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Microsuspension PVC - Introduction

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Introduction to Microsuspension Polymerisation or Paste PVC Polymer

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Microsuspension PVC - Introduction

  1. 1. PVC (POLYVINYL CHLORIDE) PASTE POLYMER - INDRODUCTION Date: 16th July 2015 Mohamed Adam.K (chem.adams@gmail.com)
  2. 2. Quick View
  3. 3. Polymerization - Introduction Polymer: Large chain molecules having high molecular weight - made up of monomers Polymerization m number of single chains PVC Particle Free radical: Highly reactive molecule having an unpaired valency electron
  4. 4. Fikentscher K-Value: Measure of mean molecular weight, derived from relative viscosity of polymer solutions Polymerization - Introduction
  5. 5. Suspension polymerisation: • Monomer soluble free radical initiator • Dispersion droplet size is large, giving polymer particles of a size greater than about 50 µm • Particles can be separated by centrifuging or filtering • Suspending agents - cellulose ethers, polyvinyl alcohol – not true surfactants • Stirring is required Emulsion polymerisation: • Water soluble initiators • Latex of particles usually of less than 1 µm • Particles cannot be separated from the aqueous phase by centrifuging or filtering • Droplet dispersion is normally stable on standing Microsuspension polymerisations: • Monomer soluble initiator • Homogeniser is used to form a dispersion • Latex particles usually less than 2 µm (sometimes up to 20 µm) • Needs special separation technique - Spray drying Polymerization - Introduction Suspension Polymer Emulsion Polymer Micro-suspension Polymer
  6. 6. Leather Cloth 76% Textile & Paper Coatings 0.3% Tarpaulin 2% Conveyor belts 3% Sealants 4% Mats 8% Plastisol 3% Others 4% Leather Cloth Textile & Paper Coatings Tarpaulin Conveyor belts Sealants Mats Plastisol Others Paste resin applications – Pie chart
  7. 7. 2010-11 2011-12 2012-13 2013-14 2014-15 2015-16 Total Demand(Kt) 79 84 103 109 126 134 Domestic Supply (Kt) 44 55 56 69 78 84 Imports (Kt) 35 29 47 40 48 50 Total Demand Growth (%) 14% 6% 23% 5% 15% 7% 0% 5% 10% 15% 20% 25% 0 20 40 60 80 100 120 140 160 Growth(%) Quantity(Kt) Year Paste resin – Supply and Demand Germany 10% Korea 44% Taiwan 18% U S A 11% Japan 7% Others 10% Avg. Imports - 2015 Germany Korea Taiwan U S A Japan Others
  8. 8. Plastisol: Dispersion of PVC in plasticizer Rheology: Study of deformation and flow of material Viscosity-η: Resistance to flow Shear stress-τ: Force per unit surface area Shear rate-D: Ratio between the speed difference of two adjacent layers of a liquid and their distance apart Rheology - overview
  9. 9. Newtonian liquid: Shear stress-τ ∞ Shear rate-D (Proportional) τ /D = Constant = η (Viscosity) Glycerine and Water Non-Newtonian liquid: Shear stress-τ ∞ Shear rate-D (Not Proportional) Diluted Aq. Starch Solution Rheology - overview
  10. 10. Pseudoplasticity: Viscosity-η decreases as Shear rate-D increases Ketchup can have its viscosity reduced by shaking Toothpaste is a Plastic Rheology - overview
  11. 11. Dilatancy: Viscosity-η increases as Shear rate-D increases Cornstarch - Common thickening agent used in cooking When a force is applied to a 1:2.5 mixture of water and cornstarch, It acts as a solid and resists the force Dilatant materials used as a liquid body armor Thixotropy: Viscosity falls following a prolonged mechanical effort Rheopexy: Viscosity increases after a prolonged mechanical effort These effects are reversible Rheology - overview Plastisol Selection & Rheology: Fabric Coating Coating penetration is deeper  low yield value plastisols (Low Viscosity) Coating penetration is shallower  Pseudoplastic plastisols (High Initial Viscosity) High Coating Speed  High shear rate fluid plastisols (Pseudoplastic) Low Coating Speed(< 15 m/min)  Low to medium shear rate fluid plastisols (Dilatant)
  12. 12. Emulsion: Stabilized mixture (dispersion) of two or more immiscible liquids, like oil and water E.g. Milk Emulsifier: Binds molecules of immiscible liquids and mixes them to form a homogenous solution Emulsion - Introduction Critical Micellar Concentration (CMC): Threshold concentration above which surfactant molecules undergo self-association Addition of further surfactant above the CMC all goes toward increasing the number of micelles Macroscopically homogeneous but microscopically heterogeneous CMC & Aggregation number decide the number of micelles formed at the start of polymerisation and hence the ultimate particle size With Co surfactant
  13. 13. Lowers the interfacial tension to a small value which facilitates dispersion process Has control on emulsion viscosity and droplet size Forms thermodynamically stable dispersion Provides sufficient flexibility to the interfacial film that can readily deform around the droplets Reduces energy input since high speed agitation is not necessary Blended Alcohol – As a Cosurfactant
  14. 14. Secondary Particles - ø: 20 to 60 µm - After Spray Drying Primary Particles - ø : 0.1 to 2.0 µm - After Polymerisation Final Resin - ø : 2.0 to 60.0 µm - After Grinding Secondary particles: Porous and contain internal cavities caused by the rapid evaporation of water enclosed in the particles during formation (Spray Drying) MSP Primary Particles: Having Mono-modal PSD that prevents efficient packing of particles during Spray drying process Produce 2º Particles with high porosity SEM Images of Resin Particles
  15. 15. Continuous gradation of sizes  Small particles  Fit into the interstices of the larger particles (efficient packing)  Releases plasticiser from the interstices between the larger particles  Comparatively low viscosity plastisol MSP 1º Particles (Broad uni-modal distribution)  low shear viscosity at low shear rates Higher shear rates  Breaks efficient packing  Dilatancy Packing of Resin Particles
  16. 16. • Partial homogenization or homogenization with different pressures & Emulsifier  Broad PSD • Proper Emulsifier Type & Quantity  Good Droplet stability  Spherical particles & No Surface damages • Residual Emulsifier (Before drying)  Reduces resin Tg / act as Cementing agent  Forms highly cohesive 2º Particles from spray drying  Reduces de-agglomeration rate  Reduces viscosity aging and its rate • Residual Emulsifier  Interact with polymer / plasticiser interface  Inter-particles repulsion  high viscosities at low shear rates Towards - pseudoplasticity S.NO Emulsifier Primary particle size 1 SLS 1 – 3 μ 2 AOS 2 – 5 μ 3 Calsolene Oil 18 – 20 μ 4 Na Dioctyl Sulfo Succinamide 0.2 – 1 μ 5 Ethoxylated Fatty Alcohol 0.2 – 1 μ Residual Emulsifiers: •Reduce gloss and clarity •Not facilitate air release •Poor heat stability •Fog formation •Affect taste/ acceptability in food packing •Poor compatibility with thermal stabilizer •Accelerate plateout • Increasing slurry viscosity  Narrow spray angle  larger droplets  coarser 1º particles  Reduces the available surface area for plasticiser absorption  Increases free plasticiser  Depresses shear viscosity • Increasing atomizer speed  Smaller droplets  highly fused porous 2º Particles  Absorption and Immobilization of some plasticiser  Swelling  Increases initial viscosity, Reduces viscosity aging and its rate • Grinding  Fragments of secondary particles  Rapid de-agglomeration (with Plasticiser)  Enhances plastisol forming process • Grinding - very high cohesive 2º Particles  Irregularly shaped fragments  Surface retention of plasticiser, Internal 1º particles swelling  Decreases free plasticiser level  Increases low shear viscosity
  17. 17. PVC / DOP – at 90ºC PVC / DOP – at 160ºC PVC / DOP – at 130ºC PVC / DOP – at 193ºC Surfactant layer prevents plasticizer adsorption at room temperature Heating diffuses plasticizer into PVC particles and fuses into a homogeneous material at higher temperatures Complete Fusion: Clarity, gloss and mechanical strength of the final composition reaches the maximum Stages of Plastisol Fusion Blowing agent decomposes before fusion  Open Cell Decomposition happens after plastisol-fusion  Closed Cell Cell Size ∞ Decomposition rate of BA & Melt viscosity of the fused plastisol
  18. 18. PVC properties - Plastisol & End product
  19. 19. Thank you… Thank you… Thank you… Thank you… Thank you… Thank you… Thank you…

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