A mechanistic and modeling study of recycled and virgin flame retarded polycarbonate.

摘要

Plastic waste from electrical and electronic equipment is an increasing problem. Consequently, it is desirable to separate and recycle these plastics, especially high-value plastics, such as polycarbonate (PC). One of the concerns is enhancing the PC flame-retardant (FR) properties so it can be reused in equipment housings. Using data on potassium diphenylsulfone sulfonate (KSS), it is shown that the flame retardancy of recycled PC can be enhanced. One major advantage of KSS is that it is non-halogenated, playing an important role as the government eliminates potentially unhealthy halogenated FRs. In this study, a PC containing KSS and one containing a halogenated FR were put through a recycling process (drying, extrusion, pelletizing, injection molding, and granulating) that was repeated eight times. Mechanical results were assessed by Izod impact and tensile tests. Flammability was measured by UL94-type tests, limiting oxygen index, and cone calorimetry. Thermogravimetric analysis (TGA), capillary rheometry, and gel permeation chromatography were also performed. Results show that KSS/PC maintains its properties just as well as the halogenated PC, revealing that KSS is likely to be an excellent non-halogenated FR for recycled PC. Mechanistic studies on the thermal degradation were also performed on the PC/KSS FR system. Data were obtained by TGA/Fourier transform infrared analysis and TGA/gas chromatography-mass spectrometry. Results show that KSS acts as a catalyst in accelerating the disproportionation of bisphenol A and dimerization of isopropylphenol which leads to an enhanced carbonaceous char. This, in combination with CO2 production, leads to an intumescent char that accounts for PC/KSS's excellent FR ability. Modeling heat release rate, as assessed by cone calorimetry, has not been extensively studied for char-forming polymers. A finite element model that considers the heat and mass transport phenomena taking place was developed, and this accurately predicts the heat release rate curve for char forming polycarbonate. This model should also be applicable to other FR systems where only the pyrolysis kinetics are different.