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Biomedical subjects

R C Rowe

Publications and source records attributed to R C Rowe.

At least 73 records · Page 4Linked to original sources
PubMed1981

The effect of the particle size of an inert additive on the surface roughness of a film-coated tablet.

The effect of the particle size of a model inert additive--a dolomite, commercially available in a wide range of grades with varying particle sizes--on the surface roughness of a coated tablet has been studied using a stylus surface roughness measuring instrument. With all grades with a maximum particle size below 10-15 microns there was only a marginal increase in roughness on the addition of the material at low concentrations with a marked increase at concentrations in excess of 20-30% v/v. With the largest particle size material (mean size 18 microns) there was a marked increase in surface roughness at low concentrations with a decrease at higher concentrations. The different trends were due to the influence of the inherent roughness of the tablet substrate used. The results illustrate the potential of this accurate, rapid, simple and non-destructive technique in the optimization of film formulations during product development.

Particle Size↗
PubMed1981

The cracking of film coatings on film-coated tablets--a theoretical approach with practical implications.

A theoretical approach of film cracking is presented using equations which allow for the calculation of both the internal stress in a film coating due to shrinkage of the film on evaporation of the solvent and the thermal stress due to differences in the thermal expansion of the film coating and tablet substrate during changes in temperature arising out of the coating processes. The practical implications of this approach in film formulation are discussed with particular reference to the choice of tablet core formulation, the grade of polymer used, the type and concentration of both plasticizers and pigments and the solvent system used in the coating process.

Chemistry, Pharmaceutical↗
PubMed1981

Theoretical considerations of the influence of polymer film coatings on the mechanical strength of tablets.

A theoretical analysis of the influence of polymer film coatings on the mechanical strength of tablets has been undertaken. Making some basic assumptions, the theory predicts that neither the thickness of the substrate nor that of the coating has any influence on which fractures first, this being solely determined by the ratio of the tensile fracture strength to the Young's modulus for the two materials. Such a finding suggests that in practice for film-coated tablets the substrate will usually fracture before the coating. Simple measurements of maximum failure loads are of little value in assessing the influence of film coating on the mechanical strength of tablets.

Polymers↗
PubMed1980

The molecular weight and molecular weight distribution of hydroxypropyl methylcellulose used in the film coating of tablets.

The molecular weight and molecular weight distributions of nine grades of hydroxypropyl methylcellulose used in the film coating of tablets have been measured using gel permeation chromatography. With the exception of Pharmacoat 603, there is a high molecular (greater than 5 x 10(5)) component present in all grades ranging from relatively small amounts in grades with low nominal viscosity to relatively large amounts in the 50 mPas grade. The peak molecular weight taken from the distribution curve--an indication of the molecular weight of the main component--could be calculated from the nominal viscosity using the equation. Peak molecular weight = 23.54 x 10(3) (viscosity)0.45. The relationship could also be expressed in the standard form [eta]=KM alpha where M is the peak molecular weight [eta] is the intrinsic viscosity and K and alpha are constants (in this case 9.94 x 10-4 and 1.096 respectively). The wide molecular weight distribution of these samples and the presence of quite high proportions of very low molecular weight (less than 5 x 10(3)) components especially in samples with nominal viscosity designations of less than 15 mPas appears to affect their mechanical properties.

Chromatography, Gel↗
PubMed1979

The mechanical strength of film-coated tablets.

The mechanical strength of film-coated tablets has been assessed using the diametral compression test. The results show that the influence of the film is more complex than that suggested by Stern (1976). The film may increase the breaking load of the core itself by acting as a padding material during the test and also by filling in surface irregularities. The film may also have enough intrinsic strength and elasticity to hold the core together once it has broken. The maximum breaking load to completely fracture the coated tablet is related to film properties, but the relation is not a simple one.

Hardness↗
PubMed1979

Plasticization of cellulose ethers used in the film coating of tablets.

Plasticizer/polymer interactions have been studied by measuring the intrinsic viscosities of both ethyl cellulose and hydroxypropyl methylcellulose in a series of dialkyl phthalates and in a series of liquid glycols respectively. A correlation was found between the intrinsic viscosity of the polymer/plasticizer solutions and the tensile strength, elongation at rupture and work done in stressing to failure of cast films--the mechanical properties being at a minimum when the intrinsic viscosity was at a maximum. This correlation held only within a homologous series of plasticizers and none was found for plasticizers of different structures. A relationship was found between the lowering of a calculated glass transition temperature of hydroxypropyl methylcellulose in the presence of the plasticizers propylene glycol, polyethylene glycol 200 and glycerol and the intrinsic viscosity of the corresponding solutions--the higher the viscosity the greater the lowering of the transition temperature.

Cellulose↗
PubMed1978

The measurement of the adhesion of film coatings to tablet surfaces: the effect of tablet porosity, surface roughness and film thickness.

The effect of tablet porosity, surface roughness and film thickness on the adhesion of hydroxypropyl methyl cellulose films to placebo tablet substrates have been studied using a specially designed tensile tester (Fisher & Rowe, 4976). There were direct relations between measured adhesion and tablet porosity and also surface roughness and tablet porosity. The effect of film thickness on the measured adhesion is complex with an initial decrease with thicknesses up to 35 micron and then a gradual increase with thicknesses up to 140 micron dut to differences in the strees distribution within the film during testing. A knowledge of these effects is necessary if results from various sources are to be compared. The findings illustrate the potential capability of the extrapolation of measured adhesion results to zero porosity and zero thickness values in order to obtain a measure of the true or intrinsic adhesion at any film/tablet interface without the confusing elements of tablet porosity, surface roughness and residual stresses in the film.

Adhesiveness↗