Unlike other plastics, PVC has a particulate structure and is porous.
After polymerization, a batch of PVC is dropped from the reactor. The reactor is rinsed with water from the spray nozzles to remove any sticking PVC particles, before next batch.
If this step is avoided, the particles sticking to the wall undergoes a second cycle of polymerization and become non porous & cross-linked
.
They don't absorb plasticizer & liquid additives, are difficult to break down into primary particles & undergo fusion during processing. Such particles are called fish eyes or gels In order to prevent fish eyes, the reactor is coated with a build up preventing coatings, after rinsing with water.
These fish eyes appear on the surface of transparent film and other products. To save time and cost, the reactor is not cleaned after every batch, and cleaned after many batches.
The first few batches containing low level of fish eyes are designated as "Film grade" or prime grade. The following batches will have higher and higher fish eye count and designated as pipe grade and so on. Thicker pipes can tolerate some fish eyes.
When the fish eyes count crosses the limit, cleaning of reactor is undertaken.
After polymerization, a batch of PVC is dropped from the reactor. The reactor is rinsed with water from the spray nozzles to remove any sticking PVC particles, before next batch.
If this step is avoided, the particles sticking to the wall undergoes a second cycle of polymerization and become non porous & cross-linked
.
They don't absorb plasticizer & liquid additives, are difficult to break down into primary particles & undergo fusion during processing. Such particles are called fish eyes or gels In order to prevent fish eyes, the reactor is coated with a build up preventing coatings, after rinsing with water.
These fish eyes appear on the surface of transparent film and other products. To save time and cost, the reactor is not cleaned after every batch, and cleaned after many batches.
The first few batches containing low level of fish eyes are designated as "Film grade" or prime grade. The following batches will have higher and higher fish eye count and designated as pipe grade and so on. Thicker pipes can tolerate some fish eyes.
When the fish eyes count crosses the limit, cleaning of reactor is undertaken.
Comments
Post a Comment