PVC Resin Specifications: SG-3, SG-5, SG-7, SG-8
Technical data sheet: SG-3, SG-5, SG-7 and SG-8 side by side
Four grades, eleven GB/T 5761-2018 figures, one table. Each row explains what the number decides on a given line, so the grade can be worked back from the end product. The figures are standard ranges, and for any specific lot the COA is the document that carries the measured numbers.
| Parameter | SG-3 rigid, high polymerisation | SG-5 the pipe grade | SG-7 profiles and cable | SG-8 soft, high plasticiser uptake |
|---|---|---|---|---|
| K value | 71 – 72 | 66 – 68 | 60 – 62 | 55 – 59 |
| Viscosity number (mL/g) | 127 – 135 | 107 – 118 | 87 – 95 | 73 – 86 |
| Average degree of polymerisation | 1251 – 1370 | 981 – 1135 | 741 – 845 | 650 – 740 |
| Impurity particles (per 100 g) | ≤ 16 | ≤ 16 | ≤ 20 | ≤ 20 |
| Volatile matter incl. water (%) | ≤ 0.30 | ≤ 0.40 | ≤ 0.40 | ≤ 0.40 |
| Apparent density (g/mL) | ≥ 0.45 | ≥ 0.48 | ≥ 0.52 | ≥ 0.52 |
| Sieve residue, 0.25 mm (%) | ≤ 1.6 | ≤ 1.6 | ≤ 1.6 | ≤ 1.6 |
| Sieve pass, 0.063 mm (%) | ≥ 97 | ≥ 97 | ≥ 97 | ≥ 97 |
| Fish eyes (per 400 cm²) | ≤ 20 | ≤ 20 | ≤ 30 | ≤ 30 |
| Plasticiser absorption (g per 100 g) | ≥ 26 | ≥ 19 | ≥ 12 | ≥ 12 |
| VCM residue (ppm) | ≤ 5 | ≤ 5 | ≤ 5 | ≤ 5 |
| Whiteness, 160 °C / 10 min (%) | ≥ 78 | ≥ 78 | ≥ 75 | ≥ 75 |
Figures in the table are the GB/T 5761-2018 standard ranges; the measured values for each shipment are on its COA.
Quick selection: end product to grade
| End product | Grade | Why this grade |
|---|---|---|
| Pipes and fittings (uPVC pressure pipe) | SG-5 | K 66-68 is the standard band for pressure pipe in India and Pakistan. |
| Window and door profiles | SG-5 / SG-7 | SG-7 if the profile is thin-walled and needs more melt strength. |
| Rigid sheet and panels | SG-5 | SG-5 gives the stiffness a rigid sheet needs without going soft. |
| Film, calendered sheet and packaging | SG-8 | The softest of the four; takes the most plasticiser. |
| Wire and cable insulation | SG-7 / SG-8 | Both are used; SG-8 for softer, SG-7 for stiffer compounds. |
| Artificial leather, footwear and artificial turf | SG-8 | Soft grades with high plasticiser absorption. |
| Injection moulding fittings | SG-3 / SG-5 | Higher K gives better melt strength for thin sections. |
What each parameter means
K value
The single number buyers quote most. It sets how much the resin softens when heated, so it decides both the end product and the processing window. Pipe makers in India and Pakistan usually work at K 66-68, which is why SG-5 travels more than any other grade here.
Viscosity number (mL/g)
A second way of expressing the same chain length, and the figure most Chinese mills put on the COA. If a supplier quotes K value but not viscosity, ask for both: a wide K band and a narrow viscosity band are not the same product.
Average degree of polymerisation
The underlying molecular number behind both values above. Higher means longer chains, better mechanical strength and lower plasticiser demand; lower means softer material that takes more plasticiser.
Impurity particles (per 100 g)
Foreign matter that would show up as specks in the finished pipe. The number belongs low on thin-wall extrusion, where a speck is visible on the surface.
Volatile matter incl. water (%)
Moisture in the resin. Too much water causes bubbles and silver streaks in the extrudate and can upset the balance on a PVC-U line.
Apparent density (g/mL)
How much a given bag volume actually weighs. It decides how many bags fill a container and how the silo feed rate behaves.
Sieve residue, 0.25 mm (%)
Coarse particles held back by the sieve. A higher figure means more gel particles breaking down during processing.
Sieve pass, 0.063 mm (%)
The fine fraction that carries the resin. A low figure here with a high 0.25 mm residue means a coarse grade rather than a well-ground one.
Fish eyes (per 400 cm²)
Small unmelted specks that look like fish eyes in a clear film or sheet. Cosmetic on pipe, but visible in clear sheet and film.
Plasticiser absorption (g per 100 g)
How much plasticiser the resin soaks up. Lower K grades absorb more, which is why soft and flexible products are usually made on SG-7 or SG-8 rather than SG-5.
VCM residue (ppm)
Residual vinyl chloride monomer. It is the number health authorities and large buyers check, and it is the one we ask the producer for on every lot.
Whiteness, 160 °C / 10 min (%)
How white the resin stays after a heat stability test. Relevant when the end product is light coloured or the customer prints on the film.
Standard and basis
The figures are the ranges given in GB/T 5761-2018 for each grade. We do not publish one producer's test results here; the actual values for a shipment are on the COA that travels with the lot. A required position inside a band, stated in the enquiry, changes which lot is offered.
How to use this table
Start from the end product, find the grade, then come back to the table and read that grade's row to see which band it sits in. A specific position inside the band, rather than any value in it, belongs in the enquiry; it is the one thing that changes which batch is offered.
About these figures
Are these measured values?
No. They are the standard GB/T 5761-2018 ranges, and the ranges are what a grade is chosen on. The measured values for a shipment are on its COA, and we do not issue reports on the producer's behalf.
Why give both K value and viscosity number?
They describe the same thing: chain length. A wide K band with a narrow viscosity band means a coarse grind, which is a different product. Both readings are needed before a grade is chosen.
What if the figure I care about is not in the table?
The figure goes into the enquiry together with the grade. Where the standard covers it, the offer states where the offered lot falls on it.
Enquire against this table
The grade, the quantity and the discharge port produce a dated offer and the COA for the lot being offered.