Transmission Electron Microscope | TEM

Working Principles:

A transmission electron microscope fires a beam of electrons through a specimen to produce a magnified image of an object.

TEM working flows.

Scanning Electron Microscope | SEM

Working Principles: Produces images of a sample by scanning the surface with a focused beam of electrons. Electrons from the beam hit the surface of the sample and bounce off it as the secondary electron, backscattered electron etc. A detector registers these scattered electrons and turns them into a picture.

SEM Working flows.

X-RAY Powder Diffractometer | XRD

Working Principles:

X-rays are collimated and directed onto the sample. As the sample and detector are rotated, the intensity of the reflected X-rays is recorded. When the geometry of the incident X-rays impinging the sample satisfies the Bragg Equation, constructive interference and a peak in intensity occur. A detector records and processes this X-ray signal and converts the signal to a count rate which is then output to a device such as a printer or a computer monitor. Every crystalline substance gives a pattern; the same substance always gives the same pattern, and in a mixture of substances each produces its pattern independently of the others. The X-ray diffraction pattern of a pure substance is, therefore, like the fingerprint of the substance.

Textile testing | Crease resistance & recovery | Measuring crease recovery

To evaluate how something works under certain established methods or test standards. Textile testing is to check its properties under certain conditions in a standard environment prescribed as per Test standards. 

Main steps for textile testing:

1. Checking raw materials
2. Monitoring production
3. Assessing the final product
4. Investigation of faulty material
5. Product development and research

Different fabric tests:

1. Dimensional Characteristics- A) Length, B) Width, C) Thickness
2. Threads/Inch – EPI, PPI, CPI, WPI
3. Count- Warp & Weft
4. Weight,
5. Crimp%,
6. Strength,
7. Abrasion & Pilling,
8. Handle a) Stiffness, b) Drape, c) Crease Resistance & crease recovery,
9. Flame Retardancy,
10. Water repellency

Thermogravimetric Analyzer | TGA

Thermogravimetric Analyser (TGA) measures weight changes in a material as a function of temperature (or time) under a controlled atmosphere. Its principle uses include measurement of a material’s thermal stability, filler content in polymers, moisture and solvent content, and the percent composition of components in a compound.

Construction

The thermogravimetric analysis instrument usually consists of a high-precision balance and sample pan. The pan holds the sample material and is located in a furnace or oven that is heated or cooled during the experiment. A thermocouple is used to accurately control and measure the temperature within the oven. The mass of the sample is constantly monitored during the analysis. An inert or reactive gas may be used to purge and control the environment. 

Principle of Operation

A TGA analysis is performed by gradually raising the temperature of a sample in a furnace as its weight is measured on an analytical balance that remains outside of the furnace.

Differential Scanning Calorimetry | DSC

Differential Scanning Calorimetry (DSC) is a thermal analysis technique in which the heat flow into or out of a sample is measured as a function of temperature or time, while the sample is exposed to a controlled temperature program. It is a very powerful technique to evaluate material properties such as glass transition temperature, melting, crystallisation, specific heat capacity, cure process, purity, oxidation behaviour, and thermal stability.

Construction

There are two pans. In one pan, the sample pan, you put your polymer sample. The other one is the reference pan. You leave it empty. Each pan sits on top of a heater. Then you tell the nifty computer to turn on the heaters. So the computer turns on the heaters and tells it to heat the two pans at a specific rate, usually something like 10ºC per minute. The computer makes absolutely sure that the heating rate stays exactly the same throughout the experiment.

Fourier Transmission Infra-Red | FTIR

Fourier Transform-Infrared Spectroscopy (FTIR) is an analytical technique used to identify organic (and in some cases inorganic) materials. This technique measures the absorption of infrared radiation by the sample material versus wavelength. The sample’s absorbance of the infrared light’s energy at various wavelengths is measured to determine the material’s molecular composition and structure.

How FTIR Works:

A simple device called an interferometer is used to identify samples by producing an optical signal with all the IR frequencies encoded into it. The signal can be measured quickly. Then, the signal is decoded by applying a mathematical technique known as Fourier transformation. This computer-generated process then produces a mapping of the spectral information. The resulting graph is the spectrum which is then searched against reference libraries for identification.

With the microscope attachment, samples as small as 20 microns can be analyzed. This allows quick and cost effective identification of unknown particles, residues, films or fibers. FTIR can also measure levels of oxidation in some polymers or degrees of cure in other polymers as well as quantifying contaminants or additives in materials.

Testing Process:

👉Step 1: Place sample in FTIR spectrometer. The spectrometer directs beams of IR at the sample and measures (1) how much of the beam and (2) at which frequencies the sample absorbs the infrared light. The sample needs to be thin enough for the infrared light to transmit through, or a thin slice of the material must be removed. Reflectance techniques can be used on some samples and no damage is done to the sample. Samples conducive to reflectance are residues, stains or films on a fairly flat reflective surface or somewhat pliable materials that are thin enough to fit under the microscope using the attenuated total reflectance attachment to the microscope.

👉Step 2: The reference database houses thousands of spectra, so samples can be identified. The molecular identities can be determined through this process.

RAMAN Spectroscope

Raman spectroscope is one of the popular characterisation tools for textile testing especially textile materials characterisation. 

Working Principles: It is based upon the interaction of light with the chemical bonds within a material. Raman is a light scattering technique, whereby a molecule scatters incident light from a high-intensity laser light source. Most of the scattered light is at the same wavelength (or colour) as the laser source and does not provide useful information – this is called Rayleigh Scatter. However, a small amount of light (typically 0.0000001%) is scattered at different wavelengths (or colours), which depend on the chemical structure of the analyte – this is called Raman Scatter.

Applications:

- Vibrational, rotational and other states in molecules,

- Chemical composition and structure of samples,

- Whether solid, liquid, gas, gel or powder.

Graph: A Raman spectrum features a number of peaks, showing the intensity and wavelength position of the Raman scattered light. Each peak corresponds to a specific molecular bond vibration, including individual bonds such as C-C, C=C, N-O, C-H etc.

What are the Test Standards?

Textile testing is done to ensure a certain level of quality and to do so different types of pieces of equipment, principles or methods can be applied. But it is essential to follow a prescribed and well-recognized methods to get valid and reliable test results. You cannot execute any test as your wish or convenience. You have to maintain a standard testing environment to conduct the testing for instance temperature, pressure, relative humidity etc. should be maintained carefully. Otherwise, there arises the question of data validity and the generated test data will not be accepted to the research society. Various national and international organizations have established standards for textile testing. Some of the organizations involved in developing textile testing standards are as follows:

- AATCC - American Association of Textile Chemists and Colorists

- ASTM - American Society for Testing and Materials

- ANSI - American National Standards Institute

- ISO - International Organization for Standardization

- BSI - British Standards Institute 

- BIS - Bureau of Indian Standards 

- BS EN - British Standard European Norm 

- IS - Indian Standards

Reference: A Practical Guide to Textile Testing by K. Amutha (Woodhead Publishing)

What is sampling? | Why sampling? | Types of sample

The true representative of the bulk or population is termed as a sample and the process of selecting a sample is called the sampling process. Sampling for textile testing can be in-

• Fibre stage 
• Yarn stage 
• Fabric stage 
• Garment stage 

Population: All elements, individuals or units that meet the selection criteria for a group to be studied and from which a representative sample is taken for detailed examination. 

Why sampling? 

As the textile is produced in huge quantity, it is impossible to test all the final output from a production process. That is why only representative samples of the material are tested. Proper sampling saves time, cost and labour. Besides, Textile testing is destructive in nature, i.e. the materials used for testing go as waste after testing and hence it is not desirable to test all of the material.

What is Textile Testing?

To evaluate how something works under certain established methods or test standards. Textile testing is to check its properties under certain conditions in a standard environment prescribed as per Test standards. 

Types of Testing?

Destructive testing: The testing which breaks the test specimen and goes as waste after testing is called destructive testing. For example, tensile test, compression test, bending test etc. 

Nondestructive testing: The testing in which test materials do not go as waste after testing is called non-destructive testing method. For example, thermal and electrical conductivity testing.

Why testing?

- To check the quality and suitability of raw material;

- To monitor the production (process control);

- To assess the quality of final product;

- To investigate the faulty materials;

- To set standards or benchmarks;

- For R&D (research and development) purpose;

- For new product development.

Reference: A Practical Guide to Textile Testing by K. Amutha (Woodhead Publishing)

Standard Testing Atmosphere | Related Terms.

Moisture equilibrium: It is the condition reached by a material when it no longer takes up moisture from or gives up moisture to, the surrounding atmosphere. 

Pre-conditioning: To bring a sample or specimen of textile to relatively low moisture content (approximate equilibrium atmosphere with relative humidity between 5% and 25%) before conditioning in a controlled atmosphere for testing. 

Conditioning: To bring a material to moisture equilibrium with a specified atmosphere. Before a textile is tested, it is conditioned by placing it in the atmosphere for testing in such a way that the air flows freely through the textile and keeping it there for the time required to bring it into equilibrium with the atmosphere. 

The Standard Atmosphere for Textile Testing

Laboratory conditions for testing fibres, yarns and fabrics in which air temperature and relative humidity are maintained at specific levels with established tolerances. Textile materials are used in a number of specific end-use applications that frequently require different testing temperatures and relative humidity. Specific conditioning and testing of textiles for end-product requirements can be carried out using as below-

Standard Atmosphere for testing various materials

Materials	Temperature (℃)	Relative Humidity (%)
Textiles	21±1	65±2
Nonwovens including papers	23±1	50±2
Glass fibre for textile applications	21±1	65±5

Textile Testing Lab

Testing 

To evaluate how something works under certain established methods or test standards. Textile testing is to check its properties under certain conditions in a standard environment prescribed as per Test standards. 

Types of Testing?

Destructive testing: The testing which breaks the test specimen and goes as waste after testing is called destructive testing. For example, tensile test, compression test, bending test etc. 

Nondestructive testing: The testing in which test materials do not go as waste after testing is called non-destructive testing method. For example, thermal and electrical conductivity testing.

Why testing?

- To check the quality and suitability of raw material;

- To monitor the production (process control);

- To assess the quality of final product;

- To investigate the faulty materials;

- To set standards or benchmarks;

- For R&D (research and development) purpose;

- For new product development.

Testing laboratories play an indispensable role in the execution of a garment order. Various types of standardized testing are required by the customers in every stage of product development like the yarn stage, fabric stage, garment stage, etc. In addition, quality executives carry out various tests at each level to ensure the quality of the material. These labs are divided into the following three categories from the point of functionality.

1. In-house Lab

2. Buying house Lab

3. 3rd Party Testing Lab

In-house Lab: 

Every manufacturing plant has the testing laboratory facilities along with the production unit. The main function of this type of lab is to ensure the right quality of the items like yarn, fabric, garments etc. Yarn count, composition, hairiness, twist factor etc. are tested and maintained to a standard limit for the yarn manufacturing plant. Fabric structure, dimensional stability, weight, spirality, standard shade and colourfastness properties, etc. are tested for the fabric manufacturing plant and the testing lab at garments check the quality of stitches, seams, and different measurements, etc.

Buying house Lab: 

This is actually the customer nominated lab up to their standards. Fabric technologist working at the buying house execute various types of test sought by the ultimate buyers. The vendors send the items to the buying house for approval and of course, they send after doing the in-house tests. Despite that buying house lab test is to ensure everything is as per the standards as mentioned in the PO or other technical package. After testing, checking and evaluating, buying-house gives approval to the vendors to proceed. Sometimes, items should be sent to the original buyers for approval for special issues. 

3rd Party Lab: 

Sometimes, customers do not have the testing setup and they then nominate some well-recognized and standard laboratory to work on behalf of the customers. These labs are termed as the 3rd Party Lab. This type of lab is designed only to test and providing certificates. While issuing an order, customers seek some standard tests done at every stage along with the products from vendors. Yarn count, fabric structure, weight, spirality, colourfastness, presence of hazardous materials, embellishment durability test, overall appearance test of the garments are the most common tests done in the 3rd party testing lab. Another very important function is doing an inspection after the production and they issue gate pass to ship the items to the customers. SGS, Intertek, TUVSUD, Bureau Veritas are some of the most renowned and reliable 3rd party testing labs.
Reference: A Practical Guide to Textile Testing by K. Amutha (Woodhead Publishing)