Low Thermal Conductivity Polyester Foam via Reactive Extrusion
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Solution Overview
Problem
Existing polyester foams have thermal conductivity values ranging from 0.032 to 0.050 W/mK, which is not sufficiently low for advanced insulation and noise shielding applications, and the availability of high viscosity resins required for foaming is limited.
Innovation Solution
The use of a reactive additive masterbatch in a twin-screw extruder with specific screw design and blowing agents to increase intrinsic viscosity above 1.2 ml/g, combined with a multihole die for significant cellular stretching, resulting in a foam with an aspect ratio greater than 1.5, achieving very low thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional polyester foaming is used, then the foam structure is formed, but the thermal conductivity remains high (0.032-0.050 W/mK)
Solution Approach 1:
The patent changes the aspect ratio parameter of the foam cells from conventional values to greater than 1.5, creating elongated cellular structures. This parameter change reduces thermal conductivity below 0.032 W/mK while maintaining foam stability through the specific cell geometry that disrupts heat transfer pathways.
Solution Approach 2:
The patent incorporates reflective particles into the polyester foam matrix to create a composite material system. These reflective particles further reduce thermal conductivity by reflecting thermal radiation, achieving enhanced insulation performance while maintaining structural integrity.
2Reliability
If high viscosity resin (IV > 1.2 ml/g) is used for foaming, then cell collapse is prevented, but resin availability is limited
Solution Approach 1:
The patent modifies the molecular weight distribution and intrinsic viscosity parameters of the polyester resin through controlled polymerization processes. This creates resins with optimized viscosities that provide sufficient melt strength to prevent cell collapse during foaming while being more readily available than conventional high IV resins.
3Object-affected harmful factors
If aspect ratio greater than 1.5 is achieved through multihole die stretching, then thermal conductivity is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent uses a multihole die with multiple small orifices arranged in specific patterns to achieve cellular stretching and aspect ratio greater than 1.5. The segmentation of the extrusion process through multiple holes creates the desired elongated cell structure while distributing the manufacturing complexity across a standardized die design that can be produced using conventional techniques.
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 process produces polyester foams with thermal conductivity below 0.032 W/mK, enabling enhanced insulation and noise shielding capabilities while utilizing virgin or post-consumer polyethylene terephthalate, and incorporating reflective particles further reduces thermal conductivity.
Implementation Method 1
a physical blowing agent is introduced to the mixture. As the mixture exits the extruder, the IV has reached a level superior to 1.2 ml/g, and consequently by sudden pressure drop the physical blowing agent rapidly expands and foaming takes place.
Implementation Method 2
a reactive additive masterbatch (MB) that increases the viscosity by chain extension and side chain branching during extrusion
Implementation Method 3
by using an incorrect choice of extrusion tooling, that is with a tooling made for higher density product having a density of 150 Kg/m3
Data Source
Figure 1~2
Figure 3a~4b
AI summary
This invention describes a foamed material wherein the foam is characterized by elongated cells, which have an aspect ratio larger than 1.5, and by a density according to ISO 845 of lower than 150 kg/m3, preferably lower than 80 kg/m3 and a process of manufacturing said material with very good thermal insulation properties. The thermal conductivity is decreased from typical 0.035 W/mK down to 0.025 W/mK by combination of cellular orientation and cell size distribution. In order to be able to achieve necessary cellular orientation level, the melt strength of the polyester resin was significantly increased by reactive extrusion and subsequent foaming, and the extrusion tooling and processing conditions were optimized.