Commercially produced PVC is inherently thermally unstable, due to some chain branching during polymerization.

1. Polyvinyl Chloride
& Heat Stabilizers

2. Content
• Introduction to PVC
• PVC Heat Stabilizers
• Types of Heat Stabilizers
• Goldstab Solutions

3. Introduction to
Polyvinyl Chloride

4. What is PVC ?
Polyvinyl chloride (PVC) is a product based on the earth’s natural resources:
Salt and Gas or Oil.
Polymerisation of Vinyl Chloride yield Polyvinyl Chloride

5. Various Polymerization Technique are used to PVC
1. Suspension Polymerization (S-PVC)
2. Micro-Suspension Polymerization (MS-PVC)
3. Emulsion Polymerization (E-PVC)
4. Bulk Polymerization (M-PVC)
Polymerization of PVC
PVC Type Particle Size Predominant Application
S-PVC 50 to 250 µm Plastisols, rigid and flexible applications
MS-PVC 5 to 50 µm Plastisols, Extender PVC in plastisols
E-PVC 1 to 2 µm Plastisols, rigid and flexible applications
M-PVC 50 to 250 µm Transparent applications, various special applications

6. Defects during
Polymerization
During polymerization, defects may occur. The most important defects are
1. Tertiary chlorine atoms, which result from branch formation during polymerization
2. Allylic chlorine atoms, which form for example by termination of the polymerization reaction.

7. Structure and Stability
• Commercially produced PVC is inherently thermally unstable,
due to some chain branching during polymerization.
• Hence, a heat stabilizer system is essential.
• The degradation process leads to polymer molecules with
conjugated polyene sequences of 2–25 double bonds.
• Polymer discoloration occurs from seven double bonds
onwards, starting with yellowing and deteriorating to brown
and black.
• Subsequent secondary reactions, if not prevented, lead to
chain scission and crosslinking.
n

8. K-Value of PVC
• The dilute solution viscosity measurements.
• K-value or viscosity number measurement done by method described in DIN EN ISO 1628-
2E/ISO 1628-2.
• Expressed in terms of relative viscosity
𝑡
𝑡𝑜
, inherent viscosity ln
𝑡/𝑡𝑜
𝐶
or Fikentscher K value.
• The so called ‘‘K value’’ can be calculated from
𝒍𝒏
𝜼
𝜼ₒ
=
𝒄𝑲
𝟏𝟎𝟎𝟎
𝟕𝟓𝑲
𝟏.𝟓𝒄𝑲+𝟏𝟎𝟎𝟎
+ 𝟏
Where 𝜂 = viscosity of the solvent,
𝜂ₒ= solution viscosity and
c = solution concentration,

9. Application & K-Value
Application
K-value of S-PVC
57-60 63-65 65-68 70-74
Pipes (compact pipes or outer skin layer) *** **
Pipe fittings (injection-molded products) ***
Ceiling/wall panels, roller shutters * *** **
Edge banding (2 mm profile) ***
Foamed technical profiles *** ** *
Door/window profiles * ***
Cables, hoses, tablecloth, shoe soles ***
Cable channels *** **
Rain gutters ** ***
Siding * ***
*recommended, **Very recommended, ***highly recommended

10. Heat Stabilizers for
Polyvinyl Chloride

11. Why PVC degrades?
• PVC in theory is a very stable molecule to decompose under the effect of heat & light
• The irregularities developed in PVC structure during polymerization.
• Presence of double bonds
• Existence of tertiary chlorine constitute important site for initiation of thermal and photo
degradation of PVC
• Traces of monomer, catalysts, initiators, terminators, suspension and emulsifying agents etc. Are
responsible for the degradation of PVC, e.g. –CH2—OC—C6H5--,. --CH2—O—SO2— , --CH2OH-- , etc.
• Formation of end groups
• Any other species generated during polymerisation, e.g., --CHCl—CH=CH2 , --CH=CHCl , --
CCl=CH2 --CH2—CHCl2, --CHCl—CH2Cl, --CH2—CH2-Cl

12. • PVC contains 56.8 % chlorine, out of which 1 – 3 % chlorine is allylic or tertiary.
• The remaining chlorine is secondary.
• These are labile chlorine sites. Degradation proceeds through initiation-propogation-termination
Mechanism of Degradation

13. • Both allylic and tertiary chlorines are labile and reactive and come out as chlorine radical or
chloride ion
• Once ‘Cl’ comes off, ‘H’ also comes off, eventually leading to dehydrochlorination or unzipping effect
of PVC molecule
• This is “degradation initiation reaction”
Initiation of Degradation

14. • Structural irregularities eliminate HCl faster than the monomer residue
• After the structural irregularities are exhausted, the degradation continues with a lower constant
rate due to elimination of secondary chlorine atoms from the monomer
• Thus, each HCl elimination introduces allylic group, which accelerates further HCl loss, leading to
polyene structure and discolours PVC, (this is propagation reaction)
• Further, the degradation is accelerated in presence of HCl, oxygen and higher temperature.
• The degraded PVC is more susceptible to further degradation
Propagation of Degradation

15. • The process of degradation (zipper elimination) randomly stops
• The polyene sequence contains 5 – 30 double bonds depending on how fast HCl & O2 are removed
from the system by thermal stabilizers & vacuum
• Subsequent reactions of highly reactive polyenes
• Crosslink or cleave polymer chain, e.g., forming benzene, condensed and/or alkylated benzenes
depends on temperature and available oxygen.
Termination of Degradation

16. • Dehydrochlorination generating HCl, is an irreversible reaction
• HCl in turn catalyses the degradation reaction
• This results in formation of conjugated double bonds, which are responsible for the yellow – brown
discolouration of PVC.
• Due to degradation, PVC loses its mechanical strength and poses problems during its recycling.
• Both chain scission and crosslinking takes place during degradation, resulting in a hard and
brittle polymer.
Effects of Degradation

17. Necessity of Stabilization
• PVC is the most heat sensitive of the major thermoplastic resins. It degrades beyond 80ºC.
• Heating unstabilized PVC above its fusion point gives rise to -
– Yellowing
– Followed by brown discolouration,
– Evolution of hydrochloric acid
– Cross linking,
– Chain scission,
– Ultimate charring to infusible, unprocessable, corrosive black mass
– Irreversible adhesion to equipment surface

18. Heat Stabilizers
• Stabilizers are used to prevent/delay thermal degradation of PVC so that it can be processed.
• Heat stabilizers retard dehydrochlorination and autoxidation & reduce fragmentation.
• Without stabilizer PVC would not be a particularly useful substance, but its compatibility with a wide
range of additives – to soften it, color it, make it more process able for long lasting results in a broad
range of potential applications from pipes, fittings, window profile, flexible films, foam board etc.
• Stabilizers can be in solid or liquid form.
• Generally, Carboxylate or sulfate salts of metals like Lead(Pb), Cadmium(Cd), Barium(Ba), Zinc(Zn),
Calcium(Ca), Potassium (K) are used as primary stabilizers along with different phosphites.

19. Role of Heat Stabilizer
1. Substitute structural defects for more stable groups.
2. Stop the dehydrochlorination zipper effect by substituting the allylic chloride formed during
degradation.
3. Scavenge evolved HCl which has a prodegradant effect.
4. React with free radicals formed (antioxidant) to avoid discoloration and crosslinking by thermal, high-
stress, or photochemical processes.
5. May provide lubrication.

20. • The stabilizers can be primary, secondary or synergistic.
• They can be multifunctional, e.g., Filler or lubricating type of stabilizers.
• Generally, they are metal compounds and classified as calcium-zinc stabilizers, lead
stabilizers, mixed metal stabilizers and tin stabilizers.
• One has to select stabilizer based on whether the product is opaque (lead stabilizers),
translucent (mixed metal stabilizers), and transparent (tin stabilizers)
• About 56% of primary stabilizers and 44% of secondary stabilizers are used in world market
• Primary stabilizer consists of 54% lead, 34% mixed metal and 12% organotin
• Secondary stabilizer consists of 83% epoxides and 17% metal soaps
Classification of Stabilizer

21. • Primary stabilizer is a substance which, when employed as a sole stabilizer in PVC, imparts
an acceptable degree of heat stability.
• The action of primary stabilizer is basically a chemical reaction wherein the primary stabilizer
molecule replaces the labile chlorine atom in PVC resin with a ligand that is less easily
thermally replaced.
• It is essential that the spent stabilizer be neutral, incapable of causing direct degradation of
PVC molecule e.g. Lead chloride
• More the metal content, more is the effectiveness
Primary Stabilizers

22. Secondary Stabilizers
• However, many metallic chlorides like ZnCl2, CdCl2, SnCl2 are lewis acids promoting
dehydrochlorination of PVC
• In such cases secondary stabilizers like epoxides, metallic soaps and chelators are used to
mitigate this effect
• A secondary stabilizer is a substance that can not be used alone. But it can extend,
compliment and synergistically improve the heat stability when used together with primary
stabilizer.

23. Types of PVC
Heat Stabilizers

24. Types of Heat Stabilizer
Heat
Stabilizer
Solid
Form
Liquid
Form
Ca-Zn
Stabilizers
Lead
stabilizers
Ca-
Organic
Stabilizers
Organotin
Compounds
Mixed
Metal
Compounds

25. Lead Stabilizers
• Very efficient HCl absorbers and cost-effective heat stabilizers.
• Based on a mixture of lead salts
• Tribasic lead sulfate (TBLS) (3PbO⋅PbSO4⋅H2O)
• Dibasic lead phosphite (DBLP) (2PbO⋅PbHPO3⋅½H2O) (also a very effective light stabilizer)
• Lead soaps with some lubricating action, dibasic lead stearate (DBLS) (2PbO⋅Pb(C17H35COO)2) or
normal lead stearate (LS) (Pb(C17H35COO)2)
• Non- or low-dusting products, which include the lead components in a safe handling state, in
combination with lubricants (one-pack), have been available in different product forms: flake,
granule, tablet
• Their cumulative toxicity has been mainly concerned with worker exposure and consequently
they have been heavily regulated.

26. Advantages of Lead Stabilizers
• Most cost effective stabilizers
• Provide best electrical properties in cables
• PbO is an excellent HCl scavenger, because of its basicity & fine particle size
• PbO is a weak base & will not degrade PVC
• PbCl2, produced from HCl & PbO, is not a strong lewis acid. Hence, does not catalyse
dehydrochlorination
• PbCl2 is one of the few metallic chlorides that is not soluble in water and is non ionisable.
Hence, it will not reduce electrical insulating properties on exposure to heat, moisture or
aging
• Continuous technological improvement allows good performance with lead content as low as
12%.

27. Disadvantages of Lead Stabilizers
• Toxic to human health
• Being solid, they have limited compatibility
• Pigment like characteristics
• Can not be used for clear applications
• Unable to impart long term initial colour hold
• Prone to sulfide staining. They discolour in contact with H2S or metal sulphides
• Lead octoate is liquid. But when used the product gets darkened on exposure to solar
radiation

28. Phase out of Lead Stabilizers
• Global best practices in phasing out Lead (Pb) in PVC pipe manufacturing
Research in the late 1980s and early 1990s in few cities of US and Europe revealed the problem of
Pb contamination through the water supply network. Because it affected children, it was taken up
with equal gravity.
• Reason behind Phase out of lead (Pb) based PVC stabilizer
Because of Pb poisoning, which is affecting human health.
Humans are exposed to different type of Pb based product directly or indirectly.
Eg: PVC pipe, PVC window profile, and other PVC moulded products.

29. Alternatives For
Lead Based Stabilizers
1. Calcium Zinc Stabilizers (Ca-Zn)
2. Calcium Organics Stabilizers (Metal free)
3. Tin based Stabilizers (Methyl tin mercaptide and Reverse tin ester)

30. Ca-Zn based Stabilizers
 Ca-Zn stabilizers are a complex blend consisting primarily of:
 Calcium soap (stearate or laurate)
 Zinc soap (stearate or laurate)
 Lubricants
 Acid scavengers such as a hydrotalcite, zeolite, and metal oxides/hydroxides
 Organic co-stabilizers such as the diketone stearoyl benzoylmethane
 Polyols,
 Antioxidant and so on.
 Calcium stearate acts as an acid acceptor in addition to providing lubrication.
 Zinc stearate is used to improve initial and early color, in combination with the co-stabilizer.
 Ca/Zn stabilizers in the ratio of 1:2 - 1:3 are typically used

31. Ca-Zn based Stabilizers
 Synthetic hydrotalcites and zeolites form addition complexes at degrading sites, Such sites tend to
be deactivated and the catalytic and highly mobile HCl captured before elimination of further HCl.
 Antioxidants are included at very low levels to inhibit the oxidation of the polymer matrix arising not
only from thermal processing but also from subsequent photochemical and environmental
influences.
 Where it is essential to prevent formation of ZnCl2, beta-diketones are used in combination with
them.
 Powder grades of Ca-Zn stabilizers provide greatest clarity, colour stability and resistance to
deposition.
 They are used at 2.5 – 12 PHR (if diluted with ESBO, higher doses are used)

32. Effect of Ingredients
• Ca-Stabilizer
• Ca-Zn Stabilizer
• Ca-Zn + Co-Stabilizers
• Optimum combination

33. • Formulated to suit the different heat stability and rheology requirements for pipe, fittings, profile, and wire
and cable applications.
• Non-dusting product forms have also been developed, due to the light and fluffy nature of the Ca-Zn
soaps (stearates).
• Ca-Zn systems have also been developed for plasticized-PVC applications as replacements for liquid
Ba-Zn stabilizers.
• Ca-Zn systems are also available for food contact and medical use meeting the strict regulations that
these materials have to satisfy.
• Processing window of new generation Calcium based Stabilizers is wide enough for trouble free
operations
Ca-Zn based Stabilizers (contd.)

34. Ca-Organic based Stabilizers
• Organic-based systems have been developed as lead replacements for rigid pipes and fittings.
• The replacement of zinc with a specific organic co-stabilizer that does not rely on zinc to generate good
initial and early color.
• The performance of the patented uracil co-stabilizer is linked to the efficiency of conjugation and electron
transfer to retard dehydrochlorination and shorten polyene sequences
• Zinc-free stabilizers are claimed to have a better processing window (no influence from zinc sensitivity)
than Ca-Zn, although initially there were also some mistaken perceptions about zinc being a ‘heavy
metal’.

35. Organotin Compounds
• Organotin stabilizers, being liquid provide better compatibility, solubility and degree of contact with
PVC resin and in turn provide better clarity.
• Tin compounds exist in two common valence states. Stannous (+2) and stannic (+4). Both stannous
and stannic chlorides are strong lewis acids which decomposes PVC. But, only stannic carboxylates
are used as stabilizers for PVC.
• Organotin compounds are primarily based on methyl, butyl, or octyl derivatives, usually mixtures of
dialkyl and monoalkyl, bound to the tin atom through a covalent C–Sn bond.
• Taking up the other positions are high molecular weight, highly ionic organic groups linked through a
sulfur atom (mercaptide) or oxygen atom (carboxylate)
• The general formula is RxSnL4–x.
• The key to use tin stabilizers effectively for PVC is to diminish the alkylating strong lewis acidity by SnCl4
> RSnCl3 > R2SnCl2 > R3SnCl
more acidic more toxic

36. Classification of Organotin
Compounds
• Organotin stabilizers are classified as non-sulphur alkyltin stabilizers and sulphur containing - organotin
mercaptides e.g. octyl/butyl/methyltin bis(isooctyl mercaptoacetates)
 However, mercaptides have poor light stability (in sunlight the stabilizer undergoes a redox reaction forming
metal tin and tin sulfide)
 It can be overcome by using UV stabilizers, TiO2 & epoxidized soyabean oil
• They have typical bad odour & are expensive
Organotin
Compounds
Tin
Mercaptides
Tin
Carboxylates

37. Tin Mercaptides (RxSnL4–x)
• Tin, acting as a base, reacts with the HCl initially released during PVC processing.
• R can be methyl, butyl, or octyl (mono- or dialkylation)
• L is 2-ethyhexyl thioglycolate (as used in rigid bottles and films) or 2-mercaptoethyloleate
• Monoalkyltin mercaptide acts quickly to react with the labile chlorine to generate the corresponding
trichloride which can further catalyze decomposition.
• Dialkyltin mercaptide neutralizes this compound and the resulting dichloride does not catalyze any
further decomposition, and also reactivates the mono-stabilizer.
• Provide good initial and long-term color hold coupled with excellent clarity
• Methyl and octyl versions are approved (up to a maximum level) for use in rigid food contact and medical
applications

38. Tin Carboxylates (RxSnL4–x)
• Organotin maleates are relatively less efficient than the tin mercaptides
• R is predominantly butyl (dialkylation). L is alkyl maleate or laurate.
• Superior light stability due to the presence of the maleic acid structure which is able to react with
conjugated double bonds (Diels–Alder reaction).
• Require particular lubrication systems due to their anti-lubricating effect.
• Addition levels are 1.5-2 times higher than the Tin Mercaptides.
• They are extremely successful for stabilizing plasticized PVC. However, they do not provide good
stability and processability to rigid PVC.
• It is discovered that the heat stability of alkyltin carboxylates is greatly increased by addition of certain
mercaptides. Hence, they can be used at low levels.

39. • Blends of metal soaps, in combination with organophosphite esters and co-stabilizers in a liquid medium.
• Used almost exclusively in PVC-P applications.
• To provide clarity, good initial color, long-term stability, compatibility with filled, pigmented systems, and
suitability for post-processing techniques.
• Aryl-alkyl or alkyl organophosphites are liquid esters, which replace the labile chlorine (particularly in the
presence of zinc), scavenge HCl, decompose peroxides, and act as complex Lewis acids.
• Strongly basic carboxylates, derived from barium or calcium, are mostly HCl scavengers. Zinc and
cadmium carboxylates are also able to scavenge HCl, but also substitute the allylic chlorine atoms.
• The synergism between the two types is attributed to a fast exchange reaction between zinc or cadmium
chloride and barium or calcium carboxylates. These reactions regenerate the active zinc (or cadmium)
carboxylate and also avoid the catalytic effect in PVC degradation of zinc (or cadmium) chlorides.
Mixed Metal Compounds

40. Mixed Metal Compounds (contd.)
1. Barium Cadmium (Ba-Cd)
• Good initial color
• Long-term stability
• Cost effectiveness
2. Barium Zinc (Ba- Zn)
Most popular stabilizer for PVC-P due to extensive formulation development based on
increasing the barium content and the important role of organic co-stabilizers.
3. Calcium Zinc (Ca-Zn)
Ca-Zn stabilizer based system Components are similar to those present in Ba Zn but vary in
concentration.

41. Parameters influencing choice of
stabilizers
• Properties and performance of finished PVC product
• Availability
• Ease of Processing
• Effect on machine output and generation of scrap
• Ease of transition from Lead to non-Lead stabilizers
• Costing of PVC compound
• Recycling

42. Comparison between various
Stabilizers
Properties Lead Tin Calcium-Zinc
Thermal Stability Very Good Excellent Good
Mechanical Properties Excellent Good Very Good
Vicat Softening Medium Low High
Weatherability Excellent Good Very Good
Transparency Poor Excellent Very good
Dosage Medium Low Higher
Surface Finish Very Good Excellent finish Very Good
Cost Medium Expensive Medium
Toxicity High Mild Medium
Processing Window Very Good Excellent Good
Recyclability Causes staining Causes staining No cross staining
Sustainability None Low High

43. Thank You
Get back to us at:
E-mail: sales@goldstab.com
Visit us: www.goldstab.com