Article

The influence of HPMC substitution pattern on solid-state properties

Department of Chemical and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
Carbohydrate Polymers (Impact Factor: 3.92). 12/2012; DOI: 10.1016/j.carbpol.2010.06.030

ABSTRACT The solid-state properties were studied for different batches of hydroxypropyl methylcellulose (HPMC). The batches had similar chemical composition, but different degree of heterogeneity with regard to the distribution of the substituents along the polymer chains. The glass transition temperature, Tg, was analysed using a new developed method where dynamic mechanic analysis, DMA, was performed in compression mode on compacts, utilizing a wedge-shaped probe. The method was verified by conventional DMA on films. Molecular interactions were studied using FT-IR. In addition, the water vapour sorption was determined by gravimetric measurements and the plasticization by water vapour was studied on film samples using DMA. The results revealed a linear relationship between increasing Tg and increasing percent glucose liberated after enzyme hydrolysis. The percent glucose liberated can in turn be considered to account for both the heterogeneity of the substituents and the total degree of substitution. The results indicated that more heterogeneously substituted cellulose derivatives and derivates with a lower degree of substitution had stronger interactions between polymer chains. As expected from these results, some small difference in the plasticization by water vapour could be detected. However, no significant differences were found in molecular interactions using FT-IR or in the sorption of water vapour. The correlation between heterogeneity in the distribution of the substituents and Tg is of much interest as heterogeneously substituted batches of HPMC have been previously shown to exhibit very different behaviour in solution and in gelling tablets.

2 Followers
 · 
172 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Voltage-time characteristics of SF<sub>6</sub> gas and an SF<sub>6 </sub>-N<sub>2</sub> gas mixture with a mixing ratio of 50/50 were measured in a 50/20-mm-diameter coaxial electrode system with and without a spacer under both lightning impulse and steep-fronted impulse voltages. A nonoscillating steep-fronted impulse with a risetime as short as 50 ns was derived from a 1.2/60-μs lightning impulse by means of a wave-front-steepening gap, and was measured using a compact resistive type voltage divider, with the measuring system response time being less than 5 ns. Experiments showed that the breakdown voltage under the steep-fronted impulse was lower than that under the lightning impulse for the same time to breakdown in both SF<sub>6</sub> and the SF <sub>6</sub>-N<sub>2</sub> gas mixture, but it was still higher than the 50% lightning impulse breakdown voltage used for insulation co-ordination. For the case with a spacer, breakdowns in both SF<sub>6 </sub> and SF<sub>6</sub>-N<sub>2</sub> were greatly scattered compared with gas insulation without any spacer
    Electrical Insulation, Conference Record of the 1992 IEEE International Symposium on; 07/1992
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the drawbacks with solid solution systems is their thermodynamic instability in solution. Considering the release of these systems from extended-release formulations, in particular swellable matrix tablets, a successful tablet formulation can be regarded as a composition able to maintain the molecular state of the poorly soluble crystalline drug through diffusion in the matrix. This may in turn provide molecular rather than particulate delivery of the substance from the matrix. In this study, the solid state and dissolution behavior of amorphous solid dispersions of a model crystalline substance, butyl paraben in HPMC and HPMCAS, was investigated. In addition, the suitability of HPMCAS as both effective solid solution carrier and as extended-release matrix forming polymer was examined. The release from all systems investigated showed extended-release capacity with a release rate similar to the rate of matrix erosion. However, a detailed study of the factors affecting the release mechanism revealed that upon hydration, the model substance crystallized in the gel layer of the HPMC-based formulation, whereas it remained in amorphous form in the HPMCAS tablets. In the case of HPMCAS formulation, this effect was attributed to (i) the ability of this polymer to keep the model substance in a supersaturated state and (ii) the very slow matrix hydration, resulting in a steep concentration gradient of the drug substance and a short diffusion path through the matrix into the dissolution bulk.
    European journal of pharmaceutics and biopharmaceutics: official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 12/2010; 78(1):125-33. DOI:10.1016/j.ejpb.2010.11.020 · 4.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Microfibrillated cellulose (MFC) films containing the water soluble and pharmaceutically approved polymer hydroxypropyl methylcellulose (HPMC) exhibited an unexpected decrease in permeability and excellent one-dimensional swelling properties above a threshold in HPMC content. It is proposed that the observed material characteristics derive from the influence of HPMC on the aggregation behavior of MFC in such a way that above a critical HPMC content the films are created through self assembly into a layered structure, composed of low swelling layers with swellable inter layer regions. The suggested structures were supported by high resolution microscopy. The findings should hold potential for direct applications, but even more as a concept for future material design.
    Carbohydrate Polymers 04/2012; 88(2):763-771. DOI:10.1016/j.carbpol.2012.01.056 · 3.92 Impact Factor