Precaution, Pretection and Safety, all in FireTC
firetc@firetc.com
 
Browse by category
 
Recommended News
Hot News
 
Your location: Home » News » Hot News » Text

Emerging High Temperature Thermoplastic Materials

Zoom  Zoom Issue Date:2012-03-07   Source: plastics solutions   Browse:1437

Industries such as aerospace, automotive and electronics are requiring an increasing balance of properties such as thermal, mechanical, electrical and chemical features. In terms of thermal performance, some polymers offer thermal resistance which exceeds 200°C. This article will provide a summary of recent developments in these polymers which provide the indicated thermal performance. It should be noted that this article will only discuss thermoplastic polymers and no discussion of high temperature thermosetting materials will be provided.

 

Among the polymers to be discussed will be polybenzimidazole (PBI), polyimides (PI's), polyetheretherketone (PEEK) and liquid crystal polymers (LCP's). In addition, there will be a brief summary of polymers with very special applications. In general, however, the major applications for these high temperature polymers is for the replacement of metals and ceramics in uses such as automotive transmissions, jet engine components and heat-resistant gears.

 

Polybenzimidazole (PBI), whose chemical structure is provided in Figure 1, has a glass transition temperature which is in the 400-425°C range. The actual value depends upon the measurement which is employed, with dynamic mechanical methods providing higher values than differential scanning calorimetry (DSC). Due to this high glass transition temperature, PBI provides excellent thermal resistance. However, also related to the high glass transition temperature is the fact that it cannot be processed using conventional thermoplastic processing methods.

 

Figure 1. Chemical Structure of Polybenzimidazole (PBI)

 

This lack of traditional thermoplastic processing of PBI has been addressed by both PBI Performance Products with their Celazole T-series and by Victrex with their Victrex T-series PBI/PEEK (polyethetherketone) blends. In these blends, the superior mechanical performance and thermal resistance of PBI is combined with the melt processability of PEEK. Typical properties for the PBI/PEEK alloys are displayed in Table 1 :

 

Property                                       Typical Value 

Tensile Strength, MPa                             98-175

Tensile Modulus, GPa                              5-24

HDT (0.46 MPa), °C                              > 305

HDT (1.8 MPa), °C                                 305

Continuous Use Temperature, °C         > 250

 

Table 1. Properties of PBI/PEEK Blends

 

 

The products are designed for injection molding and extrusion applications.

 

Along with the unfilled version of the PBI/PEEK blends, reinforced varieties which contain both carbon reinforcement and glass reinforcements are also available.The carbon reinforced PBI/PEEK blends are well suited for semiconductor and electronic applications due to their static dissipative nature.The glass reinforced PBI/PEEK blends offer thermal and electrical insulation and very high dimensional stability. As such, they make for excellent high temperature insulators.

 

Another class of high temperature polymers that has been generating a great deal of interest are polyimides (PI's). Polyimides have been known for some time but they are continuously evolving in their technology. For example, DuPont has developed new compositions in their Vespel series including an unfilled composition called Vespel SCP-5000. Parts which are made from Vespel SCP-5000 retain 50% of their original strength in ageing tests performed at both 360 and 430°C. They also possess excellent dielectric properties over a wide temperature and frequency range.

 

Several other companies have also recently introduced their own thermoplastic polyimides (TPI's). AURUM polyimides, offered by Mitsui Chemicals, are high performance polyimides for injection molding of precision components and for the production of extruded products using screw injection molding machines. They provide continuous use temperatures up to 240°C.

 

SABIC Innovative Plastics provides EXTEM High Performance Products as replacement materials for ceramics, metals and thermosets.?The series of amorphous thermoplastic polyimides (TPI's) offer a Tg up to 311°C. They provide chemical resistance to a broad range of chemicals, including chlorinated solvents.

 

Similar to what has been done with PBI, PEEK has been incorporated into mixtures with EXTEM resins. Through this blend approach, products are provided with optimized performance combining the best features of both materials. The blend technology allows for new product opportunities for the development of low weight, high-temperature continuous use connectors for harsh environments and metal replacements for aerospace environments. EXTEM UP blend resins combine the features of semi-crystalline PEEK, including excellent chemical resistance, with the positive features of an amorphous material with a high glass transition temperature. The properties of the resulting blends allow material users to achieve higher strength and stiffness using thinner walls and also provide tight dimensional control.

 

Liquid crystal polymers (LCP's) have been known for some time, with aromatic polyesters being the most common type. Due in large part to their rigid molecular conformation, LCP's are subject to molecular alignment under usual processing shear stresses. With the majority of LCP's, this alignment leads to a strong dependence of mechanical properties on the direction of orientation, with properties in the orientation direction, designated the machine direction, or MD, being significantly higher than the properties in the transverse direction, or TD.

 

This issue with the properties of parts made from LCP's being different in two directions has been addressed by Ticona with their Vectran series of products. This family of LCP's can be run on commercial extruders at processing conditions which are typical for polyolefins. On the other hand, traditional LCP's are typically processed at temperatures upwards of 300 °C. This new class of LCP's, referred to as "low processing temperature LCP's" are processed at temperatures of 220-230°C.

 

Unlike other liquid crystal polymers, "low processing temperature LCP's" can be biaxially oriented and thermoformed. This allows for the production of structures that have more balanced mechanical properties than are usual with traditional LCP's. In addition, the fact that processing temperatures are similar to those used for polyolefins means that these LCP's can be more easily incorporated into multilayer film structures which are used in packaging applications. This allows for the effective utilization of the excellent barrier properties of the LCP's.

 

As mentioned earlier in this article, there are also additional polymers that are being developed for quite specific applications. For example, Solvay has introduced a new series of MFA resins,the Hyflon F-series, which are designed as replacements for fluorinated ethylene propylene (FEP). The Hyflon MFA polymers have melting points in the 265-275°C range and provide continuous service temperatures up to 225°C.

 

New high temperature amorphous polysulfone and polyethersulfone have recently been launched by Solvay Advanced Polymers and BASF. BASF has produced Ultrason E Dimension, which exhibits high stiffness at temperatures between 120 and 220°C as well as good dimensional stability. Epispire HTS-2620 contains 20% glass fibers and is a product of Solvay Advanced Polymers. It possesses a Tg of 265°C and an HDT of 260°C.

 

Finally, Solvay Advanced Polymers has recently extended its portfolio of Amodel polyphthalamide (PPA) resins for automotive electronics applications. New AE grades reduce corrosion issues in high temperature and high humidity conditions such as electric motors and connectors. The AE line of products has been specially formulated to prevent the corrosion problems while still maintaining the high performance of the PPA resins.

 

Conclusions

Aerospace, automotive and electronics industries are among the areas which are presently leading the way for the development of polymer materials that provide thermal resistance that exceeds 200°C. Along with the temperature resistance, there are other properties such as mechanical integrity and chemical resistance that need to be balanced. This article has provided a summary of recent developments in polymers aimed at satisfactorily achieving that desired balance.

 
 
[ News Search ]  [ ]  [ Forword to friends ]  [ Print ]  [ Close ]  [ Back to Top ]

 

 
 
Home | About us | Contact | Terms & Conditions | Copyright | Site Map | Friend link | Guestbook | Old Version | 闽ICP备09009213号
©2013-2015 FIRETC.NET All Rights Reserved   ICP:闽ICP备09009213号-4