Technical Stuff About How PVC
Made You (Secretly) Always Wanted
to Know, But Were Afraid to Ask
OK, my inquisitive and eager students... time for a quick visit to "PVC University."
(Relax, there'll be no quizzes.)
PVC: Polyvinyl chloride
CPVC: Chlorinated polyvinyl chloride
PvdC: Polyvinylidene chloride
Polyvinyl chloride (PVC) is a tough, strong thermoplastic material which has an
excellent combination of physical and electrical properties. The products are usually characterized as plasticized
or rigid types. Polyvinyl chloride (and copolymers) is the second most commonly used polyvinyl resins in one of
the most versatile plastics.
The plasticized types, either soft copolymers or plasticized homopolymers, are somewhat
elastic materials which are familiar in the form of shower curtains, floor coverings, raincoats, dishpans, dolls,
bottle-top sealers, prosthetic forms, wire insulations and films, among others.
Rigid polyvinyl chloride products, which may consist of the homopolymer, copolymer,
or polyblends, are used in the manufacture of phonograph records, pipe, chemically resistant liners for chemical-reaction
vessels, and siding and window sashes.
The monomer is frequently prepare from chlorine, acetylene, and ethylene by a combination
of processes which affords complete utilization of the chlorine. (There's a nice chemical diagram that I won't
bore you with... I can tell you're already yawning.)
The polymerization of vinyl chloride, chemical reaction, and its copolymerization
with other vinyl monomers may be initiated by peroxide or azo compounds and carried out in bulk or in aqueous emulsion
or suspension systems. The structure and properties of the product are quite dependent on polymerization temperature;
the lower the temperature, the higher the softening point of the resin. Polymers prepared in bulk or suspension
are used for many applications as molded, extruded, or calendered objects. Polymers prepared in emulsion are often
molded by dipping or pouring techniques.
Because polyvinyl chloride products have a tendency to lose hydrogen chloride at
high temperatures, a stabilizer, such as a tin or lead compound, is included in the final composition. Fillers
are also commonly incorporated.
Copolymers with monomers, such as vinyl acetate or propylene can be processed at
lower temperatures than the homopolymer. The acetate copolymer is especially useful in floor tiles, though homopolymers
are used as well.
Blends or "alloys" of polyvinyl chloride with small amounts of rubbery
materials, such as the interpolymer of acrylonitrile, butadiene, and styrene (ABS) have been produced for applications
such as panels and pipe in which impact resistance, as well as hardness and strength, is desired.
Chlorination of polyvinyl chloride is sometimes effected to obtain a stiffer resin
at the expense of processability.
Are you with me so far? If so, you deserve a break. Go ahead, stand up and stretch
your legs. I'll wait.
Back so soon?
OK, moving along...
PVC is the most common of all vinyl polymers. The polymer of vinyl chloride, PVC,
is produced by three basic processes...
1. Mass Process
Vinyl chloride is polymerized in a carrying medium. The polymerization is stopped at a low conversion and the polymer
is separated from the residual monomer which is recycled.
2. Emulsion Process
Vinyl chloride is emulsified with water by use of emulsifying agents. The polymerization is carried out to a high
degree of conversion with a small amount of recovered monomer being recycled. The product is obtained as an emulsion
or spray and dried to produce a very fine powder.
3. Suspension Process
Vinyl chloride is suspended as small droplets of monomer in water and then polymerization is carried to a high
degree of conversion. A small amount of monomer is recovered and recycled. A granular product is obtained by centrifuging
and drying. While a range of products can be made by the first two methods as above, they are generally limited
to specialty products which are difficult to impossible to make by the suspension process. The largest proportion
of PVC is produced, particularly in the USA, the by suspension process because it requires the least capital investment
and has the lowers operation costs.
Advantages and Limitations of
PVC and Related Polymers
Mechanical Properties: Good combination
of stiffness and impact strength (rigid formulation), toughness, extensibility, high ratio of strength to weight
(flexible formulations). Acrylic-PVC alloy with high impact strength available. Limitations are recovery from bending
or stretching damped compared to rubber. Comparatively low heat distortion and softening temperature (even rigid
compositions - except CPVC).
Physical Properties: Good electrical
insulation (enhanced by suitable formulation).
Non-flammability (reduced or enhanced by some plasticizer) limitations are the tendency to progressive degradation
at elevated temperatures. Stiffening and embrittlement at low temperatures (rigid compositions) and flexible unless
Application to Food and Medicine:
PVC and PvdC used in packaging applications. Blown bottles and containers also made from PVC (non-toxic grades).
Formulation and Processing: Formulation
versatility giving materials ranging from elastomers to rigid engineering thermoplastics and processing possibilities
from paste coatings to injection molding. Limitation is that adhesion to many substrates limited in the absence
of a primer.
Miscellaneous: Dimensional stability
at room temperature for rigid formulations. Almost unlimited range of colors - transparent to opaque according
to formulation. Low cost. Limitation is the high specific gravity for polymeric material.
Comparison of Characteristics of
PVC and Related Polymers
PVC (Flexible): Wide range of flexibility
possible - competes for rubber applications at lower cost. Ability to form pastes (plastisols) by addition of plasticizers
for coating and casting. Limitations are that flexible grades are most susceptible to staining, chemical and microbiological
attack due to presence of plasticizers. Creep properties are inferior to rigid PVC.
PVC (Rigid): Lower coefficient of
friction and better abrasive wear resistance than flexible grades. Easier to process and cheaper than CPVC. Can
be glass fiber-reinforced to give improved strength and stiffness and lower coefficient of thermal expansion. Limitations
are that it is attacked by strong acids and alkalix, swollen hydrocarbons and it has a lower maximum service temperature
PVC Copolymners (Less Rigid than Rigid PVC):
Processing characteristics and impact strength improved by blending with copolymers. Limitations are that creep
properties are generally inferior to rigid PVC, and lower tensile strength.
CPVC (Rigid): Considerably higher
upper service temperature than rigid PVC. Best creep properties of PVC types. Resistant to acids, alkalis, most
organic solvents, oil and grease. Limitations are that it's more difficult to process than PVC due to higher softening
point and melt viscosity and it has higher cost.
PvdC (Flexible): Best resistance to
all acids and most common alkalis. Unaffected by aromatic and aliphatic hydrocarbons, alcohols and esters. Best
resistance to permeation by organic and aqueous vapors. Limitations are that it has higher cost and thermal processing
is more difficult.
Typical Applications of PVC
Rigid Piping: Potable water conduits, water mains, drainage, soil pipe systems, rain water systems and gutters,
gas conduits, venting, furniture.
Rigid Structural and Cladding Elements: Paneling and partitioning (interior), wall cladding (exterior), building
panels, glazing, roofing, window frames and hollow bricks.
Flexible Misc. Products: Flexible "see through" doors, folding doors, roof underlayment, greenhouse glazing,
suspended ceilings and floorings (continuous and tiles).
Flexible insulation and sheathing (wire and cable), batter separators. Rigid terminal boxed and conduit.
Rigid Foil (Thin Sheeting): may be fabricated into containers, blister and skin packs, nesting trays (for confectionary
Flexible Film: used directly for wrapping food and other products and "shrink" or "cling" wrap.
Rigid Blown Bottles and Containers: used for oil, wine, beverages, shampoos, and certain cosmetics.
Coated Fabric and Paper Applications (Flexible)
Leather Cloth: used in upholstery, clothing, travel and fancy goods. Protective and foul weather clothing. Tarpaulins,
life rafts, hover rafts, conveyer belts.
Rigid Foam: used as a core in sandwich structure (building and boat building), buoyancy blocks, fishing floats,
insulation (thermal and acoustic) and shock absorbent materials.
Flexible Foam: upholstery (especially automotive), leather cloth and fancy goods, carpet backing, underlays, embossed
wall papers, foam flooring, shoe soles and soft toys.
Some of these find application in adhesive and thin protective coatings (i.e. paints). Those vinyl chloride copolymers
which are of direct interest to the product designer are used mainly where a rigid polymer with PVC-like service
properties are required, but where easier thermal processing is necessary. This type of copolymer is also the material
of vinyl sheeting used for thermoforming, which must combine rigidity with easy heat-softening under fabricating
conditions. Vinyl chloride/acrylic ester copolymer has been used as the material of blow molded bottles and film,
for improved impact strength and/or heat weldability.
CPVC: The principal use for this material in in hot water pipes where its combination of generally PVC-like properties
with a much higher softening point makes it particularly suitable.
PvdC: The most important application of this material is as a coating or laminate component imparting good gas,
moisture, vapor, scent and flavor barrier properties to plastic packaging films and containers. Heat-shrinkable
and heat-sealable films have been produced from PvdC, as well as heat-sealable layers or coating on other polymer
films. The solvent resistance of PvdC pipes has been utilized in special applications, as in chemicals installations
and apparatus. Use of extruded PvdC products in this and other fields also includes gaskets, valve seats, tape
for wrapping joints and conveyer belts. PvdC moldings are represented by spray-gun handles, acid dippers and components
in equipment for rayon manufacture.
Processing of PVC and Related Polymers
Calendering: Sheet, film (flexible or rigid), flooring and floor tiles (flexible)
Extrusion: Sheet, film, pipe, profiles (all flexible or rigid), coated wire and cable (flexible coating)
Compression molding: Thin sheeting or laminates, cellular articles
Injection molding: Pipe fittings, electrical fittings, gaskets, footwear (including micro cellular soles)
Blow Molding: Bottles and other containers
Paste Processing (Coating by Dipping, Spreading or Transfer Techniques): Coated fabrics, vinyl wall-papers, PVC
Backed carpets, coated work gloves, coated metal sheet and articles
Powder Processing (Coating by Dripping or Spraying): Coated metal sheet and wire trays
Powder Processing (Spreading on Temporary Support): Sintered porous sheets for battery separators
Thermoforming: Blister packs, nesting trays, containers and ceiling panels
- fin -
Well, that's about it. Not a complete chemistry lesson,
of course. But a little of the basics. Now that you know, do you really care?
What's important is, PVC makes great projects. It's easy to work with; easy to cut,
bend, drill and form. PVC is a versatile material that gives you endless ways to be creative and make some really
neat projects. That's why, although it's technically called polyvinyl chloride, to me it's Pretty Versatile Construction
So be sure to surf around my humble little site... choose a plan or two or three...
and have some fun.
Wait... on second thought, if you've read this far, maybe there WILL be a quiz!
TO MAKE PVC FURNITURE AND OTHER FUN PVC PROJECTS
Here for Dozens of PVC Project Plans
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