I’m working with a phosphorus-containing polycarbonate (PC) flame retardant that has a DOPO-derived polyphosphonate structure. It offers intrinsic flame retardancy and thermal stability. My goal is to blend this flame retardant with fiber-grade PET (IV = 0.65 dL/g) using twin-screw extrusion, and to improve compatibility through transesterification, aided by a sodium-type nucleating agent.

However, when the flame retardant loading exceeds 40 wt%, I’ve observed increased sensitivity to moisture. This leads to hydrolytic degradation during extrusion at high temperatures (>275 °C), as evidenced by bubbling in the masterbatch—likely caused by the breakdown of phosphonate bonds resulting the decrease of flame retardancy.

Here is my extrusion temperature profile (from feed zone to die，extruder:35mm,L/D:44): 150 / 260 / 260 / 240 / 235 / 235 / 225 / 225 / 230 / 240 / 250 °C Vacuum venting: enabled Pre-drying: 10 h vacuum drying before extrusion Screw speed: 200rpm

retention time:150s

I have not yet used any anti-hydrolysis agents, though carbodiimide additives are commonly considered for such applications. However, I’m concerned that this may not be a sustainable or robust solution, as the flame retardant’s moisture content can vary depending on storage and ambient conditions.

My question is: Are there more effective or reliable ways—whether through formulation changes, extrusion conditions, or moisture management strategies—to protect phosphorus-based PC flame retardants from hydrolytic degradation during PET extrusion?

Any insights or suggestions would be greatly appreciated.