown conductivity is put between two specimens of known conductivity (usually brass plates). The setup is normally vertical with the hot brass plate at the top, the specimen in the middle supported by the cool brass plate at the base. Warmth is provided at the top and made to move downwards to stop any convection inside the example. At last ascertained by the accompanying formulae:

Thermal conductivity “K” = (MSD(r+2L) (dq/dt))/ (πr2 (2r+2L) (C1-C2)) Where,

M (mass of the disc placed over the experimental disc)

S (specific heat of the material of the disc)

D (thickness of the tested material)

r (radius of the disc)

L (thickness of the disc)

C1 (temperature of steam in degree Celsius)

C2 (steady temperature in degree Celsius) – sample temperature

Conclusion:

The module concludes and summarizes the response behavior of woven fabric for damage they might expect in actual usage. The module concludes on test methods evaluated for woven fabric for special applications. The uniqueness of specialty woven fabric is assessed against extreme conditions and their responses are included in the module.

REFERENCES and URLs

1. GAV Leaf., “Practical Statistics For The Textile Industry: Part I”, The Textile Institute, 1984.
2. Saville B.P., “Physical Testing of Textiles”, Woodhead publishing -UK, 2004.
3. Jinlian H U, “Fabric Testing”, Woodhead Publishing, 2008.
4. Arindam Basu., “Textile Testing (Fibre, Yarn and Fabric)”, SITRA, Coimbatore, 2001.
5.   W.D.Schindler and P.J.Hauser, Chemical finishing of Textiles, CRC Pr LIC             Publication, 2004.
6. http://mytextilenotes.blogspot.com
7. http://www.textileschool.com/Home.aspx