: :  About Composites  : :

Composites are materials produced from high strength fibers oriented within a matrix, usually an organic resin. They are called high performance composites when the fibers are continuous, and comprise approximately 50% by volume of the material. They are called advanced when the reinforcement and/or matrix has significantly higher properties than standard E-glass reinforced composites.

 

Composites can be molded to any shape.  When making contoured parts, composites are often lower cost and higher strength than other materials.  The physical properties of the part can vary from flexible to very rigid by varying the resin matrix and reinforcement.

 

What is FRP ?

FRP is a proven composite technology used to produce accurate, rigid, large parts with excellent strength-to-weight ratio combined with high impact strength and an exceptional surface finish.

FRP, fiberglass reinforced plastic, is a composite made from fiberglass reinforcement in a plastic (polymer) matrix. A construction analogy would be the steel reinforcing bars in a concrete matrix for highways.

By reinforcing the plastic matrix, a wide variety of physical strengths and properties can be designed into the FRP composite. Additionally, the type and configuration of the reinforcement can be selected, along with the type of plastic and additives within the matrix. These variations allow an incredible range of strength and physical properties to be obtained. FRP composites can be developed specifically for the performance required versus traditional materials: wood, metal, ceramics, etc.

Engineers can design the FRP composite to provide the needed characteristics, and avoid cost penalties of an over-engineered product.
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What is fiberglass?
Fiberglass fibers are made from molten glass extruded at a specified diameter. The fibers are gathered into bundles and the bundles combined create a roving. Rovings are a continuous rope, similar to twine, and are wound on a mandrel to form a ball called a doff. Reinforcements for FRP are made from rovings that are either chopped into short strands or woven into a cloth.

There are many factors that affect the reinforcement characteristics of fiberglass:

  • Fiber and bundle diameter and type of glass
  • Direction of the fiberglass reinforcement
  • The amount of fiberglass reinforcement
  • The physical contact (wetout) of the fiber with the polymer

All of these factors must be taken into account when designing an FRP composite so that the required physical property strengths are met.
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What are plastic/polymers?
There are two basic types of plastics/polymers: thermoplastic and thermoset.

In general, FRP composites utilize a thermoset plastic.

A plastic in which the polymer molecules are not crosslinked (not chemically bonded to other polymer molecules) is a thermoplastic. Since the molecules are not connected by crosslinks, it allows the molecules to spread farther apart when the plastic is heated. This is the basic characteristic of a thermoplastic; the plastic will soften, melt, or flow when heat is applied. Melting the plastic and allowing it to cool within a mold will form the finished product. Typical thermoplastics are: polyethylene (PE) used in making garbage bags; polyvinyl chloride (PVC) used for house siding; and polypropylene (PP) used as carpet fibers, packaging, and diapers.

A plastic in which the polymer molecules are crosslinked (chemically bonded) with another set of molecules to form a "net like" or "ladder-like" structure is a thermoset. Once crosslinking has occurred, a thermoset plastic does not soften, melt, or flow when heated. However, if the crosslinking occurs within a mold, the shape of the mold will be formed. Typical thermoset plastics are: unsaturated polyester (UP) used for bowling balls and boats; epoxy used for adhesives and coatings; and polyurethanes (PURs) used in foams and coatings.

In addition to these basic characteristics, polymers provide the FRP composite designer with a myriad of characteristics that can be selected, depending on the application. Combined with reinforcement of the polymer matrix, a vast range of characteristics are available for FRP composites.
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What are physical properties?
The properties of FRP composites are measured the same way that traditional materials are measured so that comparisons can be made for evaluation. Typical measurements include:

Compressive Strength -Describes how much of a load a material can take before it is crushed or fractured

Flexural Modulus -A number associated with the flexibility or stiffness of a material. It indicates how far a material will bend when a certain load is applied to it. The lower the modulus, the more flexible the material.

Flexural Strength Measures how much of a load a material can take before it fractures or breaks when it is in the process of being bent.

Impact Strength There are two primary impact tests; one is called IZOD impact and the other is called Gardner impact. IZOD impact measures the energy required to fracture or break a material when it is struck on its edge. Gardner impact measures the energy required to damage or puncture a material when it is struck on its front surface.

Rockwell or Barcol Hardness -Measures the surface hardness of a material. The higher the hardness value, the more resistant a material is to scratching, abrasion, and denting.

Tensile Modulus -A number associated with pulling or stretching a material (tension) and how much it elongates when a certain load is applied to it. The lower the modulus, the more the material will elongate or stretch.

Tensile Strength Measures how much of a load a material can take before it fractures or breaks when it is in the process of being stretched.
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FRP Terms
ABS(Acrylonitrile-Butadiene-Styrene)
A group of tough, rigid thermoplastics derived from the reaction of acrylonitrile, styrene, and butadiene gas. These materials are polymerized together in a variety of ratios to produce ABS resins.

Accelerator-A highly active oxidizing material suspended in a liquid carrier used to accelerate the decomposition of peroxide catalysts into highly reactive free radicals. These free radicals react readily with polymer and monomer molecules to cure a thermoset resin. Examples are diethylaniline, dimethylaniline, cobalt naphthanate, and cobalt octoate.

Acetone- A cleaning fluid used to remove uncured plastic resin from brushes and clothing.

Activator- See accelerator .

Air-inhibited Resin- A resin in which surface cure will be inhibited or stopped by the presence of air.

"B" Stage (of Resin)- The condition of a partially cured resin polymer when it is only partially soluble in monomer or acetone but still plastic and still heat fusible.

BMC(Bulk Molding Compound)- A combination of resin paste and chopped glass combined with a "sigma" blade mixer under conditions of very high mechanical "working" stress. The compound is delivered to the press in the form of a ball, slab or an extruded log and dropped into the bottom of a mold; the material is flowed outward until it assumes the shape of the mold.

Catalyst- A substance (usually a peroxide) which readily forms free-radicals. These free radicals react with polymer and monomer molecules to speed up the curing of thermoset resins. Catalyst content can vary from 0.2% to 2.0% with higher catalyst levels giving faster cure times. Examples are methyl ethyl ketone peroxide and benzoyl peroxide.

Color Pigments- Ground coloring materials supported in a thick liquid. Added to the resin, they give it color.

Crazing- Hairline cracks either within or on the surface of a laminate, caused by stresses generated during cure, removal from a mold, impact or flexing.

Crosslinking Chain-reaction polymerization which results in chemical links (bonds) between individual polymer chains. This occurs in all thermosetting resins. Styrene monomer and methyl methacrylate monomer are the most common crosslinking agents used in polyester resins.

Cure- The total crosslinking or polymerization of resin molecules which permanently alters the properties of the resin changing it from a liquid to a solid.

Cure Time- The time required for the liquid resin to reach a cured or fully polymerized state after the catalyst has been added.

Delamination- Failure of internal bending between layers of the laminate.

Dimensional Stability- Ability to retain constant shape and size under various environmental conditions, such as temperature and humidity.

End- As applied to fibrous reinforcements, a bundle of essentially parallel (i.e., entwined) fibers, usually glass.

Exotherm Curve- A graph of temperature plotted against time during the curing cycle. Peak exotherm is the highest temperature reached during the curing reaction.

Exothermic Heat- Heat given off during a polymerization reaction by the chemical ingredients as they react and the resin cures.

FBVF(Fiberglass Backed Vacuum Forming)- Combining a thermoformed thermoplastic sheet with a fiberglass mat or roving using the spray-up or hand lay-up process.

Filament- A single, hair-like fiber of glass characterized by extreme length, which permits its use in yarn with little or no twist and usually without the required spinning operation.

Fill or Sanding Resin- A general purpose polyester resin used to soak and fill reinforcing material in the initial lay-up of a surfacing application; usually contains wax.

Fillers- Any one of a number of inexpensive substances which are added to plastic resins to extend volume, improve properties and lower the cost of the article being produced. Examples are calcium carbonate, alumina trihydrate, feldspar, and calcium sulfate.

Fire Retardancy Reduction in the ability of a plastic to ignite and burn. This is accomplished by using compounds (resins or additives) that contain halogens (bromine or chlorine) or phosphorous. Usually alumina trihydrate filler is also used because of its ability to release water when exposed to high heat.

Gel- A partial cure of plastic resins; a semi-solid, jelly-like state similar to gelatin in consistency.

Gelcoat- A thin surface coat, either colored or clear, of non-reinforced plastic resin. It is occasionally used for decorative purposes but also provides a protective coating for the underlying laminate.

Gel Time-Time required to change a flowable liquid resin into a non-flowing gel.

Hand Lay-Up- The oldest and simplest molding technique in which reinforcing materials and catalyzed resin are laid into or over a mold by hand. These materials are then compressed with a roller to eliminate entrapped air.

Hardener- See catalyst .

Inhibitor- A substance that retards polymerization, thus extending the shelf life of polymers and monomers. Also used to extend the gel time and cure time of a thermoset resin.

Laminate- A material composed of successive layers of resin and fiberglass bonded together.

Lamination- The compilation of layers of glass matte and resin, and eventual bonding of these layers together.

Fiberglass Mat- A flat, coarse fabric composed of glass fibers. There are three types: chopped-strand mat, continuous strand mat, and surfacing veil.

Monomer- A single molecule capable of polymerizing.

Non-Air-Inhibited Resin- A polyester resin using phthalic anhydride as the starting point. A surfacing agent is added to exclude air from the surface of the resin.

Orthophthalic Resin-A polyester resin using phthalic anhydride as the starting point. Most thermoset polyester resins use two types of anhydrides in their production: phthalic anhydride and maleic anhydride. A higher percentage of phthalic anhydride yields a less reactive resin.

Polyester Resin- The term generally used for unsaturated polyesters. Formed by the reaction of a dibasic organic acid or anhydride and a polyhydric alcohol to form a series of ester linkages.

Polymer- The end product, usually a solid, produced from monomers.

Porosity- The formation of undesirable clusters of air bubbles in the surface or body of the laminate.

Pot Life- The length of time that a catalyzed resin remains workable.

Preform Fiber- Glass formed over a screen shaped like the mold in which the preform will be used. It eliminates the need for over-lapping or mitering the corners in molding. Used primarily to form deep draws or complex parts.

Prepreg- Glass roving or cloth loaded with B-stage resin, catalyst, and pigment ready for placement in a mold.

Promoter- See accelerator .

Release Agent- A lubricant, often wax, is used to prevent the adhesion of the molded part to the mold. A

Resin- A liquid plastic substance used as a matrix for glass fibers. It is cured by crosslinking.

Thermoset- A plastic material that will undergo or has undergone a chemical reaction caused by heat, catalyst, ultraviolet light, etc., leading to the formation of a solid. Once it becomes a solid, it cannot be reformed.

Thermoplastic- A plastic material that can be readily softened and reformed by heating and be re-hardened by cooling.

Roving- Continuous strands of glass fibers which are grouped together and wound on a tube like untwisted yarn.

SMC (Sheet Molding Compound)- An integrated, ready-to-mold fiberglass reinforced polyester material. The compound is composed of a filled thermosetting resin and a chopped or continuous strand reinforcement. The primary use is in matched die molding.

Shelf Life- The length of time a non-catalyzed resin maintains specified working properties while stored in a tightly sealed opaque container.

Spray-Up- Covers a number of techniques in which a spray gun is used to simultaneously deposit fiberglass and catalyzed resin on a mold.

Styrene Monomer- A water-thin liquid monomer used to thin polyester resins and act as the crosslinking agent.

Substrate- Any material which provides a support surface for other materials.

Tack- The stickiness of an adhesive measurable as the force required to separate an adherent from it by viscous or plastic flow of the adhesion.

Thickeners- Material added to the resin to thicken it so that it will not flow as readily.

Thinners- Material added to plastic resins to thin it. They may also be crosslinking agents.

Thixotropic- The property of becoming a gel at rest, but liquefying again on agitation.

Viscosity- A measure of the resistance of liquid to flow.

Wet-out-The ability of a resin to saturate fiberglass reinforcement.

Yarn- A twisted strand or strands of glass fibers which can be woven, braided, served, and processed.
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How durable is FRP?
FRP products are extremely durable versus many traditional products. The thermosetting resin properties provide chemical, moisture, and temperature resistance, while the fiberglass reinforcement increases strength and provides good performance over a wide temperature range (the properties of thermoplastics are greatly affected by temperature).
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How cleanable is FRP?
FRP finishes can be either smooth or embossed. Tests for bacteria and mold growth indicate that FRP does not support the growth of either.

An embossed finish has the added benefit of providing a more scuff resistant surface than smooth.

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Does FRP burn?
FRP can be modified with additives to meet the code requirements of the particular application, either building construction or use in OEM equipment.

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