A fibre which is very important. It is known for its light weight, high strength, and high stiffness that is commonly produced by pyrolysis of an organic precursor fiber (often polyacrylonitrile (PAN) or rayon) in an inert atmosphere. More background information defined on Wikipedia, click here.

Catalyst
A special chemical that increase the kinetics / rate of a chemical reaction without itself undergoing change in composition or becoming a part of the molecular structure of the product. In thermoset processing, it is a chemical that speeds up the cure of a compound when added in a small quantity when compared to the amounts of reactants.

CFRP
CFRP stands for Carbon fiber-reinforced plastic, among which Carbon Reinforced Epoxy Resin. Carbon Reinforced Epoxy Resin is still one of the best materials available in terms of mechanical properties and permeability/chemical stability. Go to discussion forum for more information on service life of CFRP.


Chemical Sizings
A special adhesive applied to fibres, to improve the binding between the fibre and the polymer matrix of the composite. Chemical sizings substantially improve the mechanical properties of the composite also when exposed to chemicals. On the other hand, they are often slowly hydrolysed by water, causing composite ageing and fatigue, limiting their operational life.

Coating - diffusion and chemical resistance
In coated equipment, permeation can result in: (1) failure of the substate from corrosive attack, (2) bond failure and blistering, resulting form the accumulation of fluids at the bond, when the substrate is less peremeable than the coating, or form corrosion/reaction products if the substrate is attacked by the permeant, (3) loss of contents through the substrate and liner as a result of eventual failure of the substrate. In unbonded coatings it is important that the specie between the coating and support member be vented to the atmosphere, not only to allow minute quantities of permeant vapours to escape, but also prevent expansion of entrapped air from collapsing the coating. In the coating material selection process, a rigid analysis of service life by using service life prediction simulation is of major importance. Go to discussion forum for integrated material knowledge on diffusion and chemical resistance of the borad and diverse range of available coatings.

Composite
A homogeneous material created by the synthetic assembly of two or more materials (a selected filler or reinforcing elements and compatible matrix binder) to obtain specific characteristics and properties. Composites are subdivided into classes on the basis of the form of the structural constituents; Laminar - Composed of layer or laminar constituents; Particular -The dispersed phase consists of small particles; Fibrous -The dispersed phase consists of fibers; Flake -The dispersed phase consists of flat flakes; Skeletal -Composed of a continuous skeletal matrix filled by a second material. Composites or multilayer materials are in the first place produced because of their specific combination of diffusion, chemical and mechanical properties. Composite failure or a shorter than expected operational material service life is usually caused by the lack of integral approach regarding diffusion (permeability), corrosion resistance and mechanical properties. The complexity of some of modern composites / multilayer materials require advanced simulation programmes and usually addtional laboratory experiments.

Compression Molding
A special technique for molding thermoset resins, but also plastics, in which a part is shaped by placing the fiber and resin into an open mold cavity, closing the mold, and applying heat and pressure until the material has cured or achieved its final form.

Compressive Strength
The maximum compressive stress a material is capable of sustaining. For material that do not fail by a shattering fracture, the values is arbitrary, depending on the distortion allowed.

Corrosion of Polymers & Composites
Corrosion of metallic materials takes place via an electrochemical reaction at a specific corrosion rate. Consequently, the life of a metallic material in particular corrosive environment can be accurately predicted. Corrosion of polymers and composites is caused by diffusion, chemical reaction, the nature of the laminate and in the case of thermoset resin: the cure. Improper or insufficient cure time will adversely affect the corrosion resistance, while proper cure time and procedures will generally improve corrosion resistance. Composite failure or accelerated composite ageing is usually caused by lack of integral approach to the diffusion (permeation, solubility, swellig etc.), corrosion resistance and mechanical properties. The complexity of modern composites / multilayer materials require advanced simulation programmes and usually additional laboratory experiments. Go to discussion forum for more free information.

Corrosion Fatigue
Fatigue aggravated by corrosion, as in parts repeatedly stressed while exposed to a corrosive environment.

Coupling Agent
Any chemical substance designed to react with both the reinforcement and matrix phases of a composite material to form or promote a stronger bond at the interface; a bonding link. Coupling agents in composites and multilayer materials are often key in the improved material properties regarding mechanical properties, chemical resistance and permeability properties that are expected from the combination of the materials.

Crosslinking
The composition of covalent chemical bonds between polymer chains. Polymers that are crosslinked are called thermosets. The crosslinkig process is often driven by temperature; the longer the cure temperature is established, the better the degree of crosslinking. Styrene monomer is a crosslinking agent in polyester and vinyl ester polymers. Materials that have crosslinks can still swell - as a results of absorption/diffusion of a chemical - to a signifcant extend without solving in the solvent (think of vulcanized rubbers).

Creep
Creep is a change of material dimensions that occurs over time when a material is subjected to a constant stress at constant temperature. Related: stress relaxation.

CTFE (Chorotrifluoroethylene)
Chlorotrifluorethylene is a thermoplastic fluorocarbon. Go to discussion forum for diffusion, chemical resistance and mechanical properties of Chlorotrifluoroethylene (CTFE).

Cure
To change the properties of a thermosetting resin irreversibly by chemical reaction, i.e., condensation, ring closure, or addition. Cure may be accomplished by addition of curing (cross-linking) agents, with or without catalyst, and with or without heat. The cure process influences the mechanical properties such as heat deflection temperature, the diffusion and solubility characteristics and chemical resistance properties to a significant extend. In many circumstance accelerated ageing / short operational service life of vinyl ester and epoxy resins are not due to the inherent material properties but due to insufficient cure by the pipeline manufacturer, coating/lining manufacturer etc. (very often caused by difficult real life conditions and unrealistic business deadlines).

ECTFE is a 1:1 alternating thermoplastic copolymer of ethylene and chlortrifluorethylene. The polymer possesses excellent chemical resistant, a broad use temperature and excellent abrasion resistance. Visit the discussion forum for more permeability, chemical resistance rate and mechanical information on Ethylenechlorotrifluoroethylene -ECTFE

E-Glass
A borosilicate glass; the type most used for glass fibers for reinforced plastics; suitable for electrical laminates because of its high resistivity.

ETFE (Ethylenetetrafluorethylene - fluoro polymer)
ETFE is a thermoplastic alternating copolymer of ethylene and tetrafluorethylene. ETFE is a rugged thermoplastic with an outstanding balance of properties. Go to the discussion forum for more on Ethylenetetrafluorethylene -ETFE.

Elongation at Break
The increase in the length of a tension specimen, usually expressed as a percentage of the original length of the specimen.

Epoxy Plastic
Epoxy based thermoset resins are the most widely and versatile thermosets. They dominated the reinforced pipelines field until the introduction of vinyl esters and they are still widely used. Epoxy resins, possibly reinforced with glass and carbon reinforced, can be used in many engineering applications, such as structural materials, adhesives, coating applications, moulded equipment, such as pultrudates. Their versatility is possible because of the wide range of chemical, diffusion and mechanical properties that can be achieved by adjusting the formulation. A large variety of epoxy thermosets and thermoplasts, chemical modifiers, and curing agents are available, which allows tailor made epoxy systems meeting the requirement of the industrial application.

The novolac epoxy resin are another class of epoxy resins. They are manufactured by a chemical reaction of novolac resin, usually formed by the reaction of phenol / o-creso and formaldehyde with epichlorohydrin. The resulting novolac epoxy resins are applied in package for electronic equipment, seals for electronic equipment and equipment that requires superior thermal properties and zero or very low chemical corrosion rates

Epoxy resins need to be cured by cross-linking agents (hardeners) or catalysts to otbained the required mechanical, permeability and chemical resistance characteristics. Cross-linking goes via the epoxy and hydroxyl groups, which are the reaction sites. Useful cross linking agents are amine chemicals, anhydrides, aldehyde condensation products, and Lewis acid catalysts. In order to achieve a balance of application properties and initial handling characteristics, careful selection of the appropriate curing agent is required. The primary types of curing agents are aromatic amines, aliphatic amines, catalytic curing agents, and acid anhydrides.

The epoxy resin family exhibits good resistance to alkalies, nonoxidizing acids and many solvents. Epoxy resins find many application in the chemical processing industry as piping, scrubbers and reaction vessels. The epoxy mateiral is also broadly used in electronic packaging, sealing and adhesives field because of so many different formulations which are possible. They range from flexible to rigid in the cured state and from thin liquids to thick pastes and molding powders in the uncured state.

Visit the discussion forum for knowledge on the physical properties regarding Epoxy Resins and its curing agents. More background information defined on Wikipedia, click here.


Exotherm
The liberation or evolution of heat during the curing of a plastic product.

Fatigue
The fracture of a material under many repititions of a stress at a level considerably less than the ultimate strength of a material.

Fiber
A general term used to refer to filamentary materials. Often, fiber is used synonymously with filament. Glass and carbon fibres are apart from conductivity reasons usually applied for improvement of mechanical properties. However, diffusion and chemical resistant properties are often influenced in a negative sense.

Fiber Diameter
A term used to denote the diameter of continuous glass filaments. Their diameter can vary depending on the purpose for which they are to be used. Can be expressed in letter designation, microns or inches.

Fiber Reinforced Plastics (FRP)
A general term for composite materials or parts that consist of a resin matrix that contains reinforcing fibers such as glass or fiber and have greater strength or stiffness than the resin. FRP is most usually used to denote glass fiber-reinforced plastics.

Fick's Law
See Wikipedia, the free encyclopedia for a proper description of Fick's law fo diffusion.
Click here.

Filament
The smallest unit of a fibrous material. The basic units formed during drawing and spinning, which are gathered into strands of fiber for use in composites. Filaments usually are of extreme length and very small diameter, usually less than 25 micron. Normally filaments are not used individually. Some textile filaments can function as yarn when they are of sufficient strength and flexibility.

Filler
A relatively inert substance added to a material to alter its physical, mechanical, thermal, electrical, and other properties or to lower cost or density. Sometimes the term is used specifically to mean particulate additives. Fillers influence solubility and diffusion coefficients of small molecules negatively, wheras the solubility and diffusivity of larger molecules improves (in the sense that permeability of large molecules reduces).

Flexural Modulus
The ratio, within the elastic limit, of stress to the corresponding strain. See also Young's Modulus

Flexural Strength
The strength of a composite material in bending expressed as the tensile stress of the outermost fibres of a bent special fabircated test samples at the instant failure. See also Young's Modulus

FRP
A commonly used acronym for fiber glass-reinforced or fiber reinforced plastic, polymer or polyester. In Germany the term GRP, Glass Reinforced Plastic is also used.

The dimensionless number derived from the effective increase in depth of impression as the load on a penetrator is increases from a fixed load to a high load and then returned to the minimum load.

Hybrid
A composite laminate comprised of laminates of two or more composite material systems, e.g., graphite and glass. It also applies to woven fabrics having more than one type of fiber.

Example of a hybrid composites are poly urethane - vinyl ester system (improved mechanical properties, such as tensile strength at break and interlaminair shear strength, this at the expense of specific chemical resistance properties) or a polydimethylsiloxane - polyphenylene sulfide composite (more flexibility at the expense of cast pps-water permeability properties). Learn more on hybrid resins via our discussion forum: you can post any question or remarks regarding for example polyurethane vinyl ester resins.

A composite made by bonding together two or more layers of different composite materials. Primarily means a composite material system made with different layers of fiber reinforcement in a resin. However, it is sometimes used as a general reference for composites or multilayer material, regardless of how made. Examples of usage laminate consumption by market, compression-molded laminate.

Low-Pressure Molding
Distributing uniform low pressure (14 bar or less) over a resin-bearing fibrous assembly of cellulose, glass, asbestos, or other material, with or without application of heat from external source, to form a structure possessing definite physical properties.

Lining - diffusion and chemical resistance
An additional layer on top of a susbtrate. Usually applied for permeation and corrosion resistance improvement. Examples are epoxy coating on corroded pipelines, vinyl ester gelcoats on yachts, pipeline field joints often also contain a lined area of e.g. polyurethane on carbon steel, ETFE lining on carbon steel tank for in case of corrosive media.

Prior to application of a lining, we always advice to carry out diffusion and corrosive attack analysis. Since in lined equipment, permeation can result in: (1) failure of the substate from corrosive attack, (2) bond failure and blistering, resulting form the accumulation of fluids at the bond, when the substrate is less permeable than the liner,or form corrosion/reaction products if the susbtrate is attacked by the permeant, (3) loss of contents through the substrate and liner as a result of eventual failure of the substrate. In unbonded linings it is important that the specie between the liner and support member be vented to the atmosphere, not only to allow minute quantities of permeant vapours to escape, but also prevent expansion of entrapped air from collapsing the liner.

Visit the discussion forum for more knowledge on pipe linings etc.

The material in which the fiber reinforcements of a composite system are embedded. Sometimes the volume of the matric is so small, that the function of the matrix is better described as glueing fibres together. Thermoplastic and thermoset resin systems can be used, as well as metal and ceramic.

Maxwell-Stefan
The Maxwell-Stefan equation is named after the two nineteenth century scientists who first derived it. The equation balances the driving force for diffusion - being the chemical potential gradient divided by the gradient in distance - with the friction coefficient multiplied by the mole fraction and diffusion rate of the respective species. The formula is suitable for diffusion calculations beyond the binary diffusion situation, by simply summarizing the friction component of each individual specie in the mixture. Moreover the definition of the driving force allows inclusion of pressure, gravitational, electrical forces. This is a major advantage compared to Fick's first law which is principally only useful for diffusion calculations in case of a concentration gradient. The use of the Maxwell-Stefan equation for simple but also for more complex diffusion problems was described very comprehensively by Wesselingh and Krishna in their book "Mass Transfer in Multicomponent Mixtures". They received the Akzo Nobel Science Award in 1997 for their work.

Metal-Matrix Composites
Materials in which continuous carbon, silicon carbide, or ceramic fibers are embedded in a metallic matrix material.

An example is the fibre-metal-laminate (FML) class, such as Glare or CentrAL. These aerospace materials exhibit excellent ageing characteristics, mainly because of their intrinsic capability to stop impact or ageing crack growth before reaching the critical Griffith crack size. Compared to carbon-epoxy composites, mechanical strength under continuous load from torsion, tensile and flexural stress of an aerospace material such as CentrAL is better. However, the interfacial behaviour of fibre-metal-laminates when exposed to water in varying environmental conditions is very probably less than carbon - epoxy composites. Visit the discussion forum to learn more on metal-metal composites and fibre - metal - laminates (fml). More background information define on Wikipedia, click here.


Mold
The dedicated cavity or matrix into or on which the plastic composition is placed and from which it takes form. To shape plastic parts or finished articles, heat and pressure is applied. Also: the assembly of all parts functioning collectively in the molding fabrication process.

Monomer
A simple or complex molecule which is capable of reacting with like or unlike molecules to form repeating units: a polymer. Also: the smallest repeating structure of a polymer; for addition polymers, this represents the original unpolymerized compound.

All materials are somewhat permeable to chemical molecules, but plastic materials tend to be an order of magnitude greater in their permeability that materals. Gases, vapor or liquids will permeate polymers.

The diffusion coefficient or diffusivity multiplied by the solubility of a chemical at a certain concentration, a certain system temperature and system pressure yields the permeability, permeation or stationay mass flux. Permeability or permeation figures are usually used to select tight or selective composite and multilayer polymer materials. However, the reader is warned that these permeability figures or permeation determinations are never sufficient to use for material selection in real life / processing circumstances. Visit the discussion forum to learn more on permeation in polymer and composite materials.


Peel Strength
Peel strenght is the adhesive bond strength, as in pounds per inch of width, obtained by a stress applied in a peeling mode.

PET
Polyethylene Terephthalate (Thermoplastic Polyester Resin).

Plastic
A material that contains as a basic ingredient an organic substance of large molecular weight, is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow; made of plastic.

Polyacrylonitrile (PAN)
An intermediate product used as a base material in the manufacture of certain carbon fibers.

Polyamide
A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fiber-forming. Polyamides are strong, tough thermoplastics with good impact, tensile and flexural strengths. Polyamide polymers exhibit excellent resistances to a broad range of chemicals and harsh environments. They have good resistance to most inorganic alkalines, particularly ammonium hydroxide and ammonia, even at elevated temperatures, and to sodium and potassium hydroxides at ambient temperatures. They also display good resistance to almost all inorganics salts and to almost all hydrocarbons and petroleum-based fuels. More background information defined on Wikipedia, click here.

Polycarbonate
Polycarbonates have a high impact strength, being several times higher than that of other enigeering polymers. They are tough, rigid, and dimensionally stable. Polycarbonate is resistant to aliphatic hydrocarbons and weak acids. Polycarbonate will be attacked by strong alkalies and strong acids, and is soluble in ketones, esters, aromatic and chlorinated hydrocarbons. Polycarbonate is not affected by UV light and has excellent weatherability.

Polyesters
Thermosetting resins, produced by dissolving unsaturated, generally linear, alkyd resins in a vinyl-type active monomer such as styrene, methyl styrene, and diallyl phthalate. Cure is effected through vinyl polymerization using peroxide catalysts and promoters, or heat, to accelerate the reaction. The resins are usually furnished in solution form, but powdered solids are also available.

Polyetherether Ketone(PEEK)
PEEK is a linaer polyaromatic thermoplast. PEEK exhibits good tensile strengths and creep properties. This makes it an appropriate material when high loadings for longer periods at high temperatures without deformation is a requirement. PEEK is resitant to water, insoluble in all common solvents and has excellent resistance to a wide range of organic and inorganic solvents. Visit the discussion forum to learn more on chemical, permeability and mechanical properties of Polyetherether Ketone (PEEK).

Polyether Sulfone (PES)
Polyether sulfone is a high-temperature engineering termoplastic with the combined characteristics of high thermal stability and mechanical strength. PES is a tough material but is sensitive to notches. PES has excellent reistance to aliphatic and some chlorinated hydrocarbons and aromatics. It is also resistant to most inorganic chemicals. Polyether sulfone will be attacked by strong oxidizing acids. Moreover PES is soluble in high polar solvents and is subject to stress cracking in ketones and esters. Since it is susceptible to degradation by UV light, the polymer does not have good outdoor weathering properties.

Polyethylene
Polyethylenes are probably among the best known thermoplasts. Polyethylene is produced in various grades that differ in molecular structure, crystallinity, molecular weight, and molecular distribution. Physical and mechanical properties differ in density and molecular weight. The three main classifications are low, medium and high. The specific gravity ranges are 0.91 to 0.925, 0.925 to 0.940 and 0.940 to 0.965. Generally, the higher the density, the better the dimensional stability and physical properties, particularly as a function of temperature. The thermal stability of polyethylenes ranges from 88 to 121 degrees Celsius for the high-density material. Toughness is maintained to low negative temperatures. Industry practive breaks the molecular weight of polyethylenes into four distinct classifications which are medium molecular weight (less than 100.000), high molecular weight (110.000 to 250.000), extra high molecular weight (250.000 to 1.500.000) and ultra high molecular weight (1.500.000 and higher). Usually the ultrahigh molecular weight material has a molecular weight of at least 3.1 million. Polyethylene exhibits a wide range of corrosion resistance, ranging from potable water to corrosive wastes. It is resistant to most mineral acids, including sulfuric up to 70% concentration, inorganic salts including chlorides, alkalies and many organic acids. It is not resistant to bromine, aromatics or chlorinated hydrocarbons. Polyethylene is subject to degradation by UV radiation. If exposed outdoors, carbon black must be added to the fromulation for portection against UV degradation. More background information define: Wikipedia, click here.

Polyimide
Polyimides are hetrocylic polymers having an atom of nitrogen in one of the reins in the molecular chain. Polyimides exhibit outstanding properties resulting from their combination of high-strength temperature stability up to 260-315 degrees Celsius in continuous service and 482 degrees Celsius for intermediate use. Polyimides alos have a very low coefficient of friction, which can be further improved by use of graphite or other fillers, have excellent electrical and mechanical properties that are relatively stable from low negative temperatures to high postive temperatures, dimensional stability (low cold flow) in most environments, very low outgassing in high vacuum, and excellent resistance to ionizing radiation.

Polyimides have excellent chemical and radiation intertness and are not subject to UV degradation. High oxidative resistance is another important property. Polyimides find applications in the automobile industry. Other applications include bearings, compressors, valves, membranes for medical application, co2 membrane and pistion rings.

Polyphenylene Sulphide (PPS)
Polyphenylene Sulphide is an engineering polymer capable of use at elevated temperatures. PPS has a symmetrical rigid backbone chain consisting of recurring para-substituted rings and sulfur atoms. PPS is noted for its high stiffness and good retention of mechanical properties at elevated temperatures. At normal ambient temperatures, unfilled PPS is a hard material with high tensile and flexural strengths. When the polymer is glass filled, appreciable increases in these properties are realized. Tensile strengths and flexural modulus decrease as the temperature increases, levelling off at approximately 260 degrees Celsius. As the temperature increases, there is an increase in elongation and a corresponding increase in toughness. Long term exposure in air at 230 degrees Celsius has no effect on the mechanical properties of PPS. The polymers is nonflammable. PPS cannot be thermally fused or sovlent semented. Joining must be by adhesive bonding. Surface to be joined must be solvent cleaned and abraded. Recommended adhesives include epoxies and urethanes.

PPS has exceptional chemical resistance. It is resistant to aqueous inorganic salts and bases and many inorganic solvents. Relatively few materials react with PPS at high temperatures. It can also be used under highly oxidizing conditions. Chlorinated solvents, some halogenated gases, and alkkyl amines will attack PPS. It stress cracks in the presence of chlorinated solvents. Weak and strong alkalies have no effect. PPS has good resistance to UV ligh degradation whcih can be increased by formulating it with carbon black.

In the automotive industry, PPS molded components are used in electrical, fuel handling, and emmision control systems. The chemical processing industry makes use of PPS in valve and pump components as well as other industrial applications. Go to forum to learn more on chemical, permeability and mechanical properties of Polyphenylene Sulphide (PPS). More background information defined on Wikipedia, click here.

Polymer
A very large molecule formed by combining a large number of smaller molecules, called monomers, in a regular pattern.

Polymerization
A chemical reaction in which the molecules of monomers are linked together to form polymers.

Polysulfone (PSF)
Polysulfone is an engineering polymer which can be used at elevated tempetures. PSF has high tensile strength and stress-strain behaviour which is typical of that found in a ductile material. In addition, as temperatures increase, flexural modulus remians high. These resins also remain stable at elevated temperature resisting creep and deformation under continuous load. PSF has an operating temperature range of from -101 to 149 degrees Celsius. Thermal gravimetric analysis shows that PSF is table in Air up to 500 degrees Celsius. PSF also exhibits excellent electrical properties that remain stable over a wide temperature range up to 177 degrees Celsius. PSF can be joined by solvent cementing, thermal fusion, and adhesive bonding. Methylene Chloride is used to solvent cement PSF while epoxy adhesives are used for adhesive bonding. No special surface treatment is required.

Polysulfone is unaffected by hydrolysis and has a very high resistance to mineral acids, alkali and salt solutions. PSF is not resistance to polar organic solvents such as ketones, chlorinated hydrocarbons and aromatic hydrocarbons. PSF has compared to other polymers, a high permeability for gases like hydrogen, helium and other noble gases. PSF has good weatherability and is not degraded by UV radiation. Polysulfone finds application as hot-water piping, lenses, iron handles, switches and circuit breakers. Its rigidity and high temperature performance make it ideal for medical, microwave and electronic application.

Visit the discussion forum to learn more on properties of Polysulfone (PSF). More background information define on Wikipedia, click here.

Polyvinylchloride (PVC)
Polyvinylchloride is probably the most commonly used of any of the thermoplasts. PVC is polymerized vinyl chloride, which is produced from ethylene and anhydrous hydrochloric acid. PVC is stronger and more rigid than other general purpose thermoplastic materials. It has high tensile strength and Young modulus of elasticity. Two types of PVC are produced, normal impact (type 1) and high impact (type 2). Type 1 is a rigid unplasticized PVC having normal impact with optimum chemical resistance. Type 2 has optimum impact resistance and reduced chemical resistance. It is modified by the addition of styrene-butadiene rubber which improves notch toughness and impact strength. PVC's are basically tough and strong, resist water and abrasion, and are excellent electrical insulators. Special tougher types are available to provide high wear resistance. In general PVC will withstand continuous exposure to temperatures ranging up to 54 degrees Celsius. PVC can be plasticized and glass filled, dependnent on its application.
Type 1 PVC (unplasticized) resists attack by most acids and strong alkalies, gasoline, kerosene, aliphatic alcohols, and hydrocarbons. It is particularly useful in the handling of hydrochloric acid. The chemical resistance of type 2 PVC to oxidizing and highly alkaline material is reduced. PVC may be attacked by aromatics, chlorinated organic compounds, and lacquer solvens. PVC is resistant to normal atmospheric pollutants including wheather and UV degradation.
The primary applications for PVC include water, gas, vent, drain and corrosive chemical piping, electrical conduit, and wire insulation. It is also used as a liner. Visit the discussion forum to learn more on properties of Polyvinylchloride.

Polytetrafluorethylene (PTFE)
PTFE is a relatively weak material and tends to creep under stress at elevated temperatures. The mechanical properties can be improved by the addition of glass or carbon fibres. Regarding corrosion resistance properties it must be noted that PTFE is chemically inert to most chemicals. Only the most violent oxidizing and reducing agents are capable to corrode PTFE. Furthermore Fluorine and related compounds are absorbed into PTFE to a problematic extent. PTFE has excellent weathering properties and is not degraded by UV.

Polyurethane Resins (PU)
Polurethane reins are reaction products of isocyanates, polyols and curing agents. Because of the hazards involved in handling free isocyanate, prepolymers of the isocyanate and the polyol are generally used in casting. Polyurethane can be formulated to produce a range of materials from elastomers as soft as Shore A of 5 to tough solids with a Shore D of 90. Polyurethane thermosets can be rigid or flexible depending on the formulation. The flexible ones have better toughness and are often used a foamed parts.

Polyurethane is resistant to most mineral and vegetable oils. They are also resistant to greases, fuels, aliphatic, and chlorinated hydorcarbons. This makes there materials particularly suited for service in contact with lubricating oils and automotive fuels. Aromatic hydrocarbons, polar sovents, esters and ketones will attack polyurethane.

Nowadays polurethane resins are combined with vinyl ester resins, obtaining a so called hybrid resin or thermosetting urethane resin. Major reason is improvement of the impact or flexural characteristics of the vinyl ester resin. At the same time mechanical properties are improved. This at the cost of chemical resistance properties and water diffusion resistance charactertistcs compared to cast vinyl ester resin.

Go to discussion forum to learn more on physical and chemical resistance properties of Polyurethane Resins. More background information defined on Wikipedia, click here.

Polyvinylidene Fluoride (PVDF - fluoropolymer)
PVDF is similar in chemical structure to PTFE except that it is not fully fluorinated. Much of the strength and chemical resistance of PVDF is maintained through an operating range of -40 to 160 degrees Celsius. It has high tensile strength and heat deflection temperature and has a low permeation of gases. The abrasion resistance of PVDF is at a level comparable with that of Polyamide and Ultrahigh Molecular Weight Polyethylene (UHMWPE), which places it among the best materials in this regard. PVDF is chemically resistant to most acids, bases and organic solvents. It is also resistant to wet or dry chlorine, bromine and other halogenes. It should not be used with strong alkalies, fuming acids, polar solvents, amines, ketones and esters. When used with strong alkalies, it stress cracks. Polyvinylidene fluoride also withstands UV light in the "visible" range. More background information defined on Wikipedia, click here.

Porosity
The presence of visible voids within a solid material into which either air or liquids can pass.

Post-Cure
Additional elevated temperature cure, usually without pressure, to improve final properties and/or complete the cure. In certain resins, complete cure and ultimate mechanical properties are attained only by exposure of the cured resin to higher temperatures than those of curing.

Recovery is the degree to which a polymer returns to its original shape after a load is removed.

Resin


Resin-Transfer Molding (RTM)


Roving
Roving is a number of yarns, strands, tows, or ends collected into a parallel bundle with little or no twist. Often related to Woven Roving.

A family of magnesium-alumina-silicate glasses with relative high mechanical strength.

SAN
Styrene Acrylonitrile (Thermoplastic Resin).

Shear
A mechanical action or stress resulting from applied forces which causes or tends to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their plane of contact. Inter laminar Shear (ILS). The plane of contact is composed of resin only.

Shear Strength
The ultimate shear stress that a material is capable of sustaining. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original cross-sectional area of the specimen.

Shelf Life
The length of time a material, substance, product, or reagent can be stored under specified environmental conditions and continue to meet all applicable specification requirements and/or remain suitable for its intended function.

Silicon Carbide Fiber
A fiber used for matrix reinforcments, with high strength and modulus; density is equal to that of aluminum. It is used in organic metal-matrix composites.

Sizings
The treatment applied to the glass fiber to allow the resin, polymer or other susbtrates, and glass to adhere to one another. Also allows glass fiber to be conveniently handled.

Specific gravity
The ratio of the weight of any volume to the weight of an equal volume of some other substance taken as standard at the stated temperature and system pressure. For polymers, the standard is water.

Storage Life (Shelf Life)
The period of time during which a liquid resin or packaged adhesive can be stored under specified temperature conditions and remain suitable for use. (Also 'shelf life.')
See also - Shelf life. Visit the discussion forum to post your question with regard to shelf and service life.

Stress Relaxation
Stress relaxation is the gradual decrease in stress at a constant temperature. Stress relaxation occurs as a result of the same polymer chain slippage found in creep. Related: creep.

Force per unit area (MPa or psi) that is required to break a material in such a manner is the ultimate tensile strength or tensile strength at break. The rate at which a sample is pulled apart in a test set-up can range from 0.2 to 20 inches per minute and this will influence the results (!). The analogous test to measure tensile properties according to the ISO quality system is ISO 527. The values reported in the ASTM D638 and ISO 527 tests in general do not vary significantly and either test will provide good results early in the material selection process. Separate tensile test methods are commonly applied to polymer films (ASTM D882) and elastomers (ASTM D412).

In the previously described set-up, the force required to break the material is determined. This is in contrast to toughness, which is a measure of energy required to break a material.

Tensile strength alone should not be used to determine the ability of a polymer to resist deformation and retain form. Other mechanical properties such as elasticity, creep, ductility, hardness and toughness must also be taken into account.

Go to discussion forum to learn more on physical properties of construction materials for - for example - civil and chemical industry applications.

Thermoplastic
Thermoplastics account for alomsot 92 weight percent of the processed polymers. They are polymers which becomes soft and fluid upon heating and can then be transformed into any desired shape, whcih is stabilized by subsequent cooling. This cycle can be repeated and permits recylcing of thermoplastic articles. This behaviour is a consequence of the absence of chemical crosslinks in these polymers, even after processing as a melt.

Thermal Expansion, coefficient of
The ability of the composite material to conduct heat; a physical constant for the quantity of heat that passes through a unit cube of a material in a unit of time when the difference in temperature of two faces is 1 degrees Celsius.

Thermoset
These resins consists of a mixture of reactive low molar mesaa compounds, which react with each other upon heating and then transform form a fluid into a solid material owing to crosslinking or curing. So, here the polymer is just formed in the mould and the product cannot be melted or dissolved any more as it consists of one giant network molecule. This means that, contrary to thermoplastics, articles of cured thermoset cannot be recycled in a simple way and have to be shaped in a single, discontinuous step by compression or injection moulding. Vulcanized rubbers or synthetic elastomers are only weakly crosslinked, in oder to preserve elasticity, but they are neither meltable nor soluble. In a proper solvent they only swell. In fact, these materials can be considered as thermoplastics before crosslinking and as thermosets afterwards.

The vinyl ester class of resins was developed during the late 1950s and early 1960s. Vinyl esters were first used as dental fillings. They had improved toughness and bonding ability over the acrylic materials that were being used at the time. Over the next several years, changes in molecular structure of the vinyl esters produced resins that found extensive use in corrosion resistant equipment. Present day, vinyl esters possess several advantages over unsaturated polyesters. They provide imporved toughness in the cured polymer while maintaining good thermal stability and physical properties at elevated temperatures. This improved toughness permits vinyl ester resins to be used in castings, as well as in reinforced products.

Vinyl ester resins are also available in halogenated modifications for ductwork and stack construction where fire retardance and ignition resistance are major concerns. Vinyl esters have a number of basic advantages, among which are:

- They cure rapidly and give high eraly strength and superior creep resistance as a result of their molecular structure.

- Vinly esters have slightly higher strenghts than polyesters, bit not as high as heat-cured epoxies.

-The chlorendic and bisphenol polyester resins have low elongation, and are essentially brittle resins, but vinyl ester resins run higher. This indicates better impact resistance and greater tolerance to cyclic temperatures, pressure fluctuations, and mechanical shocks. This results in a tough laminate that is resistant to cracking and crazing.

-Because of the basic structure of the vinyl ester molecule, it is more resistant to hydrolysis and oxidation or halogenation than the polyesters.

In order to have maximum retention of physical properties at elevated temperatures, the upper limit should be approximately 107 degrees Celsius. Exceptions to this are vinyl ester resins having a novolac backbone. These resins canbe used at 163 - 177 degrees Celsius. Flexural modulus, such as important for automotive body parts applications, must be examined at all elvated temperatures.

In general, vinyl esters can be used to handle most host, highly chlorinated, and acid mixtures at elevated temperatures. They also provide excellent resistance to strong mineral acids and bleaching solutions. Vinyl ester excell in alkaline and blech enivronments and are used extensively in the very corrosive conditions found in pulp and paper industry. Furthermore vinyl ester laminates find application in industrial equipmentt and scrubbers such as absorption towers, process vessels, sotrage tanks, piping, hood sxcrubbers, ducts and exhaust stacks, all handling highly corrosive chemicals.

Go to discussion forum to learn more on vinyl ester composites in industrial applications. More background information define on Wikipedia, click here.

Void

A physical and mechanical discontinuity occurring within a material or part which may be two-dimensional (e.g., disbonds, delaminations) or three-dimensional (e.g., vacuum-, air-, or gas-filled pockets). Porosity is an aggregation of micro-voids. Voids are essentially incapable of transmitting structural stresses or nonradiative energy fields. (See Inclusion.) Voids are only in specific cases a problem regarding diffusion, chemical resistance and mechanical properties.

The ratio of the weight of water absorbed by a material to the weight of the dry material, expressed as a percentage. Many polymers are hygroscopic, meaning that over time they absorb water. Through a process called hydrolysis, water in a polymer severs the polymer chains, reduces the molecular weight, and decrease mechanical properties. Longer exposure at elevated temperature and/or loads increase hydrolytic attack. Water absorption can also change the physical properties of polyamides without degradading them. Some polyamides absorb large amounts of water causing them to swell. As the moisture contact increases, other mechanical and electrical properties may also change. These changes are reversible. When the polyamide is dried, the mechanical properties return to their original values.
Water absorption is because of the nature of this small molecule very often important in the integral analysis of diffusion, chemical and mechanical properties of the polymer, composite or multilayer material. Material failure, defects and accelerated operational ageing are in many cases caused by water, acadic water, alkaline water or salt water.

Go to forum to learn more about water absorption in all sorts of plastic, coating, rubber and laminate materials.

Wetting
Wetting is the effective contact area between a substance and a surface, when the two are brought into contact. The degree of wetting depends on the mutual surface tensions.

Working Life
The period of time during which a liquid resin or adhesive, after mixing with catalyst, solvent, or other compounding ingredients, remains useful for the objected chemical reaction.

Woven Roving
Ths is a relatively heavy glass fibre fabric made by weaving of roving. Woven roving usually takes a considerable amount of volume in a glass or carbon reinforced composite, for example 35 volume percent, being easily around 60 wieght percent of weight (due to the difference in matrix and glass densities) Because the glass is impermeable for molecules, the dimensional change accompanying extensive uptake is limited by the presence of woven roving reinforcement. Moverover the diffusion path in increased for larger non polar molecules.