Assignment # 01 (TE-671) 10-NTU-6012

8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012

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TE-671

TEXTILE COMPOSITES

ASSIGNMENT # 01

THERMOPLASTIC AND THERMOSET POLYMERS

FOR

TEXTILE COMPOSITES

SUBMITTED BY

MUHAMMAD SAJID FAHEEM

10-NTU-6012


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INTRODUCTION:

Polymer Matrix Composites (PMCs):

Polymer Matrix Composites are materials that consist of polymer/resin (which

forms a matrix) and a reinforcing dispersed phase (which is usually in fibrous form).

Polymer Matrix Composites have popularity due to low cost and simple manufacturingmethods. Polymer Matrix Composites have two main disadvantages, low thermal

resistance and high coefficient of thermal expansion.

Types of Polymer Matrix Composites:

There are two main categories of Polymer matrix composites depending upon the

nature of polymer:

(1) Thermoplastic Polymer Matrix Composites

(2) Thermosetting Polymer Matrix Composites

THEMOPLASTIC AND THERMOSETTING POLYMERS:

Polymers have two major types based on their behavior when exposed to heat:

(1) Thermoplastic Polymers(2) Thermosetting Polymers

Characteristics of Thermoplastic Polymers:

Thermoplastic polymers are generally ductile and tougher than thermoset polymers.

Thermoplastic polymers can be melted by heating and solidified by cooling, due to whichthey are capable to undergo repeated reshaping and reforming. The individual molecular

chains in thermoplastic polymers do not cross-link and therefore these polymers are

flexible and reformable. Thermoplastic polymers may be either in amorphous or

semicrystalline form. Typically higher forming temperatures and pressures are requiredfor manufacturing of thermoplastic polymers than comparable thermoset systems.

In thermoplastic polymers, individual molecular chains have linear structure withno chemical linkage between them. These molecular chains are held together in place by

weak intermolecular forces such as Vander Waals forces and hydrogen bonding. On

application of heat and pressure, these intermolecular bonds in a solid thermoplastic

polymer can be temporarily broken, and the molecular chains can be moved relative toeach other to flow into new positions. On cooling, the molecular chains solidify in their

new positions, restoring the weak intermolecular forces between them and resulting in a

new solid shape.

Thus, a thermoplastic polymer can be softened and melted on heating, and

reshaped or reformed as many times as desired.


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Types of Thermoplastic Polymers used for PMCs:

Applications of Thermoplastic Polymers in the form of PMCs:

Nylons (Nylon 6, Nylon 6.6)

Thermoplastic Polyester (PET, PBT),

Polycarbonate (PC),Polyacetals

Used for injection molded articles in the form of

discontinuous fibers

Polyamide-imide,

Poly-ether ketone (PEEK),

Polysulfone (PSUL),Polyphenylene sulfide (PPS),

Polyether imide (PEI)

Used for moderately high temperature

applications in the form of continuous fibers


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Thermosetting Polymers:

Thermoset materials cannot be remelted or reformed after when these materials arecured. During the curing process, these materials form three-dimensional molecular

chains, which are known as cross-linkings. Due to these cross-linkings, the molecules are

not flexible and cannot be remelted and reshaped. The greater the number of cross-linkings, the more rigid and thermally stable the material will be. Thermosets may soften

to some extent at higher temperatures. Thermosets are brittle in nature and are generally

used with some form of filler and reinforcement. Easy processability and better fiberimpregnation can be achieved when thermosetting polymers are used because the liquid

resin is used at room temperature for various processes. Thermosets offer greater

dimensional stability, better rigidity, and higher electrical, chemical, and solvent

resistance.

In thermoset polymers, the molecular chains are chemically joined together by

cross-linking, forming a rigid and three-dimensional network structure. Once these cross-

links are developed during the polymerization process/reaction (which is known as thecuring reaction), the thermoset polymer cannot be softened or melted and reshaped by

applying heat and pressure. But if there is lower the number of cross-linkings between themolecular chains then it is possible to soften them at higher temperatures.

Thermoset materials are generally stronger than thermoplastic materials due 3-Dnetwork of molecular chains and also exhibit better performance at high-temperature up

to the decomposition temperature of the material.

Types of Thermosetting Polymers used for PMCs:


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Applications of Thermosetting Polymers in the form of PMCs:

Epoxies Used in aerospace and aircraft applications

Polyester,Vinyl Esters

Used in automotive, marine, chemical and electricapplications

Phenolics Used in bulk molding compounds

Polyimides,

Polybenzimidazoles (PBD),Polyphenylquinoxatine (PPQ)

Used for high temperature aerospace applications

(temperature range: 250-400C)

PROCESSING OF THERMOPLASTIC AND THERMOSETTING

POLYMER FOR MANUFACTURING PMCS:

Following are the different polymer matrix manufacturing methods, which can be

applied to both types of resins such as thermoplastic and thermosetting polymers,however different considerations must be taken into account for each.

Hand Lay-up:

The resin material is usually rolled into reinforcing fibers that are placed in the

mold (after a release film and gel coat in some cases). Hand lay-up is commonly used in

the US aircraft industry to produce PMC parts.


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Spray Lay-up:

In spray lay-up the reinforcement fibers are first chopped and mixed with resinand then sprayed into the mold. In order to achieve the complete wetting of the fiber

bundles a roller is used. Using this technique low specific strength structures are

produced.

Manual Prepreg Lay-up:

The prepreg is cut into a large number of layers depending upon the mold. The

pre-cut prepregs are then layered within the mold.

Automatic Prepreg Lay-up:

(Applicable to flat panels or parts with moderate curves.) A tape-laying machine

lays the prepreg within the mold, automatically cut the prepreg when the mold edge is

reached. This process is continued until the part is completed.


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Compression Molding:

In this process uncured resin and reinforcing material are mixed together and then

spread into the cavity of a matched mold. As the mold is closed then the pressureincreases, which results in filling the mold and the part is formed. This method may be

used with prepregs also.

Liquid Composite Molding (LCM):

Resin Transfer Molding (RTM), Structural Reaction Injection Molding

(SRIM), and Injection Compression Molding are the different types of LCM. A

reinforcing fiber preform is placed in the mold cavity and a polymeric resin is injectedinto the sealed mold. Then a curing reaction starts which results in the solidification of

the part. The cured part is then removed from the mold. LCM is best suited for highproduction volumes to lower the cost because LCM has a very high, non-recurring

tooling cost.


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Vacuum- Assisted RTM:

The resin is injected into a mold containing the reinforcing fiber material. Thenthe atmospheric pressure is applied against an evacuated system.

Resin Film Infusion:

The resin film (which is usually preformed) is placed in the bottom of the mold.

Then with the help of heat and pressure applications the viscosity of the resin film isdecreased and as a result the resin film is spread through the preformed mold shape.

Expansion RTM:

In this technique the expansion of the material takes lace when heated is placed in

the preform. The resin is infused and the mold is heated which results in the expansion of

the core material and subsequently the resin is forced into the remaining parts of the

preform.

Transfer Molding:

The mechanism is similar to compression molding but the preformed mold is

closed when the resin material is injected into it.


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Filament Winding:

In this process the spools carrying the fibers are mounted to a creel. The strands offibers from each spool are combined together and pulled through a resin bath. The strands

are then fully activated with an initiator or hardener and the excess resin is removed.

Then these strands are passed through a drying device and wound on to mandrel, whichresults into a desired part. Filament winding is used more extensively to manufacture

composites than all other lay-up methods combined.

Fiber Placement:

Similar to filament winding, but enables all axes of motion.

Pultrusion:

Similarly as in the process of filament winding the continuous reinforcing fibers

are drawn from creels, formed into a general shape, and drawn through a resin bath. The

wetted fibers are then shaped (according to the requirement) as they converge toward aheated die, where curing occurs. As the perform exit the die it passes through a pulling

system, which provides the force that pulls the materials through the entire system. The

pultruded part is then cut and trimmed to the desired size.


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Thermoforming:

The matrices are used that can repeatedly be softened or melted on heating andhardened or solidified on cooling, and that can provide increased fracture toughness and

higher hot-wet use temperatures (thermoplastics).

Assignment # 01 (TE-671) 10-NTU-6012

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