In this article, we will make a brief introduction to low-melt polyester from the aspects of history, processing way, evaluation method, and application.

History

The earliest low melting point fiber is the polyolefin composite fiber successfully developed by the Japanese company, Chisso. It is a fiber with PP as the core and PE as the skin, and the trade name is “ES”, which was industrialized in 1977. Chisso is a pioneer in this field and had almost monopolized the market for PP/PE and PET/PE fibers. Unfortunately, the compatibility and adhesion of PP and PE with PET are not good, so the application of such fibers is limited. In order to solve the problem of bonding with polyester fibers, Japan’s UNITIKA company successfully developed “Melty” low melting point copolyester products. Subsequently, some well-known foreign companies also began to create other copolyester products. For example, Teijin Corporation of Japan used a synthesis process similar to PET to produce low-melting polyester fibers with good adhesive strength for non-woven fabrics. The following products are all low-melt polyester, Kodel410 (from Eastman), Dacron 927/923/920 (from Dupont), and Bidim (from Rhodia, Brazil).

Processing Way

Foreign low-melting polyesters are mostly produced by adding third components, such as dimethyl isophthalate, adipic acid, and sebacic acid, and fourth components, like butanediol, neopentyl glycol, diethylene glycol, etc. In 1991, Dalian Synthetic fiber developed two kinds of low-melt polyester, D190, and D250. In 1992, China Yizheng Chemical Fiber company cooperated with the Beijing Institute of Fashion Technology to synthesize low-melting polyester with a melting point of 140-250 degrees by adding isophthalic acid and adipic acid into the PET molecular chain. The National Engineering Research Center for Synthetic Fibers used fatty diacids as modifiers to produce low melt polyesters with a melting point of 112℃and a softening point of 60℃. In 2003, Tianjin Petrochemical Company lowered the melting point of the copolyester by adding three modified dibasic acids and glycol components, and the melting point could be as low as 110℃. In 2006, the Research Institute of Liaoyang Petrochemical Company found that a single hexanediol monomer could also reduce the melting point of the copolyester to 110℃. And the chips did not stick when dried at 100℃. They also used three monomers, neopentyl glycol (NPG), adipic acid (AA), and isophthalic acid (IPA) as modifiers, and get a polymer with a melting point of around 110℃.

In summary, the comonomers for low melting point polyester processing at home and abroad can be roughly divided into two categories. The first one is modified acid components, including isophthalic acid, adipic acid, decanoic diacids, etc., whose purpose is to reduce the regularity of the polymer chain, thereby reducing the melting point. The second one is modified alcohol components, including hexanediol, butanediol, neopentyl glycol, polyethylene glycol Alcohol, etc. These comonomers can not only improve the flexibility of the molecular chain, thereby changing the crystalline properties of polyesters, but also play a role in reducing the melting point.

Evaluation Method of Low Melt Polyester Chip

At present, the evaluation indicators for low melt polyester chips mainly include intrinsic viscosity, melting range, softening point, terminal carboxyl group content, B value, agglomerated particles, ash content, and titanium dioxide content. Among them, the evaluation of softening point can refer to the standard GB/T 15332-94. the test methods for intrinsic viscosity, terminal carboxyl group content, B value, aggregated particles, ash content, and titanium dioxide content are roughly the same as those for testing regular PET and can be conducted according to GB/T 14190-93.  A microscope melting point apparatus usually determine the melting range of low-melt polyesters. Some companies also use the DSC curve to indicate the melt condition of low-melt polyester chips.

Application

Due to the good compatibility of low-melt polyester and regular polyester, the skin layer melts at lower heating temperatures while the core layer keeps the physical property and produces good adhesion after cooling. Because of its strong bonding strength, it can replace the traditional chemical binder. It has unique low-temperature melting characteristics and can be naturally bonded without the use of adhesives. It also has low odor, low VOC, and excellent absorption and sound insulation properties.

In the field of automotive trim, low-melt polyester staple fiber is made from virgin polyester pellets, which are pure in origin and avoid the odor problems caused by chemical additives such as dyes, dispersants, and additives. Sound-absorbing cotton made of low melt staple fiber, with a surface density of less than 40g/m2, can be used in audio applications to shield the sound waves radiated from the speakers and avoid endless reflection and refraction of sound waves.

Low-melt staple fiber can also be used in automotive acoustic package materials. Compared with recycled waste cotton, it has a better odor and acoustic properties and provides a solution for “car odor” and “noise” two major problems.

In the field of home textiles, low-melt cotton can be used for the production of mattresses, and filler inside sofas. Incorporating antibacterial metal into the low melting point fiber, the produced environmentally friendly brown cotton is used for mattresses, which can inhibit the growth of bacteria, prevent bacteria and mites, and be used for seat cushions, which are moderately soft and hard and not easy to deform.

In the industrial field, it can be used in the manufacture of sound absorption, sound insulation, filtration, insulation, and other materials. To be more specific, it can be applied in the engine compartment, luggage compartment, and other locations of sound insulation inside automobiles.

Low-melt staple fiber can also be used in construction materials, including sheet materials, packaging materials, and furniture materials, such as flooring, ceiling, wall, roof, etc. It can achieve the effect of being breathable waterproof, flame-retardant, and shock-absorbing.