Enhancing melt strength of polyglycolic acid by reactive extrusion with chain extenders

Biodegradable polyglycolic acid (PGA) has attracted wide interest as environmentally friendly polymer. However, poor melt properties and thermal instability limit its widespread applications, wherever processing technologies such as extrusion, blown film, thermoforming, are required. In order to enhance the melt strength of pure PGA material and enlarge its processing window, two reactive chain extenders (CEs), 4, 4 '-methylenebis (phenyl isocyanate) and styrene-acrylic multifunctional-epoxide oligomeric agent were incorporated concurrently into PGA using the twin-screw extruder. The PGA molecular structures were tailored by introducing CEs. Melt flow rate of the modified PGA gradually decreased with increasing CEs contents, due to chain extension. The shear rheology data showed a remarkable increase in modulus and complex viscosity together with longer relaxation time, which can be an indication of the existence of long chain branches in the molecular structure. Dynamic time sweep tests showed that the melt stability of the modified PGA improved significantly, with a loss of about 2% of the normalized storage modulus after 15 min, while the value of pure PGA was about 17%. Besides, changes of elongational melt properties can also be found, where strain hardening occurred for the modified PGA.

Automated summary

The introduction of two reactive chain extenders improved the melt flow rate, viscosity, and stability of biodegradable polyglycolic acid (PGA), leading to controllable molecular structure modifications.