Date post: | 06-Apr-2018 |
Category: |
Documents |
Upload: | sajid-faheem |
View: | 216 times |
Download: | 0 times |
of 12
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
1/12
TE-671
TEXTILE COMPOSITES
ASSIGNMENT # 01
THERMOPLASTIC AND THERMOSET POLYMERS
FOR
TEXTILE COMPOSITES
SUBMITTED BY
MUHAMMAD SAJID FAHEEM
10-NTU-6012
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
2/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
3/12
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
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
4/12
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:
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
5/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
6/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
7/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
8/12
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
9/12
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
10/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
11/12
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.
8/3/2019 Assignment # 01 (TE-671) 10-NTU-6012
12/12
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).