PVP K-Value Grades: Selection Guide

PVP (polyvinylpyrrolidone, CAS 9003-39-8) is sold in grades named by K-value. All grades share the same repeat unit; they differ in molecular weight, which controls solution viscosity, binding strength and film properties. Choosing the right K-value is the main formulation decision once you have decided to use PVP at all.

What the K-value means

The K-value is a viscosity-derived number that reflects molecular weight (the Fikentscher K-value). A higher K means a longer polymer chain, a more viscous solution at the same solids, and stronger binding; a lower K means a thinner, easier-to-handle solution with less hold. The molecular weights below are indicative approximations.

Grade	Approx. molecular weight	Solution character	Typical use
K12	about 2,500	Very low viscosity	Solubiliser, dispersant
K17	about 10,000	Low viscosity	Film former, ophthalmic, cosmetic
K25	about 25,000	Low-medium	Coatings, cosmetic
K30	about 50,000	Medium (workhorse)	Binders, adhesives, coatings, cosmetics, pharma
K60	about 400,000	High	Thickening, strong binders
K90	about 1,000,000 – 1,500,000	Very high viscosity	Maximum binding/thickening and film strength

How to choose

Need low viscosity and easy handling? Choose a low K (K12 – K25).
General binder or film former? K30 is the default workhorse grade.
Need high hold or thickening? Move up to K60.
Need maximum binding / film strength? K90.
Limited by viscosity? Remember that a higher K means lower usable solids – if your process cannot handle a thick solution, a lower K may be the practical choice.

K30 vs K60 vs K90

Aspect	K30	K60	K90
Molecular weight	Medium	High	Very high
Viscosity at equal solids	Lower	Higher	Highest
Binding strength	Good	Strong	Strongest
Usable solids	Higher	Medium	Lower
Typical role	General binder/film	Thickener/hold	Max strength/film

Practical notes

Solve for solids, not just strength – pick the highest K your process can still mix, pump and coat.
Check the COA K-band – for K90 the supplied band is 87.4 – 94.2; verify it on each batch.
Blending – grades can be blended to fine-tune viscosity, but confirm stability and performance by test.
Compatibility – PVP is non-ionic and pH-stable across the K-range, so grade selection is mostly about viscosity and strength, not compatibility.

Frequently Asked Questions

What does “K90” mean?

It is a grade label based on the K-value; K90 corresponds to a high molecular weight of roughly 1 to 1.5 million.

Is higher K always better?

No. Higher K means stronger binding but also much higher viscosity and lower workable solids; choose on the process and the effect you need.

What is the most common grade?

K30 is the general-purpose workhorse; K90 is chosen where maximum binding or film strength is wanted.

Can I convert one grade to another?

No – grades differ in molecular weight and are made separately; you cannot “thicken” a low-K grade into a high-K one.

How do I verify the grade?

Check the K-value on the batch COA; for K90 it should fall in the 87.4 – 94.2 band.