Preparation of Polyvinyl Alcohol (PVA) Solutions

The Process

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 risk. 
• Once the powder is fully dispersed the mix is heated to the temperature at which the polymer becomes solubilised (ranging from 90ºC to 98ºC - this depends on the grade of PVA used).
• Mixing continues at this temperature until the PVA is fully solubilised. Depending on the grade of material and efficiency of the agitation system this can take some time to achieve.

The Solution

A Silverson high shear mixer can disperse and solubilise PVA powder in hot water, reducing mixing times to a fraction of that taken by conventional methods. A typical operating procedure would be as follows: 

Stage 1

The vessel is charged with hot water and the mixer is started. The PVA is added to the water and is rapidly wetted out and incorporated into the liquid. The high speed rotation of the rotor creates a powerful suction which draws ingredients into the mixer's workhead.

Stage 2

Centrifugal force drives the materials to the periphery of the workhead where they are subjected to intense high shear in the gap between the rotor and stator before being forced out through the holes in the stator and projected back into the mix. Any agglomerates are rapidly dispersed.

Stage 3

Fresh materials are simultaneously drawn into the workhead, setting up a circulatory pattern of mixing. The entire contents of the vessel passes many times through the workhead, progressively breaking down any agglomerates and accelerating the solubilisation process.

Stage 1 Stage 2 Stage 3

• Stage 1
  

  Stage 1

  The vessel is charged with hot water and the mixer is started. The PVA is added to the water and is rapidly wetted out and incorporated into the liquid. The high speed rotation of the rotor creates a powerful suction which draws ingredients into the mixer's workhead.

• Stage 2
  

  Stage 2

  Centrifugal force drives the materials to the periphery of the workhead where they are subjected to intense high shear in the gap between the rotor and stator before being forced out through the holes in the stator and projected back into the mix. Any agglomerates are rapidly dispersed.

• Stage 3
  

  Stage 3

  Fresh materials are simultaneously drawn into the workhead, setting up a circulatory pattern of mixing. The entire contents of the vessel passes many times through the workhead, progressively breaking down any agglomerates and accelerating the solubilisation process.

The Advantages

• Dispersing the PVA into hot water eliminates the heating stage, dramatically reducing process time.
• 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 solubilisation 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.