Controllable Degradation Of Polycarbonate And Copolymerization Of Its Products

Polycarbonate(PC) is one of the excellent engineering plastics with excellent properties. It is widely used in building materials, electronics and automobile manufacturing for its high mechanical strength, good transparency and excellent electrical insulating properties. PC is non-biodegradable plastic, and implementation of the recovery and recycling of PC has more practical significance as environmental problems is more and more challenging. The research is to find new ways to realize degradation of PC in order to reducing the difficulty of reusing PC and expanding the application scope of PC recycled materials. Main contents of the research are as follows:(1)Viscosity average molecular weight is measured by ubbelohde viscometer, which is higher than number average molecular weight and lower than weight average molecular weight. The pyrolysis behavior of PC at high temperature and nitrogen atmosphere is studied by pyrolysis-gas chromatography-mass spectrometry. Results show that there are small molecules in the pyrolytic products because of the homolytic cleavage of C-C and C-O. Aliphatic terminated products and phenyl terminated products originate from homolytic cleavage of C-C and hydroxy terminated products from homolytic cleavage of C-O. Final pyrolysis products are mainly all kinds of phenol, including bisphenol A having the highest yield. The final product is bisphenol A and dimethyl carbonate when PC react with methanol in methylene chloride. Firs, PC degraded into oligomers with Methyl and hydroxyl end capping. Than oligomers react with methanol to generate bisphenol A. Pyrolysis method requires high temperature conditions, high energy consumption and complex means of separation but the products have high value. Methanolysis method need low energy consumption and the products are easy to recycled.(2)Methods of chemistry and extrusion are used to realize controllable degradation of PC. Hydroxyl-terminated PC oligomer was prepared by reaction of PC and ethylene glycol or by extrusion of PC and bisphenol A or glycerol. Degradation products would have different glass transition temperature and crystallization by different dosage of bisphenol A or glycerol. Chemical method needs to use organic solvent, but the reaction temperature is low. Extrusion method needs high temperature with side effects but little reaction time.(3)PC-PDMS copolymer was synthesize through hydroxyl terminated PC oligomer and Chlorine terminated polysiloxane. Copolymer has better thermal stability compared with oligomer. After blended with copolymer, PC has better processing property and improved notched impact strength. Zinc borate was added to the blends as synergistic flame retardant to improve flame retardant of the material. When the ratio of PC, PC-PDMS and zinc borate was 100:3:4, Vertical Burning Test of the material can reach V0 but the notched impact strength and tensile strength decreased obviously.