Polylactic Acid Chemical Foaming Assisted by Solid-State Processing: Solid-State Shear Pulverization and Cryogenic...

Area of Science:

• Materials Science
• Polymer Chemistry
• Chemical Engineering

Background:

• Polylactic acid (PLA) is a biodegradable polymer with potential for foaming applications.
• Traditional chemical foaming methods for PLA face limitations in achieving high void fractions and desired properties.
• Solid-state processing offers a novel approach to modify PLA's properties before foaming.

Purpose of the Study:

• To develop an effective chemical foaming process for PLA using solid-state processing techniques.
• To investigate the impact of solid-state shear pulverization (SSSP) and cryogenic milling on PLA foaming.
• To evaluate the effects of pre-foaming solid-state processing and chemical foaming agent (CFA) concentration on foam characteristics.

Main Methods:

• PLA was subjected to solid-state processing (SSSP and cryogenic milling) prior to chemical foaming.
• Chemical foaming agents (CFA) were compounded with PLA after solid-state processing.
• Foaming was achieved via compression molding.
• Characterization included density reduction, mechanical testing, thermal analysis (DSC), and cell density measurement.

Main Results:

• Solid-state processing significantly increased the extent of PLA foaming, nearly doubling void fractions compared to control foams.
• PLA's crystallization kinetics were enhanced, evidenced by DMA and DSC.
• Foams produced via solid-state processing exhibited superior mechanical robustness and low stress relaxation.
• SSSP particularly increased cell density.
• Crosslinking during pre-foaming enhanced crystallization but reduced foam effectiveness.

Conclusions:

• Solid-state processing methods like SSSP and cryogenic milling are highly effective in improving the chemical foaming of PLA.
• These techniques enhance PLA's crystallization, leading to improved foam properties and density reduction.
• The findings suggest significant promise for SSSP and cryogenic milling in advancing foaming technologies for biopolymers.