Continuous Glass Fiber

Nearly all continuous glass fibers are made by a direct draw process and formed by extruding molten glass through a platinum alloy bushing that may contain up to several thousand individual orifices.

From: Inorganic and Composite Fibers , 2018

Introduction

Valery V. Vasiliev , Evgeny V. Morozov , in Advanced Mechanics of Composite Materials and Structures (Fourth Edition), 2018

Continuous glass fibers (the first type of fibers used in advanced composites) are made by pulling molten glass (at a temperature about 1300°C) through 0.8–3.0  mm diameter dies and further high-speed stretching to a diameter of 3–19   μm. Usually, glass fibers have solid circular cross-sections. However, there exist fibers with rectangular (square or plane), triangular, and hexagonal cross-sections, as well as hollow circular fibers. The important properties of glass fibers as components of advanced composites for engineering applications are their high strength, which is maintained in humid environments but degrades under elevated temperatures, relatively low stiffness (about 40% of the stiffness of steel), high chemical and biological resistance, and low cost. Being actually elements of monolithic glass, the fibers do not absorb water and do not change their dimensions in water. For the same reason, they are brittle and sensitive to surface damage.

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Investigation of mechanical testing on hybrid composite materials

Mohd Hafizal Hamidon , ... Ahmad Hamdan Ariffin , in Failure Analysis in Biocomposites, Fibre-Reinforced Composites and Hybrid Composites, 2019

7.1.1 Glass fibers

Nearly all continuous glass fibers are made by a direct draw process and are formed by extruding molten glass through a platinum alloy bushing that may contain up to several thousand individual orifices, each being 0.793–3.175  mm in diameter [11]. Glass fibers and a resin matrix are needed by each other. Though the glass fibers themselves are quite strong, they are still vulnerable to damage. Meanwhile, certain plastics are relatively weak but still versatile and tough. Thus combining these two materials will produce a material that is strong, lightweight, and corrosion resistant. Glass fiber is known as a good reinforcement in high performance composite applications due to its combination of good properties and low cost.

Glass fiber has an amorphous structure, which means its properties are the same along the fiber and across the fiber [12]. By varying the amount of raw materials and the processing parameters, different types of glass can be produced. There are differences in composition within the glass type because of the available glass batch raw materials, or from the different environmental constraints at the manufacturing site, or in the melting and forming processesas shown in Table 7.3. However, these fluctuations do not have a significant effect on the physical and chemical properties of the glass type Table 7.3.

Table 7.3. Classification of Glass fibers [15]

Letter designation Characteristic
A, alkali Used when the strength, durability, and good electrical resistivity of E-Glass are not required
C, chemical Chemical stability in corrosive acid environments
D, dielectric Low dielectric constant for electrical applications
E, electrical High strength and high electrical resistivity
ECR, Calcium aluminosilicate High strength, electrical resistivity, and acid corrosion resistance
AR, Alkali resistant Used in cement substrates and concrete
R, reinforcement Reinforcement where added strength and acid corrosion resistance are required
S, strength High strength, modulus, and stability under extreme temperature and corrosive environments

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Design and Applications

D.D.L. Chung , Carl Zweben , in Comprehensive Composite Materials, 2000

6.38.2.1 Polymer–Matrix Composites with Continuous Fillers

Epoxy–matrix composites with continuous glass fibers and made by lamination are most commonly used for printed wiring boards, due to the electrically insulating property of glass fibers and the good adhesive behavior and established industrial usage of epoxy. Aramid (Kevlar) fibers can be used instead of glass fibers to provide lower dielectric constant ( Zussman et al., 1992). Alumina (Al2O3) fibers can be used for increasing the thermal conductivity (Bolt and French, 1988). By selecting the fiber orientation and loading in the composite, the dielectric constant can be decreased and the thermal conductivity can be increased (Bolt et al., 1989). By impregnating the yarns or fabrics with a silica-based sol and subsequent firing, the thermal expansion can be reduced (Mukherjee et al., 1992). Matrices other than epoxy can be used. Examples are polyimide and cyanate ester (Zussman et al., 1992).

For heat sinks and enclosures, conducting fibers are used, since the conducting fibers enhance the thermal conductivity and the ability to shield EMI. EMI shielding is particularly important for enclosures (Glatz et al., 1992a). Carbon fibers are most commonly used for these applications, due to their conductivity, low thermal expansion, and wide availability as a structural reinforcement. For high thermal conductivity, carbon fibers made from mesophase pitch (Bertram et al., 1992; Brookstein and Maass, 1994; Fleming and Riley, 1993; Fleming et al., 1995; Ibrahim, 1992; Kiuchi et al., 1998; Spicer et al., 1999) or copper plated carbon fibers are preferred (Foster, 1989a, 1989b; De La Torre, 1992). For EMI shielding, both uncoated carbon fibers (Wienhold et al., 1998; Luo and Chung, 1999) and metal (e.g., nickel, copper) coated carbon fibers (Morin and Duvall 1998; Lu et al., 1996) have been used.

For avionic electronic enclosures, low density (light weight) is essential for saving aircraft fuel. Aluminum is the traditional material for this application. Carbon fiber reinforced epoxy has been judged by consideration of mechanical, electrical, environmental, manufacturing/producibility, and design-to-cost criteria to be more attractive than aluminum, glass fiber reinforced epoxy, glass fiber reinforced epoxy with an aluminum interlayer, beryllium, aluminum–beryllium, and SiC particle reinforced aluminum (Smaldone, 1995). A related application is thermal management of satellites, for which the thermal management materials need to be integrated from the satellite structure down to the electronic device packaging (Glatz et al., 1992b). Continuous carbon fibers are suitable for this application due to their high thermal conductivity, low density, high strength, and high modulus.

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The use of thermosets in the building and construction industry

D. Song , R.K. Gupta , in Thermosets, 2012

6.6.1 Bridges and other composite applications

Thermosetting polymer–matrix composites, especially those reinforced with continuous glass fibers, are increasingly being used to build all-composite bridges, rebars, highway guardrails, wind turbine blades, utility poles, sound barriers, and dowel bars for joining concrete pavements, among other civil infrastructure systems. The most exciting development in the last 20 years or so has been the design and construction of composite bridge decks, which will make it possible to build bridges having a span longer than that possible with the use of steel and concrete. This is because a bridge made with traditional materials collapses under its own weight when its length exceeds about 6400 feet (1950 m), but composites, which have much larger specific strength and specific stiffness properties, have much smaller 'dead' loads. The basic building blocks of composite bridge decks are lightweight structural shapes, such as the box and multi-cellular sections shown in Fig. 6.8. These are produced by the process of pultrusion in which fiber reinforcements, such as E-glass rovings and fabric, pass continuously through a resin bath, typically vinyl ester, and enter a heated die which shapes the composite and within which the resin cures (Freed et al., 2003). This process is similar to extrusion in that profiles of constant cross-section are produced continuously. The cured composite leaving the die cools in air, passes through pullers, and is then cut to the desired length by a saw. While the design shown in Fig. 6.8 is a fail-safe one, a polymeric adhesive is still used to bond the different sections together, and these sections may also be bolted together with the use of mechanical fasteners. Clearly, the construction of these shapes is modular, and this reduces erection time. Note that, during field implementation, the bridge deck panels are placed perpendicular to the flow of traffic as shown in Fig. 6.9, and these are supported on longitudinal 'stringers' also made of FRPs or steel.

6.8. FRP bridge deck shapes: (a) box; (b) cellular.

6.9. Goat Farm Bridge, Wirt County, West Virginia, USA.

A very common use of FRPs is in the manufacture of industrial storage tanks and process equipment. When corrosive fluids, such as chlorine, bleach, caustic and strong mineral acids, have to be stored and used, one often needs to employ nickel alloy steel or stainless steel with an appropriate coating or lining. A less expensive and more desirable alternative is to use FRPs. Here the FRP matrix is typically bisphenol A epoxy vinyl ester. The addition of novolac functionality to the resin can allow for the increase in service temperature, while the incorporation of bromine in the vinyl ester molecule can endow it with flame retardant properties. In addition, note that government regulations can often spur the development of new replacement materials. Such has been the case with utility poles in the U.S. Currently there are about 130 million such poles in service in the country, and 95% of them are composed of treated wood (Hiel, 2001). Chemical treatment is needed to provide resistance to rot, decay and fungi, but the chemicals commonly used – creosote, copper chromium arsenate and penta-chloro-phenol – are toxic and can potentially contaminate the soil and water. These chemicals have now been phased out, and poles made of FRPs are benefitting from this action (Liang and GangaRao, 2004). Should the use of FRP utility poles become widespread, they will contribute to highway safety and result in a reduction in fatalities resulting from pole–vehicle collisions. This is because FRP poles can be designed to bend and fracture at the base upon impact with an automobile, reducing damage to the vehicle and its occupants. Beyond this advantage, FRP poles have more opportunities to survive during severe weather-induced incidents, which may avoid power outage or other service break (Stewart, 2003). Note that these poles can be designed to be up to 120 feet (37 m) in height and still be economically competitive.

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Fiber-reinforced polymer (FRP) composites in environmental engineering applications

R. Liang , G. Hota , in Developments in Fiber-Reinforced Polymer (FRP) Composites for Civil Engineering, 2013

16.9.4 Product development

Both structural and non-structural applications of recycled PC and ABS polymers, with chopped or continuous glass fiber/fabric reinforcements, have been extensively investigated at WVU-CFC ( Vijay et al,. 2000; Aditham, 2004; Kalligudd, 2010; Chada, 2012). Some of the products developed include: guardrail post, offset spacer block, rectangular grids, rib-stiffened panels, sign posts and sign boards, dowel bars, window panels, and wood plastics composite (WPC). A couple of these products have been field-installed in the highway systems with the approval of West Virginia Department of Transportation (Aditham, 2004).

Recycled polymers are also engineered at WVU-CFC laboratory to manufacture full-scale railroad crossties that use end-of-life railroad wood ties as the core and recycled polymer composite as a shell (Kalligudd, 2010; Chada, 2012). Figure 16.25 shows a recycled GFRP composite railroad tie before and after demolding. These railroad ties have been extensively evaluated under static and fatigue loads in the laboratory (Fig. 16.26), followed by field installation in straight and curved locations and testing under standard locomotive loads (Fig. 16.27). With over 12 million railroad ties being replaced annually in the United States, this green product is being negotiated for mass field implementation (Chada, 2012).

16.25. Manufacturing of recycled GFRP composite railroad ties (Chada, 2012): (a) before demolding; (b) after demolding.

16.26. Recycled GFRP composite railroad tie testing (Chada, 2012): (a) three-point bending test; (b) fatigue test in gravel bed.

16.27. Field testing of recycled GFRP composite railroad ties (256 Kips) on SBVR line in Moorefield, WV (Chada, 2012).

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Composites

Michel Biron , in Thermosets and Composites (Second Edition), 2013

6.4.2 Thermoplastics

It is necessary to distinguish:

•

Short glass fiber reinforcement: the main thermoplastics are proposed in such grades.

•

Mat and continuous glass fiber reinforcements: theoretically all the thermoplastics are usable in these forms, but up to now the developments have concentrated on polypropylenes (PP), polyamides (PA), thermoplastic polyesters (PET); PEEK, polyetherimide (PEI) and polyphenylene sulfide (PPS) are used for high-performance applications. They are presented in a range of forms from stampable sheets to pellets, prepregs, ribbons, impregnated or coated continuous fiber rods. More rarely (as in the case of PA 12, for example), the thermoplastic is provided in liquid form.

The thermoplastics can be classified according to their distribution in:

•

Commodities: polyethylene (PE), PP, PVC, polystyrene (PS).

•

Technical thermoplastics: PA, polyacrylic (PMMA), polyacetal (POM), polycarbonate (PC), polyphenylene oxide (PPO) or polyphenylene ether (PPE), thermoplastic polyesters – PET, PBT. Reinforced cellulosics are scarcely used.

•

Specialty thermoplastics: polysulfone (PSU), PPS, fluoroplastics, PEEK, PEI, polyamide imide (PAI), liquid crystal polymers (LCP).

Advantages versus thermosets: suppression of the condensation or reticulation or polymerization step; easier recycling and welding possibilities but these advantages are often disrupted by the reinforcement. The general properties are those of the basic polymer with a high reinforcement effect.

Drawbacks: reversibility of thermoplasticity for heat applications; lower creep resistance than thermosets; disadvantages of the basic polymer.

Uses

The short glass fiber reinforced grades are used for all sorts of injected parts.

The mat and continuous glass fiber reinforced grades have specific uses:

•

Mass production parts: bumpers, soundproofing shields, cross-pieces, inserts for dashboards, seat frames, containers, welding helmets, ventilator housings, base of lawnmowers, taping of pipes, pipelines, tanks, long fiber reinforced injected parts.

•

Technical products with PEEK, PPS, PEI, etc., matrix for aeronautics and other high-tech applications.

The properties of the main thermoplastics are highlighted below.

Polyethylene (PE)

Advantages

Low cost; easy to process; chemical inertia; good impact strength; low water absorption; low density; high insulating properties even in wet environment; low coefficient of friction; suitable grades for food contact.

Drawbacks

Limited UV resistance; risks of environmental stress cracking; heat and creep sensitivity; low rigidity; high shrinkage, difficult gluing.

Cost

Ranges roughly from U.S. cents 90 up to 110 per lb or €1.5 up to €2 per kg.

Polypropylene (PP)

Advantages

Good mechanical properties at ambient temperature; price; ratio cost/performances; chemical inertia; low absorption of water; low density; good electrical insulating properties even in wet environment; impact and fatigue behavior for suitable grades and stresses; special grades for food contact.

Drawbacks

Risks of sensitivity to UV; limited impact strength of some grades; low-temperature and creep behavior; low rigidity; difficult gluing.

Cost

Ranges roughly from U.S. cents 90 up to 110 per lb or €1.5 up to €2 per kg.

Polyvinyl chloride (PVC)

Mechanical properties are very different according to whether the PVC formulation is rigid or plasticized.

Advantages

Rigid PVC: rigidity at ambient temperature; low cost; chemical resistance except some solvents; possible food contact and transparency; naturally fire-retardant; dimensional stability, easy to weld and stick.

Flexible PVC: characteristics depend broadly on the formulations; flexibility; improved low-temperature behavior; fire-retardant grades; low cost; possible food contact and transparency; easy to weld and stick.

Drawbacks

Environmental standards, regulations and suspicions handicap the development of the PVCs.

Rigid PVC: natural UV sensitivity but special grades benefit from long-time outdoor exposure guarantees; sensitivity to heat, creep, aromatic or chlorinated hydrocarbons, esters and ketones; low-temperature brittleness; high density; toxicity and corrosivity of smoke in fires; less easy injection.

Flexible PVC: natural UV sensitivity but special UV-stabilized grades; higher sensitivity to heat, creep and chemicals; high density; higher flammability if plasticizers are flammable; toxicity and corrosivity of smoke in fires.

Cost

Ranges roughly from US cents 90 up to 110 per lb or €1.5 up to €2 per kg.

Polystyrene

Polystyrene (PS) can be modified, for example:

•

Polystyrene acrylonitrile: SAN.

•

Acrylonitrile butadiene styrene: ABS.

•

Acrylonitrile styrene acrylate: ASA.

Advantages

PS: low cost, transparency, rigidity, impact grades, dimensional stability, food contact grades, insulating properties, easy to weld and stick.

SAN: High rigidity, better chemical resistance, glossy surface, scratch resistance.

ABS: Better impact and low-temperature behaviors, better chemical resistance similar to SAN.

ASA: Better weathering resistance.

Drawbacks

PS: Sensitivity to UV, low temperatures, impact (apart from butadiene modified grades), solvents, heat; readily flammable with dripping and dense black smokes; sometimes difficult machining.

SAN: like PS but more difficult processing; a little higher cost.

ABS: like SAN but opaque except copolymers; lower chemical resistance; higher cost.

Cost

The price ranges are roughly:

•

From US cents 110 up to 130 per lb or €2 up to €2.2 per kg for PS.

•

From US cents 110 up to 170 per lb or €2 up to €3 per kg for SAN.

•

From US cents 110 up to 170 per lb or €2 up to €3 per kg for ABS.

Polyamides

Advantages

Good mechanical properties; dynamic fatigue behavior; tribological properties; low coefficient of friction; good heat and cold behaviors; resistance to numerous chemicals such as usual hydrocarbons, oils, greases, solvents and oil products.

PA 6-6 and 6: Good ratio price versus mechanical performances and fatigue resistance; heat and cold behaviors; friction behavior (coefficient and wear); resistance to oil products and solvents; very high impact strength of special grades.

PA 11 and 12: Flexibility; better behavior at low temperature; less sensitive to water and moisture.

Drawbacks

Water sensitivity and swelling; limited weathering resistance needing protection for outdoor use; significant shrinkage; limited fire ratings except special grades.

PA 6-6 and 6: Highly hygroscopic. Too dry an atmosphere makes them brittle but an excess of moisture causes swelling, plasticization and a reversible decrease of the mechanical and insulating properties. Saturation swelling can reach 10%.

PA 11 and 12: Lower rigidity and heat behavior.

Cost

The costs are roughly:

•

From US cents 185 up to 230 per lb or €3 up to €4 per kg for PA 6 and 66.

•

From US cents 350 up to 700 per lb or €6 up to €12 per kg for PA 11 and 12.

Thermoplastic polyesters

The most common are polyethyleneterephthalate (PET) and polybutyleneterephthalate (PBT).

Their properties are relatively similar except for the higher crystallinity of PBT.

Advantages

Good mechanical and electrical properties; rigidity; fair creep behavior; fatigue resistance; low moisture absorption; broad range of continuous use temperature –60°C up to 130°C; UHF transparency.

Drawbacks

Sensitivity to water above 60°C; limited fire behavior except special grades; limited weathering resistance needing protection for outdoor exposure; medium chemical resistance.

Cost

This is roughly of the order of US cents 118 up to 152 per lb or €2 up to €3 per kg.

Polyacrylics – PMMA

Advantages

Transparency; high UV and weathering resistance; gloss and color stability; fair mechanical properties, rigidity and creep behavior at ambient temperature; insulating properties notably arc resistance; food contact for suitable grades.

Drawbacks

Low impact strength; sensitivity to heat except acrylic-imides; environmental stress cracking; attacked by some common solvents.

Cost

The range is roughly:

•

from U.S. cents 125 up to 230 per lb or €2.1 up to €4 per kg for PMMA

•

from US cents 220 up to 350 per lb or €4 up to €6 per kg for acrylic-imides.

Polyacetal – POM

The polyacetals are homo- or co-polymers.

Advantages

Good ratio cost/mechanical properties; elasticity; fair creep resistance and fatigue behavior; low moisture uptake; heat and cold behaviors; tribological properties (coefficient and wear); oil and solvent resistance; high impact strength of suitable grades.

Drawbacks

High shrinkage due to the high crystallinity; high coefficient of thermal expansion; sensitivity to light; flammability except special grades; opaque, attacked by strong acids, and for certain grades by weak acids and bases; density is a little high.

Cost

The cost is roughly:

•

From US cents 120 up to 180 per lb or €2 up to €3 per kg for general-purpose grades.

•

From US cents 120 up to 300 per lb or €2 up to €5 per kg for tribological grades.

Polycarbonate (PC)

Advantages

High transparency; high mechanical and insulating properties; natural high impact strength; fair creep and fatigue resistances; low shrinkage and moisture uptake; broad range of service temperatures –100°C to +135°C; food contact and sterilization for suitable grades.

Drawbacks

Sensitivity to light, weathering and hydrolysis needing protection for outdoor exposure; flammability except special grades; attacked by bases, oils, chlorinated solvents, ketones; price.

Cost

•

Roughly from US cents 160 up to 235 per lb or €2.7 up to €4 per kg.

Polyphenylene oxide (PPO) and polyphenylene ether (PPE)

Almost always used as alloy with polystyrene or polyamide. The latter leads to a better heat resistance.

Advantages

Good ratios for cost versus mechanical and electrical properties, and fair creep resistance at room temperature; low moisture absorption, fair heat and cold behaviors; moisture and hot-water resistances; low shrinkage.

Drawbacks

Flammability except special grades; attacked by hydrocarbons, oils, chlorinated solvents, strong mineral acids; cost; high friction coefficient.

Cost

•

Roughly from US cents 125 up to 240 per lb or €2 up to €4 per kg.

Polyphenylene sulfide (PPS)

The properties of PPS are strongly influenced by the degree of crystallinity, which is optimized with hot processing and after annealing.

Advantages

Good mechanical and electrical properties, rigidity, good creep behavior, fatigue resistance, and broad range of service temperatures –196°C up to 200/240°C; low shrinkage and moisture uptake; good chemical resistance; good fire behavior.

Drawbacks

Sensitivity to notched impact; price.

Cost

•

Roughly from US cents 380 up to 765 per lb or €6 up to €13 per kg.

Fluoroplastics

The fluoroplastics can be classified into three categories:

•

Perfluoroplastics:

 PTFE, polytetrafluoroethylene
FEP, perfluoropoly (ethylene propylene)
PFA, perfluoro-alkoxy
•

Fluorochlorinated:

 PCTFE, polychlorotrifluoroethylene
•

Partially fluorinated:

 ETFE, ethylene-tetrafluoroethylene
PVDF, polyvinylidene fluoride.

Advantages

PTFE: Exceptional chemical resistance; high heat and cold behavior; high heat and wet insulating properties; UV, light and weathering resistances; low coefficient of friction, anti- adherent; flexural dynamic fatigue endurance; high resistance to fire; food contact and medical grades; very low water absorption.

PFA: Injection and extrusion grades with the same advantages as PTFE.

FEP: Injection and extrusion grades with the same advantages as

PTFE but a little lower performance: 200°C maximum continuous use temperature instead of 260°C.

PCTFE, ETFE: The same advantages as PTFE but lower performance: 150°C maximum continuous use temperature instead of 260°C. PVDF: Excellent weathering resistance; other advantages similar to PCTFE and ETFE; piezoelectric properties.

Drawbacks

All these polymers incorporate high halogen levels that are environmentally harmful.

PTFE: Creep and abrasion sensitivity; impossible injection and extrusion by conventional processes; high dimensional variation at glass transition temperature (19°C); high cost; high density; very difficult to stick; corrosive and toxic smoke generated in fires.

PFA: The same drawbacks as PTFE, except injection and extrusion possibilities; very high cost.

FEP: The same drawbacks as PTFE, except injection and extrusion possibilities; very high cost.

ETFE, PCTFE, PVDF: The same drawbacks as PTFE, except injection and extrusion possibilities; high cost and lower resistance to heat and chemicals.

Cost

The costs are roughly:

•

PTFE: from US cents 670 up to 765 per lb or €11 up to €13 per kg.

•

ECTFE: from US cents 1250 up to 1450 per lb or €21 up to €25 per kg.

•

PVDF: from US cents 720 up to 1060 per lb or €12 up to €18 per kg.

Polysulfone (PSU)

Some PSU derivatives are also marketed as

•

Polyethersulfone – PES or PESU – more heat resistant than PSU.

•

Polyarylsulfone.

Advantages

Good mechanical and electrical properties, fair creep resistance, fatigue behavior, fair shrinkage; fair moisture uptake; heat and cold behaviors with a broad range of continuous use temperature –100°C to +150/180°C; optical and UHF transparency; food contact and sterilization for suitable grades.

Drawbacks

Sensitivity to light needing protection for outdoor exposure; flammability except special grades; attacked by aromatic hydrocarbons, chlorinated solvents, ketones; cost.

Cost

The costs are roughly:

•

From US cents 390 up to 650 per lb or €7 up to €11 per kg for PSU.

Polyetheretherketone (PEEK)

Advantages

Good mechanical, chemical and electrical properties; rigidity, good creep resistance, fatigue behavior, fair moisture uptake, fair shrinkage; heat behavior with continuous use temperature up to 250°C; high-energy radiation behavior.

Drawbacks

Sensitivity to light needing protection for outdoor exposure; cost justified by the performances.

Cost

•

Roughly US cents 4500 per lb or €76 per kg.

Polyetherimide (PEI)

Advantages

Good mechanical and electrical properties, rigidity, fair moisture uptake, fair shrinkage; heat behavior with continuous use temperatures up to 170/180°C; naturally resistant to UV, light, weathering; naturally fire resistant; optical and UHF transparency; food contact and sterilization for suitable grades.

Drawbacks: Sensitivity to some chemicals; cost justified by the performance.

Cost

•

Roughly from US cents 660 up to 900 per lb or €11 up to €15 per kg.

Polyamide imide (PAI)

Advantages

Good thermo-mechanical and electrical properties rigidity, impact strength, fatigue endurance; heat behavior with continuous use temperatures from –196°C up to +220°C; tribological properties for suitable grades.

Drawbacks

Sometimes difficult processing; high cost justified by the performance.

Cost

•

Roughly from US cents 1800 up to 2600 per lb or €30 up to €44 per kg.

Liquid crystal polymers (LCP)

Advantages

Good thermo-mechanical, chemical and electrical properties; rigidity; gamma irradiation resistance; UHF transparency; good creep resistance and fatigue behavior; low moisture uptake; low shrinkage; heat behavior; fire resistance; low coefficient of thermal expansion.

Drawbacks

Cost justified by the performance; particular mold and part design; density; anisotropy.

Cost

•

Roughly from US cents 550 up to 1200 per lb or €9 up to €20 per kg.

Schematic comparison of thermoplastic matrix properties

Figures 6.3 to 6.6 compare the main mechanical and thermal properties of the main neat thermoplastics.

Figure 6.3. Neat thermoplastic matrices: Examples of continuous use temperatures at unstressed state

Figure 6.4. Neat thermoplastic matrices: Examples of HDT A (1.8 MPa), °C

Figure 6.5. Neat thermoplastic matrices: Examples of tensile modulus, GPa

Figure 6.6. Neat thermoplastic matrices: Examples of tensile strength, MPa

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Polymer Matrix Composites: Matrices and Processing

C.J.G. Plummer , ... J.-A.E. Månson , in Encyclopedia of Materials: Science and Technology, 2001

2.1 Fibers, Prepregs, Feedstocks

Fibers are usually supplied in the form of rovings (glass fibers) or tows (carbon fibers). Rovings consist of straight continuous glass-fiber strands or bundles of about 200 filaments; the number of strands depends on the end use, and these may be several kilometers long. Tows are likewise available in various configurations. The fibers are typically sized (coated) during production to promote wetting and adhesion, silane coupling agents being widely used for glass fibers. They may be woven into fabrics if required, including ad hoc fiber preforms for specific applications. Chopped fiber lengths range from less than 1   mm for injection, to around 50   mm in randomly oriented mats for laminates.

Of major concern in FRP processing are trapped air and volatiles, since voids substantially reduce the final strength. Low-viscosity resins, vacuum outgassing, and consolidation all help reduce porosity. Use of preconsolidated sheets or prepregs also facilitates certain processes (see Fig. 1). These are available as impregnated fabrics or continuous warp sheet typically containing 60–65   vol.% uniaxially oriented fibers. Impregnation with thermosets may be achieved by dipping or hot melt processing (rolling of the fibers together with a resin film). When the viscosity is high, flow distances must be kept to a minimum, and intimate mixing of fine polymer powders or fibers with the fiber reinforcement often precedes melt processing of thermoplastic composites. Solvent processing is one alternative; it may lead to problems with residual solvent in the later stages of fabrication but has been used with success for PEI prepregs, for example. Another possibility is to chain extend relatively low molar mass precursors in situ by reaction of suitable end groups, an approach frequently used for high-performance thermoplastic FRPs.

Sheet and dough molding compounds are mostly based on unsaturated polyester resins containing filler and chopped fibers. Sheet molding compounds (SMCs) are produced from chopped strand mat placed between layers of filled resin containing thickening agents to promote moldability. Impregnation involves rolling of the resulting sandwich structure. SMCs usually contain 25–35   wt.% fibers but the fiber content can be up to 65   wt.%, in which case they are called HMCs. XMCs are similar to SMCs, but incorporate surface layers containing continuous fiber rovings. Dough molding compounds (DMCs), or bulk molding compounds (BMCs), contain shorter fibers than SMCs and are produced by mechanical mixing, which results in a more markedly three-dimensional fiber orientation distribution. Glass mat thermoplastics (GMTs) can be produced in a similar manner to SMCs, but the high matrix viscosity means that success is very dependent on the choice of fiber mat. Powder processing routes are an interesting alternative in this case.

It is sometimes advantageous to preassemble reinforcing fibers to fit a given shape, rather than rely on flow to distribute them throughout a mold. If displacement of the fibers during subsequent introduction of the resin is a problem, they can be anchored in place by spraying with a binder, or substituted by a preimpregnated fabric shaped into a suitable perform.

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Polymer Matrix Composites

M.D. WAKEMAN , C.D. RUDD , in Comprehensive Composite Materials, 2000

2.27.2.1.1 Melt impregnation

Melt impregnation is the dominant method used to produce GMTs where (typically) two mats of random (chopped at 25–50   mm or continuous) glass fibers are impregnated with two polymer films and an extruded molten layer. This is shown schematically in Figure 4. The principal materials suppliers are Azdel (Azdel Inc., 2000) and Symalit (Symalit AG, 2000), producing a range of materials often tailored for an application. GMTs produced by melt impregnation are available at 20–40   wt.%, with different needling densities, fiber lengths, matrix viscosities, and additives interacting to give the final flow and mechanical properties. For example, "high flow" grade products are reported to reduce minimum permissible wall thickness and consolidation pressures (BASF, 2000). Other products introduce aligned reinforcements, often in combination with a random core. Similarly, a semioriented continuous strand mat formed of interleaved layers of elongated elliptical and random loops to tailor mechanical properties has been patented (Neubauer et al., 1987). A final variant adopts a single glass mat, giving a final consolidated thickness of 1.1   mm, which is often used in sandwich structures with polypropylene honeycomb or foam core. Table 1 lists the mechanical properties of a range of commercially available materials.

Fig. 4. Double belt press.

Table 1. Properties of thermoplastic matrix composites for nonisothermal compression molding.

Material W f (%) Reinforcement Matrix Density (g m−3) UTS (MPa) E t (GPa) Strain to failure (%) Flex strength (MPa) E flex (GPa) HDT (°C)
Flow molding
GMT 40 PP (melt impregnated) 40 random, needled mat PP 1220 90 6 1.7 150 5.5 156
GMT 30 PP/SH (melt impregnated) 30 random, needled mat PP 1130 85 4.7 1.8 135 4.8 153
GMT 20 PP (melt impregnated) 20 random, needled mat PP 1020 55 3.5 1.8 90 3.5 149
GMT 20R/20UD A (melt impregnated) 42 20% random, 20% UD PP 1240 223/69 9.6/4.9 2.0 298/157 9.5/5.1 160
GMT PBT 35 (melt impregnated) 35 random, needled mat PBT 1590 104 8.3 2.0 220 8.3 218
GMT PET 35 (melt impregnated) 35 random, needled mat PET 1570 120 7.8 1.5 207 7.7 233
GMT PC 35 (melt impregnated) 35 random, needled mat PC 1390 124 7.6 2.5 207 6.9 142
GMT PC/PBT 30 (melt impregnated) 30 random, needled mat PC/PBT 1420 90 6.9 1.7 188 7.6 195
CPI 40 PP (long fiber thermoplastic) 40 25   mm fibers PP 123 10.9/? 190/? 6.8/?
CPI 40 PA6 (long fiber thermoplastic) 40 25   mm fibers PA6 214 13.1/? 324/? 10.3/?
LFT 12   mm pellets, (RT) (long fiber thermoplastic) 30 12   mm fibers PP 30/55 3/6
Slimtec 30 (melt impregnated) 30 random, needled mat PP 1100 55 4.2
Sandwich materials
GMTex (c1:g4:c1=commingled skins to GMT) 42 r. core, fabric skins PP 141 7.5 204 9.3
GMTex (c25:g50:c25=commingled skins to GMT) 52 r. core, fabric skins PP 185 9.0 280 11.3
75% wt. 4/1 commingled glass/PP+500   μm PP core < 75 PP film+fabric skins PP 377 25 410 21
Aligned fiber V f (%)
Plytron GN 638T5(melt impregnated) 35 UD PP 1480 620 27.5 2.1 570 22 156–164
Thermopreg (interdispered fibers) 35 stitched 0/90 fabric PP 1700 256 13 170
Twintex PP (commingled) 35 Bal. Twill Weave PP 1500 240–00 13 300 12
Twintex PP (commingled) 35 4/1 weave PP 1500 390 22 350/160 18/6
Twintex PP (commingled) 45 UD PP 1700 790 31 590 31
Twintex PET (commingled) 50 UD PET 1900 870 37.6 1025 37.7
Twintex PET (commingled) 50 0/90 weave PET 1900 310 25 600 21
Glass/PET 48 Warp Knit PET 87/6.6 8.2/3.5 747/25 35/4.6
Glass/PBT 56 0° PBT 810 40.5
Porcher Industry (power impregnation) 52 2/2 Twill carbon fabric PA 12 603 44
Vestopreg 52 Bal.Weave PA 12 1850 350/350 26/26 1.6/1.6 500 22 177
EMS/Schappe fabric (commingled) at 20°C 56 5HS carbon fabric PA 12 1440 801 61 1.3 606 52
EMS/Schappe fabric (commingled) at 80°C 56 5HS carbon fabric PA 12 1440 631 58 1.2 332 42
EMS PA12/carbon (anionically polymerized) 54 2/2 Twill carbon fabric PA 12 1430 790 62.6 1.3
TEPEX 101-glass FG300/45% (melt impregnated) 45 Glass PA 6.6 1800 420/380 23/22 2.0 620/580 24/22 258
TEPEX 201 –carbon C365/55% (melt impregnated) 55 Carbon PA 6.6 1500 880/865 66/64 1.3 805/720 53/50 258
Schulzer Innotech (powder impregnated) 65 Carbon, UD PEEK 2600 150 1.9
Schulzer Innotech (powder impregnated) 60 Carbon, 0°/907±45° PEEK 1100
CETEX PEI-glass 50 8H satin glass fabric PEI 1905 350 20
CETEX PEI-carbon 50 5H satin carbon fabric PEI 1510 830 59
APC-2 (Cytex-fiberite) (melt impregnated) 61 0° PEEK 2070 138

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Material profiles

Michael F. Ashby , in Materials and the Environment (Second Edition), 2013

GFRP (Isotropic)

The material. Composites are one of the great material developments of the 20th century. Those with the highest stiffness and strength are made of continuous fibers (glass, carbon, or Kevlar, an aramid) embedded in a thermosetting resin (polyester or epoxy). The fibers carry the mechanical loads, while the matrix material transmits loads to the fibers and provides ductility and toughness as well as protecting the fibers from damage caused by handling or the environment. It is the matrix material that limits the service temperature and processing conditions. Polyester-glass composites (GFRPs) are the cheapest and by far the most widely used. A recent innovation is the use of thermoplastics at the matrix material, either in the form of a co-weave of cheap polypropylene and glass fibers that is thermoformed, melting the PP, or as expensive high-temperature thermoplastic resins such as PEEK that allow composites with higher temperature and impact resistance. High-performance GFRP uses continuous fibers. Those with chopped glass fibers are cheaper and are used in far larger quantities. GFRP products range from tiny electronic circuit boards to large boat hulls, body and interior panels of cars, household appliances, furniture, and fittings.

Composition
Epoxy+continuous E-glass fiber reinforcement (0, + −45, 90), quasi-isotropic lay-up
General properties
Density 1,750 – 1,970 kg/m3
Price 19 – 21 USD/kg
Mechanical properties
Young's modulus 15 – 28 GPa
Yield strength (elastic limit) 110 – 192 MPa
Tensile strength 138 – 241 MPa
Elongation 0.85 – 0.95 %
Hardness—Vickers 10.8 – 21.5 HV
Fatigue strength at 107 cycles 55 – 96 MPa
Fracture toughness 7 – 23 MPa·m1/2
Thermal properties
Maximum service temperature 413 – 493 °C
Thermal conductor or insulator? Poor insulator
Thermal conductivity 0.4 – 0.55 W/m·K
Specific heat capacity 1,000 – 1,200 J/kg·K
Thermal expansion coefficient 8.6 – 32.9 µstrain/°C

GFRP body shell by MAS Design, Windsor, UK.
Electrical properties
Electrical conductor or insulator? Good insulator
Electrical resistivity 2.4×1021 – 1.91×1022 µohm·cm
Dielectric constant 4.86 – 5.17
Dissipation factor 0.004 – 0.009
Dielectric strength 11.8 – 19.7 106  V/m
Eco properties: material
Embodied energy, primary production 107 – 118 MJ/kg
CO2 footprint, primary production 7.47 – 8.26 kg/kg
Water usage 105 – 309 L/kg
Eco properties: processing
Simple composite molding energy 9 – 12.9 MJ/kg
Simple composite molding CO2 0.77 – 0.89 kg/kg
Advanced composite molding energy 21 – 23 MJ/kg
Advanced composite molding CO2 1.7 – 1.8 kg/kg
End of life
Recycle fraction in current supply 0 %
Heat of combustion 12 – 13 MJ/kg
Combustion CO2 0.9 – 1.0 kg/kg

Typical uses. Sports equipment such as skis, racquets, skateboards, and golf club shafts, ship and boat hulls; body shells; automobile components; cladding and fittings in construction; chemical plant.

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Nonmetallic materials—coupling of multiphysics for ageing rate prediction

Sebastien Didierjean , Högni Jónsson , in Trends in Oil and Gas Corrosion Research and Technologies, 2017

33.3.2 Fiber breakage

To the contrary of weeping, fiber breakage can result in rupture of a pipeline. In most pipelines, pressure is the dominating mechanical load and continuous glass fiber is the material ensuring structural integrity by its natural mechanical strength and chemical resistance, when combined with the appropriate resin system.

This chapter will, from now on, focus only on fiber breakage as mode of failure. It is worth mentioning that so far weepage has not been clearly identified as a precursor to fiber breakage in particular for water application (see Section 33.5.1.2).

The aging of a GRP pipe has many stages and it is up to the user to determine which phase constitutes failure. In Fig. 33.4, Stage 1 corresponds to a fresh pipe right after manufacturing. In the case of water due to the presence of moisture in the air, the pipe enters Stage 2 almost immediately. The molecular propagation is often driven by two reversible mechanisms: diffusion and reaction following a Langmuir catch-and-release scheme. Stage 3 corresponds to the saturation level whose gradient through the pipe wall depends on the amount of the given chemical species at both extremities (inner and outer surface). The time to saturation level depends mostly on the thickness of the pipe wall and on its temperature. It is generally fast when compared to the expected lifetime of the GRP pipeline (∼1   year vs. 20   years of expected lifetime). Stage 4 represents the beginning of nonreversible damage caused by the penetration of the fluid in the pipe wall. This chapter concentrates mostly on stages 1–3 as Stage 4 shall in most cases be avoided for normal pipeline operation.

Figure 33.4. Evolution of molecular (in blue) propagation of a fluid through a pipe wall before penetration of liquid (in red).

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