The specialty resins are expensive, produced in relatively small volumes either for a specific application or looking for a market niche. Their Tg > 200°C and modulus > 3 GPa.
In 1991 the total world consumption of polysulfones (PSF) and polyethersulfones (PES) was 8.5 kton.
Blends of the following polymers are known: polyfluorocarbons, polysiloxanes, sulfur-containing polymers (PPS, PPSS, PES, and PSF), polyetherketones (PEK, PEEK, PEKK), polyimides (PI, PEI, and PAI), PAr, COPO, polyphosphazene (PHZ) and LCP.
1- Fluorocarbon Polymers:
A- Polytetrafluoroethylene (PTFE): (Teflon)
Known in Germany since 1933.It is a semicrystalline resin (92-98% crystallinity), with Tm = 342°C and melt viscosity of ? = 10 GPas.
B-Polychlorotrifluoroethylene (PCTFE), Hostaflon™ commercialized in 1934
C- Fluorinated ethylene-propylene (FEP), Teflon™-FEP introduced
in 1972
D- Numerous copolymers with Tm = 260 to 304°C, processable at
Tprocess = 315 to 425°C, and having the degradation temperature,
Tdeg = 425 to 440°C.
The fluoropolymers are characterized by :
1- Stability at high Ts 2- Toughness and flexibility at low Ts
3- Low friction 4- Insolubility and inertness to chemicals
5-Low dielectric losses and high dielectric strength.
The world consumption of fluoropolymers in 1991 was 72 kton.
In blends, fluoropolymers are used in small quantities to:
1- Enhance throughput
2- Reduce the frictional properties( improved anti-friction properties)
3- Increase the wear resistance.
4- PPS and PEEK blended with a fluoro(co)- polymers and reinforced with either CF or GF were wear resistant with a short break-in period for forming a self lubricating film.
2- Siloxane Polymers:
Polysiloxanes, [-O-Si(RR’)-], are linear resins that can be branched or crosslinked into elastomers.
They have high compressibility, permeability to gases, low Tg and viscosity, exceptional weatherability, low surface tension coefficient and are relatively expensive.
Siloxane polymers or copolymers have been incorporated into engineering or specialty resins to improve:
1- Processability 2-Toughness 3- HDT
4- Solvent resistance 5-Weather resistance.
Main polymers of this type are:
Polydimethylsiloxane (PDMS), and polymethylphenylsiloxane (PMPhS). Their Tg = -127 and -86°C, respectively. They start oxidizing at 290 and
375°C and undergo structural rearrangement at 435 and 410°C.
Polysiloxanes have been used as high temperature impact modifiers that improve: 1- Flame resistance 2- Processability 3- Optical properties
Several commercial blends are on the market
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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