Understanding and minimizing polycaprolactone degradation during processing using multi-detector GPC and rheology
Malvern measures degradation related changes in molecular weight and rheology during polycaprolactone processing
Polycaprolactone (PCL) is a synthetic polymer that has recently received increasing attention thanks to its biodegradability.  Its most common use is in the manufacture of polyurethanes or as a plasticizer for other polymers such as PVC.  It is also often used in molding and prototyping thanks to its low melting temperature and is used as a feedstock in some additive manufacturing (3D printing) systems.  Finally, it is also used in some drug delivery applications as a control release mechanism, in the same way as polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA).  A potential advantage over PLA and PLGA is that PCL has a slower degradation rate and therefore may allow for slower drug release.
As with all polymers, PCL’s molecular properties (e.g. molecular weight) will strongly affect its bulk properties such as strength, toughness, and melt-flow.  Being biodegradable, PCL is at a high risk of degradation during processes such as extrusion for molding, particularly at high temperatures.  Some mechanisms have been described in the literature to reduce this.  For instance, extrusion in the presence of carbon dioxide (CO2) can reduce the melt flow viscosity of PCL by acting as a ‘molecular lubricant’.  Decreasing the viscosity of the polymer reduces the temperature at which extrusion can be performed and could thereby protect the polymer from degradation during the process [1].
In this application note, a commercially available sample of PCL was extruded alone and in the presence of CO2­.  Multi-detector GPC measurements were made of the virgin sample before and after extrusion, while rotational rheometry was used to study the polymer’s melt viscosity.