Joint venture will rank among world's top 10 producers, companies say PTT Global Chemical CEO Narongsak Jivakanun, left, and SCG Chemicals CEO Sakchai Patiparnpreechavud at a press conference on Thursday. (Photo by Yuiya Shibata) BANGKOK -- Thailand's PTT Group and Siam Cement Group will establish a joint venture to manufacture commodity-grade plastics, the companies announced on Thursday, creating what will be one of Southeast Asia's largest producers in the sector.