Study on the Melting Characteristics, Crystallization Behavior, and Morphology of Poly-p-dioxanone (PDO)
1. Research Background and Significance
Poly-p-dioxanone (PDO) is an important biodegradable aliphatic polyester material with broad application prospects in biomedical engineering. This material was first developed by Ethicon in the United States in the 1980s for producing absorbable surgical sutures. The unique ether bond structure (-O-CH2-CH2-O-) within its molecular chain endows PDO with excellent flexibility and controllable degradation properties, making it a significant supplement to traditional medical polymers such as polylactic acid (PLA) and polyhydroxyacetic acid (PGA).
From a molecular structural perspective, PDO's repeating unit contains both an ether bond and an ester bond; this special structural combination gives it characteristics of both polyether and polyester. In terms of crystallization performance, PDO exhibits typical semi-crystalline polymer features with crystallinity usually ranging from 50% to 70%, which directly affects its mechanical properties and degradation behavior. This study aims to systematically reveal the melting-crystallization transition mechanism of PDO through thermal analysis and morphological observation, providing theoretical support for optimizing processing techniques and expanding clinical applications.
2. Material Preparation and Experimental Methods
2.1 Raw Material Treatment and Sample Preparation The raw materials used in this experiment were purple PDO sutures provided by Johnson & Johnson Company No. 2-0 thread type. To ensure accuracy in experimental results, analytical-grade dichloromethane (Merck) was used for Soxhlet extraction over a period of 48 hours to completely remove organic dyes and processing additives from the raw materials. After vacuum drying, purified PDO was dissolved in hexafluoroisopropanol (HFIP，Aldrich), preparing a uniform solution at a concentration of 10 wt%. Thin film samples were prepared using solvent casting method as follows: The mixed solution of PDO/HFIP was placed on a magnetic stirrer at room temperature for continuous stirring for two hours until fully dissolved before pouring into pre-cleaned glass molds measuring (50 imes 30 imes 5 mm). It was then transferred into a controlled temperature-humidity evaporation system equipped with constant flow dry air supply device ((1 L/min)), where it dried under ambient conditions for twenty-four hours. The resulting primary films required further treatment in a vacuum oven at (60℃) for twenty-four hours to thoroughly remove residual solvents; after drying, samples were stored in sealed containers filled with desiccant.
2.2 Thermal Analysis Testing Method Differential scanning calorimetry (DSC) tests utilized Perkin Elmer DSC model number seven instruments following standard operating procedures strictly during testing processes including accurately weighing four-five mg samples placed inside standard aluminum crucibles heating initially at (40℃/min) up to (150℃), maintaining that temperature for one minute eliminating thermal history; subsequently cooling down rapidly back towards preset crystallization temperatures ((Tc)) followed by isothermal crystallization lasting thirty-sixty minutes under those conditions before reheating again at ten degrees Celsius per minute up till reaching (150℃,) all conducted under nitrogen protection throughout. Modulated differential scanning calorimetry(MDSC)testings employed TA Instruments DSC2920 utilizing only heat mode performed setting base heating rate(=,2 ℃/min, modulating cycle =,60 seconds, temperature amplitude ±0．32 ℃; sample subjected prior precrystallizing duration sixty minutes beginning test observing irreversible heat flow signal changes closely thereafter analyzing results accordingly。 2．3 Crystalline Morphological Observation For studying crystalline morphology thin film specimens underwent hot pressing preparation process involving placing adequate amounts between polished stainless steel plates applying pressure sustaining them momentarily post warming their surfaces around two hundred degrees Celsius transferring quickly onto ice-water baths quenching forming uniformly thickened films approximately forty micrometers thick .Crystalline growth observations made via Zeiss Axiophot polarizing microscope equipped precision hot stage commencing experiments wherein specimens melted firstly one minute ensuring elimination existing thermal histories swiftly cooled transitioning setpoint temperatures equaling seventy degrees Celsius conducting isothermal crystal formation documenting snapshots periodically capturing spherulite growth patterns focusing primarily analyzing frontiers’ morphologies dynamics therein.