PVC has a different Morphology than other plastics.
Morphology deals with how the physical structures fit together.
Open a bag of PVC, & we see white particles of 90 - 250 microns having popcorn like shape.
These grains are called secondary particles or stage III particles.
Each grain is coated with a pericellular membrane or skin of 0.2-2 micron size which is harder than the polymer & is porous.
This porosity allows the liquid additives to enter in PVC particle.
This hard skin is not broken during mixing.
PVC remains free flowing even up to 140 C after mixing.
The hard skin makes fusion very difficult. The secondary particle in turn consists of several particles PVC grain consists of sub grain of average 30 microns. Sub grains consist of Agglomerates of average 10 microns size.
Agglomerates consist of primary particles or stage II particles of average 1 micron size In the void space between primary particles the plasticizers & liquid additives are absorbed, still maintaining free flowing nature of PVC dry blend The primary particle contains 10 million PVC chains held together by crystallites or stage I particle & tie molecules.
Unless these crystallites melt during processing, PVC chains can not come out of primary particles for fusion
Morphology deals with how the physical structures fit together.
Open a bag of PVC, & we see white particles of 90 - 250 microns having popcorn like shape.
These grains are called secondary particles or stage III particles.
Each grain is coated with a pericellular membrane or skin of 0.2-2 micron size which is harder than the polymer & is porous.
This porosity allows the liquid additives to enter in PVC particle.
This hard skin is not broken during mixing.
PVC remains free flowing even up to 140 C after mixing.
The hard skin makes fusion very difficult. The secondary particle in turn consists of several particles PVC grain consists of sub grain of average 30 microns. Sub grains consist of Agglomerates of average 10 microns size.
Agglomerates consist of primary particles or stage II particles of average 1 micron size In the void space between primary particles the plasticizers & liquid additives are absorbed, still maintaining free flowing nature of PVC dry blend The primary particle contains 10 million PVC chains held together by crystallites or stage I particle & tie molecules.
Unless these crystallites melt during processing, PVC chains can not come out of primary particles for fusion
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