Recycled Polystyrene Composition for Low Residual Monomer Emission

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Solution Overview

Problem

Existing polystyrene compositions suffer from high residual monomer content due to thermal and mechanical degradation during recycling, which is a concern for their use in food packaging, and there is a lack of methods to improve thermal stability in recycled polystyrene compositions.

Innovation Solution

A thermally stable polystyrene composition is achieved by using recycled polystyrene prepared through thermally initiated and 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane radical polymerization, combined with a sterically hindered phenolic antioxidant, to minimize residual monomer content and enhance processing properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional polystyrene is used in recycling, then processing is easier and cost is lower, but residual monomer content increases due to thermal degradation

Engineering Contradiction:

Improveresidual monomer contentVSAvoidthermal stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the chemical parameters of polystyrene by using different initiation mechanisms (thermal initiation versus radical initiation with benzoyl peroxide) to create polymers with different end group structures. This parameter change results in reduced residual monomer content while maintaining processingability, as the thermally initiated polystyrene has fewer labile end groups that would otherwise decompose and release monomers during recycling

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the typically harmful effect of thermal degradation into a beneficial outcome by selecting an initiation method that creates thermally stable end groups. The thermal initiation process, which would normally be expected to cause degradation, actually produces polystyrene with fewer weak links and better thermal stability, turning a potential harm into a benefit for recycled material quality

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Productivity

If repeated thermal processing is applied to recycled polystyrene, then recycling productivity increases, but residual monomer emission increases

Engineering Contradiction:

Improverecycling throughputVSAvoidstyrene monomer emission

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent applies beforehand cushioning by pre-selecting polystyrene with thermally stable end groups through thermal initiation before the recycling process begins. This preliminary measure cushions against the harmful effects of repeated thermal processing, allowing the material to withstand multiple recycling cycles without significant monomer emission, thus enabling high productivity without compromising safety

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Productivity

If benzoyl peroxide initiation is used, then polymerization efficiency is high, but thermal stability during recycling deteriorates

Engineering Contradiction:

Improvepolymerization rateVSAvoidthermal stability

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

The patent applies inversion by reversing the conventional approach: instead of using radical initiators like benzoyl peroxide to achieve high polymerization rates, it uses thermal initiation which operates in the opposite manner. This inversion creates polystyrene with thermally stable end groups that resist degradation during recycling, demonstrating that the opposite initiation method can simultaneously achieve both high polymerization efficiency and superior thermal stability

Inventive Principle:

Principle #13The other way round (Inversion)

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 composition exhibits reduced residual monomer emission and improved thermal stability, making it suitable for repeated use in food packaging applications.

Implementation Method 1

at least one sterically hindered phenolic antioxidant as component B

Methodology Applied

Scientific EffectRadical scavenging: Oxidation

Implementation Method 2

thermally initiated and/or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane initiated radical polymerization

Methodology Applied

Scientific EffectThermal decomposition: Thermolysis

Implementation Method 3

thermally initiated and/or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane initiated radical polymerization

Methodology Applied

Scientific EffectRadical polymerization: Chemical Bonding

Data Source

PatentEP4558561B1Recycled, thermally stable polystyrene composition and process for providing superior thermal stability in the mechanical recycling of polystyrene

Publication Date: 2026.03.04 INEOS STYROLUTION GRP GMBH

AI summary

The invention relates to a recycled, thermally stable polystyrene composition P, comprising a recycled polystyrene composition A, which comprises at least one polystyrene A-1 that is prepared by a thermally initiated and/or 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane initiated radical polymerization, and at least one sterically hindered phenolic antioxidant as component B. The invention also relates to a process for providing superior thermal stability in the mechanical recycling of polystyrene. Further, a recycled, thermally stable polystyrene composition P, a process for preparing the recycled, thermally stable polystyrene composition P and the use of the recycled, thermally stable polystyrene composition P for preparing molded articles are described.