PVC resin is made by electrolyzing salt into chlorine, reacting that chlorine with ethylene to form ethylene dichloride (EDC), cracking the EDC into vinyl chloride monomer (VCM), and polymerizing the VCM in water into a powder that is then stripped of leftover monomer, dried, and sieved.
For a compounder or a resin buyer, the reason to follow the chain is that each step fixes a line you later read on the certificate of analysis. Polymerization temperature fixes the K-value, the suspension recipe fixes grain size and porosity, the stripper fixes residual VCM, and the dryer and sieves fix volatile matter and sieve residue. The first three steps happen upstream of any resin plant and are covered briefly; the depth is in what happens once VCM reaches the reactor.
1. Produce chlorine from salt
Chlorine is made by passing electricity through brine in a membrane cell, which splits sodium chloride and water into chlorine gas, caustic soda, and hydrogen:
2 NaCl + 2 H₂O → Cl₂ + 2 NaOH + H₂
The three products come out in a fixed ratio, 1.1 kg of caustic soda per kilogram of chlorine, so a chlor-alkali plant cannot run harder for PVC alone; it has to sell the caustic too. That coupling is why chlorine supply, and behind it VCM and resin supply, is tied to the caustic soda market and not to PVC demand alone.
2. Combine chlorine with ethylene
Chlorine and ethylene are converted to 1,2-dichloroethane (EDC) by two reactions run side by side in the same plant: direct chlorination adds chlorine to ethylene, and oxychlorination makes the same molecule from ethylene, hydrogen chloride, and oxygen.
C₂H₄ + Cl₂ → C₂H₄Cl₂
C₂H₄ + 2 HCl + ½ O₂ → C₂H₄Cl₂ + H₂O
The second route exists because cracking releases one HCl for every VCM made, and oxychlorination consumes it. A plant that runs both, a balanced unit, turns all of that HCl back into EDC and imports only ethylene, chlorine, and oxygen. Both EDC streams are washed, dried, and distilled before cracking.
3. Convert EDC into vinyl chloride monomer
Purified EDC is cracked in a gas-fired furnace at 500–550 °C and 2.5–3.0 MPa, splitting each molecule into vinyl chloride and hydrogen chloride:
C₂H₄Cl₂ → C₂H₃Cl + HCl
Only part of the EDC converts on each pass, so the furnace gas is separated by two-stage distillation: HCl returns to oxychlorination, unconverted EDC returns to purification and the furnace, and liquid VCM goes to storage at about 99.9% purity.
That last figure is where monomer chemistry starts to matter to a resin buyer. Trace species such as 1,3-butadiene and monovinyl acetylene alter polymerization kinetics at milligram-per-kilogram levels, so a resin plant specifies its VCM tightly and, in most cases, takes it by pipeline from the cracker next door.
4. Polymerize VCM into PVC
VCM is polymerized by free radicals in water at 35–70 °C and 0.4–1.2 MPa, and the batch is stopped once 85–95% of the monomer has converted. About 80% of the world’s PVC is made by the suspension process; emulsion supplies the paste and specialty grades.
Two choices in the recipe define the grade. The first is polymerization temperature, which sets the average chain length and therefore the K-value: the lower the temperature, the longer the chains and the higher the K-value. The SG numbers on Chinese suspension grades under GB/T 5761-2018 are the same quantity sorted into viscosity-number classes, SG1 the highest and SG8 the lowest.
The second is particle morphology, which is what separates S-PVC from E-PVC. Suspension gives porous grains with a mean size of 50–200 µm that soak up plasticizer in the dry blend and melt-process cleanly; emulsion gives a latex of 0.1–3 µm primary particles that is spray-dried into the fine powder a plastisol needs.
The two also carry very different loadings of surface-active additive, about 1 kg per tonne in suspension against about 10 kg per tonne in emulsion. That residue is what shows up as higher water uptake and poorer clarity in E-PVC compounds.
4.1 Suspension PVC manufacturing
Suspension PVC is made batch-wise in a stirred, jacketed reactor: liquid VCM is dispersed as droplets in demineralized water, and each droplet polymerizes on its own as a miniature bulk reaction. A suspension agent, usually a partially hydrolyzed polyvinyl acetate, keeps the droplets apart, and the initiator, a perester, percarbonate, or peroxide, dissolves in VCM but not in water, so it sits inside the droplets where the reaction runs. The water carries the heat of polymerization out to the jacket.
Inside each droplet, solid primary particles precipitate from the monomer and aggregate into the grain, giving S-PVC its “cauliflower” structure under the microscope. Grain size follows droplet size, so agitation and suspension-agent dose set the particle-size distribution, while suspension-agent type and the conversion end-point set porosity, which governs how fast the grain takes up plasticizer in the blender. Running the batch further would fill the pores and leave a dense grain that plasticizes slowly.
Two things in this step decide defects you meet later. Initiator that is not evenly spread across the droplets by the time it starts generating radicals polymerizes unevenly and forms gels, the fish-eyes that later show up as specks in film and calendered sheet. And the head space is evacuated and nitrogen-purged before charging, because oxygen causes side reactions that discolor the resin and add low-molecular-weight fractions.
5. Recover unreacted VCM
The 5–15% of VCM that did not polymerize is recovered in two stages: the reactor is vented down to near-atmospheric pressure, sending the gas to a gas-holder and recovery unit, and the slurry is then stripped with steam, vacuum, or nitrogen, in the reactor or in a separate column, to pull out the monomer held inside the grains.
Stripping is the step that sets the residual VCM line on the CoA. European suspension and emulsion grades now all carry less than 1 ppm, and EU food-contact rules cap vinyl chloride at 1 mg/kg in the finished article with no detectable migration, so a resin for food or medical use is stripped harder and certified to a tighter limit than a general-purpose grade. Porous suspension grains strip easily; a latex is harder to strip, and its result depends more on how the column is run.
6. Separate and dry the PVC resin
The stripped slurry is dewatered in a centrifuge to a wet cake and then dried in hot air, in a flash dryer, cyclone dryer, or fluidized bed, often two in series, until moisture is down to 0.2–0.3 wt%. That figure is what the CoA reports as volatile matter, and it is worth holding: moisture that survives into the extruder or calender turns into porosity and surface defects, and damp powder flows badly out of silos and hoppers.
Emulsion PVC cannot be centrifuged, because its particles are too small to separate from the water, so the whole latex is spray-dried. The spray dryer agglomerates the primary particles into secondary particles of roughly 30 µm, and the drying conditions decide whether the same latex comes out as a paste grade or a general-purpose emulsion grade.
7. Screen, classify, and package the resin
Dried suspension resin is sieved to remove coarse particles, which would otherwise pass through the compounding line unmelted and surface as hard specks; emulsion resin for paste applications is additionally ground and classified, while general emulsion grades are not. The powder then goes to silos for bulk shipment or to the bagging line.
The outgoing lot test is where every earlier step shows up as a number. For a general-purpose suspension grade tested to GB/T 5761-2018 that means volatile matter, apparent density, residue on the 250 µm and 63 µm sieves, fish-eye count, whiteness after 160 °C for 10 minutes, and residual vinyl chloride in µg/g. The sieve residues check the droplet control of step 4.1, volatiles check the dryer, residual VCM checks the stripper, and whiteness checks oxygen exclusion and heat history together.
PVC resin is not yet the finished PVC product
The powder that leaves the bagging line is not a processable material: heated on its own it degrades before it flows, and it has no lubricity, impact strength, or flexibility beyond what the polymer backbone provides. Every PVC article is a compound of resin plus a formulation, heat stabilizer at minimum, then lubricants, fillers, pigments, impact modifiers, and for flexible products a plasticizer.
The two resin families part ways here. Suspension grades are dry-blended with their additives and melt-processed by extrusion, calendering, or injection molding. Paste grades are dispersed cold in a plasticizer such as DOP or DOTP to form a plastisol, which is spread, dipped, or sprayed and then heat-fused. The resin sets the ceiling on what the compound can do; the additives, above all the plasticizer, decide where under that ceiling the finished product lands.
Conclusion
Salt and ethylene become PVC resin through electrolysis, EDC synthesis, EDC cracking, and aqueous polymerization, followed by monomer stripping, drying, and sieving. The first three steps belong to the monomer supplier; from the reactor onward, every setting is a line on the certificate of analysis. Knowing which step wrote which number is what lets you question an off-spec lot with the supplier instead of simply rejecting it.