External and internal plasticization of cellulose acetate with caprolactone:: Structure and properties

Cellulose acetate was modified with caprolactone in an internal mixer at temperatures between 120 and 220 degrees C, and reaction times between 5 and 45 min in the presence of tinoctoate catalyst. The effect of plasticization on the properties of the polymer was studied by dynamic mechanical analysis and tensile testing. The dynamic mechanical spectrum of cellulose acetate exhibits three main relaxation transitions. These can be assigned to segments (alpha), to smaller structural units of the main chain, probably individual glucose rings (beta), and to hydroxyl or hydroxylmethyl groups (gamma). Plasticization by caprolactone leads to the decrease of the glass transition temperature of CA, but also to the breakdown of relatively large segments to smaller structural units. Free hydroxyl groups interact with the plasticizer forming larger units with higher transition temperature. Grafting decreases the intensity of the gamma-transition peak. External plasticization creates a larger number of small structural units, but the external plasticizer is less efficient in the decrease of stiffness than grafted polycaprolactone chains. Internal plasticization is more advantageous because it leads to higher flexibility at larger strength than external plasticization, and the migration of the plasticizer is prevented at the same time. (c) 2007 Wiley Periodicals, Inc.