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Plasticizers01:31

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Water-reducers, or plasticizers, are chemical admixtures used in concrete to improve strength and workability. These additives reduce the water-cement ratio without compromising workability, lower the cement content while maintaining the same workability, or increase workability to assist concrete placement in inaccessible areas.
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Superplasticizers are advanced admixtures that enhance the workability of concrete by lowering the water content without compromising the strength of the material. These substances are highly effective water reducers, improving concrete flow, making it easier to work with, and enabling concrete to reach inaccessible areas or densely reinforced sections without mechanical vibration. The key components in superplasticizers are either sulfonated melamine or naphthalene formaldehyde condensates,...
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Citric acid as a solid-state plasticizer for Eudragit RS PO.

Sandra U Schilling1, Navnit H Shah, A Waseem Malick

  • 1Drug Dynamics Institute, College of Pharmacy, University of Texas at Austin, Austin, TX 78712, USA. sschilling@mail.utexas.edu

The Journal of Pharmacy and Pharmacology
|November 3, 2007
PubMed
Summary
This summary is machine-generated.

Citric acid monohydrate (CA MH) effectively plasticizes Eudragit RS PO for hot-melt extrusion, improving processability and creating controlled-release matrix systems. Anhydrous citric acid was less effective due to lower solubility in the polymer.

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Area of Science:

  • Pharmaceutical Technology
  • Materials Science
  • Polymer Chemistry

Background:

  • Solid-state plasticizers offer advantages over liquid plasticizers in pharmaceutical hot-melt extrusion.
  • Eudragit RS PO is a common polymer for extended-release dosage forms.
  • Citric acid (CA) is a potential solid plasticizer for pharmaceutical applications.

Purpose of the Study:

  • To evaluate citric acid (CA) as a solid plasticizer for Eudragit RS PO extended-release matrix systems prepared by hot-melt extrusion.
  • To investigate the influence of citric acid monohydrate (CA MH) and anhydrous CA on extrusion parameters and polymer properties.

Main Methods:

  • Hot-melt extrusion of Eudragit RS PO with varying concentrations of CA MH and anhydrous CA.
  • Analysis of extrusion process parameters (screw speed, motor load) as a function of temperature.
  • Characterization of CA solubility using modulated differential scanning calorimetry (MDSC) and powder X-ray diffraction (PXRD).
  • Evaluation of physico-mechanical properties of cast films (tensile strength, elastic modulus, elongation).
  • In vitro release studies of CA from extruded tablets over 12 hours.

Main Results:

  • Citric acid monohydrate (CA MH) significantly improved the hot-melt extrusion of Eudragit RS PO, while anhydrous CA was less effective.
  • The plasticizing effect of CA MH reached a plateau at 25%, coinciding with its solubility limit in the polymer, confirmed by MDSC and PXRD.
  • CA MH enhanced polymer flexibility, reducing tensile strength and elastic modulus while increasing elongation.
  • CA release from matrix tablets followed an extended-release profile, with CA MH showing a faster dissolution rate than anhydrous CA.

Conclusions:

  • Citric acid monohydrate (CA MH) is an effective solid plasticizer for Eudragit RS PO in hot-melt extrusion.
  • CA MH facilitates the production of controlled-release matrix systems with improved processability and desired release characteristics.
  • The higher solubility of CA MH in Eudragit RS PO explains its superior plasticizing performance compared to the anhydrous form.