Solutions for Your TOUGHESTMIXING CHEMICAL Introduction
The Process
The Problem
The Solution
The Advantages
Preparation of Polyvinyl Alcohol (PVA) Solutions Polyvinyl Alcohol (PVA, sometimes referred to as PVOH) is a water soluble polymer used widely in adhesives, paints, sealants, coatings, textiles, plastics etc. The polymer is normally supplied in powder form and several grades are available with varying viscosity This should not be confused with Polyvinyl Acetate, also known as PVA (sometimes PVAc) which is insoluble in water. PVAc emulsions are also used for adhesives, paints and various coatings but processing is different. This will be covered in a separate PVA is soluble in hot and cold water. A solution would typically be prepared as follows: • The powder is slowly added to cold water to avoid formation of lumps, as it becomes sticky and the tendency to form lumps increases as temperature rises. In some cases water at lower than ambient temperature may be used to reduce this • Once the powder is fully dispersed the mix is heated to the temperature at which the polymer becomes solubilized (ranging from 194 - 208˚F [90˚C to 98˚C] - this • Mixing continues at this temperature until the PVA is fully solubilized.
Depending on the grade of material and efficiency of the agitation system this can Using conventional mixers and agitators, a number of problems can be encountered during production:• Incorporation and dispersion of the powder becomes increasingly difficult as the • Lumps cannot readily be broken down by agitation and long mixing times are required to complete solubilization.
• The vigorous agitation required to wet out the powder can lead to aeration • Inefficient agitation takes longer to achieve full solubilization at temperature.
A degree of shear is required to accelerate the process.
• The heating stage of the process adds to costs and process time.
A Silverson High Shear Mixer can disperse and solubilize PVA powder in hot water, reducing mixing times to a fraction of that taken by conventional methods. A typical Centrifugal force drives the Fresh material is gap between the rotor and of the vessel passes many which draws the ingredients back into the mix. Any • Dispersing the PVA into hot water eliminates the heating stage, dramatically reducing • Rapid dispersion of powder eliminates operator error.
• Powder is fully dispersed before viscosity build-up commences.
• Any agglomerates are broken down by the intense high shear mixing, resulting in accelerated solubilization and better batch consistency.
Typically PVA solutions are prepared in bulk. In-Line mixers are commonly used for very large volumes. In-tank mixers are also used depending on batch size, viscosity of end product etc. The Flashblend powder/liquid mixing system is not suitable as a vacuum cannot be generated above 176˚F [80˚C] High Shear In-Line Mixers
• Must be used in conjunction with an efficient in- • Easily retro fitted to existing plant • Self pumping, depending on product viscosity • Multistage units available for higher degree of shear • Units for Explosion proof or Hazardous duties High Shear Batch Mixers:
• Units for ATEX Category 2 duties available • Special units for abrasive products available • “V” Range mixers available with inverted workhead for incorporating low density powders which float Silverson Ultramix
• Capable of rapidly incorporating large volumes of • Single-piece dynamic mixing head designed for CIP • Units for Explosion proof or Hazardous duties High Shear Bottom Entry Mixers.
• Normally used in conjunction with an anchor stirrer/scraper on high viscosity products; can be • Two-speed units available. Variable speed can be • Units for Explosion proof or Hazardous duties Silverson Machines,Inc. 355 Chestnut Street, East Longmeadow, MA 01028
Ph: (413) 525-4825 • Fax:(413) 525-5804 •
Information contained in this report is believed to be correct and is included as a guide only. No warranty is expressed or implied as to fitness for use or freedom from patents. Silverson Machines reserve the right to change product specification without notice.


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