Investigation of thermal and viscoelastic properties of polymers relevant to hot melt extrusion, I: Polyvinylpyrrolidone and related polymers
Polymers are essential components of melt extruded products. The objective of the paper was to generate physicochemical data on polyvinylpyrrolidone-based polymers and copolymers that are relevant to hot melt extrusion (HME). It also highlights the importance of viscoelastic analysis to predict HME processing conditions. Powder X-ray diffraction (XRD) patterns of polymers were recorded to determine the physical nature of polymers. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to determine their glass transition temperature (Tg) and weight loss due to degradation (Td) respectively. Rheological studies were conducted to quantitate storage modulus (G´), loss modulus (G˝), tan δ and complex viscosity (η) of the polymers at various temperatures. Powder XRD analyses showed that all polymers were amorphous in nature, with distinct single or dual halos. DSC ascertained that the amorphous polymers had single Tg values. The conversion of the polymers from solid to liquid forms with an increase in temperature was established by the tan δ = 1 values. The overall complex viscosity for all polymers decreased with an increase in temperature. The complex viscosity of one of the polymers, Soluplus®, was correlated with torque analysis by HME to establish an extrudable temperature range. The results will help the selection of polyvinylpyrrolidone-based polymers for HME.