Fabrics such as cotton and linen are treated with thermosetting resins such as urea formaldehyde and melamine formaldehyde to get a durable finish, writes Mr. Surya Kumar of Tuticorin.
A thermosetting resin is a plastic that Solidifies when heated under pressure. They improve the capacity of the fabrics to resist and recover from creases formed during wear. According to him, only when clothes are pressed by a heated iron, under slight pressure, the resins develop cross linked chains between them which give stiffness to the clothes. A cold iron will not be able to do that.
Dr. J. Venkat Rao, Head of the Department of Textile Technology, Anna University, Madras, says that this explanation holds good only for certain fabrics. There are a few other factors which are to be considered for ironing clothes, he says.
The first is moistening the cloth. The water makes fabrics such as wool or silk to swell whereas it imparts plasticity to polyester. This allows the fabric to set in any predetermined pattern when pressed with a hot iron box. Because of the heat the moisture evaporates and the cloth sets neatly (as it is made mouldable) as the creases are removed.
According to Dr. Rao, different kinds of clothes are capable of withstanding varying quantities of heat. Natural fabrics such as cotton and linen are not thermoplastic by nature and hence are capable of withstanding high temperature. Synthetic fabrics such as nylon and polyester are thermoplastic. They melt at even slightly high temperatures and hence too much heat should not be applied to these fabrics. Another factor that controls ironing is the pressure applied – heavier iron boxes can exe greater pressure. This explains why dhobi’s ironing is far better than the housewife’s.
A soft bed above a hard surface perhaps helps in distributing the pressure evenly on the cloth.