Thermal behaviour of zircon/zirconia-added chemically durable borosilicate porous glass

Macroporous alkali resistant glass has been developed by making additions of zirconia (ZrO2) and zircon (ZrSiO4) to the sodium borosilicate glass system SiO2–B2O3 Na2O. The glass was made using a traditional high temperature fusion process. Differential thermal analysis (DTA) was carried out to identify the glass transition temperature (Tg) and crystallisation temperature (Tx). Based on these findings, controlled heat-treatments were implemented to separate the glass into two-phases; a silica-rich phase, and an alkali-rich borate phase. X-ray diffraction (XRD) was used to identify any crystal phases present in the asquenched and heat-treated glasses. Fourier transform infrared (FTIR) spectroscopy also proved effective in investigating phase separation and crystallisation behaviour. After leaching, a silica-rich skeleton with an interconnected pore structure and a uniform pore distribution was observed. Pore characterisation was carried out using mercury porosimetry. The size and shape of the pores largely depended on the heattreatment temperature and time. ZrO2/ZrSiO4 additions increased the alkali resistance of the porous glass 3–4 times

Development of cobalt ferrite powder preparation employing the sol-gel technique and its structural characterisation

This work focuses on the development of a method to make nano cobalt ferrite powder using a solgel process. A particular emphasis is devoted to the understanding of the role of the chemical parameters involved in the solgel technique, and of the heat treatment on the structures and morphologies of the materials obtained. Several samples of cobalt ferrite powder were obtained by varying the initial parameters of the process in addition to the heat treatment temperature. Xray diffraction and scanning electron microscopy were used to identify the structure and morphology of samples demonstrating the influence of the initial parameters. DTA/TGA was carried out on one sample to identify important reaction temperatures during the heat treatment. The average particle size, as estimated for one sample by the full width at half maximum (FWHM) of the strongest Xray diffraction (XRD) peak, was found to be about 45 nm. It has been found that the chelating agent and the crosslinker have a critical influence on the resultant structure, the particle size and the particle size distribution

Regime-separated approach for population balance modelling of continuous wet granulation of pharmaceutical formulations

peer-reviewedA two-dimensional population balance model (PBM) was developed in order to predict granule size distribution (GSD) in continuous twin-screw granulation. The model predicts the GSD as well as granule liquid content at different spatial locations. In order to understand the different mechanisms involved in the twin-screw granulation process, a regime-separated approach was used in which the population balance model was solved for different zones along the extruder, i.e. kneading and conveying zones. For the conveying zone, the flow regime was assumed to be plug flow, whereas a well-mixed regime was assumed for modelling of particulate events in the kneading zone. In the development of the population balance model, breakage and aggregation phenomena were considered as particulate events. The unknown parameters of the model were estimated using experimental data obtained for granulation of pure microcrystalline cellulose using a 12 mm twin-screw granulator. Among five experimental runs, three runs were used for model calibration and two runs for validation. The results indicated that the model is rigorous and reliable for prediction of GSD as function of process parameters in twin-screw granulation. Moreover, in order to capture tri-modality in the granule size distribution, a partial wetting approach was used in which 50% of particles were assumed dry at low liquid to solid ratio. The latter assumption resulted in prediction of tri-modal GSD by the developed PBM. The results revealed that aggregation is dominant in the conveying zone, while in the kneading zone the breakage rate is much higher than the aggregation rate

Bioactive PCL matrices with a range of structural & rheological properties

Safer pharmaceutical and medical device excipients are being sought as alternatives to polyvinyl polymers that are commonly plasticised by carcinogenic phthalates. This paper demonstrates a biodegradable and non-toxic bioactive polymer matrix that can be easily modified through plasticiser addition in the presence of low dosage active pharmaceutical ingredient (API). Poly(ε-caprolactone) (PCL) was selected as an alternative polymer to polyvinyls as it is biodegradable and has high amorphous content, which improves drug solubility. Bulk PCL and various blends with 5 and 25% polyethylene glycol (PEG, a plasticiser and pore former) and 5% nalidixic acid (NA, the API) were processed using extrusion and pressed into plaques. The resultant material properties were investigated in terms of microscopic, morphological and topographical modification. No evidence of miscibility was found by IR. The rheology and contact angle of the matrix could be easily manipulated through the addition of PEG. Increased loading of PEG to 25% (w/w) caused a 10-fold increase in the melt flow index, a similar increase in the elongational viscosity, and a contact angle decrease of 10°, indicating that the resultant fluid was becoming more Newtonian. It was concluded that the structural and rheological properties of the blend, while easily modified through the addition of PEG, were unaffected by the monodispersion of the API, nalidixic acid.Scopu

Effect of poly ethylene glycol on the mechanical and thermal properties of bioactive poly(epsilon-caprolactone) melt extrudates for pharmaceutical applications

This paper investigates the effects of polyethylene glycol (PEG), on the mechanical and thermal properties of nalidixic acid/poly ε-caprolactone (NA)/PCL blends prepared by hot melt extrusion. The blends were characterized by tensile and flexural analysis, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. Results show that loading PEG in the PCL had a detrimental effect on the tensile strength and toughness of the blends, reducing them by 20–40%. The partial miscibility of the PCL-PEG system, causes an increase in Tg. While increases in the crystallinity is attributed to the plasticisation effect of PEG and the nucleation effect of NA. The average crystal size increased by 8% upon PEG addition. Experimental data indicated that the addition of NA caused loss of the tensile strength and toughness of PCL. Thermal analysis of the PCL showed that on addition of the thermally unstable NA, thermal degradation occurred early and was autocatalytic. However, the NA did benefit from the heat shielding provided by the PCL matrix resulting in more thermally stable NA particle