Published November 2015
Thermoplastic polyester engineering resins, sometimes referred to as terephthalate engineering resins, include polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and polycyclohexylene dimethylene terephthalate (PCT). These products are all thermoplastic linear condensation polymers based on dimethyl terephthalate (DMT) or terephthalic acid (TPA), but on different glycols.
Polybutylene terephthalate (PBT) resins and polyethylene terephthalate (PET) engineering resins are high-performance, high-molecular-weight materials that can be converted into functional components and parts that are in turn used in a diverse array of assemblies for automotive, electrical/electronic, appliance and industrial equipment applications. PBT resins and PET engineering resins share many of the same markets; however, PBT is consumed in much larger volumes than PET (accounting for about 87% of the total consumption of PBT and PET) because of its easier processability and shorter processing times.
The following pie chart shows world consumption of polybutylene terephthalate:
Overall use of PBT in automotive applications has increased as a result of greater use of electrical/electronic devices such as housings for electric motors for window and seating adjusters, as well as passenger airbags, safety belt tensioners, and others. Newer PBT grades with improved hydrolytic stability are being used in under-the-hood parts such as plugs, connectors, and housing parts, which must withstand the increasingly stressful demands of the automotive industry. Also, polyester resins have benefited from improvements in mold design, better understanding of flow behavior in molds, increased robotics, and increased computer simulation, which have improved the efficiency and economics of the production of large, molded parts.
In recent years, the industry has been researching methods to become more environmentally friendly as part of the global “green” movement. Since 2006, DuPont has been marketing commercialized polytrimethylene terephthalate (PTT) engineering thermoplastic resin, which is made from purified terephthalic acid (PTA) and biopropanediol (bio-PDO). The bio-PDO is made from renewable resources. Also, SABIC Innovative Plastics now offers Valox iQ resins, which are made by converting postconsumer PET bottles into engineering plastics as replacements for PBT. Valox iQ compound is now used to make brackets for side air deflection systems for Volvo heavy-duty trucks.
During the last decade, the global growth rate for thermoplastic polyester engineering resins was well above that for most engineering thermoplastic resins. PBT resin demand grew at an average annual rate of about 5.4% during 2005–15. Overall consumption of PBT resin fell in 2008–09 as a result of the global economic crisis, but demand recovered in 2010 and has continued to grow. Global consumption of PBT resin is expected to grow at an average annual rate of 3.4%.
In China, the fastest growing segment is expected to be for lighting parts, as the Chinese government announced plans in 2008 to phase out incandescent lamps in the country and promote energy-saving lighting products nationwide. Exports of alternative lighting products will grow rapidly as the United States, Europe, and a number of other countries are also in the process of phasing out traditional incandescent lighting. PBT is used heavily in compact fluorescent bulbs, but less so in LED lamps, which are expected to experience the greatest growth in the lighting market.