Multilayer rPET Foam Sheet Extrusion With Closed-Cell Structure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The processing of recycled PET (rPET) for extrusion foaming is challenging due to low melt strength, hygroscopicity, and high viscosity, leading to cell rupture and coalescence, and conventional modifications like solid-state polycondensation or reactive extrusion are costly and time-intensive.
Innovation Solution
A method for producing a multilayer foam sheet using low intrinsic viscosity (I.V.) rPET feedstock without pre-processing, involving co-extrusion with a supercritical physical blowing agent at reduced temperatures and pressures, forming a foam sheet with closed cells and solid layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional solid-state polycondensation or reactive extrusion is used to modify rPET, then melt strength and viscosity are improved, but processing time and cost increase significantly
Solution Approach 1:
The patent applies preliminary action by pre-drying the rPET flakes to remove moisture before extrusion. This preliminary moisture removal prevents hydrolysis during processing, thereby maintaining melt strength and viscosity without requiring time-intensive solid-state polycondensation or reactive extrusion modifications. The drying step is performed in advance to eliminate the harmful effect of hygroscopicity, allowing direct extrusion foaming with low I.V. rPET feedstock.
2Temperature
If rPET is processed at high temperature for extrusion foaming, then melting and foaming occur, but cell rupture and coalescence increase due to low melt strength
Solution Approach 1:
The patent applies parameter changes by optimizing the extrusion processing temperature to a specific range that balances melting requirements with melt strength maintenance. By carefully controlling temperature parameters and combining them with pre-drying to remove moisture, the process achieves sufficient melting for foaming while preventing cell rupture and coalescence that would occur at higher temperatures with undried low I.V. rPET.
3Ease of manufacture
If rPET with low intrinsic viscosity is used directly, then production cost is reduced, but hydrolysis during processing increases due to hygroscopicity
Solution Approach 1:
The patent applies preliminary anti-action by implementing a pre-drying step that removes moisture from rPET flakes before extrusion. This preliminary removal of water counteracts the hygroscopicity of low I.V. rPET, preventing hydrolysis during high-temperature processing. This approach enables the use of low-cost low I.V. rPET feedstock while eliminating the harmful hydrolysis effect that would otherwise occur during extrusion foaming.
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 achieves a lightweight, high-stiffness foam sheet with improved printing quality and reduced production costs, suitable for packaging applications, utilizing up to 100% recycled PET without the need for costly pre-modification processes.
Implementation Method 1
introducing supercritical physical blowing agent into melted polyester feedstock
Implementation Method 2
processing the polyester feedstock at a processing temperature in the range of 15% lower than the melting temperature and 15% higher than the melting temperature
Data Source
AI summary
A method of making multilayer foam sheet from recycled polyester sources, which may be used for packaging applications. The method comprises a co-extrusion system comprising at least two single screw extruders. A low I.V. polyester feedstock comprising up to 100% of the polyester flakes from recycled sources with an intrinsic viscosity (I.V.) of lower than 0.8 dL/g as measured by ASTM D4603-18 is directly being fed into the extruders. Supercritical physical blowing agent is introduced into the melted polyester feedstock in at least one of the extruders wherein the processing temperature is in the range of 15% lower than the melting temperature and 15% higher than the melting temperature. Then, coextruding the feedstock from the extruders of the co-extrusion system through a flat sheet die to make a multilayer foam sheet, wherein at least one layer is a foam layer comprising low I.V. polyester.