Goldstab Organics-An Innovation-Driven Global Force PowerPoint Presentation

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Polyvinyl Chloride & Heat Stabilizers

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Content Introduction to PVC PVC Heat Stabilizers Types of Heat Stabilizers Goldstab Solutions

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Introduction to Polyvinyl Chloride

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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

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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

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Defects duringPolymerization During polymerization, defects may occur. The most important defects are 1. Tertiary chlorine atoms, which result from branch formation during polymerization2. Allylic chlorine atoms, which form for example by termination of the polymerization reaction.

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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

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K-Value of PVC

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Application & K-Value *recommended, **Very recommended, ***highly recommended

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Heat Stabilizers for Polyvinyl Chloride

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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

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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

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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

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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

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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

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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

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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

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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.

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

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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

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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

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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.

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Types of PVC Heat Stabilizers

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

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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.

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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%.

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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

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Phase out of Lead Stabilizers Global best practices in phasing out Lead (Pb) in PVC pipe manufacturingResearch 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 stabilizerBecause 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.

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Alternatives ForLead Based Stabilizers Calcium Zinc Stabilizers (Ca-Zn) Calcium Organics Stabilizers (Metal free) Tin based Stabilizers (Methyl tin mercaptide and Reverse tin ester)

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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

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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)

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

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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.)

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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’.

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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

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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

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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

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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.

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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

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Mixed Metal Compounds (contd.) Barium Cadmium (Ba-Cd) Good initial color Long-term stability Cost effectiveness 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. Calcium Zinc (Ca-Zn) Ca-Zn stabilizer based system Components are similar to those present in Ba Zn but vary in concentration.

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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

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Comparison between various Stabilizers

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