Odor-Reduced HDPE-Lignin Blends by Use of Processing Additives

Area of Science:

• Polymer Science
• Materials Science
• Sustainable Materials

Background:

• Technical lignin is an underutilized natural polymer with potential for replacing mineral oil-based commodities.
• Polyolefin-lignin blends offer a sustainable alternative, but lignin's inherent odor limits high-quality applications.
• Processing, especially extrusion, can intensify the odor of technical lignin and resulting blends.

Purpose of the Study:

• To optimize the odor of kraft and soda high-density polyethylene-lignin (HDPE-lignin) blends.
• To investigate the effectiveness of activated carbon and a stripping agent in reducing odor.
• To identify and quantify odor-active molecules and elucidate odor reduction mechanisms.

Main Methods:

• In-process addition of 5% activated carbon or 0.7% stripping agent during twin-screw extrusion compounding.
• Sensory evaluation by a trained human panel to assess odor intensity and characteristics.
• Gas chromatography-olfactometry (GC-O) and 2D-GC-MS/O for odorant identification.
• Odor-enabled-differential-analysis (OEDA) for relative odor potency.

Main Results:

• Over 30 sulfur-containing odorants, neo-formed during extrusion, were identified in kraft HDPE-lignin blends, contributing to burnt and sulfurous smells.
• Activated carbon addition reduced sulfurous compounds, leading to a 48% overall odor reduction in kraft HDPE-lignin blends.
• The stripping agent reduced odor by 26% in soda HDPE-lignin blends, with less impact on neo-formed sulfur odorants.

Conclusions:

• Activated carbon is highly effective in deodorizing kraft HDPE-lignin blends by targeting sulfurous compounds.
• The stripping agent shows moderate effectiveness, particularly for soda HDPE-lignin blends.
• These odor reduction strategies can enhance the use of lignin in sustainable materials and potentially benefit other natural-fiber based materials.