C T M E E T A C

Materials used in Windowss structures

Professors:

Santiago Arias Caldern

Josep Ignaci Rojas Gregorio

Students:

Joaquim Villen

Yanik Lacroix

Jaume Baratech

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Abstract Do you remember the first time you took a flight? It is an incredible experience and for sure you wanted

to sit next to the window to see all that what was happening outside the aircraft. Windows are an

essential component of the aircraft. Without them, planes will be very closed and claustrophobics.

The objective of this project is to understand what is inside aircrafts windows. For that, we are going to

explain what materials are used in aircrafts windows and windshields, why these materials are used and

which are their properties. We also will see how the maintenance has to be done to take care of them

and to be sure that them keep being safe and gleaming.

Finally we are going see how windows may change in the future to be more interactive with the

passenger.

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Table of Contents

ABSTRACT ....................................................................................................................................... 2

INTRODUCTION ............................................................................................................................... 4

A LITTLE BIT OF HISTORY: DE HAVILLAND COMET LONG-RANGE JETLINER .......................................................... 4

TRANSPARENT MATERIALS FOR THE WINDOW ............................................................................... 6

POLYMETHYL METHACRYLATE (PMMA) ...................................................................................................... 6

Background ..................................................................................................................................... 6

The Manufacturing Process ............................................................................................................ 7

Characteristics ................................................................................................................................ 7

Kind of PMMA allowed to be used in windows by the FAA ............................................................. 8

Uses PMMA ..................................................................................................................................... 9

The Future ..................................................................................................................................... 10

CHEMICALLY STRENGTHENED GLASS-HERCULITE .......................................................................................... 10

Manufacturing process ................................................................................................................. 10

Characteristics .............................................................................................................................. 11

Uses ............................................................................................................................................... 13

POLYCARBONATE ................................................................................................................................... 14

Background ................................................................................................................................... 14

Manufacturing process ................................................................................................................. 15

Characteristics .............................................................................................................................. 16

Uses ............................................................................................................................................... 17

POLYURETHANE .................................................................................................................................... 19

Background ................................................................................................................................... 19

The Manufacturing Process .......................................................................................................... 19

Characteristics .............................................................................................................................. 20

Uses ............................................................................................................................................... 21

The Future ..................................................................................................................................... 23

OTHER MATERIALS ........................................................................................................................ 24

SEALANTS ............................................................................................................................................ 24

COMPARISON COMMERCIAL, MILITARY AND REGIONAL AIRCRAFTS WINDOW ............................. 25

AIRCRAFT WINDSHIELD AND WINDOW CARE AND MAINTENANCE ............................................... 28

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FUTURE ......................................................................................................................................... 31

ALTEOS INTERACTIVE WINDOW SYSTEMS, FOR PASSENGER CABIN WINDOWS .................................................. 31

CONCLUSIONS ............................................................................................................................... 33

BILBIOGRAFIA ............................................................................................................................... 34

Introduction In this Project we are going to see the materials windows are made of. More in particular we will talk

about Polymethyl methacrylate (PMMA), the Chemically strengthened glass-Herculite, the Polycarbonate

and the Polyurethane. This kind of material are used for the main glass windows, but there are other

components such as the sealeants, we will took a look to them too.

The materials are very important when designing the windows, but we want them to last as long as

posible, thats why we explian also how to properly do the maintainance. We are also interested to know

how the windows will change in the future. Will the manufacturers improve the materials or will they

redifine the concept of the window for the passanger?

First of all, we will introduce the importance of this component of the aircraft by explaining how the

fatigue was discovered and show how really significant the windows are.

A little bit of history: De Havilland Comet Long-Range Jetliner

One of the most tragic stories of the jet age

revolves around the unfortunate de Havilland

Comet. With the turbojet engine mounted in

the wing root leading edge and squared

windows (see Illustration 1), it represented a

revolutionary advance and the Comet was put

through an extensive series of test flights and

Illustration 1 Comet 1 prototype (with square windows) {2}

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certifications over three years. {1}

In spite of having successfully completed the tests with no apparent difficulties, a Comet mysteriously

crashed shortly after take-off on 2 May 1953, one year after the Comet received permission to begin

commercial operations. Two similar crashes forced British authorities to ground the entire fleet pending

investigation. Over the following months, extensive tests were performed on the aircraft to determine

what could have caused these mysterious accidents. {1}

The answer finally came after a fuselage had been submerged in a tank of water and repeatedly

pressurized and depressurized to represent repeated flight cycles (see Illustration 2). After several

thousand of these cycles, fatigue cracks were found to be spreading from the square edges of the

windows in the passenger cabin. These cracks would eventually reach a critical size where they would

grow rapidly resulting in a catastrophic depressurization that would destroy an aircraft in flight. {1}

Thanks to the Havilland Comet, the fatigue effect was investigated in more detail, even though

nowadays we cannot fully understand it. All the aircraft now are always designed with rounded-corner

windows to correct the fatigue problem. {1}

Illustration 2 Aerial view of Comet G-ALYU in testing tank {3}

Illustration 3 view from inside of failure at the forward escape hatch on the port side - Comet G-ALYU {4}

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Transparent materials for the window

Polymethyl methacrylate (PMMA) Polymethyl methacrylate (PMMA) is a transparent thermoplastic, often used as a lightweight or shatter-

resistant alternative to glass. Although it is not technically a type of class its commonly known as acrylic

glass. Chemically, it is the synthetic polymer of methyl methacrylate. The non-modified PMMA behaves

in a brittle manner when loaded, especially under an impact force, and is more prone to scratching than

conventional inorganic glass. However, the modified PMMA achieves very high scratch and impact

resistance. {5}

Background

The first plastic polymer, celluloid, a combination of cellulose nitrate and camphor, was developed in

1869. It was based on the natural polymer cellulose, which is present in plants. Celluloid was used to

make many items including photographic film, combs, and men's shirt collars.{6}

In 1909, Leo Baekeland developed the first commercially successful synthetic plastic polymer when he

patented phenol formalde-hyde resin, which he named Bakelite. Bakelite was an immediate success. It

could be machined and molded. It was an excellent electrical insulator and was resistant to heat, acids,

and weather. It could also be colored and dyed for use in decorative objects. Bakelite plastic was used in

radio, telephone, and electrical equipment, as well as counter tops, buttons, and knife handles.{6}

Acrylic acid was first prepared in 1843. Methacrylic acid, which is a derivative of acrylic acid, was

formulated in 1865. When methacrylic acid is reacted with methyl alcohol, it results in an ester known

as methyl methacrylate. The polymerization process to turn methyl methacrylate into polymethyl

methacrylate was discovered by the German chemists Fittig and Paul in 1877, but it wasn't until 1936

that the process was used to produce sheets of acrylic safety glass commercially. During World War II,

acrylic glass was used for periscope ports on submarines and for windshields, canopies, and gun turrets

on airplanes. {6}

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The Manufacturing Process

Acrylic plastic polymers are formed by reacting a monomer, such as methyl methacrylate, with a

catalyst. A typical catalyst would be an organic peroxide. The catalyst starts the reaction and enters into

it to keep it going, but does not become part of the resulting polymer.{6}

Acrylic plastics are available in three forms: flat sheets, elongated shapes (rods and tubes), and molding

powder. Molding powders are sometimes made by a process known as suspension polymerization in

which the reaction takes place between tiny droplets of the monomer suspended in a solution of water

and catalyst. This results in grains of polymer with tightly controlled molecular weight suitable for

molding or extrusion.{6}

Acrylic plastic sheets are formed by a process known as bulk polymerization. In this process, the

monomer and catalyst are poured into a mold where the reaction takes place. Two methods of bulk

polymerization may be used: batch cell or continuous. Batch cell is the most common because it is

simple and is easily adapted for making acrylic sheets in thicknesses from 0.06 to 6.0 inches (0.16-15

cm) and widths from 3 feet (0.9 m) up to several hundred feet. The batch cell method may also be used

to form rods and tubes. The continuous method is quicker and involves less labor. It is used to make

sheets of thinner thicknesses and smaller widths than those produced by the batch cell method. {6}

Characteristics

PMMA is a strong and lightweight material. It also has good impact strength, higher than both glass and

polystyrene; however, PMMAs impact strength is still significantly lower than polycarbonate and some

engineered polymers. {5}

Physical Properties

This material is made up of lightweight, rigid thermoplastic material that has many times the breakage

resistance of standard window pane glass. It is highly resistant to weather conditions. It is suitable for

most utilitarian applications and is ultraviolet light absorbing up to approximately 360 nanometers.

PMMA also is more impact-resistant than glass. If subjected to impact beyond the limit of its resistance, it

does not shatter into small slivers but breaks into comparatively large pieces. {7]

Focusing in terms of weight PMMA is less than half the weight of glass and 43% the weight of aluminum

and it is not as rigid as glass or metals. However, it is more rigid than many other plastics such as

acetates, polycarbonates, or vinyls. {7}

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Although the tensile strength of Acrylic is 69 at room temperature, stress crazing can be caused by

continuous loads below this value. For most applications, continuously imposed design loads should not

exceed 10.4 MPa. Its surface is not as hard as that of glass.{7}

PMMA can be used at temperatures from (-40C) up to 93C depending on the application. Also the

clear, colorless PMMA has a light transmittance of 92%. {7}

Crazing

Both basic forms of acrylics used in aircraft transparencies are affected by crazing. Crazing is a network

of fine cracks that extend over the surface of the plastic sheet (it is not confined to acrylic materials) and

are often difficult to discern. These fine cracks tend to be perpendicular to the surface, very narrow, and

are usually less than 0.025 mm in depth. Crazing is induced by prolonged exposure to surface tensile

stresses above a critical level or by exposure to organic fluids and vapours. [8}

Chemical resistance of acrylic materials

Typically, acrylic materials are resistant to inorganic chemicals and to some organic compounds, such as

aliphatic (paraffin) hydrocarbons, hydrogenated aromatic compounds, fat and oils. Acrylic materials are

attacked and weakened by some organic compounds such as aromatic hydrocarbons (benzene), esters

(generally in the form of solvents, and some de-icing fluids), ketones (acetone), and chlorinated

hydrocarbons. Some hydraulic fluids are very detrimental to acrylic materials.{8}

Some detrimental compounds can induce crazing; others may dissolve the acrylic or be absorbed in the

material. Crazing induced by solvent and other organic compounds has more severe effects on the

mechanical properties than stress crazing. Dissolution of the acrylic and chemical absorption into the

acrylic degrades the mechanical properties. {8}

Kind of PMMA allowed to be used in windows by the FAA

FAA allows two kind of PMMA to build aircraft windshield and window panels, as-cast and biaxially

stretched (stretched from a cross-linked base material).{8}

- As-cast acrylic material: Forming acrylic material to a certain shape by pouring it into a mold and

letting it harden without applying external pressure. Although not as notch sensitive as glass,

unstretched acrylics have a notch sensitivity. This unplasticised methyl-methacrylate base polymer has

good forming characteristics, optical characteristics and outdoor weathering properties.{8}

- Biaxially stretched acrylic material: Stretching acrylic material aligns the polymer chains to give a

laminar structure parallel to the axis of stretch, which enhances resistance to crazing, reduces crack

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propagation rates, and improves tensile properties. Stretching acrylic material reduces the materials

formability. In addition, stretched acrylics have less notch sensitivity than unstretched acrylics. {8}

Uses PMMA

Aircrafts related uses

Historically, PMMA was an important improvement in the design of

aircraft windows, making possible such iconic designs as the

bombardier's transparent nose compartment in the Boeing B-17 Flying

Fortress or the aircraft windows. {5}

Also there are a lot of aircrafts canopies and windshields of little

regional aircrafts are made of PMMA, as for example Robin DR 400. {9}

Illustration 5: Robin DR 400 {11}

Curiosities related to aeronautic world

PMMA has a good degree of compatibility with human tissue, and it is used in the manufacture of rigid

intraocular lenses in the eye when the original lens has been removed in the treatment of cataracts.

This compatibility was discovered in WWII RAF pilots, whose eyes had been riddled with PMMA

splinters coming from the side windows of their Supermarine Spitfire fighters the plastic scarcely

caused any rejection, compared to glass splinters coming from aircraft such as the Hawker Hurricane.

{5}

Illustration 4: Boeing B-17G nose detail. (U.S. Air Force photo) {10}

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Other common uses

Industrial Uses: water tank liner, hand-held computer case, liquid chemical pump, conveyor rollers,

soap dispensers hatch covers, bumper guards

Automotive Industry: lenses of exterior lights, trunk release handles, master cylinder, dashboard

lighting

Consumer products: aquariums, motorcycle helmet lenses, paint, furniture, picture framing, umbrella

clamps, cell phone antennas, bicycle air pumps {6}

The Future

The average annual increase in the rate of consumption of acrylic plastics has been about 10%. A future

annual growth rate of about 5% is predicted. Despite the fact that acrylic plastics are one of the oldest

plastic materials in use today, they still hold the same advantages of optical clarity and resistance to the

outdoor environment that make them the material of choice for many applications. {6}

Chemically strengthened glass-Herculite Herculite II is a chemically strengthened glass produced by PPGs industries the main manufacturer of

windows in all over the world. As it is a registered it has only been possible to access to the properties

of the general chemical strengthened glass.

Manufacturing process

The glass is chemically strengthened by a surface finishing process. The glass to be treated is dipped into

a bath of dissolved potassium salts at a temperature about 380C for duration from 4 to 30 hours,

producing an ionic exchange between the superficial sodium ions in the glass and potassium ions inside

the bath. The cycle time would be greatly reduced if the glass is made of certain elements such as

lithium or magnesium because ion mobility between potassium and these elements is a lot faster. The

process parameters such as ion exchanging time and temperature would be modified according to the

type of glass to be treated and the required strengthen specification. {12}

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The introduction of potassium ions which are larger in size than the sodium ions results in the

establishment of a system of residual stress characterized by compression stretches on the surface

counterbalanced by traction stretches within the glass. {12}

Sodium ions and thus, creates stress on glass surface. During cooling, the potassium on surface

shrinks little while the sodium in inner shrinks larger. Hence, stress is induced between glass surface and

inside and consequently, the glass is strengthened. {12}

There also exists a more advanced two-stage process for making chemically strengthened glass, in

which the glass article is first immersed in a sodium nitrate bath at 450 C, which enriches the surface

with sodium ions. This leaves more sodium ions on the glass for the immersion in potassium nitrate to

replace with potassium ions. In this way, the use of a sodium nitrate bath increases the potential for

surface compression in the finished article. {12}

Ilustration 5:Manufacturing Process Chemically Strengthened Glass {13}

Characteristics

Chemically strengthened glass is a type of glass that has increased strength as a result of a post-

production chemical process. Chemical strengthening is the name given to glass products that have

been strengthened by means of an ion-exchange process. It is a surface treatment which occurs at a

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temperature lower than glass melting temperature. The process is particularly useful for thin glass, tiny

glass and shape glass which cannot be tempered by ordinary physical tempering. {12}

Chemically strengthened glass is typically six to eight times the strength of float glass. In the case of

breakage, chemically strengthened glass breaks into bigger pieces which are not as sharp as those of

non-toughened glass. The surface compression condition which is higher in the case of a chemically

strengthened glass also involves an increase of flexion resistance, which is one of the main

characteristics of chemically strengthened glass. {12}

Chemical strengthening results in a strengthening similar to toughened glass. Chemically strengthened

glass has little or no bow or warp, optical distortion or strain pattern. This differs from toughened glass,

in which slender pieces can be significantly bowed.{12}

Chemically strengthened glass may be cut after strengthening, but loses its added strength within the

region of approximately 20 mm of the cut. Similarly, when the surface of chemically strengthened glass

is deeply scratched, this area loses its additional strength. Chemically strengthened glass retains its

colour and light transmission properties after treatment. {12}

Chemically strengthened glass offers an improved scratching, impact and bending strength, as well as an

increased temperature stability {12}

Properties

Chemically strengthened glass is eight times stronger than comparable annealed glass.

The surface compression of chemically strengthened glass may reach up to 690 MPa for a thickness

of approx. 32 m.

Chemically strengthened glass retains its colour and light transmission properties after treatment.

Due to its manufacturing process, chemically strengthened glass has little or no bow or warp, optical

distortion or strain pattern.

Chemically strengthened glass breaks into sharp fragments like annealed glass. Chemically

strengthened glass cannot be used alone as safety glass; it must be laminated.

Chemically strengthened glass may be cut after tempering, but totally loses its added strength for

about 1 254 mm on either side of the cut. These strips revert to annealed glass. It is preferable to cut

and edge the glass before it is chemically strengthened.

When the surface chemically strengthened glass is deeply scratched, this area loses its added

strength. {14}

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Uses

Aeronautic uses

One variety of a chemically strengthened glass very important in the aeronautic world is Herculite II.

This strengthened glass is the main material of most of the windows and -windshields of most Airbus

and Boeing aircrafts, as for example B-737, 747, 767, 777 787 or A300, A310, A330, A340, or all the

series of the A320. {15}

Illustration 6: Boeing 787 Windshields structure {16}

Illustration 7: Airbus A320 Series windshields structure{17}

{17}

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Ilustration 8: Airbus 320 Series windows structure {17}

Other uses

It can be used in numerous applications that demand toughness and optical clarity. The material is also

useful for viewports, protective covers, and front surface optics in hostile environments whose

elements may include high temperature, high pressure and vacuum conditions. Less demanding

applications include point of sale scanner windows used in grocery store and retail scanners. {12}

Polycarbonate Polycarbonate plastic is a lightweight, high-performance plastic found in commonly used items such as

automobiles, cell phones, computers and other business equipment, sporting goods, consumer

electronics, household appliances, CDs, DVDs, food storage containers and bottles. The tough, durable,

shatter- and heat-resistant material is ideal for a myriad of applications and is found in thousands of

every day products. {18}

Polycarbonate's versatility makes it excellent for creating functional, as well as aesthetically pleasing

products. It can be easily moulded and dyed in hundreds of colours - for products from car mirror

housings to mobile phone coverings to microwaveable containers, and can also be perfectly

transparent, making it ideal for use in eyeglasses. {18}

Background

In 1953, polycarbonate was discovered by Dr. H. Schnell at Bayer AG, Germany, and by D. W. Fox at

General Electric Company, USA working independently. In the late 1950s polycarbonate began to be

used in commercial applications. {18}

Polycarbonate was initially used for electrical and electronic applications such as distributor and fuse

boxes, displays and plug connections and subsequently for glazing for greenhouses and public buildings.

Soon polycarbonates outstanding combination of beneficial characteristics made it the material of

choice for many other applications. {18}

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In 1982, the first audio-CD was introduced to the market, quickly replacing audio records. Within 10

years optical media technology included CD-ROMs, and within 15 years DVDs. All these optical data

storage systems depend on polycarbonate. {18}

Since the mid 1980s, 18 litre water bottles made of polycarbonate have increasingly replaced heavy

and fragile glass bottles. These light-weight and shatter resistant bottles can now be found in many

public buildings and offices. {18}

Already used in the USA since the end of the 1980s, automotive headlamps made of polycarbonate

became authorised in Europe in 1992. Today, only 10 years later, almost every new European car is

equipped with polycarbonate headlamps.{18}

Manufacturing process

Originally, the first industrial process proposed for the production of polycarbonate was via melt

transesterification between diphenyl carbonate (DPC) and bisphenol A (BPA). From the mid-1990s,

there has been renewed interest in this production method and a significant emergence of the use of

melt technology. {19}

First, the use of phosgene, owing to its extreme toxicity, requires rigorous process design standards and

controls as well as specialized training. The interfacial process produces corrosive byproducts that need

to be contained in particular equipment and require constant maintenance. Additionally, the typical

solvent used for the interfacial system is methylene chloride which also has strict exposure

limits. Disposal of the corrosive byproducts of the interfacial system, the chlorinated solvent and the

other waste salt solutions formed from the caustic soda are serious environmental concerns. Growing

worry about environmental effects of the interfacial process, its byproducts and the use of phosgene

have pushed the commercialization of melt techniques (where no phosgene or chlorinated solvents are

required) and newer, more efficient, catalysts and process designs. {19}

There are some engineering design differences and individual plant specifications but the general

chemistry of polycarbonate production via melt transesterification remains the same. Major technology

differences are in the production route to the key feedstock, diphenyl carbonate (DPC). {19}

Melt transesterification takes place in two stages. In the first stage, DPC and BPA are combined with

small amounts of basic catalysts such as sodium, lithium or tetraalkylammonium hydroxides or

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carbonates in a melt reactor and the reaction shown below occurs, giving a pre-polymer and liberating

phenol.

This phenol is removed via distillation. By the end of all the reaction stages, the melt is so viscous that

usually specialized equipment such as stirred tanks, helical reactors, screw extruders and wiped film

evaporators must be used. As no solvent is used, the polycarbonate melt, when isolated from the

phenol formed, is spun in the form of strands and granulated. {19}

One of the key requirements for the transesterification process is the use of clean starting materials and

most technologies incorporate specific techniques for rigorous purification of BPA and DPC. Initial

incarnations of the melt process produced sub-par polycarbonate that was discolored due to extensive

heat exposure and impure reactants. In recent years, improved catalyst systems, more reactive

carbonates and more efficient processes (discussed further) have enabled polycarbonate equivalent to

interfacial polycarbonate to be produced. {19}

Characteristics

Polycarbonate derived from BPA is a very durable material. Although it has high impact-resistance. The

characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA, acrylic), but

polycarbonate is stronger, usable in a wider temperature range. This polymer is

highly transparent to visible light and has better light transmission characteristics than many kinds of

glass. Unlike most thermoplastics, polycarbonate can undergo large plastic deformations without

cracking or breaking. As a result, it can be processed and formed at room temperature using sheet

metal techniques, such as forming bends on a brake. Even for sharp angle bends with a tight radius, no

heating is generally necessary. This makes it valuable in prototyping applications where transparent or

electrically non-conductive parts are needed, which cannot be made from sheet metal. Low water

absorption high heat resistance, thermal stability and good electrical properties and very high impact

strength are among the many desirable properties that Polycarbonates possess.{20}

Polycarbonate exhibits very high deflections under impact conditions, which can result in higher loading

into the aircraft structure, compared to glass or acrylic windshield and window panels. This polymer it is

very susceptible to degradation by the environment due to moisture absorption and solvent stress

cracking, as well as UV degradation. It is possible to prevent degradation by using good design and

production practices and incorporating coatings and other forms of encapsulation. It also suffers from

phenomena known as physical aging. This results in change from ductile properties to brittle properties

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that occur when polycarbonate is exposed to temperatures between 80C and 130C. This materials

fatigue properties are similar to metals when working stresses are used for operating pressure loading

design. {8}

Uses

Aeronautic uses

The cockpit canopy of the F-22 Raptor jet fighter is made from a piece of high optical quality

polycarbonate, and is the largest piece of its type formed in the world. {21}

[http://www.globalsecurity.org/military/systems/aircraft/f-22-cockpit.htm]

Illustration 9: F-22 Raptor Cockpit {22}

The Gulfstream G100 windshield is also made of polycarbonate.

Illustration 10: Gulfstream G100 windshield structure

Other uses

The characteristics explained above make polycarbonate suitable for many applications, including:

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Automotive: Polycarbonate plastic moulded mirror housings, tail lights, turn signals, back-up lights, fog

lights, and headlamps all contribute to a vehicles unique style.

Packaging: Polycarbonate bottles, containers and tableware can withstand extreme stress during use

and cleaning, including sterilisation. They can be used to serve, freeze and reheat food in the microwave

making them time and energy savers. Shatterproof and virtually unbreakable, polycarbonate is a safer

alternative to glass.

Appliances & Consumer Goods: Polycarbonates moulding flexibility styling and colouring possibilities

make it perfect for use in electric kettles, fridges, food mixers, electrical shavers and hairdryers, while

fulfilling all safety requirements such as heat resistance and electrical insulation.

Electrical & Electronics: Polycarbonates light weight and impact- and shatter-resistant qualities make it

perfect for housing cell phones, computers, fax machines, and pagers while at the same time

withstanding the bangs, scratches and accidental drops of everyday use. Also its very important that

CDs and DVDs are made from Polycarbonate.

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Polyurethane

Polyurethane (PUR and PU) is a polymer composed of a chain of organicunits joined

by carbamate (urethane) links. While most polyurethanes are thermosetting polymers that do not melt

when heated, thermoplastic polyurethanes are also available. {23}

Polyurethane polymers are formed by reacting an isocyanate with a polyol. Both the isocyanates and

polyols used to make polyurethanes contain on average two or more functional groups per molecule.

{28}

Background

In the 1990s new two-component polyurethane and hybrid polyurethane-polyurea elastomers were

used for spray-in-place load bed liners and military marine applications for the U.S. Navy. A one-part

polyurethane is specified as high durability deck coatings under MIL-PRF-32171 for the US Navy. This

technique for coating creates a durable, abrasion resistant composite with the metal substrate, and

eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners. {24}

Rising costs of petrochemical feedstocks and an enhanced public desire for environmentally

friendly green products raised interest in polyols derived from vegetable oils. One of the most vocal

supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company. {24}

The Manufacturing Process

While polyurethane polymers are used for a vast array of applications, their production method can be

broken into three distinct phases. First, the bulk polymer product is made. Next, the polymer is exposed

to various processing steps. Finally, the polymer is transformed into its final product and shipped. This

production process can be illustrated by looking at the continuous production of polyurethane foams.

{24}

Polymer reactions

At the start of polyurethane foam production, the reacting raw materials are held as liquids in large,

stainless steel tanks. These tanks are equipped with agitators to keep the materials fluid. A metering

device is attached to the tanks so that the appropriate amount of reactive material can be pumped out.

A typical ratio of polyol to diisocyanate is 1:2. Since the ratio of the component materials produces

polymers with varying characteristics, it is strictly controlled. {24}

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The reacting materials are passed through a heat exchanger as they are pumped into pipes. The

exchanger adjusts the temperature to the reactive level. Inside the pipes, the polymerization reaction

occurs. By the time the polymerizing liquid gets to the end of the pipe, the polyurethane is already

formed. On one end of the pipe is a dispensing head for the polymer. {24}

Processing

The dispensing head is hooked up to the processing line. For the production of rigid polyurethane foam

insulation, a roll of baking paper is spooled at the start of the processing line. This paper is moved along

a conveyor and brought under the dispensing head. {25}

As the paper passes under, polyurethane is blown onto it. As the polymer is dispensed, it is mixed with

carbon dioxide which causes it to expand. It continues to rise as it moves along the conveyor. (The sheet

of polyurethane is known as a bun because it "rises" like dough.) {25}

After the expansion reaction begins, a second top layer of paper is rolled on. Additionally, side papers

may also be rolled into the process. Each layer of paper contains the polyurethane foam giving it shape.

The rigid foam is passed through a series of panels that control the width and height of the foam bun.

As they travel through this section of the production line, they are typically dried. {25}

At the end of the production line, the foam insulation is cut with an automatic saw to the desired

length. The foam bun is then conveyored to the final processing steps that include packaging, stacking,

and shipping. {25}

Characteristics

Parts made of polyurethane will often outwear other materials by a margin of 5 to 50/one when

severe abrasion is a factor. It has been proven to be vastly superior to rubber plastics and metal in many

applications.

Polyurethane has excellent resistance to oils, solvents, fats, greases and gasoline.

Polyurethane has a higher load-bearing capacity than any conventional rubber. Because of this

characteristic, it is an ideal material for load wheels, heavy duty couplings, metal-forming pads, shock

pads, expansion joints and machine mounts.

Tear-strength ranges between 500-100 Ibs./linear inch, which is far superior to rubbers. As a result,

urethane is often used as drive belts, diaphragms, roll covers, cutting pads, gaskets and chute liners.

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Polyurethane has outstanding resistance to oxygen, ozone, sunlight and general weather conditions.

The hard urethanes are now being used as gears in products where engineers desire sound

reduction. The soft urethanes are used to replace rubbers for improved sound/vibration dampening.

Most formulations offer extremely high flex-life and can be expected to outlast other elastomer

materials where this feature is an important requirement. Dust boots, bellows, diaphragms, belts,

couplings and similar products are made from urethane for this reason.

Polyurethane has excellent electrical insulating properties and is used successfully in many moulded

wire and cable harness assemblies.

Continuous use above 225F is not recommended nor is urethane recommended in hot water over

175F. At low temperatures, polyurethane will remain flexible down to -90F. A gradual stiffening will

occur at 0F, but will not become pronounced until much lower temperatures are obtained. {25}

Table 1 Polyurethane Material Properties {26}

Uses

Aerospace: polyurethane is used as a material in the production of commercial and military aircrafts

transparencies.

Automotive: Polyurethanes are used throughout cars. In addition to the foam that makes car seats

comfortable, bumpers, interior headline ceiling sections, the car body, spoilers, doors and windows all

use polyurethanes. Polyurethane also enables manufacturers to provide drivers and passengers

significantly more automobile mileage by reducing weight and increasing fuel economy, comfort,

corrosion resistance, insulation and sound absorption.

22

Building and Construction: Polyurethane helps conserve natural resources and helps preserve the

environment by reducing energy usage. With its excellent strength-to-weight ratio, insulation

properties, durability and versatility, polyurethane is frequently used in building and construction

applications.

Composite Wood: Polyurethanes play a major role in modern materials, such as composite wood.

Polyurethane-based binders are used in composite wood products to permanently glue organic

materials into oriented strand board, medium-density fiberboard, long-strand lumber, laminated-

veneer lumber and even strawboard and particleboard.

Furnishings: Polyurethane, mostly in the form of flexible foam, is one of the most popular materials

used in home furnishings such as furniture, bedding and carpet underlay. As a cushioning material for

upholstered furniture, flexible polyurethane foam works to make furniture more durable, comfortable

and supportive.

Marine: Polyurethane epoxy resins seal boat hulls from water, weather, corrosion and elements that

increase drag, affect hydrodynamics and reduce durability. In addition, rigid polyurethane foam

insulates boats from noise and temperature extremes, provides abrasion and tear resistance, and

increases load-bearing capacity all while adding minimal weight. Thermoplastic polyurethane is also

great for use in the maritime industry. It is elastic, durable and an easily processed substance, well

suited for wire and cable coatings, engine tubing, drive belts, hydraulic hoses and seals and even ship

molding.

Packaging: Polyurethane packaging foam (PPF) can provide more cost-effective, form-fitting

cushioning that uniquely and securely protecting items that need to stay safely in place during transit.

PPF is widely used to safely protect and transport many items, such as electronic and medical diagnostic

equipment, delicate glassware and large industrial parts. A versatile on-site solution for many

packaging challenges, PPF can save time and be more cost-effective by providing a custom-fit container

with each shipment. {27}

23

The Future

The quality of polyurethanes has steadily improved since they were first developed. Research in a

variety of areas should continue to help make superior materials. For example, scientists have found

that by changing the starting prepolymers they can develop polyurethane fibers which have even better

stretching characteristics. Other characteristics can be modified by incorporating different fillers, using

better catalysts, and modifying the prepolymer ratios.

In addition to the polymers themselves, the future will likely bring improvements in the production

process resulting in faster, less expensive, and more environmentally friendly polyurethanes. A recent

trend in polyurethane production is the replacement of toluene diisocyanates with less-volatile

polymeric isocyanates. Also, manufacturers have tried to eliminate chlorinated fluorocarbon blowing

agents which are often used in the production of polyurethane foams. {28}

24

Other materials

Sealants A sealant may be viscous material that has little or no flow characteristics and stay where they are

applied or thin and runny so as to allow it to penetrate the substrate by means of capillary action.

Anaerobic acrylic sealants generally referred to as impregnants are the most desirable as they are

required to cure in the absence of air, unlike surface sealants that require air as part of the cure

mechanism that changes state to become solid, once applied, and is used to prevent the penetration

of air, gas, noise, dust, fire, smoke or liquid from one location through a barrier into another. Typically,

sealants are used to close small openings that are difficult to shut with other materials, such

as concrete, drywall, etc. Desirable properties of sealants include insolubility, corrosion resistance,

and adhesion. Uses of sealants vary widely and sealants are used in many industries, for example,

construction, automotive and aerospace industries. {29}

The main difference between adhesives and sealants is that sealants typically have lower strength and

higher elongation than do adhesives. Since the main objective of a sealant is to seal assemblies and

joints, sealants need to have sufficient adhesion to the substrates and resistance to environmental

conditions to remain bonded over the required life of the assembly. When sealants are used between

substrates having different thermal coefficients of expansion or differing elongation under stress, they

need to have adequate flexibility and elongation. Sealants generally contain inert filler material and are

usually formulated with an elastomer to give the required flexibility and elongation. They usually have a

paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often

required. Many adhesive technologies can be formulated into sealants. {29}

A sealant that is used in the aircraft window is PR-1425 Class B Windshield and Canopy Sealant it has a

service temperature range from -54C to 121C. This material is designed for a fillet sealing of properly

prepared glass, polycarbonate, acrylic and other aircraft sealing application. This sealant exhibits

excellent resistance to UV and weather exposure. PR-1425 class B is a two-part, dichromate cured

polysulfide compound. The uncured material is low sag, thyrotrophic paste, suitable for application by

extrusion gun or spatula. This sealant has excellent adhesion to common aircraft substrates. {30}

Another sealant used is PR-1829 Class B Rapid Curing Windshield and Canopy Sealant, it has a service

temperature range from -62C to 216C. This material is designed for a fillet sealing of properly

prepared glass, polycarbonate, acrylic and other aircraft sealing application. PR-1829 Class B is a two-

part, epoxy cured Permapol P-3 polythioether compound. The uncured material is a low sag, thixotropic

25

paste, suitable for application by extrusion gun or spatula. Unlike standard polysulfide windshield

sealants, it can cure at low temperatures and unaffected by changes in relative humidity. This sealant

has excellent adhesion to commn aircraft substrates. {31}

Comparison Commercial, military and regional aircrafts window

With the aim to compare different aircraft windows from military, commercial and regional aircrafts, all

materials for each window will be introduced.

For commercial aircrafts the example that it will be taken is the window of and Airbus

A318/319/320/321. Herculite II Chemically Strengthened Glass Structural Plies is used as a main glass

material, it has high strength-to-weight ratio and Chemical and abrasion resistance as it was introduced

before.Between the two Herculite II coats a Vinyl interlayer is used.At the outbound Thermally

Tempered Glass Outboard Ply can be found it has Chemical and abrasion resistance and High load-

carrying capabilities, it has to work as outbound glass. Between Herculite II and outbound glass S-123

Urethane Interlayer can be found, it provides maximum adhesion to glass, have high resistance to

moisture damage and Its Elasticity at low temperatures reduces delamination and cold chipping

potential. . Between interlayer coat and the Silicone gasket a sealant is used, in this case the PR-2060

Internal Moisture Seal it works as a Superior moisture barrier that less moisture absorption and it have

Environmentally friendly formulation. {32}

26

In the case of military aircrafts the example took is the Lockheed Martin F-16. The canopy

transparencies of F-16 are composed of 2 main ply coats and an interlayer, that are protected in

inbound and outbound with protective coat and metal coat respectively. The main plies of the F-16 can

be made by Herculite II chemically strengthened glass that provides superior strength and durability,

special-composition glass that incorporates enhanced optical properties such as high light

transmittance, acrylic that is strong and lightweight, and polycarbonate that has superior impact

resistance and a high strength-to-weight ratio. {33}

In the Regional Aircraft case the example choosed was Bombardier Aerospace

CRJ100/CRJ200/CRJ700/CRJ900/CRJ1000 that uses a main windshield structure similar at commercial

aircfrats one. Herculite II Chemically Strengthened Glass Structural Plies is used as a main glass material,

it has high strength-to-weight ratio and Chemical and abrasion resistance as it was introduced before.

But in this case 3 coats of Herculite II are used, the third one was used for outbound glass. Between

each Herculite II coat it can be found a Vinyl interlayer and in the boundary with vinyl interlayer and

outbound coat it can be found another coat. That coat is PPG 112 Urethane that is applied as another

interlayer. {34}

27

Depending of the function of the aircraft that is window made for, it will have a different structure.

Three different aircraft function structure has been briefly explained and looked the difference between

three ones. The regional and commercial have a very different function than militaries so the materials

and structure are similar, taking in account that commercial aircrafts flight higher and at more speed.

Military aircraft have a different structure and materials because the function is to resist attacks for

example, and they have to be prepared.

28

AIRCRAFT WINDSHIELD AND WINDOW CARE AND MAINTENANCE

Most aircraft windows used in regional aviation are acrylic plastic (as opposed to "Lexan" or

polycarbonate), and acrylic plastic is scratchable. Proper care involves preventing scratches that are

preventable and properly taking care of those that are not.

When cleaning a window, always remove as much abrasive dirt as possible without touching the

surface. Ideally this would involve flushing the surface with water and allowing the accumulated bug

residue to soak, possibly with a little dish washing liquid added to the water. If a little rubbing is needed,

it has to be done lightly with the bare hand. After a final flushing with more water and carefully drying

with a clean soft cloth, it is needed to use a good grade cleaner/polish intended for acrylic windows.

We need to step back here and take a look at cleaner/polishes. The good ones, at least those that are

safe to use on acrylic plastics, tend to be the commercial ones, intended to be used on this specific

material. The bad ones, including the very dangerous, tend to be materials never intended to be used as

an aircraft window cleaner/polish, such as glass cleaners and furniture polish. Glass cleaners invariably

contain ammonia, a killer of acrylics. It is very important to avoid use anything containing ammonia on

acrylic plastics. It will cause crazing (thousands of microscopic cracks) in short order. Furniture polish

seems to be safer, but its long-term use is undocumented and reports indicate it builds up and produces

smears that are hard to polish off. Something to consider about furniture polish - it is intended to be

used indoors, not outdoors, and on furniture, not aircraft windows. Furthermore, it's not much less

expensive than many aircraft window products.

Other products to keep away from your windows include any aromatic solvent, such as methyl ethyl

ketone, acetone, lacquer thinner, gasoline (a minor fuel spill should do no harm), and, heaven forbid,

paint stripper. If it is needed to remove masking tape residue or other sticky or greasy stuff, the safest

solvents are 100% mineral spirits or kerosene. Some alcohols are safe, such as isopropyl alcohol, but not

all.

Concerning the polishing cloth, it is better the softest cotton cloth available. One hundred per cent

cotton flannel is ideal and available in yard goods stores. Old washed-out cotton T-shirts are a good

second choice. One benefit of cotton cloth is that it can be washed, thereby effectively recycling the

material.

29

First, it's best to understand what types of products are available. They can be loosely grouped into

three categories:

1. Non-abrasive liquid sprays, in pumps or aerosols, that may or may not have scratch filling properties.

2. Non-abrasive creams that have scratch filling properties.

3. Mildly-abrasive creams that have scratch removing properties.

Since windows do accumulate minute scratches as part of everyday life (the kind you can't feel with a

fingernail but can really see when flying into the sun), the products that fill fine scratches are great for

regular use. If scratches still appear when flying toward the sun, the abrasive variety and some elbow

grease are called for. This type of cleaner should be used occasionally only as needed. Most

manufacturers of abrasive cleaners recommend following up with a scratch filling product as a second

step.

So what happens when you have scratches that you can't take care of with the above methods and

perhaps you can feel with a fingernail? You have to get more aggressive. The danger, though, is in

getting too aggressive.

Practically speaking, the only way to remove a scratch from clear acrylic is to remove material from

around the scratch down to the greatest depth of the scratch, then polishing the window back to clarity.

There are two problems with this process. First, polishing back to clarity can be a difficult process

especially if you started with a coarser than necessary abrasive. Second, it is very easy to induce an

annoying and possibly dangerous optical distortion if you have not worked evenly in a large enough

area.

Another consideration, especially on light aircraft, is the feasibility of trying to repair some windows.

The windshield on the Cessna 150, for instance, is .125 (or 1/8") thick, and some Piper Cherokee rear

windows are only .080 (or 5/64") thick. So when you start to remove material, you have to be aware of

what you will have left structurally. Keep in mind that most repairable windows, such as those found on

pressurized air liners, have published specifications for minimum allowable thickness. Most light aircraft

have no such specification. Sometimes, labor spent on a repair attempt would probably be better spent

installing a new window.

Another word of caution. If you are working on a homebuilt with polycarbonate, or "Lexan," windows,

there is no good way to remove scratches. Polycarbonate is so soft that any attempt to remove material

30

by abrasion will do more harm that good. There are hard coated varieties of polycarbonate that are less

scratchable, but trying to repair a scratch in these will only remove the hard coating. Your only option

will be to fill minor scratches with a scratch-filling polish or replace the window.

OTHER CARE PROBLEMS

Occasionally, there are reports of canopy covers and sun shields that do damage in ways that are

surprising. Canopy covers, the ones that cover the outside of the windshield and windows, certainly

have to be made of a soft material on the side that contacts the windows, but they must also be cinched

down tight to prevent fluttering in the wind. Keep in mind that minute abrasive particles between the

canopy cover and the windows are practically impossible to eliminate, and any movement of the cover

grinds away at the windows.

Sun shields, the reflective curtains applied to the inside of the windshield and windows, sometimes have

sharp metallic edges (especially the home made variety) that can scratch severely enough to warrant

window replacement in short order. Trying to remove scratches from the inside of a sharply sloping

windshield can be especially trying. But both canopy covers and sun shields can cause damage of a

chemical nature also. Some plastics, especially vinyls, can release plasticizers that will attack acrylics. A

common example of this type of reaction is a fresh photocopy placed inside a vinyl notebook with the

ink touching the vinyl. Soon you have everything sticking together. On an aircraft, if you have a volatile

plastic in close proximity to your windows and add the heat of the sun, you may soon have severely

crazed and damaged windows.

Certainly not all canopy covers and sun shields cause this problem, but it is a good question to ask at

purchase time. Just be sure you are not sacrificing your windshield and windows at the same time you

are protecting the avionics and interior.

But for all that can go wrong and shorten the life of aircraft windshields and windows, many flying today

are well over 20 years old. If properly installed and maintained, longevity can, and regularly is, attained.

It is needed to understand the material and the processes, and the rest is easy. {35}

31

Future

ALTEOS Interactive window systems, for passenger cabin windows

Designed to replace conventional plastic pull-down shades, Alteos interactive window systems afford

operating efficiencies while putting passengers in control of their environment.

The worlds first electrochromic window shades for commercial aircraft passenger cabins, these

advanced systems switch from a bright clear state to a totally dark state or a comfortable intermediate

level all at the touch of a button.

Passengers can enjoy expansive views from their seats without annoying glare for a feeling of openness

in the cabin. Or they can darken the window system at their seat to keep light out.

Alteos interactive window systems are self-contained with no moving parts and lightweight, making

them easy to maintain. An electronically dimmable panel is installed between the inboard dust cover

and outboard structural cabin window system. A window-seat control allows the passenger to activate

the system and change the amount of visible light transmitted to maximize it, minimize it or select an

intermediate setting. Passengers see only a stylish window and control button. With Alteos interactive

window systems, keeping the cabin comfortable is easy. Ultraviolet and infrared radiation transmission

are reduced, lowering the heat load inside the cabin and enhancing the operating efficiency of the

aircrafts heating, ventilating and air conditioning system. If desired, the interactive devices can be

linked via the onboard network to allow for flight crew override and continuous monitoring of system

performance. Should a power loss occur, the window systems default to a clear state to maintain

maximum light transmittance, ensuring compliance with aviation standards.

Benefits of Alteos Interactive Window System

Time-tested chemistry and durable device construction designed to perform more than 70,000

darken/bleach cycles

Low-voltage DC operation

Color neutral throughout transmission range

High vision clarity at all light transmittance levels

Operation across typical flight temperature ranges

Widest available light transmission range through an electrochromic panel

32

Default to clear state on loss of power

Complete ultraviolet blocking

Electrochomic Technology

Electrochromic technology uses electricity to change the color of and light transmission through a

transparent medium (very thin films, gels, etc.) that is typically sandwiched between two thin glass

plies. The electric current passes across transparent conductive coatings on the

inner-facing surfaces of the glass, causing a chemical reaction to occur in the electrochromic medium.

This chemical reaction causes the electrochromic medium to change opacity. The Gentex

electrochromic technology utilizes gel as the electrochromic medium. Applying a small electrical voltage

across the gel causes it to darken, while removing the voltage allows the gel to return to its natural

transparent state. The voltage can be precisely controlled and adjusted in small increments to allow

intermediate states of light transmittance to be selected. {36}

ComparativaPMMA is an economical alternative to polycarbonate (PC) when extreme strength is not

necessary. Additionally, PMMA does not contain the potentially harmful bisphenol-A subunits found in

polycarbonate. It is often preferred because of its moderate properties, easy handling and processing,

and low cost.

33

Conclusions

In this project we have learned about:

The importance on the aircrafts windows. Them have to be there for aloud pilots and

passengers to see through them.

How it can affect the shape that the windows have. It is important that them have rounded

shapes to avoid fatigue problems.

Which are the main materials used. The more used material in aviation windows is Herculite,

manufactured by the PPG Company and it is a Chemical strengthened glass that aloud to do the

glass more thin for the same pressure difference.

How to properly take care of the windows to avoid cracks and to how to treat them.

The future of the windows that will probably be replaced by a display that aloud the passenger

to moderate the brightness.

34

Bilbiografia {1} http://www.aerospaceweb.org/aircraft/jetliner/comet/

{2} David Cardinal, May 25, 2012 at 10:00 am. Tech wrecks: Lessons from some of the biggest hardware screw-ups. [http://www.extremetech.com/wpcontent/uploads/2012/05/de-Havilland-Comet-1-showing-square-windows.jpg]

{3} http://www.oocities.org/capecanaveral/lab/8803/p5cyp06.jpg

{4} http://www.oocities.org/capecanaveral/lab/8803/p5cyp07.jpg

Autor(Apellidos, Nombre). "Ttulo del recurso",[tipo de recurso]. Fecha de creacin, fecha de

actualizacin, [fecha de la cita]. Direccin de la Pgina Web.

{5} PMMA-Wikipedia. [Online]. [2013].

http://en.wikipedia.org/wiki/Poly%28methyl_methacrylate%29 {6} Evelyn S. Dorman /Chris Cavette. How products are made. Acrylic [Online] [2002] http://www.madehow.com/Volume-2/Acrylic-Plastic.html {7} Physical Properties of Acrylic Sheets, [PDF] http://www.builditsolar.com/References/Glazing/physicalpropertiesAcrylic.pdf {8} L.Lipski Advisory Circular: Windows and Windshields. FAA [PDF]. [2003].

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2025.775-

1/$FILE/AC25-775-1.pdf

{9} Josef Weiss. Canopies Side Transparencies &Co.[Online]. [2013].

http://www.plexiweiss.de/en/aircraft-glazing-corporate/canopies-and-transparencies.php

{10} U.S. Air Force Boeing B-17 nose detail. [Photo]. [1944].

http://www.nationalmuseum.af.mil/shared/media/photodb/photos/060518-F-1234S-002.jpg

{11} Karsten Palt. Robin DR 400. [Photo]. [2013].

http://www.flugzeuginfo.net/acdata_php/acdata_robindr400_en.php

{12} Glazzete Co. Chemically Strengthened Glass [Online]

35

http://www.glazette.com/Glass-Knowledge-Bank-87/Chemically-Strengthened-Glass.html

{13} Prel Co. Chemically Strengthened Glass manufacturing process [Photo] [2004].

http://www.prelco.ca/en/?p=prod_prelgard-tc

{14} Prel Co. Chemically Strengthened [Online] [2004]. http://www.prelco.ca/en/?p=prod_prelgard-tc

{15} PPG Co. Aerospace Transparencies [Online ] [2013].

http://www.ppg.com/coatings/aerospace/transparencies/Pages/default.aspx

{16} PPG Co. Boeing 787 Transparencies [Online ] [2013].

http://www.ppg.com/coatings/aerospace/transparencies1/B787_tb_v9.pdf

{17} PPG Co. Airubs A320 series Transparencies [Online ] [2013].

http://www.ppg.com/coatings/aerospace/transparencies/Documents/Airbus_A318_319_320_321_final

.pdf

{18} Plastics Europe What is polycarbonate?[Online]

http://www.plasticseurope.org/what-is-plastic/types-of-plastics/polycarbonate/what-is-

polycarbonate.aspx

{19} Nexant Inc.PERP Program Polycarbonate. [Online] [2013].

http://www.chemsystems.com/about/cs/news/items/PERP0910_7_Polycarbonate.cfm

{20} Laird Plastics Co. Polycarbonate. [Online]

[http://www.lairdplastics.com/product/materials/polycarbonate.

{21} Global Security. F-22 Raptor Cockpit. [Online]

http://www.globalsecurity.org/military/systems/aircraft/f-22-cockpit.htm

{22} U.S. Air Force photo by Lisa Carroll Maj. Michael Hoepfner completes his checkout flight in Raptor

No. 18 recently as the first local F/A-22 fighter pilot to finish his training here. [2008] [Photo]

http://www.af.mil/shared/media/photodb/photos/040114-F-0000S-001.jpg

36

{23} {PPG Co. Gulstream G100 Transparencies PPG [Online ] [2013].

http://www.ppg.com/coatings/aerospace/transparencies1/IAI-Astra-GulfstreamG100.pdf

{24} http://www.wisegeek.org/what-is-polyurethane.html

{25} http://en.wikipedia.org/wiki/Polyurethane

{26} http://www.sdplastics.com/polyuret.html

{27}

http://www.ppg.com/coatings/aerospace/ballistics/Documents/Polyurethanes_Specialty_Product.pdf

{28} http://polyurethane.americanchemistry.com/Introduction-to-Polyurethanes/Applications

{29} http://www.madehow.com/Volume-6/Polyurethane.html

{30} http://en.wikipedia.org/wiki/Sealant

{31} http://www.ppg.com/coatings/aerospace/sealants1/pr_1425_class_b.pdf

{32} http://www.ppg.com/coatings/aerospace/sealants1/pr_1829.pdf

{33}

http://www.ppg.com/coatings/aerospace/transparencies/Documents/Airbus_A318_319_320_321_final

.pdf

{34} http://www.ppg.com/coatings/aerospace/transparencies1/F-16_tb.pdf

{35} http://www.ppg.com/coatings/aerospace/transparencies1/CRJ100_tb_final.pdf

{46} http://www.lpaero.com/CAREINS.html

{37} http://www.ppg.com/coatings/aerospace/transparencies1/alteos_comm_tb_09.pdf

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6168-2.

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Myer Ezrin Plastics failure guide: cause and prevention, Hanser Verlag, 1996 ISBN 1-56990-

184-8, p. 168

^ Chiemi Ishiyama, Yoshito Yamamoto and Yakichi Higo (2005). "Effects of Humidity

History on the Tensile Deformation Behaviour in Poly(methyl-methacrylate) (PMMA) Films".

MRS Proceedings 875: O12.7.

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