Viscoelastic behaviour of cellulose acetate/triacetin blends by rheology in the melt state.

The viscoelastic behaviour of cellulose acetate with a degree of substitution (DS) of 245 plasticized by triacetin was studied at short times by dynamic oscillatory measurements. Two distinct regimes and unexpected scaling behaviour according to plasticizer content were highlighted. The dynamics of chains and their structural organization are not modified up to 35 wt% of triacetin. The rheological behaviour is led by a constant correlation length corresponding to the distance between strong intermolecular interactions subsisting in the melt state at high temperature even in the presence of plasticizer. This particular structure involves the apparition of strain hardening effects during uniaxial extensional flow tests and an important elasticity corresponding to the apparition of a Weissenberg effect at really low shear rates during shear sweeps. Intramolecular hydrogen bonds are responsible of the high rigidity of cellulose acetate chains. Plasticized cellulose acetate in the melt state belongs to the class of associating polymers and its rheological behaviour is mainly led by stickers.

Mechanical and ultimate properties of injection molded cellulose acetate/plasticizer materials.

The mechanical properties of injection molded plasticized cellulose acetate polymers processed with two different plasticizers (Triacetine and Diethyl phthalate) and various weight fractions comprised between 15 and 30 wt % have been investigated. Plasticized cellulose acetate exhibit a brittle-to-ductile transition from a low impact strength to a high impact strength of order 40 kJ/m². Obtaining a high impact resistance at room temperature requires plasticizer content larger than 25 wt.%. An important strain hardening is obtained for samples with both plasticizers during tensile experiment. At 15 wt.% plasticizer content, the measured strain hardening modulus is around 148 MPa at 60 °C. Different parameters influencing the strain hardening behavior have been identified: the tensile direction as compared to that of the injection flow, the temperature and the plasticizer, consistent with studies on pre-strained samples of synthetic amorphous polymers.

Miscibility and dynamical properties of cellulose acetate/plasticizer systems.

Due to its biodegradability and renewability, a great interest has been devoted to investigating cellulose acetate in order to expand its potential applications. In addition, secondary cellulose acetate (CDA) could also be considered as a model system for strongly polar polymer system. The dynamical behavior of CDA is supposed to be governed by H-bonding and dipolar interaction network. Due to their high glass transition temperature, cellulose acetate-based systems are processed when blended with plasticizers. It is thus of utmost importance to study the miscibility and plasticizing effects of various molecules. We prepared CDA films via solvent casting method with diethyl phthalate as the plasticizer. Miscibility diagrams were established by calorimetry and thermo-mechanical (DMTA) experiments. Dynamical properties were analyzed by DMTA and broadband dielectric spectroscopy. We could identify the α-relaxation of these CDA-plasticizer systems in the frequency range from 0.06 Hz to 10(6)Hz, which allowed for describing the dynamics in the so-called Williams-Landel-Ferry/Vogel-Fulcher-Tammann regime.