Polymer Science: History, Structure, Synthesis, Properties, And Uses Of PEEK

History of Polymer

Discuss about the Polymer Science.

Polyether ether ketone is thermoplastic polymer, used in the engineering applications. This organic compound belongs to linear aromatic polyether ketone family known as polyaryletherketone (PAEK) family. PEEK polymer was invented by ICI (Imperial chemicals industries) in the year 1982, which is an aromatic polyketone. ICI revealed that the prospective for excellent features of PEEK and test marketing was carried out in 1978, after 1 year of the development of the material. In 1993, ICI sold PEEK business to Victrex plc via a management buyout, at that time, till several years, PEEK was the only commercial manufacturer as well as supplier of PEEK in the market. In, 1990, the volume for polyketone was 500,000 lbs per year, which was estimated to reach 3 to 4 million by 2000 (Goodson et al., 2012), this data is also highlighted by Olabis (2012) and Isayev (1991). Victrex PEEK has an annual production capacity is about 2800 tonnes, however, due to its excellent properties, demand is enhancing. According to the analysis in October 1998, cost for aromatic polyketone is $30 per round. There are other companies, which have started manufacturing PEEK to meet the market demands.

Polyetheretherketone is a semicrystaline, high temperature engineering thermoplastic, used as matrix polymer for high performance composites. The structural chemical formula of the aromatic crystalline compound is [-oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene-]. The density of this compound is 1320 kg/m³. The study of crystalline structure of PEEK has shown that due to very high nucleation density of PEEK on fibre surface, crystal growth unimpeded in the path normal to fibre axis, which is the reason behind transcrystallinity development. At the time of transcrystallinity, lamellae are arranged in a perpendicular position to the fibre axis, thereby representing optical properties of transcrystallinity (Fortney & Fossum, 2012; Ward, 2012). 

Figure: Structure of PEEK

(Source: Goodson et al., 2012)

PEEK polymer is obtained through “step-growth polymerization” by “dialkylation of bisphenolate salts”. The typical reaction of PEEK synthesis involve 4,4'-difluorobenzophenone (DFBP) and disodium salt of hydroquinone (HQ), hydroquinone. The disodium salt of hydroquinone is prepared in situ through the deprotonation with sodium carbonate. The main reaction occurs at 300 °C in polar aprotic solvent or anhydrous potassium carbonate (K2CO3) respectively, under microwave irradiation; mostly used solvent is diphenyl sulphone.

Figure: Synthesis of PEEK

(Source: Ashrafi et al., 2012)

Due to PEEK’s robust properties, it’s demand is increasing. Several superlatives can be used for demonstrating PEEK’s properties, as it is the best performing thermoplastic polymer. The polymer has unique physical, chemical, mechanical, thermal and electrical properties, which are enhancing it’s compatibility to be used in different applications (Rudin & Choi, 2012).

Structure and Synthesis

PEEK has excellent chemical resistance properties, which are retained in the polymer till very high temperature. This property is making PEEK an ideal material to be used as a magnetic stir bar in high mechanical stress induced application. The polymer is exceptionally resistant to most organic and inorganic chemicals. However, in concentrated anhydrous or strong oxidizing agents, the polymer loses its chemical resistance and dissolved. The aromatic polymer has is extremely resistant to hydrolysis in hot water and it remains unchanged after thousand hours at about 250ºC at high pressure in water. However, the compound is not highly resistant to UV radiation, however, it consist notable resistance towards X rays, beta rays and excellent resistance towards gamma rays, which is estimated as 1000 Mrad, instead of losing its mechanical properties. Several researchers have investigated the compatibility of PEEK with many chemicals at 20 ºC (68 ºF) and revealed an “A” grade rating in most of the chemicals. In addition, the compound has a very high compatibility with approximately any kinds of solvents used in HPLC (Ehrenstein, 2012; Manson, 2012) This information is also supported by Fries and Zarfl (2012). However, the compound is attacked by concentrated nitric and sulphuric acid, though PEEK tubing can resist 20-30 % nitric acid, during system passivating. In contrast, THF, methylenechloride and DMSO can make the compound to swell. The highest temperature at which the polymer PEEK can maintain its tubing and pressure rating is 100ºC. It has a thermal expansion of 3.000 and heat deflection temperature is 340 ºF. These properties enhance the opportunity for sterilization; along with its excellent biocompatibility, the compound has become a pivotal candidate for medical applications.

PEEK is a semicrystalline thermoplastic, having a density of 1320 kg/m3. The processing condition during molding of PEEK promotes the crystallinity property of the compound, thereby facilitating its mechanical properties. This molding pressure is a significant processing property of the polymer, which is 0.011. It’s glass transition temperature is 143 °C (289 °F) and meting point is approximately 343 °C (662 °F). The useful operating temperature for this polymer is up to 250 °C (482 °F). Between its room temperature and solidus temperature, the thermal conductivity enhances nearly linearly against temperature. The polymer is optically opaque. It has a maximum water absorption rate of 0.1 to 0.14 % (Ashrafi et al., 2012). The polymer has good oxidation resistance, UV resistance, alkaline resistance and acid resistance properties.

Properties of PEEK

PEEK has excellent mechanical resistance, which is influenced by it’s physical properties. PEEK has a tensile strength of 10,000 psi to 15,000 psi, a tensile module of 500K. It has a tensile elongation percentage of 30 to 150 %. On the other hand, impact strength is 0.6 to 2.2 ft-lb/in. PEEEK has a hardness of R120 and CLTE of 10^-6mm/mm/C. Flexural strength is 17,500 Psi and flexural modulus is 0.50 Psi. Tensile strength of the compound is 90 to 100 MPa and the young’s modulus is 3.6 GPa.

The PEEK has an excellent thermal capability and can with stand am temperature up to 250 degree Celsius. The compound also has the property to resistance to burning and lower flame spread. The Limiting Oxygen Index is 35%, which cause lower smoke generation even when burning of the material occurs. Thus, it can use as a useful engineering material

PEEK is used for fabricating items used in different demanding application, due to its robustness; these applications include bearings, piston parts, HPLC column, pumps, cable insulation and compressor plate valves. It has a good UV resistance property, thus it is compatible with ultra-high vacuum applications. The polymer is being considered as an advanced biomaterial having rapid opportunity to be used in medical implants. In spinal fusion devices and reinforcing rods, the use of PEEK is being increased. In aerospace, chemical and automotive industries are significantly using PEEK (Chawla, 2012). This is also supported by Hallmann et al., (2012).

As the polymer has a mechanical property of maintaining its properties at very high temperature, it is being used in least two types of Reprap extruder for playing the role of thermal insulation (Heaton, 2012). Therefore, it can be said that the mechanical structure of extruder can be prepared by the substance that is being extruded; however, it should be assured that the PEEK insulator is preventing heat from travelling beyond the intended melt zone. In preparation of prosthetics, instruments and diagnostics, it is widely used in medical science. It is also used in making appliances like handles and cooking equipments. It is used for producing woven products for belting, filter and meshes.

Due to the high chemical resistance power of PEEK, it can be used with adverse chemical agents and also due to the longer life power of the material they can be economical. Moreover, due to the capability of hydraulic resistance, the material has the power resist condition of high pressure and thus can be used in all adverse environmental situations.

Chemical Properties of PEEK

PEEK is a notable polymer for reducing negative impact upon environment. A component that is minimizing environmental impact is ensuring that the component is safe for use and reliable. Appropriate use of PEEK in different application can enhance part like and reliability, during the reduction of equipment downtime. Excellent properties of PEEK provide a reliable alternative to petrochemical applications and thereby reducing the negative impacts of petrochemical applications. PEEK is lighter compared to other metals replaced by the compound; thereby it is directly reducing fuel consumption requirements. Moreover, significantly higher strength and stiffness it can be used in lighter-weight parts. PEEK plastic is easy to recycle and the recycled PEEK has significant applications (Ashrafi et al., 2012; Heaton, 2012; Shukla et al., 2012). Thus, it is an environment-friendly compound. Its toxicity is low, fire, smoke and toxic gas emission is also low, which makes it more reliable for using in fire proof substances.

PEEK has lower amount of toxicity as it is based on the lower amount of insolubility in water. Natural PEEK has lower amount of toxic element. As PEEK is very expensive material, it is important to recycle the usage of those materials. The thermosetting polymers can be used in the purpose of recycling and dispose of PEEK (Carraher & Seymour, 2012). There is also the incineration process that helps to in non-combustible ways of disposing and recycling of PEEK. On the other hand, the mechanical non-combustion technique, which is based on comminuting and granulation, can help in the recycling process. All the chemical process of recycling of PEEK has proved to be effective and help to protect the environment. The recycled PEEK can prove to be economical and also is cost effective. Nevertheless, there is still higher potential for the application of recycled PEEK. This provides a wide chance of future research for the application of recycled PPEK.      

Reference List

Ashrafi, B., Díez-Pascual, A. M., Johnson, L., Genest, M., Hind, S., Martinez-Rubi, Y., ... & Johnston, A. (2012). Processing and properties of PEEK/glass fiber laminates: Effect of addition of single-walled carbon nanotubes. Composites Part A: Applied Science and Manufacturing, 43(8), 1267-1279.

Carraher Jr, C. E., & Seymour, R. B. (2012). Structure—Property Relationships in Polymers. Springer Science & Business Media.

Chawla, K. K. (2012). Composite materials: science and engineering. Springer Science & Business Media.

Ehrenstein, G. W. (2012). Polymeric materials: structure, properties, applications. Carl Hanser Verlag GmbH Co KG.

Fortney, A., & Fossum, E. (2012). Soluble, semi-crystalline PEEK analogs based on 3, 5-difluorobenzophenone: Synthesis and characterization. Polymer, 53(12), 2327-2333.

Fries, E., & Zarfl, C. (2012). Sorption of polycyclic aromatic hydrocarbons (PAHs) to low and high density polyethylene (PE). Environmental Science and Pollution Research, 19(4), 1296-1304.

Goodson, M. L., Farr, D., Keith, D., & Banks, R. J. (2012). Use of two-piece polyetheretherketone (PEEK) implants in orbitozygomatic reconstruction. British Journal of Oral and Maxillofacial Surgery, 50(3), 268-269.

Hallmann, L., Mehl, A., Sereno, N., & Hämmerle, C. H. (2012). The improvement of adhesive properties of PEEK through different pre-treatments. Applied Surface Science, 258(18), 7213-7218.

Heaton, C. A. (Ed.). (2012). The chemical industry. Springer Science & Business Media.

Isayev, A. (1991). U.S. Patent No. 5,006,402. Washington, DC: U.S. Patent and Trademark Office.

Manson, J. A. (2012). Polymer blends and composites. Springer Science & Business Media.

Olabis, O. (2012). Polymer-polymer miscibility. Elsevier.

Rudin, A., & Choi, P. (2012). The Elements of Polymer Science & Engineering. Academic Press.

Shukla, D., Negi, Y. S., Uppadhyaya, J. S., & Kumar, V. (2012). Synthesis and modification of poly (ether ether ketone) and their properties: a review. Polymer Reviews, 52(2), 189-228.

Ward, I. M. (Ed.). (2012). Structure and properties of oriented polymers. Springer Science & Business Media.