Chemiluminescence-based evaluation of styrene block copolymers' recyclability

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Chemical Engineering

Background:

• Linear styrene block copolymers like SIS, SBS, and SEBS are widely used but their recyclability is limited by degradation during processing.
• Understanding the thermal stability and degradation pathways of these copolymers is crucial for developing effective recycling strategies and minimizing energy consumption.
• Chemiluminescence (CL) offers a sensitive method to evaluate material degradation and predict performance under thermal stress.

Purpose of the Study:

• To evaluate the recyclability of linear styrene block copolymers using chemiluminescence (CL) based methods.
• To determine the thermal stability and oxidative degradation kinetics of styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), and styrene-ethylene-butadiene-styrene (SEBS) copolymers.
• To correlate CL data with other analytical techniques (IR, DSC) for a comprehensive understanding of degradation mechanisms.

Main Methods:

• Isothermal and non-isothermal chemiluminescence (CL) analysis was employed to study the thermal degradation of four different copolymer structures.
• Oxidation induction times were determined from CL intensity profiles to calculate activation energies for oxidative degradation.
• Infrared (IR) spectroscopy and differential scanning calorimetry (DSC) were used for complementary analysis of material properties and degradation.

Main Results:

• The activation energies for oxidative degradation followed the sequence: SBS (30% styrene) ≈ SIS < SBS (40% styrene) < SEBS.
• SIS and SBS (30% styrene) copolymers exhibited the fastest degradation, attributed to rapid hydroperoxide radical accumulation.
• SBS (40% styrene) showed slower degradation with minimal mass loss due to less reactive keto degradation products, while SEBS degraded gradually at higher temperatures (>220 °C).

Conclusions:

• Chemiluminescence is an effective tool for assessing the recyclability and predicting the thermal stability of styrene block copolymers.
• The molecular structure, specifically the sequence and type of composing units, significantly influences the degradation behavior and stability of these copolymers.
• The findings provide valuable insights for optimizing recycling processes and material selection based on copolymer structure and expected thermal stress.