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Additives for Polymer Processing: Stabilizers and Lubricants

Learn about the different types of additives used in polymer processing, including stabilizers that prevent degradation and discoloration, and lubricants that improve flow and reduce friction. Discover the importance of selecting stable and compatible additives for optimal performance.

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Additives for Polymer Processing: Stabilizers and Lubricants

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  1. WELCOME

  2. ADDITIVES • Polymers unsuitable for processing in pure unmodified form e.g. Polyolefins – Oxidative degradation due to heat and pressure during processing PVC - Degradation at processing temperature

  3. ADDITIVES Any Substance that is added generally in small concentration to resins in order to : Alter their properties Facilitate processing Change the physical, chemical or electrical properties of end products. Reduce the cost

  4. Requirements of Additives • Effectiveness in their function • Stable under processing conditions • Stable under service conditions • Economic • Compatibility with Polymer Matrix • At molecular level • Neither Volatile nor extrude to the surface • Neither bleed nor bloom • Must have low vapour pressure at high temperature • Non Hazardous, non impart taste & odour

  5. CLASSIFICATION

  6. CLASSIFICATION

  7. Processing Stabilizers • Prevent degradation which is caused by • Heat • Oxygen • What Happens ? • Oxygen combines with Polymer under high temp to form carbonyl compounds which leads to yellow & brown discolouration.

  8. Processing Stabilizers • Primary Stabilizers – Antioxidants • Secondary Stabilizers – Peroxide decomposes • Chelating Agents – Metal deactivators • Special Stabilizers (Heat Stabilizers) – for halogenated polymers

  9. Antioxidants( Primary Stabilizer ) They inhibit or retard the oxidative degradation of materials at normal or elevated temperature during processing, storage or service due to Heat Light Chemical Induction How it works? It interrupt the chain reaction by combining with the free radicals forming a non reactive products (Amount : 0.1 – 0.5%)

  10. Effect of Oxidation • Loss in Tensile Properties • Discolouration i.e. yellowing, • Increase in Brittleness • Melt Flow Instability • Change in appearance. • Hardness increases. • Loss of Gloss. • loss of transparency. • Cracking. • Hindered Phenols or Aromatic Amines

  11. Secondary Stabilizer – Peroxide decomposes • How it works? • Peroxides are reduced to alcohols & are deactivated. • EX: • Sulphur & Phosphorus Compounds such as Sulphides, thioethers, tertiary phosphites & phosphorates.

  12. Chelating Agents – Metal Deactivators • Prevent degradation by metal ions (impurities in polymers – ziegler-natta redox initiators, fillers, pigments etc.) • EX: • Organic Phosphines & Phosphites • Higher Nitrogenated compounds – Melamine, diamine etc

  13. Heat Stabilizers • Prevent Degradation • Absorb & Neutralize HCl gas evolved • Prevent Oxidation reactions • Prevent Discolouration • Displace active substituents with stable substituents

  14. Heat Stabilizers • Lead • Tri Basic Lead Sulphate (TBLS) • Dibasic Lead Sulphate (DBLS) • Basic Lead Carbonate • Dibasic Lead Phosphite • Organo-tin • Dibutyltin meleates • Dibutyltin bis mercaptides • Cadmium / Barium /Zinc • Cadmium/Barium laurates • Cadmium/Barium/Zinc Complexes

  15. Synergistic Stabilizer Systems • The term Synergism is used to describe the combined effect of two or more stabilizers, which is greater than the sum of the effects of the individual stabilizers used in isolation. Effect (A+B) > Effect A + Effect B

  16. Lubricants or Flow Promoters Functions :- • To reduce friction between the material and the processing equipment. ( Adhesive forces) • To reduce heat & wear between two surfaces either between the polymer molecules ( Cohesive forces) or between the polymeric material and the equipment. • Reduces thermal degradation of the polymer. • Modifies flow characteristics. • Homogenous the polymer melt with other polymer additives. • To prevent the plastic from sticking to the mould surface during processing

  17. Lubricants or Flow Promoters • External Lubricants • Internal Lubricants

  18. External Lubricants • Prevent friction between polymer melt & metal surface • Prevent sticking to the metal parts • They are usually high molecular compounds and have non-polar groups. • They have low compatibility with the polymer but have high affinity for the metal surface. • During processing they form a thin film between polymer melt & metal surface. • They improve surface finish & gloss. • They help to reduce melt viscosity and give a high output rate.

  19. External Lubricants • Metal Soaps • Metal Stearates • Zinc Stearates • Calcium Stearates • Magnesium Stearates • Hydrocarbon waxes • Stearic Acid & its calcium, lead, Ba, Cd Salt, Hydro carbon & Esters

  20. Internal Lubricants • Promotes Flow by reducing cohesive forces between molecular interfaces within the resin • They are usually low molecular weight compounds, having polar groups. • They function by reducing intra-molecular friction before and during the melt formation of the polymer by promoting flow and reducing melt viscosity of the polymeric mass. • They also enhance polymer properties like heat stability, impact strength, colour & clarity.

  21. Internal Lubricants • Amine Waxes • Ester Derivatives • Glyceryl mono stearate • Long chain esters • Fatty Acids & Amides • Ethylene bi stear amide • Zinc Stearates

  22. Selection of Lubricants • Metal Soaps – Low Compatibility with polymer, so used as external lubricants • Long Chain Fatty Acids – Used as Internal Lubricants for polar polymers. • Long Chain di-alkyl esters – Medium compatibility, so act as external & internal lubricants. • High Molecular weight paraffin wax – low compatibility with polar polymer, so used as external lubricants.

  23. Plasticizers or softeners • Improve process ability by reducing Tg • These are high boiling non-volatile solvents • Polar with a high Mol. Wt. ester type organic compounds. • Reduce internal friction between polymer chain.

  24. Effect of Plasticizers • Easy melt • Improve flexibility • Increase Softness and Flexibility. • Improve Process ability. • Alters Softening point, Tensile Strength, Elongation at break & Impact.

  25. Types of Plasticizers • Primary – These are highly compatible with PVC and can be used alone. • e.g. • Phthalates – Di-Octyl Phthalate (DOP), Di Iso Octyl Phthalate (DIOP) • Phosphates – Tricresyl Phosphate (TCP), • Sebacates, • Adipates.

  26. Types of Plasticizers • Secondary – These are less compatible with resin & and are usually employed together with primary plasticizers. • e.g. • Di Octyl Sebacate (DOS) • Adipic Acid Polyesters • Epoxidised oil.

  27. Extenders • These are not used alone as plasticizers. • They are limited compatibility with polymer. • In conjunction with true plasticizers it enhance the efficiency of plasticizers. • Low Cost. • It replaces the plasticizers without any adverse effect on polymer. e.g. • Chlorinated paraffin wax, • oil extracts.

  28. Selection of Plasticizers • Solvating power • Efficiency • Compatibility • Flame retardant • Toxicity • Low Temp. Performance • Cost

  29. FILLERS It is used to modify mechanical properties & to reduce the cost.

  30. Effect of Fillers • The use of inert fillers can influence the polymer properties in the following ways :- • Increase in density. • Increase in modulus of elasticity. • Lower shrinkage. • Increase in hardness. • Increase in HDT. • Reduction of raw material cost. • For e.g. Calcium Carbonate,Red mud

  31. Fillers

  32. Fillers

  33. Fillers

  34. Fillers

  35. Fillers

  36. Fibrous Fillers & Reinforcement Reinforcing fillers are those which enhance the mechanical properties like : • Tensile Strength • Modulus • Hardness of a polymer compound. The product become stiffer and stronger than the base polymer.

  37. Fibrous Fillers & Reinforcement Glass Fibres – Increase (Tensile, Compressive,Flexural ) Strength ,Increase rigidity, creep resistance hardness and decrease thermal expansion co-efficient, elongation at break. Minerals such as talc, calcuim carbonate, mica – increases the compound rigidity, improve the temperature resistance and reduces shrinkage & warpage.

  38. Coupling Agents Ex: Methacrylato-chromo chloride used for glass fibres & Polyester resin Organosilanes are used for PVC , ABS and PA These are used to increase the adhesion between polymer & filler, fiber by covalent bonds.

  39. Antistatic Agents • Static charge may built up simply by friction with the ambient air • Most plastics have low surface conductivity • Static charge is not discharged fast enough Troublesome effects like: • Heavy contamination of plastics parts • Shock as charge flows ( floor covering , door handles)

  40. Antistatic Agents • Chemicals added to plastics to reduce built up of electrostatic charges on the surface of materials Accumulations can occur during processing and at various handling points • Static charges are dissipated by increasing the surface conductivity

  41. Antistatic Agents • Prevent electrostatic charges – mostly seen in PE, PP, PS, Nylons, Polyesters, Urathenes, Cellulosics, Acrylics & Acrylonitriles • Because of insulation properties electrical charge may get deposited on the surface of the plastics produced during processing. • This may cause severe damage to the products & equipments. • It may cause accumulation of dust. • The accumulation of static charge can be minimized by the use of antistatic agents.

  42. Antistatic Agents • EX: • Amines • Quaternary ammonium compounds, • Phosphates, • Esters, • Polyethylene glycol esters

  43. Slip & Anti block Agents • Slip : Reduces coefficient of friction- They are high molecular weight fatty alcohols • Amount (0.05 – 0.2% ) • e.g. For film of 25 micron 0.01% of Oleamide

  44. Slip & Anti block Agents • Anti block Agents : Prevent adhesion between the film surface • Amount (0.05 – 0.2%) • e.g. • Calcium Carbonate in PVC film • Metal Salts • Fatty Acids • Natural & Synthetic Waxy Materials

  45. Selection of Slip & Anti block Agents • Must not spoil optical properties. • Must not interface with the adhesion ink to film. • Must not prevent the sealing of film. • Must be colour less • Must be odour less • Must be non toxic

  46. Nucleating Agents • Aiding transmission of white light in Plastics • Forms large nos. of nuclei & reduces the size of spherulites. e.g. • Sodium, Potassium, Lithium benzoates. • Inorganic Powders – Clays, Silica Flour

  47. Optical Brighteners • It makes a mask over the yellowness formed during processing. • Optical Brighteners are organic substance which absorb UV radation e.g. • Benzosulphonic & Sulphonamides derivatives. • Vinylene bisbenzoxazoles. • 4-alkyl-7-dialkyl amino coumarins.

  48. Colorants • Produces varieties of coloured polymers • Also improves • Mechanical Strength • Specific Gravity • Clarity

  49. Colorants • Dyes (Soluble in Polymers) • Impart brilliant transparent colour to clear plastics • Inorganic & Organic • AZOS (,180 – 2000C) for brightness and clarity • Anthraquinone (AQ) –Good heat transparent weathearibility • (Auto tube light)

  50. Colorants • Pigments (In-Soluble in Polymers) • Inorganic • Organic

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