Morphology and enzymatic degradation of solution-grown single crystals of poly(ethylene succinate)

Solution-grown lamellar single crystals of poly(ethylene succinate) (PES) were prepared from a 0.025% solution of monochlorobenzene under an isothermal crystallization condition. Lozenge-shaped lamellar crystals with and without spiral growth were obtained at different crystallization temperature. The crystals produced well-resolved electron diffractograms'. Polyethylene decoration of the crystals resulted in a "cross-sector" surface morphology and showed that the average direction of chain-folding is parallel to the crystal growth planes. In some cases, the lamellar crystals showed spiral growths originating from screw dislocations with both left-handed and right-handed forms. Two extracellular poly(hydroxybutyrate) (PHB) depolymerases purified from Alcaligenes faecalis T1 and Pseudomonas stutzeri YM1006 were used for the enzymatic degradation of the PES lamellar crystals. Adsorption of both the extracellular PHB depolymerases onto the crystal surface was observed using immuno-gold labeling technique. The enzyme molecules were homogeneously distributed on the surface of PES lamellar crystals. When the extracellular PHB depolymerase from A. faecalis T1 was applied to a suspension of PES crystals, the turbidity of crystal suspension did not decrease. This indicated that the A. faecalis T1 depolymerase could not degrade the PES crystals even though it can adsorb onto the crystal surface. On the other hand, enzymatic hydrolysis by the extracellular PHB depolymerase from P. stutzeri YM1006 was confirmed by the decrease in turbidity. The degradation progressed from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The difference in enzymatic activity seems to be due to the recognition of the distance between ester bonds in molecular chain by the active site of the enzyme molecule.