Formation of UHMWPE Nanofibers during Solid-State Deformation

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Ultra-high molecular weight polyethylene (UHMWPE) typically exists in entangled states, hindering controlled processing.
• Disentangled UHMWPE (dis-UHMWPE) offers potential for novel nanostructured materials.
• In situ formation of polymer nanofibers is a key area in advanced materials development.

Purpose of the Study:

• To investigate the in situ formation of nanofibers from dis-UHMWPE within a polyolefin elastomer matrix.
• To explore the influence of processing parameters (shearing duration and temperature) on nanofiber morphology.
• To understand the limitations and mechanisms governing the minimum achievable nanofiber diameter.

Main Methods:

• Preparation of dis-UHMWPE powder via low-temperature polymerization to prevent entanglement.
• Compounding dis-UHMWPE with a polyolefin elastomer below the dis-UHMWPE melting point.
• Solid-state deformation of dis-UHMWPE particles into nanofibers through controlled shearing.
• Characterization of nanofiber diameter and structure using microscopy and thermal analysis.

Main Results:

• A network of dis-UHMWPE nanofibers (110-340 nm diameter) was successfully formed in situ.
• Further shearing reduced nanofiber diameter to below 40 nm, maintaining crystalline/amorphous composition.
• Excessive shearing led to nanofiber melting and fragmentation due to reduced dimensions and amorphous defects.

Conclusions:

• In situ nanofiber formation from dis-UHMWPE is achievable through solid-state deformation.
• Processing parameters significantly impact nanofiber dimensions, with a critical limit to achievable thinness.
• Nanofiber fragmentation at smaller diameters is attributed to thermal instability and localized melting, preventing further size reduction.