Saferworld, an independent international NGO, has done a lot of work on China's relations with Sudan and South Sudan. In January 2012, Larry Attree published a report titled China and Conflict-Affected States between Principle and Pragmatism: Sudan and South Sudan Case Study. Click here to read the report.
On 30 May 2012, Saferworld published a summary of a seminar it held in Juba on the role of China in South Sudan. The seminar resulted in some informative conclusions that you can read by clicking here.