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Polymer Matrix Composites (PMC)

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Title: Polymer Matrix Composites (PMC)


1
Polymer Matrix Composites (PMC)
2
Reasons for the use of polymeric materials as
matrices in composites
  • i. The mechanical properties of polymers are
    inadequate for structural purposes, hence
    benefits are gained by reinforcing the polymers
  • Processing of PMCs need not involve high pressure
    and high temperature
  • The equipment required for PMCs are much simpler

3
Disadvantages of PMC
  • Low maximum working temperature
  • High coefficient of thermal expansion-
    dimensional instability
  • Sensitivity to radiation and moisture

4
Classification of Polymer Matrices
  • 1. Thermoset
  • 2. Thermoplastic- crystalline amorphous
  • 3. Rubber

5
Thermoset
  • Thermoset materials are usually liquid or
    malleable prior to curing, and designed to be
    molded into their final form
  • has the property of undergoing a chemical
    reaction by the action of heat, catalyst,
    ultraviolet light, etc., to become a relatively
    insoluble and infusible substance.
  • They develop a well-bonded three-dimensional
    structure upon curing. Once hardened or
    cross-linked, they will decompose rather than
    melt.
  • A thermoset material cannot be melted and
    re-shaped after it is cured.
  • Thermoset materials are generally stronger than
    thermoplastic materials due to this 3-D network
    of bonds, and are also better suited to
    high-temperature applications up to the
    decomposition temperature of the material.

6
  • Some examples of Thermosets are
  • Polyester resin (used in glass-reinforced
    plastics/fibreglass (GRP))
  • Epoxy resin (used as an adhesive and in fibre
    reinforced plastics such as glass reinforced
    plastic and graphite-reinforced plastic)
  • Polyimides used in printed circuit boards and in
    body parts of modern airplanes
  • Vulcanized rubber
  • Phenolic

7
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8
  • Polyester
  • polyester resins are generally copolymers of
    unsaturated polyesters with styrene
  • Styrene is the crosslinking monomer and curing is
    effected by the use of an organic peroxide
    initiator which generates free radicals leading
    to the formation of 3-D network
  • Are relatively inexpensive and have low
    viscosities, which is beneficial in many
    fabrication processes

9
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10
  • Epoxy
  • is a thermosetting epoxide polymer that cures
    (polymerizes and crosslinks) when mixed with a
    catalyzing agent or "hardener".
  • More expensive and more viscous than polyester
  • Epoxies have a major advantage in that they are
    usually cured in two or more stages. This allows
    preforms to be pre-impregnated with the epoxy in
    a partially cured state
  • The pre-preg may be stores, before moulded into
    the final shape and then cured

11
  • Generally start as linear low molecular weight
    polymer, curing agents such as polyamides
    polyamines were used as curing agents
  • The mechanical properties depend on the
    particular resin system and the curing generally
    epoxies are stiffer and stronger, but brittle
    than polyester
  • Epoxies maintain their properties to higher
    temperature than polyester

12
Phenolic
  • Produced by reacting phenol and formaldehyde,
    characteristics of the resin product depending on
    the proportions of the reactant and catalyst
  • Good fire resistance
  • An undesirable feature of phenolic resin-
    volatile by-product are evolved during curing
    hence high pressures are often necessary in
    composite production

13
Polyimides
  • More expensive, less widely used than polyester
    and epoxies, but can withstand relatively high
    service temperature
  • The presence of ring structure, results in high
    stiffness, low CTE, and service temperature as
    high as 425C for several hours
  • Like other thermoset, polyimides are brittle

where R' and R? are two carbon atoms of an
aromatic ring.
14
Thermoplastic
  • is a plastic that melts to a liquid when heated
    and freezes to a brittle, very glassy state when
    cooled sufficiently.
  • Most thermoplastics are high molecular weight
    polymers whose chains associate through weak van
    der Waals forces (polyethylene) stronger
    dipole-dipole interactions and hydrogen bonding
    (nylon) or even stacking of aromatic rings
    (polystyrene).
  • The bondings are easily broken by the cobined
    action of thermal activation and applied stress,
    thats why thermoplastics flow at elevated
    temperature
  • unlike thermosetting polymers, thermoplastic can
    be remelted and remolded.

15
  • Thermoplastics can go through melting/freezing
    cycles repeatedly and the fact that they can be
    reshaped upon reheating gives them their name
  • Some thermoplastics normally do not crystallize
    they are termed "amorphous" plastics and are
    useful at temperatures below the Tg. They are
    frequently used in applications where clarity is
    important. Some typical examples of amorphous
    thermoplastics are PMMA, PS and PC.
  • Generally, amorphous thermoplastics are less
    chemically resistant

16
  • Depends on the structure of the thermoplastics,
    some of the polymeric structure can be folded to
    form crystalline regions, will crystallize to a
    certain extent and are called "semi-crystalline"
    for this reason.
  • Typical semi-crystalline thermoplastics are PE,
    PP, PBT and PET.
  • Semi-crystalline thermoplastics are more
    resistant to solvents and other chemicals. If the
    crystallites are larger than the wavelength of
    light, the thermoplastic is hazy or opaque.
  • Why HDPE exhibits higher cystallinity than LDPE?

17
  • Polyetheretherketone (PEEK) is a semicrystalline
    polymer having 20-40 crystallinity.
  • It has a rigid backbones, which gives high Tg and
    Tm (Tg 143C and Tm 343C). Can be employed at
    temperature as high as 230C)
  • It is possible to blend two or more polymers to
    obtain a multi-phase product with enhances
    properties

18
Comparison of typical ranges of property values
for thermoset and thermoplastics
  • Properties t/set t/plastic
  • Youngs Modulus (GPa)1.3-6.0 1.0-4.8
  • Tensile strength(MPa) 20-180 40-190
  • Max service temp.(ºC) 50-450 25-230
  • Fracture toughness,KIc 0.5-1.0 1.5-6.0
  • (MPa1/2)

19
Thermoplastics are expected to receive attention
compared to thermoset due to
  • Ease of processing
  • Can be recycled
  • No specific storage
  • Good fracture modulus

20
Rubber
  • Common characteristics
  • Large elastic elongation (i.e. 200)
  • Can be stretched and then immediately return to
    their original length when the load was released
  • Elastomers are sometimes called rubber or rubbery
    materials
  • The term elastomer is often used interchangeably
    with the term rubber
  • Natural rubber is obtained from latex from Hevea
    Brasiliensis tree which consists of 98
    poliisoprena
  • Synthetic rubber is commonly produced from
    butadiene, spt styrene-butadiene (SBR) dan
    nitrile-butadiene (NBR)

21
  • To achieve properties suitable for structural
    purposed, most rubbers have to be vulcanized the
    long chain rubber have to be crosslinked
  • The crosslinking agent in vulcanization is
    commonly sulphur, and the stiffness and strength
    increases with the number of crosslinks

22
PREPREG
  • It is short form for pre-impregnation material
  • It is a semifinished product
  • It will be used in next processing technique to
    obtain a finish product
  • It can be produced from thermoset or
    thermoplastic matrix

23
Thermoplastic prepregs are getting attention due
to
  • Easy storage
  • High toughness
  • Fast easy processing
  • Can be recycled
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