Hydroxypropyl cellulose/thermoplastic polyurethane blend films with reversible optical performance triggered by water

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Materials

Background:

• Growing demand for sustainable materials drives interest in cellulose-based additives for polymer blends.
• Environmentally responsive materials are crucial for advanced applications.
• Hydroxypropyl cellulose (HPC) and thermoplastic polyurethane (TPU) are key polymers in this field.

Purpose of the Study:

• To fabricate and investigate the water-triggered optical and physical responses of hydroxypropyl cellulose/thermoplastic polyurethane (HPC/TPU) blend films.
• To understand the molecular mechanisms behind the reversible optical transitions.
• To evaluate the potential of HPC/TPU blends for moisture-responsive applications.

Main Methods:

• Fabrication of HPC/TPU blend films using a one-step casting method.
• Characterization using phase contrast optical microscopy and confocal microscopy with dye tracing.
• Analysis of molecular interactions with Fourier Transform Infrared Spectroscopy (FTIR) and differential Scanning Calorimetry (DSC).
• Evaluation of water-induced swelling and deswelling via bulk swelling tests and sorption analysis.

Main Results:

• HPC/TPU films demonstrated reversible transparency changes: opaque when hydrated, transparent when dry.
• Microphase separation of HPC-rich domains within the TPU matrix was observed.
• These HPC domains selectively absorbed water, swelled, and increased refractive index contrast, causing light scattering.
• FTIR and DSC confirmed hydrogen bonding between water and HPC hydroxyl groups, correlating with swelling.
• Bulk swelling tests confirmed reversible water uptake and deswelling cycles.

Conclusions:

• HPC/TPU blends exhibit tunable, reversible optical properties triggered by moisture.
• The observed behavior is linked to water-induced swelling of HPC domains and molecular interactions.
• These sustainable blends are promising candidates for moisture-responsive coatings and devices.