Depolymerization Of ODPA/ODA Polyimide With Catalyst In Sub-critical Water

Polyimide materials are lightweight, highly chemically resistance andthermally stable. In light of their properties, polyimides are wildly used.Disposal of waste polyimide（PI） has become a serious environmental andeconomic problem because of increased PI production.Depolymerization of polyimide synthesized from4,4’-oxydiphthalicanhydride and4,4’-diaminodiphenyl ether monomers （ODPA/ODA PI） insub-critical water was carried out in a batch autoclave reactor system underdifferent conditions. The depolymerization products were analyzedqualitatively and quantitatively by gas chromatography and massspectrometry （GC-MS）, high performance liquid chromatography （HPLC）,fourier transform-infrared spectroscopy （FT-IR）. The influence ofdepolymerization condition on ODPA/ODA PI depolymerization andproducts yield were studied. The visual observation of phase behaviorchanges about depolymerization of ODPA/ODA PI in sub-critical waterwas carried out in fused silica capillary reactor （FSCR） under a microscope.The vapor phase product in FSCR was analyzed by Raman spectroscopywithout sample.The effects of temperature （280³50°C）, reaction time （20¹00min） and the dosage of sodium hydroxide （NaOH） on the depolymerization yieldof flaky ODPA/ODA PI and products yields in batch autoclave reactor wereinvestigated at ratio of H₂O/ODPA/ODA PI20. Flaky ODPA/ODA PI （φ9×2mm） could be depolymerized efficiently to4,4’-Oxydibenzoic acid（OBBA）,4,4’-Diaminodiphenyl ether （ODA）, Aniline, Hydroquinon,4-Aminophenol and Carbon dioxide （CO₂）. The ODPA/ODA PIdepolymerization rate and products yields were effected with the reactiontemperature and time but little relationship with the dosage of catalyst.Over98%ODPA/ODA PI was converted, producing yields of35.5%forOBBA,80.7%for Aniline,78.7%for Hydroquinone and only2.4%forODA and2.34%for4-Aminophenol, when the reaction was conductedwith NaOH0.02g at340℃and60min. Additional kinetic analysissuggests that the depolymerization of flaky ODPA/ODA PI withtemperature below340℃in sub-critical water follows a first-orderreaction kinetics with an activation energy of119.35kJ/mol.The effects of temperature （280³50°C）, and the presence of sodiumhydroxide as catalysts （0.02⁰.08g） on the depolymerization yield ofpowder ODPA/ODA PI （60mesh） and products yields in batch autoclavereactor were investigated at the ratio of H₂O/ODPA/ODA PI20, reactiontime40min. Powder ODPA/ODA PI could be depolymerized efficiently tothe same products as flaky ODPA/ODA PI. The ODPA/ODA PIdepolymerization rate and products yields were effected with the reaction temperature and time, but little relationship with the dosage of catalystwhich were the consistent with flaky ODPA/ODA PI.The investigation of the effect of reaction condition ODPA/ODA PIdepolymerization showed that the reaction temperature and time have asignificant impact on ODPA/ODA PI depolymerization rate and the yield ofthe depolymerization products.The visual observation of phase behavior changes aboutdepolymerization of ODPA/ODA PI in sub-critical water was carried out infused silica capillary reactor （FSCR） under a microscope. ODPA/ODA PIswelled at208.9°C and did not dissolve completely in water following40min at350°C. And the vapor product was analyzed by Raman spectroscopywithout sampling in FSCR. The result showed that CO2is the only gasproduct which was the same result of gas from a batch autoclave reactoranalysis by FT-IR. Additionally, an understanding of the reaction pathwayof ODPA/ODA PI catalytic depolymerization in sub-critical water wasdeveloped.