TechPlas have developed a material specifically for PVC window manufacture.
Our PTFE tape or fabric can be used during the weld process. It's used in welding plates, allowing heat to pass through to create a joint weld; the melted PVC will not adhere to the tape or the fabric allowing a clean weld.
The hot platen is covered with PTFE-glass tape on both sides. The angle edge of the PVC profile becomes molten against the platen. The platen is then automatically removed and the two molten ends are pushed together and held in place while the molten plastic is held in place, forming the corner of a PVC window frame.