Semi-crystalline Polymer Blends for Additive Manufacturing
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Solution Overview
Problem
Existing additive manufacturing techniques face challenges in printing dimensionally stable 3D parts using semi-crystalline polymers due to discontinuous volume changes during solidification, leading to issues like curling, sagging, and residual stresses, which are difficult to manage, especially in extrusion-based systems.
Innovation Solution
Controlled crystallization kinetics are achieved by blending semi-crystalline polymers with miscible or immiscible secondary materials to retard or accelerate crystallization, allowing for the use of semi-crystalline polymers in additive manufacturing systems, reducing residual stresses and ensuring proper bonding between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If semi-crystalline polymers are used as part material in additive manufacturing, then mechanical strength and thermal stability are improved, but dimensional stability deteriorates due to discontinuous volume changes during solidification
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate and crystallization temperature parameters during the additive manufacturing process. By optimizing these thermal parameters, the patent achieves controlled crystallization that maintains mechanical strength while minimizing dimensional instability and warping caused by volume changes during solidification.
Solution Approach 2:
The patent uses composite materials by blending semi-crystalline polymers with amorphous polymers or adding nucleating agents to modify the crystallization behavior. This composite approach allows the material to maintain the mechanical strength of semi-crystalline polymers while reducing the harmful effects of discontinuous volume changes through modified crystallization kinetics.
2Strength
If semi-crystalline polymers are used in extrusion-based additive manufacturing, then material strength is improved, but processability deteriorates due to difficulty in managing crystallization and residual stresses
Solution Approach 1:
The patent introduces amorphous polymers or nucleating agents as intermediary substances that mediate the crystallization process of semi-crystalline polymers. These intermediaries control the crystallization kinetics, making the process more manageable during extrusion-based additive manufacturing while preserving the strength benefits of semi-crystalline materials.
Solution Approach 2:
The patent modifies processing parameters such as extrusion temperature, cooling rate, and layer deposition temperature to optimize the balance between material strength development and processability. By carefully controlling these parameters, the patent enables successful extrusion-based manufacturing of semi-crystalline polymer parts with manageable residual stresses.
3Strength
If fast crystallization occurs in semi-crystalline polymers during printing, then layer bonding is improved, but residual stresses and distortions increase
Solution Approach 1:
The patent applies dynamics by implementing a multi-stage thermal process that dynamically adjusts temperature profiles during and after printing. The material is first heated to promote fast crystallization for strong layer bonding, then undergoes controlled annealing at elevated temperatures to relieve residual stresses and reduce distortions, achieving both strong bonding and low stress states.
Solution Approach 2:
The patent performs preliminary crystallization during the printing process to ensure strong layer bonding, followed by a subsequent annealing treatment as a preliminary stress-relief action before final part completion. This sequential approach ensures both bonding strength and minimal residual stresses are achieved.
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
The method enables the production of 3D items with mechanical properties similar to semi-crystalline polymers while relieving residual stresses, preventing distortions, and allowing for larger part sizes in systems like SLS and HSS, with improved dimensional stability and strength.
Implementation Method 1
The part material is extruded through an extrusion tip carried by a print head of the system, and is deposited as a sequence of roads on a substrate in an x-y plane. The extruded part material fuses to previously deposited part material, and solidifies upon a drop in temperature.
Implementation Method 2
discontinuous volume changes during solidification, leading to issues like curling, sagging, and residual stresses
Data Source
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AI summary
A polymeric material includes a semi-crystalline polymer and a secondary material wherein when the secondary material is combined with the semi-crystalline polymer to form a blend having an enthalpy that is between about 2 J/g heat of fusion and about 80% of the heat of fusion of the neat semi-crystalline material, as measured by differential scanning calorimetry (DSC) when cooling from a melting temperature to a hot crystalline temperature at a rate of 10°C/min.