Abstract


CORTERRA PTT is the Shell trademark name for the aromatic polyesters known as polytrimethylene terephthalate (PTT). CORTERRA PTT polymers are produced by the polycondensation reaction of purified terephthalic acid (PTA) and 1,3-propanediol (PDO). PTT competes with the other aromatic polyesters - polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) - as well as with nylon. CORTERRA PT is used in:


  • Fibres for carpet and textiles
  • Non-woven fabrics


Other emerging applications, including monofilament, film and engineering thermoplastics (ETPs). PTT greatly reduces the amount of acrolein generated during thermal decomposition of the polymer. This stabilisation is effective at temperatures well above the melt temperature and is active for days at these temperatures. 


Introduction:


CORTERRA Polymer is aromatic polyester known generically as PTT, (polytrimethylene terephthalate). PTT is produced by the polycondensation reaction of PTA (purified terephthalic acid) and PDO (1,3-propanediol) and has unique properties as compared to the other aromatic polyesters, PET (polyethylene terephthalate) and PBT (polybutylene terephthalate).


The unique properties of PTT have been known for many years, but the polymer has not been commercially available because of the high cost of production of the PDO raw material. Extensive research efforts has resulted in a cost-effective process to manufacture PDO. With this breakthrough in processing technology for PDO, CORTERRA Polymers are now commercially available for use in carpet and textile fibers monofilament, film, nonwoven fabric, and engineering thermoplastic applications.


CORTERRA 200 can be used by itself, as the base polymer for compounds, or as a polymer modifier for many engineering thermoplastic applications. Compounded engineering resins based on CORTERRA PTT polymer provide physical properties that are equivalent to or better than those of similar PBT compounds. Extrusion and injection molding conditions, and processing characteristics are very similar to those established for PBT. PTT compounds generally exhibit higher tensile strength, flexural modulus and heat deflection temperatures but with slightly lower impact strength than the PBT counterparts.


Development of PTT Polymer:


CORTERRA Polymer is an aromatic polyester known generically as PTT, polytrimethylene terephthalate). PTT is produced by the polycondensation reaction of PTA (purified terephthalic acid) and PDO (1,3-propanediol) and has unique properties as compared to the other aromatic polyesters, PET (polyethylene terephthalate) and PBT (polybutylene terephthalate).


The unique properties of PTT have been known for many years, but the polymer has not been commercially available because of the high cost of production of the PDO raw material. Extensive research efforts by Shell Chemicals** has resulted in a cost-effective process to manufacture PDO. With this breakthrough in processing technology for PDO, CORTERRA Polymers are now commercially available for use in carpet and textile fibers monofilament, film, nonwoven fabric, and engineering thermoplastic applications.


CORTERRA 9240 is a semi-dull, PTT homopolymer. The polymer properties which provide resilience, elastic recovery, high bulk, soft hand, inherent stain resistance, and ease of dyeing, make it well-suited for carpet and textile fibers. CORTERRA 9240 has TiO2 added as a dulling agent and is used when a bright or shiny luster is not desired in the end product.


Many of these same properties make CORTERRA 9240 a good candidate for nonwoven applications. CORTERRA 9240 can be compounded to provide performance properties and processing characteristics that are similar to PBT.


 

Process Parameters:


CORTERRA 200 has been successfully compounded using both single-screw and twin-screw extruders. It is not necessary to dry PTT polymer before use in vented single-screw or twin-screw compounding machines as long as the moisture content is less than 0.2%. However, if the moisture content is greater than 0.2%, or the compounding equipment is not vented, it is recommended that the polymer be dried to a moisture level below 50 ppm to obtain optimum properties.


Typical drying equipment would include a dehumidifying air hopper dryer with regenerative desiccant beds using the following conditions:



Process

Conditions


Drying Temperature



130C


Residence Time


4 hours



Air Dew Point


-40C



Minimum Air Flow Rate


62 liters/minute per kilogram polymer (1.0 ft3/min per pound)



Typical physical properties

Property

Typical Value

Intrinsic Viscosity (IV), dl /g

0.92


Melting Point, C



228



b* color



4.5



L* color



85



Polymer Density, g/cc



1.35



Bulk Density, kg/m3



833



Weight of 100 pellets, g



2.4



TiO2 content, %



0




 

Different classes in PTT Fibre


CORTERRA Polymer 200


CORTERRA 200 can be used by itself, as the base polymer for compounds, or as a polymer modifier for many engineering thermoplastic applications. Compounded engineering resins based on CORTERRA PTT polymer provide physical properties that are equivalent to or better than those of similar PBT compounds. Extrusion and injection molding conditions, and processing characteristics are very similar to those established for PBT. PTT compounds generally exhibit higher tensile strength, flexural modulus and heat deflection temperatures but with slightly lower impact strength than the PBT counterparts.


CORTERRA Polymer 9200


CORTERRA 9200 is a clear, PTT homopolymer. The polymer properties which provide resilience, elastic recovery, high bulk, soft hand, inherent stain resistance, and ease of dyeing, make it well-suited for carpet and textile fibers. CORTERRA 9200 is used when a very bright and shiny luster is desired in the end product.


CORTERRA Polymer 9240


CORTERRA 9240 is a semi-dull, PTT homopolymer. The polymer properties which provide resilience, elastic recovery, high bulk, soft hand, inherent stain resistance, and ease of dyeing, make it well-suited for carpet and textile fibers. CORTERRA 9240 has TiO2 added as a dulling agent and is used when a bright or shiny luster is not desired in the end product.


Polymer Production


There are two routes to synthesis PTT: the transesterifi-cation of dimethylterephthalate (DMT) with PDO and the esterification route starting with terephthalic acid (PTA) and PDO - these are similar to PET synthesis. With the exception of the process temperature and catalysts, the synthesis of PTT follows more or less the same chemical rules as the PET process. As a consequence, it is possible, in general, to convert existing PET production facilities to produce PTT. The easiest way is to use an existing redundant PET batch-plant. In any case, it is necessary to have a separate PDO rectification unit available. Depending on the design of the polycondensation reactor, it is possible to produce PTT of an intrinsic viscosity, in a range of 0.65-0.85dl/g. More complicated, but still possible, is the conversion of a continuous polycondensation plant from PET to PTT. 


If the molecular weight of the PTT out of the melt-phase polycondensation is too low it is also possible to increase it afterwards by solid-state polycondensation (SSP). Technology and equipment for the SSP of PTT are again very similar to those of PET solid-state polycondensation processing. Finally, the best but most expensive solution is to build a polycondensation line that is tailor made for PTT. There are reliable equipment and matured melt-phase polycondensation technologies from leading engineering companies, including Zimmer AG and EMS-Inventa- Fischer to produce PTT, to high quality, on continuous lines. To reach the desired intrinsic viscosity in the melt-phase polycondensation, the finisher equipment, as used in PBT production, is useful for PTT. 


Origin for PTT Production


The production of PDO is key to the manufacture of PTT. Both process economy and PTT-polymer quality are strongly dependent on PDO purity. Especially aldehydes and ketones which are side products of the PDO and PTT production should be reduced to a very low level. However, this demand for PDO purity is similar to that for fibre-grade ethylene glycol, as it is used for PET production. Larger industrial facilities producing PDO, including DuPont use the acrolein process from Degussa and Shell, based on ethylene oxide, carbon monoxide and hydrogen. Recently, DuPont has announced the start up of PDO production, based on a biochemical route, using cornstarch as feed stock. DuPont has applied for a patent for this process. Because of high development activities in the field of PTT from some Japanese companies, such as ASAHI, TORAY and TEIJIN one can assume that PDO might soon available from the Japanese chemical industry. Finally, 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. 



 

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.  

 

 

FIGURE

PTT

PET

IV [dl/g]

0.8-1.2

0.55-0.65

TG [C]

50-60

76-80

TK [C]

80-120

130-150

TM [C]

226-229

254-258

Crystallization

non

1 h at 150C

Drying temp. [C]

125

160

Time [h]

6

6

Dew temp. [C]

-40

-25

Extrusion Zones [C]

240-270

280-300

Melt temp. [C]

255-265

285-295 in the die


Comparison of polymer properties and process features for spinning


PTT and PET

Conclusion:


Unlike other introductions of new polymers to the industry, the introduction of PTT was accompanied by powerful marketing activities from the first. Shell has announced that it has a PDO production unit of 75,000t/a capacity on stream. Shells PTT polymer production is estimated to be in the range of 21,000t/a. Shells PTT activities are covered by the trade name Corterra. In 1998, DuPont acquired the PDO production of Degussa in Wesseling, Germany. This plant is producing about 12,000t/a PDO with the option to expand the capacity to 50,000t/a. DuPonts PTT activities are covered by the trade name Sorona.


The question of poly trimethylene terephthalate (PTT) is only appearing now and not 60 years ago, when it was invented, has many different answers. One reason is that at that time of invention, poly ethylene terephthalate (PET) was found to be the polymer with the broadest application potential in different industrial fields, including films for video and audio, textile fibre, technical films and packaging. Another reason was the limited avail-ability of 1,3-propanediol (PDO), which was expensive. However, PDO is now playing the major role in the industrial development of PTT. 


References:


1)       www.freepatentsonline.com/6495254

2)       www.intota.com/multisearch.asp

3)       www.technica.net/NF/NF1/eptt.htm

4)       sciencelinks.jp/j-east/article

5)       www.fbi.gov/hq/lab/fsc/backissu/july2001/houck.htm

6)       www.wipo.int/pctdb/en/wo.jsp

7)       www.swicofil.com/polytrimethyleneterephthalate.html

8)       en.wikipedia.org/wiki/Polyethylene_terephthalate

9)       www.springerlink.com/index/AV1DWAWEDCQPHTC3.pdf

10)     jit.sagepub.com/cgi/content/refs/31/3/159



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