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

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 present study was to generate physicochemical data of polyvinylpyrrolidone-based polymers and copolymers that are used in hot melt extrusion (HME). This study focused on investigating the importance of viscoelasticity for predicting HME processing conditions. Powder X-ray diffraction (XRD) patterns of polymers were recorded to determine the physical nature of the polymers. Differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA) were carried out 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 showed that the amorphous polymers had single Tg values. The conversion of the polymers, from solid to liquid forms, with increasing temperature was established by the tan δ = 1 values. The overall complex viscosity for all polymers decreased with increasing temperature. The complex viscosity of one of the polymers, Soluplus®, was correlated using torque analysis through HME to establish an extrudable temperature range. The results are expected to assist in the selection of polyvinylpyrrolidone-based polymers for HME. Once the appropriate polymers are selected, further studies may be carried out using drugs, plasticizers and, so on, to optimize processing conditions

Investigation of thermal and viscoelastic properties of polymers relevant to hot melt extrusion - II: Cellulosic polymers

The purpose of this study was to determine the thermal and viscoelastic properties of cellulosic polymers that may have potential for use in hot melt extrusion (HME). Cellulose ethers of different molecular weight (MW) with varied degrees of substitution and differences in substituted groups were analyzed using modulated differential scanning calorimetry (MDSC), thermogravimetric analysis (TGA) and oscillatory rheometry. The results indicated that the glass transition temperature (Tg) and viscoelastic characteristics of polymers appear to depend on their chain length, molecular weight (MW), and degree and type of substitutions in the main chain. In general, an increase in the chain length or MW increased Tg, as well as, the viscosity (HPMC, MW10000 < MW 25000 < MW 150000 Da). Additionally, substitutions with bulkier groups decreased both the Tg and the viscosity of the polymer. Most of the cellulosic polymers had high viscosity between their Tg and degradation temperature (Td), and could not be extruded by themselves. The thermal properties in combination with polymer viscosity at different temperatures may assist formulating scientists in determining the processability when using HME

Investigation of thermal and viscoelastic properties of polymers relevant to hot melt extrusion - III: Polymethacrylates and polymethacrylic acid based polymers

Polymers are a major part of final medicinal drug products prepared by hot melt extrusion (HME). Therefore it is necessary to understand their behavior when subjected to heat and mechanical stresses during the development of the HME processes. The aim of this work was to generate a database of the physicochemical properties for polymethacrylates and polymethacrylic acid based polymers relevant to HME. All six polymers tested were amorphous and had < 2% moisture. In differential scanning calorimetric (DSC) studies, the three homo block copolymers, Eudragit® E PO, Eudragit® RL PO and Eudragit® RS PO, had glass transition temperatures (Tg) of 57°C, 63°C and 64°C, respectively, and thermogravimetric analysis (TGA) showed weight loss due to thermal degradation at 250°C, 166°C and 170°C, respectively. Thermomechanical analysis was carried out to investigate the rheological properties of the polymers predicting that the melt extrusion ranges of Eudragit® E PO, Eudragit® RL PO and Eudragit® RS PO would be 127-150, 165-170 and 142-167°C, respectively. In contrast, the hetero block copolymers Eudragit® L 100, Eudragit® S 100 and Eudragit® L 100-55 had Tg values of 195, 173 and 111°C, respectively. Onsets of their degradation, as measured by TGA, were in the range of 173 to176°C. The predicted HME processing temperatures of Eudragit® L 100, Eudragit® S 100 and Eudragit® L 100-55 were greater than 200°C and therefore these polymers cannot be processed by themselves without the addition of plasticizers