High-performance plastics are plastics that meet higher requirements than standard (commodity) or engineering plastics. They are more expensive and used in smaller amounts. [1]
High-performance plastics are plastics that meet higher requirements than standard (commodity) or engineering plastics. They are more expensive and used in smaller amounts. [1]
High performance plastics differ from standard plastics and engineering plastics primarily by their temperature stability, but also by their chemical resistance and mechanical properties, production quantity, and price.
There are many synonyms for the term high-performance plastics, such as: high temperature plastics, high-performance polymers, high performance thermoplastics or high-tech plastics. The name high temperature plastics is in use due to their continuous service temperature (CST), which is always higher than 150 °C by definition (although this is not their only feature, as it can be seen above).
The term "polymers" is often used instead of "plastics" because both terms are used as synonyms in the field of engineering.
However, the differentiation from less powerful plastics has varied over time; while nylon and poly(ethylene terephthalate) were initially considered powerful plastics, they are now ordinary. [2]
The improvement of mechanical properties and thermal stability is and has always been an important goal in the research of new plastics. Since the early 1960s, the development of high-performance plastics has been driven by corresponding needs in the aerospace and nuclear technology. [3] Synthetic routes for example for PPS, PES and PSU were developed in the 1960s by Philips, ICI and Union Carbide. The market entry took place in the early 70s. A production of PEEK (ICI), PEK (ICI) and PEI (General Electric and GE) via polycondensation was developed in the 1970s. PEK was offered since 1972 by Raychem, however, made by an electrophilic synthesis. Since electrophilic synthesis has in general the disadvantage of a low selectivity to linear polymers and is using aggressive reactants, the product could hold only a short time on the market. For this reason, the majority of high-performance plastics is nowadays produced by polycondensation processes. [2]
In manufacturing processes by polycondensation a high purity of the starting materials is important. In addition, the stereochemistry plays a role in achieving the desired properties in general. The development of new high-performance plastics is therefore closely linked to the development and economic production of the constituent monomers. [2]
High performance plastics meet higher requirements than standard and engineering plastics because of their more desirable mechanical properties, higher chemical and/or a higher heat stability. Especially the latter makes processing difficult, often requiring specialized machinery. Most high-performance plastics are exploited for a single property (e.g. heat stability), in contrast to engineering plastics which provide moderate performance over a wider range of properties. [1] Some of their diverse applications include: fluid flow tubing, electrical wire insulators, architecture, and fiber optics. [4]
High performance plastics are relatively expensive: The price per kilogram may be between $5 (PA 46) and $100 (PEEK). The average value is slightly less than 15 US-Dollar/kg. [5] High-performance plastics are thus about 3 to 20 times as expensive as engineering plastics. [2] In the future, a significant price decline cannot be expected, since the investment costs for production equipment, the time-consuming development, and the high distribution costs are going to remain constant. [5]
Since production volumes are very limited with 20.000 t/year the high-performance plastics are holding a market share of just about 1%. [1] [3]
Among the high-performance polymers, fluoropolymers have 45% market share (main representatives: PTFE), sulfur-containing aromatic polymers 20% market share (mainly PPS), aromatic polyarylether and Polyketones 10% market share (mainly PEEK) and liquid crystal polymers (LCP) 6%. [5] [6] The two largest consumers of high-performance plastics are the electrical and electronics industries (41%) and the automotive industry (24%). All remaining industries (including chemical industry) have a share org 23%. [5]
Thermal stability is a key feature of high-performance plastics. Also mechanical properties are closely linked to the thermal stability.
Based on the properties of the standard plastics some improvements of mechanical and thermal features can already be accomplished by addition of stabilizers or reinforcing materials (glass and carbon fibers, for example) or by an increase in the degree of polymerization. Further improvements can be achieved through substitution of aliphatic by aromatic units. Operating temperatures up to 130 °C are reached in this way. Thermosets (which do not belong to the high-performance plastics, see above) have a similar temperature stability with up to 150 °C. An even higher service temperature can be reached by linking of aromatics (e.g. phenyl) with oxygen (as diphenyl ether group e. g. PEEK), sulfur (as diphenyl sulfone groups in PES or diphenyl group, for example in PPS) or nitrogen (imide group in PEI or PAI). Resulting operating temperatures might be between 200 °C in the case of PES to 260 °C in case of PEI or PAI. [7]
The increase in temperature stability by incorporating aromatic units is due to the fact, that the temperature stability of a polymer is determined by its resistance against thermal degradation and its oxidation resistance. The thermal degradation occurs primarily by a statistical chain scission; depolymerization and removal of low molecular weight compounds are playing only a minor role.
The thermal-oxidative degradation of a polymer starts at lower temperatures than the merely thermal degradation. Both types of degradation proceed via a radical mechanism. [8] Aromatics offer a good protection against both types of degradation, because free radicals can be delocalized through the π-system of the aromatic and stabilized. In this way the thermal stability is strongly increasing. Poly(p-phenylene) can serve as an example, it consists exclusively of aromatics and provides extremely stability, even at temperatures above 500 °C. On the other hand the rigidity of the chains makes it more or less inprocessible. To find a balance between processability and stability, flexible units can be incorporated into the chain (e.g., O, S, C(CH3). Aromatics can also be substituted by other rather rigid units (e. g. SO2, CO). By mixing these different elements the diversity of high-performance plastics is created with their different characteristics. [2]
In practice a maximum temperature resistance (about 260 °C) can be obtained with fluoropolymers (polymers, in which the hydrogen atoms of the hydrocarbons have been replaced by fluorine atoms). [7] Among them, PTFE has the largest market share with 65–70%. [6] Fluorine-containing polymers are, however, not suitable to serve as construction material due to poor mechanical properties (low strength and stiffness, strong creep under load). [7]
High-performance plastics can be divided in amorphous and semi-crystalline polymers, just like all polymers. Polysulfone (PSU), poly(ethersulfone) (PES) and polyetherimide (PEI) for example are amorphous; poly(phenylene sulfide) (PPS), polyetheretherketone (PEEK) and polyether ketones (PEK), however are semi-crystalline.
Crystalline polymers (especially those reinforced with fillers) can be used even above their glass transition temperature. This is because semi-crystalline polymers have, in addition to a glass temperature Tg, a crystallite melting point Tm, which is usually much higher. For example PEEK possesses a Tg of 143 °C but remains usable up to 250 °C (continuous service temperature = 250 °C). Another advantage of semi-crystalline polymers is their high resistance against chemical substances: PEEK possesses a high resistance against aqueous acids, alkalis and organic solvents. [2]
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene.
Polyether ether ketone (PEEK) is a colourless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. It was invented in November 1978 and brought to market in the early 1980s by part of Imperial Chemical Industries (ICI) that later became Victrex PLC.
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment and recycling. The rate of this degradation varies significantly; biodegradation can take decades, whereas some industrial processes can completely decompose a polymer in hours.
Polyvinyl fluoride (PVF) or –(CH2CHF)n– is a polymer material mainly used in the flammability-lowering coatings of airplane interiors and photovoltaic module backsheets. It is also used in raincoats and metal sheeting. Polyvinyl fluoride is a thermoplastic fluoropolymer with a repeating vinyl fluoride unit, and it is structurally very similar to polyvinyl chloride.
Polychlorotrifluoroethylene (PCTFE or PTFCE) is a thermoplastic chlorofluoropolymer with the molecular formula (CF2CClF)n, where n is the number of monomer units in the polymer molecule. It is similar to polytetrafluoroethene (PTFE), except that it is a homopolymer of the monomer chlorotrifluoroethylene (CTFE) instead of tetrafluoroethene. It has the lowest water vapor transmission rate of any plastic.
Polyamide-imides are either thermosetting or thermoplastic, amorphous polymers that have exceptional mechanical, thermal and chemical resistant properties. Polyamide-imides are used extensively as wire coatings in making magnet wire. They are prepared from isocyanates and TMA in N-methyl-2-pyrrolidone (NMP). A prominent distributor of polyamide-imides is Solvay Specialty Polymers, which uses the trademark Torlon.
Polybenzimidazole (PBI, short for poly[2,2’-(m-phenylen)-5,5’-bisbenzimidazole]) fiber is a synthetic fiber with a very high decomposition temperature. It does not exhibit a melting point, it has exceptional thermal and chemical stability, and it does not readily ignite. It was first discovered by American polymer chemist Carl Shipp Marvel in the pursuit of new materials with superior stability, retention of stiffness, and toughness at elevated temperature. Due to its high stability, polybenzimidazole is used to fabricate high-performance protective apparel such as firefighter's gear, astronaut space suits, high temperature protective gloves, welders’ apparel and aircraft wall fabrics. Polybenzimidazole has been applied as a membrane in fuel cells.
Polylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a plastic material. As a thermoplastic polyester it has the backbone formula (C
3H
4O
2)
n or [–C(CH
3)HC(=O)O–]
n. PLA is formally obtained by condensation of lactic acid C(CH
3)(OH)HCOOH with loss of water. It can also be prepared by ring-opening polymerization of lactide [–C(CH
3)HC(=O)O–]
2, the cyclic dimer of the basic repeating unit. Often PLA is blended with other polymers. PLA can be biodegradable or long-lasting, depending on the manufacturing process, additives and copolymers.
Engineering plastics are a group of plastic materials that have better mechanical or thermal properties than the more widely used commodity plastics.
Polyphthalamide is a subset of thermoplastic synthetic resins in the polyamide (nylon) family defined as when 55% or more moles of the carboxylic acid portion of the repeating unit in the polymer chain is composed of a combination of terephthalic (TPA) and isophthalic (IPA) acids. The substitution of aliphatic diacids by aromatic diacids in the polymer backbone increases the melting point, glass transition temperature, chemical resistance and stiffness.
Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.
Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl-SO2-aryl subunit. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for polycarbonates.
Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include naturally occurring chemicals, such as in plants and insects, as well as synthetics such as polybutyrate. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing.
Polymethylpentene (PMP), also known as poly(4-methyl-1-pentene), is a thermoplastic polyolefin. It is used for gas-permeable packaging, autoclavable medical and laboratory equipment, microwave components, and cookware. It is commonly called TPX, which is a trademark of Mitsui Chemicals.
A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle.
Polyaryletherketone (PAEK) is a family of semi-crystalline thermoplastics with high-temperature stability and high mechanical strength whose molecular backbone contains alternately ketone (R-CO-R) and ether groups (R-O-R). The linking group R between the functional groups consists of a 1,4-substituted aryl group.
Crystallization of polymers is a process associated with partial alignment of their molecular chains. These chains fold together and form ordered regions called lamellae, which compose larger spheroidal structures named spherulites. Polymers can crystallize upon cooling from melting, mechanical stretching or solvent evaporation. Crystallization affects optical, mechanical, thermal and chemical properties of the polymer. The degree of crystallinity is estimated by different analytical methods and it typically ranges between 10 and 80%, with crystallized polymers often called "semi-crystalline". The properties of semi-crystalline polymers are determined not only by the degree of crystallinity, but also by the size and orientation of the molecular chains.
Poly(ethylene adipate) or PEA is an aliphatic polyester. It is most commonly synthesized from a polycondensation reaction between ethylene glycol and adipic acid. PEA has been studied as it is biodegradable through a variety of mechanisms and also fairly inexpensive compared to other polymers. Its lower molecular weight compared to many polymers aids in its biodegradability.
Perfluoroalkoxy alkanes (PFA) are fluoropolymers. They are copolymers of tetrafluoroethylene (C2F4) and perfluoroethers (C2F3ORf, where Rf is a perfluorinated group such as trifluoromethyl (CF3)). The properties of these polymers are similar to those of polytetrafluoroethylene (PTFE). Compared to PTFE, PFA has better anti-stick properties and higher chemical resistance, at the expense of lesser scratch resistance.
