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Polyvinyl Chloride

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Title: Polyvinyl Chloride


1
Polyvinyl Chloride
Introduction
  • Polyvinylchloride (PVC) is the worlds most
    versatile thermoplastics with a wide range of
    applications than any other plastics.
  • It plays an important role in every field such
    as agriculture, electrical, irrigation, house
    roofs, shoe soles and many other fields .
  • It is having limited thermal stability.

2
Polyvinyl Chloride
  • Introduction
  • Vinyl Chloride was first synthesized and
    reported by Reghawlt in 1835 .
  • The first report of polyvinyl bromide was
    published by Hoffmann in 1860.
  • The full scale commercial production of PVC
    resin began in 1931 in Germany.
  • In India the manufacturing of PVC began in 1961
    when Calico started its plant in Mumbai.
  •  

3
Preparation of Monomer
  • Commercial Method
  • Vinyl chloride monomer is prepared by cracking
    1,2-dichloro ethane.
  • - Vinyl Chloride may be produced by the addition
    of HCl to acetylene.

4
Polymerization
  • Suspension Polymerization
  • Emulsion Polymerization

5
Suspension Polymerization
  • About 85 of the worlds PVC production are by
    suspension polymerization.
  • Dr. Berg at Wacker-Chemie Polymerization
    developed this technique in 1935.
  • Vinyl chloride is dispersed in water with
    stirring.
  • Monomer soluble organic peroxides are used as
    initiators.
  • Protective collides such as Cellulose ethers
    are added to prevent the monomer droplets from
    coalescing.
  • After the polymerization reaction, unreacted
    vinyl chloride is removed and is passed to
    monomer recovery plant.
  • The polymer is then centrifuged to remove free
    water and resulting wet polymer is dried by hot
    air.
  • The particle size of PVC resin is about
    100-150µm.

6
Suspension Polymerization
7
  • Emulsion Polymerization
  • The system consists of the monomer- water
    containing emulsifier and water soluble
    initiator.
  • In presence of the emulsifier, agitation of the
    charge in the autoclave disperse the monomer into
    very fine droplets. Initiator starts
    polymerization.

8
Structure Property Relationship
  • - PVC is polar in nature due to presence of C-Cl
    dipole.
  • Resistant to non- polar solvents.
  • Flame retardant and self extinguishing.
  • - Presence of chlorine atom causes an increase in
    inter chain attraction and increase hardness and
    stiffness of polymer.

9
Properties of Poly Vinyl Chloride
 
Name Value Unit
Specific gravity 1.18-1.70 --
Tensile Strength 5.5-26.2 MPa
Tensile modulus 4.8-12.4 MPa
Flexural modulus 30 MPa
Elongation at break 150-450
Hardness A85 ---
Glass transition temperature 80-85 C
Dielectric Strength 9.9-15.8 KV/mm
10
Dilute Solution Viscosity(K Value Of PVC)
  • PVC is heat sensitive material and therefore
    instead of melt flow index, K-value is
    calculated.
  • The K-values of PVC for processing lie between
    55 and 60.
  • Higher K-values lead to better mechanical and
    electrical properties of the moulded material at
    the cost of decreasing processibility.
  • Optimum results can be achieved in each type
    of processing using products of suitable
    K-value.

11
The value of k is calculated by the
relationship Log10 ?rel 75 k2 x 10-6
(k x 10-3) C 1 1.5
kc x 10 -3 ?rel
relative viscosity ?/ ?o k k-value
C concentration in
gm/ml.From K-value one will know the grade of
PVC material K-Value 60-65 Injection
Moulding 65-67 Extrusion Process 67-70 Calen
daring Process
  • Dilute Solution Viscosity
  • (K Value Of PVC)

12
Additives and Compounding
  • A PVC compound may contain the following
    ingredients.
  • - Polymer
  • - Stabilizers
  • - Plasticizers
  • - Polymeric Processing Aids - Impact
    Modifiers
  • - Fillers
  • - Pigments
  • Some other miscellaneous materials include flame
    (fire) retardants, optical bleaches and blowing
    agents.

13
  • Stabilizers
  • - Heating of PVC at temperature above 70C has a
    number of adverse effects on the properties of
    the polymers. Sufficient degradation may take
    place during standard processing operations
    (150-200C) making the product useless.Therefore
    to avoid degradation stabilizers are found
    useful.
  • - The compounds of Cd, Ba, Ca and Zn are
    prominent as PVC stabilizers.

14
  • Plasticizers
  • Plasticizers are used
  • - For reducing processing temperature of polymer
    below the decomposition temperature.
  • - To modify the properties of finished products
    such as flexibility.
  • To modify processability.
  • All PVC plasticizers have a solubility parameter
    to that of PVC.
  • Di-iso-octyl phthalate (DIOP) and di ethyl
    hexylphthalate (DEHP) are most important
    plasticizers used in PVC.

15
  • Extenders
  • Sometimes plasticizers are not found useful in
    PVC because of their limited compatibility with
    the polymer.
  • When mixed with true plasticizer
    (commercially called extenders), a reasonable
    compatibility is acquired.
  • Extenders are cheaper than plasticizers.
  • Plasticizers can often be used along with
    Extenders without any adverse effects on the
    properties of compound.
  • Commonly used extenders in PVC are
  • - Chlorinated paraffin waxes
  • - Chlorinated liquid paraffin fraction
  • - Oil extracts

16
  • Lubricants
  • - Two types of lubricants are generally used in
    PVC - internal lubricants and external
    lubricants.
  • External lubricants prevent sticking of the
    compound to the processing equipments by forming
    a film between the bulk of the compound and the
    metal surface of the processing equipment.
  • Internal lubricants improves flow behaviour of
    the materials.
  • Calcium Stearate, normal Lead Stearate, Dibasic
    Lead Stearate, Graphite are employed to improve
    flow properties.

17
  • Fillers
  • Fillers are commonly employed in order to reduce
    cost. They may also be incorporated for
    technical reasons such as
  • To increase the hardness of a flooring compound,
  • To reduce tackiness of highly plasticized
    compounds,
  • To improve electrical insulation properties
  • To improve the hot deformation resistance of
    cables.
  • For electrical insulation, china clay is
    commonly employed while various carbonates are
    used for general purpose work.

18
  • Pigments
  • To add a pigment, firstly the following facts are
    to be considered
  • - Will it decompose, fade or plate out?
  • - Will the pigment adversely affect the
    functioning of stabilizer and lubricant.
  • - Will it fade, bleach out or will it bleed.
  • - Will the pigment adversely affect properties
    that are relevant to the end usage (because many
    pigments will reduce the volume resistivity of a
    compound).

19
  • Polymeric Impact Modifiers Processing Aids
  • Unplasticized PVC has a high melt viscosity
    leading to some difficulties in processing. The
    finished product is also too brittle for some
    applications. In order to overcome these
    problems impact modifiers are generally added.
  • Impact modifier are semi-compatible and often
    somewhat rubbery in nature.
  • - Examples for Impact modifier are ABS graft
    copolymers, Methacrylate butadiene - styrene
    (MBS) terpolymers, Chlorinated Polyethylene,
    EVA-PVC graft polymers.
  • - Chlorinated Polyethylene is being widely used
    as an impact modifier particularly where good
    aging properties are required.

20
Formulations
  • The formulation given below is intended as a
    general guide but not for a specific application
    (Flexible Pipe).
  • Suspension polymer ( K- 65) 100
  • DIOP 40
  • Trixylyl Phosphate 20
  • China clay 20
  • Tribasic lead sulphate 7.0
  • Stearic Acid 0.5
  • Pigment 2.0

21
Compounding of PVC
  • This is the most important operation in the PVC
    processing where the PVC resin is formulated
    into a compound with the desired properties
    with respect to processing and end product by
    addition of selected additives. Adding and
    mixing additives into plastics is an integral
    part of a much broader operation called
    compounding in which ingredients including the
    colorants are intimately mixed together into a
    nearly homogenous mass.
  • Compounding operation can be classified into
    following two
  • Categories
  • Melt blending , where the mix is fluxed or
    fused.
  • Dry blending, where the resultant compound is a
    dry relatively free flowing powder containing
    the liquid ingredients absorbed on the polymer
    particles.

22
  • Melt compounding
  • In this process a premix is prepared which is
    then fluxed.
  • The fluxed mixture is made into pallets and fed
    to process equipment.
  • Simple mixers like ribbon or tumble blenders
    are used for the preparation of premix of the
    ingredients.

23
  • Dry Blending
  • The dry blending process constitutes the
    following steps
  • Addition of polymer to blender and heating it
    at a temperature of 80-105C.
  • The premixed and heated plasticizers are added
    to blender through a spray spread over a period
    of 10-20 minutes.
  • The stabilizer, pigments are added.
  • Other compounding additives are added and the
    mixture is allowed to dry up.
  • The lubricants dissolved in the plasticizers
    are added and the mixer is agitated thoroughly.
  • The mixture is then cooled to below 60C,
    screened and transported to storage.

24
Processing Considerations
  • Polymer lacks thermal stability and
    degradation is rapid during processing evolving
    hydrochloric acid. All the metal surfaces that
    come in contact with the melt should be
    resistant to this acid. Good ventilation of the
    working area is also essential.
  • Polymer doesnt absorb water but some
    plasticizers may do so.
  • uPVC melts are viscous and typical flow path
    ratio is in the order of 60 1 viscosity of
    plasticized PVC depends on plasticizer level.
  • Polymer is amorphous in nature so that
    shrinkage is low.

25
Processing Techniques
  • Injection Moulding
  • Typical Injection Moulding Conditions
  • Recommended melt temperatures are 180-200 C
    for uPVC and 150-190 C for PPVC.
  • Mould temperature is 20-60 C.
  • Injection pressures are in the range of 100-175
    Mpa for uPVC and 80 120 Mpa for PPVC.

26
  • Extrusion
  • Typical Extrusion conditions are
  • Temperature profile is 150-180C for uPVC and
    140- 175C for PPVC.
  • Recommended screw L/D ratio 141 to 171 for
    uPVC and 171 to 201 for PPVC.
  • Recommended compression ratio is 21

27
  • Blow molding
  • UPVC has a much lower average specific heat
    between the processing temperature and room
    temperature than polyethylene.
  • Because of this much less heat is removed on
    cooling of mouldings and hence very short cycle
    times are possible.
  • Blow molding is confined to UPVC using general
    conditions given under extrusion.

28
  • Calendaring
  • Calendaring is an important process for making
    UPVC film or sheet.
  • High molecular weight PVC is compounded and
    partly agglomerated in an extruder mixer.
  • The heated mix is then fed to an L- type
    calendar mixer. The hot calendar rolls simply
    partly consolidate the granules so that the
    resulting film or sheet is strong enough to be
    drawn over a train of heated drums which are well
    above the fluxing temperature of the compound.
  • The PVC is therefore subjected to only a very
    short but intense heating process. The resulting
    films with the high mechanical properties are
    used for packaging applications.

29
PVC Plastisol and Organosol
  • Plastisol and organosol are pastes types
    obtained when the voids between particles are
    completely filled with a plasticiser so that the
    polymer particles are suspended in it.
  • A typical plastisol includes paste making
    polymer, plasticizer, small mount of stabilizer
    and filler.
  • Organosols are distinguished by the presence of
    volatile diluent used for reducing the paste
    viscosity.
  • Most PVC pastes are used in the manufacture of
    leathercloth.
  • Coating of objects are also done by pastes.
  • Rotational casting , paste injection moulding
    processes have been developed for making
    flexible products.

30
Trade names
  • IPCL, India - Indovin
  • Reliance, India - Relcair
  • Mitsubishi gas Ind, Japan - Vinylfoil
  • Mitsui toatsu chemical, Japan - Vinychol
  • B.F. Goodrich, US - Vynaloy
  • Goodyear, US - Vycell
  • ICI - Vynide
  • Solvay - Benvic

31
Applications of PVC
  • Automotive
  • PVC is widely used in air filters, boat
    bumpers, mats, seat belts, head and arm rests,
    spark plug covers, seat covers, transmission
    covers.
  • Agriculture
  • PVC is used in manufacturing of irrigation
    pipes and profiles, pipe fittings, drip
    irrigation systems, reservoir liners,
    horticultural and green house irrigation system,
    sprinkler system fittings.
  • Building
  • Floor tiles covering, fencing, wall
    coverings, furniture covers, sofa seats, house
    sidings, windows, doors, cabinets, swimming pool
    liners, carpet backing, heat seal adhesives,
    foil coatings.

32
  • Electrical/ Electronics
  • Pipe and profiles, wire extrusions, cable
    insulation, TV back, cable fittings, wire sacks,
    electrical parts, plating racks, tool handles.
  • Industrial
  • PVC is used in manufacturing of film, fittings,
    printing plates, screens, steel strip coatings,
    profiles, printing inks, conveyor belting,
    battery separators, storage tanks, gloves.
  • Medical
  • PVC is used in medical sector to manufacture of
    blood bag, glucose bag, urine bag, syringes,
    infusion set, tubing, catheter tubes.

33
Applications of PVC
Vinyl records PVC flexible blood bag
PVC Automobile interiors PVC wire
and cable
34
Applications of PVDC
  • Copolymers may be used in the manufacturing of
    extruded pipe and moulded fittings and in
    chemical plants.
  • Copolymers are used in the manufacture of
    filament which may be extruded from steam
    heated extruders with L/D ratio 101 and
    compression ratio 51 into a quench bath. These
    filaments are used for deck chair fabrics, car
    upholstery, decorative radio grills, dolls hair,
    filter brushes.
  • - Biaxially oriented film is used in packaging
    for exceptional clarity, brilliance, toughness,
    and water and gas impermeability.
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