The Degradation Behavior Of Poly(3HB-co-4HB) By Pseudomonas Mendocina DS04-T

Polyhydroxyalkanoates (PHAs) have developed rapidly in recentyears. PHAs, which showed desirable biocompatibility andbiodegradability, have attracted much attention as biodegradablepolymer because of their similar physical and chemical properties topetrochemical derived plastics. Poly(3HB-co-4HB), a kind of PHAs,has applied in medical, agriculture and packaging fields, and hasbecome a promising polymer material to replace traditional plastics.In this work, the biodegradation behavior of poly(3HB-co-4HB)films in submerged culture by Pseudomonas mendocina DS04-T wasinvestigated. The degradation rate was analyzed by gravimetric method,which followed a two steps degradation mechanism with first slowlyand then faster. When the degradation time reached10d, thedegradation rate was94.67%. Surface morphology of the degradedfilms at different degradation stages was observed by scanning electronmicroscopy (SEM). It was observed that the surface of the films waseroded and covered with holes, and the erosion and the size of holesincreased dramatically with the extension of degradation time. Thefilms after degradation were further evaluated by Differential ScanningCalorimeter (DSC), Thermo Gravimetric Analyzer (TGA) and X-rayPower Diffraction (XRD). DSC results revealed that the meltingtemperature (Tg) of the degraded films increased and the relativecrystallinity decreased with the extension of degradation timerespectively. XRD results further evidenced the decrease of thecrystallinity. TGA results indicated that the thermal stability of thedegraded films decreased after degradation. Moreover, SEM, DSC and XRD results revealed that the bacterium preferentially degraded theamorphous parts of the films over the crystalline zone, and the orderedstructure of the polymer decreased gradually with increasing exposuretime.The yield of hydroxybutyrate (HB) monomer in submerged cultureby Pseudomonas mendocina DS04-T was also investigated withpoly(3HB-co-4HB) powder as sole carbon source. The optimal culturemedium (w/v) was determined according to single factor andorthogonal experiment as follows: poly(3HB-co-4HB)0.15%;(NH4)2SO40.1%; Na2HPO4·12H2O1.6%; KH2PO40.4%; MgSO4·7H2O0.05%; ZnSO4·7H2O0.0075%. The optimum parameters for liquidfermentation were further observed as follows: cultivation time is28h;cultivation temperature is30℃; rotary speed is150r/min; liquidmedium volume in flask is120mL/250mL; initial pH is7.3andinoculum content is1.5%(v/v). The yield of HB monomer and PHAsdepolymerase activity at optimized conditions were (43.2±0.42)%and(39.6±0.37)U/mL, respectively. The yield of HB monomer obtainedunder optimized conditions was3.5times that obtained under the basicculture medium and initial conditions.