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US patent # 13/840,818 "Degradable polymers and method for fracking applications" has this classification: C09K8/68.
C = Chemistry & Metallurgy
C 09 K = Materials for Miscellaneous Applications, not provided for elsewhere
C 09 K 8 = Compositions for drilling of boreholes or wells
C 09 K 8/68 = ...containing organic compounds
Patent classification systems
Patent classification systems are designed for classifying and retrieving technical subject matter such as patents. They are similar to library classification systems like Dewey and Library of Congress.
The US Patent Classification System was used for over 100 years.
In 2015, the U.S. Patent and Trademark Office completed the transition to the Cooperative Patent Classification (CPC) system, developed jointly with the European Patent Office.
The Cooperative Patent Classification scheme is based on the International Patent Classification System (IPC), which was created in 1975 by the European nations who signed the Strasbourg Agreement.
The top level of the CPC scheme is Section. There are 8 sections: A – Human Necessities, B – Operations & Transporting, C – Chemistry & Metallurgy, D – Textiles, E – Fixed Constructions, F – Mechanical Engineering, G – Physics, and H – Electricity.
Next there are Classes, then Subclasses, then Groups, then Subgroups. Classes are numbered 01, 02, etc. Subclasses get capital letters while Groups are again numbered starting with 1.
Subgroups are indicated by a slash (/) and then a 2 (or more) digit number. The “top” group in each subclass is “00”. See the box on the right for an example breakdown of a patent number.