Polymorphism and Stretch-Induced Transformations of Sustainable Polyethylene-Like Materials

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Bioderived, biodegradable, and recyclable aliphatic polyesters offer sustainable alternatives to conventional plastics.
• Understanding the crystalline structures of these polymers is crucial for tailoring their mechanical properties.

Purpose of the Study:

• To investigate the crystal structures of polyethylene-like bioderived polyesters.
• To explore the thermal and mechanical transformations between different crystal forms.
• To identify structure-property relationships for enhanced material performance.

Main Methods:

• Melt quenching of polyethylene-like polyesters (PE-2,18) at various temperatures.
• Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) for structural analysis.
• Uniaxial tensile deformation experiments to study mechanical response.

Main Results:

• Hexagonal crystal structures form upon quenching below ~50 °C, characterized by conformational disorder.
• Orthorhombic-like packing forms at higher quenching temperatures or during isothermal crystallization, featuring all-trans CH2 sequences.
• Hexagonal crystals transform to orthorhombic crystals around 60 °C via melt recrystallization.
• Uniaxial tensile deformation induces a stretch-induced transformation from hexagonal to orthorhombic structure.
• This transformation leads to larger strains and enhanced strain hardening, improving material toughness.

Conclusions:

• Bioderived polyesters exhibit distinct crystalline structures dependent on processing conditions.
• The hexagonal crystal form offers a pathway to enhanced mechanical properties through a stretch-induced phase transformation.
• These findings provide insights for designing tougher, high-performance biodegradable polymers.