Development of Silylated Lignin-Based Intumescent Flame Retardants for Biodegradable Plastics

Area of Science:

• Materials Science
• Polymer Chemistry
• Fire Safety Engineering

Background:

• Polylactic acid (PLA) is a biodegradable polymer with potential in various applications.
• PLA exhibits poor flame retardancy, releasing high heat and toxic smoke during combustion.
• Developing sustainable and effective flame-retardant solutions for PLA is crucial.

Purpose of the Study:

• To chemically modify Kraft lignin to improve its char-forming ability.
• To create flame-retardant polylactic acid (PLA) composites using modified lignin and ammonium polyphosphate (APP).
• To evaluate the flame retardancy and mechanical properties of the developed PLA composites.

Main Methods:

• Kraft lignin was modified via phenolation and silylation with tetraethoxysilane.
• Modified lignin was combined with APP and melt-mixed with PLA.
• Flame retardancy was assessed using UL-94 vertical burning tests and limiting oxygen index (LOI) measurements.
• Mechanical properties were evaluated through tensile strength tests.

Main Results:

• Successful grafting of phenolic and silane functionalities onto lignin was confirmed.
• The modified lignin exhibited enhanced thermal stability.
• The PLA/APP/SPKL composite achieved a V-0 UL-94 rating and 31.95% LOI, significantly higher than neat PLA (19-21% LOI).
• The composite maintained comparable mechanical strength to V-2 flame-retardant PLA-APP composites.

Conclusions:

• Chemically modified lignin, combined with APP, effectively enhances the flame retardancy of PLA composites.
• This method offers a sustainable approach to producing PLA composites with both high flame retardancy and retained mechanical strength.
• The developed materials present a viable alternative for fire-safe applications in transportation, construction, and electronics.