Preparatory chemical processing for polyester

Singeing is a pretreatment for PET-cellulosic blend fabrics (not 100% PET fabric). The modern gas singeing machines have efficient and computer controlled burners, which can control the width, height, angle and intensity of the flames.

In order to achieve good shape retention and prevent running creases from marking during wet processing, PET fibres and their blends must be stabilised. In other words, tension within the individual fibres and in the fabric is leveled out by relaxation. Heat setting of PET is carried out at 1800C, to ensure 0% residual shrinkage (natural shrinkage) and completion of primary crystallization.

Processing aids are applied during sizing of microfilament yarns in order to help and protect the delicate polymer fabric during processing. The common feature of all washing processes is the exchange of substances in an aqueous media.

Printing of polyester is a specialized subject that needs elaborate study. Polyester can be printed with the following class of dyestuffs:

Disperse printing of polyester consists of following fundamental principles:

The methods of fixation after printing and drying are:

Thickening agent is the most important component of the printing paste and it should be cost effective. The fact is that since the printing paste is acidic the thickener should have very good stability in the pH range of 2-5 for long time. The most favoured thickener the world over is guar gum. Others include:

The disperse dyes usually become dull under alkaline conditions. To improve this, the pH of the print paste is controlled to pH of 4.5-5 by addition of citric or tartaric acid the more common being citric acid. However, tartaric acid is selective in some real cases where the acidic conditions are more stable than citric acid.

Staining during after treatment if proper sequence of rinsing is not followed, because superfluous disperses dyes get re-deposited on the unprinted cloth during hot water rinsing

Good printing can be spoiled by bad or improper washing techniques. Essentially, the best washing sequence has to follow the following steps:

The author is associated with Resil Chemicals, Ahmedabad

Problems and Their Remedies in Polyester Processing-Part III

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