PVC Resin SG-5 (K 66-68): Specification and Applications

SG-5 is the grade most buyers mean when they write "PVC resin" on an enquiry. It sits in the middle of the suspension range: enough molecular weight to hold a pressure pipe together, enough flow to run at production speed on a normal twin-screw line. If your end product is pipe, fittings, window profile or rigid board, this is almost certainly the grade you are looking at.

We hold and ship SG-5 as a first-tier distributor working out of Shandong, China. We are not the plant that polymerises it. The batch certificate comes from the producing plant, and we obtain it for you.

Quick answer: SG-5 is defined by GB/T 5761-2018 as a viscosity number band of 107–118 mL/g, which is the same thing as a K value of 66–68 and an average degree of polymerisation of 981–1135. It is bought for water and drainage pipe, electrical conduit, uPVC profiles, pipe fittings and rigid sheet. The band is wide enough that "SG-5" alone is not a complete specification. Name the position in the band you need, and the standard edition.

1. What SG-5 actually is

Chinese suspension PVC is graded SG-1 to SG-8. The number marks a viscosity band; it says nothing about quality. SG-5 sits at the general-purpose middle.

The three numbers you will see quoted for SG-5 all describe the same property, measured or expressed differently:

• Viscosity number is the direct measurement. The standard defines the band as 107–118 mL/g.
• K value is the industry shorthand derived from it, quoted here as 66–68. Buyers outside China usually write K67.
• Average degree of polymerisation is the third expression of the same chain length, 981–1135 for this band.

There is one thing about this band worth being specific about, because it costs buyers money. A viscosity number of 107 and a viscosity number of 118 are both "SG-5", but they are not the same material in your extruder. The lower end fuses faster and gives you a wider processing window; the upper end gives you more strength and better long-term hydrostatic performance, and asks more of your torque and your stabiliser package. If you have validated a formulation on a resin sitting at 112, a delivery at 107 will run, but your reject rate and your weld strength are not the same as they were on the validation run.

So when you enquire, name the position in the band. "SG-5, viscosity number 112–118" is a specification; "SG-5" on its own is only a category.

2. Specification

Values below are the requirement figures for the SG-5 band under GB/T 5761-2018.

Three notes on how to read this table, because it is the part buyers get wrong most often.

These figures define the SG-5 band under GB/T 5761-2018. Any conforming batch has to sit inside them, and they are the frame the actual lot sits in. What that lot measured is on its certificate, with the test method. A batch certificate will give you a measured value with a test method, and that measured value is what your incoming inspection should be checking against your own acceptance range, not against this table.

Batch COA comes from the producing plant. Each lot carries a certificate issued by the plant that polymerised it. Tell us at enquiry stage and we will obtain the certificate for the lot we are actually offering you and send it before you commit, so you are not ordering against a generic sheet. We do not issue certificates ourselves and we will not present a re-typed figure as one.

Watch which standard edition your contract cites. GB/T 5761-2018 is still in force. The official record shows it was last reviewed on 1 July 2025 with a conclusion of continuing validity. Separately, the standards that govern how vinyl chloride resins are designated and how their properties are tested, GB/T 3402.1-2026 and GB/T 3402.2-2026, were published on 2 July 2026 and take effect on 1 February 2027, replacing the 2005 and 2010 editions. That does not change what SG-5 is, but it changes the test methods written on the certificate. We wrote up what is confirmed and what a buyer should now check.

3. Where SG-5 goes, and how it is processed

A practical point that comes up in most first orders: SG-5 is rarely converted on its own. It goes into a formulation with stabiliser, lubricant, filler and, for pipe, impact modifier. If you are moving an existing formulation onto a new resin source, expect to re-tune lubricant levels even when the K value matches. Particle morphology and porosity differ between plants, and that shows up as a change in fusion time before it shows up as a change on any certificate.

4. Naming it correctly on a purchase order

If two suppliers quote "SG-5" at the same price and one turns out to be 118 and the other 108, nothing on either document was wrong. That is why we ask for the position in the band up front. It is the difference between a repeat order and a formulation problem in month two.

5. Packaging, marking and documents

Every bag is marked with grade, batch number, net weight and the plant's identity, so a bag sampled at your warehouse can be traced back to its certificate. How to read the markings on a PVC resin bag walks through what each field means and which ones your own incoming sheet should be recording.

6. What to send us for a firm offer

Give us these and we can quote a specific lot:

1. Grade and position in the band: SG-5, plus a viscosity number or K value target.
2. End product and process: pipe, profile, fitting, sheet; extrusion, injection or calendering.
3. Line and formulation context: twin-screw or single-screw, what you are currently using, and whether you are switching source.
4. Quantity: first order and expected monthly volume. FCL and LCL are both workable.
5. Packaging: 25 kg bags, jumbo bags, palletised, or private label.
6. Discharge port: name it and we will quote FOB, CFR or CIF against it.
7. Documents you need: Certificate of Origin, Form E, third-party inspection at loading.
8. Payment terms: so we can put the total cost of the order in front of you.

7. Frequently asked

Is SG-5 the same as K67? In practice yes. SG-5 is the Chinese grade designation and K67 is the same molecular weight band expressed as a K value. For contractual purposes it is worth writing both, plus the viscosity number band, so there is no room to argue about where in the band a delivery sits.

Can I get the COA before I place the order? Yes. Tell us the quantity you are considering and we will obtain the certificate for the lot we are offering from the producing plant and send it to you for review. If the measured values do not sit inside your acceptance range, you have not spent anything.

For pipe, should I be looking at SG-5 or SG-7? SG-5 is the standard choice for pressure pipe and profiles. SG-7 and SG-8 are lower viscosity grades bought for rigid sheet, bottles, transparent work and high-flow injection. The full grade comparison is here.

Do you supply in jumbo bags, or with our own bag design? Both are possible. 800 kg jumbo bags and palletised loading we arrange on request; private-label bag printing is available for volume orders. Send the artwork and we will confirm the requirement against the quantity.

What does the price depend on? The feedstock route the lot came from, the volume and packaging, the delivery basis and the payment terms, and (more than anything else on a PVC order) when you are buying. Quotes are held for a shorter window than on most plastics, because the feedstock side moves faster. Give us the parameters above and we will put a dated offer in front of you.