Title: Polyvinyl Chloride
1Polyvinyl 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. -
3Preparation 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
5Suspension 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.
6Suspension 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.
8Structure 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.
9Properties 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
10Dilute 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.
11The 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.
20Formulations
- 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
21Compounding 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.
29PVC 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.
30Trade 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
-
31Applications 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.
33Applications 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.