Bio-resorbable Polyester Powder Drying Process
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Solution Overview
Problem
The formation of microscopic pores during the drying process of bio-resorbable polyesters makes it difficult to meet specific specifications for controlled release articles or medical devices, leading to reproducibility and reliability issues in further processing, such as injection molding for surgical articles like stents or implants.
Innovation Solution
A process involving dissolving bio-resorbable polyester in a first solvent, contacting it with a non-solvent under high shear forces, forming a wet polymer mass, pre-drying below the glass transition onset temperature, comminuting, and further drying to reduce residual water content, followed by post-treatment within the glass transition range to prevent pore formation, resulting in a powder with enhanced bulk and tapped density and specific surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional drying processes are used to remove water from polymer mass, then water content is reduced, but microscopic pores are formed in the material
Solution Approach 1:
The invention changes the temperature parameter during drying by implementing a two-stage process: initial drying below glass transition temperature (Tg) to remove bulk water, followed by post-treatment heating above Tg to close pores. This parameter change resolves the contradiction by allowing water removal without pore formation, and subsequently eliminating pores through controlled heating.
Solution Approach 2:
The invention performs preliminary drying below Tg before the main drying stage. This preliminary action removes excess water while maintaining the polymer in a glassy state that prevents pore formation, then follows with post-treatment heating to close any pores that may form during subsequent drying stages.
2Reliability
If powder density and surface area specifications are met for medical devices, then processing reliability improves, but conventional processes cannot achieve these specifications
Solution Approach 1:
The invention changes the thermal parameters during processing by implementing controlled heating above and below glass transition temperature. This allows precise control over powder density and pore structure, achieving bulk density ≥0.3 g/ml and tapped density ≥0.4 g/ml specifications that are critical for reliable injection molding and medical device fabrication.
3Manufacturing precision
If glass transition temperature post-treatment is applied, then pore formation is prevented and density specifications are met, but additional processing time is required
Solution Approach 1:
The invention performs preliminary drying below Tg to remove bulk water while maintaining the polymer in a glassy state, preventing pore formation during the initial water removal phase. This reduces the burden on the subsequent post-treatment heating stage, allowing pore closure to occur more efficiently and reducing overall processing time.
Solution Approach 2:
The invention utilizes the glass transition phase transition of the polymer to control pore formation. By drying below Tg where the polymer is glassy and pore-resistant, then applying post-treatment heating above Tg to close any pores formed, the process efficiently controls pore formation while minimizing processing time through targeted use of phase transition properties.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process significantly reduces the formation of microscopic pores, enhancing the reproducibility and reliability of bio-resorbable polyester powders for medical applications by achieving desired bulk and tapped densities and specific surface areas, improving the production of bio-degradable pharmaceutical active ingredients and surgical articles.
Implementation Method 1
contacting the polymer solution with a second solvent which is a non-solvent for the polymer to result the precipitation of the polymer
Implementation Method 2
contacting the polymer solution with a second solvent under high shear forces in a turbulent shear field
Implementation Method 3
drying the comminuted polymer particles below the glass transition onset temperature to a residual water content of 1% or less by weight/weight
Implementation Method 4
post-treatment of the polymer particles from step e at a temperature in the range from the glass transition onset temperature to the glass transition end temperature
Implementation Method 5
the formation of microscopic pores in the material during the drying processes probably induced by water evaporation. Such pores are unwanted in the further processing
Data Source
AI summary
The invention refers to a Process for preparing a bio-resorbable polyester the form of a powder with a bulk density of 0.3 g/ml or more, a tapped density of 0.4 g/ml or more and a specific surface area of 2.0 m2/g or less comprising the steps a. dissolving a bio-resorbable polyester in a first solvent to form a polymer solution, b. contacting the polymer solution with a second solvent which is a non-solvent for the bioresorbable polyester and which is mainly water to result the precipitation of the bio-resorbable polyester in the form of a wet polymer mass, c. pre-drying the wet polymer mass at a temperature below the T gO of the bio-resorbable polyester, d. comminuting the pre-dried polymer mass to polymer particles with a size below 10 mm, e. drying the comminuted polymer particles below the T gO of the bio-resorbable polyester to a residual water content of 1 % or less by weight/weight, f. post-treatment of the polymer particles from step e at a temperature in the range from the T gO to the T gE of the bio-resorbable polyester, g. comminuting the polymer particles from step f to a powder with a particle size of d50 of 1 - 300 μm and d90 of more than 30 and up to 3000 μm.