PVC resins are manufactured in SolVin factories under the most strict safety measures, and according the most demanding standards.
As you probably know, only 43 % of the weight of PVC comes from crude oil. The other 57 % comes from a material with unlimited availability: salt (NaCl).
In some of our factories, salt is a by-product for some processes, and PVC manufacturing activity is using this salt as a raw material.
Some of the improvements introduced during the last years in PVC manufacturing are:
- Elimination/reduction of monomer transport.
- Elimination of the storage of chlorine.
- Improved safety for workers.
PVC resins are manufactured according to four main processes:
- Suspension.
- Micro suspension.
- Emulsion.
- Mass.
Every single grade is obtained under a severe quality control. Technical data sheets and safety data sheets are available for each single grade of our resins.
a. Suspension
1. Could you describe the Suspension PVC process?
2. How to produce the copolymers?
3. Why is the bulk density very different between K57 and K71?
4. Is there a link between the morphology of the resin and the additives absorption?
5. Is there a link between particle size distribution and processing behavior?
6. Is a very high bulk density economical for my production?
b. µ-suspension
7. Could you describe the micro-suspension PVC process?
c. Emulsion
8. Could you describe the Emulsion PVC process?
9. Is the flowability between E- and S-PVC similar?
d. Quality control
10. Which quality controls are made on PVC resins before leaving the plant?
11. What’s the Kvalue of the PVC?
a. Suspension
1. Could you describe the Suspension PVC process?
This manufacturing process is used for producing vinyl resins in the SolVin 200 and 500 series. Suspension polymerization is carried out in an autoclave, which generally contains the following substances:
• demineralized water
• the monomer vinyl chloride
• an initiator soluble in the monomer (for example an organic peroxide)
• a protective colloid (e.g. polyvinyl alcohols, cellulose derivates, etc.)
Depending on the dosage and nature of the protective colloid and the stirring conditions, the monomer droplets can agglomerate to a greater or lesser extent in the course of the polymerization.
The suspension of PVC particles obtained at the end of the polymerization process is commonly known as ”slurry". After the polymerization, the slurry is transported to centrifugal dryers for washing and removal of the greater part of the mother liquor.
The wet cake of PVC is dried by using different kind of technology (fluid bed dryers, rotary dryers, flash dryers, …). Finally the dry product is sieved and bagged. In general, the average size of PVC grains in suspension is about 125 microns.
2. How to produce the copolymers?
The copolymers in the SolVin 500 series are prepared using the same process as that used for manufacturing suspension homopolymers.
Vinyl chloride - vinyl acetate copolymers (VC-VAC) in the 500 series generally contain 5-15 % of vinyl acetate.
The properties of these copolymers are appreciably different from those of the homopolymers:
• can be processed at considerably lower temperatures and pressures than those needed for vinyl chloride and homopolymers of the same molecular weight
• particularly suited for thermoforming
• can be used to obtain highly transparent ("crystal-clear") finished products
3. Why is the bulk density very different between K57 and K71?
The morphology of PVC Suspension resins can be managed by adjusting polymerization conditions but a high bulk density is generally associated with a lower porosity and vice versa. The grade K57 is used in rigid applications so it is important to have a high bulk density and porosity is not so important. The grade K71 is used in plasticized application so the porosity and the kinetics of plasticizer uptake are more important than bulk density.
4. Is there a link between the morphology of the resin and the additives absorption?
Yes, additive absorption is linked to the capacity of PVC to get liquid in the grains. This capacity is evaluated by porosity and kinetics of plasticizer uptake. Polymerization conditions are managed to get these properties and they affect also other morphology parameters as bulk density, particle size and flow-ability.
5. Is there a link between particle size distribution and processing behavior?
The particle size distribution and in particular the amount of fine particles has an impact on the flow-ability of the PVC. In case of poor flow-ability it is more difficult handling the resin in processing unit, so that processing is more difficult.
6. Is a very high bulk density economical for my production?
High bulk density gives the advantage of the higher feed of the processing machine, this allows higher output at the extrusion.
b. µ-suspension
7. Could you describe the micro-suspension PVC process?
This process is used for producing certain resins for plastisols in the SolVin 300 series. Polymerization is carried out in an autoclave which generally contains the following substances:
• demineralized water
• the monomer vinyl chloride
• an initiator soluble in the monomer
• an emulsifier
The mixture is transferred to the polymerization autoclave via a homogenizer which causes it to disperse into very fine droplets.
At the end of the polymerization process, the autoclave contains a stable dispersion of fine particles of PVC in water. This liquid is commonly called "latex". The diameter of the PVC particles in this latex is generally between 0.1 and 3 µm (process giving a continuous particle size distribution).
The subsequent operations for obtaining the final product are the same as for the emulsion polymerization process.
c. Emulsion
8. Could you describe the Emulsion PVC process?
This process is used to manufacture most of the homopolymer resins in the SolVin 100 and 300 series. Polymerization is carried out in an autoclave which generally contains the following substances:
• demineralized water
• the monomer vinyl chloride
• a water-soluble initiator (e.g. persulphate, hydrogen peroxide, ...)
• an emulsifier (e.g. a soap)
A the end of the polymerization stage, the autoclave contains a stable dispersion of fine PVC particles in water (emulsion). This milky emulsion is commonly called "latex". The diameter of the PVC particles in this latex is generally between 0.1 and 2 µm.
The PVC is separated from the water by pulverizing the latex into fine droplets in a current of hot air in installations known as "atomizer" dryers.
The resin retains most of the emulsifiers used during polymerization. These impart, in certain conditions, special properties such as improved thermal stability and greater ease of processing.
9. Is the flowability between E- and S-PVC similar?
No. The flow-ability of Suspension PVC is higher compared to emulsion PVC. The reason is that the average particle size of S-PVC is bigger (average diameter from 100 up to 170 microns) compared to the average particle size of Emulsion PVC that is much lower (average diameter of 10 – 20 microns for paste E-PVC and average diameter of 20 -60 microns for not milled E-PVC).
d. Quality control
10. Which quality controls are made on PVC resins before leaving the plant?
For each grade of PVC resin the plant applies a defined control plan which checks all necessary properties of the resin in order to be able to guarantee the quality of the delivered resin.
The main properties which are regularly controlled for all types of resins are:
• the molecular weight of the polymer (Kvalue)
• the absence of foreign particles
• the bulk density
• the particle size distribution of the powder
• moisture content
Specific controls are also on some grades when it is relevant for the dedicated application, for example:
• the porosity of the resin in the case of plasticised applications.
• rheology for paste resins
11. What’s the Kvalue of the PVC?
It’s the measure of the viscosity of PVC in cyclohexanone solution (ISO 1628-2) giving an indication of the molecular weight of the polymer. The higher the Kvalue, the higher the molecular weight.
Disclaimer
[Health, Safety & Environmental issues] [Manufacturing of PVC resin]
[Properties] [Processing] [Additivves] [Applications and markets]
[PVC compared to other materials] [End of life / Recycling]
