When the raw material costs of PTT are similar to those of polyamides, we will see fast growth, especially in the application of PTT for fibre and filament spinning. For the spinning industry, the price should not significantly exceed the figure of PET+20 per cent. There is still some distance to travel because PDO is not a commodity and only a few companies are active in this chemistry.

Spinning of PTT Fibre:

Currently, PTT is extrusion spun. Because PTT, like PET, is sensitive to hydrolysis degradation, a drying process is necessary before extrusion. The drying temperature should not exceed 150C because at higher temperatures an oxidative destruction will occur. Unlike PET, PTT chips do not need to be crystallized before drying. When considering the adaptation of the spinning and winding process from PET to PTT, one has to take in account three properties:

• Melt Temperature
• Glass Transition Temperatures
• Intrinsic Elasticity

The lower melt temperature (by approximately 30C) means that there is a shorter time until the spin filament in the thread line is cooled down and, consequently, the quench-air adjustment and the cooling length dimension are different to the PET spinning process. The next important difference to PET is the lower glass transition temperature, which causes much faster cold crystallization. This significantly impacts on the development of the fibre morphology during solidification and cooling down. The spinning conditions of PTT are more comparable to PA6 than to those of PET. Table 1 presents a collection of some polymer and processing properties of PTT and PET. The intrinsic elasticity of PTT is directly connected to the unique molecular structure. Unlike all other known linear polyester polymers, PTT shows a repeatable elastic recovery of about 10-12 per cent. A team of British scientists recently discovered that the crystal structure of PTT is spiral shaped, which explains the elastic recovery of PTT fibres. 

Spinning and winding an elastic filament at high speed will prove more difficult than a non-elastic filament. During POY spinning, the cheese package might tighten or bulge, both of which are undesirable winding failures. Texturing of PTT-POY is, again under adapted conditions, is performed in a similar manner to PET-POY texturing. The last five years have brought a large number of patents related to PTT high-speed spinning processes. A number of those patents have come from Japan, where ASAHI is at the forefront. Any newcomer to PTT spinning should study the patent situation carefully. 

Application of PTT Fibre:

The applications of PTT are to be found mainly in the textile industry. Until now, all of the common fields or textile application, including filament yarns, stable fibre and bulked continuous filament (BCF) for carpets are in an intensive investigation phase. The amount of PTT fibres and filament in production worldwide is estimated to be beneath 50,000t/a.  

There are two main factors responsible for the velocity of further industrialization of PTT: highly effective polymer production and processing technology, and the price of PDO. 

Important driving forces for the development of PTT fibres and filaments are the elastic recovery, soft hand of the fibre and its ease of dyeing. PTT fibres can be dyed at 100C and ambient pressure, without the addition of carrier substances. Because of the lower melt temperature, melt-soluble and dispersible dyestuffs can be used. Dye fastness and light fastness of dyed PTT fibre are, despite the lower dyeing temperature, comparable to those of PET fibre. The combination of fast crystallization and elasticity makes PTT a well-liked candidate for BCF carpet yarn. BCF yarn made of PTT shows in excellent bulk resistance and appearance retention as well as elastic recovery and stain resilience. 

For now, most applications make use of PTTs high elasticity, in leisure and sportswear. Textiles made of PTT fibres combine the properties of common fibres, such as spandex, nylon, acrylic and PET. High stretch, bulk and softness are providing the potential to replace the expensive high elastic polyurethane fibres. Most of the mechanical properties, including tensile or bending strength, are similar to PET but they are also easy to dye. PTT fibres are providing a completely new tool to design consumer fabrics, with optimal processing and application values. Finally, the price of PTT will dictate the speed at which it replaces other fibres. The real earnings in PTT are hidden in large quantities.