High-performance plastics are plastics that meet higher requirements than standard or engineering plastics. They are more expensive and used in smaller amounts. [1]
High-performance plastics are plastics that meet higher requirements than standard 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. If the term "high-performance thermoplastics" is used, it is because both standard and technical as well as high-performance plastics are always thermoplastics. Thermosets and elastomers are outside of this classification and form their own classes.
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] Also in future there cannot be expected a significant price decline, 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 of 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, alkalies and organic solvents. [2]
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Polyether ether ketone (PEEK) is a colourless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. The polymer was first developed in November 1978, initially being brought to the market in the early 1980s by the part of Imperial Chemical Industries (ICI) that became Victrex PLC.
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. Its chemical formula is (C2H2F2)n.
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.
Polyphenylene sulfide (PPS) is an organic polymer consisting of aromatic rings linked by sulfides. Synthetic fiber and textiles derived from this polymer resist chemical and thermal attack. PPS is used in filter fabric for coal boilers, papermaking felts, electrical insulation, film capacitors, specialty membranes, gaskets, and packings. PPS is the precursor to a conductive polymer of the semi-flexible rod polymer family. The PPS, which is otherwise insulating, can be converted to the semiconducting form by oxidation or use of dopants.
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, 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 thermoplastic polyester with backbone formula (C
3H
4O
2)
n or [–C(CH
3)HC(=O)O–]
n, 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.
Engineering plastics are a group of plastic materials that have better mechanical and/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 the ester functional group 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.
Commodity plastics or commodity polymers are plastics produced in high volumes for applications where exceptional material properties are not needed. In contrast to engineering plastics, commodity plastics tend to be inexpensive to produce and exhibit relatively weak mechanical properties. Some examples of commodity plastics are polyethylene, polypropylene, polystyrene, polyvinyl chloride, and poly(methyl methacrylate). Globally, the most widely used thermoplastics include both Polypropylene and Polyethylene.
Polymer stabilizers are chemical additives which may be added to polymeric materials, such as plastics and rubbers, to inhibit or retard their degradation. Common polymer degradation processes include oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues, dyes, or impurities. All of these degrade the polymer at a chemical level, via chain scission, uncontrolled recombination and cross-linking, which adversely affects many key properties such as strength, malleability, appearance and colour.
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.
Fire-safe polymers are polymers that are resistant to degradation at high temperatures. There is need for fire-resistant polymers in the construction of small, enclosed spaces such as skyscrapers, boats, and airplane cabins. In these tight spaces, ability to escape in the event of a fire is compromised, increasing fire risk. In fact, some studies report that about 20% of victims of airplane crashes are killed not by the crash itself but by ensuing fires. Fire-safe polymers also find application as adhesives in aerospace materials, insulation for electronics, and in military materials such as canvas tenting.
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.
Nylon 46 is a high heat resistant polyamide or nylon. DSM is the only commercial supplier of this resin, which markets under the trade name Stanyl. Nylon 46 is an aliphatic polyamide formed by the polycondensation of two monomers, one containing 4 carbon atoms, 1,4-diaminobutane (putrescine), and the other 6 carbon atoms, adipic acid, which give nylon 46 its name. It has a higher melting point than nylon 6 or nylon 66 and mainly used in applications which must withstand high temperatures.
