Methods to determine the dye chemistry.

DANISH RAJADanish_raja1@hotmail.com

CONTENTS:

• Introduction• Methods to determine

dye structure.• FTIR• DSC• IR spectroscopy.• Examples• Conclussion.

Methods to determine dye structure:

• There are main three methods to determine dye chemistry

• 1) FTIR• 2) DSC• 3)IR SPECTROSCOPY

Introduction:• A dye is a colored substance that has an affinity to the

substrate to which it is being applied. The dye is generally applied in an aqueous solution and requires a mordant to improve the fastness of the dye on the fiber. Dyes have complex structures which are different for each dye, making it different in application ,property , and substantivity to fibers. To understand the chemical structure and functional groups ,there are different methods to determine the dye chemistry.

FTIR FT-IR stands for Fourier Transform Infra Red, the

preferred method of infrared spectroscopy. In infrared spectroscopy, IR radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it is passed through(transmitted). The resulting spectrum represents the molecular absorption and transmission, creating a molecular finger print of the sample. Like a finger print of two unique molecular structures produce the same infrared spectrum. This makes infrared spectroscopy useful for several types of analysis.

FTIR is most useful for identifying chemicals that are either organic or inorganic. It can be utilized to quantitative some components of an unknown mixture. It can be applied to the analysis of solids, liquids, and gasses. The term Fourier Transform Infrared Spectroscopy (FTIR) refers to a fairly recent development in the manner in which the data is collected and converted from an interference pattern to a spectrum. Today's FTIR instruments are computerized which makes them faster and more sensitive than the older dispersive instruments.

To identify types of chemical bonds (functional groups). The wavelength of light absorbed is characteristic of the chemical bond as can be seen in this annotated spectrum.

DSC:

DSC stands for differential scanning calorimeter . calorimeter: It measures the heat into or out of a sample.

Differential calorimeter : It measures the heat into or out of a sample relative to reference .it has two reactions endothermic and exothermic reactions ,

• Endothermic heat flows into the sample

• Exothermic heat flows out of the sample.

DSC measures the temperature and heat flow associated with transitions in materials as a function of time and temperature in a controlled atmosphere .

Metal 1

Metal 2

Metal 1

Metal 2

Sample Empty

Sample Temperature

Reference Temperature

Temperature Difference = Heat Flow

A “linear” heating profile even for isothermal methods

What can DSC measure?• Glass transitions• Melting and boiling points• Crystallisation time and temperature• Percent crystallinity• Heats of fusion and reactions• Specific heat capacity• Oxidative/thermal stability• Rate and degree of cure• Reaction kinetics• Purity• chemicals

Infra Red Spectroscopy:• Infrared (IR) spectroscopy is a technique used to identify the

structure of chemicals based on the interaction of atoms with infrared radiation. Molecular vibration and rotation can be excited by the absorption of radiation in an infra red region. Such molecular vibrations and rotation scan be directly measured as absorbance in the infrared spectrum. When infrared radiation interacts with an organic compound, certain frequencies of energy are absorbed while others are transmitted or reflected. The frequencies absorbed or transmitted are determined by the functional groups present in the substance. The molecular vibrations are localized with in the functional groups and do not extend over the rest of the molecules. Such functional groups can be identified by their absorption bands Hence, IR can be used as a means for identifying the chemical composition of the material.

Example:

Determining Functional Groups of Commercially Available Ink-Jet Printing Reactive Dye Using Infrared Spectroscopy:

In textile ink-jet printing, the chemical structures of the reactive

dyes present in the ink were not disclosed due to commercial reasons. As a result, it was not easy for researchers to study the actual chemical reaction between the dye molecules and the fibers to determine the printing mechanism Therefore, the aim of this study was to determine the chemical structure of the functional groups available in one primary color Cyan of the commercially available reactive dye used for ink-jet printing.

• Separating and Purifying Ink.• Preparing a Sample for IR Analysis.• Interpreting an IR Spectrum: An IR spectrum consists of two main regions: (i) above

1500cm-1 there are absorption bands that can be assigned to individual functional groups, whereas (ii) the region below 1500cm-1 (the fingerprint region) contains many bands and characterizes the molecule as a whole. The bands within the fingerprint region, which arise from functional groups, can be used for identification,

• Table 1. Regions of the Infrared Spectrum for Preliminary Analysis (Lambert et al. 1998)

• Region (cm-1) Group Possible Compounds Present (or Absent)

• 3700-3100 -OH Alcohol, aldehyde, carboxylic acids• -NH Amides, amines• ≡C-H Alkynes• 3100-3000 =C-H Aromatic compounds• -CH2 or –CH=CH- Alkenes or unsaturated rings• 3000-2800 -CH, -CH2-, -CH3 Aliphatic groups• 2800-2600 -CHO Aldehydes (Fermi doublet)• 2700-2400 -POH Phosphorus compounds• -SH Mercaptans and thiols• -PH Phosphine• 2400-2000 -C≡N Nitriles -N=N+=N- Azides -C≡C- Alkynes

Regions of the Infrared Spectrum for Preliminary Analysis

Region (cm-1)

• 3700-3100• 3100-3000

• 3000-2800

• 1300-1000

• Alcohol, aldehyde, carboxylic acids • Aromatic compounds Alkenes or

unsaturated rings• Aliphatic groups, Nitriles Azides

Alkynes 1870-1650 C=O Acid halides, aldehydes, amides, amino acids, anhydrides, carboxylic acids, esters, ketones, lactams

• Ethers, alcohols, sugars Sulphur, phosphorus, and fluorine compounds

Possible Compounds Present (or Absent)

Conclusion: The functional groups and compounds of one commercially available reactive

dye of primary color, Cyan, was examined by the IR technique. The IR spectrums of the purified dye samples were obtained and the distribution of the functional groups and chemical compounds in the dye samples were analyzed. The experimental results showed that the commercially available reactive dye used for ink-jet printing contained the essential functional groups and chemical compounds when compared with the reference table and referencing reactive dyes. However, the IR spectrum did not actually reveal the chemical structure of the reactive dyes being studied, but

the IR spectra obtained from this study could be compared with the dye databases (Yuen et al. 1996) which contain the IR spectra of reactive dyes with known chemical structures .